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Experimental and simulative determination and correction of the effective gap extension in structured coaxial measuring systems

S. Josch, S. Jesinghausen, C. Dechert, H. Schmid, Rheologica Acta (2023)

<jats:title>Abstract</jats:title><jats:p>The use of structured measuring systems to prevent wall slip is a common approach to obtain absolute rheological values. Typically, only the minimum distance between the measuring surfaces is used for further calculation, implying that no flow occurs between the structural elements. But this assumption is misleading, and a gap correction is necessary. To determine the radius correction <jats:inline-formula><jats:alternatives><jats:tex-math>$$\Delta r$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:mi>r</mml:mi> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> for specific geometries, we conducted investigations on three Newtonian fluids (two silicon oils and one suspension considered to be Newtonian in the relevant shear rate range). The results show that <jats:inline-formula><jats:alternatives><jats:tex-math>$$\Delta r$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:mi>r</mml:mi> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> is not only shear- and material-independent, but geometry-dependent, providing a Newtonian flow behaviour in a similar viscosity range. Therefore, a correction value can be determined with only minute deviations in different Newtonian fluids. As the conducted laboratory measurements are very time-consuming and expensive, a CFD-approach with only very small deviations was additionally developed and compared for validation purposes. Therefore, simulation is an effective and resource-efficient alternative to the presented laboratory measurements to determine <jats:inline-formula><jats:alternatives><jats:tex-math>$$\Delta r$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:mi>r</mml:mi> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> for the correction of structured coaxial geometries even for non-Newtonian fluids in the future.</jats:p>


Influence of a prolonged shelf time on PA12 laser sintering powder and resulting part properties

S.H. Klippstein, I. Kletetzka, I. Sural, H. Schmid, The International Journal of Advanced Manufacturing Technology (2023)

In the laser sintering technology, the semi-crystalline polymer material is exposed to elevated temperatures during processing, which leads to serious material ageing for most materials. This has already been investigated intensively by various authors. However, the ageing of the material at ambient temperatures during shelf life has not been the focus so far. The need to analyse the shelf life can be derived from an ecological and economic point of view. This work is focusing on the shelf life of PA2200 (PA12). To reduce the potential influences of powder production fluctuations, two different powder batches stored for 5.5 years and 6.5 years are investigated and compared to a reference powder produced 0.5 years before these investigations. Multiple powder analyses and part characterisations have been performed. A significant yellowing and molecular chain length reduction can be derived from the measurement results. Whereas the influence on mechanical part performance was minor, the parts built with the stored powders are more yellowish. As it is most likely that this is due to the consumption of polyamide stabilisers, it can be assumed that these parts will be subject to significantly faster ageing. Therefore, it is still not recommended to use the stored powders for critical parts or light intense and humid environments.





Influence of the filler matrix adhesion and the effects of conditioning on tensile properties of laser sintered parts built with polyamide glass bead dry blends

I. Kletetzka, M. Kosanke, D. Meinderink, V. Neßlinger, G. Grundmeier, H. Schmid, 2023

<jats:title>Abstract</jats:title> <jats:p>In this work, the influence of the filler matrix adhesion on the tensile properties of laser-sintered parts built with Polyamide 613 filled with glass beads was investigated. For this purpose, dry blends of glass beads with and without organosilane coupling agents and polyamide powder were prepared and processed into tensile specimens on an EOS P396. The samples were tested both in the dry state and after an accelerated conditioning in a climate chamber. Furthermore, FEM simulations were performed to model the limiting cases of optimum adhesion and no adhesion. By correlating the tensile tests with the simulation results and by analyzing the fracture surfaces, it was shown that the filler matrix adhesion is sufficient in the dry state but is strongly degraded by conditioning. Even the presence of various organosilane thin films could not prevent a strong deterioration of the filler-matrix adhesion and the associated deterioration of the mechanical properties. Since a comparison with an injection molded sample of the same polymer filler combination shows identical behavior after conditioning, it is assumed that this problem is not limited to additively manufactured parts.</jats:p>


Influence of the filler matrix adhesion and the effects of conditioning on tensile properties of laser sintered parts built with polyamide glass bead dry blends

I. Kletetzka, M. Kosanke, D. Meinderink, V. Neßlinger, G. Grundmeier, H. Schmid, 2023

<jats:title>Abstract</jats:title> <jats:p>In this work, the influence of the filler matrix adhesion on the tensile properties of laser-sintered parts built with Polyamide 613 filled with glass beads was investigated. For this purpose, dry blends of glass beads with and without organosilane coupling agents and polyamide powder were prepared and processed into tensile specimens on an EOS P396. The samples were tested both in the dry state and after an accelerated conditioning in a climate chamber. Furthermore, FEM simulations were performed to model the limiting cases of optimum adhesion and no adhesion. By correlating the tensile tests with the simulation results and by analyzing the fracture surfaces, it was shown that the filler matrix adhesion is sufficient in the dry state but is strongly degraded by conditioning. Even the presence of various organosilane thin films could not prevent a strong deterioration of the filler-matrix adhesion and the associated deterioration of the mechanical properties. Since a comparison with an injection molded sample of the same polymer filler combination shows identical behavior after conditioning, it is assumed that this problem is not limited to additively manufactured parts.</jats:p>


Flowability of polymer powders at elevated temperatures for additive manufacturing

M.J. Rüther, S.H. Klippstein, S. Ponusamy, T. Rüther, H. Schmid, Powder Technology (2023), 422, 118460

DOI


CDMA: Centrifugal Differential Mobility Analyzer - Ein Messprinzip zur Bestimmung von Multidimensionalen Partikeleigenschaften (Vortrag)

T. Rüther, H. Schmid. CDMA: Centrifugal Differential Mobility Analyzer - Ein Messprinzip zur Bestimmung von Multidimensionalen Partikeleigenschaften (Vortrag). 2023.


Reproducibility in Polymer Laser Sintering

S.H. Klippstein. Reproducibility in Polymer Laser Sintering. 2022.


Low Temperature Laser Sintering with PA12 and PA6 on a standard system

D. Menge, H. Schmid, Macromolecular Symposia (2022)

The laser sintering (LS) process has been a very established Additive Manufacturing (AM) process for many years. Disadvantages of LS are the low material variety and the thermal damage of the not processed material. The low temperature laser sintering attacks at this point and processes powder material at a build chamber temperature lower than the recrystallization temperature. This drastic reduction in temperature results in significantly less thermal damage to the material. This work deals with the low temperature laser sintering (LTLS) of polyamide 12 (PA12) on a commercial, unmodified laser sintering system to compare it to standardly laser sintered PA12 and to create the basis for low temperature laser sintering of high temperature materials on such a system. Initial results by changing the exposure parameters and by fixing parts on a build platform show a processing of PA12 on an EOS P396 at a build chamber temperature of 80 °C instead of standard approx. 175 °C which prevents thermal damage of the material. An extensive study of exposure parameters was carried out and the mechanical properties were considered. Furthermore, a first transfer of the method and the results to PA6 was obtained.


Neue Polymerwerkstoffe - Der Schlüssel für die Industrialisierung

S.H. Klippstein. Neue Polymerwerkstoffe - Der Schlüssel für die Industrialisierung. 2022.


Powder Spread Flaws in Polymer Laser Sintering and its Influences on Mechanical Performance

S.H. Klippstein, H. Schmid, in: Proceedings of the 33nd Annual International Solid Freeform Fabrication Symposium, 2022

By monitoring the recoating process within polymer laser sintering production, it was shown that multiple powder-spread-flaws can be detected. Those groove-like flaws are expected to be the result of agglomerates jamming between the recoater and the last powder layer. This work is analyzing the interaction between powder-spread-flaws and part properties, showing the influence of the recoating process on the performance of laser sintering parts. Therefore, artificial powder-spread-flaws are applied to the build jobs of tensile test specimens which are measured and analyzed regarding the elongation at break, strength and fracture position. For the characteristics of the flaws, the artificial grooves are varied in depth and width. Furthermore, the position of the flaw is changed form mid part to close to surface areas. It was shown, that several flaws are visible at the part surface, resulting in stress concentration and reduced performance. But there are as well parts with flaw-layers, which are not visible after the build process on the part. Those parts can have significantly reduced mechanical properties as well.


Model droplet formation in extensional filament stretching within a Filament Extension Atomizer

M. Neukötter, S. Jesinghausen, H. Schmid, Rheologica Acta (2022)

<jats:title>Abstract</jats:title><jats:p>Further innovation in the field of selective laser sintering (SLS) is strongly connected to the availability of new materials since the market is dominated by polyamide 12 (&gt;90%). The aim of this publication is to develop a descriptive model for the droplet formation process in a Filament Extension Atomizer to predict the applicability to exploit further polymers for the SLS process. The feasibility was tested, investigated and characterized using a “Dripping out of a nozzle” setup for uniaxial extension. The droplet formation process was then observed via high-speed camera imaging and classified for certain parameters. The experiments were carried out using semi-diluted polyethylene oxide (600–4000 kg/mol), glycerol and water solutions as model fluids. Driven by the Plateau-Rayleigh instability, different types of spherical droplets were observed and various droplet formation mechanisms demonstrated and analyzed. Based on the experimental results, a predictive model is derived to describe various essential parameters.</jats:p>



Triggering instabilities of polymer solution suspensions under uniaxial extension (Presentation)

M. Neukötter, S. Jesinghausen, H. Schmid. Triggering instabilities of polymer solution suspensions under uniaxial extension (Presentation). 2022.


Instability analysis of suspensions with a polymer solution matrix (Presentation)

M. Neukötter, S. Jesinghausen, H. Schmid. Instability analysis of suspensions with a polymer solution matrix (Presentation). 2022.






Flowability of polymer powders at elevated temperatures for additive manufacturing

M.J. Rüther, S.H. Klippstein, H. Schmid. Flowability of polymer powders at elevated temperatures for additive manufacturing. 2022.


A combined flue gas cleaning system with a novel entrained flow SCR using an online synthesized catalyst (Poster)

J. Beimdiek, H. Schmid. A combined flue gas cleaning system with a novel entrained flow SCR using an online synthesized catalyst (Poster). 2022.


Pulver im 3D-Druck - von Mascarabürsten bis zum Interieur eines Mini-Coopers (Vortrag)

I. Kletetzka, S.H. Klippstein. Pulver im 3D-Druck - von Mascarabürsten bis zum Interieur eines Mini-Coopers (Vortrag). 2022.


Innovative Werkstoffherstellung für das Polymer Laser Sintern – Teil 2

M.J. Rüther, S.H. Klippstein, S. Ponusamy, S. Jesinghausen, H. Schmid, Werkstoffe (2022), 6, pp. 18 - 19


Innovative Werkstoffherstellung für das Polymer Laser Sintern – Teil 1

M.J. Rüther, S.H. Klippstein, S. Ponusamy, S. Jesinghausen, H. Schmid, Werkstoffe (2022), 5, pp. 28-29


Effects of spherical fillers on the processability and mechanical properties of PA613 and PP-based LS dry blends

I. Kletetzka, R. Gawlikowicz, H. Schmid, in: Proceedings of the 33nd Annual International Solid Freeform Fabrication Symposium, Laboratory for Freeform Fabrication and University of Texas, 2022

In this work, the influences of spherical fillers on the processing properties and the resulting mechanical properties of laser sintered components are investigated. For this purpose, micro glass spheres, hollow glass bubbles and mineral spheres are dry blended to the matrix polymers polyamide 613 and polypropylene with a filling ratio of 20 and 40 vol%. First, relevant properties of the blends, such as powder flowability, thermal behavior and melt viscosity, are investigated. Based on the results, processing parameters are then developed for the LS process and the mechanical properties of the components are investigated. The aim is to be able to tailor the mechanical properties of LS components by adding fillers and thus to create new application areas for additively manufactured components.


Combined filtration process for biomass combustion plants to comply with legal requirements (Presentation)

J. Beimdiek, F. Prill, M. König, M. Müller, I. Hartmann, H. Schmid, in: 13th World Filtration Congress Proceedings, 2022


A combined flue gas cleaning system with a novel entrained flow SCR using online synthesized catalyst particles (Poster)

J. Beimdiek, H. Schmid. A combined flue gas cleaning system with a novel entrained flow SCR using online synthesized catalyst particles (Poster). 2022.


Shelf Life of Polyamide 12 (PA2200) Laser Sintering Powder

I. Kletetzka, S.H. Klippstein, H. Schmid, in: Proceedings of the 33nd Annual International Solid Freeform Fabrication Symposium, Laboratory for Freeform Fabrication and University of Texas, 2022


Novel entrained flow SCR using online synthesized catalyst particles (Poster)

J. Beimdiek, H. Schmid. Novel entrained flow SCR using online synthesized catalyst particles (Poster). 2022.


Novel entrained flow SCR using online synthesized catalyst particles in flue gas cleaning systems (Presentation)

J. Beimdiek, H. Schmid. Novel entrained flow SCR using online synthesized catalyst particles in flue gas cleaning systems (Presentation). 2022.




A novel correction method for the shear rate in a couette rheometer (Vortrag)

T. Rüther, S. Jesinghausen, H. Schmid. A novel correction method for the shear rate in a couette rheometer (Vortrag). 2022.


NEW CORRECTION APPROACHES FOR DETERMINING THE TRUE SHEAR RATE IN A COAXIAL-RHEOMETER (Vortrag)

T. Rüther, S. Jesinghausen, H. Schmid. NEW CORRECTION APPROACHES FOR DETERMINING THE TRUE SHEAR RATE IN A COAXIAL-RHEOMETER (Vortrag). 2022.


Multidimensional particle characterization: Centrifugal Differential Mobility Analyzer (Poster)

T. Rüther, H. Schmid. Multidimensional particle characterization: Centrifugal Differential Mobility Analyzer (Poster). 2022.


Dreidimensionale Oberflächenanalyse und Topografie-Simulation additiv hergestellter Laser-Sinter Bauteile

P. Delfs, Shaker Verlag GmbH, 2021

Anwendungen von Laser-Sinter Bauteilen als Sichtteile sind aufgrund der vergleichsweise schlechten Oberflächenqualität sehr begrenzt. In dieser Arbeit werden dreidimensionale Kennwerte benutzt, um die Oberflächenqualität von Laser-Sinter Bauteiloberflächen und die Einflüsse aus unterschiedlichen Bereichen der gesamten Prozesskette zu evaluieren. Beispielsweise wurden objektive Kennwerte, mit deren Hilfe Orangenhaut zu identifizieren ist, und Prozessparameter, die diese deutlich vermindern, gefunden. Mittels Durchführung von haptischen Versuchen wurde das subjektive Empfinden ermittelt und konnten zu objektiven Kennwerten korreliert werden. Eine mikroskopische Betrachtung des flachen Oberflächenwinkels mit verschieden farbigen Pulvern zeigt neue Erkenntnisse zum Anschmelzvorgang von Partikeln an die Schmelze. Zur nachträglichen Glättung von Oberflächen wurden mechanische, chemische und optische Nachbehandlungsmethoden verwendet und deren Potential aufgezeigt. Eine abschließende neuartige Simulation der dreidimensionalen Topografie bildet die Grundlage für ein Programm zur automatischen und funktionsgerechten Orientierung von Bauteilen, welche am Beispiel eines realen Bauteils erfolgreich validiert wurde. Zusammengenommen zeigen die Ergebnisse, dass die richtige Wahl von Bauorientierung und Prozessparametern entscheidend für die Bauteilqualität ist und selbst eine aufwendige Nachbearbeitung eine ungeschickte Wahl derer nur schwerlich ausgleichen kann.


Mechanical characterization and numerical modeling of laser-sintered TPE lattice structures

C. Kummert, H. Schmid, L. Risse, G. Kullmer, Journal of Materials Research (2021)

Additive Manufacturing provides the opportunity to produce tailored and complex structures economically. The use of lattice structures in combination with a thermoplastic elastomer enables the generation of structures with configurable properties by varying the cell parameters. Since there is only little knowledge about the producibility of lattice structures made of TPE in the laser sintering process and the resulting mechanical properties, different kinds of lattice structures are investigated within this work. The cell type, cell size and strut thickness of these structures are varied and analyzed. Within the experimental characterization of Dodecahedron-cell static and cyclic compression tests of sandwich structures are focused. The material exhibits hyperelastic and plastic properties and also the Mullins-Effect. For the later design of real TPE structures, the use of numerical methods helps to reduce time and costs. The preceding experimental investigations are used to develop a concept for the numerical modeling of TPE lattice structures.



Low Temperature Laser Sintering on a Standard System: First Attempts and Results with PA12

D. Menge, H. Schmid, 2021

The laser sintering process has been a well-established AM process for many years. Disadvantages of LS are the low material variety and the thermal damage of the unprocessed material. The low temperature laser sintering attacks at this point and processes powder material at a build chamber temperature lower than the recrystallization temperature. This drastic reduction in temperature results in significantly less thermal damage to the material. This work deals with the low temperature laser sintering of Polyamide 12 (PA12) on a commercial, unmodified laser sintering system to compare it to standard laser sintered PA12 and to create the basis for low temperature laser sintering of high temperature materials on such a system. First results by changing the exposure parameters and by fixing parts on a building platform show a processing of PA12 on an EOS P396 at a build chamber temperature less than 100 °C instead of standard approx. 175 °C.


Powder Spread Process Monitoring in Polymer Laser Sintering and its Influences on Part Properties

S.H. Klippstein, F. Heiny, N. Pashikanti,, M. Gessler, H. Schmid, JOM - The Journal of The Minerals, Metals & Materials Society (TMS) (2021), 74, pp. 1149–1157

Confidence in additive manufacturing technologies is directly related to the predictability of part properties, which is influenced by several factors. To gain confidence, online process monitoring with dedicated and reliable feedback is desirable for every process. In this project, a powder bed monitoring system was developed as a retrofit solution for the EOS P3 laser sintering machines. A high-resolution camera records each layer, which is analyzed by a Region-Based Convolutional Neural Network (Mask R-CNN). Over 2500 images were annotated and classified to train the network in detecting defects in the powder bed at a very high level. Each defect is checked for intersection with exposure areas. To distinguish between acceptable imperfections and critical defects that lead to part rejection, the impact of these imperfections on part properties is investigated.


Online Monitoring des Beschichtungsprozesses im Laser Sintern, Systementwicklung und Einflussanalyse

S.H. Klippstein. Online Monitoring des Beschichtungsprozesses im Laser Sintern, Systementwicklung und Einflussanalyse. 2021.


Einfluss der Zerstäubung auf die Partikelsynthese in Sprayflammen

R. Tischendorf, H. Schmid, M. Bieber, M. Reddemann, R. Kneer, F. Fröde, T. Grenga, H. Pitsch. Einfluss der Zerstäubung auf die Partikelsynthese in Sprayflammen. 2021.



Flowability Measurements of Different SLS Materials at Elevated Temperatures with a Modified Schulze Ring Shear Tester

M.J. Rüther, D. Schulze, H. Schmid. Flowability Measurements of Different SLS Materials at Elevated Temperatures with a Modified Schulze Ring Shear Tester. 2021.


Adaption of a PGSS-System for the production of SLS-Materials

M.J. Rüther. Adaption of a PGSS-System for the production of SLS-Materials. 2021.


Effektivität von Luftreinigern zur Reduzierung des COVID-19-Infektionsrisikos/ Efficacy of air purifiers in reducing the risk of COVID-19 infections

S. Schumacher, C. Asbach, H. Schmid, Gefahrstoffe (2021), pp. 16-28

Luftreiniger werden derzeit häufig als mögliches Hilfsmittel zur Minimierung des Infektionsrisikos im Rahmen der COVID-19-Pandemie diskutiert. Dabei taucht oft die Frage auf, ob Luftreiniger grundsätzlich in der Lage sind, Viren oder virenbeladene Tröpfchen abzuscheiden. Ziel dieses Artikels ist es, die wesentlichen Grundlagen der Wirkungsweise von Luftreinigern und Filtern zu beschreiben, Methoden zur Messung der Reinigungswirkung im Größenbereich von Viren und virenbeladenen Tröpfchen aufzuzeigen sowie typische Szenarien zum Betrieb von Luftreinigern in einem mathematischen Modell zu erfassen. Darauf basierend können die Möglichkeiten und Grenzen von Luftreinigern für reale Anwendungsfälle besser eingeschätzt werden.


Theoretische Beschreibung des Tropfenbildungsprozesses bei der Filament Extension Atomization: Entwicklung eines Vorhersagemodells für die Tropfengröße (Poster)

M. Neukötter, S. Jesinghausen, H. Schmid. Theoretische Beschreibung des Tropfenbildungsprozesses bei der Filament Extension Atomization: Entwicklung eines Vorhersagemodells für die Tropfengröße (Poster). 2021.


Filament Extension Atomization – A novel Process for Powder Production? (Presentation)

M. Neukötter, S. Jesinghausen, H. Schmid. Filament Extension Atomization – A novel Process for Powder Production? (Presentation). 2021.



Laser Sintering Design Guidelines for media transmitting Components

I. Kletetzka, C. Kummert, H. Schmid, in: Proceedings of the 32nd Annual International Solid Freeform Fabrication Symposium, Laboratory for Freeform Fabrication and University of Texas, 2021

In automotive and other fields of application media-carrying components often have complex, flow-optimized geometries and are made of plastics for reasons of weight and cost. Therefore, the laser sintering technology is predestinated to manufacture these components as it offers a very high degree of design freedom and good mechanical properties. For industrial applications the long-term properties of the SLS material in contact with liquid media are important and were therefore investigated for PA12, PP and PA613. Hereby, different media such as motor oil or Glysantin based coolant were tested with different temperatures and immersion times of up to 26 weeks. The mechanical properties were tested after immersion and compared to injection molded samples. Furthermore, laser sintering design guidelines for media-carrying components were developed. These guidelines for instance include the minimum wall thickness to ensure media tightness and the removal of powder from channels with a high length to diameter ratio.


Assessing spreading and removal of virus laden aerosols in different settings using an aerosol method (Presentation)

J. Ludwig, C. Kykal, H. Schmid. Assessing spreading and removal of virus laden aerosols in different settings using an aerosol method (Presentation). 2021.


Synthese und asymmetrische Funktionalisierung von submikronen Janus-Polymer-Partikeln in der Gasphase (Poster)

J. Ludwig, H. Schmid. Synthese und asymmetrische Funktionalisierung von submikronen Janus-Polymer-Partikeln in der Gasphase (Poster). 2021.




Additive Leichtbaustrukturen für die Flugzeugkabine

D. Menge, S.H. Klippstein, H. Schmid, 2020


Interlaboratory study on rheological properties of cement pastes and reference substances: comparability of measurements performed with different rheometers and measurement geometries

M. Haist, J. Link, D. Nicia, S. Leinitz, C. Baumert, T. von Bronk, D. Cotardo, M. Eslami Pirharati, S. Fataei, H. Garrecht, C. Gehlen, I. Hauschildt, I. Ivanova, S. Jesinghausen, C. Klein, H. Krauss, L. Lohaus, D. Lowke, O. Mazanec, S. Pawelczyk, U. Pott, N.W. Radebe, J.J. Riedmiller, H. Schmid, W. Schmidt, E. Secrieru, D. Stephan, M. Thiedeitz, M. Wilhelm, V. Mechtcherine, Materials and Structures (2020)

<jats:title>Abstract</jats:title><jats:p>This paper presents the results of an interlaboratory study of the rheological properties of cement paste and ultrasound gel as reference substance. The goal was to quantify the comparability and reproducibility of measurements of the Bingham parameters yield stress and plastic viscosity when measured on one specific paste composition and one particular ultrasound gel in different laboratories using different rheometers and measurement geometries. The procedures for both in preparing the cement paste and carrying out the rheological measurements on cement paste and ultrasound gel were carefully defined for all of the study’s participants. Different conversion schemes for comparing the results obtained with the different measurement setups are presented here and critically discussed. The procedure proposed in this paper ensured a reasonable comparability of the results with a coefficient of variation for the yield stress of 27% and for the plastic viscosity of 24%, despite the individual measurement series’ having been performed in different labs with different rheometers and measurement geometries.</jats:p>


An Apparatus to Synthesize Ceramic Nanoparticles with a Precisely Adjusted Temperature History and a Significant Mass Output

D.B. Rasche, L. Tigges, H. Schmid, Review of Scientific Instruments (2020), 91, pp. 055104

For gas phase nanoparticle production, hot wall reactors are widely used. In this article, we will describe the fundamental design considerations for a hot wall reactor system able to produce oxide nanoparticles. The system is outstanding in its ability to produce mostly spherical nanoparticles at particle sizes of up to 100 nm and even larger at mass outputs in the order of grams per hour by being able to rapidly quench the aerosol. While high production rates or larger particle sizes are already easily obtained with hot wall reactors, it is very challenging to produce these spherical particles at high mass rates. We will show in this research that the temperature and the particle number concentration are the major aspects influencing the particle morphology at the end of the process. Investigation on the performance of the setup shows good control over the temperature and the particle production stability. A representative particle characterization using SEM and scanning mobility particle sizer showed that particles are mostly spherical, while the particle size distribution had a geometric standard deviation close to 1.5. In addition to the aspects mentioned above, a possibility to manipulate the aggregation downstream of the reactor is to be presented as well. We found that applying electrical charges to the aerosol particles (in opposite polarity) can significantly foster aggregation.


Influence of Part Microstructure on Mechanicl Properties of PA6X Laser Sintered Specimens

C. Kummert, W. Diekmann, K. Tews, H. Schmid, in: 29th Annual International Solid Freeform Fabrication Symposium, 2020, pp. 735-744

DOI


Influence of differing nozzle configurations on the final particle characteristics and particle structure evolution in spray flames

R. Tischendorf, H. Schmid, M. Bieber, M. Reddemann , R. Kneer, F. Fröde, T. Grenga, H. Pitsch. Influence of differing nozzle configurations on the final particle characteristics and particle structure evolution in spray flames. 2020.


Interlaboratory study on rheological properties of cement pastes and reference substances: comparability of measurements performed with different rheometers and measurement geometries

M. Haist, J. Link, D. Nicia, S. Leinitz, C. Baumert, T. von Bronk, D. Cotardo, M. Eslami Pirharati, S. Fataei, H. Garrecht, C. Gehlen, I. Hauschildt, I. Ivanova, S. Jesinghausen, C. Klein, H. Krauss, L. Lohaus, D. Lowke, O. Mazanec, S. Pawelczyk, U. Pott, N.W. Radebe, J.J. Riedmiller, H. Schmid, W. Schmidt, E. Secrieru, D. Stephan, M. Thiedeitz, M. Wilhelm, V. Mechtcherine, Materials and Structures (2020)

This paper presents the results of an interlaboratory study of the rheological properties of cement paste and ultrasound gel as reference substance. The goal was to quantify the comparability and reproducibility of measurements of the Bingham parameters yield stress and plastic viscosity when measured on one specific paste composition and one particular ultrasound gel in different laboratories using different rheometers and measurement geometries. The procedures for both in preparing the cement paste and carrying out the rheological measurements on cement paste and ultrasound gel were carefully defined for all of the study’s participants. Different conversion schemes for comparing the results obtained with the different measurement setups are presented here and critically discussed. The procedure proposed in this paper ensured a reasonable comparability of the results with a coefficient of variation for the yield stress of 27% and for the plastic viscosity of 24%, despite the individual measurement series’ having been performed in different labs with different rheometers and measurement geometries.


Absolute Rheological Measurements of Model Suspensions: Influence and Correction of Wall Slip Prevention Measures

S. Pawelczyk, M. Kniepkamp, S. Jesinghausen, H. Schmid, Materials (2020), 467

<jats:p>Since suspensions (e.g., in food, cement, or cosmetics industries) tend to show wall slip, the application of structured measuring surfaces in rheometers is widespread. Usually, for parallel-plate geometries, the tip-to-tip distance is used for calculation of absolute rheological values, which implies that there is no flow behind this distance. However, several studies show that this is not true. Therefore, the measuring gap needs to be corrected by adding the effective gap extension δ to the prescribed gap height H in order to obtain absolute rheological properties. In this paper, we determine the effective gap extension δ for different structures and fluids (Newtonian, shear thinning, and model suspensions that can be adjusted to the behavior of real fluids) and compare the corrected values to reference data. We observe that for Newtonian fluids a gap- and material-independent correction function can be derived for every measuring system, which is also applicable to suspensions, but not to shear thinning fluids. Since this relation appears to be mainly dependent on the characteristics of flow behaviour, we show that the calibration of structured measuring systems is possible with Newtonian fluids and then can be transferred to suspensions up to a certain particle content.</jats:p>


On the Influence of Thermal Histories within Part Cakes on the Polymer Laser Sintering Process

S. Josupeit, Shaker Verlag GmbH, 2019

Polymer Laser Sintering (LS) is one of the most used Additive Manufacturing (AM) technologies for the tool-less production of polymer parts. The raw material is a polymer powder which is melted layerwise by the use of laser energy. Especially for the production of single parts, small series, individualized and complex structures, the technology is yet established in few branches. However, inhomogeneous and hardly controllable thermal effects during manufacturing limit the build reproducibility. The present work focuses on temperatures within so-called part cakes, their time dependency and their influence on process quality. Therefore, a temperature measurement system is implemented into a commercial laser sintering machine. Based on the experimental data a model to simulate heat transfer within part cakes is set up. Individual thermal histories during processing are successfully correlated with position dependent powder ageing effects. Another focus is on the analysis of a recycling optimized material. First results of correlations between thermal histories and part properties are shown in order to provide an outlook to further research. The data and knowledge gained through this work can be used to understand thermal effects in greater depth and to increase the process quality via optimizations.


Zum Laserstrahlschmelzen neuer Kunststoffmaterialien

J. Lohn, Shaker Verlag GmbH, 2019

Stand der Technik beim Lasersintern von Kunststoffen (SLS) ist die Fertigung von Prototypen aus z.B. Polyamid 12. Die industrielle Serienproduktion mittels SLS erfordert die Qualifizierung von produktspezifischen Materialien. Kernthema dieser Arbeit ist die Verarbeitung von neuen Kunststoffen. Hierzu wird eine optimierte Anlagentechnik entwickelt. Die Verarbeitung von schlecht rieselfähigen Pulvern wird durch ein innovatives Beschichtungssystem ermöglicht. Durch eine zwölf Zonen Heizungsregelung erfolgt die Pulvervorwärmung in der erforderlichen Präzision. Zudem ermöglicht ein variabler Laserspot eine Belichtung mit hoher Detailauflösung bei gleichzeitig hoher Aufbaurate. Der Energieeintrag im SLS Prozess und die Belichtung mit variablem Laserspotdurchmesser werden theoretisch betrachtet und mittels Computertomographie experimentell untersucht. Abschließend wird eine Systematik zur Identifizierung von Prozessparameter für die Verarbeitung neuer Materialien erarbeitet und exemplarisch wird das neue Material Polyamid 613 prozessiert.


FVA-Nr. 813 I - Generative Verfahren zur Herstellung von Polymerbauteilen

D. Menge, R. Walter, H. Schmid, U.P. Breuer, 2019


Understanding and Manipulation of Nanoparticle Contact Forces by Capillary Bridges

H. Schmid, G. Grundmeier, M. Dörmann, A.G. Orive, T. de los Arcos, B. Torun, in: Particles in Contact, 2019

Since, in the presence of humidity the inter-particle processes are dominated by capillary forces, a fundamental understanding of the water adsorption and the capillary bridge formation is very important. However, the adsorbed water structure and thus the capillary bridge formation is influenced by various parameters like the particle morphology (e.g. particle size, roughness) as well as the surface chemistry (surface energy, adsorbate structure) and therefore needs to be analyzed on a submicroscopic or even molecular basis. A multi-scale approach ranging from experiments on an individual particle level (AFM and liquid bridge simulation) and investigations on small particle ensembles (combined QCM-D/FTIR) up to macroscopic description of bulk behavior is presented in this chapter. In this context, the combined in situ QCM-D/FTIR experiments are bridging the gap between experiments on an individual particle level and macroscopic bulk behavior. Variation of surface chemistry by means of adsorption of functional organic molecules allows for the correlation of macroscopic particle behavior to nanoscopic effects like the presence and structure of adsorbate layers as well as the formation of capillary bridges while keeping the disperse properties constant. Besides extensive experimental work, simulations of capillary bridges formed by condensation from humid air are presented. It is clearly shown that well known approximations which have been introduced for micron-sized particles are not valid any more for nano-scaled particles. The forces between nanoparticles by static liquid bridges and their dependency on particle size, contact angle, humidity and interparticle distance are discussed in detail. Furthermore, capillary forces during separation of particles are studied thoroughly and a constitutive law based on a contact stiffness allows the transfer to DEM simulations of wet powders. Finally, it is demonstrated by comparison to Molecular Dynamics simulations, that the used continuum approach to simulate capillary bridges might even be used down to particle sizes of a few nanometers, if some additional effects are considered correctly.


Methodik zur Qualifizierung des Lasersinter Prozesses für die Serienfertigung

S.H. Klippstein, H. Schmid, in: Proceedings of the 16th Rapid.Tech Conference, 2019

Zuverlässige, wiederholbare Bauteileigenschaften sind unabdingbar um das Herstellungsverfahren Polymer Lasersintern im industriellen Prozess-Portfolio vieler Firmen aufnehmen zu können. Einige Unternehmen und Institute haben sich daher in jüngster Zeit mit dem Thema der reproduzierbaren Bauteileigenschaften beschäftigt. Mit der hier vorgestellten und angewandten Methodik wird nicht nur der Prozessablauf vom Bauteil bis zu Nachbearbeitung betrachtet, sondern auch die Maschinenperformance in einem Ringversuch und über einen längeren Zeitraum geprüft. Rückgrat dieser Untersuchung bildet hierbei der aus der Six Sigma Lehre stammende DMAIC (Define - Measure - Analyse - Improve - Control) Verbesserungszyklus. Hierfür wird ein Standard-Prozess definiert. Diesem folgend werden die für die Industrie oder den Anwender interessanten Messungen aufgenommen und analysiert. Anschließend wird der Prozess sowie die Messmethodik optimiert und auch Kontrollmethoden definiert. Für die Anwendung der entwickelten Methodik wird exemplarisch der Maschinentyp EOS P396 mit PA2200 untersucht. Daten für die Bestimmung der Mechanik, der Optik und der Haptik sowie für die Dimensionen und die Bauteildichte werden als Qualitätskriterium aufgenommen und über einen längeren Zeitraum analysiert. Weiteres Ziel ist es, den Messaufwand zu reduzieren und die Qualitätssicherung im Serienbtrieb zu gewährleisten.


Representative Sample Extraction from Spray Flames for SMPS and HR-TEM Measurements

R. Tischendorf, M. Bieber, R. Kneer, H. Schmid. Representative Sample Extraction from Spray Flames for SMPS and HR-TEM Measurements. 2019.



Water adsorption and capillary bridge formation on silica micro-particle layers modified with perfluorinated organosilane monolayers

I. Giner, B. Torun, Y. Han, B. Duderija, D. Meinderink, A.G. Orive, M.T. de los Arcos de Pedro, C. Weinberger, M. Tiemann, H. Schmid, G. Grundmeier, Applied Surface Science (2019), pp. 873-879

Monodisperse micron-sized silica particle monolayers deposited onto plasma-grown SiOx-ultra-thin films have been used as reference systems to investigate wetting, water adsorption and capillary bridge formation as a function of silica surface functionalization. 1H,1H, 2H,2H perfluorooctyltriethoxysil (FOTS) monolayers, have been deposited on the respective surfaces by means of chemical vapor deposition resulting in macroscopically low energy surfaces. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) reflection absorption spectroscopy confirmed the monolayer formation. Water adsorption isotherms were studied by a combination of in-situ FTIR reflection spectroscopy and quartz crystal microbalance (QCM) while macroscopic wetting was analysed by contact angle measurements. The comparative data evaluation indicates that the macroscopic wetting behaviour was changed as expected, however, that water nanodroplets formed both at intrinsic defects of the FOTS monolayer and at the FOTS/SiOx interface. Capillary bridges of liquid water are dominantly formed in the confined particle contact areas and between surface asperities on the particles. The comparison of wetting, adsorption and capillary bridge formation shows that the hydrophobization of porous materials by organosilane monolayers leads to the formation of morphology dependent nanoscopic defects that act as sites for preferential capillary bridge formation.


Devolopment, Production and post-processing of a topology optimized aircraft bracket

S.H. Klippstein, A. Duchting, T. Reiher, F. Hengsbach, D. Menge, H. Schmid, in: 30th Annual International Solid Freeform Fabrication Symposium, 2019, pp. 1932-1945

Structural parts for aviation have very high demands on the development and production process. Therefore, the entire process must be considered in order to produce high-quality AM metal parts. In this case study, a conventional part was selected to be optimized for AM. The process presented includes component selection, design improvement with a novel approach for topology optimization based on the AMendate algorithm as basis of MSC Apex Generative Design,component production on a SLM 250 HL and post-processing including heat treatment and surface smoothing. With the topology optimization a weight reduction of ~60 % could be realized, whereby the stress distribution is more homogeneous. Furthermore, the challenges of support optimization and post-processing have to be addressed, in order to produce competitive parts.


Representative domain size for the simulation of coalescence filtration in nonwoven and foam media

S. Abishek, A. King, J. Schuler, G. Kasper, H. Schmid, B. Mullins, Separation and Purification Technology (2018), pp. 344-352

Pore-scale filtration simulations require high spatio-temporal resolutions and significant computational effort, hence, keeping the domain size to a minimum is desirable. Previous studies have considered domains based on Brinkman length, or are limited by computing power, and little information is available for conditions involving high fluid saturation – typical of steady state mist filtration. In this study, simulations are performed to characterize the effect of domain size on pressure drop, residual saturation, liquid film thickness and interfacial area concentration, using virtual nonwoven and foam filters with similar micro-structural properties. Further, experiments using micro-CT are performed to validate the present computational simulations. It is found that two phase flow through filters are more sensitive to local geometric variations or mesh resolution in the porous media than single phase flow. Statistical uncertainties in the steady state quantities of less than +-10% can be expected to cope with the increase in computing power required for practical mesh sizes. A computational domain size of about 50–100xd (where d is the strut or fibre diameter) was found to be required for CFD for the operating conditions considered.


Topology Optimized Heat Transfer Using the Example of an Electronic Housing

D. Menge, P. Delfs, M. Töws, H. Schmid, in: 29th Annual International Solid Freeform Fabrication Symposium, 2018, pp. 687-697

Function integration is a key issue for an efficient and economic usage of Additive Manufacturing. An efficient heat transfer by topology optimized structures is a rarely considered approach which will be outlined with an exemplary electronic housing which has been newly designed. A commercial projector unit, whose electrical components in total produce 38 W, shall be integrated in the closed housing and passively cooled by natural convection. Topology optimized structures shall be generated in the inner part of the housing to transfer the heat homogenously from the projector components to the housing wall while simultaneously minimizing the mass. At the outside of the housing walls, lattice and rib structures are applied to increase the effective surface for heat transfer by natural convection and radiation. Furthermore, the housing geometry is optimized regarding a minimization of support structures to reduce the post-processing effort. Finally, the housing shall be built of AlSi10Mg by SLM.


Thermoplastic Elastomer Part Color as Function of Temperature Histories and Oxygen Atmosphere During Selective Laser Sinterung

C. Kummert, S. Josupeit, H. Schmid, Journal of Minerals, Metals and Materials Society (2018), 70(3), pp. 425-430

The influence of selective laser sintering (SLS) parameters on PA12 part properties is well known, but research on other materials is rare. One alternative material is a thermoplastic elastomer (TPE) called PrimePart ST that is more elastic and shows a distinct SLS processing behavior. It undergoes a three-dimensional temperature distribution during the SLS process within the TPE part cake. To examine this further, a temperature measurement system that allows temperature measurements inside the part cake is applied to TPE in the present work. Position-dependent temperature histories are directly correlated with the color and mechanical properties of built parts and are in very good agreement with artificial heat treatment in a furnace. Furthermore, it is clearly shown that the yellowish discoloration of parts in different intensities is not only temperature dependent but also influenced by the residual oxygen content in the process atmosphere. Nevertheless, the discoloration has no influence on the mechanical part properties.


Bestimmung von Nanopartikeleigenschaften eines Aerosols

H. Schmid, D. Rasche. Bestimmung von Nanopartikeleigenschaften eines Aerosols, Patent 10 2017 101 766.6. 2018.

Zusammenfassung: Bei einem Verfahren und einer Vor- richtung zur Bestimmung von Nanopartikeleigenschaften ei- nes nanopartikelbeladenen Aerosols (17), mit einer Test- kammer (1) zur Bestimmung der Nanopartikeleigenschaften des Aerosols (17), wobei die Testkammer (1) einen Aero- soleinlass (9) zum Einleiten des Aerosols (17) und ein Hül- lenluftstromeinlass (10) zur Einleitung eines Hüllenluftstroms (16) aufweist, die Oberseite (2) und die Unterseite (3) der Testkammer (1) jeweils eine flächige Elektrode (4, 5) auf- weist, so dass zwei im Abstand zueinander angeordnete Elektroden (4, 5) bereitstehen, zwischen denen ein elektri- sches Feld (6) erzeugbar ist, soll ein kompaktes Messgerät für die Vermessung der Eigenschaften von Aerosolnanopar- tikeln zur Verfügung gestellt werden, bei dem es ermöglicht wird, im selben Gerät die zweidimensionale Verteilung be- züglich des aerodynamischen und des volumenäquivalen- ten Durchmessers zu bestimmen, wodurch eine Lösung ge- schaffen wird, die es ermöglicht Aussagen über die Größe, die Masse, die Form und die geometrische Struktur einer Partikel zu treffen. Dies wird dadurch erreicht, dass der Inhalt der Testkammer (1) in Rotation versetzt wird, wobei die Ro- tationsachse (18) parallel zum elektrischen Feld (6) verläuft.





Aufbau einer Lasersinter-Versuchsanlage und Verarbeitung neuer Materialien am Beispiel von Polyamid 6 und Polyamid 613

J. Lohn, H. Schmid, in: Rapid.Tech – International Trade Show & Conference for Additive Manufacturing, 2017

Selective Laser Sintering (SLS) is an Additive Manufacturing technology, which allows the production of functional polymer parts. Conventionally mainly Nylon 12 (PA 12), Polyamide 11 (PA 11), glass- or aluminum filled materials enable rapid prototyping during the product development process. Those materials do not always meet the requirements for direct production of functional parts by laser sintering. For Direct Manufacturing of functional parts out of required materials and in high quality, the laser sintering process and the material palette needs to be further developed. During this research a laser sintering test equipment for material qualification has been built up. The forthcomings are an optimized software solution, an innovative optical system, an alternative powder coating system and an improved temperature control. The functionality of the test equipment is proved with the standard material PA2200 and two new laser-sintering-materials, Nylon 6 (PA 6) and Polyamide 613 (PA 613), are investigated. The process parameters are derived and mechanical properties are determined by tensile tests.


Dependencies of the Adhesion Forces between TiO2 Nanoparticles on Size and Ambient Humidity

J. Laube, M. Dörmann, H. Schmid, L. Mädler, L. Colombi Ciacchi, The Journal of Physical Chemistry C (2017), pp. 15294-15303

We study the variation of the adhesion forces between wet TiO2 nanoparticles as a function of their size and the ambient relative humidity. Combining all-atom molecular dynamics and capillary simulations we demonstrate that the linear scaling of the interparticle forces with the particle diameter, well established for microscopic and macroscopic particles, can be extended down to diameters of a few nm. At this size scale, however, the molecular nature of the water adsorbates dictates the adhesion forces both via solvation effects and influencing parameters of analytical capillary models such as the equilibrium particle–particle separation distance and the water/particle contact angle. Moreover, the water surface tension becomes considerably larger than the macroscopic bulk value due to combined effects of thin-film confinement and tight curvature, in a way that strongly depends on humidity and particle size. Taking these effects into proper account, classical capillary equations can be used to predict the interparticle forces even of the smallest particles considered here (4 nm), although the circular approximation fails to reproduce the distance at which the water meniscus breaks. Finally, the transition between the dominating effects at the nanoscopic scale and conventional capillary theory valid at microscopic size scales can be only rationalized if the presence of roughness asperities on the surface of the large particles is explicitly taken into account.


Distance-dependency of capillary bridges in thermodynamic equilibrium

M. Dörmann, H. Schmid, Powder Technology (2017), pp. 175-183

Capillary forces are very important considering the handling of powders as they, in general, exceed other adhesion forces. These capillary forces are dependent on several different parameters. Especially the distance between the particles is an important parameter. For example, in moving bulk solids a large variety of distances between particles will occur. Therefore, the distance-dependence of capillary bridges was investigated with a numerical simulation method, assuming thermodynamic equilibrium which is attained very fast for small particles. This method uses the Kelvin equation and the Young-Laplace equation to calculate numerically the shape of the capillary bridge without any assumption regarding the shape. The force is eventually derived from the meniscus shape. The distance becomes extremely important when the capillary liquid bridge between two surfaces is only determined by capillary condensation depending on relative humidity. Only a slight increase of the distance within the fraction of a nanometer changes the behaviour of the capillary force significantly. Furthermore, the influence of the force on the separation of particles will be presented. The force decreases almost linearly with increasing distance for a wide range of distances and consequently, a contact stiffness for capillary bridges could be derived. These results may e.g. be used in DEM models. Also, the maximum separation distance of capillary bridges in thermodynamic equilibrium and the correlation with the according bridge volume was investigated. As two limiting cases for capillary bridges at varying distances one can assume either a constant curvature, i.e. infinitely fast attainment of equilibrium, or a constant volume, i.e. infinitely slow attainment of equilibrium. Therefore, a comparison of these two possibilities will be presented and discussed as well.


Herstellbarkeit und mechanische Charakterisierung von lasergesinterten Gitterstrukturen

D. Menge, S. Josupeit, P.. Delfs, H. Schmid, in: Additive Fertigung von Bauteilen und Strukturen, Springer Vieweg, 2017, pp. 105-120

DOI


Experimental analysis and modeling of local ageing effects during laser sintering of polyamide 12 in regard to individual thermal histories

S. Josupeit, H. Schmid, Journal of Applied Polymer Science (2017), 134(42)

Polymer laser sintering (LS) is an important additive manufacturing (AM) technology. Individual and complex parts are directly produced from CAD data without the need of specific tools. The raw material is a polymer powder, which is deposited layerwise and melted selectively with a laser. Built parts are embedded in residual unmolten powder, the so-called part cake, which undergoes thermal ageing effects due to the exposure to high temperatures for long times during the manufacturing process. Hence, the recyclability of the unmolten powder is limited. This article focuses on a fundamental analysis of the ageing kinetics dependent on time, temperature, and oxygen content in the gas atmosphere. A model is developed and applied to measured, position-dependent process temperature histories to successfully predict the ageing distribution within a part cake. The results can be used to optimize the thermal process management in LS and to develop new efficient powder recycling methods.


Maßtoleranzen für die additive Fertigung: Experimentelle Untersuchungen für das Lasersintern

T. Lieneke, G. Adam, S. Josupeit, P. Delfs, D. Zimmer, in: Proceedings of the 14th Rapid.Tech Conference, Hanser Verlag, 2017, pp. 327-344

DOI



Modelling of temperatures and heat flow within laser sintered part cakes

S. Josupeit, L. Ordia, H. Schmid, Additive Manufacturing (2016), pp. 189-196

Temperature effects in the polymer laser sintering process are an important aspect regarding the process reproducibility and part quality. Depending on the job layout and position within the part cake, individual temperature histories occur during the process. Temperature history dependent effects are for example part warpage, the crystallization rate and powder ageing effects. This work focuses on temperatures and heat flow within laser sintered part cakes. Therefore, a thermal Finite Element (FE) model of a part cake is developed based on experimental in-process temperature measurements. Thermal boundary conditions and properties of the used bulk polymer powder are analyzed and relevant parameters are identified. The model is validated and optimized considering different job heights and ambient conditions during the cooling phase. It is finally possible to predict position-dependent temperature histories as a function of significant job parameters. The model allows a transfer of the results for varied boundary conditions during cooling. In combination with an implementation of built parts, this model will be an important tool for the development of optimized process controls and cooling strategies.


Guard ring induced distortion of the steady velocity profile in a parallel plate rheometer

H. Schmid, S. Pieper, Applied Rheology (2016)

The shape and fracture of the free surface frequently limits the measuring range and impedes the use of optical velocimetric techniques in parallel plate and cone plate setups. To prevent this, various kinds of edge guards are often employed. In the present study, we elucidate how an edge guard distorts the steady velocity profile in a parallel plate setup. To this end, we analyzed the velocity field of a strongly shear-thinning fluid, a Newtonian fluid and a set of suspensions via particle image velocimetry in a parallel plate device. Several guard ring sizes were studied. The distortion is described by a simple three parameter model. These parameters are mostly constant for different fluids and suspensions with particle volume fractions below 45%. With increasing radius, the guard ring.s influence approaches a limiting value that we attribute to the influence of the fluid surrounding the gap. Our results indicate a limiting ratio of the difference between plate radius and guard to gap size that should always be exceeded. In the presence of a guard ring, even Newtonian fluids do not exhibit a constant shear rate for most radial distances within the gap. This distortion of the velocity field challenges the simple superposition approach of unguarded device and guard influence that is prevalent in the literature.


Geometrische Genauigkeit von Lasersinter-Bauteilen: Einflüsse und Maßnahmen / Dimensional accuracy of polymer laser sintered parts: Influences and measures

W. Kniffka, M. Eichmann, G. Witt, S. Josupeit, P. Delfs, T. Lieneke, G. Adam, H. Schmid. Geometrische Genauigkeit von Lasersinter-Bauteilen: Einflüsse und Maßnahmen / Dimensional accuracy of polymer laser sintered parts: Influences and measures. 2016.

In the polymer laser sinter process, part quality depends on many influencing factors along the process chain. For application of the technology in series production and an integration of laser sintered parts into a technical environment, the dimensional accuracy of parts has to be taken into account. Therefore, occurring deviations of the process have to be known to define tolerances for part design. Dimensional deviations and their scattering have to be reduced and homogenized based on process parameters and build job layout. In this work, the dimensional accuracy of laser sintered parts is analyzed for varied parameter values. Influences of different process and geometrical build job parameters on dimensional deviations are figured out. The experimental results allow an evaluation of more and less important influences. Finally, measures are deduced to reduce and homogenize dimensional deviations.


Layer-formation of non-colloidal suspensions in a parallel plate rheometer under steady shear

S. Pieper, H. Schmid, Journal of Non-Newtonian Fluid Mechanics (2016), pp. 1-7

Suspensions are subject to confinement induced structuring, i.e. layering, at the confining surfaces. While most of the previous work focused on layering in Couette cells, the present study aimed to characterize the resulting layers at the plates of a parallel plate rheometer with regard to their relative particle concentration. The particle concentration profile over the radial distance was characterized for various mean concentrations and gap heights. To this end, we mapped the distribution of fluorescently dyed tracer particles in density and refractive index matched suspensions. The results indicate that layering at the surfaces stabilizes as the ratio between gap height and particle diameter increases. For lower gap heights, i.e. as the suspension approaches a two dimensional state, the layer concentration was non-uniform over the plates. In general, results were quantitatively different for the upper and lower plate and the concentration profiles were noticeably asymmetric. We conclude that this is probably the result of the rheometer loading or the start-up process. The stable layers as well as the inhomogeneous particle distribution in general offer an explanation for the lack of transferability of viscosimetric results between different setups.


Additive Fertigung

J. Gausemeier, M. Schmidt, R. Anderl, H. Schmid, C. Leyens, G. Seliger, M. Karg, M. Kage, acatech - Deutsche Akademie der Technikwissenschaften, 2016


Manufacturability and Mechanical Characterization of Laser Sintered Lattice Structures

S. Josupeit, P. Delfs, D. Menge, H. Schmid, in: 27th Annual International Solid Freeform Fabrication Symposium , 2016, pp. 2077-2086

The implementation of lattice structures into additive manufactured parts is an important method to decrease part weight maintaining a high specific payload. However, the manufacturability of lattice structures and mechanical properties for polymer laser sintering are quite unknown yet. To examine the manufacturability, sandwich structures with different cell types, cell sizes and lattice bar widths were designed, manufactured and evaluated. A decisive criterion is for example a sufficient powder removal. In a second step, manufacturable structures were analyzed using four-point-bending tests. Experimental data is compared to the density of the lattice structures and allows for a direct comparison of different cell types with varied geometrical attributes. The results of this work are guidelines for the design and dimensioning of laser sintered lattice structures.


Optimized build orientation of additive manufactured parts for improved surface quality and build time

P. Delfs, M. Tows, H. Schmid, Additive Manufacturing (2016), 2(12, Part B), pp. 214-320

The layered structure of Additive Manufacturing processes results in a stair- stepping effect of the surface topographies. In general, the impact of this effect strongly depends on the build angle of a surface, whereas the overall surface roughness is additionally caused by the resolution of the specific AM process. The aim of this work is the prediction of the surface quality in dependence of the building orientation of a part. These results can finally be used to optimize the orientation to get a desired surface quality. As not all parts of the component surface are equally important, a preselection of areas can be used to improve the overall surface quality of relevant areas. The model uses the digital AMF format of a part. Each triangle is assigned with a roughness value and by testing different orientations the best one can be found. This approach needs a database for the surface qualities. This must be done separately for each Additive Manufacturing process and is shown exemplarily with a surface topography simulation for the laser sintering process.


Extended Analysis of the Surface Topography of Laser Sintered Polymer Parts

P. Delfs, H. Schmid, in: Fraunhofer Direct Digital Manufacturing Conference, 2016, pp. 411-414

DOI


Thermal properties of polyamide 12 powder for application in laser sintering

S. Josupeit, H. Schmid, in: International Congress on Particle Technology (PARTEC) , 2016


Dimensional accuracy of polymer laser sintered parts: Influences and measures

S. Josupeit, P. Delfs, T. Lieneke, G. Adam, M. Gessler, H. Pfisterer, H. Schmid, in: Rapid Tech - International Trade Show & Conference for Additive Manufacturing , 2016, pp. 107-120

In the polymer laser sinter process, part quality depends on many influencing factors along the process chain. For application of the technology in series production and an integration of laser sintered parts into a technical environment, the dimensional accuracy of parts has to be taken into account. Therefore, occuring deviatons and their scattering have to be reduced and homogenized based on process parameters and build job layout. In this work, the dimensional accuracy of laser sintered parts is analyzed for varied parameter values. Influences of different process and geometrical build job parameters on dimensional deviatons are figured out. The experimental results allow an evaluation of more and less important influences. Finally, measures are deduced to reduce and homogenize dimensional deviations.


Additive Manufacturing of a Lightweight Rotor for a Permanent Magnet Synchronous Machine

S. Lammers, G. Adam, H. Schmid, R. Mrozek, R. Oberacker, M. Hoffmann, F. Quattrone, B. Ponick, in: EDPC 2016, 2016

Additive Manufacturing (AM), also known as 3D printing, is a relatively new technology which enables the toolless production of components and entire assemblies directly from a CAD file. Today, the technology is still not widely used in industrial production. It is mainly limited to special applications, although it shows great potential. In this paper, first approaches are shown to apply AM to the production of rotors for permanent magnet synchronous machines (PMSM). The possibilities of a lightweight design with a low moment of inertia as well as the influence on the magnetic anisotropy for an improved sensorless control of PMSM are pointed out. The results clearly demonstrate the great potential of additive manufacturing in electrical engineering applications.


Influences on the dimensional Accuracy of Laser Sintered Parts along the Process Chain

S. Josupeit, P. Delfs, T. Lieneke, H. Schmid, in: 27th Annual International Solid Freeform Fabrication Symposium , 2016


Direct measurement of wall slip and slip layer thickness of non-Brownian hard-sphere suspensions in rectangular channel flows

S. Jesinghausen, R. Weiffen, H. Schmid, Experiments in Fluids (2016)

Wall slip is a long-known phenomenon in the field of rheology. Nevertheless, the origin and the evolution are not completely clear yet. Regarding suspensions, the effect becomes even more complicated, because different mechanisms like pure slip or slip due to particle migration have to be taken into account. Furthermore, suspensions themselves show many flow anomalies and the isolation of slip is complicated. In order to develop working physical models, further insight is necessary. In this work, we measured experimentally the wall slip velocities of different highly filled suspensions in a rectangular slit die directly with respect to the particle concentration and the particle size. The slip velocities were obtained using a particle image velocimetry (PIV) system. The suspensions consisting of a castor oil–cinnamon oil blend and PMMA particles were matched in terms of refractive indexes to appear transparent. Hereby, possible optical path lengths larger than 15 mm were achieved. The slip velocities were found to be in a quadratic relation to the wall shear stress. Furthermore, the overall flow rate as well as the particle concentration has a direct influence on the slip. Concerning the shear stress, there seem to be two regions of slip with different physical characteristics. Furthermore, we estimated the slip layer thickness directly from the velocity profiles and propose a new interpretation. The PIV technique is used to investigate the viscosity and implicit the concentration profile in the slit die. It is shown that the particle migration process is quite fast.



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Veröffentlichungen und Konferenz-Proceedings

  • Stephan Schmidt, Melanie Gräßer, Hand-Joachim Schmid
    A Shape Newton Scheme for Deforming Shells with Application to Capillary Bridges
    Submitted (29.12.2020): SIAM Journal on Scientific Computing
    Preprint: https://arxiv.org/abs/2012.15016
     

  • Christina Kummert, Stefan Josupeit, Hans-Joachim Schmid
    Thermoplastic Elastomer Part Color as Function of Tmeperature Histories and Oxygen Atmosphere During Selectice Laser Sintering
    JOM (The Journal of The Minerals, Metals  Material Society (TMS)) (2017)
     
  • Jens Laube, Michael Dörmann, Hans-Joachim Schmid, Lutz Mädler, Lucio Colombi Ciacchi
    Dependencies of the Adhesion Forces between TiO2 Nanoparticles on Size and Ambient Humidity
    J. Phys. Chem. C (2017), 121 (28), pp 15294–15303
     
  • Patrick Delfs, Hans-Joachim Schmid
    Areal Surface Characterization of Laser Sintered Parts for various Process Parameters
    Solid Freeform Fabrication Symposium (SFF), Austin, USA (2017)
     
  • Stefan Josupeit, Hans-Joachim Schmid
    Experimental analysis and modeling of local ageing effects during laser sintering of polyamide 12 in regard to individual thermal histories
    Journal of Applied Polymer Science (2017)
     
  • Tobias Lieneke, Guido Adam, Stefan Josupeit, Patrick Delfs, Detmar Zimmer
    Maßtoleranzen für die additive Fertigung: Experimentelle Untersuchung für das Lasersintern
    Rapid.Tech, Erfurt (2017)
     
  • Dennis Menge, Stefan Josupeit, Patrick Delfs, Hans-Joachim Schmid
    Herstellbarkeit und mechanische Charakterisierung von lasergesinterten Gitterstrukturen
    Springer Vieweg Fachbuch: Additive Fertigung von Bauteilen und Strukturen (2017), pp. 105-120
     
  • Michael Dörmann, Hans-Joachim Schmid
    Distance-dependency of capillary bridges in thermodynamic equilibrium
    Powder Technology 312 (2017), pp. 175-183
     
  • Steffen Jesinghausen, Hans-Joachim Schmid
    Direct measurement of wall slip and slip layer thickness of non-Brownian hard-sphere suspensions in rectangular channel flows
    Experiments in Fluids 57 (2016), Issue 9, 1-15
     
  • Sven Pieper, Hans-Joachim Schmid
    Guard ring induced distortion of the steady velocity profile in a parallel plate rheometer
    Applied Rheology 26 (2016), Issue 6, p. 64533
     
  • Stefan Josupeit, Patrick Delfs, Dennis Menge, Hans-Joachim Schmid
    Herstellbarkeit und mechanische Charakterisierung von lasergesinterten Gitterstrukturen
    DVM-Tagung "Additiv gefertigte Bauteile und Strukturen", Berlin, Deutschland, pp. 51-61 (2016)
     
  • Friedrich Prill, Sascha Schiller, Hans-Joachim Schmid
    Development of a Filtration System for the Combined Separation of Ultrafine Dust Particles and Gaseous Pollutants from Biomass Combustion Processes
    FILTECH (2016)
     
  • Stefan Josupeit, Hans-Joachim Schmid
    Temperature history within laser sintered part cakes and its influence on process quality
    Rapid Prototyping Journal 22 (2016) 5, pp. 788-793
     
  • Stefan Josupeit, Patrick Delfs, Dennis Menge, Hans-Joachim Schmid
    Manufacturability and Mechanical Characterization of Laser Sintered lattice Structures
    Solid Freeform Fabrication Symposium (SFF), Austin, USA (2016)
     
  • Stefan Josupeit, Lavish Ordia, Hans-Joachim Schmid
    Modelling of temperatures and heat flow within laser sintered part cakes
    Additive Manufacturing (2016)
     
  • Patrick Delfs, Marcel Töws, Hans-Joachim Schmid
    Optimized build orientation of additive manufactured parts for improved surface quality and build time
    Additive Manufacturing (2016)
     
  • Sven Pieper, Hans-Joachim Schmid
    Layer-formation of non-colloidal suspensions in a parallel plate rheometer under steady shear
    Journal of Non-Newtonian Fluid Mechanics 234 (2016), pp 1-7 
     
  • Stefan Josupeit, Patrick Delfs, Tobias Lieneke, Guido Adam, Hans-Joachim Schmid
    Dimensional accuracy of polymer laser sintered parts: Influences and measures
    Rapid.Tech, Erfurt, Deutschland (2016), pp. 107-120
     
  • Stefan Josupeit, Hans-Joachim Schmid
    Thermal properties of polyamide 12 powder for application in laser sintering
    International Congress on Particle Technology (PARTEC), Nürnberg, Deutschland (2016)
     
  • Michael Dörmann, Hans-Joachim Schmid
    Continuum-mechanical simulation of capillary bridges between nanoscale particles
    International Congress on Particle Technology (PARTEC), Nürnberg, Deutschland (2016)
     
  • Sascha Schiller, Hans-Joachim Schmid
    Modelling and Simulation of pressure drop at non-homogeneous filtration conditions
    World Filtration Congress, Taipeh, Taiwan (2016)
     
  • Patrick Delfs, Hans-Joachim Schmid
    Extended Analysis of the Surface Topography of Laser Sintered Polymer Parts
    Fraunhofer Direct Digital Manufacturing Conference, Berlin, Deutschland (2016)
     
  • Sascha Schiller, Hans-Joachim Schmid
    Evaluation of the efficiency of filtration processes using precoat materials
    Chemical Engineering & Technology 39 (2016) 3, pp 491–498
     
  • Sascha Schiller, Hans-Joachim Schmid
    Evaluation of the Efficiency of Filtration Processes Using Precoat Materials
    FILTECH (2015)
     
  • Lena Tigges, Alfred Wiedensohler, Kay Weinhold, Jay Gandhi, Hans-Joachim Schmid
    Bipolar charge distribution of a soft X-ray diffusion charger
    Journal of Aerosol Science, 90 (2015), pp 77-86
     
  • Stefan Josupeit, Sabine Tutzschky, Monika Gessler, Hans-Joachim Schmid
    Powder ageing and material properties of laser sintered polyamide 12 using low refresh rates
    Neue Entwicklungen in der Additiven Fertigung: Beiträge aus der wissenschaftlichen Tagung der Rapid.Tech 2015, (2015), pp 63-78
     
  • Lena Tigges, Ankit Jain, Hans-Joachim Schmid
    On the bipolar charge distribution used for mobility particle sizing: Theoretical considerations
    Journal of Aerosol Science, 88 (2015), pp 119-134
     
  • Tobias Lieneke, Guido Adam, Stefan Leuders, Frederick Knoop, Stefan Josupeit, Patrick Delfs, Nils Funke, Detmar Zimmer
    Entwicklung einer Methode zur systematischen Erarbeitung von Maßtoleranzen für additive Fertigungsverfahren
    Rapid.Tech, Erfurt, Deutschland (2015)
     
  • Stefan Josupeit, Johannes Lohn, Eduard Hermann, Monika Gessler, Stephan Tenbrink, Hans-Joachim Schmid
    Material properties of laser sintered polyamide 12 as function of build cycles using low refresh rates
    Solid Freeform Fabrication Symposium (SFF), Austin, USA (2015)
     
  • Stefan Josupeit, Hans-Joachim Schmid
    Temperature history within laser sintered part cakes and its unfluence on process quality
    Solid Freeform Fabrication Symposium (SFF), Austin, USA (2015)
     
  • Tobias Lieneke, Guido Adam, Stefan Leuders, Frederick Knoop, Stefan Josupeit, Patrick Delfs, Nils Funke, Detmar Zimmer
    Systematical determination of tolerances for additive manufacturing by measuring linear dimensions
    Solid Freeform Fabrication Symposium (SFF), Austin, USA (2015)
     
  • Patrick Delfs, Zhiyuan Li, Hans-Joachim Schmid
    Mass Finishing of Laser Sintered Parts
    Solid Freeform Fabrication Symposium (SFF), Austin, USA (2015)
     
  • Patrick Delfs, Marcel Töws, Hans-Joachim Schmid
    Surface Roughness optimized Alignment of Parts for Additive Manufacturing Processes
    Solid Freeform Fabrication Symposium (SFF), Austin, USA (2015)
     
  • Sascha Schiller, Hans-Joachim Schmid
    Highly efficient filtration of ultrafine dust in baghouse filters using precoat materials
    Powder Technology 279 (2015), pp 96-105
     
  • Michael Dörmann, Hans-Joachim Schmid
    Simulation of Capillary Bridges between Particles
    Procedia Engineering 102 (2015), pp 14-23
     
  • Sven Pieper, Nadine Kirchhoff, Hans-Joachim Schmid
    Absence of pressure sensitivity of apparent wall slip in pressure-driven flow of non-colloidal suspensions
    Rheologica Acta 54 (1) (2015), pp 69-75
     
  • Michael Dörmann, Hans-Joachim Schmid
    Simulation of Capillary Bridges between Nanoscale Particles
    Langmuir, 30 (2014) 4, pp 1055–1062
     
  • Stefan Josupeit, Stefan Rüsenberg, Nicola Rupp, Monika Gessler, Hans-Joachim Schmid
    Thermal Ageing of Polyamide 12 used for Polymer Laser Sintering - Influence on Part Quality Characteristics
    Annual Technical Conference of the American Spciety of Plastics Engineers (ANTEC) (2014), pp 2383-2388
     
  • Sascha Schiller, Hans-Joachim Schmid
    Ultrafine Dust Filtration Using Precoat Materials Considering the Influence of Filter Media
    Chemical Engineering & Technology, 37 (2014) 6, pp 1009-1020
     
  • Stefan Rüsenberg, Stefan Josupeit, Hans-Joachim Schmid
    A Method to Characterize the Quality of a Polymer Laser Sintering Process
    Advances in Mechanical Engineering, Volume 2014, Article ID 185374
     
  • Stefan Josupeit, Hans-Joachim Schmid
    Three-Dimensional In-Process Temperature measurement of Laser Sintered Part Cakes
    Solid Freeform Fabrication Symposium (SFF) (2014)
     
  • Stefan Josupeit, Lavish Ordia, Hans-Joachim Schmid
    Development of a Basic Model to Simulate the Laser Sintering Cooling Process
    International Conference on Additive Technologies (ICAT) (2014)
     
  • Patrick Delfs, Ashrith Ananthraj Herale, Zhiyuan Li, Hans-Joachim Schmid
    Simulation of the Surface Topography on Laser Sintered Polymer Parts
    Solid Freeform Fabrication Symposium (SFF) (2014)
     
  • Sascha Schiller, Hans-Joachim Schmid
    Hocheffiziente Feinstaubabscheidung aus Kleinfeuerungsanlagen mit einem Schlauchfilter
    Chemie Ingenieur Technik (CIT), 85 (2013) 8, pp 1324-1328
     
  • Sascha Schiller, Hans-Joachim Schmid
    Multiple-Use of Precoat Materials for the Fine Dust Filtration of a Baghouse Filter for Wood-Fired Heaters
    Filtech (2013)
     
  • Stefan Josupeit, Stefan Rüsenberg, Hans-Joachim Schmid
    A Material Based Quality Concept for Polymer Laser Sintering
    Solid Freeform Fabrication Symposium (SFF) (2013), pp 44-54
     
  • Stefan Rüsenberg, Agnes Bagsik, Johannes Büsching, Hans-Joachim Schmid
    Additiv versus Konventionell: Benchmarking am Beispiel eines Designs aus der Luftfahrtindustrie
    Rapid.Tech (2013)
     
  • Stefan Rüsenberg, Hans-Joachim Schmid
    Advanced Characterization Method of nylon 12 Materials for Application in Laser Sinter Processing
    International Conference of the Polymer Processing Society (PPS), 1593, 713 (2014)
     
  • Sven Pieper, Hans-Joachim Schmid
    Apparent Wall Slip and Particle Migration in Laminar Flow of Suspensions through a Slit Die
    International Congress on Particle Technology (PARTEC) (2013)
     
  • Jacqueline Erler, Stefanie Machunsky, Philipp Grimm, Hans-Joachim Schmid, Urs Peuker
    Liquid-Liquid Phase Transfer of Magnetite Nanoparticles - Evaluation of Surfactants
    Powder Technology, 247 (2013), pp 265-269
     
  • Philipp Grimm, Hans-Joachim Schmid
    An efficient process for producing high-quality organosols
    International Congress on Particle Technology (PARTEC) (2013)
     
  • Agnes Bagsik, Stefan Josupeit, Volker Schöppner, Eric Klemp
    Mechanical analysis of lightweight constructions manufactured with fused deposition modeling
    International Conference of the Polymer Processing Society (PPS), 1593, 696 (2014)
     
  • Sascha Schiller, Hans-Joachim Schmid
    Development of a baghouse filter for domestic wood-fired heaters
    World Filtration Congress (2012)
     
  • Sascha Schiller, Hans-Joachim Schmid
    Höchst effiziente Feinstaubabscheidung aus Kleinfeuerungsanlagen und dauerhafte Einhaltung von extrem niedrigen Emissionswerten mit einem Schlauchfilter
    VDI-Berichte 2165: "Emissionsminderung 2012" (2012)
     
  • Stefan Rüsenberg, Rene Weiffen, Frederick Knoop, Hans-Joachim Schmid
    Controlling the Quality of Laser Sintered Parts along the Process Chain
    Solid Freeform Fabrication Symposium (SFF) (2012)
     
  • Stefan Rüsenberg, Lukas Schmidt, Hendrik Hosse, Hans-Joachim Schmid
    Mechanical Properties as a result of multitude of parameters
    European Forum on Rapid Prototyping (2012)
     
  • Nadine Kirchhoff, Cathrin Schröder, Daniel Stute, Elmar Moritzer, Hans-Joachim Schmid
    Wood-Plastic-Composites: Rheologische Charakterisierung und Füllverhalten im Spritzgießprozess
    Chemie Ingenieur Technik (CIT), 84 (2012) 9, pp 1584-1589
     
  • Martin J. Kirchhof, Henning Förster, Hans-Joachim Schmid, Wolfgang Peukert
    Sintering Kinetics and Mechanisms of Vitreous Nanoparticles
    Journal of Aerosol Science, 45 (2012), pp 26-39
     
  • Hans-Joachim Schmid, Stefan Rüsenberg, Zhenpeng Sun
    Powder Aging upon Laser Sintering – Characterization and Consequences
    Solid Freeform Fabrication Symposium (SFF) (2011)
     
  • Jianquan Bo, Josef Noeke
    Sprachliche Vorbereitung von chinesischen Studierenden auf ein Maschinenbaustudium und auf ein Fachpraktikum in Deutschland
    CDAH-Tagung (Chinesisch-Deutsches Forum für Anwendungsorientierte Hochschulausbildung) (2011)
     
  • Josef Noeke
    Aufbau und Betrieb der Chinesisch-Deutschen Technischen Fakultät Qingdao
    Tagungsband des zweiten Chinesisch-Deutschen Forums in Hannover (2011)
     
  • Martin J. Kirchhof, Henning Förster, Hans-Joachim Schmid, Wolfgang Peukert
    Sintering Kinetics and Mechanisms of Vitreous Nanoparticles
    Journal of Aerosol Science, 45 (2012), pp 26-39
     
  • Stefan Rüsenberg, Lukas Schmidt, Hendrik Hosse, Hans-Joachim Schmid
    Porosity as a Key to Increase Material Properties of Laser Sintered Parts
    Innovative Developments in Virtual and Physical Prototyping (VRAP), Bartolo et al. (Hrsg.), CRC Press, (2011) 81
     
  • Stefan Rüsenberg, Lukas Schmidt, Hans-Joachim Schmid
    Mechanical and Physical Properties – A Way to assess quality of Laser Sintered Parts
    Solid Freeform Fabrication Symposium (SFF) (2011)
     
  • Lena Knobel, Hans-Joachim Schmid
    Bipolar Stationary Charge Distribution - A Closer Look to Relevant und Irrelevant Influences
    European Aerosol Conference (EAC) (2011)
     
  • Hans-Joachim Schmid, Martin J. Kirchhof
    Sintering of Silica Nanoparticles
    International Aerosol Conference (IAC) (2010)
     
  • Stefan Gerkens, Frank Bayer, Klaus Huber, Hans-Joachim Schmid
    Structure Analysis of Nanocomposites using QELS
    World Congress on Particle Technology (WCPT) (2010)
     
  • M. Seipenbusch, S. Rothenbacher, Martin J. Kirchhof, Hans-Joachim Schmid, A. P. Weber
    Interparticle forces in silica nanoparticle agglomerates
    Journal of Nanoparticle Research, 12 (2010) 6, pp 2037-2044
     
  • Richard Körmer, M.P.M. Jank, H. Ryssel, Hans-Joachim Schmid, Wolfgang Peukert
    Aerosol synthesis of silicon nanoparticles with narrow size distribution-Part 1: Experimental investigations
    Journal of Aerosol Science, 41 (2010) 11, pp 998-1007
     
  • Richard Körmer, Hans-Joachim Schmid, Wolfgang Peukert
    Aerosol synthesis of silicon nanoparticles with narrow size distribution-Part 2: Theoretical analysis of the formation mechanism
    Journal of Aerosol Science, 41 (2010) 11, pp 1008-1019
     
  • Martin J. Kirchhof, Hans-Joachim Schmid, Wolfgang Peukert
    Three-dimensional simulation of viscous flow agglomerate sintering
    Physical Review E, 80 (2009) 2, 026319
     
  • Stefanie Machunsky, Philipp Grimm, Hans-Joachim Schmid, Urs Peuker
    Liquid-liquid phase transfer of magnetite nanoparticles
    Colloids and Surfaces A, 348 (2009) 1-3, pp 186-190
     
  • Belal Al-Zaitone, Hans-Joachim Schmid, Wolfgang Peukert
    Simulation of structure and mobility of aggregates formed by simultaneous coagulation, sintering and surface growth
    Journal of Aerosol Science, 40 (2009) 11, pp 950-964
     
  • Vassil Vassilev, Michael Gröschel, Hans-Joachim Schmid, Wolfgang Peukert, G. Leugering
    Interfacial energy estimation in a precipitation reaction using the flatness based control of the moment trajectories
    Chemical Engineering Science, 65 (2009) 6, pp  2183-2189
     
  • Stefanie Machunsky, Philipp Grimm, Hans-Joachim Schmid, Urs Peuker
    Liquid-liquid phase transfer of magnetite nanoparticles
    World Congress on Chemical Engineering (2009)
     
  • Henning Förster, D. Kilian, Hans-Joachim Schmid, Wolfgang Peukert
    Novel Arc Plasma System for the Aerosol Synthesis of Metal Nanoparticles
    European Aerosol Conference (EAC) (2009)
     
  • Jacqueline Erler, Stefanie Machunsky, Philipp Grimm, Hans-Joachim Schmid, Urs Peuker
    Flüssig/Flüssig-Phasentransfer von Nanopartikeln
    Chemie Ingenieur Technik (CIT), 80 (2008) 9, pp 1424-1425
     
  • Michael Horn, Hans-Joachim Schmid
    A comprehensive approach in modeling Lagrangian particle deposition in turbulent boundary layers
    Powder Technology, 169 (2008), pp 189-198
     
  • Richard Körmer, Hans-Joachim Schmid, Michael P.M. Jank, H. Ryssel, Wolfgang Peukert
    Aerosol synthesis of monodisperse, high-purity silicon nanoparticles
    European Aerosol Conference (EAC) (2008)
     
  • Stefanie Machunsky, Philipp Grimm, Hans-Joachim Schmid, Urs Peuker
    Flüssig-flüssig-Phasentransfer von Magnetit Nanopartikeln
    Processnet Jahrestagung / Chemie Ingenieur Technik, 80 (2008), pp 1424-1425
     
  • L. Schneider, Hans-Joachim Schmid, Wolfgang Peukert
    Influence of particle size and concentration on the second harmonic signal generated at colloidal surfaces
    Applied Physics B, 87 (2007) 2, pp 333-339
     
  • Michael Horn, Hans-Joachim Schmid
    Neuer Ansatz zur Modellierung der Abscheidung in einem modifizierten Rohrelektrofilter
    Gefahrstoffe - Reinhaltung Luft, 67 (2007) 4, pp 147-151
     
  • Michael Horn, Hans-Joachim Schmid
    Soot separation in a modified pipe electrostatic precipitator
    Filtech (2007)
     
  • Hans-Joachim Schmid
    Modelling of Structure-Property Relationships of Nanoscaled Powders
    International Congress on Particle Technology (PARTEC) (2007)
     
  • Michael Horn, Hans-Joachim Schmid
    Influence of Convergence Control on Lagrangian Predictions of Particulate Two-Phase Flow
    International Congress on Particle Technology (PARTEC) (2007)
     
  • Michael Horn, Hans-Joachim Schmid
    Soot Separation in a Modified Pipe Electrostatic Precipitator
    International Congress on Particle Technology (PARTEC) (2007)
     
  • Martin J. Kirchhof, Henning Förster, Hans-Joachim Schmid, Wolfgang Peukert
    Investigation o f the Sintering Kinetics of Airborne Nanoparticles in a High-Temperature Reactor System
    International Congress on Particle Technology (PARTEC) (2007)
     
  • Richard Körmer, Hans-Joachim Schmid, Michael P.M. Jank, T. Erlbacher, H. Ryssel, Wolfgang Peukert
    Synthesis of Functional Nanoparticles
    International Congress on Particle Technology (PARTEC) (2007)
     
  • Vassil Vassilev, M. Gröschel, Wolfgang Peukert, G. Leugering, Hans-Joachim Schmid
    Interfacial energy estimation in a precipitation reaction using the flatness based control of the moment trajectories
    International Conference on Population Balance Modelling (2007)
     
  • Christian Artelt, Hans-Joachim Schmid, Wolfgang Peukert
    Modelling titania formation at typical industrial process conditions: effect of structure and material properties on relevant growth mechanisms
    Chemical Engineering Science, 61 (2006) 1, pp 18-32
     
  • Hans-Joachim Schmid, Belal Al-Zaitone, Christian Artelt, Wolfgang Peukert
    Evolution of the Fractal Dimension for Simultaneous Coagulation and Sintering
    Chemical Engineering Science, 61 (2006) 1, pp 293-305
     
  • H.-C. Schwarzer, F. Schwertfirm, M. Manhart, Hans-Joachim Schmid, Wolfgang Peukert
    Predictive simulation of nanoparticle precipitation based on the population balance equation
    Chemical Engineering Science, 61 (2006) 1, pp 167-181
     
  • Michael Horn, Hans-Joachim Schmid
    Modellierung der wandnahen Bereiche in turbulenten Zweiphasenströmungen
    Chemie Ingenieur Technik (CIT), 78 (2006) 6, pp 694-699
     
  • C. Binder, C. Feichtinger, Hans-Joachim Schmid, N. Thürey, Wolfgang Peukert, U. Rüde
    Simulation of the Hydrodynamic Drag on Aggregated Particles
    Journal of Colloid and Interface Science, 301 (2006) 1, pp 155-167
     
  • Hans-Joachim Schmid
    Simulation of Aerosol Synthesis by Simultaneous Coagulation, Sintering and Growth: Structure and Product Property Formation
    World Congress on Particle Technology (WCPT) (2006)
     
  • Hans-Joachim Schmid, Martin J. Kirchhof, Henning Förster, Wolfgang Peukert
    Theoretical and Experimental Investigations on Sintering Kinetics of Silica Nanoparticles
    World Congress on Particle Technology (WCPT) (2006)
     
  • Hans-Joachim Schmid, Christian Binder, Nils Thürey, Wolfgang Peukert
    Simulation of the Hydrodynamic Behaviour of Aggregated Particles
    World Congress on Particle Technology (WCPT) (2006)
     
  • Michael Horn, Hans-Joachim Schmid
    Convergence Control and Convergence Improvement in Lagrangian Predictions of Particulate Two-Phase Flows
    World Congress on Particle Technology (WCPT) (2006)
     
  • Michael Horn, Hans-Joachim Schmid
    Modelling of the Boundary Layer in Turbulent Two-Phase-Flows
    World Congress on Particle Technology (WCPT) (2006)
     
  • J. Gradl, F. Schwertfirm, H.-C. Schwarzer, Hans-Joachim Schmid, M. Manhart, Wolfgang Peukert
    Nanoparticle Precipitation in a T-Mixer: Coupling Experimental and Numerical Investigations of the Fluid Dynamics with the Solid Formation Processes
    ASME Fluids Engineering Summer Meeting (2006)
     
  • Martin J. Kirchhof, Hans-Joachim Schmid, Henning Förster, Wolfgang Peukert
    Sintering Kinetics of Silica Nanoparticles: Comparison of Theory and Experiment
    International Aerosol Conference (IAC) (2006)
     
  • Hans-Joachim Schmid
    Aerosol Synthesis by Simultaneous Nucleation, Coagulation, Sintering and Growth: Simulation of Structure and Product Property Formation
    International Aerosol Conference (IAC) (2006)
     
  • Hans-Joachim Schmid
    Struktur-Eigenschafts-Beziehungen nanoskaliger Pulver
    GVC-Jahrestagung (2006)
     
  • Christian Artelt, Hans-Joachim Schmid, Wolfgang Peukert
    On the impact of accessible surface and surface energy on particle formation and growth from the vapour phase
    Journal of Aerosol Science, 36 (2005) 2, pp 147-172
     
  • Hans-Joachim Schmid, Belal Al-Zaitone, Wolfgang Peukert
    Strukturbildung bei der Aerosolsynthese unter Berücksichtigung von simultaner Agglomeration, Sinterung und Oberflächenwachstum
    NanoMat Szene (2005)
     
  • Martin J. Kirchhof, Henning Förster, Hans-Joachim Schmid, Wolfgang Peukert
    Sintering Kinetics of Silica Nanoparticles: Theory and Experiment
    European Aerosol Conference (EAC) (2005)
     
  • Hans-Joachim Schmid, Belal Al-Zaitone, Wolfgang Peukert
    Simulation of Structure Formation in Aerosol Synthesis by Simultaneous Coagulation, Sintering and Growth
    European Aerosol Conference (EAC) (2005)
     
  • Martin J. Kirchhof, S. Froeschke, Hans-Joachim Schmid, A. P. Weber
    Characterization of First-Stage Sintering Kinetics
    European Aerosol Conference (EAC) (2005)
     
  • Martin J. Kirchhof, R. Diaz, Henning Förster, Hans-Joachim Schmid, Wolfgang Peukert
    Sintering Kinetics of Silica Nanoparticles: Theory and Experiment
    International Conference on Sintering (2005)
     
  • Messerer, Hans-Joachim Schmid, C. Knab, U. Pöschl, R. Nießner
    Erhöhung der Abscheidung ultrafeiner Dieselrußpartikeln durch Mikrokugelbeschichtung auf metallträgerbasierten Katalysatorstrukturen
    Chemie Ingenieur Technik (CIT), 76 (2004) 8, pp 1092-1096
     
  • Martin J. Kirchhof, Hans-Joachim Schmid, Wolfgang Peukert
    A New Reactor System for the Study of High Temperature Short-Time Sintering Kinetics of Nanoparticles
    Review of Scientific Instruments, 75 (2004) 11, pp 4833-4840
     
  • Hans-Joachim Schmid, Saurabh Tejwani, Christian Artelt, Wolfgang Peukert
    Monte Carlo simulation of aggregate morphology for simultaneous coagulation and sintering
    Journal of Nanoparticle Research, 6 (2004) 6, pp 613-626
     
  • Martin J. Kirchhof, Hans-Joachim Schmid, Wolfgang Peukert
    Experimental Study of the Sintering Progress of Ceramic Nanoparticles in a High Temperature Reactor System
    International Congress on Particle Technology (PARTEC) (2004)
     
  • Hans-Joachim Schmid, S. Teijwani, Christian Artelt, Wolfgang Peukert
    Aggregate Structure Evolution Accounting for Simultaneous Agglomeration and Sintering
    International Congress on Particle Technology (PARTEC) (2004)
     
  • Michael Horn, Hans-Joachim Schmid
    New method in numerical modelling of electric wet painting
    International Congress on Particle Technology (PARTEC) (2004)
     
  • Christian Artelt, Hans-Joachim Schmid, Wolfgang Peukert
    On the relevance of aggregate structure in population balance modelling of aerosol generation and growth processes
    International Congress on Particle Technology (PARTEC) (2004)
     
  • Christian Artelt, Hans-Joachim Schmid, Wolfgang Peukert
    Modelling titania formation at typical industrial process conditions: effect of structure and material properties on relevant growth mechanisms
    International Conference on Population Balance Modelling (2004)
     
  • Hans-Joachim Schmid, S. Tejwani, Christian Artelt, Wolfgang Peukert
    Evolution of the Fractal Dimension During Aerosol Processes
    International Conference on Population Balance Modelling (2004)
     
  • Martin J. Kirchhof, Hans-Joachim Schmid, Wolfgang Peukert
    Sintering Kinetics of Ceramic Nanoparticle Doublets
    European Aerosol Conference (EAC) (2004)
     
  • Martin J. Kirchhof, A. Rozas, Hans-Joachim Schmid, Wolfgang Peukert
    Simulation of Viscous Flow Aerosol Sintering by Three-Dimensional Computational Fluid Dynamics
    European Aerosol Conference (EAC) (2004)
     
  • Martin J. Kirchhof, S. Froeschke, Hans-Joachim Schmid, A. P. Weber
    Determination of First-Stage Nanoparticle Sintering Contacts by Impact Fragmentation
    European Aerosol Conference (EAC) (2004)
     
  • Hans-Joachim Schmid, Martin Kirchhof, Wolfgang Peukert, Heike Mühlenweg, Georg Skillas, Catrin Becker
    Simulation der Partikelsynthese in Aerosolprozessen
    Tandem-Vortrag GVC-Jahrestagung (2004)
     
  • Hans-Joachim Schmid, Wolfgang Peukert
    Aggregate Structure Formation During Aerosol Synthesis
    AIChE Annual Meeting (2004)
     
  • Christian Artelt, Hans-Joachim Schmid, A. Saxena, Wolfgang Peukert
    Particle charging and coagulation during aerosol formation by nucleation
    AIChE Annual Meeting (2004)
     
  • Martin J. Kirchhof, Hans-Joachim Schmid, S. Froeschke, A.P. Weber
    Investigation of early stages of airborne nanoparticle sintering by impact fragmentation
    AIChE Annual Meeting (2004)
     
  • Martin J. Kirchhof, Hans-Joachim Schmid, Wolfgang Peukert
    Experimental Study of the Sintering Kinetics of Airborne Nanoparticles
    AIChE Annual Meeting (2004)
     
  • Martin J. Kirchhof, Hans-Joachim Schmid, Wolfgang Peukert
    Simulation of Viscous Flow Nanoparticle Sintering
    AIChE Annual Meeting (2004)
     
  • Christian Artelt, Hans-Joachim Schmid, Wolfgang Peukert
    On the Relevance of Accounting for the Evolution of the Fractal Dimension in Aerosol Process Simulations
    Journal of Aerosol Science, 34 (2003) 5, pp 511-534
     
  • Wolfgang Peukert, Hans-Joachim Schmid
    Herausforderungen für die Lehre am Beispiel der Mechanischen Verfahrenstechnik
    Chemie Ingenieur Technik (CIT), 75 (2003) 3, pp 177-183
     
  • Hans-Joachim Schmid, L. Vogel
    On the Modelling of the Particle Dynamics in Electro-Hydrodynamic Flow-Fields I: Com-parison of Eulerian and Lagrangian Modelling Approaches
    Powder Technology, 135/136 (2003), pp 118-135
     
  • Hans-Joachim Schmid
    On the Modelling of the Particle Dynamics in Electro-Hydrodynamic Flow-Fields II: Influences of Inhomogeneities on Electrostatic Precipitation
    Powder Technology, 135/136 (2003), pp 136-149
     
  • Christian Artelt, Hans-Joachim Schmid, Wolfgang Peukert
    Modelling Aerosol Processes with Evolving Fractal Behaviour
    European Aerosol Conference (EAC) / Journal of Aerosol Science, 34 (2003), pp 53-54
     
  • Christian Artelt, Hans-Joachim Schmid, Wolfgang Peukert
    Structural Effects on Modelling Relevant Nucleation and Growth Processes During Aerosol Generation
    European Aerosol Conference (EAC) / Journal of Aerosol Science, 34 (2003), pp 877-878
     
  • Martin J. Kirchhof, Hans-Joachim Schmid, Wolfgang Peukert
    Experimental Study of First-Stage Short-Time Sintering Kinetics of Airborne Silica Nanoparticles
    European Aerosol Conference (EAC) / Journal of Aerosol Science, 34 (2003), pp 107-108
     
  • Hans-Joachim Schmid, Christian Artelt, H. Mühlenweg, Wolfgang Peukert
    Comparison of Numerical Methods to Model Aerosol Dynamics
    European Aerosol Conference (EAC) / Journal of Aerosol Science, 34 (2003), pp 55-56
     
  • Martin J. Kirchhof, Hans-Joachim Schmid, Wolfgang Peukert
    Study of Short-Time Sintering Kinetics of Nanoscaled Aerosols at High Temperatures
    Particulate Systems Analysis Conference (PSA) (2003)
     
  • Hans-Joachim Schmid, S. Stolz, Hans Buggisch
    On the Modelling of the Electrohydrodynamic Flow Field in Electrostatic Precipitators
    Flow, Turbulence and Combustion, 68 (2002) 1, pp 63-89
     
  • Hans-Joachim Schmid, Susanne Veith, Heinz Umhauer
    In-Situ Measurement of Local Particle Flux Densities in a Complex Two-Phase Flow
    Particle & Particle Systems Characterization, 19 (2002) 3, pp 203-215
     
  • Hans-Joachim Schmid, Heinz Umhauer
    Electrostatic Precipitator Efficiency in the Fine Particle Regime
    Filtration, 2 (2002) 5, pp 135-141
     
  • Wolfgang Peukert, Hans-Joachim Schmid
    Novel Concepts for Teaching Particle Technology
    Chemical Engineering Education, 36 (2002) 4, pp 272-276
     
  • Annette Schiel, Alfred P. Weber, Gerhard Kasper, Hans-Joachim Schmid
    In-Situ Determination of the Charging of Nanometer and Submicron Particles at High Temperatures
    Particle & Particle Systems Characterization, 19 (2002) 6, pp 410-418
     
  • Hans-Joachim Schmid
    On the Modelling of Particle Transport in Electro-Hydrodynamic Flow-Fields
    European Congress of Chemical Engineering (2001)
     
  • Martin J. Kirchhof, Hans-Joachim Schmid, Wolfgang Peukert
    A New High-Temperature Reactor System for the Study of Short-Time Sintering Kinetics of Airborne Nanoparticles
    European Aerosol Conference (EAC) / Journal of Aerosol Science, 32 (2001), pp 225-226
     
  • Hans-Joachim Schmid, Martin J. Kirchhof, Wolfgang Peukert
    Study of High-Temperature, Short-Time Kinetic Processes in Airborne Nanoparticulate Systems
    International Workshop ’The Challenge of Nano-Particles’ (2001)
     
  • Hans-Joachim Schmid, Heinz Umhauer, Hans Buggisch
    Investigations on Electro-Hydrodynamic Flow-Fields in Electrostatic Precipitators and its Effect on Particle Transport
    Workshop on Two-phase Flow Predictions (1999)
     
  • Hans-Joachim Schmid, S. Stolz, Hans Buggisch
    On the Electro-Hydrodynamic Flow-Field in Electrostatic Precipitators
    International Symposium on Turbulence and Shear Flow Phenomena (1999)
     
  • Hans-Joachim Schmid, Heinz Umhauer, Hans Buggisch
    Investigations on Local Particle Fluxes in a Laboratory Scaled Electrostatic Precipitator
    Symposium Separation of Particles from Gases / PARTEC (1998)
     
  • Hans-Joachim Schmid, Hans Buggisch
    On the Modelling of Particle Transport in Electrostatic Precipitators
    International Conference on Electrostatic Precipitation (1998)
     
  • Hans-Joachim Schmid, Heinz Umhauer
    In-Situ Measurement of Local Particle Fluxes in a Laboratory-Scaled ESP
    International Conference on Electrostatic Precipitation (1998)
     
  • Hans-Joachim Schmid, A.M. Meroth, Heinz Umhauer, Hans Buggisch
    Modelling of Particle Transport in the Electro-Hydrodynamic Flow-Field of Electrostatic Precipitators
    American Association for Aerosol Research (AAAR) Annual Conference (1997)
     
  • J. Miller, Hans-Joachim Schmid, E. Schmidt, A.J. Schwab
    Local Deposition of Particles in a Laboratory-Scale Electrostatic Precipitator with barbed discharge Electrodes
    International Conference on Electrostatic Precipitation (1996)
     
  • Hans-Joachim Schmid, Heinz Umhauer
    Investigations on Particle Dynamics in a Plate-Type Electrostatic Precipitator Using Double-Pulse Holography
    International Conference on Electrostatic Precipitation (1996)
     
  • Hans-Joachim Schmid, E. Schmidt
    Investigations on Local Mass Flux of Dust to be Precipitated at the Collecting Electrode
    International Conference on Electrostatic Precipitation (1996)
     
  • Hans-Joachim Schmid, Heinz Umhauer
    The Holographic Determination of the Particle Dynamics in an Electro-Hydrodynamic Flow-Field
    International Symposium on Applications of Laser Techniques to Fluid Mechanis (1996)
     
  • Hans-Joachim Schmid, Heinz Umhauer
    Impulsholographische Untersuchung des Bewegungszustandes von Partikelkollektiven in einem Elektrischen Abscheider
    Lasermethoden in der Strömungsmeßtechnik 5. Fachtagung, B. Lehmann (Hrsg.), Shaker (1996)
     
  • Gutsch, Hans-Joachim Schmid, Hans Buggisch, Heinz Umhauer
    Investigations on Extent and Kinetics of Discharging Aerosol Particles
    Symposium Separation of Particles from Gases / PARTEC (1995)

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