@article{26133, abstract = {{The sintering of vitreous nanoparticle doublets is investigated numerically by a volume of fluid method coupled to Hamaker summation and experimentally by a high-temperature sintering flow reactor as well as by doublet shape analysis in the transmission electron microscope. In particular, the characteristic differences between nanoparticulate and bulk sintering are studied. The sintering mechanism of vitreous nanoparticles is determined to be viscous flow with interparticle van der Waals interactions acting as additional driving force. The early stages of the nanoparticle sintering kinetics are inversely proportional to the square of the particle size, instead of an indirect proportionality to the first order of the particle size for the entire bulk process. The transition between nanoparticulate and bulk sintering is localised to primary particle diameters of approx. 200–300 nm.}}, author = {{Kirchhof, M.J. and Förster, H. and Schmid, Hans-Joachim and Peukert, W.}}, issn = {{0021-8502}}, journal = {{Journal of Aerosol Science}}, pages = {{26--39}}, title = {{{Sintering kinetics and mechanism of vitreous nanoparticles}}}, doi = {{10.1016/j.jaerosci.2011.10.006}}, volume = {{45}}, year = {{2012}}, } @inproceedings{22174, abstract = {{The quality of laser sintered parts, in this work, manufactured by polymer laser sintering by using an EOSINT P395 Laser Sintering system, depends on several steps along the process chain. The first step is the characterization of the powder quality, whereas the rheological and physical investigations of nylon 12 powder are shown. By changing some important influencing factors, for example the powder ratio, the powder ageing and the moisture content, the influence on mechanical and physical properties, density and porosity, are investigated. The composition of the used powder is known. The previous process (storage conditions, etc.) as well as the laser sintering process (regarding energy density, temperature, etc.) is kept constant for the duration of this work. Regarding the post process in this work the cooling down phase is investigated as well. With an automatically blasting system it is possible to keep the post process parameters blasting distance and blasting time, constant. All of the tests will be performed using dry and conditioned test specimens. This work is showing the dependence on mechanical, rheological and physical parameters by varying important influencing factors along the laser sintering process quality chain.}}, author = {{Rüsenberg, Stefan and Weiffen, R. and Knoop, F. and Schmid, Hans-Joachim}}, booktitle = {{23rd Annual International Solid Freeform Fabrication Symposium}}, pages = {{1024--1044}}, title = {{{Controlling the Quality of Laser Sintered Parts Along the Process Chain}}}, doi = {{http://utw10945.utweb.utexas.edu/Manuscripts/2012/2012-78-Ruesenberg.pdf}}, volume = {{23}}, year = {{2012}}, } @inproceedings{22204, abstract = {{Material properties of parts from additive manufacturing are influenced by a huge number of material, operational and job parameters. This work aims to identify the most important ones and to investigate mechanical properties as depending on those parameters. Test specimens were produced with standard PA12 powder on an EOSINT P390 and P395, respectively. The influence of the orientation and placement of parts in the building chamber were investigated systematically. The mechanical properties}}, author = {{Rüsenberg, Stefan and Schmid, Hans-Joachim}}, booktitle = {{The European Forum on Additive Manufacturing}}, title = {{{Mechanical Properties as a Result of multitude of Parameters}}}, doi = {{https://afpr.asso.fr/content/assises/2012/actes/papiers/s5_2.pdf}}, volume = {{17}}, year = {{2012}}, } @inproceedings{22188, abstract = {{The aim of this paper is the description and evaluation of physical properties like porosity and density and their influence on mechanical properties of laser sintered polyamide parts. For example, by reducing the porosity an increase of mechanical properties is possible. The correlation of laser parameters to these properties is investigated in detail. The energy density is an important parameter for the laser sintering process. By changing laser power, scan velocity and hatch distance an influence on manufactured components is given. A systematic variation of all three laser parameters is performed. A comparison of results obtained at constant energy densities obtained by varying these relevant parameters accordingly is shown as well.}}, author = {{Rüsenberg, Stefan and Schmidt, L. and Schmid, Hans-Joachim}}, booktitle = {{22th Annual International Solid Freeform Fabrication Symposium}}, pages = {{239--251}}, title = {{{Mechanical and Physical Properties - A Way to asses quality of Laser Sintered Parts}}}, doi = {{http://utw10945.utweb.utexas.edu/Manuscripts/2011/2011-19-Ruesenberg.pdf}}, volume = {{22}}, year = {{2011}}, } @book{22191, author = {{Rüsenberg, Stefan and Schmidt, L. and Hosse, H. and Schmid, Hans-Joachim}}, isbn = {{978-0-429-21774-6}}, pages = {{531--538}}, title = {{{Porosity as a key to increase material properties of laser sintered parts}}}, doi = {{10.1201/b11341}}, year = {{2011}}, } @article{26134, abstract = {{This work investigates the mechanisms which lead to the formation of silicon nanoparticles with narrow size distributions by means of population balance modeling. The model accounts for the full aerosol process, including chemical reaction, nucleation from supersaturated vapor, growth and agglomeration. The results are in good agreement with experimental data. The effects of the process parameters temperature, silane concentration and reactor total pressure are systematically investigated. The simulation allows an in-depth insight into the particle formation mechanism and reveals the key requirements which are necessary for the generation of narrow particle size distributions. In this mechanism, only a short nucleation burst occurs, while surface growth plays the dominant role in silane precursor consumption. A key role is attributed to condensation, because the numerical calculations can only reflect the experimental observations, if the condensation mechanism is included in the model.}}, author = {{Körmer, R. and Schmid, Hans-Joachim and Peukert, W.}}, issn = {{0021-8502}}, journal = {{Journal of Aerosol Science}}, number = {{11}}, pages = {{1008--1019}}, title = {{{Aerosol synthesis of silicon nanoparticles with narrow size distribution—Part 2: Theoretical analysis of the formation mechanism}}}, doi = {{10.1016/j.jaerosci.2010.08.002}}, volume = {{41}}, year = {{2010}}, } @article{26135, abstract = {{A study on the feasibility of aerosol processing of nearly monodisperse silicon nanoparticles via pyrolysis of monosilane in a hot wall reactor is presented. For optimal conditions silicon nanoparticles with a geometric standard deviation of 1.06 were synthesized at a production rate of 0.7 g/h. The size of the particles could be precisely controlled in the range of 20–40 nm, whilst maintaining a geometric standard deviation in the range of 1.06–1.08, by proper choice of the governing parameters temperature, residence time and precursor concentration. The results show that narrow particle size distributions can only be obtained in the temperature range between 900 and 1100 °C, as long as both the initial silane concentration (1 mbar silane partial pressure) and the reactor total pressure are low (25 mbar). This regime for the production of narrow particle size distributions has not been identified in prior work on the thermal decomposition of silane. Narrowly distributed particles can be obtained under conditions where nucleation and particle growth are separated and the agglomeration rates are negligible.}}, author = {{Körmer, R. and Jank, M.P.M. and Ryssel, H. and Schmid, Hans-Joachim and Peukert, W.}}, issn = {{0021-8502}}, journal = {{Journal of Aerosol Science}}, number = {{11}}, pages = {{998--1007}}, title = {{{Aerosol synthesis of silicon nanoparticles with narrow size distribution—Part 1: Experimental investigations}}}, doi = {{10.1016/j.jaerosci.2010.05.007}}, volume = {{41}}, year = {{2010}}, } @article{26136, abstract = {{To improve the understanding of the poor dispersability of fumed silica nanoparticle agglomerates, the stability of highly defined agglomerated model particles was investigated. The high temperature synthesis conditions for fumed silica were simulated by tempering. Along with electron-microscopical analysis of the sintering necks, the interparticle forces were investigated by energy resolved fragmentation analysis based on low pressure impaction. At temperatures above 1,000 °C the fragmentability of the agglomerates rapidly decreased while the energy necessary for fragmentation increased. The development of sintering necks was observed for temperatures exceeding 1,300 °C. Comparison of the experimental data with the fragmentation behaviour of a commercially produced fumed silica indicated solid state contacts (sintering necks) as being most numerous in the agglomerates resulting in limited fragmentability.}}, author = {{Seipenbusch, M. and Rothenbacher, S. and Kirchhoff, M. and Schmid, Hans-Joachim and Kasper, G. and Weber, A. P.}}, issn = {{1388-0764}}, journal = {{Journal of Nanoparticle Research}}, number = {{6}}, pages = {{2037--2044}}, title = {{{Interparticle forces in silica nanoparticle agglomerates}}}, doi = {{10.1007/s11051-009-9760-5}}, volume = {{12}}, year = {{2010}}, } @misc{58272, author = {{Woppowa, Jan and Schmid, Hans-Joachim}}, booktitle = {{rhs}}, number = {{2011}}, pages = {{139--140}}, title = {{{Gastfreundschaft. Ein Modell für den konfessionellen Religionsunterricht der Zukunft}}}, volume = {{54}}, year = {{2010}}, } @article{26137, abstract = {{In this paper, we consider a model for precipitation experiments based on the population balance equation. The study revealed a high sensitivity of the system with respect to the modeling of intrinsic parameters, motivating a comprehensive validation of the estimates. In the forward simulation the impact of the influencing parameters including surface energy, nucleus size and distribution is investigated. Subsequently we construct a simplified model of the precipitation process in such a way that it is orbitally flat in terms of control theory, which enables the inverse calculation of the parameters. The numerical results of the inverse simulation for the interfacial energy have been compared to a physical model. The possibility of solving the inverse problem provides a promising way of estimating hardly measurable quantities for more complex molecules.}}, author = {{Vassilev, Vassil and Gröschel, Michael and Schmid, Hans-Joachim and Peukert, Wolfgang and Leugering, Günter}}, issn = {{0009-2509}}, journal = {{Chemical Engineering Science}}, number = {{6}}, pages = {{2183--2189}}, title = {{{Interfacial energy estimation in a precipitation reaction using the flatness based control of the moment trajectories}}}, doi = {{10.1016/j.ces.2009.12.014}}, volume = {{65}}, year = {{2009}}, } @article{26138, abstract = {{In this work, a new model for the simulation of nanostructured aggregates by simultaneous coagulation, sintering and surface growth is presented. Coagulation is treated as cluster–cluster agglomeration along the line connecting the center of mass of both agglomerates and is implemented using a Monte Carlo algorithm. Sintering is modeled as successive overlapping of spheres which cause reduction in the surface area based on a rate law for surface reduction. Surface growth is modeled as an increase in primary particle diameter, e.g. as a result of surface reactions. The evolved aggregates are analyzed by calculating their fractal dimension, radius of gyration, mobility diameter and mobility shape factor. It is found that the aggregates structure tends to be more compact when introducing the surface growth in shorter time comparing to the coagulation-sintering step only. Fractal dimension and the mobility shape factor of the resulting aggregates are correlated to an effective dimensionless time that combines the characteristic times of these three fundamental mechanisms. It is shown that the mobility diameter in the free molecular regime is not proportional to the radius of gyration. A power law relation that correlates the aggregates projected area and the equivalent number of primary particles is found to be in a very good agreement with estimates published in literature.}}, author = {{Al Zaitone, Belal and Schmid, Hans-Joachim and Peukert, Wolfgang}}, issn = {{0021-8502}}, journal = {{Journal of Aerosol Science}}, number = {{11}}, pages = {{950--964}}, title = {{{Simulation of structure and mobility of aggregates formed by simultaneous coagulation, sintering and surface growth}}}, doi = {{10.1016/j.jaerosci.2009.08.007}}, volume = {{40}}, year = {{2009}}, } @article{26139, abstract = {{The study presents first experimental results of the transfer of magnetite nanoparticles from an aqueous to a second non-miscible non-aqueous liquid phase. The transfer is based on the adsorption of macromolecular surfactants onto the particle surface at the liquid–liquid interface. For a successful direct phase transfer, it is essential to have cations, like ammonium ions, present in the aqueous phase as well as a threshold concentration of surfactant in the organic liquid phase. While penetrating the liquid–liquid interface, the particles are covered with the surfactant and therefore a partial de-agglomeration is initiated. Based on literature and experimental data a mechanism of surfactant adsorption is proposed. The competing adsorption of the surfactant molecules at the liquid–liquid interface leads to the formation of emulsions and therefore to a hindrance for particles passing the interface. Nevertheless a high efficiency of 100% yield can be reached using optimized process parameters for the phase transfer process.}}, author = {{Machunsky, Stefanie and Grimm, Philipp and Schmid, Hans-Joachim and Peuker, Urs A.}}, issn = {{0927-7757}}, journal = {{Colloids and Surfaces A: Physicochemical and Engineering Aspects}}, number = {{1-3}}, pages = {{186--190}}, title = {{{Liquid–liquid phase transfer of magnetite nanoparticles}}}, doi = {{10.1016/j.colsurfa.2009.07.014}}, volume = {{348}}, year = {{2009}}, } @article{26140, abstract = {{The viscous-flow sintering of different agglomerate particle morphologies is studied by three-dimensional computer simulations based on the concept of fractional volume of fluid. For a fundamental understanding of particle sintering characteristics, the neck growth kinetics in agglomerate chains and in doublets consisting of differently sized primary particles is investigated. Results show that different sintering contacts in agglomerates even during the first stages are not completely independent from each other, even though differences are small. The neck growth kinetics of differently sized primary particles is determined by the smaller one up to a size difference by a factor of approximately 2, whereas for larger size differences, the kinetics becomes faster. In particular, the agglomerate sintering kinetics is investigated for particle chains of different lengths and for different particle morphologies each having ten primary particles and nine initial sintering contacts. For agglomerate chains, the kinetics approximately can be normalized by using the radius of the fully coalesced sphere. In general, different agglomerate morphologies show equal kinetics during the first sintering stages, whereas during advanced stages, compact morphologies show significantly faster sintering progress than more open morphologies. Hence, the overall kinetics cannot be described by simply using constant morphology correction factors such as fractal dimension or mean coordination number which are used in common sintering models. However, for the first stages of viscous-flow agglomerate sintering, which are the most important for many particle processes, a sintering equation is presented. Although we use agglomerates consisting of spherical primary particles, our methodology can be applied to other aggregate geometries as well.}}, author = {{Kirchhof, M. J. and Schmid, Hans-Joachim and Peukert, W.}}, issn = {{1539-3755}}, journal = {{Physical Review E}}, number = {{2}}, pages = {{026319 }}, title = {{{Three-dimensional simulation of viscous-flow agglomerate sintering}}}, doi = {{10.1103/physreve.80.026319}}, volume = {{80}}, year = {{2009}}, } @article{26142, abstract = {{Modeling of particle deposition on adjacent walls is a key issue in various applications like separation or transport processes. The present paper focuses on the modeling of turbophoretic deposition of particles in the micron size range. The first step is to evaluate the important range where turbophoresis plays an important role in comparison to other mechanisms e.g. gravity or electrostatic separation. The disadvantages of commonly used models will be analyzed and overcome by implementing a more sophisticated approach considering damping of turbulent fluctuations in the wall-boundary layer. In contrast to previous work, commonly used turbulence models are applied to solve the mean flow field of the examples under consideration. The results will show a good prediction of particle deposition in comparison to experimental values [B.Y.H. Liu, J.K. Agarwal, Experimental observation of aerosol deposition in turbulent flow, Aerosol. Sci. 5 (1974) 145–155.] by using the advanced model.}}, author = {{Horn, M. and Schmid, Hans-Joachim}}, issn = {{0032-5910}}, journal = {{Powder Technology}}, number = {{3}}, pages = {{189--198}}, title = {{{A comprehensive approach in modeling Lagrangian particle deposition in turbulent boundary layers}}}, doi = {{10.1016/j.powtec.2007.11.048}}, volume = {{186}}, year = {{2008}}, } @article{26147, abstract = {{Second harmonic generation (SHG) spectroscopy is a recently developed technique for the investigation of surface properties of particles. To apply the method to technical colloidal systems, the dependences of several experimental parameters on the signal have to be studied. In this work the influence of particle concentration on the SHG signal from the surfaces of colloids (polystyrene beads in a size range of 0.1 μm to 2.9 μm) is investigated. A simple model, based on Lambert–Beer’s law, to describe the measured dependences is derived. The model agrees with the experimental observations for particles smaller 1.1 μm and with a small modification also for larger particles. Based on the new model an analytical equation for determining the optimum concentration, where highest signals in colloidal SHG spectroscopy measurements are obtained, is derived. }}, author = {{Schneider, L. and Schmid, Hans-Joachim and Peukert, W.}}, issn = {{0946-2171}}, journal = {{Applied Physics B}}, pages = {{333--339}}, title = {{{Influence of particle size and concentration on the second-harmonic signal generated at colloidal surfaces}}}, doi = {{10.1007/s00340-007-2597-7}}, volume = {{87}}, year = {{2007}}, } @article{29827, abstract = {{Die Entwicklung neuer Konfigurationen zur Rußabscheidung in Elektrofiltern im Hinblick auf Kfz-Applikationen bedingt die Notwendigkeit, diese auch mithilfe von Simulationen bewerten zu können. Der Beitrag stellt einen neuen Ansatz zur Simulation des Abscheideprozesses für einen Temperaturbereich bis 400 Grad C vor. Entscheidend ist die Möglichkeit, das raumladungsbehaftete elektrische Feld für alle Betriebszustände zu simulieren. Für den Transport der Raumladungen wird ein Ansatz aus der Mehrphasenströmungssimulation verwendet. Die Abscheidung der Partikeln wird mithilfe eines Lagrangeschen Ansatzes modelliert, der die zeitabhängige Aufladung unter lokalen elektrischen Bedingungen berücksichtigt. Die Simulation des Gesamtprozesses wird mit experimentellen Untersuchungen anhand eines Laborabscheiders verifiziert. Simulation und Experiment stimmen gut überein. Insbesondere der dominierende Einfluss durch die Bereiche in der Nähe der Platten konnte gut abgebildet werden. Das Gleiche gilt für die parabolische Form der Strom-Spannungs-Kennlinie. Weitere Untersuchungen sind erforderlich, um die gezeigten Methoden auf die Rußabscheidung zu übertragen. Die Problematik liegt in der Charakterisierung der Rußeigenschaften in Abhängigkeit von der Rußentstehung. Auch die Randbedingungen der Methoden zur elektrischen Charakterisierung können zurzeit noch nicht auf allgemeine Fälle übertragen werden. }}, author = {{Schmid, Hans-Joachim}}, issn = {{0949-8036}}, journal = {{Gefahrstoffe, Reinhaltung der Luft. Air Quality Control}}, number = {{4}}, title = {{{Neuer Ansatz zur Modellierung der Abscheidung in einem modifizierten Rohrelektrofilter}}}, volume = {{67}}, year = {{2007}}, } @article{26145, abstract = {{The drag force on aggregates and partially sintered agglomerates is assessed using the lattice Boltzmann method (LBM) and accelerated Stokesian dynamics (ASD). Both methods have been compared in terms of accuracy and computational effort. It is shown that they give comparable results if all numerical parameters are controlled carefully. LBM requires a much higher computational effort, however, in contrast to ASD it is able to simulate partially sintered agglomerates as well. The results show that even a very small amount of sintering leads to a significant reduction in the drag force. The analysis of the drag force on agglomerates as well as on aggregates shows that there is no simple geometric quantity which is uniquely related to the drag force. Moreover, there is a significant variation in drag force for single aggregates at different orientations or for the orientation averaged drag force of different aggregates of the same size. This is explained by the structural effects which may lead to a variation in the drag force up to +-20%.}}, author = {{Binder, Christian and Feichtinger, Christian and Schmid, Hans-Joachim and Thürey, Nils and Peukert, Wolfgang and Rüde, Ulrich}}, issn = {{0021-9797}}, journal = {{Journal of Colloid and Interface Science}}, number = {{1}}, pages = {{155--167}}, title = {{{Simulation of the hydrodynamic drag of aggregated particles}}}, doi = {{10.1016/j.jcis.2006.04.045}}, volume = {{301}}, year = {{2006}}, } @article{26148, abstract = {{Die Modellierung der wandnahen Bereiche bei der Simulation von Zweiphasenströmungen spielt in der Praxis eine entscheidende Rolle, wenn erwünschter oder unerwünschter Transport der dispersen Phase zu einer Oberfläche bedeutend ist. Zweiphasenströmungen mit einer dispersen Phase werden heutzutage häufig mit dem Euler-Lagrange-Verfahren in modernen CFD-Codes simuliert. Im Folgenden wird darauf eingegangen werden, wie solche Berechnungen in kommerziellen CFD-Codes durchgeführt werden.}}, author = {{Horn, M. and Schmid, Hans-Joachim}}, issn = {{0009-286X}}, journal = {{Chemie Ingenieur Technik}}, number = {{6}}, pages = {{694--699}}, title = {{{Modellierung der wandnahen Bereiche in turbulenten Zweiphasenströmungen}}}, doi = {{10.1002/cite.200500110}}, volume = {{78}}, year = {{2006}}, } @article{26150, abstract = {{This work investigates the effects of reduced accessible surface area of aggregate particles and of surface energy on relevant particle formation and growth mechanisms during titania formation from the vapour phase at industrial process conditions. Growth due to surface reaction and due to condensation is related to the fraction of the surface area that is exposed to the collision with single molecules. Surface shielding is found to hamper surface reaction and condensation once fractal aggregates start to form. It leads to significantly retarded precursor consumption and produces aggregate particles, which consist of more, but smaller primary particles. Surface energy data are varied within a range as proposed by available literature data. Moderate and high surface energy values result in a thermodynamic barrier to the formation of new particles and are shown to reduce the formation of seed particles by several orders of magnitude. This leads to the formation of aggregate particles which consist of a rather small number of primary particles and mainly grow by surface reaction. The primary contribution of condensation to growth of individual primary particles is shown to be very little. However, condensation should not be neglected as it has a strong impact on particle formation rates and hence on product characteristics such as the number of primary particles and primary particle size.}}, author = {{Artelt, C. and Schmid, Hans-Joachim and Peukert, W.}}, issn = {{0009-2509}}, journal = {{Chemical Engineering Science}}, number = {{1}}, pages = {{18--32}}, title = {{{Modelling titania formation at typical industrial process conditions: effect of surface shielding and surface energy on relevant growth mechanisms}}}, doi = {{10.1016/j.ces.2004.12.053}}, volume = {{61}}, year = {{2006}}, } @article{26149, abstract = {{Nanoparticle precipitation is an interesting process to generate particles with tailored properties. In this study we investigate the impact of various process steps such as solid formation, mixing and agglomeration on the resulting particle size distribution (PSD) as representative property using barium sulfate as exemplary material. Besides the experimental investigation, process simulations were carried out by solving the full 1D population balance equation coupled to a model describing the micromixing kinetics based on a finite-element Galerkin h-p-method. This combination of population balance and micromixing model was applied successfully to predict the influence of mixing on mean sizes (good quantitative agreement between experimental data and simulation results are obtained) and gain insights into nanoparticle precipitation: The interfacial energy was identified to be a critical parameter in predicting the particle size, poor mixing results in larger particles and the impact of agglomeration was found to increase with supersaturation due to larger particle numbers. Shear-induced agglomeration was found to be controllable through the residence time in turbulent regions and the intensity of turbulence, necessary for intense mixing but undesired due to agglomeration. By this approach, however, the distribution width is underestimated which is attributed to the large spectrum of mixing histories of fluid elements on their way through the mixer. Therefore, an improved computational fluid dynamics-based approach using direct numerical simulation with a Lagrangian particle tracking strategy is applied in combination with the coupled population balance–micromixing approach. We found that the full DNS-approach, coupled to the population balance and micromixing model is capable of predicting not only the mean sizes but the full PSD in nanoparticle precipitation.}}, author = {{Schwarzer, Hans-Christoph and Schwertfirm, Florian and Manhart, Michael and Schmid, Hans-Joachim and Peukert, Wolfgang}}, issn = {{0009-2509}}, journal = {{Chemical Engineering Science}}, number = {{1}}, pages = {{167--181}}, title = {{{Predictive simulation of nanoparticle precipitation based on the population balance equation}}}, doi = {{10.1016/j.ces.2004.11.064}}, volume = {{61}}, year = {{2005}}, }