TY - JOUR A1 - Müller, Ralf A1 - Prado, M. O. A1 - Zanotto, E. D. T1 - Model for sintering polydispersed glass particles JF - Journal of non-crystalline solids N2 - We propose a model to describe the sintering kinetics of polydispersed glass particles, having no adjustable parameter. The model is based on three sintering stages: a pure ‘Frenkel' (F) first step, a mixed ‘Frenkel/Mackenzie–Shuttleworth' stage, and a third, pure ‘Mackenzie–Shuttleworth' (MS) step. The model considers sample shrinkage as the sum of the partial shrinkage of several clusters, each consisting of equally sized particles and each showing independent F or MS behavior. The overall set of clusters mimics the specimen's real particle size distribution. We then introduce the concept of neck forming ability, which allows the formation of necks among particles of different sizes, relaxing the clustering condition. Using experimental physical parameters: particle size distribution, viscosity, surface energy, and the theoretical neck forming ability, the model describes well the sintering kinetics of an alumino-borosilicate glass powder having polydispersed, irregular shaped particles in a variety of temperatures. The sintering kinetics of the real powder is slower, but not far from the calculated kinetics of a monodispersed distribution containing only particles of average size. Thus the model provides a tool for estimating the sintering kinetics of real glass powders, for any size distribution and temperature, thus minimizing the number of laboratory experiments. PY - 2001 DO - https://doi.org/10.1016/S0022-3093(00)00399-9 SN - 0022-3093 VL - 279 IS - 2-3 SP - 169 EP - 178 PB - North-Holland Publ. Co. CY - Amsterdam AN - OPUS4-935 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Deubener, Joachim A1 - Müller, Ralf A1 - Behrens, H. A1 - Heide, G. T1 - Water and the glass transition temperature of silicate melts JF - Journal of non-crystalline solids N2 - Literature data on the effect of water on the glass transition in silicate melts are gathered for a broad range of total water content cw from 3 × 10-4 to 27 wt%. In terms of a reduced glass transition temperature Tg*=Tg/TgGN, where TgGN is Tg of the melt containing cw?0.02 wt% total water, a uniform dependence of Tg* on total water content (cw) is evident for silicate melts. Tg* decreases steadily with increasing water content, most strongly at the lowest water content where H2O is dominantly dissolved as OH. For water-rich melts, the variation of Tg* is less pronounced, but it does not vanish even at the largest water contents reported (?27 wt%). Tg* vs. cw is fitted by a three-component model. This approach accounts for different transition temperatures of the dry glass, hydroxyl and molecular water predicting Tg* as a weighted linear combination of these temperatures. The required but mostly unknown water speciation in the glasses was estimated using IR-spectroscopy data for hydrous sodium trisilicate and rhyolite. PY - 2003 DO - https://doi.org/10.1016/S0022-3093(03)00472-1 SN - 0022-3093 VL - 330 SP - 268 EP - 273 PB - North-Holland Publ. Co. CY - Amsterdam AN - OPUS4-3120 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmelzer, J.W.P. A1 - Müller, Ralf A1 - Möller, J. A1 - Gutzow, I.S. T1 - Theory of nucleation in viscoelastic media: application to phase formation in glassforming melts JF - Journal of non-crystalline solids N2 - Glassforming melts behave, in the vicinity of the temperature of vitrification Tg, as viscoelastic bodies. A general theory of nucleation in a viscoelastic body developed elsewhere is applicable to the description of phase formation processes in such systems. The present contribution is directed to the demonstration of the relevance of this proposed general theory to describing phase transformation processes in glassforming melts. The application of the theory is shown to explain a number of experimental results on crystallization of glassforming melts, which have not found a satisfactory interpretation so far. PY - 2003 DO - https://doi.org/10.1016/S0022-3093(02)01428-X SN - 0022-3093 VL - 315 SP - 144 EP - 160 PB - North-Holland Publ. Co. CY - Amsterdam AN - OPUS4-2078 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Unger, Brita A1 - Rurack, Knut A1 - Müller, Ralf A1 - Resch-Genger, Ute A1 - Buttke, K. T1 - Effects of the Sol-Gel Processing on the Fluorescence Properties of Laser Dyes in Tetraethoxysilane Derived Matrices JF - Journal of sol gel science and technology N2 - Two fluorescent dyes were incorporated into sol-gel derived SiO2 matrices. The dye was added to SiO2 precursors of different degrees of pre-condensation and the spectroscopic properties of the immobilized dye were measured at various aging and drying stages of the resulting gels. The significant influence of the processing parameters on the spectroscopic properties is manifested in the relative intensity of a second red shifted emission band (550–560 nm), which was observed besides the typical coumarin emission band (495 nm). The appearance of this long wavelength emission might be attributed to dye aggregation or to other reactions with the ambient matrix forced by micro porosity phenomena. KW - Sol-gel KW - Precursor chemistry KW - Fluorescence properties KW - Optical solids PY - 2000 DO - https://doi.org/10.1023/A:1008768318418 SN - 0928-0707 SN - 1573-4846 VL - 19 SP - 799 EP - 802 PB - Kluwer Academic Publ. CY - Dordrecht AN - OPUS4-1080 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Unger, Brita A1 - Rurack, Knut A1 - Müller, Ralf A1 - Jancke, Harald A1 - Resch-Genger, Ute T1 - Microscopic vs. macroscopic structural evolution of SiO2 sols and gels employing a tailor-made fluorescent reporter dye JF - Journal of materials chemistry N2 - The short- and long-term structural evolution and aging of sol–gel materials prepared under mild conditions are studied by fluorometry, dynamic light scattering (DLS), 29Si NMR and gravimetry. In combination with the first, a newly developed donor–acceptor-substituted fluorescent probe with two acidophilic sites of different strength and topology is introduced. Its performance in detecting changes in parameters such as polarity, proticity, and pore volume on the microscopic scale is compared to two other dyes and to the macroscopic changes revealed by DLS, NMR and gravimetry. At early stages of the sol–gel process, fluorometry, DLS and NMR reveal similar changes which are typical of the structural evolution of SiO2 sols having different synthesis parameters. During later times of sol aging, DLS and NMR reflect the growth of the network and indicate that all sols approach similar structural equilibria. Fluorometry supports these findings by signalling a gradual decrease in mobile species with high proton activity. The formation of the spanning cluster upon gelation is strongly evident only from DLS results while the local environment of the fluorophore remains largely unchanged. However, the fluorescent dye is able to report microscopic changes even during long-term aging. Drying of the gels with a pronounced contraction of solvated pores is readily observable by fluorometry and gravimetry. During the late reaction stages, the fluorescence properties of the tailor-made dye are still sensitive toward the environment. PY - 2005 DO - https://doi.org/10.1039/b501622c SN - 0959-9428 SN - 1364-5501 VL - 15 IS - 30 SP - 3069 EP - 3083 PB - Royal Society of Chemistry CY - Cambridge AN - OPUS4-10378 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmelzer, J.W.P. A1 - Potapov, O. V. A1 - Fokin, V. M. A1 - Müller, Ralf A1 - Reinsch, Stefan T1 - The effect of elastic stress and relaxation on crystal nucleation in lithium disilicate glass JF - Journal of non-crystalline solids N2 - In the framework of a general theoretical approach recently developed, the effect of elastic stresses on the rate of nucleation of crystallites of critical sizes in the process of crystallization of lithium disilicate glasses is studied. Hereby both the evolution of elastic stresses – due to changes in the specific volume of the crystallizing system (i.e., differences in the densities of the melt and the crystal) – and their relaxation – connected with viscous flow – are taken into consideration. If the classical theory of nucleation is employed for the determination of the nucleation rates (modified by taking into account elastic stresses), elastic stresses may lead, for the system under consideration, to a decrease of the nucleation rate by up to two orders of magnitude. As shown, the theory allows an at least qualitatively correct incorporation of the effect of elastic stresses and stress relaxation into the description of nucleation phenomena in glass-forming melts. PY - 2004 DO - https://doi.org/10.1016/j.jnoncrysol.2003.10.002 SN - 0022-3093 VL - 333 IS - 2 SP - 150 EP - 160 PB - North-Holland Publ. Co. CY - Amsterdam AN - OPUS4-6236 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Müller, Ralf A1 - Gaber, Martin A1 - Gottschling, Peter T1 - Water release and crystallisation of glass powders JF - European journal of glass science and technology / B T2 - Physics and Chemistry of Glasses / VII Symposium on Crystallization in Glasses in Liquids CY - Sheffield, England, UK DA - 2004-07-06 PY - 2004 SN - 1753-3562 SN - 0017-1050 SN - 0031-9090 SN - 1750-6697 VL - 45 IS - 2 SP - 1 EP - 5 PB - Society of Glass Technology CY - Sheffield AN - OPUS4-6237 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Marzok, Ulrich A1 - Müller, Ralf A1 - Schadrack, Reinhard A1 - Krauhausen, M. A1 - Burgstedt, F. A1 - Brode, W. A1 - Reetz, R. T1 - High-temperature laser profilometry for ceramic tapes JF - Ceramic Forum International : cfi N2 - Advanced ceramics are promising key components for microsystems engineering, communication Technology and medical engineering. Driven by steadiiy increasing demands on dimensional accuracy of components and Integration density, sintering has to be controlled at an unprecedented degree of precision. Being most crucial for components of complex shape, graded or heterogeneous-composed parts like LTCC multilayers for microsystems, precise control of sintering has a decisive influence on the dimensional accuracy, mechanical integrity and reliability of sintered components. Thus, permanent or temporary shape distortions or warping during sintering may result from spatially heterogeneous microstructure and temperature distribution, e.g. during the co-firing process of green multilayer Stacks printed with metallization and other functional pastes. Whereas permanent warping can be easily measured after sintering, temporary warping during firing is more difficult to measure. Nonetheless, this effect may cause latent failures later, which often limit the applicability of ceramic components. PY - 2013 SN - 0173-9913 SN - 0196-6219 VL - 90 IS - 4 SP - E35 EP - E40 PB - Göller CY - Baden-Baden AN - OPUS4-28500 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Marzok, Ulrich A1 - Müller, Ralf A1 - Schadrack, Reinhard A1 - Krauhausen, M. A1 - Burgstedt, F. A1 - Brode, W. A1 - Reetz, R. T1 - Hochtemperatur-Laserprofilometrie an keramischen Bauteilen JF - Ceramic Forum International : cfi N2 - Hochleistungssinterwerkstoffe spielen eine wachsende Rolle in derzeitigen Schlüsseltechnologien wie der Mikrosystem-, Informations-, Kommunikations- und Medizintechnik. Dabei steigen die Anforderungen an die präzise Steuerung der Sinterung. Besonders für komplexe, gradierte oder heterogen zusammengesetzte Formkörper wie zum Beispiel keramische LTCC-Multilayer für die Mikrosystemtechnik hat die exakte Beherrschung dieses Prozessschrittes wesentlichen Einfluss auf die Maßhaltigkeit, mechanische Integrität und Zuverlässigkeit der gesinterten Bauteile. Bedingt durch die Heterogenität der mehrlagigen und mit Leit- und anderen Funktionspasten bedruckten Sinterkörper hinsichtlich ihrer sinterphysikalischen oder thermischen Eigenschaften können bleibende oder temporäre Verwerfungen beim Schrumpfungsprozess auftreten, wobei letztere unter Umständen Ursache latenter Fehler im späteren Bauteil sind. PY - 2013 SN - 0173-9913 SN - 0196-6219 VL - 90 IS - 3 SP - D19 EP - D24 PB - Göller CY - Baden-Baden AN - OPUS4-28013 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zocca, Andrea A1 - Wirth, Cynthia A1 - Bernardo, E. A1 - Müller, Ralf A1 - Günster, Jens A1 - Colombo, P. T1 - LAS glass-ceramic scaffolds by three-dimensional printing JF - Journal of the European Ceramic Society N2 - Highly porous (>60% open porosity) glass–ceramic scaffolds with remarkable mechanical properties (compression strength of ~15 MPa) were produced by indirect 3D printing. Precursor glass powders were printed into 3D ordered structures and then heat treated to sinter and develop crystalline phases. The final glass–ceramic contained a β-spodumene solid solution together with a secondary phase of lithium disilicate. The precision of the printed geometry and the density of the struts in the scaffold depended on several processing parameters (e.g. powder size and flowability, layer thickness) and were improved by increasing the binder saturation and drying time. Two types of powders with different particle size distribution (PSD) and flowability were used. Powders with a larger PSD, could be processed within a wider range of printing parameters due to their good flowability; however, the printing precision and the struts density were lower compared to the scaffolds printed using the powder in a smaller average PSD. KW - Glass ceramics KW - Porosity KW - Shaping KW - Strength KW - Additive manufacturing PY - 2013 DO - https://doi.org/10.1016/j.jeurceramsoc.2012.12.012 SN - 0955-2219 SN - 1873-619X N1 - Geburtsname von Wirth, Cynthia: Gomes, C. M. - Birth name of Wirth, Cynthia: Gomes, C. M. VL - 33 IS - 9 SP - 1525 EP - 1533 PB - Elsevier CY - Oxford AN - OPUS4-28284 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -