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 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 - TY - JOUR A1 - Nagamine, K. A1 - Reinsch, Stefan A1 - Müller, Ralf A1 - Honma, T. A1 - Komatsu, T. T1 - Crystallization behavior of lithium iron phosphate glass powders in different atmospheres N2 - Crystallization behavior in different atmospheres (air, Ar, and 7% H2/Ar) of lithium iron phosphate glass (33Li2O–33Fe2O3–1Nb2O5–33P2O5 (LFNP)) powders with different sizes of 2–1000 µm was examined. The crystallization peak temperature (Tp) in Ar and 7% H2/Ar decreased with decreasing the particle size of glass powders, but the value of Tp in air was independent of particle size. The crystallized glass obtained by heating to Tp showed the formation of the α-Li3Fe2(PO4)3 and LiFePO4 crystalline phases. Fe2O3 crystals were formed only in the inside of crystallized glass plates in the heating in air. The crystallization of LiFePO4 was largely enhanced in the particle size of <2 µm during the heating in Ar and 7% H2/Ar atmospheres. The main crystallization mechanism in LFNP glass was found to be surface crystallization. Significant shrinkages were observed for glass compacts (pellets) in the heating in 7% H2/Ar. These results suggest that controlling particle sizes and atmospheres enables the design the morphology of LiFePO4 crystals in LFNP glass. KW - DTA KW - Kristallisation KW - Phasenentwicklung KW - Unterschiedliche Atmosphären KW - Lithiumionen-Batterie PY - 2011 DO - https://doi.org/10.1111/j.1551-2916.2011.04579.x SN - 0002-7820 SN - 1551-2916 VL - 94 IS - 9 SP - 2890 EP - 2895 PB - Blackwell Publishing CY - Malden AN - OPUS4-24914 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Apel, E. A1 - Deubener, J. A1 - Bernard, A. A1 - Müller, Ralf A1 - Kappert, H. A1 - Rheinberger, V. A1 - Höland, W. T1 - Phenomena and mechanisms of crack propagation in glass-ceramics N2 - Lithium disilicate, leucite and apatite glass-ceramics have become state-of-the-art framework materials in the fabrication of all-ceramic dental restorative materials. The goal of this study was to examine the crack propagation behaviour of these three known glass-ceramic materials after they have been subjected to Vickers indentation and to characterize their crack opening profiles (δmeas vs. (a-r)). For this purpose, various methods of optical examination were employed. Optical microscopy investigations were performed to examine the crack phenomena at a macroscopic level, while high-resolution techniques, such as scanning electron microscopy (SEM) and atomic force microscopy (AFM), were employed to investigate the crack phenomena at a microscopic level. The crack patterns of the three glass-ceramics vary from fairly straightforward to more complex, depending on the amount of residual glass matrix present in the material. The high-strength lithium disilicate crystals feature a high degree of crosslinking, thereby preventing crack propagation. In this material, the crack propagates only through the residual glass phase, which constitutes 30%–40% by volume. Having a high glass content of more than 65% by volume, the leucite and apatite glass-ceramics show far more complex crack patterns. Cracks in the leucite glass-ceramic propagate through both the glass and crystal phase. The apatite glass-ceramic shows a similar crack behaviour as an inorganic–organic composite material containing nanoscale fillers, which are pulled out in the surroundings of the crack tip. The observed crack behaviour and the calculated View the MathML source values of the three types of glass-ceramics were compared to the Kkic values determined according to the SEVNB method. KW - Glass KW - Viscosity KW - Water content PY - 2008 DO - https://doi.org/10.1016/j.jmbbm.2007.11.005 SN - 1751-6161 VL - 1 IS - 4 SP - 313 EP - 325 PB - Elsevier CY - Amsterdam AN - OPUS4-18308 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Eberstein, Markus A1 - Müller, Ralf A1 - Reinsch, Stefan A1 - Rabe, Torsten A1 - Schiller, Wolfgang Arno A1 - Thiel, A. A1 - Deubener, J. T1 - Kinetic Modeling of LTCC Shrinkage: Effect of Alumina Content N2 - We studied sintering of LTCC-type glass matrix composites (GMCs) consisting of small glass and alumina particles of equal size. Primarily, crystals act as rigid inclusions, decelerating the densification rate. In later stages, they also dissolve, partially increasing the viscosity. Release of alumina finally induces crystallization of alumosilicates, which enables post-firing stability. To study both effects, two model GMCs were prepared: an α-Al2O3 + barium alumoborosilicate glass (BABS)–GMC, which shows neither significant dissolution nor crystallization, and an α-Al2O3 + calcium alumoborosilicate glass (CABS)–GMC, which dissolves readily and promotes crystallization. The kinetics of shrinkage for both GMC were modeled by utilizing Frenkel theory for the early stage and Mackenzie–Shuttleworth theory for the late stage, assuming that sintering is superimposed by the weighted contributions of triparticle glass–crystal clusters, their random occurrence (ideal mixing), and a shrinkage rate controlled by the GMC effective viscosity. In agreement with modeling, the experimental results showed that the shrinkage rate of BABS–GMC decreases progressively for crystal volume fractions Φ > 0.15. The attainable shrinkage is reduced by up to 8% for Φ = 0.45. For the CABS–GMC with Φ = 0.25, a reduction of Φ to 0.20 was evident due to partial α-Al2O3 dissolution. This effect was found able to increase the sintering temperature by ~50–60 K. KW - LTCC KW - Glas Matrix Composites KW - Inclusions KW - Sintering Kinetics KW - Modeling PY - 2007 SN - 1551-4897 VL - 4 IS - 4 SP - 173 EP - 180 CY - Washington, DC AN - OPUS4-16506 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Müller, Ralf A1 - Reinsch, Stefan A1 - Eberstein, Markus A1 - Deubener, J. A1 - Thiel, A. A1 - Schiller, Wolfgang Arno T1 - Effects of dispersed Al2O3 particles on sintering of LTCC N2 - The sintering of Low Temperature Co-fired Ceramics prepared from alumoborosilicate glass- and Al2O3 powders of similar small particle size was studied by dilatometry, heating microscopy, microstructure analysis, glass- and effective viscosity measurements. The steric effect of Al3O3 inclusions was studied using a gnon-reactiveh model composite. With increasing Al3O3 volume fraction (Φ ≤ 0.45), sintering decelerates and its final stage shifts to higher temperature. The attainable shrinkage is reduced as Al2O3 particle clusters bearing residual pores become more frequent. The kinetics of sintering could be described formally superposing the weighed contributions of differentially sized and randomly composed glass-crystal particle clusters and assuming a sintering rate controlled by the effective matrix viscosity, which increases with Φ and with progressive wetting of Al2O3 particles during densification. The "reactive" model composite shows significant dissolution of Al2O3 into the glass, which has two opposed effects on sintering: reducing Φ and increasing glass viscosity. For the present case (Φ = 0.25), the latter effect dominates and sintering is retarded by Al2O3 dissolution. Crystallization of wollastonite starts after full densification. Dissolution of Al2O3 was found to promote the subsequent growth of anorthite. KW - LTCC KW - Glass matrix composites KW - Al2O3-inclusions KW - Sintering kinetics PY - 2005 SN - 1022-6680 SN - 1662-8985 VL - 39-40 SP - 375 EP - 380 PB - Trans Tech Publ. CY - Zurich AN - OPUS4-18441 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zietka, S. A1 - Deubener, J. A1 - Behrens, H. A1 - Müller, Ralf T1 - Glass transition and viscosity of hydrated silica glasses N2 - The viscosity of silica glasses with different water contents was measured by penetration of sapphire microspheres in the range from 1012-1014·7 Pas at ambient pressure. Commercial silica glasses were used together with hydrous silica glasses, which were prepared by melting glass powder plus water in an internally heated pressure vessel at 2-3 kbar and 1350-1450°C. The temperature dependence of the viscosity of silica glasses with total water contents Cw of 5·4×10-4, 7·0×10-4, 1·00×10-2, and 1·55×10-2(Cw in mass fractions) can be described by Arrhenius equations. From the results, the linear dependence of the T12 isokom (K) with the logarithm of the water content was determined as T12=192-409 logCw. The analysis of the compositional dependence of the T12 isokom in the H2O-Na2O-SiO2 system reveals a temperature depression of up to 200 K for mixed water- and sodium-bearing glasses compared to H2O-SiO2 and Na2O-SiO2 glasses with same molar silica content. From these findings we conclude that protons may contribute significantly to the mixed alkali effect in glasses. KW - Wassergehalt KW - Silicatgläser KW - Viskosität PY - 2007 SN - 1753-3562 SN - 0017-1050 SN - 0031-9090 SN - 1750-6697 VL - 48 IS - 6 SP - 380 EP - 387 PB - Society of Glass Technology CY - Sheffield AN - OPUS4-18396 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Reinsch, Stefan A1 - Nascimento, M.L.F. A1 - Müller, Ralf A1 - Zanotto, E. D. T1 - Crystal growth kinetics in cordierite and diopside glasses in wide temperature ranges N2 - We measured and collected literature data for the crystal growth rate, u(T), of µ-cordierite (2MgO · 2Al2O3 · 5SiO2) and diopside (CaO · MgO · 2SiO2) in their isochemical glass forming melts. The data cover exceptionally wide temperature ranges, i.e. 800–1350 °C for cordierite and 750–1378 °C for diopside. The maximum of u(T) occurs at about 1250 °C for both systems. A smooth shoulder is observed around 970 °C for µ-cordierite. Based on measured and collected viscosity data, we fitted u(T) using standard crystal growth models. For diopside, the experimental u(T) fits well to the 2D surface nucleation model and also to the screw dislocation growth mechanism. However, the screw dislocation model yields parameters of more significant physical meaning. For cordierite, these two models also describe the experimental growth rates. However, the best fittings of u(T) including the observed shoulder, were attained for a combined mechanism, assuming that the melt/crystal interface growing from screw dislocations is additionally roughened by superimposed 2D surface nucleation at large undercoolings, starting at a temperature around the shoulder. The good fittings indicate that viscosity can be used to assess the transport mechanism that determines crystal growth in these two systems, from the melting point Tm down to about Tg, with no sign of a breakdown of the Stokes–Einstein/Eyring equation. KW - Crystal growth KW - Oxide glasses KW - Silicates KW - Kristallwachstumsgeschwindigkeit KW - Kinetik KW - Silikatgläser PY - 2008 DO - https://doi.org/10.1016/j.jnoncrysol.2008.09.007 SN - 0022-3093 VL - 354 IS - 52-54 SP - 5386 EP - 5394 PB - North-Holland Publ. Co. CY - Amsterdam AN - OPUS4-18383 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Müller, Ralf A1 - Eberstein, Markus A1 - Reinsch, Stefan A1 - Schiller, Wolfgang Arno A1 - Deubener, J. A1 - Thiel, A. T1 - Effect of rigid inclusions on sintering of low temperature co-fired ceramics KW - Sintering KW - Glass Matrix Composites KW - Rigid Inclusion KW - Effective Viscosity KW - Kinetic Modelling KW - LTCC PY - 2007 SN - 1753-3562 SN - 0017-1050 SN - 0031-9090 SN - 1750-6697 VL - 48 IS - 4 SP - 259 EP - 266 PB - Society of Glass Technology CY - Sheffield AN - OPUS4-16211 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schiller, Wolfgang Arno A1 - Müller, Ralf A1 - Rabe, Torsten ED - R. Clasen, ED - M. Herrmann, ED - Roosen, A. T1 - Über das Sintern von LTCC KW - LTCC KW - Komposite KW - Multilayer-Technik KW - Sintern KW - Simulation PY - 2007 SN - 0177-6983 VL - 21 IS - 1 SP - 41 EP - 46 PB - Göller CY - Baden-Baden AN - OPUS4-16428 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Reinsch, Stefan A1 - Gaber, Martin A1 - Müller, Ralf A1 - Schiller, Wolfgang Arno T1 - Rate controlled debindering of glass ceramic composites N2 - Green compacts of ceramics, glass ceramic composites and sinter glass ceramics contain different amounts of organic materials added as pressing aids or binders. Before sintering, these organics have to burn out completely. In oxidising atmospheres, the debindering process is mostly exothermic and therefore difficult to control. This uncontrolled heat production due to locally enhanced debindering and respective gas release may cause damages in the green compact microstructure. Therefore, debindering is usually operated with very low heating rates (< 3 K/min) which requires long processing times of many hours. In this paper, we will show that it is possible to reduce the processing time for debindering dramatically by using the decomposition rate of the organic binder, detected by the weight loss of the sample, as a control factor of the furnace. T2 - 9th ESG (European Society of Glass) Conference with the Annual Meeting of the ICG Glass - "The challenge for the 21st century" CY - Trencin, Slovakia DA - 2008-06-22 KW - Debindering KW - Thermo gravimetry KW - Glass ceramic composites PY - 2005 SN - 1022-6680 SN - 1662-8985 VL - 39-40 SP - 583 EP - 586 PB - Trans Tech Publ. CY - Zurich AN - OPUS4-17840 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -