TY - CONF A1 - Müller, Ralf T1 - Glass Sintering with Concurrent Crystallization and Foaming N2 - Glass powders are promising candidates for manufacturing a broad diversity of sintered materials like sintered glass-ceramics, glass matrix composites or glass bonded ceramics with tailored mechanical, thermal, electrical and optical properties and complex shape. Its wide and precise adjustability makes this class of materials a key component for advanced technologies. Processing of glass or composite powders often allow even more flexibility in materials design. At the same time, however, processing can have substantial effects on the glass powder surface and sinterability. Thus, mechanical damage and surface contamination can strongly enhance surface crystallization, which may retard or even fully prevent densification. Whereas sintering and concurrent crystallization have been widely studied, partially as cooperative effort of the TC7 of the ICG, and although glass powder sintering is predominantly applied for glasses of low crystallization tendency, sintering is also limited by gas bubble formation or foaming. The latter phenomenon is much less understood and can occur even for slow crystallizing glass powders. The lecture illustrates possible consequences of glass powder processing on glass sintering, crystallization and foaming. T2 - 7th Int Congress on Ceramics, Symposium Frontiers of Glass Science CY - Iguacu, Brazil DA - 17.06.2018 KW - Glass KW - Powder KW - Sintering KW - Foaming PY - 2018 AN - OPUS4-45670 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Müller, Ralf T1 - Sintering and foaming of silicate N2 - Glass powders are promising candidates for manufacturing a broad diversity of sintered materials like sintered glass-ceramics, glass matrix composites or glass bonded ceramics with properties and complex shape. Powder processing, however, can substantially affect sinterability, e.g. by promoting surface crystallization. On the other hand, densification can be hindered by gas bubble formation for slow crystallizing glass powders. Against this background, we studied sintering and foaming of silicate glass powders with different crystallization tendency for wet milling and dry milling in air, Ar, N2, and CO2 by means of heating microscopy, DTA, Vacuum Hot Extraction (VHE), SEM, IR spectroscopy, XPS, and ToF-SIMS. In any case, foaming activity increased significantly with progressive milling. For moderately milled glass powders, subsequent storage in air could also promote foaming. Contrarily, foaming could be substantially reduced by milling in water and 10 wt% HCl. Although all powder compacts were uniaxially pressed and sintered in air, foaming was significantly affected by different milling atmosphere and was found most pronounced for milling in CO2 atmosphere. Conformingly, VHE studies revealed that foaming is mainly driven by carbonaceous species, even for powders milled in other gases. Current results of this study thus indicate that foaming is caused by carbonaceous species trapped on the glass powder surface. T2 - ICG Annual Meeting 2018 CY - Yokohama, Japan DA - 23.09.2018 KW - Foaming KW - Glass KW - Powder KW - Sintering PY - 2018 AN - OPUS4-46474 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Müller, Ralf T1 - Sintering and crystallization of glass powders – effects, challenges and chances N2 - Chemical variability is a main strength of glass. Glass powders are therefore promising candidates for manufacturing a broad diversity of sintered materials like sintered ¬glass-ceramics, glass matrix composites or glass bonded ceramics with tailored mechanical, thermal, electrical and optical properties and complex shape. Its wide and precise adjustability makes this class of materials, even if it may not be obvious at first sight, a key component of advanced technologies. Manufacture and processing of initial glass powders often allow even more flexibility in materials design. At the same time, however, they can cause additional problems. The lecture illustrates possible consequences of glass powder processing upon glass crystallization and sintering as well as chances for targeted utilization. Simple kinetic models describing the effect of particle size distribution, surface crystallization and rigid inclusions on sintering as well effects of different milling and seeding on sinter crystallization are presented. T2 - Institutskolloquium CSIC CY - Madrid, Spain DA - 28.4.2016 KW - Glass KW - Powders KW - Sintering KW - Crystallization KW - SOFC KW - LTCC PY - 2016 AN - OPUS4-38333 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Müller, Ralf T1 - High-temperature laser profilometry N2 - Advanced methods for 3D green density characterization like computed tomography and 3D FE sinter modeling can be utilized for increasing the reliability of sintered components. The experimental in situ observation of sintering, however, is currently restricted to silhouette methods, i.e. heating microscopy. For complex shaped samples, in situ shape screening during shrinkage would allow much better validation of 3D sinter simulation models. Further, by revealing temporary sinter warpage, 3D high-temperature shape screening allows to locate potential defects of complex sintered components. Against this background, BAM developed a testing device for in situ 3D high-temperature shape screening for ceramic and glass-ceramic tapes up to 1000°C [1-3]. Current work is focused on dropping this restriction in sample shape and temperature. The poster illustrates the current state of this work and possible applications of the method e.g. in detecting sinter warpage of metallized glass-ceramic LTCC tapes. T2 - SGT Centenary Conference, & ESG 2016 CY - Sheffield, UK DA - 04. 09. 2016 KW - Laser profilometry KW - 3D High-temperature shape screening KW - Sintering PY - 2016 AN - OPUS4-38320 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Müller, Ralf T1 - Sintering and foaming of barium silicate glass powders N2 - The manufacture of sintered glasses and glass-ceramics, glass Matrix composites and glass-bounded ceramics or pastes is often affected by gas bubble formation. Against this background, we studied sintering and foaming of barium silicate glass powders used as SOFC sealants using different powder milling scenarios. Sintering was measured by means of heating microscopy backed up by XPD, DTA, Vacuum Hot Extraction (VHE) and optical and electron microscopy. Foaming increased significantly as milling progressed. For moderately milled glass powders, subsequent storage in air could also promote foaming. Although the powder compacts were uniaxially pressed and sintered in air, the milling environment significantly affected foaming. The strength of this effect increased in the order Ar >> N2 < air < CO2. Conformingly, VHE studies revealed that the pores of aerated samples predominantly encapsulated CO2, even for powders milled in Ar and N2. Results of this study thus indicate that foaming is caused by carbonaceous species trapped on the glass powder surface. Foaming could be substantially reduced by milling in water and 10 wt% HCl. T2 - 12th Pacific Rim Conference on Ceramic and Glass Technology CY - Waikoloa, Hawaii, USA DA - 21.5.2017 KW - Sintering KW - Gas bubble formation KW - Foaming PY - 2017 AN - OPUS4-44220 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Müller, Ralf A1 - Körner, S. T1 - Dissolution and reprecipitation of silver in sintering silver-glass dispersions N2 - Electric contacts based on silver-glass dispersions are key components in optoelectronic microsystems and control modules for medical, information & communication and energy technology in our networked society. Driven by the complexity of modern production processes and ever shorter time-to-market requirements, the fast and specific development of tailored silver-glass dispersions has become a bottleneck of technology development. Nevertheless, the underlying mechanisms of silver dissolution, transport, and reprecipitation, and the resulting micro structure evolution during firing are poorly understood. The broad literature on the precipitation of colloidal silver particles and the related processes of silver dissolution and diffusion mostly refer to very small volume fractions of silver. Transferring these results to the sintering of glass-containing silver dispersions, is therefore highly questionable. In this case, silver dissolution, electrical contact between silver particles, transport and reprecipitation take place under special conditions. This includes short diffusion lengths (particle size < 10 μm), the presence of three-phase contacts silver - glass - sintering atmosphere, as well as silver reprecipitation at the sintering contacts as the driving force of silver transport. Here, a dynamic balance of the silver concentration can be expected to result from the ratio between silver dissolution and reprecipitation. The aim of the project is to gain basic insight into the mechanisms of dissolution, transport and reprecipitation of silver in sintering silver glass dispersions. In this context, the main focus is on gaining basic knowledge about the dissolution of metallic silver in low melting oxide glasses as the limiting factor of the sintering of silver-glass composites. In particular, we will strive to gain insight into the effect of the oxygen content of the sintering atmosphere, of the oxygen dissolved in the silver particles, of silver oxide on the surface of the silver powder, of the electric contact between the silver particles, as well as the basicity of the glass. Furthermore, we strive for insights into the silver mobility and the silver concentration that can be attained (silver solubility) in oxide glasses with a low melting point. Summing up all these aspects, a closed explanatory model for silver dissolution, transport and reprecipitation during the sintering of glass silver dispersions will be introduced. T2 - DFG Begutachtungskolloquium (PAK 949/1 und PAK 950/1) CY - Bonn, Germany DA - 07.03.2017 KW - Sintering KW - Silver KW - Glass KW - Solubility KW - Reprecipitation PY - 2017 AN - OPUS4-44227 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Müller, Ralf A1 - Körner, S. T1 - Dissolution and reprecipitation of silver in sintering silver-glass dispersions N2 - Electric contacts based on silver-glass dispersions are key components in optoelectronic microsystems and control modules for medical, information & communication and energy technology in our networked society. Driven by the complexity of modern production processes and ever shorter time-to-market requirements, the fast and specific development of tailored silver-glass dispersions has become a bottleneck of technology development. Nevertheless, the underlying mechanisms of silver dissolution, transport, and reprecipitation, and the resulting micro structure evolution during firing are poorly understood. The broad literature on the precipitation of colloidal silver particles and the related processes of silver dissolution and diffusion mostly refer to very small volume fractions of silver. Transferring these results to the sintering of glass-containing silver dispersions, is therefore highly questionable. In this case, silver dissolution, electrical contact between silver particles, transport and reprecipitation take place under special conditions. This includes short diffusion lengths (particle size < 10 μm), the presence of three-phase contacts silver - glass - sintering atmosphere, as well as silver reprecipitation at the sintering contacts as the driving force of silver transport. Here, a dynamic balance of the silver concentration can be expected to result from the ratio between silver dissolution and reprecipitation. The aim of the project is to gain basic insight into the mechanisms of dissolution, transport and reprecipitation of silver in sintering silver glass dispersions. In this context, the main focus is on gaining basic knowledge about the dissolution of metallic silver in low melting oxide glasses as the limiting factor of the sintering of silver-glass composites. In particular, we will strive to gain insight into the effect of the oxygen content of the sintering atmosphere, of the oxygen dissolved in the silver particles, of silver oxide on the surface of the silver powder, of the electric contact between the silver particles, as well as the basicity of the glass. Furthermore, we strive for insights into the silver mobility and the silver concentration that can be attained (silver solubility) in oxide glasses with a low melting point. Summing up all these aspects, a closed explanatory model for silver dissolution, transport and reprecipitation during the sintering of glass silver dispersions will be introduced. T2 - DFG Begutachtungskolloquium (PAK 949/1 und PAK 950/1) CY - Bonn, Germany DA - 07.03.2017 KW - Sintering KW - Silver KW - Glass KW - Solubility KW - Reprecipitation PY - 2017 AN - OPUS4-44228 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Müller, Ralf T1 - Sintering and Foaming of Silicate Glass Powders N2 - The lecture focuses on the mechanisms of non-desired gas bubble formation and foaming during the sintering of glass powder compacts. It is shown that foaming is driven by carbon gases and that carbonates, encapsulated in micropores or mechaniacally dissolved beneath the glass surface, provide the major foaming source. T2 - Sandanski Workshop Sinter crystallization 27th-29th September 2021 PROJECT “THEORY AND APPLICATIONS OF SINTER-CYSTALLIZATION” DN 19/7 CY - Online meeting DA - 27.10. 2021 KW - Sintering KW - Non-desired foaming PY - 2021 AN - OPUS4-53772 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Agea Blanco, Boris A1 - Blaess, C. A1 - Reinsch, Stefan A1 - Brauer, D. A1 - Müller, Ralf T1 - Sintering and foaming of barium and calcium silicate glass powders N2 - Sintering and foaming of barium and calcium silicate glass powder compacts have been studied for different powder milling. Sintering was measured by means of heating microscopy backed up by XRD, DTA, Vacuum Hot Extraction (VHE) and electron microscopy. Foaming intensity strongly increased with decreasing glass partiefe size. Although powder compacts were uniaxially pressed and sintered in ambient air, foaming was affected by the milling atmosphere and most intensive for milfing in C02. Conformingly, VHE studies revealed that foaming of fully sintered samples was mainly driven by C02, even for powders milled in technical air, Ar and N2. Prolonged storage of air milled barium silicate glass powders in ambient air before pressing and sintering caused further increase of foaming intensity. These findings indicate that carbonaceous species are preferentially trapped to or close beneath the powder surface during milling and later storage. The temperature range of C02 degassing from fully sintered barium and calcium silicate g/ass powder compacts fits the temperature ranges of decomposition of BaC03 and CaC03 mix-milled with the respective barium and calcium silicate glass powders. T2 - IMAPS/ACerS 11th International CICMT conference and exhibition CY - Dresden, Germany DA - 20.04.2015 KW - Sintering KW - Foaming KW - Silicate glass powders KW - Barium and calcium silicate plass powders KW - Degassing PY - 2015 SN - 978-1510804562 SP - 31 EP - 37 AN - OPUS4-35250 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gaber, Martin A1 - Müller, Ralf A1 - Höland, W. T1 - Degassing phenomena during sintering and crystallization of glass powders N2 - Degassing may cause trouble in manufacture of sintered glass-ceramics via the Formation of bubbles (deteriorate mechanical strength or surface Quality) T2 - 6th Int. Otto Schott Colloquium CY - Jena, Germany DA - 06.09.1998 KW - Bulk diffusion KW - Sintering KW - Crystallization KW - Melting PY - 1998 AN - OPUS4-35785 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -