Browsing by Author "Winter, Wolfgang"
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- ItemCrystallization sequence of barium osumilite and MAS osumilite glass-ceramics with low thermal expansion(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Winter, Wolfgang; Bogdanow, Christina; Müller, Gerd; Pannhorst, WolfgangGlass powders with compositions of the series BaMg2Al6Si9O30 (barium osumilite)-Mg2Al4Si11O30 were crystallized isothermally and with a constant heating rate schedule. The phase diagram of the series was constructed from equilibrium solid state reaction studies in order to distinguish stable from metastable crystallization products. Depending on the glass composition and the conditions of heat treatment different phases can crystallize. Metastable crystallization products are a high-quartz solid solution (MgAl2SixO4+2x). hexacelsian (BaAl2Si2O8) and MAS osumilite (Mg2Al4Si11O30). As accessories which can also be metastable with respect to the chosen conditions, cordierite, celsian and a spinel-Al2O3 solid solution appear in the products. BaO-rich glasses of the series crystallize easily to give a monophase barium osumilite glass-ceramic. Glass-ceramics which mainly consist of MAS osumilite can be prepared by crystallizing glasses of the series with low BaO content. Barium osumilite and especially MAS osumilite have very low thermal expansion coefficients: 2.6 ∙ 10^-6 and 1.7 ∙ 10^-6 K^-1 respectively, in the temperature range 25 to 1000 °C. The expansion behaviour of MAS osumilite is similar to that of the low-expansion phase cordierite.
- ItemSintering and crystallization of glasses with roedderite-type composition (Na, K)2Mg5Si12O30(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1992) Winter, Wolfgang; Müller, Gerd; Pannhorst, WolfgangTwo glass powders of roedderite-type composition (Na2Mg5Si12O30 and NaKMg5Si12O30) have been prepared for sintering and crystallization experiments. Glass powder of sodium roedderite composition sinters to a dense body after 15 to 60 min at 800 to 850 °C before crystallization. The sintered body crystallizes easily to give roedderite as the main phase. Sodium-potassium-roedderite glass powder can be sintered to a dense body, too, though the sintering rate is lower. This is due to the higher viscosity of the sodium-potassium-roedderite glass. The amount of crystallized roedderite is smaller in the sodium-potassium composition whereas the amount of residual glass is higher. This influences the thermal expansion of the compact, which is higher than in the sodium roedderite glass-ceramic. The thermal expansion coefficient of the latter is close to that of pure crystaline sodium roedderite.