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- ItemEffect of TiO2 , ZrO2 and ZnO addition on the hydrolytic durability, viscosity and crystallization behaviour of fibre glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Tauch, Diana; Wange, Peter; Rüssel, ChristianGlasses of the System Na2O-K2O-MgO-CaO-BaO-AI2O3-SiO2-B2O3 with additions of TiO2, ZrO2 and ZnO were melted from the raw materials. The glasses were characterized with respect to their hydrolytic durabilities, the working ranges (difference of temperatures attributed to viscosities of 10^2 and 10^4 dPa s), the temperatures attributed to the working point (η = 10^3.5 dPa s), and the crystal growth velocities. In the most cases, the additions led to an increase in viscosity and to a slight decrease in the workability range. The crystal growth velocities decreased with the addition of Ti02 and/or Zr02, while they increased if adding ZnO. The addition of ZnO or of TiO2 and ZrO2 resulted in better chemical durability.
- ItemChemical solubility of phosphate glasses in the system Na2O-CaO-MgO-P2O5-Al2O3-TiO2 in aqueous solutions of different pH values(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Vogel, Jürgen; Wange, Peter; Knoche, Silke; Rüssel, ChristianPhosphate glasses of different composition ranges show very different solubility behaviour in aqueous solutions of pH 4 and 5.8. With inereasing P2O5 concentrations between 38 and 52 mol% , in the system Na2O-CaO-MgO-P2O5-Al2O3-TiO2 , the dissolution rate generally increases, however, the most notable increase is observed at P2O5 concentrations larger than 48 mol%. Additives of TiO2 and AI2O3 increase the stability to corrosion. Glasses with compositions in the metaphosphate range show larger dissolution rates in slightly acidic medium than glasses near the invert glass range. Glasses in the invert glass range show a stronger increase in the dissolution rates with decreasing pH value and also deceleration of the dissolution with time.
- ItemAlumina and zirconia as inhibitors of crystallization during sintering of borosilicate glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2002) Pascual, M. Jesus; Pascual, Luis; Durán, Alicia; Wange, Peter; Rüssel, ChristianThe glass composition (in mol%) 16 Na2O ∙ 24 B2O3 ∙ 60 SiO2 has suitable viscosity and dilatometric properties to be used as sealing material for the gas manifolds of molten carbonate fuel cells (MCFC). Nevertheless, quartz crystallization takes place during sintering of the borosilicate glass powder at temperatures between 600 and 700 °C. The quartz crystallization leads to the formation of pores and a variation in the thermal expansion coefficient; both giving rise to defects and tensions in the seal. In this work, the possibility of inhibition of quartz crystallization by substituting AI2O3 or ZrO2 for 2 or 5 mol% of SiO2 is described. The thermal properties and the viscosity-temperature curve of the new compositions, especially those containing alumina do not differ much from the original glass.
- ItemCrystallization and vicosity of phosphate melts in the system Na2O-CaO-MgO-P2O5-Al2O3-TiO2(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Wange, Peter; Vogel, Jürgen; Knoche, Silke; Rüssel, ChristianGlasses in the system Na2O-CaO-MgO-P2O5-Al2O3-TiO2 were studied with respeet to their crystallization and viscosity. Glasses in the metaphosphate range are composed of phosphate chains, and possess a comparably small tendeney to crystallization. Here, AlPO4 in a cristobalite-like modification and Ca2P2O7 are formed. Glasses in the intermediate range between metaphosphate and invert glass structures are composed of smaller phosphate units and show higher erystal growth velocities as well as higher viscosities. Additions of MgO, AI2O3 and TiO2 result in a strengthening of the glass network, and hence, inereasing viscosities and a notably smaller tendeney to crystallization.