Properties and structure of periclase — Yttrium materials

Conclusions An analysis was carried out of the properties of a ceramic material in the system MgO-Y₂O₃ containing 5–64.8% yttrium oxide.The vaporization of a periclase-yttrium ceramic is attributable to its large surface area and to the state of the material (monocrystalline grains and a fine-ground component). The addition of yttrium oxide to the periclase material results in a lower weight loss in a vacuum of 1.5·10^–5 mm Hg at 1700°C, more especially in the case of a mix produced from chemically pure materials. The weight loss was lowest for a composition designed as a chemical compound, viz., 1.1% after holding for 20 h.Granular mixes (2-0, 1-0 mm) are more stable to vacuum than a fine-grain material. An analysis of the structure of the cylindrical surface of the specimens showed that the vaporization rate is greater for the fine-ground component.Translated from Ogneupory, No. 1, pp. 50–54, January, 1976.     

Calculation of the liquid phase in the Al2O3-B2O3-SiO2 system for the composition of commercial quartzite powders

Conclusions A calculation of the percent liquid phase from the phase diagram Al₂O₃-B₂O₃-SiO₂ showed that quartzite powders containing 97.5% or less SiO₂ are unsuitable as lining for crucible, especially at the reheating temperature of cast iron (1550°C), owing to the possible melting of about 30% of the working zone of the lining, the migration of the melt into the colder zones, and the consequent increase in the rate of sintering.The erosion of a crucible in service depends on the percent and viscosity of the liquid phase being formed. The viscosity of the boroaluminosilicate melts forming in the Al₂O₃-B₂O₃-Si₂ system at 1550°C is high so that their activity relative to the substance in the solid state is insignificant and the sintering effect is inhibited.However, owing to the nonequilibrium course of the process mainly low-temperature liquid phases are formed and then overheated. The B₂O₃ content of these phases is high (up to 18.3%) so that their fluidity is high; Since the erosion rate of the lining depends on the action of these melts the quartzite powders used for the lining of induction furnaces should contain not more than 1.1% Al₂O₃ and not more than 1% B₂O₃.Translated from Ogneupory, No. 6, pp. 68–70, June, 1978.