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Oxide system PbO–ZnO–B2O3–SiO2 with the content of lead oxide of more than 45 mol.% is the basis of non-crystallizable low-melting glasses with softening temperature of lower than 450Ñ. Lead-containing glasses are very aggressive, therefore they are melted in the platinum crucibles or ceramic crucibles which are resistant to the aggressive action of the lead glass melt. During the process of the melting of lead glasses in ceramic crucibles, the additives (Al2O3 and SiO2) are transferred from the crucible to the glass melt. An uncontrolled amount of these additives affects the properties of the glasses. The objective of this work was to establish the effect of the temperature-time conditions of melting on the physical and chemical properties of high-lead glasses prepared in both platinum crucibles and ceramic ones. The results of the study showed significant difference in properties of glasses synthesized in crucibles fabricated from different materials. Glass synthesized in the platinum crucible under various temperature-time conditions was characterized by stable physical and chemical characteristics and low softening temperature (~380°Ñ) without any traces of crystallization under repeated heat treatment. The melting in the alumina crucible and quartz crucible under the same temperature-time conditions resulted in both a decrease in physical and chemical characteristics of low-melting glass and an increase in the glass softening temperature to 450–470Ñ due to crystallization of glass during a heat treatment.

Effect of the melting conditions on the properties of glasses in the system PbO–ZnO–B2O3–SiO2