Hot-pressed constructional ceramic materials

Abstract

UDC 666.775Ultradispersed compositions of silicon nitride-yttrium oxide, silicon nitride-magnesium oxide, and mixtures of them with hexagonal boron nitride were used as the original powders for production of constructional ceramic materials.Various production methods used in the Special Design Office for Inorganic Materials of the Institute of Inorganic Chemistry of the Latvian Academy of Sciences and providing high chemical, phase, and grain size uniformity of the ultradispersed compositions were used. For example, the uniformity of nitrogen, free silicon, and yttrium content reaches 0.1-0.2 wt. %. The granulated original powders have a volume weight of 0.4-0.7 g/cm 3, which makes it possible to produce large parts up to 250 mm in weight and 2-2.5 kg in weight. The hot pressing method was developed on equipment designed and built in Technology Okhtinsk Scientific and Production Union. The set of equipment includes three presses with capacities of 0.05, 0.i, and 0.25 MN.In the silicon nitride-yttrium oxide system OTM-906 and OTM-914 materials were developed. They differ from one another in the content of sintered addition to the original raw material, which determines the differences in physico-mechanical, thermophysical, and special properties. The OTM-914 material exceeds the OTM-906 in the level of working temperatures, hightemperature strength, and crack resistance (Fig. i).The high service properties of the materials developed are the result of the optimum microstructure and phase composition, for which the presence of primarily elongated grains of hexagonal 8-SiBN ~ surrounded by refractory crystalline yttrium silicate phases is characteristic (Fig. 2).

Nanosized Powders of Refractory Compounds for Obtaining of Fine-Grained Ceramic Materials

“…It is possible to obtain a material with fine homogeneous structure (Fig. 8) and good mechanic and anticorrosion properties with low friction coefficient and wear rate, from it [6,7].…”