New periclase-spinel refractories from densely sintered high purity magnesite and new synthetic compositions based on spinel. Part 1. Study of mineral composition, microstructure, thermal expansion, and ultimate strength in compression

Abstract

Six specimens of magnesia-spinel material are made under laboratory conditions. Specimens are prepared at 1600°C from sintered magnesite and three different compositions based on spinel, previously synthesized at 1760 °C. Sintered magnesite and synthesized spinel properties are provided. Raw material properties in relation to different spinel content within them, apparent density, additions introduced, and also their effect on final product, are shown. Three forms of final product contain 8 – 11 wt.% Al2O3, and the rest contain from 19 – 21 wt.% Al2O3. Photographs taken in a scanning electron microscope, and results of microstructural analysis of raw material and final product, point to formation of direct periclase–periclase and periclase–spinel bonds, and also secondary calcium aluminate and calcium silicate phases. Secondary spinel is detected in the form of a solution within periclase, and also at grain boundaries within magnesia-spinel refractories. On the basis of petrographic criteria (mineral composition, microstructure), and also linear thermal expansion coefficient (LTEC) and ultimate strength in compression for final materials, the authors of this article propose a most suitable material with respect to quality for testing in high-temperature branches of industry.