Influence of halides on formation and densification of magnesium aluminate spinel: an overview

Abstract

Magnesium aluminate (MgAl₂O₄) spinel (MAS) is a very promising synthetic material of cubic crystal structure with its excellent mechanical, thermal, chemical, dielectric and optical properties. Due to its superior high-temperature properties and eco-friendliness, it has gained importance as a refractory material for use in steel-teeming ladles, cement rotary kilns and glass tank furnaces. Apart from refractory, polycrystalline MAS is extensively used in optically transparent windows, armours and domes, owing to its high transparency with acceptable pyro-chemical properties. MAS formation from alumina and magnesia involves a volume expansion of 5–8%, which prohibits the formation of dense MAS bodies through a single-stage sintering process. As a result, a more expensive double-stage firing process is required to produce dense MAS ceramics. However, various additives play a significant role in the formation and sintering of MAS through the reaction sintering process. Research has shown that halide doping can lower the spinel formation temperature, enhance densification during sintering and modify the microstructure of MAS, resulting in a notable improvement in its thermo-mechanical properties. This review aims to explore the spinel formation and sintering characteristics of halide-doped MAS.