Sintering and microstructure of spinel–forsterite bodies

Abstract

Spinel–forsterite phase mixtures formed by the addition of different proportions of alumina to forsterite grog's mixes, containing 10–15% alumina, showed a good compromise of high density, cold crushing strength and microstructure after firing at 1450 and 1500 °C. Forsterite was first prepared from Egyptian talc and calcined magnesite at 1400 °C/2 h. Forsterite shows good density but the microstructure contains cracks along the grain boundaries affecting the mechanical properties. The sintering and mechanical properties are improved through the addition of alumina. Alumina reacts with equimolar MgO from forsterite to form MgAl 2O 4 spinel on sintering at 1450 °C/2 h. Forsterite occurs in either patches or euhedral rhombic grains. Spinel exists in different crystal habits; either in spots within forsterite patches, prismatic euhedral crystals or on rims of forsterite grains. Considerable amount of low melting enstatite phase was formed on 20% alumina addition as a result of the decrease in the MgO/SiO 2 of forsterite after the formation of spinel. Enstatite improves the sintering through enhancing the formation of glassy phase.