Function of magnesium aluminate hydrate and magnesium nitrate as MgO addition in crystal structure and grain size control of α-Al2O3 during sintering

Chemically pure reactive alumina (α-Al2O3) which is commercially available was used for densification study in presence of widely accepted dopant MgO as additive. MgO was added both as spinel (MgAl2O4) forming precursor i.e. magnesium aluminate hydrate, and magnesium nitrate. Sintering investigations were conducted in the temperature range 1500–1600°C with 2 h soaking. Structural study of sintered pellets was carried out by extensive XRD analysis. Scanning electron mode SEM images of the specimens were considered to understand the effect of both types of additions. Addition of MgO within and beyond optimum amount had some effect on development of microstructure of sintered bodies. Densification, around 99% ρ th, with fine grain microstructure was achieved. These different types of additions caused two distinct changes in crystal structure of alumina—one small contraction and the other expansion of unit cell parameters.