Synthesis of MgAl_2O_4 at Low Temperature with CaCO_3 Additions

摘要

Ever since spinel MgAl_2O_4 was proposed as a substitute material for chromium based refractories, manufacturers have been encouraged to seek alternative forms of production. Addition of mineralizers has been widely employed as a method for reducing processing temperatures, which are above 1800℃ without additives. Mixtures of MgO and Al_2O_3 (molar ratio 1:1) have been prepared in this work, together with different additions of CaCO_3 (up to 30 mol%) in a resistance furnace at 1400℃. All formed phases are identified by X-ray diffractometry and microstructures are characterized by scanning electron microscopy. Results show that samples contain mainly the spinel phase with a small amount of calcium aluminates (CaAl_2O_4 and Ca_(12)Al_(14)O_(33)). The X-ray patterns suggest that calcium compounds as well as spinel are present as mixtures because both, angle peak location and relative intensities are maintained like in the mixtures of powders randomly orientated. This assumption is confirmed by EDX analysis that shows zones in the samples with spinel grains over calcium aluminates. The synthesized spinel has a density of 3.19 g/cm~3 after 5 hours at 1400℃.