Characterization and Sinterability of Mg-Al Spinel Powders Prepared with a Thermal Decomposition of a Freeze-dried Sulfate
1982 Volume 90 Issue 1042 Pages 312-319
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1982 Volume 90 Issue 1042 Pages 312-319
The freeze-dried sulfate was prepared from the equi-mole mixed aqueous solution of magnesium and aluminum sulfates and calcined at 900°-1400°C for 1h. These calcined spinel powders were characterized and their sinterability was investigated. The results obtained were as follows:
(1) The freeze-dried sulfate was amorphous and its composition was MgAl2(SO4)4⋅8-9H2O which corresponded to partially dehydrated MgAl2(SO4)4⋅22H2O.
(2) The sulfate completely decomposed to spinel above the firing temperature of 1000°C.
(3) Powders obtained from the calcination of sulfate at 1100°-1300°C were nearly perfect spinel crystals, showing that their lattice parameter was 8.082Å, but their apparent crystallite size was small, about 600Å, and their specific surface area was relatively large, 20-30m2/g.
(4) Initial sintering of these specimens was mainly controlled by volume diffusion mechanism and the apparent activation energy of sintering for the specimen calcined at 1300°C was 127kcal/mol.
(5) The bulk density of these speciments fired at 1500°C for 2h was higher than that of spinels prepared from oxide mixture, hydroxide mixture and coprecipitated materials reported previously and its maximum density was 3.47g/cm3, 97% of theoretical density, with specimen consisting of the powder calcined at 1300°C.
