Compound ceramic coatings with the main crystalline of Al2TiO5 (as-coated samples) were
prepared on Ti-6Al-4V alloy by pulsed bi-polar micro-plasma oxidation (MPO) in NaAlO2 solution. The
coated samples were calcined in Ar and air at 1000oC, respectively. The phase composition, morphology
and element content of the coatings were investigated by XRD, SEM and XRF. The samples treated in Ar
and the as-coated ones were calcined in air at 1000oC to study the oxidation resistance of the samples. The
results showed that Al2TiO5 decomposed and transformed into corundum and rutile TiO2 during the high
temperature calcination. Al2TiO5 decomposed very quickly in air and the proportion of Al2O3 to TiO2 was
44:55 after a complete decomposition. On the contrary, Al2TiO5 decomposed very slowly in argon with
the final proportion of Al2O3 to TiO2 of 81:18 on the coating surface. The morphology of the ceramic
coatings after the calcination was also different. The coatings calcined in argon were fined: the grains and
pores were smaller than those of the coatings calcined in air. The weight gains of both coatings changed in
the form of parabola law, and the weight gains of the coated samples treated in argon were comparatively
lower than that of the as-coated samples. During the high temperature calcination, the samples treated in
argon cannot distort easily, compared with the as-coated ones.
Purification of fused alumina by high temperature calcination in vacuum
