Transformation of η -Al₂0₃ Prepared by Thermal Decomposition of Al₂(SO₄)₃, 18 H₂0 and Al(NO₃)₃, 9 H₂0 to α -Al₂0₃ and ZnAl₂O₄ Formation

Abstract

ny A120s(S) and n-A120s(N) were prepared by thermal decomposi, tion of A12 SOD 3, 18 H20and Al(NOs)3, 9H20, respectively., The difference between the reactivity, of resulting op-A1203was examined in terms of the transformation to a-A120s and the fOrmation of ZnA120d.
By means of DTA and X-ray powder diffraction, it was observed that both T-A120s(S) and op-A120s(N) trans, formed to, a-AlaOs via e-AlaOs and the transformation temperature of opAl, O C(s)X ind T-A120s(N), aefined-asV the maxiniurb of DTA exothermic peak, was 1250 C arid 11000C, respectively. The higher transformation temperature of n-A12Qs(S) coqld be explajned by the stabilization of op-A120g(S) due to SO2 remained in it up to 12300C. ln the, present -experiments, however, a quantitative correlatien was not obtained between the ttansfpr, matiQn temperature and the residual. SO 2 content in n-A120s(S), which was estimated by, chemical analysis. On the other hand, the Washing, of op-A120s(S) with hot water, which e!iminated SO42nt existing on the surface, resulted in an increase in DTA exothermic peak height at 1250eC and no change in the peak temperature. ln the case of V-A1203(N), such an increase in peak height was not observed.
The rate of reaction of n-AlxOg with ZnO was measured and fitted to Jander s equation. The reaction rate constant (K) of T-AleOs(S) ZnO system, ZnA120di was found to be approximately ninety times as high as that of T-A120s(N) ZnO system at 7500C, This difference was mainly explained by the difference in radius of T-A1203 particles estimated by electron microphotographs and BET surface areas, and the very slight effect of residual SO 2 on the rate of ZnA120s formation was also observed.