Phase transformation of aluminium hydroxide to aα- alumina prepared from different aluminium salts

The study intends to look at the most suitable aluminium salt to produce a single-phase a-alumina by the hydrothermal method. In the process to produce alumina from the calcination of aluminium hydroxide (Al(OH)3), three different aluminium salts namely aluminium sulfate (Al2(SO4)2), aluminium nitrate (A(NO3)3) and aluminium chloride (AlCl3) were tried. The process involved the used of NH4OH as the precipitating medium. Aluminium hydroxide produced from each of these salts were characterised by x-ray diffraction (XRD) technique to identity the crystalline phase. Aluminium hydroxide produced by all the different aluminium salts is present as boehmite or pseudo-boehmite phase. Aluminium hydroxide produced from Al2(SO)2, Al(NO)3 and AlCl3 shows the transformation of the boehmite phase to a α-alumina phase at 500 0C. On further heating, the α-alumina continuously formed at 800 oC followed soon at 1000 oC. But for the Al(NO3)3 salts a different phase transitions occurs on heating especially at 1000 oC. Here it was observed not a single alumina phase is presence but the presence of both α and γ--alumina phases. At 1300 oC, the single α-alumina phase was formed. The study concluded that aluminium sulphate is recommended in order to obtain a single-phase α-alumina with the required characteristics. (Author)