抄録
Aluminium hydroxide (Al(OH)3) was mechanically activated in a dry condition using high energy media agitating mill. The reaction between the activated Al(OH)3 and Mg(OH)2 in aqueous solutions of various pHs was investigated, and the effectiveness of the use of the activated Al(OH)3 was discussed for the synthesis of spinel (MgAl2O4) powder. Milling up to 1h apparently reduced grain size and promoted amorphization. Milling longer than 2h, however, did not give further physical changes. Al(OH)3 milled for 2h showed almost 1000 times higher solubility than as-received Al(OH)3 and easily reacted with Mg(OH)2 to form a complex hydroxide (Mg4Al2(OH)14·3H2O). Especially, the formation of the complex hydroxide was remarkably promoted in acidic and basic solution. The complex hydroxide decomposed to MgAl2O4 and MgO at about 400°C. MgO, which decomposed from the complex hydroxide, reacted with Al2O3, which was converted from Al(OH)3, to form a spinel phase at lower temperature than that of an ordinary solid-state reaction between MgO and Al2O3. Accordingly, the use of the activated Al(OH)3 was effective for low temperature synthesis of spinel powder. Furthermore, it was found that mixing of Al(OH)3 and Mg(OH)2 with a ball mill remarkably enhanced the formation of the complex hydroxide. Consequently, almost monolithic spinel powder was obtained at heat-treatment temperature as low as 1000°C when the activated Al(OH)3 was mixed with Mg(OH)2 using a ball mill.
