The Research On The Effect Of Additives Bearing Alumina On The Mullitization Of South Affrica Andalusite

Various samples composing mainly South Africa andalusite and four kinds of additives containing alumina including super grade bauxite clinker,fused brown corundum,active alumina and fused sub-white corundum were sintered at temperatures every 50℃in the range from 1150℃to 1600℃for 2 hours.The linear changes,bulk densities,apparent porosities and other parameters were measured on them after being cooled down naturally.The characteristics of the South Africa andalusite fine powder are investigated by SEM and XRD. The effects of the kinds of the additives and their addition and those of the sintering temperature on the mullitilization of the South Africa andalusite fine powder are discussed.The results show that:1.The initial decomposition temperature of the South African andalusite fine powders is about 1150℃～1200℃and the totally decomposition temperature is about 1500℃.2.The decomposition of andalusite was restrained by the kinds of additives containing alumina to different extent from which the fused brown corundum had the most intensive influence,while the effect of sub-white fused corundum the weakest.3.The silica freed from the andalusite powder during the decomposition process reacted with the alumina brought from the additives to form the secondary mullite.When the amount of alumina added to samples was beyond 20%,a large amount of secondary mullite was synthesized at above 1450℃,and the degree of secondary mullitization gets the highest level.4.The suitable amount for each of superfine bauxite clinker,fused brown corundum,and fused sub-white corundum is about 20%,and that for the active alumina is about 15%.