Study On Dependence Of Andalusite Mullitization On Particle Size And Impurities

In this paper, different sources of andalusite with different Al2O3contents (D55with~55%Al2O3, Y with~57%, P57with~57%and D59with~59%), and differentparticle sizes (0.088mm~8mm) from South Africa and China, which have beenwidely used in refractories, were employed as experimental raw materials. Thecontents of Al2O3, SiO2, Fe2O3and R2O in the four kinds of andalusite were analyzedby XRF, with emphasis on whether andalusite grade (Al2O3contents) was consistentwith impurity amounts.The phase compositions of andalusite and the mineral distribution (feldspar,biotite, ilmenite, hematite and quartz) in andalusite particles were studied by XRD,SEM and EDS.Phase compositions of the four kinds of andalusite with different particle sizes(0.088mm~8mm) fired at different temperatures (1200C~1550C) were determinedby XRD. The dependence of mullitization of andalusite on particle size, impuritiesand firing condition were investigated. The effects of particle size and impurityamounts on the appearing temperature of cristobalite and the disappearingtemperature of quartz during firing process were also investigated.Andalusite D59(5~8mm) fired at different temperatures were observed by SEMto study mullite formation and the microstructure development of the phases.High-energy ball milling was used to grind the andalusite powder. The change inphases and particle morphology of D59with different milling time was studied byXRD and SEM. The influence of the milling time on crystal structure of andalusiteand quartz as well as aggregation of the andalusite grains in mechanical activationprocess were investigated.The phases of D59after mechanical activation for different durations and firingat different temperatures were examined by XRD. The effects of mechanicalactivation on the inception and complete temperatures of mullitization as well as thephase transformation of quartz in the andalusite were investigated.