Mullitization from a multicomponent oxide system in the temperature range 1200 degrees-1500 degrees C

Mullitization from a multicomponent oxide system (aluminakaolin-quartz-feld spar-talc) was analyzed as a function of firing temperature from 1200 degre es to 1500 degrees C based on quantitative XRD and SEM, In the present stud y, whisker forms of mullite grew in three characteristic stages. In the fir st stage (1255 degrees-1295 degrees C), mullitization (nucleation) took pla ce from glass via alumina dissolution into glass under the condition of no apparent change in glass content. The reaction in this stage was rate-limit ed by alumina dissolution into glass. Extensive mullitization occurred in t he 1295 degrees-1335 degrees C range (second stage) directly from glass. Un like in the sol-gel-based binary system, alumina dissolution into glass was not shown to be the rate-controlling mechanism during this extensive mulli tization stage. Finally (>1335 degrees C, third stage), the reaction was sa turated, accompanied by an apparent decrease in glass consumption rate. The impingement of mullite whiskers by other whiskers and crystals was specula ted to cause mullite to grow in the transverse direction, yielding a dimini shed reaction rate in the final stage. Mullitization stages in this work we re compared with those of the alumina-silica binary system shown in the lit erature.