Synthesis, Phase Composition And Property Research Of BaO-Al₂O₃-SiO₂Glass-ceramics

BAS (BaO-Al2O3-SiO2) glass-ceramics have been fabricated by an improvedsol-gel process. It was designed to find a phase composition controlled way toimprove the mechanical property by adjusting the sintering process and compositionof raw materias. In this study, BAS gel glass was prepared at low temperature bysol-gel process using silica sol、alumina sol and Ba(NO3)2as raw materials. The gelglass after granulation and molding can achieve densification sintered at1430-1470℃.The influence of sintering temperature, holding time, heat treatment, the compositionof precursor gel powder and the amount of nucleating agent on the phase compositionand properties of BAS glass-ceramics were investigated. BAS glass-ceramics whichhave better mechanical property can be obtained with hexacelsian for main phase,mullite or monoclinic celsian for the second phase.The range of bulk density of the BAS glass-ceramics prepared by sample(nucleating agent content1wt%) whose composition point are in the single-phaseregion of celsian was about2.58-2.67gcm-3, the range of bending strength was about41-65MPa. The range of bulk density of the BAS glass-ceramics prepared by sample(nucleating agent content1wt%) whose composition point is in the single-phaseregion of mullite was about2.21-2.25gcm-3, the range of bending strength was about31-46MPa. There are many closed pores in BAS glass-ceramics prepared by samplewhose composition point is in the single-phase region of mullite. So the bulk densityand bending strength of BAS glass-ceramics prepared by sample whose compositionpoint is in the single-phase region of mullite were significantly lower than BASglass-ceramics prepared by sample whose composition point are in the single-phaseregion of celsian. After phase analysis, the main phase in BAS glass-ceramicsprepared by two samples was hexacelsian and a small amount of mullite was alsodetected. Mullite content in BAS glass-ceramics prepared by sample whosecomposition point is in the single-phase region of mullite was more than it in BASglass-ceramics prepared by sample whose composition point is in the single-phaseregion of celsian. A small amount of monoclinic celsian was detected in BAS glass-ceramicsprepared by sample (nucleating agent content2wt%) sintered first at1200℃for2hours and then sintered at1450℃for1hour, but it was not detected in BASglass-ceramics prepared by samples(nucleating agent content1wt%). So we canaccount that more nucleating agent will help hexacelsian take change into monocliniccelsian. A small amount of monoclinic celsian was detected in BAS glass-ceramicsprepared by all samples sintered not at1200℃for2hours and directly sintered at1450℃for1hour. So we can take conclusion that if the glass crystallization occursat a higher temperature, it is conductive to the promotion of hexacelsian to monocliniccelsian transformation.