The Study On Process Of Preparing Quartz Ceramics By Nano-SiO₂

The starting materia ls used in the investigation were nano SiO2 powders, Al2O3powders, H3BO3, Al-Si fibers and so on. First, samples were prepared by gel-castingmethod, in which the liq uid were prepared by the ratio water: AM: MBAM=100:20:2.Green samples were sintered at different temperatures, different hold ing times, andthen influences of additives and sintering schedule on improvement of quartz ceramicmade by nano SiO2 were investigated. According to XRD, SEM and DSC, phasetransformation mecha nism of quartz ceramic made by nano SiO2 and inhibitingmecha nism by additives were investigated. Secondly, effects of ions adding methodand powders pre-sintering on preparing quartz ceramic made by nano SiO2 werestudied. Finally, prelimina ry investigation on VPI process was carried out. The resultsshowed that: sma ll amount of Al2O3 and H3BO3 improved the density of ceramics, butwith the increasing of Al2O3,the density of samples decreased; samples with 7%Al2O3 had great bending strength(12.4MPa); with the increasing of sinteringtemperature, density of samples were improved, however, due to the cristoba litetransformation being stronger, the mecha nical properties were weakened; when adding4% H3BO3 and 7% Al2O3, better strength appeared at 1300℃; samples with 5hhold ing time had poor sintering properties and low bending strength. Aluminum saltswere used as crysta llization inhibitors. Comparing with the method of adding 10wt%Al3O2(bending strength: 4.7MPa), adding Al3+ ions could improve the phasecomposition and bending strength(5.9MPa) of quartz ceramic made by nano SiO2 byadjusting pH, filtration way and washing way, the results showed that: 19.9g/L AlCl3and 400r/min agitation speed prepared fine powders with 4.844% Al. Slurry preparedby pre-sintering powders at 800℃had highest solid content(71.4%), while samplesmade by pre-sintering powders at 600℃had best bending strength(24MPa). Accordingto the study on VPI process, it is found that powder sizes of matrix, solid content ofmatrix slurry and pressure hold ing time had great influ ences on the impregnation.