Improved 3D printed silica ceramics impregnated with an alumina sol by controlling atmosphere, vacuum pressure and holding time

When the content of cristobalite is in the appropriate range, the mechanical properties of silica ceramics can be improved. The formation and growth of cristobalite in silica ceramics can be promoted by introducing alumina into silica ceramics by vacuum impregnation. In this study, the influence of different conditions on the impregnation of silica ceramics by alumina sol was studied by controlling the impregnation atmosphere, vacuum impregnation pressure and vacuum impregnation time. The results proved that the impregnation atmosphere has a great influence on the impregnation effect. The flexural strength of vacuum impregnated sample increased by 278.8 % compared with that of air impregnated sample. The smaller the pressure, the greater the difference between the pressure and the external pressure, and the better the impregnation effect of the sample. The flexural strength of the sample with vacuum impregnation pressure of 0.015 MPa was 138.1 % higher than that of the sample with vacuum impregnation pressure of 0.065 MPa. The increase of vacuum impregnation holding time can improve the performance of the sample, but the improvement effect has an upper limit. When the vacuum impregnation time was 3.0 h, the strength of the sample improved by 98.3 % compared with that of the sample with vacuum impregnation time of 1.5 h. Based on the mechanical properties and economic benefits, the best mechanical properties of silica ceramics were obtained by impregnating 3.0 h with 25 wt% alumina sol at a temperature of 60 °C and a vacuum pressure of 0.015 MPa. In these conditions, the flexural strength of the samples was 19.9 ± 0.4 MPa, the bulk density was 1.68 ± 0.02 g/cm3, and the porosity was 25.9 ± 0.9 %.