| Silica fiber reinforced fused quartz (SiO2f/SiO2) ceramics have good dielectric and mechanical properties. However, the ceramics have poor moisture resistant due to the presence of porosity. In the paper, borosilicate glass was fabricated by melting method and solid phase method, and ZnO was added to reduce the melting and sintering temperature. Dense borosilicate glass layer was formed on the surface of SiO2f/SiO2 composite. Microstructure, phase component of the coatings and the properties of slurry were characterized by SEM, XRD and viscometer techniques, respectively. The effect of different ZnO contents and mechanical alloying time on the behaviors of melting and sintering were investigated.The monox-boron oxide-alumina (SiO2-B2O3-AL2O3) ternary system was fired to be borosilicate glass at 1400℃. The powders’sintering activity was improved by mechanical alloying. When powders was balled 20h, its crystallization peaks were receded. While powders was balled 40h, all the crystallization peaks changed to be amorphous peaks. After mechanical alloying process, irregular particle shaped into sphere. With the extension of time, the distribution of powders particle size was more and more concentrated, and powder particle size increased because of the powders’ welding in the process of high energy crashing.To prepare the good dispersive slurry, chose ethanol and xylene(E:X=50) as solvent composition. Without dispersant, the isoelectric point of powders was 2.5, the PH of maximum Zeta potential is 11. Adding castor oil as dispersant, the isoelectric point offset to lower PH slightly and Zeta potential increased, forming more stabilized slurry.with content of dispersant increasing, Zeta potential rose and viscosity decreased. In order to increase the cohesiveness between the slurry and matrix, added PVB as binder. With the increasing of PVB content, the viscosity of the slurry decreased firstly and then increased. When PVB content was 1.0%, the slurry had lowest viscosity.Before coating, fused quartz was impregnated in ethyl orthosilicate 2-3 times. After pretreatment, absorptivity reduced from 14.17% to 2.7%, and the pores in matrix was filled with silica particles of different size.In the paper, used the vacuum impregnation method to coat slurry and sintered into borosilicate glass layer at high temperature. The paper studied the effect of sintering temperature, glaze composition and mechanical alloying on the properties of the glaze layer. It found that with the increase of sintering temperature, the glass phase spread better on the matrix, the density of the glaze layer was higher. When ZnO content was about 2.5%, it showed the best flux effect and the molten glass spread out on surface well. However, when it increased to 5%, the flux effect reduced greatly, and sintering performance decreased markedly. As the extension of milling time, sintering activity also increased accordingly, density of glaze layer increased, porosity reduced, and the glass phase spread out on the matrix surface more evenly. The borosilicate glass composition that had the best moisture-proof was Z2.5, and the water absorption was between 3.5%～4.68%. While the water absorption of Zo and Z5.0 glaze layer were between 3.89%-6.14% and 5.67%-7.4%, respectively. The dielectric constant and dielectric loss of Z2.5 glaze layer were between 3.34-3.62 and 6.61～8.34×10-3, respectively. |
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