Study On Fabrication Of Quartz Glass/Ceramics Based On Nano-silica Hydrsol

Quartz glass/ceramic has many excellent properties,and it is widely used in optical components,microwave substrates and refractories,etc.However,its preparation methods still have some problems such as high cost,complicated process or unsuitable for precision manufacturing.Silica hydrosol is a type of colloid solution that disperses nanosized silica in water.It is an effective molding agent and sintering aid because of the good bonding and adsorption properties.Moreover,it is widely used in precision casting and other fields because of the mature preparation technology and low price.In present thesis,spherical SiO₂with different particle sizes were synthesized by St（?）ber method and silica hydrosol spray method.Quartz glass or ceramics were prepared from silica hydrosol as raw material or binder.The sintering,crystallization,optical and dielectric properties of quartz glass or ceramics were investigated,and some useful results were also obtained.In present thesis,transparent silica glass is fabricated from low-cost commercial nano-silica hydrosol.To obtain transparent glass,the crystallization temperature of bulk materials must be higher than their densification temperature.Based on XRD analysis,impurity ions such as Na⁺have a strong influence on the crystallization characteristics of sintered samples.Purification can be performed by soaking preheated samples in boiling water for a given duration.Transparent silica glass was obtained for purified samples from acidic silica hydrosol sintered at 900-950℃.The optical characteristics of the samples were investigated for the presence of silica glass,and the transparency was enhanced for samples sintered in vacuum.The mechanical properties of self-made transparent quartz glass are better than that of commercial fused quartz glass,but the dielectric loss is higher than that of commercial fused quartz glass.In present thesis,spherical SiO₂with different particle sizes were synthesized by St（?）ber method and silica hydrsol spray method,and quartz ceramics were prepared by using self-made or commercial spherical SiO₂as disperse phase and silica hydrsol as binder.The results show that silica hydrsol can promote the sintering of quartz ceramics at high temperature,but also promote the crystallization of quartz ceramics.The doping results show that the high valence cations can inhibit the crystallization of fused quartz,while the low valence cations can promote the crystallization of fused quartz.The fused quartz ceramics with a density of 2.1 g cm^-3can be prepared by sintering at 1000℃,and the translucent fused quartz ceramics with a small amount of cristobalite can be prepared by sintering at 1200℃.The solid content and crystallization temperature of the suspension prepared with St（?）ber and spray spherical powders are lower than those of commercial spherical SiO₂powders.Quartz ceramics with the density of about 2.2 and 1.86 g cm^-3containing the mixed phase of cristobalite and tridymite were obtained at the sintering temperature of 1000-1200℃and900-1300℃,respectively.