Preparation Of Silica Based Porous Ceramics And The Joining With Quartz Fiber Weaves

This paper prepared silica based porous composites and realized the joining between the s ilica ba sed composite a nd quartz fiber w aves t o make a s ealed component w ith good heat insulation at high temperature. Firstly, silica based porous composites were prepared by gel-casting with fused silica as raw material and fly ash cenosphere (FAC) as pore-forming agent. And the effects of FAC on the properties of silica based composites were discussed to obtain the optimal formula of s ilica/FAC composites. Secondly, the mechanical pr operties o f q uartz fiber a nd q uartz fiber waves treated at different temperatures were studied to determine the temperature at which for joining and working. And then, the joining between silica based composite and quartz fiber waves was made with three materials (B₂O₃, Na₂CO₃ and Na₂SiO₃) as interlayers. At last, the ceramic/fiber wave joint was compared with the existing joint systems.Results showed that the silica based light-weight porous composite with the density of 0.94 g/cm³, the bending strength of 15.6 MPa, the porosity of 60% and the conductivity of 0.21 W/( m·K) was prepared by adding 45 wt.% fly ash cenonsphere after s intered a t 1200℃. In t he p rocess o f s intering, FACs not o nly a cted a s a pore-forming agent but also as a sintering aid to promote the densification o f s ilica. An interlaced microstructure of lath-like and needle-like mullite crystals was found in the composites, which was a beneficial factor for strengthening of framework. Quartz fiber's strength decreased as the temperatures i ncreased. There w as still 60% compressibility and 5% resilience in 3D silica fiber braid when treated at 800℃. During three interlayer materials (B₂O₃, Na₂CO₃, Na₂SiO₃), the joint with Na₂SiO₃ performed best as its easy process, high joining intensity and small damage to quartz fiber. The joining mechanism of using Na₂SiO₃ as joining interlayer was diffusion sintering bonding (600-800℃), and it was brazing for B₂O₃ and B₂O₃/SiO₂ mixed powders i nterlayer and reaction j oining ( 800℃) for Na₂CO₃ interlayer. What's different about ceramic/fiber wave joint was that the loose and porous structure in fiber wave could release the stress in the joining substrate.