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Preparation of Silica Based Porous Ceramics and the Joining with Quartz Fiber Weaves

Author: WangCaiFen
Tutor: LiuJiaChen
School: Tianjin University
Course:
Keywords: silica fly ash cenosphere porous fiber joining
CLC: TQ174.1
Type: Master's thesis
Year: 2012
Downloads: 74
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Abstract


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.

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CLC: > Industrial Technology > Chemical Industry > Silicate > Ceramic Industry > Basic theory
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