Structures And Properties Of Ceramic Fabrics Preparaed By A Template Method

Ceramic fabrics have been widely used in many fields such as insulating materials, battery separators and photocatalysts due to their excellent properties such as high-temperature resistance, low heat-conductivity, chemical stability and photo-electron property, etc. But it is very difficult for the traditional process to prepare the high performance ceramic fabrics such as high melting point ceramic fabrics （like zirconia fabirc） and high purity ceramic fabrics （like alumina fabirc）. In this paper, based on the process for preparation of carbon fiber, we used organic fabric as the template to prepare the ceramic fabric. The pre-swelling process of viscose fibers and diffusion behavior of metal ion in the viscose fiber have been investigated. The effects of three key techniques, such as template design、impregnation and heat-treatment, on the structures and properties of the ceramic fabircs have also been studied. Based on above research, the zirconia fabric titania fabric and high purity alumina fabric have been prepared by such method and the relationships between their structures and properties, have been discussed. The main conclusions were summarized as follow:（1） The impregnated metal ions in the viscose fibers increased when the viscose fibers were swelled in water or alkaline solution in advance.（2） The process of impregnation displayed a physical absorption behavior. The absorption is an isothermal diffusing process, by which the metal ions moved from the solution to the viscose fibers. Hill Formula can be applied to describe these processes.（3） The thickness, surface density and mechanical property of ceramic products were mainly determined by the factors including the configuration of template, the concentration of impregnating solution, impregnating temperature and sintering process, which indicates we can obtain the desired products by adjusting the process conditions. The zirconia, titania and alumina fabric were prepared by the above mentioned process.（4） The zirconia fabric was very soft and showed the similar shape to the templates. The crystal structure of zirconia was tetragonal, and the crystal size was about 30nm. The other properties are listed as follow:thickness is 0.291mm; break force is 213g/1.5cm width（landscape orientation）, 320g/1.5cm width （portrait）; surface density is 217 g/m2; alkali absorption rate is 223%. The zirconia fabric prepared under above conditions is fully satisfied the demands of Ni-H2 batteries.（5） Model of fiber bundle （MFB） simulation technique was employed to predict the distribution of fibers in the bundle of zirconia fabric and the "Liquid flow in the shaped fiber bundle" （LFSFB） model was firstly employed to predict the alkaline absorption and sucking rate of electrolytes in zirconia fabric. The results showed that the proposed model was rational to describe the process of electrolyte retention and sucking rate in zirconia fabrics.（6） The prepared titania fabrics exhibited the similar configuration to the template, and embodied about 3.3wt%rutile phase when the sample obtained by sintering at 700℃. When the sintering temperature was 500℃, the sample exhibited highest photo-catalytic efficiency among the samples. This is attributed to the high degree of crystallinity and small crystal size. The products prepared using the template with more shaped fibers showed higher photo-catalytic efficiency due to their larger surface area. Zr was an effective doping element to improve the mechanical performance and photo-catalytic property of ceramic materials. The 18wt% Zr-doped TiO₂ fabric exhibited the highest efficiency of degrading methylene blue after 8 hours, and 30wt% Zr-doped TiO₂ fabric showed the lowest efficiency among the samples. This is attributed to the smaller crystal size for the samples with the content of Zr from 3wt% to 18wt%. In this case, Zr-ion acted as the trap to capture the photo-induced carriers and prevented the electron-hole recombination. In the 30wt% Zr-doped sample, ZrO₂ could be the electron-hole recombination center, thus decreased the photoactive sites. The mechanical property of 18wt% Zr-doped TiO₂ fabrics increased 230% compared to the bare samples. The 18wt% Zr-doped TiO₂ fabrics showed the most potential photo-catalysts.（7） The high purity alumina fabric was also successfully prepared by the template method. The purity of such alumina fabric is more than 99%, which could never be produced by the traditional melting process. The highest working temperature was up to 1500℃. Zirconia was doped to improve the mechanical property of alumina fabric. The flexibility and intensity of alumina fabric were improved by doping 2wt% zirconia.