Preparation Of Porous Thermal Insulation Ceramics Using Foaming Gel-casting Process

At present, ceramic fiber is the most widely used thermal insulation material in kilns industry. But it is easy to appear chalking and cracking which has seriously affected its using performance. In response to these problems, a method which combined ceramic foam with gel-casting technology was used to prepare a kind of porous thermal insulation material with uniform internal structure, good insulation properties and excellent thermal shock resistance.Based on the proportion of silica and alumina, a series of ceramic material, such as aluminum silicate and mullite were prepared using the dry-pressing method. Through their water absorption, density, apparent porosity, bending strength and thermal shock resistance test, combined with XRD analysis, two formula groups C1: kaolin 19.8%, bauxite 60.4%, silica powder 19.8%, D1:kaolin 36.8%, bauxite 12.5%, alumina 50.7%, AlF3 0.75%, V2O5 1%, were chosen to prepare porous ceramics products using foaming gel-casting process.The glyceroltripalmitate was used as the foaming agent while PVA and stearic acid glyceryl were used as the foam stabilizer. By studying the mechanism of the synthesis, the palmitic foaming agent was produced and characterized by infrared spectra. Through studying the influence of the concentration on foaming ability and the stability of the froth after adding different kinds and different concentration of foaming agent, the ultimate foaming system composition was determined:the foaming agent 3wt%,10% of the PVA solution 48wt%, stearic acid glyceryl 4wt% and deionized water 45wt%.The effect of the concentration of different dispersants, pH value and solid content on rheological stability of the aluminum silicate and mullite slurry was studied, and the optimal conditions was obtained, the results show that:when the pH was 9, the ammonium polyacrylate could disperse the aluminum silicate slurry well, the best addition of dispersant were 0.25wt%. while the mullite slurry had good dispersion with 0.2wt% of polyacrylic acid adding when pH was 8.5. The largest solid content of the aluminum silicate and mullite slurry for gel-casting can be 62% and 64%.The conditions of the cross-linked system was obtained:the addition of hydrochloric acid and glutaraldehyde were respectively 4wt% and 10wt% of PVA. Combined with scanning electron microscopy (SEM), density and porosity and compressive strength, the influence of different proportion of foam and slurry system on material properties was studied. The results showed that the increase of the proportion of slurry will lead to the increasing of viscosity, pore wall, density and the compressive strength porosity, while the porosity and pore size decreased. The SEM, density, porosity, compressive strength, thermal conductivity, thermal shock resistance and other analysis of the aluminum silicate and the mullite samples were measured. It showed that the samples had uniform distribution pore size, their density were 0.55g/cm3 and 0.59g/cm3, porosity were 75% and 73%, compressive strength were 2357KPa and 2641KPa, thermal shock resistance were 32 times and 37 times, the thermal conductivity were 0.044W/(m2·K) and 0.052W/(m2·K), so they could be used as insulation material.