Preparation And Properties Of Porous Acicular Mullite Ceramics

Due to high strength, excellent high temperature performance and chemical stability, acicular mullite has been widely used as a reinforcing agent in the preparation of composite materials. Using as a substrate material in porous ceramics, acicular mullite may bring high porosity and high strength at same time. In this paper, porous mullite ceramics have been fabricated by foam-gel casting method and pressureless sintering using α-Al2O3 and SiO2 powders as raw material. XRD and SEM were used to analyze the phase composition and microstructure of porous mullite ceramics respectively. Porosity, bulk density, compressive strength and thermal conductivity were tested too.Effects of the variety and content of sintering additive, solid volume content in the slurry and foaming agent concentration on microstructure and properties of samples were researched. Matching rule between thermal conductivity and mechanical property of porous acicular mullite ceramics was preliminarily investigated through comprehensive analysis of all the experimental data. The variety and content of sintering additive have some great impact on the microstructure of porous mullite ceramics. Porous acicular mullite ceramics has not been obtained by adding 1-4wt.% La2O3. Porous mullite ceramics with partly acicular mullite grains have been prepare with the addition of 2wt.% Mnd. And porous mullite ceramics with whole acicular mullite grains have been fabricatedwith the addition of 10wt.%or 12wt.%AlF3·3H2O respectively.As solid volume content of slurry increased, the porosity and pore size of materials declined, while thickness of sphere pore’s wall increased, which resulted in the increasing of compressive strength and thermal conductivity. As the concentration of foaming agent increased, the porosity increased and pore wall got thinner, which resulted in the decreasing of compressive strength and thermal conductivity. Through adjusting sintering temperature, solid loading and foaming agent, porosity, compressive strength and thermal conductivity of porous mullite ceramics with partly acicular mullite grainswere in the range of 58.22±0.95～86.03±0.10%,3.13±0.16～14.25±5.46 MPa and of 0.18±0.02～0.95±0.08 W/(m-K). Using 12 wt.%AlF3·3H2O as sintering add, the porosity, compressive strength and thermal conductivity of porous ceramics with whole acicular mullite grains were in the range of 73.1±0.9-87.3±0.4%, 1.29±0.47～7.58±2.19 MPa and 0.20±0.04-0.85±0.05 W/(m·K)respectivel y.Within the scope of the experimental data,the relationship between thermal conductivity and porosity of porous mullite ceramics through a Mn02 content of 2 wt.％ can be coincided with common model and the relationship between compressive strength and porosity was fitted by σ=250×(1-P).2.16.The relationship between thermal conductivity and porosity of porous mullite ceram.ics through a AlF3·3H20 content of 12 wt.%Can be coincided with and the relationship between compressive strength and porosity was fitted by σ=72×(1-P)1.74.