Preparation And Properties Of Porous Anorthite/ Mullite Composite Ceramics

Porous anorthite/mullite composite ceramics with porosity within the range 38～80%, compressive strength from 9 to 130 MPa and thermal conductivity of 0.27-1.33 W/(m-K) were fabricated by foam-gelcasting method, using CaCO3, SiO2 andα-Al2O3 as raw materials. Effects of mullite content, solid loading, foaming agent on microstructure and properties of samples were researched. The thermal insulation mechanisms and matching rule between thermal conductivity and mechanical property of porous anorthite/mullite composite ceramics were investigated. Mullite content had great influence on component, microstructure and poroperties of porous anorthite/mullite composite ceramics. Samples with designed mullite content of 40 mol% had best combined properties. Dense pore wall and rod-like mullite grain are benefit for compressive strength of porous composite ceramics. As solid loading of slurry increased, the total porosity and pore size of materials declined, while thickness of pore's wall increased. These resulted in the increasing of compressive strength and thermal conductivity. Compared with rosin soap, samples prepared by sodium lauryl sulfate had better combined properties. As concentrantion of sodium lauryl sulfate increased, total porosity increased and pore wall got thinner, which caused thermal conductivity and compressive strength declined. The relationship between thermal conductivity and total porosity of porous anorthite/mullite composite ceramics with designed mullite content of 40mol% coincided with common modle (d=3, k'=0.7). Complex pore structure was the main reason for low thermal conductivity. The relationship between compressive strength and porosity was fitted byσ=1293exp(-5.9P). Based on the two equations, thermal conductivity and compressive strength of porous anorthite/mullite ceramics can be forcasted and designed.