The Preparation And Properties Of Mullite Insulation Material By Gel-casting

With the social progress and the rapid economic development of science and technology, environmental pollution and resources exhaustion get more and more attention, it has become a research focus to decrease the energy consumption of high temperature furnace. So, developing new insulation material with higher mechanical properties and lower thermal conductivity has important significance.Mullite insulation material was fabricated using bauxite, silica fume and polystyrene spheres as starting materials by aqueous gel-casting process; the best solid content, pH value and dispersant dosage were determined according to the research result of the rheology of slurry; the best catalyst and initiator amount were determined according to the gelation mechanism and gelation time; the DSC-TG curves of green bodies and the XRD curves of the samples sintered at different temperatures were analyzed to determine the best sintering technology; the effect of monomer content, bulk density, particle size of pore-forming agent and sintering temperature on the properties and structure of samples were studied; and the influence of porosity, particle size of pore-forming agent and testing temperature on thermal conductivity of the samples were researched by building the calculation model of effective thermal conductivity. The main results were as follows:The slurry had high solid content, good fluidity for casting if pH= 9, dispersant was 0.33 wt% and solid content was 60 vol%; In order to make the operation easy and improve the production efficiency, when the gelation time was set to 0.5 h, the best catalyst and initiator amount was respectively 0.05 wt% and 0.035 wt%.The volatilization temperature of organisms was 285℃～600℃, and the mullization was began at 1000℃, when the temperature was up to 1550℃, mullite became the main crystal phase, the compressive and flexural strength were respectively reached 1.7 MPa and 0.8 MPa(0.4 g/cm3). The samples(sintered at 1550℃) had uniform structure, the crystal developed integrallty, it could be seen that the needle like particles formed a layer of nanometer wall in the matrix. So, the best sintering temperature under laboratory conditions was 1550℃.A strength calculation model was built according to the Budiansky self-coordination theory, and the analysis result showed that decreasing both grains size and porosity was an effective method to improve not only strength but also toughness of material matrix. This was the main reason for the sintered samples to obtain such high strength.By means of the calculation model of effective thermal conductivity, the calculation results showed that the thermal conductivity of the samples was lower when the particle size of pore-forming agent was smaller, porosity was higher or the testing temperature was lower; the experimental results was anastomosed to the calculation results:the thermal conductivity of the samples was as low as 0.16 w·m-1·k-1 when the particle size of pore-forming agent was below than lmm, the porosity was 87% and the testing temperature was 600℃, so the heat insulation effect of samples was excellent.