Gel - Foam Preparation of porous alumina insulation materials
|School||Kunming University of Science and Technology|
|Keywords||gel-foaming Porous alumina ceramics insulation gel mechanism thermal conductivit|
Porous ceramics are widely used in thermal insulation materials, filters, catalyst supports, biological materials, fuel cell materials and heat exchangers because of their chemical stability, permeability, mechanical properties, high temperature oxidation and thermal shock, etc.When porous ceramics are used as thermal insulation material, their pores are usually closed pores. But there are many disadvantages in traditional preparation, such as difficultly to control pore size and uneven distribution. In this thesic, alumina porous ceramics were fabricated successfully by gel injection molding and foaming methods, and they were all high closed pore porosity, small aperture and uniformity distribution.Calculating formula of thermal conductivity were derived to analyze their influence factors. Gel-foaming mechanism were studied preliminarily, the gel formation was affected by foaming agent. The row was determined by using to DSC—TG. Properties and structure of sample were impacted by the solid content, foaming agent additive quantity, amount of additives and temperature.and thermal performance was impacted by porosity. The conclusions as follows:According to the analysis of thermal conductivity calculating formula:the higher porosity, the lower testing temperature was, while the smaller aperture of alumina porous ceramics, the less thermal conductivity was, and the better adiabatic effect.Gel formation was influenced by added foaming agent because of oxygen inhibitor effect, and gel time was increased, gel strength was decreased. Gel time was reduced and gel strength was increased to a certain extent, because of appropriate organic monomer, crosslinking agent and initiator.Temperature range of organic decomposition are from 200℃to 500℃, row glue craft as from room temperature to 200℃at 5℃/min, from 200℃～500℃at 3℃/min; and kept warm one hour at 500℃were determined.When the paste solid content was 45%, vesicant addition amount was 1%, sintering fertilizer addition amount was 1%, sintering temperature was 1500℃, the excellent porous alumina ceramic can be prepared, and their porosity was 56% including closed pore porosity 51%, bending strength was 23MPa, distribution uniformity, aperture about 15 120μm.The thermal expansion coefficient of A12O3 porous ceramics were approximately equal to alumina ceramics, and porosity was no effect on expansiveness of A12O3 porous ceramics.