Fabrication and characterization of porous alumina with a surface layer composed of alumina platelet by direct-foaming method

Porous alumina with the surface layer was fabricated from an alumina platelet / novolac-HexaMethyleneTetramine (HMT) composite. HMT was used as a blowing agent as well as a curing one for the novolac binder. When the alumina platelet / novolac composite was heated with covering its surface with fi lter papers, a porous structure formed inside the composite due to blowing from HMT. On the other hand, the blowing gas near the surface was evolved outward through the fi lter paper, which resulted in the formation of the surface layer composed of the aligned alumina platelets. E ff ect of the surface layer on the mechanical strength was examined by three-point bending measurement. The bending strength of the obtained porous alumina increased by 94 % compared to the porous alumina without the surface layer.

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