Fabrication and characterization of porous alumina with denser surface layer by direct foaming

Porous alumina with a denser surface layer is fabricated from an alumina/novolac composite body containing hexamethylenetetramine (HMT) that is used as a blowing agent and a curing agent for the novolac resin. A gas blown from HMT leads to the formation of pores up to submillimeter inside the alumina/novolac composite body. On the other hand, the denser surface layer without large pores is formed by the gas released from the surface during blowing. The blowing condition for the alumina/novolac composite body is examined as a function of heat-treatment temperature in order to investigate the formation of the pore and the surface layer. Porous alumina with the denser surface layer is obtained through de-binding and sintering of the body. This paper also describes the microstructure and mechanical strength of the sintered porous alumina, and advantages of the denser surface layer. (C) 2017 The Ceramic Society of Japan. All rights reserved.