The porous alumina tube with pore gradient along the radial direction was successfully fabricated, where PMMA particles were used as pore former agent. The specimen was expected as a filter subjected to high temperatures. Alumina and PMMA particle were mixed with water to form aqueous slurry, compacted using centrifugal molding technique. The green body was dried in partial vacuum atmosphere, calcinated at 273 K to remove the organic component, sintered at 1623 K to obtain sintered porous a-alumina tubes. The control on the pore gradient of porous tubes was attempted by two ways; lamination and continuous methods. The microstructure observation showed that the inner part of the tubes had higher porosity than the outer part irrespective of the method used. Porous alumina tubes were characterized by microstructure observation, porosity and air permeability.
The binary pores of 10µm and submicron in diameter were visible, which were formed by the burning-out PMMA particles and lower sintering temperature, respectively. The influence of PMMA amount on the pore morphology of the tubes was investigated. Fracture strength was carried out by the O-ring diametral compression testing. An analytical formula subject to the diametral testing was
introduced with considering the porosity gradient. The correlations between the fracture strength and pore gradient were investigated, where a reduction in fracture strength was observed with the increase in laminated layers, and minimum strength was found in continuous porous tubes.
Fabrication and characterization of alumina tube by thermal spray forming
