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Formation Mechanism of Porous Alumina With Oriented Cylindrical Pores Fabricated by Unidirectional Solidification

Authors

  • Shunkichi Ueno,

    Corresponding author
    1. The Institute of Scientific and Industrial Research, Osaka University, Ibaraki 567-0047, Japan
      †Author to whom correspondence should be addressed. e-mail: ueno23@sanken.osaka-u.ac.jp
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    • *Member, American Ceramics Society.

  • Li M. Lin,

    1. The Institute of Scientific and Industrial Research, Osaka University, Ibaraki 567-0047, Japan
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  • Hideo Nakajima

    1. The Institute of Scientific and Industrial Research, Osaka University, Ibaraki 567-0047, Japan
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  • J. Blendell—contributing editor

  • This work was supported by a Grant-in-Aid for Scientific Research (C) (No. 18560655) by the Japan Society for the Promotion of Science.

†Author to whom correspondence should be addressed. e-mail: ueno23@sanken.osaka-u.ac.jp

Abstract

Porous alumina whose pores were aligned in one direction was fabricated by the unidirectional solidification method under a pressurized hydrogen atmosphere. The porous structure is formed at the solid–liquid interface during solidification due to a hydrogen solubility gap at the melting point. The hydrogen gas is dissolved into molten alumina according to Sieverts' law and insoluble gas that corresponds to the amount of solubility gap evolves from the solid phase at the solid–liquid interface during the unidirectional solidification to form the pores. The porosity and pore size of the solidified samples decreased with increasing total pressure where the environmental gas consisted of pure hydrogen or hydrogen–argon mixed gases. There is a reverse proportion relation between the pore diameter and the total pressure according to Boyle's law.

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