Porous Materials With Alligned Open Pores
Making
materials porous leads them to interesting material properties as well
as lower specific weights. If the pores are open to air, specific area
is greatly increased resulting in additional material functions such as
capabiliteis of a high heat exchange rate and sound absorption,
a high reaction rate, and so on. Furthermore, the allignment of
elongated pores in one direction gives special characteristics to the
material, that is, nondegraded specific mechanical strength and
transport coefficients in the direction of pore elongation. We are
going to apply the Lotus-type porous materials, which have been
developed by Prof. H. Nakajima and co-workers at Osaka University, to
various fields.
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Temperature denpendent solubilities of gas species in materials
The solubilities of gas species such
as hydrogen and nitrogen discontinuously decreasess in solidification
of various materials.
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Fabrication principle
The decrease in the gas
solubility results in the formation of pores in solidification (more
strictly, simaltaneous formation of solid and gas phases). Controlling
the formation of pores, one can fabricate porous materials. Directional
solidification leads to the allignment of elongated pores.
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Fabrication techniques
The left figure shows one
of fabrication techniques of the lotus-type porous materials. This
technique enables us to prepare rod-shaped porous materials. A rod
sample is unidirectionally solidified using the zone melting technique.
Pores grow in the direction of solidification, which is almost parallel
to the rod.
In addition to the zone melting technique, continuous casting and
thermal decomposition technique, which does not require the atmosphere
of the gas species which is dissolved in the liquid of the sample
material, have been developed.
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References
1. H. Nakajima, Fabrication,
properties, and applications of porous metals with directional pores,
Proc. Jpn. Acad. Ser., 86B (2010), 864. (a review article)
2. T. Ikeda, T. Aoki, H. Nakajima, Fabrication of lotus-type porous
stainless steel by continuous zone melting technique and mechanical
property, Metall. Mater. Trans., 36A (2005), 77. (a technical paper on the zone melting technique)
