Dielectric properties of Lanxide™ Al2O3/Al composites
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The dielectric properties of unreinforced Lanxide™ Al2O3/Al composites have been investigated over a wide range of temperatures and frequencies. These composites were formed by the directed oxidation of suitably doped aluminium-based alloy melts, with no filler or reinforcing material in the reaction path. As-grown composite materials were good electrical conductors in all directions owing to the presence of an interconnected metallic constituent. As the metallic phases were partially removed (in favour of porosity) by continuing the oxidation reaction to completion, the composites remained electrically conducting parallel to, and became insulating transverse to, the original growth direction of the composite. This anisotropy apparently was caused by different connectivity of the metal phase between the two directions. Thermal treatments at 1600°C in argon resulted in volatilization of the residual metal in the composite, thus further increasing the porosity. As the metal content was decreased, the composites changed from conducting to insulating along the growth direction. When the metallic phase was removed completely, the porous alumina ceramic maintained anisotropic dielectric properties, due to c-axis alignment of the alumina (corundum) phase along the growth direction. The dielectric constants were 8.0 and 6.4, respectively, parallel and perpendicular to the c-axis aligned directions of the porous alumina ceramic. A dielectric relaxation phenomenon was observed in some samples of both as-grown and thermally treated material, and was attributed to an unidentified impurity effect.
KeywordsDielectric Constant Dielectric Property Corundum Growth Direction Dielectric Relaxation
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- 4.J. C. Maxwell, “Treatise on Electricity and Magnetism”, Vol. 1, 3rd Edn (Oxford University Press, London, 1904).Google Scholar
- 6.R. W. Sillars, J. Inst. Electr. Eng. 80 (1937) 378.Google Scholar
- 7.A. S. Bhalla, unpublished data (1985).Google Scholar
- 8.W. D. Kingery, H. K. Bowen and D. R. Uhlmann, “Introduction to Ceramics”, 2nd Edn (Wiley, New York, 1976) p. 933.Google Scholar
- 9.K. Lichtenecker and K. Rother, Physi. Z. 32 (1931) 255.Google Scholar