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Journal of Materials Science

, Volume 5, Issue 9, pp 719–730 | Cite as

Temperature induced structural changes in sapphire whiskers

  • W. Bonfield
  • A. Markham
Papers

Abstract

The effect of high temperature annealing (800 to 1500° C) on the structure of individual sapphire whiskers has been determined with an electron microscope technique. Two types of whiskers, grown by a similar process, but containing different levels of silicon impurity (6 and 0.2% respectively) were studied. Discrete second phase particles were observed within and at the surface of many of the whiskers with 6% silicon. After heat treatments at 1000 to 1300° C in high purity argon, these particles coarsened and coalesced in the larger whiskers and spheroidised on the surface of the smaller whiskers. In addition, a dispersion of fine particles was formed in some whiskers free from “grown in” particles.

Some melting of the second phase occurred between 1000 and 1400° C, with an attendant disintegration of the whiskers. Although the sapphire whiskers with 0.2 silicon % did not contain second particles, some breakdown of the whiskers also occurred at about 1300° C, a process which is attributed to the presence, and melting, of a surface coating.

Surface pits were formed at temperatures above 1000° C, and became extensive at 1400 to 1500° C, particularly in the 6% silicon whiskers. It is considered that the surface pitting is a consequence of impurity diffusion and internal stress in the sapphire whiskers.

Keywords

Silicon Heat Treatment Sapphire Fine Particle Surface Coating 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Chapman and Hall Ltd. 1970

Authors and Affiliations

  • W. Bonfield
    • 1
  • A. Markham
    • 1
  1. 1.Department of MaterialsQueen Mary CollegeLondon

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