Electron microscopy and diffraction of aluminium oxide whiskers

Abstract

Whiskers of α-Al₂O₃ have been grown by the condensation and oxidation of aluminium on an alumina substrate, and examined by transmission electron microscopy and diffraction. Unbroken whiskers invariably terminate in a small globule of aluminium and have a ‘drumstick’ form. The most perfect whiskers are ribbons with their principal surfaces parallel to the (0001) planes; the majority of these have a 〈1120〉 growth direction. With intense heating in the electron beam, such ribbons can be thermally etch-pitted. Many drumsticks are tubular rather than ribbon-like and drumsticks containing axial dislocations have also been seen. The effect of intense heating on these whiskers has been investigated. Occasionally, the aluminium globules melt and react with the carbon support film in the microscope to give crystalline Al₄C₃. Alternatively, a globule may explode to form many small globules that immediately develop stems; thus, new whiskers are formed in the microscope. The relevance of these observations to proposed mechanisms for the growth of drumstick whiskers is discussed.