Mfg. long graphite whiskers e.g. of graphite - by injecting vapour into space in which supersaturation zone is created by temp. gradient

Abstract

Abstract The process is claimed for growing whiskers, e.g. in aluminium oxide, graphite, barium, sapphire, etc., by crystallisation from the vapour phase. It comprises establishing a pptn. zone through which the vapour passes and in which a zone of optimum supersatn. is created by maintaining a temp. gradient so that whiskers are produced in that zone. PPtn. may be promoted by seeding, e.g. by introducing electron-emitting particles such as oxides of barium, strontium or calcium. The particles may be introduced in the form of carbonates. The growing whiskers may themselves emit electrons so that they have a positive charge relative to the vapour. Seeding may be by introducing electrons (electron gun 137, e.g. radio-active cobalt). Used for growing long whiskers of different materials in continuous process by pptn. from vapour. The process does not require accurate control of temp. pressure and supersatn. conditions in a pre-determined area as this zone is automatically created somewhere within the chamber. It permits producing long whiskers in large quantity on an economical scale and allows removal rate to be adapted to the growth rate or vice versa.

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