Particle size analysis of sub-micrometer WC powders

摘要

In spite of its title, the emphasis of this paper was very much on powders of less than 0.5 urn grain size. Schwenke's theme was that all methods of measuring ultrafine powders are very much at the limit of their capabilities. Whilst some producers speak blithely of grain sizes of 0.2 urn or even less, they often choose the measuring method to give the lowest apparent value and may have little or no idea of true accuracy or reprodu-cibility. The author stated firmly--and a little surprisingly--that Osram Sylvania had never observed any tungsten carbide particles finer than 0.24 urn. One trouble with measurements of very fine particles is that they are not based on direct measurement. They measure some other property which in principle depends on grain size but should be calibrated against an absolute standard by some other method. Unfortunately no absolute standards exist and each alternative method has its own problems.