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An industrial survey of particle size methods currently in use and a correlation study on a group of tungsten metal powders were conducted to establish the present state of affairs in the refractory metals industry. Results indicate a wide diversity of techniques and no correlation between measurements, and confirm the need for standardization in the measurement of the particle size distribution of refractory metal powders. The turbidimetric sedimentation technique is concluded to be most suitable for these powders.
The theories of turbidimetry, sedimentation, and turbidimetric sedimentation are thoroughly reviewed and the sources of error inherent in each are analyzed. The author concludes that the errors arising in the turbidimetric sedimentation analysis of refractory metal powders tend to compensate each other, giving a measured distribution which differs from the true value only by an overestimation of the per cent weight in the 1 to 8 μ size range.
The causes of poor correlation between measurements obtained on refractory metal powders by different laboratories are discussed. Various methods for deagglomeration and suitable sedimentation media are described.
Physicist, Metallurgical Research Laboratory, Sylvania Electric Products, Inc., Towanda, Pa.