A Rapid Method for Determination of Changes in Shape of Comminuted Particles Using a Laser Diffractometer

The size distributions of carefully screened √2 size fractions of ground materials were determined using a Microtrac laser diffractometer. The size distributions were fitted to the empirical function P(x) = 1/[1 + (x₅₀/x)^λ] where P(x) is cumulative mass fraction less than Microtrac size, x. The standard deviation of λ for a 50 second test time was approximately 0.5, so that seventeen test times give a mean with an estimated error within ± 0.25 (95% confidence level). Values of λ were 5.44, 4.82, 4.40 for a coal ground under different conditions, indicating statistically different shape distributions; the average value for mica was 2.91 owing to the high aspect ratio of the particles. The ratio of x₅₀ to the geometric mean sieve size was 1.2 for the coal and 0.70 for mica.