IMPACT ATTRITION OF SODIUM-CARBONATE MONOHYDRATE CRYSTALS

The mechanism of impact attrition of sodium carbonate monohydrate crystals has been elucidated by recording the impact event using a high-speed image converter camera. It was -found that the attrition mechanism depended on the impact velocity and on particle orientation on impact. For impacts on sharp corners and edges, particle damage appeared to result from semi-brittle failure at all velocities tested. For impacts on crystal faces, however, a threshold velocity was identified, above which brittle fracture occurred, and below which no visible damage was detected. The impact attrition rate was measured as a function of number of impacts and particle size for an impact velocity below the threshold identified. The attrition rates were initially high, but as the number of impact cycles increased the rate decreased to a constant value. These steady-state attrition rates are shown to be directly proportional to the original particle size. This trend supports a semi-theoretical model for the prediction of attrition rates using fracture mechanics.