Effect of grinding and water vapour on the particle size of kaolinite and pyrophyllite

The increase in specific surface of kaolinite (K) and pyrophyllite (P) indu ced by dry grinding in an oscillator), mill. proceeded during storage in wa ter vapour. The average particle thickness, delta. changed from 42 nm (K) a nd 66 nm (P) in the original materials to 12 nm (Kf and 20 nm (P) after wat er sorption (20 days at relative humidity RH = 1.01 at room temperature and pressure) and to similar values of 13 nm (K) and 16 nm (P) after grinding for 10 min tin agreement with some published data). The action of water mol ecules on ground clays (at the conditions indicated) resulted in a further decrease in a. In pyrophyllite, prolonged grinding (30 min) and prolonged a ction of water molecules (36 days) caused a particle collapse. After pre-st oring at RH = 0.5 the successive decrease in delta at RH = 1.0 was smaller.