Wet size measurements for the evaluation of the deagglomeration behaviour of spray-dried alumina powders in suspension

Spray drying produces spherical agglomerates to obtain powders with good flowability. Three alumina powders of different size and/or specific surface area were spray-dried without any binder using either two-fluid or ultrasonic nozzle technology. Compared to the two-fluid nozzle, the ultrasonic one shows a better ability to form agglomerates from a coarse powder and increases the size of the agglomerates when spray drying is carried out under the same operating conditions. The redispersion of spray-dried agglomerates in solution was analysed by applying variable ultrasound durations during size measurement by wet laser diffraction. The initial state of the powder plays a predominant role in relation to the spray drying operating conditions both in terms of size characteristics and redispersion properties. Regardless of the alumina powders and spray drying conditions, a similar trend in deagglomeration behaviour was observed with first-order kinetics and a characteristic kinetic time depending on the initial powder properties.