ROLE OF CAPILLARY FORCES IN THE REDUCTION OF DUST POLLUTION DURING TRANSPORT AND HANDLING OF POWDERS

摘要

Mixing of dry powders with oil or liquid binder is often done to minimize segregation and dust pollution during handling and transport. The amount of binder required is determined empirically due to inadequate models. Oil as a binder forms capillary bridges between particles. In the present study, theoretical expressions are developed for the calculation of the capillary force at different oil interlayer thickness between particles. Experimental measurements using AFM were conducted to validate the theory for particle/particle and particle/wall interactions. To initiate flow in a cohesive powder, the work of shear stress is primarily utilized to break the oil bridges. The mechanical work done due to shear is compared with the energy of breakage of the oil bridges. Using the capillary energy approach, a theoretical expression is developed for the calculation of the unconfined yield strength of the powder. This expression was validated experimentally by measuring the unconfined yield strength of silica powder in a Schulze' cell with different oil concentrations.