FILTRATION OF REAL-WORLD PARTICLES IN LIQUIDS BY MICROPOROUS MEMBRANEFILTERS

The filtration effect of irregular-shaped, real-world particles, such as silicon, alumina, and silicon nitride particles, has been experimen tally investigated using 0.1, 0.22, and 0.45-mu m-rated polyvinylidenc e difluoride (PVDF) and 0.2-mu m polytetrafluoroethylene (PTFE) membra ne filters. Particle retention tests were performed by measuring parti cle concentrations upstream and downstream of the test filter using an automatic liquid-borne laser particle counter (LPC). The test apparat us for the particle retention studies used a pump-driven water recircu lating system. Zeta potential values play an important role in liquid filtration. The higher-charged particles, such as PSL and silicon, deg raded filter efficiency during filter loading, while the lower-charged alumina and silicon nitride particles achieved complete retention ove r the entire range of test particle size, i.e., from 0.1 mu m to 0.4 m u m. Experimental results showed that if the filter and contaminant pa rticles had a high charge of similar polarity, the electric double lay ers would interact in a repulsive manner, making the adsorptive deposi tion of the particle unfavorable and leaving sieving as the active fil tration mechanism. If the contaminants had a low charge, they coagulat ed due to colloidal instability and were easily retained on the pore s urfaces.