| Summary: | 碩士 === 中原大學 === 化學工程研究所 === 98 === In this study, atmospheric plasma spray was used for making tubular aluminum oxide membranes. The membranes had porous structure in the surface and high flux for pure water permeation. Moreover, it had 95% rejection rate using average particle size 0.18 μm silica particle.
As results, average pore size of the coating layer increased as substrates with larger pore sizes were utilized. Besides, for the plasma parameters, for example plasma power, spray times, spray distance and powder feed rate, changed for discussing the pure water permeation rate, particle rejection and surface structure of the sprayed membrane. At low plasma power, particles heated insufficiently, caused melt poorly. On the other hand, at high plasma power, the temperature of the plasma plume exceeded the particles boiling point, caused particles evaporated. No matter what kind of secondary gas injected into the plasma, the plasma power was so high that particles were evaporated. The optimum plasma power was 18 kW to 21 kW. As increasing the spray times, the thickness of the coating layer increased and the average pore size decreased. The optimum spray times were 5 times to 7 times in the wet process because the pure water declination rate kept at 20%. Increasing the spray distance resulted in decreasing particle rejection rate and coating efficiency due to the affecting of the ambient atmosphere on in-flight particles. Thus, the optimum spray distance was 7 cm to 10 cm. With the powder feed rate increased, the amount of injecting aluminum oxide particles increased. Plasma could not melt the particles totally, caused poor coating efficiency. The optimum powder feed rate was 1 rpm to 3 rpm.
For the application of the membrane, BSA and yeast mixed protein solution was used for studying the steady state flux and protein transmission rate under different operating pressure and cross-flow velocity. With the pressure increased, steady state flux increased to 0.5 bar. After that, the denseness cake resulted in a decrease of the steady state flux. Moreover, protein transmission rate decreased with the pressure because of the concentration polarization phenomenon. As a result, the best operating pressure was 0.5 bar, which had higher steady state flux and protein transmission rate. On the other hand, with the cross-flow velocity increased, the steady state flux increased because of higher amount of particles swept away from the membrane surface. But the effect on protein transmission rate was not clear. The best cross-flow velocity was determined to be 0.9 m/s, which had higher steady state flux and protein transmission rate.
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