Simulative And Experimental Study On Transport Properties Of Porous Ceramics

Porous ceramic membrane is one of the important materials used in chemical engineering, energy, metallurgy and environmental engineering because of its high mechanical properties, high chemical and thermal stability and good microbial erosion resistance.The quantitative characterization of transport properties of pore structure provides guidance for the preparation and application of porous ceramic membranes. Based on the three-dimensional data of pore structure, a (3-D) numerical simulation of diffusion was used to analyze the pore connectivity and tortuosity. The object of the study includes porous alumina prepared by phase-inversion tape casting method and virtual sample with randomly distributed pores produced by computer.Chapter1briefly describes the research and application status of porous ceramic membrane, including the classification, characterization techniques, preparation technology and3-D computed tomography research of pore structure.Chapter2takes a virtual sample with randomly distributed pores for example, I detailed introduce the method of simulative diffusion. It pointed out that the pores of the porous sample are successively classified according to their accessibility and the effective porosity which contributes to transport is calculated based onthe(fluid) concentration in the pores under steady state. The tortuosity and effective tortuosity are analyzed based on diffusion flux and effective porosity. What’s more, in this chapter the influencing factors including the porosity, thickness to side and sampling size on tortuosity are also analyzed.In Chapter3, porous alumina membranes were prepared by phase-inversion tape casting method and its3-D data of pore structure was obtained by SRCT technology. The transport properties are analyzed by simulative diffusion method, For comparison, transport properties were calculated of a virtual sample with the same size and porosity but with randomly distributed pores.For two samples with the same total porosity of34.7%, simulation results showed that the effective flow-through porosity of the ceramic wafer, prepared by phase-inversion tape casting, is27.98%, while the effective flow-through porosity of the virtual sample is9.96%. These simulations also demonstrated that the total tortuosity, the tortuosity modified by flow-through porosity and the tortuosity modified by effective flow-through porosity of the ceramic wafer are2.01,1.94and1.62, while the three types of tortuosity of the virtual sample are67.28,46.17and19.30,respectively. Obviously, the geometrical connectivity of the ceramic prepared by phase-inversion tape casting has a low tortuosity in the growth direction of the finger-like macropores.The simulation results quantitatively indicated that porous ceramic prepared by phase-inversion tape casting has good transport properties.In Chapter4, porous alumina membrane and asymmetric YSZ-LSM oxygen-permeable membrane were prepared by phase-inversion tape casting method and traditional sacrificial template method using graphite powders as pore forming agent. Gas permeability test demonstrated that the porous ceramic prepared by phase-inversion tape casting method has good transport properties.In Chapter5, summary of the dissertation is presented, and future researches about the pore transport properties of porous ceramic membranes are discussed.