Long Liang

Preparation of Porous Wollastonite Ceramics for Filtration

Wollastonite powder was selected as a starting material with carbonate as pore-forming agent and binder added. The porous ceramics were prepared at different temperature by sintering method. The process includes batching, granulating, pressing molding, drying and sintering. It is discussed the influence of sintering temperature, dosage of binder, dosage of pore-forming agent, pressure of molding and holding time on the performance of porous ceramics. According to the principle of particles stack, the porous wollastonite ceramics for filtration with various diameters, shapes and porosity were fabricated by serial experiments. These products have 1 to 10 microns in pore size, 30.04 to 66.15% in porosity, 2.82 m2/g in specific surface area.

Relation between Porosity and Permeability of Ceramic Membrane Supports

A membrane support provides mechanical strength to a membrane top layer to withstand the stress induced by the pressure difference applied over the entire membrane and must simultaneously have a low resistance to the filtrate flow. Due to their low thermal-expansion coefficient and good thermal-shock resistance as well as excellent mechanical and chemical stability at elevated temperatures, porous SiC ceramics have been widely used as catalyst supports and hot-gas or molten-metal filters. In this work, the influence of the particle size, sintering time and sintering temperature on the porosity and permeability of supports made by dry-pressing of micron-sized SiC powders is investigated. The present work presents a comparison of properties and performance data for samples made with different particle size. The effects of sintering time and temperature were analyzed in view of overall porosity and permeability. From calculations it becomes clear that optimum values exist for the material properties of the support.

Catalyst-Free Synthesis of Mullite Nanosticks

The nonstoichiometric Al-rich single crystal mullite nanosticks were prepared by sol-gel method without any catalysts. The nanosticks are straight and uniform with a width of 300-350nm and length of 3-5m. The nanosticks’ growth direction is along[210] . Detailed structural characterizations suggested that the growth of this novel nonstoichiometric structure was induced by the self-catalyzed process.

Preparation of Porous Ceramic Support with Inorganic Filtration Membrane

The press-sintering process was developed to prepare porous ceramics with carborundum as its basic material and sodium silicate as its binder. Millet, polystyrene pellet, graphite or organic particulates is used as the pore forming agent to adjust pore diameter and porosity. The effect of particle size the starting powders, the sintering temperature and the pore forming agent on properties of the porous ceramic support were studied. The properties of support can be controlled by one or more factors. The microstructure, pore size distribution and porosity of the support were measured. The pore-forming agent distribution in the support body is different when the amount 5% to15%, the efficiency is different too. In the press-sintering process, the starting powders were grinded and controlled at 200um, 250um and 300um in size, then pressed and sintered at 1250 ◦ C,1300 ◦ C and 1350 ◦ C,and pore ceramic supports with pore diameter of 38.0um,39.5um and 53.5um, open pore ratio higher than 40%,fracture strength of 50N could be achieved. The support can be directly used in filtration as an inorganic membrane for gas or liquid, especially be used as gas-solid filtration at high temperature.

Microstructural Evolution and Mechanical Properties in Yb2O3–Fluxed Silicon Nitride Ceramics

Silicon nitride ceramics were fabricated with Yb2O3 as the sintering additive. The effects of the amount of Yb2O3 on the microstructure and the mechanical properties such as the flexural strength and the fracture toughness were investigated. Almost fully densified Si3N4 was obtained when only 4 wt% Yb2O3 was added. Both the flexural strength and the fracture toughness increased steadily with the Yb2O3 content. The transgranular fracture mode was observed in the specimen containing 4 wt% Yb2O3, however, the intergranular fracture mode was observed in the specimen containing 10 wt% Yb2O3.