Study On The Novel Freeze Casting Technique And Its Applications Of Preparation For Porous Ceramics

Porous ceramic is a new type of inorganic functional materials with more Pores. It has many good characteristics such as high intensity, enduring high temperature, good temperature resistant, large surface and so on. It can be used as biomaterials, catalyst carrier materials, filtering materials and heat exchanger materials. Freeze-casting as a oriented and aligned ceramic forming process has been developed in recent years since it fabricates porous ceramics which have the advantages of high porosity, controllable pore direction and size, mechanical properties in a direction parallel to the pores. Therefore, its favours fabrication of porous ceramics and has drawn much attention of researchers.In this paper, the oriented and aligned porous alumina ceramic which has definite porosity and flexural strength had been prepared by alumina powders as aggregate, camphene as liquid medium and forming by a novel freeze-casting technique as well as sintering at1550～1650℃. The freeze-casting process of alumina ceramic/camphene slurry and the structure and properties of sintered body were analyzed by the NDJ-ltype rotating viscometer, scanning electronic microscope, apparent porosity and bulk density tester. The main results were as foll wing:The results of slurry rheology tests showed that the slurry viscosity increased with increasing content of solid loading. According to the result of the rheology tests, it can be determined that when the solid loading content was10～45vol.%, dispersant Texaphor963was3wt.%, the ceramic slurry with equality and stabilization, excellent rheological slurry and suitable to pour slurry can be obtained. The research on forming method indicated that the green ceramic after forming need to be dried more than20hours under ambient atmosphere was0.01～0.05m/s, then it can be sintered. It can be determined that the sintering temperature of green ceramic was1600℃The research on the effect of solid loading、sintering temperature on the properties of porous alumina ceramic and the pore direction and fracture microstructure of porous alumina ceramics. The results show that high-porosity alumina ceramics with oriented and aligned pores were prepared by freezing alumina/camphene slurries and porosity is in14-78%with solid loading ranging from10vol.%to50vol.%, followed by freeze-drying in air and fired at1600℃. All of the samples had the moderate pore size in10-50μm and the compressive strength is more than15.6Mpa with10vol.%solid loading, the linear equation of solid loading and porosity is obtained. the solid loading of the slurry and sintering temperature have remarkable effects on porosity, compressive strength and shrinkage of porous alumina ceramics, freezing temperature and sintering temperature have greater influence on pore size distribution and fracture microstructure of porous alumina ceramics. The porous ceramics with directional pore channels structure can be prepared by a camphene-based freeze-casting technique, by adjusting process parameters to control the pore structure and properties of porous ceramics, in order to meet different needs of the user.