Fabrication On Ceramics With Graded Pores By Centrifugal-gelcasting Technique

Ceramics with graded pores possess the unique advantages of porous ceramics and functional gradient ceramics, which can be applied as thermal-insulating materials, filter materials and bio-materials. These years more and more attentions have been taken on the routes to produce these kind of ceramics, among which centrifugal casting, with many outstanding advantages, is one of the most potential techniques. However, the deficiency of basic research on both the mechanism of centrifuging process and solidification procedure of slurry after centrifuged has been a bottleneck to the further development of this technique.This work develops aiming to find an industrialized centrifugal casting route to produce ceramics with graded pores. The movement patterns of particles in centrifugal field and different effects of various interior and exterior factors on the solidification procedure of concentrated suspension were systematically analyzed. A novel technique that equilibrium concentration suspension was centrifuged to produce ceramics with graded pores was proposed first time. The suspension, with initiator and without catalyst, solidified at elevated temperature after centrifuged, thus the graded distribution profile of pore forming agents were kept in the green body. After drying, burn-out and sintering, the ceramics with graded pores were obtained. From the view of Compress Yield Strength-the intrinsic character of suspension, the effects of solid loading and centrifugal rate on the change of concentration after centrifugation were analyzed. On the basis of movement law of particles in ultra-diluted solution in centrifugal field, the movement pattern of particles in high solid-loading suspension was studied. An equation describing the movement of particles in centrifugal field was obtained. A model of centrifugal process was presented with the help of MATLAB, and some quantity relations between distribution profile of pore forming agents and processing parameters were determined. The results show that both the external factors including centrifugal time and centrifugal rate and the interior factors including density, particle size and concentration of pore forming agents can affect the distribution profile of pores. Different graded distribution profile can be achieved via adjusting parameters above.The route to prepare suspension with equilibrium concentration was studied. It is believed that the electrostatic stabilization dispersant agent is necessary to prepare the suspension suitable to centrifugal casting. The effects of amount of initiator and catalyst and temperature on the solidification procedure were studied. The key factors controllable of solidification procedure of suspension were proposed. Temperature induced polymerization was realized via adjusting the factors above. A novel"centrifugal-gelcasting"technique was invented, by which ceramics with graded pores were fabricated. The results show that there are three types of pores in the ceramics produced by centrifugal-gelcasting technique. The first kind of pores is induced by accumulation of particle. The second kind of pores is formed from the burnt out of pore forming agents. The third kind of pores is interconnecting channel of pore forming agents, which shows the connecting status of the pores. The pore gradients from 60% to about 0% can be achieved via adjusting processing parameters. Comparison of results between the numerical simulation and experiment shows that the two routes are in coincidence.