| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 87 === In this research, low-pressure injection molding (IM) process was used to prepare PZT samples which contains either one commercial or two developed powders. The effects of IM parameters, including IM pressure and mold temperature on the feedstocks were investigated. The IM samples were analyzed by the measurement of shrinkage dimensions, mass loss variation, density, microstructure, and piezoelectric constant after sintering. Besides, the measurements of torque and viscosity were performed to determine the appropriate parameters of injection molding, while a thermogravimetric analysis was used to investigate the debinding kinetics.
The results of wetting angle of various plastics on PZT plate were reported. In this study, LDPE, PW, and SA in a ratio of 5:90:5 in mass% were mixed to prepare feedstocks. The results show that an optimum kneading condition and minimal evaporation of SA can be achieved if the addition of the SA is performed in the final stage of the kneading and at the temperatures greater than 80℃. The kneading steps enable one to prepare well-mixed feedstocks with lower viscosity.
The optimized conditions of the low pressure IM were determined. The injection pressure is 4 atm, the IM time for holding pressure is 10 s, the mold temperature is 40℃, and the feedstock is injection-molded at 120℃.
The optimized sintering temperature of the PZT samples prepared by IM is 1200℃ for 1 h. The bulk density of the PZT body is 7.35±0.05 g/cm3. When the sintering time increases from 1 h to 4 h, the density increases to 7.47 ±0.13 g/cm3. However, the variation of the density increases. Thus, increasing sintering time is not a good choice to obtain a sintered body with higher density. The density of die-pressed samples is 7.49 ±0.02 g/cm3。
The activation energy and the order of reaction kinetics were calculated by using Friedman’s and Ozawa’s kinetic equations. The results show that the oxide powders play a role, like catalyst, which accelerates the decomposition rate of the plastics in feedstocks. The kinetic analysis shows that the addition of LDPE to SA/PW plastics increases the activation energy of the decomposition. However, the addition of PbO, ZrO2, TiO2, and PZT powders decreases the energy. From the analysis of the reaction rate and the residue of decomposing feedstocks, there are two different reaction regions where the amount of the residue, 15%, is a turning point. As the residue is higher 15 %, the reaction order is nearly or less than unity, implying the diffusion control is the control mechanism. When the residue is less than 15%, the reaction is chemical reaction controlled for the plastics. It is because the probability of the decomposition by collision decreases when the residue is in a small quantity. The results and relationship of the reaction rate and residue helps us to design the debinding parameters of thermal decomposition process.
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