| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 88 === Kinetics on the direct nitridation of titanium pellet by nitrogen gas was studied. The morphology of the partially reacted titanium pellet was studied and the ground powder of solid sample was monitored by an X-ray diffractometer to determine the concentrations of Ti, TiN0.5 and TiN. The experimental variables are: (1)reaction temperature (1,173-1,473K); (2)sample thickness(1.2x10-3-6.38x10-3m) and (3)reaction time(0-18ks).
Experimental results indicated that the overall reaction was controlled by chemical reaction when reaction temperature was in the range of 1,173- 1,473K and the pellet thickness was under or equal 1.2x10-3m. As the reaction temperature was 1,373K or 1,473K and the pellet thickness was 6.38x10-3m, the overall reaction was controlled by gas pore diffusion. As the reaction temperature was between 1,173K and 1,473K and the pellet was between 3.0x10-3m and 5.5x10-3m as well as reaction temperature was 1,173K or 1,273K and the pellet thickness was 6.38x10-3m, the overall reaction was controlled by both chemical reaction and gas pore diffusion.
A physico-chemical model has been formulated to provide the description of the experimental data. The chemical reaction rate expressions which were used after the model had been employed for interpreting the experimental data. The expression for effective gas diffusivity, which has been left as a fitting parameter for calculation of theoretical prediction was determined as
De=1.373x10-5exp(-13,065.7/RT) m2/s
The correlation between the geometrical factor, g, and the pellet thickness L was found to be
g=1/(1+11.47L)
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