DENSIFICATION MECHANISM OF PREFORM WITH THERMAL GRADIENT CVI
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摘要: 主要是关于热梯度化学气相过程中预制体致密机理的探讨。通过对沉积试验的结果分析发现:在热梯度化学气相沉积的大部分阶段,预制体沉积致密的动力学方程符合低分子填充孔隙的动力学方程,即指数形式致密方程,这说明热梯度法致密预制体的过程从本质上来说,仍是受制于裂解产物在预制体上孔隙填充的这一动力学过程的,与文献中提到的常规均热法沉积致密模式是一致的。另外,从机理分析和实验结果的对比中发现:热梯度化学气相沉积能够较大幅度提高预制体致密速率的原因是存在于沉积过程的温度梯度和浓度梯度可以较大幅度提高沉积分子的定向扩散速率,所以提高了预制体的致密速率。但这一沉积速率的加快并不改变预制体的致密模式。Abstract: On the basis of experimental data, a densification rate mode to describe the woven preform deposited in the thermal gradient CVI process was put forward. It was found to be fit to the index densification equation which was usually used to describe the kinetic process that organic molecules filled in pores of substrate as well as in the ICVI process. Simultaneously, it was also found that the thermal gradient field and the directional flow field of input gas within the deposited preform could largely raise the densification rate of the preform, for they can accelerate the diffusion rate of filled molecules and reduce the surface crust formation of the preform in the thermal gradient CVI process.
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