Reaction, Transport, and Structure Evolution Phenomena in the Densification of Fibrous Substrates

低密度材料具有高强度和 在高度紧张的压力下坚持下来， 温度、压力等在许多高- 温度航空航天和能源应用。 纤维- 增强陶瓷基复合材料是这样的材料， 满足低密度和可接受的要求 韧性，因为纤维增强通常会导致 均匀各向同性材料的强化， 复合材料的基体。 化学气相渗透 (CVI)是一种可用于制造陶瓷基体方法 不破坏纤维或晶须的预制体的复合材料 用于加固。 在这个过程中，气体 反应物或其在气体中的分解产物 围绕纤维预制件的相被输送， 并在整个孔中形成陶瓷基质。 通过化学气相沉积（CVD）预成型。 CVI导致 产品的机械性能非常好，可以生产 形状复杂、体积大的物体，可用于 许多陶瓷-陶瓷复合材料包括氧化物和 非氧化物 除了复合材料制造外，CVI还可以 用于部分致密化由陶瓷或其他材料制成的膜 材料，并以这种方式产生选择性渗透 用于特殊应用的膜（如分离）。 计划进行理论和实验工作， 运输过程相互作用的基本原理（热 和质量），反应和结构演变过程中， 通过CVI致密化多孔预制件。 的沉积 来自甲基三氯硅烷的碳化硅将被用作 在这些研究中， 实验工作将 包括使用多孔和无孔沉积实验 基材、薄膜和孔结构表征以及质量 传输系数测量。 沉积 实验将在热壁反应器中进行， 在重力布置中操作，而结构 将使用显微镜，拉曼， XRD、电子探针、气体吸附和汞 孔隙率测定法 理论工作将涉及发展 模型总结了各种因素的相对重要性， 在CVI期间发生的因素。 除了有助于 阐明CVI的基本原理，本项目将 还可以为任何涉及 在由纤维状结构组成的介质中输送。*//

Low-density materials exhibiting high strength and an ability to hold up under highly strenuous conditions of stress, temperature, pressure, etc. are needed in many high- temperature aerospace and energy applications. Fiber- reinforced ceramic matrix composites are materials that satisfy the requirements of low density and acceptable toughness because fiber reinforcement usually leads to strengthening of the homogeneous isotropic material that forms the matrix of the composite. Chemical vapor infiltration (CVI) is a method that can be used to fabricate ceramic matrix composites without damaging the preform of fibers or whiskers used for reinforcement. During this process the gaseous reactants, or the products of their decomposition in the gas phase that surrounds the fibrous preform, are transported through the pores and form a ceramic matrix throughout the preform by chemical vapor deposition (CVD). CVI leads to products of very good mechanical properties, can produce objects of complex shape and large size, and can be used for many ceramic-ceramic composites including oxides and nonoxides. In addition to composite fabrications, CVI can be used to partially densify membranes made from ceramic or other materials and in this way produce selectively permeable membranes for special applications (such as separations). Theoretical and experimental work is planned to study the fundamentals of the interaction of transport processes (heat and mass), reaction, and structure evolution during densification of porous preforms by CVI. The deposition of silicon carbide from methyltrichlorosilane will be used as the model system in these studies. The experimental work will include deposition experiments using porous and nonporous substrates, film and pore structure characterization, and mass transport coefficient measurements. The deposition experiments will be carried out in a hot-wall reactor, operating in a gravimetric arrangement, while structure characterization will be carried out using microscopy, Raman, XRD, electron microprobe, gas adsorption and mercury porosimetry. Theoretical work will involve the development of models that summarize the relative importance of the various factors that occur during CVI. In addition to contributing to the elucidation of the fundamentals of CVI, this project will also generate information for any application involving transport in media consisting of fibrous structures.***//