Reaction Engineering Aspects of Manufacturing of Finite Inorganic Fibers

陶瓷很有价值，因为它们能经受热和化学侵蚀。它们有一个关键的缺点--它们很脆，不会在载荷下变形，因此很容易破裂或断裂。它们结构上的缺陷导致了这种裂纹，因此陶瓷研究的大量努力旨在开发新的加工技术，将微观缺陷降至最低。当材料以细纤维的形式生产时，脆性性能大大改善，因为随着样品尺寸的减小，材料样品中包含足以导致脆性失效的缺陷的概率降低。此外，如果束中的一根纤维发生故障，则裂纹不能进一步扩展，而其他纤维保持完好。复合材料利用纤维的诱人特性，并通过将它们嵌入另一种材料的基质中来消除它们的缺点。对于高温应用，这些纤维通常与耐温、增强纤维和金属的延展性一起嵌入到金属基体中，从而增加了复合材料的实用性。轻金属--铝、镁和钛--是常见的基质。碳化硅纤维具有高的固有强度、刚性、高温稳定性和良好的抗氧化性，是一种很有前途的增强材料。碳化硼(B4C)、二硼化钛(TiB2)、碳化钛(TiC)和溴化钛(TiB)纤维也具有利用化学气相沉积(CVD)法制备碳化硅、B4C、TiC和TiB纤维的潜力。CVD过程涉及通过加热的衬底获得固体的信息。通常，一根小直径的衬底导线穿过玻璃反应管，并引入合适的气体。衬底被电阻加热，导致气体在加热磨损时发生反应并沉积。高效生产批量到连续流动系统的一个关键问题是，将实验室连续系统扩大到中试工厂单元，对CVD反应进行建模和模拟，并确保CVD过程所需的廉价前体来源。PI将进行实验和建模工作，以研究：(1)用氢气、水蒸气和硝酸对基纤维进行前处理对沉积速度、强度、韧性和附着力的影响。(2)原料纯度对纤维机械质量的影响。(3)气体流量对沉积速率的影响。(4)氢硅烷比和温度对化学计量比碳化硅形成的影响。(5)BC13、碳氢化合物(CH4/CC14)和H2浓度对B4C沉积的影响。(6)用于生产TiC的C/Ti比。详细的动力学研究实验将在间歇反应器中进行，以确定反应控制制度、活化能等动力学参数。这将用于更大规模的连续装置的设计。

Ceramics are valuable because they can withstand heat and chemical attack. They have a critical drawback--they are brittle, do not deform under load and therefore crack or break easily. Flaws in their structure cause this cracking, therefore much effort in ceramic research is aimed at developing new processing techniques that minimize microscopic flaws. When the material is produced in the form of fine fibers, the brittleness properties are greatly improved because the probability that a sample of material will contain a flaw large enough to cause brittle failure deceases as the sample size is reduced. Also, if one fiber in a bundle fails, the crack cannot propagate further and the other fibers remain intact. Composites harness the fiber's attractive properties and eliminate their drawbacks by imbedding them in the matrix of another material. For use in high temperature applications, these fibers are often imbedded in metal matrices along with the temperature resistance, reinforcing fiber and the metal's ductility lends added usefulness to the composite. Light metals--aluminum, magnesium and titanium--are common matrices. Silicon carbide (SiC) fibers are promising for reinforcing because of their high intrinsic strength, stiffness, high temperature stability, and excellent oxidation resistance. Boron carbide (B4C), titanium-diboride (TiB2), titanium carbide (TiC), and titanium bromide (TiB) fibers also have potential to use chemical vapor deposition (CVD) to manufacture SiC, B4C, TiC and TiB fibers. The CVD process involves the information of a solid by a heated substrate. Typically, a small-diameter substrate wire is run through a glass reaction tube, and suitable gases are introduced. The substrate is resistance heated causing the gas to react and deposit in the heating wore. A key problem of efficient manufacturing batch to continuous flow systems, scale-up of the laboratory continuous system to a pilot plant unit, modeling and simulation of the CVD reactions and securing cheap sources of precursors necessary for the CVD process. The PI will do both experimental and modeling work to study the effect of: (1) Pretreatment of the substrate fiber by hydrogen, steam and nitric acid on deposition rate, strength, toughness and adhesivity. (2) The purity of the material on the mechanical quality of the fiber. (3) Gas flow rate on the rate of deposition. (4) Hydrogen to silane ratio and temperature on the formation of stoichiometric SiC. (5) BC13, hydrocarbon (CH4/CC14) and H2 concentrations on the deposition of B4C. (6) The ratio of C to Ti fed for production of TiC. Detailed kinetic study experiments will be carried out in a batch reactor to determine kinetic parameters such as reaction control regimes, activation energy, etc. This will be used in the design of the larger scale continuous units.