Reaction Engineering Aspects of Manufacturing of Finite Inorganic Fibers

陶瓷很有价值，因为它们能承受高温和化学侵蚀。它们有一个关键的缺点——它们很脆，在负载下不会变形，因此很容易破裂或断裂。陶瓷结构上的缺陷导致了这种裂纹，因此陶瓷研究的很多努力都是为了开发新的加工技术，使微观缺陷最小化。当材料以细纤维的形式生产时，脆性性能大大提高，因为随着样品尺寸的减小，材料样品中含有足够大的缺陷导致脆性破坏的概率降低。此外，如果一束纤维中的一根纤维断裂，裂缝就不能进一步扩展，而其他纤维则保持完整。复合材料利用纤维吸引人的特性，并通过将其嵌入另一种材料的基体中来消除其缺点。在高温应用中，这些纤维通常嵌入金属基体中，随着耐温性，增强纤维和金属的延展性为复合材料增加了实用性。轻金属——铝、镁和钛——是常见的基质。碳化硅（SiC）纤维具有较高的固有强度、刚度、高温稳定性和优异的抗氧化性，在增强材料中具有广阔的应用前景。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）技术制备SiC、B4C、TiC和TiB纤维的潜力。CVD工艺涉及到通过加热衬底获得固体的信息。通常，一根小直径的基板导线穿过玻璃反应管，并引入合适的气体。基材被电阻加热，使气体发生反应并沉积在加热磨损中。一个关键问题是有效的批量生产连续流系统，扩大实验室连续系统到中试装置，CVD反应的建模和模拟，以及确保CVD过程所需的廉价前体来源。PI将进行实验和建模工作，研究：(1)基材纤维经氢气、蒸汽和硝酸预处理对沉积速率、强度、韧性和粘附性的影响。(2)材料的纯度对纤维机械质量的影响。(3)气体流速对沉积速率的影响。(4)氢硅比和温度对化学计量SiC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TiC生产的C与Ti的配比。详细的动力学研究实验将在间歇式反应器中进行，以确定动力学参数，如反应控制机制，活化能等。这将用于更大规模连续装置的设计。

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.