Engineering Design and Scale-Up of Combustion Synthesis Reactors

许多放热的非催化性固-固或固-气反应释放出足够的热量，使它们在被点燃后能够自我传播。这些反应，被短期服务的外部能量源局部点燃，可能以一定的速率在整个样品中传播，并发生在分离新鲜物质和反应产物的狭窄区域内。这个过程有许多名称：在苏联，它被称为自传播高温合成（SHS），在美国被称为无机材料燃烧合成（CSIM）。发展这一工艺的目的是学习如何有效地利用反应释放的热量。在实现这一目标的理想情况下，合成反应是热自维持的，产物是非常细的粉末（可以很容易地热压或烧结）或完全致密的形状，不需要后续处理。PI的研究目的是将化学反应工程原理应用于CSIM所使用的反应器的放大（最终目标是将CSIM技术扩大到工业规模）。他在这一领域工作了8年，已经获得了CSIM动态的定性和定量信息。在这个项目中，计划通过在专门设计的显微镜下观察CSIM反应的微观过程。他计划利用这些结果来估计动力学因素，如活化能、频率因素等。由于传热特性随着反应器尺寸的增大而变得更加重要，他计划测量传热参数，同时也考虑到辐射。从动力学和输运机制的实验研究中评估的参数将用于CSIM系统的数值模拟。将开发新一代的非传统模型，该模型将考虑薄膜开裂、熔化、蒸发和烧结的影响。为了了解同时合成和致密化的机理，将对整体体进行热塑性应力分析。数值模拟可以预测合成所需产物的条件，从而设计出最优的实验过程。它们还将有助于可视化导致CSIM系统失去稳定性的条件和相关的非线性现象。将研究以下制度：由钛和碳合成碳化钛（固固反应，适度排出吸收气体）。2. 镁热还原钛和硼氧化物合成二硼化钛（固体-固体与紫色气体排出）。3. 氧化铌铝热法制备铌（固-固相熔炼）。4. 用钛和氮（低压气固）合成氮化钛。5. 由硅和氮合成氮化硅（高压下气固）。6. 高密度碳化钛瓦的制造（同时合成和致密化）。

Many exothermic noncatalytic solid-solid or solid-gas reactions liberate enough heat so that they can, after being ignited, self-propagate. These reactions, being ignited locally by an external energy source with short term service, may propagate throughout the sample at a certain rate and occur in a narrow zone which separates the fresh substances and reaction products. This process has many names: in the USSR it is referred to as self-propagating high temperature synthesis (SHS) and in the US as combustion synthesis of inorganic materials (CSIM). The objective in development of this process is to learn how to effectively utilize the heat release from the reaction. In ideal fulfillment of this objective, the synthesis reaction is thermally self-sustaining and the product is a very fine powder (which can be easily hot pressed or sintered) or a fully dense shape that does not need follow-on processing. The purpose of the PI's research is to apply chemical reaction engineering principles to the scale-up of reactors used for CSIM (the ultimate goal is the scale-up of CSIM technology to industrial scale). He has been working in this area for eight years and has already obtained qualitative and quantitative information on the dynamics of CSIM. In this project the plan is to follow the microscopic progress of CSIM reactions by observing them under a specially designed microscope. He plans to use these results to estimate kinetics factors such as activation energy, frequency factors, etc. Because heat transfer characteristics become more significant as the reactor size increases, he plans to measure heat transfer parameters, taking into account radiation also. The parameters evaluated from experimental investigations of kinetics and transport mechanisms will be utilized in numerical modelling of CSIM systems. New generation non-tradition models will be developed which will take into account the effects of film cracking, melting, evaporation and sintering. In order to understand the mechanism for simultaneous synthesis and densification, a thermoplastic stress analysis in monolithic bodies will be performed. The numerical simulation will help design an optimal experimental course by predicting the conditions under which the desired products can be synthesized. They will also help in visualizing the conditions which lead to loss of stability and the associated non-linear phenomena occurring in the CSIM system. The following systems will be investigated: 1. Synthesis of titanium carbide from titanium and carbon (solid-solid reaction with moderate expulsion absorbed gases). 2. Magnesiothermic reduction of titanium and boric oxides for synthesis of titanium diboride (solid-solid with violet gas expulsion). 3. Aluminothermic preparation of niobium from niobium oxide (solid-solid with melting). 4. Synthesis of titanium nitride from titanium and nitrogen (gas-solid at low pressures). 5. Synthesis of silicon nitride from silicon and nitrogen (gas-solid at high pressures). 6. Manufacture of high density tiles of titanium carbide (simultaneous synthesis and densification).