Investigation of Field Effects in Combustion Synthesis

这是一项通过实验和模拟研究电场对自蔓延高温合成(SHS)反应的影响的研究。它有三个一般推动力：(A)场在通过电迁移(电子风效应)和点缺陷(空位)的产生而增强质量传输中的作用，(B)场对功能材料的结构和性质的影响，以及(C)电点燃SHS反应的模拟。该研究评估了电场对燃烧合成反应过程中的质量传输、产物演化以及结构和微结构发展等过程的影响。它将热(外在)效应与场对这些反应的内在效应(例如，电迁移、空位产生)分开。这项工作的技术影响包括：(A)合成许多未活化的SHS无法制备的材料体系的能力；(B)通过影响SHS产品的组成和微晶尺寸(包括纳米材料)来改变SHS产品的性质和性能；(C)改变(分层)功能梯度材料(FGM)和热障涂层(CBCs)等应用中的界面相互作用；以及(D)一步合成和致密化材料可节省能源。另一个相关的例子是最近的证明，致密的纳米材料可以通过场激活来合成。溴化物影响这是关于电场(电流)在燃烧合成反应中的作用的研究。这项工作既有科学意义，也有实际意义。从基本的观点来看，它的目的是了解场对自传播和其他类型的燃烧反应的热和非热贡献的性质。从实用的角度来看，这项研究可以导致在合成单块、复合和功能梯度材料时使用场作为工艺参数。过去的工作充分证明了电场对这类材料的合成反应有显著的影响。电场已被证明对波的传播动力学和合成机理有显著的影响，决定了产物相的性质及其均匀性和微观结构。通过机械活化和场激活相结合的方法，证明了合成致密纳米结构材料是可行的。

PROJECT SUMMARYThis is an investigation of the effect of electric fields on self-propagating high-temperature synthesis (SHS) reactions using experimental and modeling studies. It has three general thrusts: (a) the role of the field in mass transport enhancement through electromigration (electron wind effect) and point defect (vacancy) generation, (b) the effect of the field on the structure and properties of functional materials, and (c) the modeling of electrically ignited SHS reactions. The research provides an assessment of the effect of the field on such processes as mass transport, product evolution, and structural and microstructural development during combustion synthesis reactions. It separates the thermal (extrinsic) effects from the intrinsic effects (e.g., electromigration, vacancy generation) of the field on these reactions. The technological implications of the work include (a) the ability to synthesize many materials systems which could not be prepared by unactivated SHS, (b) the modification of the nature and properties of SHS products by influencing composition and crystallite size (including nanomaterials), (c) the modification of interfacial interactions in such applications as (layered) functionally graded materials (FGMs) and thermal and chemical barrier coatings (TBCs and CBCs), and (d) the energy savings available from a one-step synthesis and densification of materials. Another relevant example is the recent demonstration that dense nanometric materials can be synthesized by field activation.Broader impactsThis is an investigation of the role of an electric field (current) in combustion synthesis reactions. The work has both scientific and practical implications. From a fundamental point of view, it aims at understanding the nature of both the thermal and non-thermal contributions of a field to self-propagating and other types of combustion reactions. From a practical point of view, the research can lead to the use of a field as a processing parameter in the synthesis of monolithic, composite, and functionally-graded materials. That the field has a marked influence on the synthesis reactions of such materials has been amply demonstrated by past work The field has been shown to have a significant influence on the dynamics of wave propagation and on the mechanism of synthesis, dictating the nature of the product phases and their homogeneity and microstructure. Through the use of combined mechanical and field activation, it has been shown that the synthesis of dense nanostructured materials is feasible.