Investigation of Field Effects in Combustion Synthesis

这是一个调查的影响电场的自蔓延高温合成（SHS）反应，使用实验和模拟研究。 它有三个主要目标：（a）电场通过电迁移（电子风效应）和点缺陷（空位）的产生在质量输运增强中的作用，（B）电场对功能材料的结构和性能的影响，以及（c）电点火SHS反应的建模。该研究提供了一个评估领域的影响，如质量传输，产品的演变，结构和微观结构的发展过程中燃烧合成反应。 它将热（非本征）效应与本征效应（例如，电迁移、空位产生）。本工作的技术意义包括：（a）合成许多未活化SHS不能制备的材料体系的能力;（B）通过影响组成和晶粒尺寸来改变SHS产物的性质和性能（包括纳米材料），（c）在（层状）功能梯度材料（FGM）等应用中改变界面相互作用以及热和化学屏障涂层（TBC和CBC），以及（d）通过一步合成和材料致密化可节省的能量。另一个相关的例子是最近证明，致密的纳米材料可以通过场激活合成。更广泛的影响这是一个电场（电流）在燃烧合成反应中的作用的调查。 这项工作具有科学和实际意义。 从一个基本的观点来看，它的目的是了解的性质的热和非热贡献的领域的自蔓延和其他类型的燃烧反应。从实用的角度来看，研究可以导致使用的字段作为工艺参数的单片，复合材料和功能梯度材料的合成。电场对这类材料的合成反应有显著的影响，这已被过去的工作充分证明 该领域已被证明有显着的影响波传播的动力学和合成的机制，决定了产品相的性质和它们的均匀性和微观结构。 通过使用组合的机械和场活化，已经表明致密纳米结构材料的合成是可行的。

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.