Investigation of Field Effects in Combustion Synthesis

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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.