The effect of an electric field on the microstructural development of combustion synthesized ceramic composites.

摘要

Self-propagating high-temperature synthesis (SHS) is a process in which an exothermic reaction between precursor components is utilized to obtain a useful material. The objective of the present research was to study the role of the electric field on the microstructural development of several ceramic materials during SHS. This objective was accomplished by choosing several SHS systems that exhibited different reaction characteristics. The systems chosen for this study were TiNi-TiC, TiB₂-TiC and TaC. The choice of reactions for this study was based on two criteria: (a) that the materials be able to react without the application of an electric field. In this way, comparisons between the microstructures of field and no-field reactions can be made; and (b) that the amount of molten phases during the reaction vary amongst systems. In this way, differences in grain growth, if any, can be documented.; As the electric field is increased the following results have been evidenced for the systems in this study:; chj="*" cst="*" cwl="66:31:227" ncols="3" wdm="100" dispwid="7.29in"> row rht="0.18in"> cell chj="l">TiNi/TiC cell chj="l">→ cell chj="l">The TiC particles increase in size with increasing electric field. row rht="0.18in"> cell chj="l"> cell chj="l"> cell> row rht="0.18in"> cell chj="l" cvj="b">TiB₂/TiC cell chj="l">→ cell chj="l">The TiB₂ particles do not change in size with increasing electric field. row rht="0.18in"> cell chj="l"> cell chj="l"> cell> row> cell chj="l">TaC cell chj="l">→ cell chj="l">The TaC particles exhibit a bimodal distribution up to a certain electric field value, at higher values the particles increase in size. ; The growth of the particles can be explained by a simple particle coarsening process in which, as the temperature of the reaction is increased, the diffusion of matter from the small particles to the large particles increases. During this process, there is a driving force to eliminate surface area by the movement of solute atoms from the small particles to the larger ones, that promotes the formation of larger particles. The average size of the particles of the dispersed phase increases during coarsening due to the diffusion through the matrix phase, and their total number decreases.; The TiB₂ particies for the TiB₂/TiC composite did not change in size because there was no change in temperature with increasing electric field.