Flash Sintering of Multiphase Ceramics

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Traditionally, the process to make a components from ceramic powders or clays requires firing (sintering) in a furnace at high temperatures for a long time (many hours or days), a costly process that consumes a large amount of energy. A new process known as "flash sintering" involves running electrical current directly through the piece, to densify the ceramic and produce a usable component in a matter of seconds. Initial studies show that many types of ceramics can be fired this way, but these studies have focused on single phase materials, while practical applications often require multiple phases made of different types of ceramics. This award supports fundamental research to investigate how the electrical and thermal behavior of each component of a multi-phase ceramic responds to flash sintering. This work will lead to new understanding of the flash sintering process, which will allow for lower cost, higher efficiency processing and manufacture of these critical materials. The processing and the strength of these materials will be studied, to ensure that the components made by this new process are comparable to or better than those made by traditional methods. The scientific results of the project are integrated into video modules for outreach to elementary and middle school children, to demonstrate the ways that scientists and engineers are studying methods to save energy while making new materials. Multiple phases are often required for ceramic components in order to improve mechanical strength, enhance thermal conductivity, and increase thermal shock resistance. In contrast to conventional sintering approaches which expend significant energy heating the sample and furnace cavity, a high applied electric field with current flowing through the sample can be used to densify oxide ceramics in air and without applied pressure and at much lower temperatures. This research program will evaluate how the direct application of electric fields can be used to flash sinter multiphase ceramic powder compacts. Multicomponent oxide systems with phases of varying electrical/ionic and thermal conductivity are used to determine the role of these material properties in promoting flash sintering. This information is used to create compositional design parameters to optimize flash sintering via incorporation of minor phases. Mechanical properties of flash sintered multiphase ceramic composites are compared to conventional sintered materials to evaluate any differences, with microstructural characterization by electron microscopy.