Ultrafast synthesis and sintering of materials in a single running experiment approach by using electric fields
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Processing of materials in the form of ceramics normally involves several steps including calcination at a relatively low temperature for synthesis of the end-product powder and sintering at a high temperature for densification. The work we have been developing introduces a novel approach enabling synthesis plus sintering of materials in a single running experiment by using electric fields, ending with dense ceramics that display grains noticeably finer than in conventional processing. This new paradigm is fully illustrated with experiments conducted on amorphous CaCu3Ti4O12 precursor powder, shown to experience, on heating, crystallization through intermediate phases, followed by chemical reaction leading to synthesis of the end-product powder, plus densification depending on field adjustment. The processing time and furnace temperature are considerably reduced, demonstrating that enhanced synthesis and sintering rates applied under field input. Similar results found in Bi2/3Cu3Ti4O12 are also shown. The different factors that may contribute to this unique scenario, including Joule heating, defect generation, and reduction of free energy for nuclei formation promoted by the applied field, are briefly discussed. Overall, the findings we bring here are exclusive as they show an exploitable way that allows rapid processing of materials with good control over particle and grain coarsening.
Keywordsfield-assisted processing synthesis sintering microstructure dielectric response
This work was partly supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior — Brasil (CAPES) — Finance Code 001, through Grant Nos. BEX 3276/14-7 and BEX 9291/13-0. J.-C. M’Peko devised the work. L. M. Jesus and R. S. Silva were responsible for chemical synthesis. L. M. Jesus conducted the field-assisted processing experiments, plus material characterization (XRD, SEM, and dielectric measurements) under J.-C. M’Peko’s supervision. J.-C. M’Peko wrote the first draft of the manuscript, and all present authors participated in manuscript revision, followed by submission approval. L. M. Jesus and J.-C. M’Peko are profoundly grateful to Prof. R. Raj (at CU Boulder, USA) for introduction to flash sintering experiments and for allowing collection of some data presented here. S. K. Jha and J.-M. Lebrun are also thanked for assistance in some of the conducted flash experiments, as well as B. E. Francisco for help with some of the XRD measurements carried out.
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