Cold sintering with dimethyl sulfoxide solutions for metal oxides
Cold sintering of ZnO and MnO with dimethyl sulfoxide (DMSO)-based solutions is demonstrated. For ZnO ceramics, density values approach 99% theoretical when cold-sintered at 180 °C with DMSO-HOAc and DMSO-Zn(OAc)2 solutions. MnO densified with aqueous HOAc solutions produces ceramics of 84% theoretical density that contain significant amounts of Mn(OH)2 secondary phases. In comparison, using DMSO-HOAc solutions produces density values of 94% theoretical at 250 °C with trace quantities of Mn3O4, verified via X-ray diffraction. Scanning electron microscope analysis of sample fracture surfaces containing Mn3O4 reveals numerous crystallites smaller than 100 nm that nucleate on or between the considerably larger starting MnO grains. With increasing temperature, these precipitates appear to coalesce and fill the porosity that remains after initial compaction. These results identify an avenue to cold sinter metal oxides that, in the presence of aqueous media, favor hydroxide formation which inhibits further densification.
This work was performed in part at the Analytical Instrumentation Facility (AIF) at North Carolina State University, which is supported by the State of North Carolina and the National Science Foundation (award number ECCS-1542015). The AIF is a member of the North Carolina Research Triangle Nanotechnology Network (RTNN), a site in the National Nanotechnology Coordinated Infrastructure (NNCI). The authors acknowledge support from The Center for Dielectrics and Piezoelectrics, a national research center and consortium under the auspices of the Industry/University Cooperative Research Centers program at the National Science Foundation under Grant Nos. IIP-1361571 and 1361503. The authors would like to acknowledge the use of the Huck Institutes of the Life Sciences’ Microscopy and Cytometry Facility. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1746939. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors(s) and do not necessarily reflect the views of the National Science Foundation.
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Conflict of interest
The authors are unaware of any conflicts of interest regarding the data and findings presented in this manuscript.
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