Zn-dust derived ultrafine grained ZnO non-linear ceramic resistors via in-situ thermal oxidation of cermet reactant mixture

Highlights: • Mechanically deformed metallic Zn dust transformed to several micrometre long ZnO nanowires upon direct oxidation. • Varistor grade cermet mixture was derived from Zn dust. • Sintering at 1250 °C of cermet mixture resulted in dense ultrafine grained ZnO varistor ceramics. Ceramic–metal composite (cermet) varistor mixture was processed by mechanical blending of micron sized metallic Zn dust with rare earth oxides (La₂O₃, CeO₂) and other varistor forming minor additives (CoO, Cr₂O₃, Al₂O₃, MnO₂ and SiO₂). Toxic Bi₂O₃ and Sb₂O₃ additives were avoided. The cermet varistor mixture was uniaxially pressed into cylindrical pellets and sintered at various temperatures to obtain ZnO varistors. At 1250 °C, Zn dust derived cermet composition showed 99% theoretical density, average sintered grain size b = 477 V mm⁻¹ and non-linear coefficient α = 38. A comparative study of varistor property was also performed with the commercial ZnO counterpart. The sintering analysis revealed early densification in cermet-derived ZnO varistors. In addition to varistor fabrication, temperature controlled production of ZnO nanostructures via direct thermal-oxidation of Zn dust was also investigated. Evolution of nanostructures was systematically analysed using TGA, XRD, SEM and TEM. From the microstructural analyses, the growth of well-defined ZnO nanowires with several micrometre length was confirmed. In this exploratory research, the results clearly suggest that Zn dust can be a potential source for technologically important nanostructures and for developing functional grade electronic devices such as miniaturized high energy field varistors.