• A SIL

Articles written in Bulletin of Materials Science

• Microstructural and electrical characteristics of SiO2 doped ZnO-Bi2O3 varistors

Varistors in the new system ZnO-Bi2O3-SiO2 were prepared through conventional ceramic processing route. The effect of sintering temperature and time (0·5 h to 2 h between 1000° and 1250°C) on the microstructure and current/voltage characteristics of the varistors of the new system were investigated and the results were compared with those of ZnO-Bi2O3 system varistors prepared. An increase in nonlinear coefficient (α) value was observed in the SiO2 added varistors. The microstructure and the phase of the varistors were examined by means of SEM and XRD. The Zn2SiO4 spinel phase was found to be present in the intergranular region. The grain growth exponent was determined to be 2·5±0·2 and the activation energy for the ZnO grain growth was estimated to be 251±11 kJ/mol. These values were compared with those estimated for ZnO-Bi2O3 system varistors.

• Chemical nature of catalysts of oxide nanoparticles in environment prevailing during growth of carbon nanostructures by CCVD

Carbon nanostructures (CNS) are often grown using oxide nanoparticles as catalyst in chemical vapour deposition and these oxides are not expected to survive as such during growth. In the present study, the catalysts of cobalt- and nickel oxide-based nanoparticles of sizes varying over a range have been reduced at 575$^{\circ}$C under environment resulting from the introduction of C$_2$H$_2$ $+$ NH$_3$ during growth of CNS as well as under introductionof C$_2$H$_2$ and NH$_3$ separately. The structure of the reduced nanoparticles is often different from the equilibrium structure of the bulk. Nanoparticles of cobalt oxide with and without doping by copper oxide are reduced to cobalt alloy or cobalt nanoparticles having fcc structure, but the rate of reduction is relatively less in NH$_3$ environment. However, reduced nickel oxide nanoparticles with and without doping shows a mix of fcc and hcp phases. The presence of hydrogen and nitrogen in the environment appears to discourage the formation of hcp nickel as inferred from the results in NH$_3$ environment. Cobalt carbide forms when the 10 wt.% or less doped cobalt oxide is reduced in C$_2$H$_2$ $+$ NH$_3$ environment. At higher level of doping of 20 wt.%, separate metallic phase of copper appears andcarbide formation gets suppressed.

• # Bulletin of Materials Science

Volume 44, 2021
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020