Papers by Author: S.K. Sharma

Abstract: The CNT-ZnO nanocomposites were synthesized by addition of commercially available MWCNT during growth of ZnO nanoparticles employing a wet chemical route. These nanocomposites were then spin coated and characterized using X-ray diffraction, scanning electron microscopy, current-voltage characteristics and O2 (5-20%) / NO2 (2-20 ppm) gas sensing at 250°C operating temperature in N2 atmosphere (0.4±0.03 mbar). The addition of CNT in ZnO is found to increase the sensitivity for both O2 and NO2 gas sensing. The 0.1 wt % CNT addition in ZnO is observed to appreciably enhance the NO2 gas sensitivity while 1.0 wt % CNT addition in ZnO showed highest sensitivity for O2 gas detection.

Abstract: Amorphous alloys, in general, exhibit superior mechanical and chemical properties as compared to their crystalline counterparts, which is attributed to their chemical homogeneity and to the absence of crystal-like structural defects. Nanocrystalline and fully crystallized forms of these alloys can be easily obtained by a suitable thermal annealing treatment. It is important to have the knowledge of corrosion/oxidation behavior of amorphous and nanocrystalline alloys for various possible applications. In contrast to many investigations on corrosion and oxidation behavior of amorphous alloys reported in the literature, only limited studies have been carried out on comparison of corrosion/oxidation behavior of amorphous and nanocrystalline states of the same alloy. With this motivation potentiodynamic polarization studies were carried out on amorphous and nanocrystalline states of the alloy Ti60Ni40 in several aqueous media at room temperature. The oxidation in air was also investigated in the temperature range 2800C-3800C using a thermogravimetric analyzer. It was found from these investigations that nanocrystalline state exhibits the maximum corrosion/oxidation resistance in comparison to amorphous and crystalline states. The better corrosion/oxidation resistance of nanocrystalline state can be explained in terms of the nature of the nanocrystalline phase/phases and the size of the crystallites. The results of the present study are supported by other similar studies reported in the literature. A short review on comparison of corrosion/oxidation behaviour of amorphous and nanocrystalline Ti-based alloy is also presented in the paper.

Abstract: Corrosion studies were carried out using potentiodynamic polarization method on amorphous, nanocrystalline and crystalline states of the alloy Ti60Ni40 in 0.5 M H2SO4 and 0.5 M HNO3 aqueous media at room temperature. The nanocrystalline state of Ti60Ni40 was obtained by removing about 10 μm from the air side surface (crystalline state) by polishing. The presence of nanocrystalline phase was confirmed by X-ray diffraction (XRD). It was found from polarization results that the corrosion current density was higher in the amorphous state than in the nanocrystalline state in both 0.5 M H2SO4 and 0.5 M HNO3 aqueous media. These results are corroborated by the weight loss studies which were carried out in both of these media. Results are discussed in the paper in the light of data reported in the literature on similar type of alloys.

Abstract: Potentiodynamic polarization studies were carried out on amorphous, nanocrystalline and crystalline states of the alloy Ti60Ni40 in 0.1 M HNO3, 0.5 M HNO3 and 1 M HNO3 aqueous solutions at room temperature. It was observed that the amorphous state exhibited higher corrosion current density than that by the nanocrystalline state. These results are corroborated by the weight loss studies performed on the different structural states of Ti60Ni40 alloy in 0.1 M HNO3, 0.5 M HNO3 and 1 M HNO3 aqueous media. Thus the nanocrystalline state is least prone to corrosion than the amorphous and the crystalline states.