Nanda Gopala Krishna

Surface modification of type 304 stainless steel with duplex coatings for corrosion resistance in sea water environments

Abstract An attempt was made to improve the localised corrosion resistance of AISI type 304 stainless steel by modifying the surface with duplex coating (titania over ceria). Simple chemical immersion method was adopted for ceria coating, whereas sol–gel route with dip coating method was followed for titania coating. The adherence of the coating was evaluated by ASTM D3359 standard, and the composition of the duplex coatings was evaluated by X-ray photoelectron spectroscopy. The experimental parameters, namely, bath composition, temperature, immersion time and withdrawal speed of the specimens, were optimised to get homogeneous adherent coating. The localised corrosion resistance of ceria, titania and duplex coatings in sea water was studied by potentiodynamic anodic polarisation experiments. These coatings were characterised also by optical and scannning electron microscopes for analysing their pit morphologies. Duplex coated 304 SS exhibited superior corrosion resistance, and the probable reason for the improvement is discussed in detail in this investigation.

Enhanced supercapacitance of activated vertical graphene nanosheets in hybrid electrolyte

Supercapacitors are becoming the workhorse for emerging energy storage applications due to their higher power density and superior cycle life compared to conventional batteries. The performance of supercapacitors depends on the electrode material, type of electrolyte, and interaction between them. Owing to the beneficial interconnected porous structure with multiple conducting channels, vertical graphene nanosheets (VGN) have proved to be leading supercapacitor electrode materials. Herein, we demonstrate a novel approach based on the combination of surface activation and a new organo-aqueous hybrid electrolyte, tetraethylammonium tetrafluoroborate in H2SO4, to achieve significant enhancement in supercapacitor performance of VGN. As-synthesized VGN exhibits an excellent supercapacitance of 0.64 mF/cm2 in H2SO4. However, identification of a novel electrolyte for performance enhancement is the subject of current research. The present manuscript demonstrates the potential of the hybrid electrolyte in enhancin...

Interpretation of friction and wear in DLC film: role of surface chemistry and test environment

In spite of the large amount of tribological work carried out to explain the friction and wear mechanism in diamond-like carbon (DLC) films, some of the core issues relating to the evolution of reactive species across sliding interfaces and their role on the friction and wear mechanism remain unclear. The phase composition, film density and hydrogen content present in a DLC film can be tailored by substrate biasing during film deposition to achieve a nearly vanishing friction coefficient. Furthermore, nitrogen doping in DLC films significantly improves wear resistance, and sliding occurs in a nearly wearless regime. Undoped and nitrogen-doped DLC films exhibit a nearly frictionless value with ultra-low wear behavior when tests are performed in argon, nitrogen and methane atmospheres. The antifriction and antiwear properties of the DLC films were improved with the reduction of adsorbed oxygen impurities on the film surface. This behavior was understood by correlating the oxygen impurities present at the surface/subsurface region of the DLC film while using x-ray photoelectron spectroscopy and depth-resolved Auger electron spectroscopy.

Growth and characterization of a-axis oriented Cr-doped AlN films by DC magnetron sputtering

Wurtzite type Cr-doped AlN thin films were grown on Si (100) substrates using DC reactive magnetron sputtering with a function of N2 concentration (15 to 25%). Evolution of crystal structure of these films was studied by GIXRD where a-axis preferred orientation was observed. The electronic binding energy and concentration of Cr in these films were estimated by X-ray photoemission spectroscopy (XPS). We have observed indentation hardness (HIT) of around 28.2 GPa for a nitrogen concentration of 25%.

Formulation of Vermiwash and Humic Acid and Its Application on Allium Cepa

The continuous use of chemical fertilizers is leading to the contamination of soil and adversely affects the flora and fauna. Look out for natural forms of fertilizers is unceasing. The aim of the present investigation was to determine the influence of vermiwash and humic acid and their combinations various concentrations on the growth of Allium cepa. Vermiwash and humic acid and combinations of vermiwash and humic acid are used as plant growth promoters in varying concentrations. In this study, the concentration of 3:1.5 % (vermiwash: humic acid) was found to be the most effective formulation which was manifested in increase in growth, soft shoots, number of branches, total carbohydrate content and total protein content followed by a concentration of 3:2 % (vermiwash: humic acid). This study was effective in formulating an efficient chemical free fertilizer that can be further used in agriculture on a large scale.