C. Anandan

Investigation of surface composition of electrodeposited black chrome coatings by X-ray photoelectron spectroscopy

: Solar selective black chromium coating was electrodeposited on pre-treated electroformed nickel substrates from a hexavalent chromium containing bath. The composition of the film was investigated before and after annealing at 400 degreesC for different durations. In the as-deposited condition. the surface of the film was found to have trivalent chromium hydroxide and chromium in the chromate form contrary to previous studies which report the presence of hydroxides and metallic chromium. However in the present study, no evidence for metallic chromium was found. The major component. chromium hydroxide, was converted to Cr2O3 on annealing at 400 degreesC with the loss of water vapor. The chromate form remains but with a lowered concentration.

Characterization of iron impregnated polyacrylamide catalyst and its application to the treatment of municipal wastewater

The persistent organic pollutants and bio diversities (pathogenic and non-pathogenic) present in treated municipal wastewater cause environmental deterioration besides adversely affecting human health. In the present investigation, an attempt was made to treat the municipal wastewater using iron impregnated polyacrylamide (IIPA) powder catalyst in a fluidized reactor. The IIPA catalyst was characterized by carbon, 12.23%, hydrogen, 1.63%, nitrogen, 2.93%, iron, 58%, silicon, 15.25%, surface area 96.66 m2 g−1 and pore diameter, 58.32 A. IIPA was crystalline with an energy gap of 1.93 eV and it was capable of generating hydroxyl radicals for the oxidation of dissolved organics in municipal wastewater with minimum sludge yield (0.05 g VSS/g of COD). The oxidation of dissolved organics in municipal wastewater by IIPA was carried out under batch and continuous mode operations. The pseudo first order rate kinetic constants for the oxidation of organics in municipal wastewater were found to be 2.2 × 10−2, 3.01 × 10−2, 3.33 × 10−2 and 3.72 × 10−2 min−1. The activation energy for the oxidation of dissolved organics in municipal wastewater was 13.15 kJ mol−1. The pollution parameters BOD5, COD, ammonia, TKN and sulphide were removed from the municipal wastewater by 72.72%, 82.87%, 71.76%, 65.3% and 86.66% respectively.

Study of the structural, thermal, optical, electrical and nanomechanical properties of sputtered vanadium oxide smart thin films

Vanadium oxide thin films were grown on both quartz and Si(111) substrates, utilizing a pulsed RF magnetron sputtering technique at room temperature with the RF powers at 100 W to 700 W. The corresponding thicknesses of the films were increased from 27.5 nm to 243 nm and 21 nm to 211 nm as the RF power was increased from 100 W to 700 W for the quartz and silicon substrates, respectively. X-ray diffraction and field emission scanning electron microscopy were carried out to investigate the phase and surface morphology of the deposited films. The electronic structure and the vanadium oxidation states of the deposited films were investigated thoroughly by X-ray photoelectron spectroscopy. The as-grown films show only stoichiometric vanadium oxide, where vanadium is in V5+ and V4+ states. The phase transitions of the vanadium oxide films were investigated by the differential scanning calorimetric technique. The reversible i.e. smart transition was observed in the region from 337 °C to 343 °C. The average hemispherical infrared emittance of the deposited vanadium oxide films was evaluated by an emissometer in the wavelength range of 3 μm to 30 μm. The sheet resistance of the deposited films was measured by a two-probe method and the data were in the range of 106 to 105 Ω per square. The optical properties of the films, such as solar transmittance, solar reflectance and solar absorptance, as well as optical constants e.g. optical band gap, were also evaluated. Finally, mechanical properties such as the hardness and the Young’s modulus at the microstructural length scale were evaluated by employing a nanoindentation technique with a continuous stiffness mode.

Electroless deposition of ternary Ni–W–P alloys from sulphate and chloride based baths

Abstract The present investigation focuses on the preparation of ternary electroless Ni–W–P alloy deposits using sulphate (B1) and chloride (B2) based baths. The characteristics of the deposits were studied using XRD, SEM, XPS and atomic force microscopy (AFM) techniques. XRD patterns showed that the tungsten influences the structure and grain size of the deposits produced using B1 and B2 based baths. EDX analysis showed that a drastic reduction of phosphorus content owing to the addition of tungsten in both types of deposits. XPS studies showed that W content was approximately 2 at.-% and in the coatings deposited using B1 baths the elemental form of tungsten is twice that in the coatings deposited using B2 baths. From SEM analysis coarse nodular structure was found for the deposits obtained using B1 baths. It was also found from AFM images that the roughness values of ternary deposits using B2 baths were lower than those using B1 baths. Heat treatment at different temperatures on the deposits showed a higher increase in hardness in the coatings from B2 baths.

XRD and XPS studies of room temperature spontaneous interfacial reaction of CeO2 thin films on Si and Si3N4 substrates

X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) investigations of interfacial reactions between Ce and Si have been carried out on the same set of as-deposited and 15 month aged films. XRD patterns demonstrate the presence of several peaks associated with CeO2 planes in aged CeO2/Si3N4 thin film in comparison with as-deposited nanocrystalline film, whereas the peak is broadened in the CeO2/Si film after aging. XPS studies show that interfacial reaction occurs spontaneously in CeO2/Si thin film at room temperature. Ce is present as both Ce4+ and Ce3+ oxidation states in as-deposited CeO2/Si thin film, whereas Ce4+ is the main species in CeO2 thin film deposited on the Si3N4 substrate. When XPS is recorded after 15 months, the concentration of Ce3+ species is observed to increase drastically in the CeO2/Si thin film. In contrast, interfacial reaction between the CeO2 and the Si3N4 substrate is not significant in the film even after 15 months of deposition. This shows that the initial room temperature spontaneous interfacial reaction observed in the CeO2/Si film continues at a much higher rate, whereas the nature of the CeO2/Si3N4 interface remains the same after 15 months, proving its stability.

Formation of a protective nitride layer by electrochemical nitridation on 316L SS bipolar plates for a proton exchange membrane fuel cell (PEMFC)

In the present study, an attempt has been made to increase the corrosion resistance of 316L stainless steel (SS) bipolar plates (Bp) through electrochemical nitridation using a nitrate bearing electrolyte solution of 0.1 M HNO3 and 0.5 M KNO3. The X-ray photoelectron spectroscopy (XPS) studies revealed that the modified SS was covered with ammonium ions and mixed nitrides, namely CrN and Cr2N, on the surface. The average contact angle value with water for nitrided SS favored a PEMFC operating environment. The electrochemical corrosion behaviour was studied in a simulated PEMFC environment (0.5 M H2SO4 and 2 ppm of HF) to ensure that the modified SS exhibits enhanced corrosion resistance. Surface resistance values for both untreated and nitrided SS showed low values and increased conductivity after the polarization studies.

Microstructural studies of e-beam evaporated alumina thin films

Abstract Alumina thin films of different thicknesses, e.g. 90, 120 and 150 nm, were grown on SS304 thin foil by electron beam evaporation technique. The films were post-heat treated at 500, 700 and 800°C in air and subsequently characterised by X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy and X-ray photoelectron spectroscopy. The effects of thicknesses and post-heat treatment on microstructure have been studied. The deposited alumina film was almost stoichiometric. The alumina film of the lowest thickness, i.e. 90 nm post-heat treated at 700°C, showed preferential growth of nanorods and irregular polygonal nanostructures with random orientation.

CHARACTERIZATION AND MICROHARDNESS OF ELECTRODEPOSITED Ni–W COATINGS OBTAINED FROM GLUCONATE BATH

Ni–W alloy coatings are electrodeposited with direct and pulse current using gluconate bath at pH5. Effects of direct current (DC) and pulse current (PC) on structural characteristics of the coatings have been investigated by energy dispersive X-ray spectroscopy (EDXS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS). EDXS shows that W contents are 13.3 and 12.6 at.% in DC and PC (10:40) Ni–W coatings, respectively. FESEM analysis exhibits the homogeneous coarse nodular morphology in DC plated deposits. DSC studies reveal that Ni–W coatings are thermally stable up to 400°C. XPS studies demonstrate that DC plated coating has significant amount of Ni and W in elemental form along with their respective oxidized species. In contrast, mainly oxidized metals are present in the as-deposited coatings prepared with PC plating. The microhardness of pulse current (100:400) deposited Ni–W coating is about 750 HK that is much higher than DC plated coating (635 HK). Heat treatment of the deposits carried out at different temperatures show a significant increase in microhardness which can be comparable with hard chromium coatings.

GROWTH, STRUCTURAL CHARACTERIZATION AND INTERFACIAL REACTION OF MAGNETRON SPUTTERED CeO2 THIN FILMS ON DIFFERENT SUBSTRATES

CeO2 thin films were deposited on Si, Al, Ti–6Al–4V alloy, Si3N4 and glass substrates by magnetron sputtering at room temperature. Growth of CeO2 films on Si and Si3N4 and effect of annealing were investigated by XRD, FESEM and AFM. Interaction between deposited CeO2 films and Si, Al, Ti–6Al–4V alloy, Si3N4 and glass substrates was investigated by XPS. XRD studies show that films are oriented preferentially to (200)-direction of CeO2 and no significant change is observed in the XRD patterns of films after heat treatment. CeO2 film on Si3N4 exhibits rough morphology, whereas very fine morphology is observed in CeO2 film on Si. CeO2 film on Si shows lower roughness in relation to that on Si3N4 as demonstrated by AFM studies. XPS results show that Ce is present as both +4 and +3 oxidation states in CeO2 film deposited on Si and Al substrates, whereas Ce4+ is the main species in CeO2 films deposited on Ti–6Al–4V alloy, Si3N4 and glass substrates. Ce3d, Si2p and O1s core level spectra demonstrate that Ce2O3 or cerium silicate and SiOx type of species are formed at the interface of CeO2 and Si. Similarly, formation of interfacial species like Ce2O3 or cerium aluminate is evident in CeO2 film on Al as demonstrated by XPS studies. On the other hand, interfacial reactions between CeO2 and Ti–6Al–4V alloy, Si3N4 and glass substrates are limited in the respective films.

Characterization and corrosion behavior of Co and Co–P coatings electrodeposited from chloride bath

Co–P coatings with low and high phosphorous contents are electrodeposited using direct current (DC) and pulse current (PC) methods from cobalt chloride baths. The low phosphorous content coatings obtained from DC and PC methods are crystalline with predominantly fcc structure, while the high P content coatings are amorphous. Electrochemical corrosion studies reveal an increase in corrosion resistance with increasing phosphorous content in both DC and PC plated coatings. The PC coatings show a higher polarization resistance (Rp) and a lower corrosion current density (icorr), indicating better corrosion resistance. Compositional analysis shows a slight or no increase in P content after corrosion in PC coatings with a high P content, indicating better corrosion resistance. Comparisons of the surface morphologies before and after corrosion illustrate that the PC plated coatings are less affected than their DC counterparts. X-ray photoelectron spectroscopy (XPS) reveals a larger amount of oxidized cobalt in the PC electrodeposited coatings, whereas mainly metallic Co species are found in the DC plated coatings. This study demonstrates that the overall corrosion resistance for the PC deposited coatings is better than that of the DC deposited coatings because of the high P content, amorphous structure, smooth morphology, and higher metal oxide content in the deposits.