V. Jayaram

An XPS study on binary and ternary alloys of transition metals with platinized carbon and its bearing upon oxygen electroreduction in direct methanol fuel cells

The present X-ray photoelectron spectroscopic study on carbon-supported Pt, Pt–Cr, Pt–Co, Pt–Ni, Pt–Co–Cr and Pt–Co–Ni electrocatalysts suggests that while Pt–Cr/C, Pt–Co/C and Pt–Ni/C binary alloy electrocatalysts are surface rich in platinum, both Pt–Co–Cr/C and Pt–Co–Ni/C ternary electrocatalysts happen to be surface rich in base metals. Among these electrocatalysts, Pt–Co/C electrocatalyst is found to possess a minimum amount of platinum oxides. Accordingly, Pt–Co/C exhibits a higher electrocatalytic activity towards oxygen-reduction reaction in the solid-polymer-electrolyte direct methanol fuel cells.

Combustion synthesis of nanometal particles supported on α-Al2O3: CO oxidation and NO reduction catalysts

Nanoparticles of Pt, Pd, Ag and Au supported on alpha-Al2O3 have been synthesized by the combustion method for the first time and characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Catalytic activities of these nanosized materials have been investigated. For the CO+O-2 reaction, 100% CO conversion occurs below 300 degrees C over supported Pt, Pd and Ag metals whereas 90% conversion is observed over Au at 450 degrees C. Similarly 100% NO conversion is seen over 1% Pd/Al2O3 and 1% Pt/Al2O3 below 400 degrees C for the NO+CO reaction whereas approximate to 90% NO is converted into N-2 above 650 degrees C on 1% Ag/Al2O3 and 1% Au/Al2O3.

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.

XPS and XAES investigations of electrochemically deposited Cu-Ni solar selected black coatings on molybdenum substrate

Electrodeposition of Cu-Ni black solar selective coatings from a triethanolamine (TEA) complex bath solution containing ammonium persulfate (AP) was presented. Optical properties and atomic compositions of the surface and surface inclusions of the coatings were analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray initiated Augur electron spectroscopy (XAES). XRD pattern of the deposit confirmed the deposited alloy phase to be Cu-Ni. XPS studies of the coating showed the presence of Cu in both metallic and + 1 oxidation state and the absence of CuO species.

An X-ray photoelectron spectroscopic study of electrochemically deposited Fe-P thin films on copper substrate

Electrochemically deposited Fe-P magnetic thin film from acidic tartarate complex bath solution was characterized by X-ray photoelectron spectroscopy. As-prepared film contains both Fe3+- and P5+ -like species, whereas the same film after 10 and 20 min sputtering shows peaks corresponding to Fe metal as well as P(I´-) species along with P5+ species. The film after heat-treatment contains Fe3+ together with P5+ and PI´- species, whereas heat-treated film after sputtering shows the presence of both Fe metal and Fe2+ species. There is an increase in PI´- intensity on sputtering the heat-treated film. © 2002 Elsevier Science B.V. All rights reserved.

Material processing and surface reaction studies in free piston driven shock tube

Recently established moderate size free piston driven hypersonic shock tunnel HST3 along with its calibration is described here. The extreme thermodynamic conditions prevalent behind the reflected shock wave have been utilized to study the catalytic and non-catalytic reactions of shock heated test gases like Ar, N2 or O2 with different material like C60 carbon, zirconia and ceria substituted zirconia. The exposed test samples are investigated using different experimental methods. These studies show the formation of carbon nitride due to the non-catalytic interaction of shock heated nitrogen gas with C60 carbon film. On the other hand, the ZrO2 undergoes only phase transformation from cubic to monoclinic structure and Ce0.5Zr0.5O2 in fluorite cubic phase changes to pyrochlore (Ce2Zr2O7±δ) phase by releasing oxygen from the lattice due to heterogeneous catalytic surface reaction.

Experimental Investigation of Nano Ceramic Material Interaction with High Enthalpy Argon under Shock Dynamic Loading

Indigenously designed and fabricated free piston driven shock tube (FPST) was used to generate strong shock heated test gases for the study of aero-thermodynamic reactions on ceramic materials. The reflected shock wave at the end of the shock tube generates high pressure and temperature test gas (Argon, Ar) for short duration. Interaction of materials with shock heated Ar gas leads to formation of a new solid or stabilization of a material in new crystallographic phase. In this shock tube, the generated shock waves was utilized to heat Ar to a very high temperature (11760 K) at about 40-55 bar for 2-4 ms. We confirmed the phase transformation and electronic structure of the material after exposure to shock by XRD and XPS studies. This high enthalpy gas generated in the shock-tube was utilized to synthesize cubic perovskite CeCrO3 from fluorite Ce0.5Cr0.5O2+δ oxide. We were able to demonstrate that this ceramic materials undergoes phase transformations with the interaction of high enthalpy gas under shock dynamic loading.

Investigation of strong shock wave interactions with CeO 2 ceramic

Strong shock wave interactions with ceramic material ceria (CeO2) in presence of O2 and N2 gases were investigated using free piston driven shock tube (FPST). FPST is used to heat the test gas to very high temperature of about 6800–7700 K (estimated) at pressure of about 6.8–7.2 MPa for short duration (2–4 ms) behind the reflected shock wave. Ceria is subjected to super heating and cooling at the rate of about 106 K/s. Characterization of CeO2 sample was done before and after exposure to shock heated test gases (O2 and N2). The surface composition, crystal structure, electronic structure and surface morphology of CeO2 ceramic were examined using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Results obtained from the experimental investigations show that CeO2 can withstand high pressure accompanied by thermal shock without changing its crystal structure. Reducible CeO2 releases lattice oxygen making it possible to shift between reduced and oxidized states upon the interaction with shock heated gas. Due to such reaction mechanism, CeO2 ceramic undergoes nitrogen doping with decrease in lattice parameter. Investigations reveal that CeO2 retains its crystal structure during strong shock interaction, even at elevated pressure.

Sustainability of Carbon Nanocomposites Under High Temperature and Pressure

In this article we explored the sustainability of carbon nanocomposite material under high temperature and pressure shock waves developed in an air ambience. The changes in the morphology, crystal structure and electrical properties of carbon nanostructures are discussed by comparing with untreated structures. After shock wave treatment, we have noticed two typical modifications such as weight-loss in the deposited material and formation of diamond nanoparticles. However, the impact of shock wave is limited to the carbon nanoparticles those are residing on the top-surface of the films. Degrade in the overall quality of treated films and increase in their electrical resistance has been noticed.

Experimental investigation of catalytic and non-catalytic surface reactions on SiO2 thin films with shock heated oxygen gas

The present study is to investigate the interaction of strong shock heated oxygen on the surface of SiO2 thin film. The thermally excited oxygen undergoes a three-body recombination reaction on the surface of silicon dioxide film. The different oxidation states of silicon species on the surface of the shock-exposed SiO2 film are discussed based on X-ray Photoelectron Spectroscopy (XPS) results. The surface morphology of the shock wave induced damage at the cross section of SiO2 film and structure modification of these materials are analyzed using scanning electron microscopy and ion microscopy. Whether the surface reaction of oxygen on SiO2 film is catalytic or non-catalytic is discussed in this paper.