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The development of high-temperature heavy-duty turbine disk materials is critical for improving the overall efficiency of combined cycle power plants. An alloy development strategy to this end involves superalloys strengthened by ‘compact’ γ′-γ″ coprecipitates. Compact morphology of coprecipitates consists of a cuboidal γ′ precipitate such that γ″ discs coat its six {001} faces. The present work is an attempt to investigate the microstructure and creep behavior of a fully aged alloy exhibiting compact coprecipitates. We conducted heat treatments, detailed microstructural characterization, and creep testing at 1200 °F (649 °C) on an IN718-variant alloy. Our results indicate that aged IN718-27 samples exhibit a relatively uniform distribution of compact coprecipitates, irrespective of the cooling rate. However, the alloy ruptured at low strains during creep tests at 1200 °F (649 °C). At 100 ksi (689 MPa) load, the alloy fails around 0.1% strain, and 75 ksi (517 MPa) loading causes rupture at 0.3% strain. We also report extensive intergranular failure in all the tested samples, which is attributed to cracking along grain boundary precipitates. The results suggest that while the compact coprecipitates are indeed thermally stable during thermomechanical processing, the microstructure of the alloy needs to be optimized for better creep strength and rupture life.

Titanium and titanium alloys are excellent candidates for aerospace applications owing to their high strength to weight ratio. Alpha/beta titanium alloys are used in nearly all sections of the aircraft, including the fuselage, landing gear, and wing. Ti-6Al-4V is the workhorse alloy of the titanium industry, comprising of nearly 60% of total titanium production. TIMETAL® 407, Ti-0.85Al-3.9V-0.25Si-0.25Fe (Ti-407) is an excellent candidate for alloy applications requiring excellent machinability and increased energy absorption. These properties are a result of the alloy’s increased ductility while maintaining moderate levels of strength. In this study, the deformation mechanisms of Ti-407 have been studied at high strain rates using split-Hopkinson bar testing. Utilizing post-mortem characterization, Ti-407 has been shown to deform significantly by ⟨c+a⟩ slip and deformation twinning. The observation of ⟨c+a⟩ slip is in contrast with other studies and will be discussed further.

A new synthetic approach was followed for the preparation of mesoporous titania, where polyethylene glycol-400, a water soluble polymer was employed as hydrolysis retarding agent. Mesoporous titania was characterized by low angle XRD, N2 adsorption, transmission electron microscope and thermal analysis, which confirm the formation of mesophase and also the thermal stability of the prepared material. � 2008 al-Farabi Kazakh National University.

Catalytic Oxidation of Carbon Monoxide on Spinel Type Ferrites - Role of Magnetic Exchange Interactions

Anode Materials for Direct Metanol Fuel Cell

15 Years of Strong Metal Support Interaction

The preparation of nanoparticles of tin sulfide is reported employing the hydrothermal method. The X-ray diffraction results of tin sulfide nanopowder confirm its orthorhombic crystalline structure. Transmission electron micrographs show that the as-prepared SnS nanoparticles are spherical in shape with the average size of 3-5 nm. Control over the particle size and size distribution have been achieved by optimizing the experimental parameters such as precursor concentration, water concentration, reaction time and temperature. The scanning electron micrographs suggest the presence of spherical aggregates of smaller as well as larger sizes. Thermal stability of these nanoparticles is investigated by thermogravimetric analysis and differential scanning calorimetry. The prepared nanomaterial shows good gas sensing response for liquefied petroleum gas at low operating temperatures. The high crystallinity and control over the particle size make the as-synthesized SnS an ideal candidate for LPG sensing.

Tin salt precursor capped by oleic acid under solvothermal conditions gives tetragonal rutile phase of SnO2 with average particle size of 14 nm with a band gap of 4.27 eV. The SnO2 nanoparticles exhibit photoluminescence with an intense purple emission band at 425 nm. The transmission electron micrographs show the growth of nanoparticles in specific orientation. The petroleum gas sensing response of this material decreases with increase of sensing temperature.

Using state-of-the-art energy dispersive spectroscopy, it has been established for the first time that there exists significant compositional variation (enrichment of Co and Cr and deficiency of Ni and Al) associated with superlattice intrinsic stacking faults created in the ordered γ′ precipitates following intermediate temperature deformation of two commercial superalloys. The results indicate that long range diffusion of these elements is intimately involved in the precipitate shearing process and is therefore closely linked to the time-dependent deformation of the alloys.

A single-step organic-free process has been evolved to prepare phosphate-modified titania, a nanomaterial, from titanium oxysulphate solution. The adsorption of phosphate ions from aqueous solution onto titania has been studied by XRD, XPS, and DRIFT which show strong adsorption of phosphate, as Ti-O-P on the surface of titania. An increase in crystallinity and decrease in surface area are observed with calcination temperature. XPS results reveal a pentavalent oxidation state for P and the substitution of P for oxygen. The phosphate-modified titania displays good thermal stability, an essential property required for the application as catalyst and active support.

It is known that carbon dioxide undergoes electrochemical reduction to a variety of products like CO, hydrocarbons and alcohols on metallic surfaces and that the nature of the metal has a role to play in the observed selectivity of products. Rationalization of the results obtained on different metallic surfaces and accounting for the selectivity have been the points of contention in literature. This presentation examines these aspects from the point of view of surface activation of carbon dioxide and proposes a site specific and geometry constrained adsorption of carbon dioxide as the possible reason for the variation in the results reported in literature.

Photocatalytic conversions on titania utilizing sunlight as the energy source have been studied extensively for a variety of processes/ synthesis, like removal of pollutants in air and liquid streams, self-cleaning, anti-fogging and anti-bacterial applications, splitting of water into hydrogen and oxygen and photoreduction of CO 2 by water to yield hydrocarbons. These processes are receiving global attention as an off-shoot of the frantic search for alternative energy sources. Though titania continues to be the preferred catalyst in view of its low toxicity, ability to resist photo-corrosion, versatility, and abundant availability at low cost, critical limitations do exist in terms of its inability to get activated with visible light and in achieving high conversion efficiency and quantum yield. Several techniques of modifying titania to improve its performance have evolved over the years resulting in correlations and concepts on structure-property-activity and the role of preparation methods. Such modifications have lead to changes in light absorption efficiency, electronic structure, energy levels, morphology, phase composition and other photophysical properties with moderate improvements in the performance. Efforts to understand the mode of action of the modifiers in terms of the first principles, i.e., rationalization of the activity in terms of electronic and structural properties and establishing theoretical basis for the photocatalytic action, have met with only partial success, due to conflicting observations/results. The objectives towards modifications, namely, extending the light absorption range, retarding charge carrier re-combination, facilitating their fast transport to the active sites on titania surface and incorporation of active elements suitable for redox reactions, have been achieved to a reasonable level. However, commensurate improvement in activity/CO 2 conversion has not been observed. Maximization of selectivity (to methane or methanol) and arresting catalyst deactivation are the two major issues yet to be understood in clear terms. An in-depth study to understand the surface transformations at molecular level under activation by light energy, is needed to achieve further improvements in the activity of the catalysts and the process. This review brings forth an account of the investigations on modified titania, capturing some significant and selected contributions out of the vast literature available, with an emphasis on application for photocatalytic reduction of CO 2 with water.

Nickel nanoparticles have been synthesized using nickel nitrate, vegetable oil and sucrose. Ethanol has been used as a solvent since the heat of reaction shows the destabilization of nickel particles if water is present in the synthesis mixture. Nickel with fcc phase is obtained by reduction with sucrose followed by stabilization using vegetable oil. Nickel or possibly nickel carbide with hcp structure is obtained by treatment with a mixture of oleylamine and methanol. The fcc and hcp crystal structures have been characterized by XRD. The calcination of nickel nanoparticles at 450 �C results in the sintering of nickel nanoparticles, thereby increasing the crystallite size. The scanning electron micrograph reveals that the particle size is in the range of 5 - 58 nm for fcc-Ni nanoparticles calcined at 450 �C for 10 min.

Two distinct ferromagnetic phases of LaMn$_{0.5}$Co$_{0.5}$O$_{3}$ having monoclinic structure with distinct physical properties have been studied. The ferromagnetic ordering temperature $\textit{T}_{c}$ is found to be different for both the phases. The origin of such contrasting characteristics is assigned to the changes in the distance(s) and angle(s) between Mn - O - Co resulting from distortions observed from neutron diffraction studies. Investigations on the temperature dependent Raman spectroscopy provide evidence for such structural characteristics, which affects the exchange interaction. The difference in B-site ordering which is evident from the neutron diffraction is also responsible for the difference in $\textit{T}_{c}$. Raman scattering suggests the presence of spin-phonon coupling for both the phases around the $\textit{T}_{c}$. Electrical transport properties of both the phases have been investigated based on the lattice distortion., Comment: 9 figures

The structures of phosphated titania and sulphated titania are studied with a combined approach using DFT/B3LYP/Lanl2DZ and experimental studies such as XRD, XPS, and DRIFT spectra. The infrared absorptions, Mulliken charges, bond lengths, and dipole moments are investigated for the phosphated and sulphated titania structures optimized by DFT calculations. The XRD patterns obtained for both the modified titania show that the as-synthesized materials are amorphous in nature. The DRIFT spectra show the presence of bidentate complex in both sulphated and phosphated titania. The XPS data show the presence of Ti-O-S and Ti-O-P linkages in sulphated and phosphated titania respectively. The evaluation of IR absorptions obtained by DFT and DRIFT spectra reveal the most favorable structure of bridged bidentate for sulphated titania and a combination of monodentate and chelating bidentate for phosphated titania.

The appropriate combination of surface functionalities and their relative contribution to the total surface functionalities of oxidized carbon by nitric acid are evaluated by density functional theory calculations. Though the computed and experimental spectra do not exactly match in all respects, the methodology adopted has a definite role in understanding the complex surface functionalities of treated carbon.

A DFT investigation of hypothesized molybdenum(VI)-amino acid complexes has been considered as a model for xanthine oxidase. All these complexes have been optimized and analyzed by vibrational analysis. The complexes have been subjected to one electron reduction to produce anionic analogs. All complexes and reduced species are optimized in vacuum as well as in water and the associated free energy changes have been estimated. From these changes, the qualitative redox energy has been calculated by thermodynamic cycle which reveals that the complexes are expected to show similar redox behavior. This is also supported by a similar HOMO-LUMO energy gap. The population analysis shows that molybdenum d-orbital contributes >50% to LUMO, suggesting that the oxidation is metal-based in these systems. Also, 30% orbital contribution from sulfido center reveals the possible electronic delocalization through sulfur during oxidation of substrate. As a preliminary step for xanthine oxidation, pyrimidin-4-ol has been studied as a model substrate and the reduced sulfhydryl Mo(V) and sulfido Mo(IV)-substrate intermediates have been optimized with molybdenum in distorted square pyramidal geometry. The bond distances clearly show that Mo-S distance is longer in the sulthydryl analogue than in the sulfide intermediate to support the involvement of hydride transfer in the catalytic cycle. The Mo-C2 (carbon flanked between both the nitrogens) distance of 3.237 A and the C2-O distance of 1.28 A are comparable with values reported for the Mo-imidazole intermediate. This study proposes that the hydroxyl oxygen is being inserted in the C-H bond of the substrate to afford pyrimidin-2,4-diol as the product.

The effect of calcination on P25 titania at different temperatures has been studied by XRD, nitrogen adsorption desorption isotherm, BET-surface area, pore volume, pore size, particle size and crystallite size in order to understand the conversion of anatase phase to rutile phase. The fraction of anatase and rutile has been determined using XRD. Although the crystallinity remains the same, the phase change of anatase to rutile is inevitable with temperature. The isotherms show the non porous characteristics of the P25 samples. In addition, nitrogen adsoption by the samples decreased appreciably with crystallinity. The pore volume and BET surface area show a large decrease at 900�C. The particle size, crystallite size, and pore size show an increasing trend with increase in temperature. Analysis of the physical characteristics indicates that P25 titania samples can be used for catalytic applications at less than 500�C.

This paper reviews the presently proposed mechanisms for creep of {\gamma^{\prime}} strengthened Ni-base superalloys that are typically used for disk applications. Distinct creep strength controlling modes, such as dislocation-coupled antiphase-boundary shearing, shearing configurations involving superlattice stacking faults, Orowan looping, climb by-pass, and microtwinning have been observed. These are strongly influenced by the scale of the {\gamma^{\prime}} precipitating phase and are operative within specific ranges of temperature and stress. Insight from more recent experimental findings concerning microtwinning and extending stacking fault mechanisms suggest important similarities between these deformation modes. It is suggested that local atomic reordering in the wake of Shockley partials is responsible for the temperature dependence exhibited in this regime.

Deformation mechanisms, operative during intermediate temperature creep of Ni-based polycrystalline superalloys, are poorly understood. The creep deformation substructure has been characterized in Rene 88DT following rapid cooling from the super-solvus temperature, yielding a fine $\gamma^{\prime}$-precipitate microstructure. After creep to modest strain levels (up to 0.5% strain) at 650°C and an applied tensile stress of 838 MPa, microtwinning is found to be the predominant deformation mode. This surprising result has been confirmed using diffraction contrast and high-resolution transmission electron microscopy. Microtwinning occurs via the sequential movement of identical 1/6[11-2] Shockley partials on successive (111) planes. This mechanism necessitates reordering within the $\gamma^{\prime}$ precipitates in the wake of the twinning partials, so that the $L1_2$ structure can be restored. A quantitative model for creep rate has been derived on the basis that the reordering process is rate-limiting. The model is in reasonable agreement with experimental data. The results are also discussed in relation to previous studies under similar deformation conditions.

Normally, carbon materials, especially, Vulcan XC 72 are used as supports for Pt for the electrodes in fuel cells. The use of CDX 975 (a product of Columbian Chemical Company, Georgia) for support for electrode applications in methanol fuel cell is described here. The effect of the extent of Pt loading and the performance of various electrodes in methanol oxidation reactions has been studied. It is shown that 10% Pt is the optimal loading for electrode applications.

The electrochemical synthesis of conducting poly(3-methylthiophene) nanocones on carbon cloth, employing an alumina membrane as a template, is reported. The morphological characterization has been done using high- resolution transmission electron microscopy and scanning electron microscopy for both the template-synthesized and the template-free poly(3-methylthiophene). The morphology of the template-synthesized poly(3-methylthiophene) varies from hollow oriented nanocones to deformed nanocones and agglomerated forms (not in cone form) depending on the experimental conditions. The electrochemical properties of the nanocone electrode have been compared with those of the conventionally synthesized poly(3-methylthiophene) on carbon cloth, using cyclic voltammetry and impedance spectroscopy. The impedance and cyclic voltammetric measurements revealed that there is a rapid charge transport within the nanocones and between the nanocones and the electrolyte. The low impedance of dendritic poly(3-methylthiophene) nanocones is promising for their application in polymer electrolyte membrane fuel cells, where the internal resistances need to be minimized.

The equilibrium CO pressure over the condensed phase region of CeO 2(s)-CeC2(s)-C(s) was determined by adopting a method termed as the dynamic effusion MS method, which involves the measurement of the CO effusing out from the sample using a quadrupole mass spectrometer, even during carbothermic reduction of the oxide. The formation of oxicarbide has been ruled out. The Gibbs energies of the reaction, CeO2(s)+4C(s) = CeC2(s)+2CO(g), at various temperatures in the range 1350-1550 K were then determined from the equilibrium CO pressures. From the Gibbs energies of the reaction, the Gibbs energy of formation of CeC2(s) at 298 K was derived. Similarly, from the data on the second and third-law enthalpies of the above reaction, the enthalpy of formation of CeC2(s) at 298 K was calculated. The recommended Gibbs energy and enthalpy of formation of CeC2(s) at 298 K are (103.0�6.0) and (120.1�11.0) kJmol- 1, respectively. ? 2003 Elsevier Science B.V. All rights reserved.

Rare earth cuprates of composition Ln 2-XM xCu 1-yM' yO 4.� (where Ln=La, Nd, Sm and Dy; M=Sr,Ca and Ba; M'=Ru,Sb and Mn; 0.0�X�0.4 and Y=0.1) have been examined as anodes for methanol oxidation These materials display significant activity towards methanol oxidation in alkaline medium at room temperature. The electrocatalytic activity for methanol oxidation is higher for noble metals like platinum than that for perovskite oxides. However, latter systems seem to have better electrode stability.

Cyclic voltammetry (CV), control potential electrolysis (CPE), gas chromatography (GC) and photometric techniques have been used to investigate the electrochemical reduction of carbon dioxide using the title complex as catalyst at hanging mercury drop electrode (HMDE) in aqueous and aqueous mixtures of organic solvents. The products were found to be carbon monoxide and hydrogen in gaseous phase and trace amounts of formic acid in solution phase. The product selectivity is determined by the protophilic or protophobic nature of the solvent.

Partial oxidation of 2-propanol has been carried out on AB1-xB?xO3 (A = Ba; B = Pb, Ce ; B? = Bi, Sb, Cu) type perovskite oxides. Acetone is the major product observed on all the catalysts. All the catalysts undergo partial reduction during the reaction depending upon the composition of the reactant, nature of the B site cation and the extent of substitution at B site. The catalytic activity has been correlated with the reducibility of the perovskite oxides as determined from Temperature Programmed Reduction (TPR) studies.

CO partial pressures over the univariant three-phase region containing NdO1.5(s), C(s) and NdC2(s) were measured by using a quadrupole mass spectrometer (QMS) between 1403 and 1588 K. The NdC2(s) phase was generated in situ starting from a mixture of NdO1.5(s) and C(s). The second-law and third-law enthalpies of the reaction NdO1.5(s) + 3.5C(s) = NdC2(s) + 1.5CO(g) at 298 K were calculated. The enthalpy of formation of NdC2(s) was derived from the enthalpy of reaction and the enthalpies of formation of NdO1.5(s) and CO(g) taken from the literature. The Gibbs energy of formation of NdC2(s) was derived from the Gibbs energy of formation of NdO1.5(s) and CO(g) from the literature. The third-law enthalpy of the reaction is (648.1 � 1.0) and (647.6 � 1.0) kJ mol-1 based on thermal functions of NdC2(s) derived from those of UC1.94 and ThC1.94, respectively. The recommended enthalpy and Gibbs energy of formation of NdC2(s) at 298 K are -(90.8 � 6.0) and -(122.2 � 6.0) kJ mol-1, respectively. ? 2001 Elsevier Science B.V.

The redox potentials of intra-zeolite copper oxinate complexes evaluated by cyclic voltammetry are correlated with the electronegativity as well as the symmetric stretching frequency of O-H and asymmetric stretching frequency of Si-O bonds in zeolites.

Pt–Ru nanoparticles (1.6 nm) were supported on carbon nanotubes (200 nm diameter, 8–10 µm length) obtained by the carbonisation of polypyrrole on an alumina membrane.

Partial oxidation of benzyl alcohol is carried out on BPb(1-x)Bi(x)O(3) (x = 0-1) type perovskite oxides. Benzaldehyde and toluene are obtained as the major products when the reaction is carried out in the absence of oxygen. When the reaction is carried out in the presence of gas phase oxygen small amounts of benzoic acid and benzyl benzoate are also obtained. Catalysts have been characterised by XRD after the reaction. Catalyst undergoes partial decomposition when the reaction is carried out in the absence of gas phase oxygen. Extent of reduction of catalyst depends on the partial pressure of oxygen. XPS studies reveal that bismuth rich compounds are more basic. High activity and selectivity of bismuth rich systems have been attributed to their high basicity.