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The excess free energies of sub-binary Al–Sn, Sn–Zn and Zn–Al alloys and ternary Al–Sn–Zn alloy were computed using the optimised exponential parameters of R–K polynomial at 973, 1073, 1173 and 127...

In this present works, a generalized approach for the two-phase flow analysis of a natural circulation in hybrid boiler. The model uses the combination of node and loop equations and the Newton Raphson technique for the solution of the set of equations. Loop equations have been developed for each evaporator tube with the unique driving force and pressure drop of the concerned loop. Node equations are mainly developed for common risers and downcomers. A unique connectivity matrix has been used to correlate each branch flow with loop and node equations. The model is validated by a unique indirect method by comparing the actual water level and calculated water level. Experiments have been performed with uniform diameter of tubes in 53 channels circulating loop to find the volume of steam. The model shows good agreement with experimental investigations with a maximum of 3.57% absolute error. The model can be used for the design, analysis, and optimization of the natural circulation network.

Fast propagation of sawtooth induced heat pulse is observed in the magnetohydrodynamic (MHD) active plasmas of ADITYA tokamak. The sawtooth crash deposits heat beyond the inversion radius, which gets transported to the edge region of the plasma, and is reflected as inverted sawtooth modulation in the edge channels of electron cyclotron emission (ECE) and H α spectral line emission. The time-lag analysis on ECE signal reveals the propagation time from plasma core to edge of ∼150 µs. From this analysis, the estimated transient electron heat diffusivity χ e hp is found to be ∼50–60 m2 s−1, which is ten times higher than that of power balance heat diffusivity χ e pb , in the MHD active discharges of ADITYA. It has been observed that the presence of MHD (m/n = 2/1, 3/1) activity in the intermediate region between the q = 1 and the edge radii, significantly influences the heat transport from the plasma core to the edge region. Stochastic magnetic field region formation with overlapping m/n = 2/1 and 3/1 MHD islands facilitates the fast heat-pulse propagation during a sawtooth crash in ADITYA tokamak. The disparity between the measured and the power-balance estimated diffusivity is significantly reduced by considering the electron heat diffusivity due to stochastization of magnetic field in the intermediate region.

Hot compression tests were conducted to determine the processing window for deformation of solutionized Inconel 718 over a range of high temperature and strain rate. Hot working map based on the dynamic material model was developed to establish the hot-processing regime. Maximum hot deformation efficiency within the processing regime is marked by the dynamic recrystallization, whereas an instability regime exhibits the highly deformed grains with shear bands. Further, selected deformed specimens were aged at 750 °C for 8 hours. Using electron back scattered diffraction and microhardness analyses, different microstructural properties such as grain size, twin fraction, grain average misorientation, and hardness were correlated. For deformed specimens, it was found that hardness is a function of misorientation and grain size. However, after aging treatment, hardness for all the specimens was found to lie in the range of 400 to 425 HV. Further, through transmission electron microscopy analysis, it was confirmed that deformed specimens are devoid of any precipitates while the deformed specimens followed by aging showed γ″ precipitates. Thus, the lack of correlation between the hardness and the grain size in the aged specimen was due to evolution of precipitates.

In the present work, a β-Ti alloy (Ti–15V–3Sn–3Cr–3Al) was unidirectionally cold rolled to 80% thickness reduction, followed by recrystallization at two temperatures: (i) 1013 K and (ii) 1053 K. The microstructural developments were studied using light optical microscopy, scanning electron microscopy X-ray peak profile analysis, and electron backscattered diffraction. The bulk texture of deformed and fully recrystallized samples was studied using X-ray diffraction. The deformed microstructures showed the presence of high fraction of shear bands, and these bands were preferentially formed in γ-fiber grains than in the grains with other orientations. Cold rolled β-Ti alloy samples were fully recrystallized in 10 min at 1053 K and in 90 min at 1013 K. Strong α- and γ-fibers were formed after 80% cold rolling, while strong discontinuous γ-fiber (with very strong {111}〈112〉 component) was formed after complete recrystallization. Oriented nucleation was found to be the dominant mechanism for the development of recrystallization texture.

Hot deformation behaviour of Ti-6Al-4V with transformed microstructure was investigated for very high deformation. Hot compression tests were carried out up to 80% height reduction at 950°C and str...

Hot compression tests were performed on Inconel 718 to study high temperature flow stress-strain response and activation mechanism in the hot deformation. To model the flow stress response, we employed two physically based models namely Schӧcks-Seeger-Wolf and Kocks model in addition to extensively used Sellers model. Flow curves from all three models were compared and it was found that predictions of Sellers model closely resemble the experimental results. However, activation energy calculated using Sellers model differs significantly from the activation energy of micro mechanism as reported in the literature. Schӧcks-Seeger-Wolf model predictions are in close agreement with experiments at low strain rate and the activation energy corresponds to diffusion activation energy. Though Kocks model shows much deviation from the experimental results, qualitative comments on the activation energy profile can be made using this model. We utilized hardening models to derive a constitutive model for DRX and simultaneously establish an understanding of rate controlling deformation mechanism in Inconel 718.

The best fit value of order energy parameter (W) has been estimated over the entire range of concentration in Al-Sn binary liquid alloy at a specified temperature to determine the thermodynamic properties and concentration fluctuations, obtained by a theoretical formalism in which the combined effect of size ratio, entropic and enthalpic effect is considered. The values of W at different temperatures have been determined by finding the temperature derivative of W which are then used for the optimization procedure in order to determine the corresponding values of excess free energy of mixing, partial excess free energy of mixing and activity of the components involved in the alloy. These parameters have been used to calculate the concentration fluctuations in long wavelength limit {Scc(0)} at different temperatures over the entire range of concentration which predict the stability of the alloy at different temperatures.

The dual-phase titanium alloy Ti-6Al-4V can be thermomechanically treated to produce a variety of microstructures to obtain desired mechanical properties. The extreme microstructure morphologies were developed by heat treatment of mill annealed microstructure to equiaxed, and transformed-β microstructures (lamellar) of coarser α-lath and α′-laths (martensite). The uniaxial tensile test shows the highest elongation in the equiaxed microstructure followed by coarse α-lath lamellar, while the α′-lath morphology has the least elongation. The higher ductility in the equiaxed microstructure is due to smaller slip length compared to coarse α-lath lamellar. On the other hand, the poor ductility of the α′-lath is due to premature crack initiation. Both equiaxed and coarse α-lath lamellar microstructures mostly show prismatic and pyramidal slip / . In addition to this, though less prevalent, these microstructures exhibit twinning as the other deformation mechanism, which is uncommon in Ti-6Al-4V. The twin boundary interaction with the grain boundary led to the damage nucleation, causing the intra-grain crack. In the coarse lath lamellar (furnace cooled) morphology, the crack was mostly observed at the junction of α-colonies as well at the α-layer grain boundary/α-colony interface due to strain localization. However, in the lamellar (water quenched), the primary α′-lath shows the void nucleation at the junction of the primary and secondary-α′ interface, which coalesce to form microcrack and further grow instantly to fracture. The void nucleation is generally observed in a basal orientation along the primary α′-lath, oriented 45° to the loading axis, and having dominant pyramidal slip ( / ). Thus, the deformation mechanisms slip, twin, and fracture depend on the microstructure morphology in Ti-6Al-4V.

The thermodynamic properties, such as free energy of mixing, heat of mixing, activity and structural properties, such as concentration fluctuation in long wavelength limit, short-range order parameter of Pb–Hg liquid alloy at 600 K have been calculated using theoretical modelling. It has then been correlated with modified Butler model to compute the surface tension of the alloys at different temperatures. The Pb–Hg system at 600 K is found to be ordering at higher concentration of Pb.

Thermodynamic and structural properties of mixing of molten Tl–Na alloys at 673 K have been investigated using quasi-chemical model. To understand the mixing behaviour in more detail, emphasis is placed on the role of interaction energy term, and viscosity and surface tension of the alloys have also been analysed under statistical considerations. Our study shows negative deviation from the Raoultian behaviour in the properties of Tl–Na alloy thereby indicating hetero-coordination in the Tl–Na melt at 673 K in the full range of concentration. Theoretically, computed thermodynamic data at 673 K agree very well with the corresponding experimental data. The viscosities of the alloys computed from Kaptay equation show small negative deviation and those computed from Singh and Sommer’s formulation show small positive deviation from ideal values while the Budai-Benko-Kaptay equation predicts noticeable negative deviation in Na-rich end and positive deviation in Tl-rich end of the composition. The calcula...

A thin film of a type II Ge clathrate, NaxGe136, was epitaxially grown on a (111) substrate of Ge with a diamond structure (α-Ge). A Zintl phase NaGe film was synthesized in advance by a reaction of the substrate surface with Na vapor under an Ar atmosphere, and was highly oriented such that the NaGe(100) planes were parallel to the Ge(111) surface. The NaGe film was transformed to the NaxGe136 film by heat treatment under dynamic vacuum. XRD measurements demonstrated that the prepared film consisting of twin crystals with a (111) twin plane was epitaxially grown with the direction normal to the substrate surface. It was also suggested that the lattice mismatch between NaxGe136 and the Ge substrate is relaxed by a buffer layer of α-Ge having a triple-period superlattice. The electrical resistivity of the NaxGe136 film was estimated from the I–V measurements to be in the order of 101–102 Ω m.

Influence of substrate temperature (TS) on the structural and electrical properties of cubic silicon carbide (3C-SiC) films deposited using hot wire chemical vapor deposition technique has been investigated. The films are deposited on fused quartz and crystalline silicon wafer substrates using pure silane, hydrogen and methane gas as precursors. X-ray diffraction patterns, Raman scattering and Fourier transform infrared spectroscopy revealed that the films prepared below TS ≤ 450 °C are nanocrystalline embedded in amorphous SiC matrix while those with TS > 450 °C are highly crystalline. As TS increases from 350 to 850 °C the dark conductivity (at ~50 °C) increases from ~2 × 10−9 to 6 × 10−2 Ω−1 cm−1 and activation energy decreases from 0.57 to 0.086 eV. A reasonable deposition rate of ~10 nm min−1 is obtained for highly crystalline films deposited at high TS. The deposition rate for nanocrystalline embedded amorphous films deposited at TS ~ 350 °C is quite high ~92 nm min−1. The improvement in crystallinity and decrease in deposition rate for high TS films is due to enhanced surface diffusivity of film forming radicals on the substrate surface and etching of weak bonds. Our studies indicates that it is possible to grow highly 3C-SiC films at moderate temperature of 550 °C.

Silicon carbide (SiC) thin films have been deposited using a hot-wire chemical vapor deposition technique on quartz substrates with a mixture of silane, methane, and hydrogen gases as precursors at a reasonably high deposition rate of approximately 15 nm/min to 50 nm/min. The influence of the filament temperature (TF) on the structural, optical, and electrical properties of the SiC film has been investigated using x-ray diffraction, Raman scattering, Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy, ultraviolet–visible–near infrared transmission spectroscopy, and dark conductivity (σd) studies. Films deposited at low TF (1800°C to 1900°C) are amorphous in nature with high density of Si–Si bonds, whereas high-TF (≥2000°C) films are nanocrystalline embedded in an amorphous SiC matrix with higher concentration of Si–C bonds and negligible concentration of Si–Si bonds. The bandgap (Eg) varies from 2.5 eV to 3.1 eV and σd (50°C) from ∼10−9 Ω−1 cm−1 to 10−1 Ω−1 cm−1 as TF is increased from 1900°C to 2200°C. This increase in Eg and σd is due to microstructural changes and unintentional oxygen doping of the films.

Aluminium is a third group element according to the periodic table. Chemically it is a reactive metal often forming complexes within its binary alloys. In the present work we have dealt with the impact of eigenvalues on the superconducting state parameter viz. the electron-phonon coupling strength of this metal. We have also dealt with the same for two binary alloys of it viz. aluminium-magnesium and aluminium-zinc. For this purpose we have computed the non-local screened form factor for each of them. Initially the orthogonalised plane wave parameter has been taken as unity. Thereafter Vashishta-Singwi form of exchange and correlation is employed. The core energy eigenvalues of Herman-Skillman have been used. Our results are quite satisfactory for the metal as well as its present alloys. Our computation reveals that the superconducting state parameter can be reasonably reproduced by Harrison’s first principle pseudopotential technique along with McMillan’s formalism provided a proper choice of the core energy eigenvalues is made.DOI: http://dx.doi.org/10.3126/bibechana.v12i0.11699BIBECHANA 12 (2015) 35-39

Highly crystalline cubic Silicon carbide (3C-SiC) thin films were deposited on quartz and silicon substrate at low substrate temperature of 400 °C by hot wire chemical vapour deposition technique using Silane, methane and hydrogen gases. The influence of methane flow rate (MFR) on structural and electrical properties of films has been investigated. All the deposited films are highly crystalline with crystallite size as high as 27 nm for film deposited with MFR = 6 SCCM. A decrease in crystallite size is observed with increase in MFR. Electrical conductivity of films deposited at low MFR (6–12 SCCM) is ~1 Ω−1 cm−1, however an order of decrease in conductivity has been observed as MFR increases beyond 12 SCCM. Activation energy of films also decreases monotonically with increasing MFR. The variation in dark conductivity and activation energy could be attributed to the microstructural changes in films with increasing MFR. No trace of any contamination of filament material is observed in these films. These highly crystalline and conductive films find applications in various microelectronic and optoelectronic devices.

We have used simple statistical theory to report the segregating nature of In–Tl liquid alloys. The energetic of mixing in liquid alloys has been analyzed through the study of surface properties, transport properties and various thermodynamic and microscopic functions. Positive deviation from Raoultian behavior has been observed in the computed mixing thermodynamic and microscopic parameters of the alloys. The computed results are in good agreement with experimental data and support a weak phase-separation tendency in molten In–Tl system. Surface properties have also been analyzed using two different approaches which reveal that with the addition of In atoms in In–Tl alloys, surface tension of the alloy increases and Tl atoms tend to segregate at the surface.

The superior catalytic activity along with improved CO tolerance for formic acid electro-oxidation has been demonstrated on a NiO-decorated reduced graphene oxide (rGO) catalyst. The cyclic voltammetry response of rGO-NiO/Pt catalyst elucidates improved CO tolerance and follows direct oxidation pathway. It is probably due to the beneficial effect of residual oxygen groups on rGO support which is supported by FT-IR spectrum. A strong interaction of rGO support with NiO nanoparticles facilitates the removal of CO from the catalyst surface. The chronoamperometric response indicates a higher catalytic activity and stability of rGO-NiO/Pt catalyst than the NiO/Pt and unmodified Pt electrode catalyst for a prolonged time of continuous oxidation of formic acid. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Single, bi and a few layer graphene films of large sp2 domain size were grown on Ni foil using hot filament chemical vapor deposition at a relatively low substrate temperature of 700 °C. The number of layers was found to vary from 1 to 6 and 7 to 12 for the films deposited at a process pressure of 1.5 mbar for the deposition time of 30 and 20 min, respectively. Further at a lower process pressure of 1 mbar, 2–8 layers were obtained for 10 min deposition time. The measured average sp2 domains size was found to be in the range of 117–279 nm in the case of 1–6 layers of graphene films. These large domain size graphene films could be very useful for graphene based electronic devices and other applications.

The segregating nature of Cd–Pb liquid alloys has been reported using simple statistical theory of mixing. The energetics of mixing in liquid binary alloys has been analysed through the study of surface properties (surface tension and surface concentration), transport properties (viscosity and chemical diffusion) and various thermodynamic and structural functions. Positive deviation from Raoultian behaviour has been observed in the computed mixing parameters of the alloys. Our results are in good agreement with experimental data and support a weak demixing tendency in Cd–Pb liquid alloys.

Extensive calculations of energy levels and radiative data such as transition wavelengths, radiative rates, oscillator strengths, and line strengths for electric dipole (E1) transitions have been performed for Se XXIV using the multiconfiguration Dirac–Fock method. For other types of transitions, namely, magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2), only the radiative rates (A) are listed. The importance and effect of valence-valence and core-valence correlations on the excitation energies have been studied. For additional accuracy assessments, analogous calculations have been carried out by employing the flexible atomic code and configuration interaction technique. Comparisons are made with the available experimental and theoretical data in the literature. Close agreement has been found ensuring the accuracy and reliability of our results. The effect of plasma temperature on the line intensity ratio, electron density, plasma frequency, and skin depth has been analyzed for hot dense plasma (HDP) in local thermodynamic equilibrium. The present work might be beneficial in the modeling and characterization of HDP.Extensive calculations of energy levels and radiative data such as transition wavelengths, radiative rates, oscillator strengths, and line strengths for electric dipole (E1) transitions have been performed for Se XXIV using the multiconfiguration Dirac–Fock method. For other types of transitions, namely, magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2), only the radiative rates (A) are listed. The importance and effect of valence-valence and core-valence correlations on the excitation energies have been studied. For additional accuracy assessments, analogous calculations have been carried out by employing the flexible atomic code and configuration interaction technique. Comparisons are made with the available experimental and theoretical data in the literature. Close agreement has been found ensuring the accuracy and reliability of our results. The effect of plasma temperature on the line intensity ratio, electron density, plasma frequency, and skin depth has been analyzed for ...

The deviation from ideal mixture behavior and concentration dependent symmetry in the microscopic and surface properties of K-Na liquid alloy is investigated within a simple statistical model. The concentration dependent of microscopic functions(concentration fluctuation in the long wavelength limit, Warren-Cowley short range order parameter) and surface properties(surface concentration and surface tension) has got special attention to show a tendency of like atom pairing in the mixture. The theoretical analysis reveals that energy parameter is temperature dependent, K-Na alloys is of weakly interacting system and K-atoms segregates on the surface of K-Na liquid alloys at bulk concentration of Na.The Himalayan Physics Vol. 4, No. 4, 2013 Page: 40-45 Uploaded date: 12/23/2013

Thermodynamic, transport and surface properties of liquid In–Pb alloys have been investigated using the simple statistical model. The free energy of mixing, heat of mixing, entropy of mixing and activity of components of liquid alloys In–Pb at 637 K have been computed. The microscopic function, concentration–concentration fluctuations in long wavelength limit have been studied to investigate the stability and microscopic structural information about liquid alloys and chemical short range order parameter has been calculated to quantify the degree of atomic order. The same energy parameters have been used to compute diffusion coefficients ratio, viscosity, surface tension and surface concentration of liquid In–Pb alloys. The study reveals that liquid In–Pb alloy is weakly interacting and phase separating system.

The mixing behaviour of liquid cadmium–indium alloys has been analysed on the basis of quasi-chemical approximation by computing thermodynamic parameters, such as free energy of mixing (G M), entropy of mixing (S M), heat of mixing (H M) and chemical activities (a i) and structural functions, such as concentration fluctuation in the long wavelength limit (S cc(0)), the Warren–Cowley short-range order parameter (α 1) and the ratio of diffusion coefficients (D m/D id) of the alloys at 800 K. The analysis suggests that there is a tendency of like atom pairing (Cd–Cd, In–In) in Cd–In alloy over entire concentrations and ordering energy is found to be temperature dependent. Cd–In alloy at 800 K in the molten state is slightly segregating in nature.

The mixing behaviour of cadmium–zinc binary liquid alloys have been examined by computing thermodynamic properties, such as free energy of mixing (GM), heat of mixing (HM), entropy of mixing (SM), activity (ai) and microscopic functions, such as concentration fluctuations in long wavelength limit (Scc(0)), Warren–Cowley short range order parameter (α1) and ratio of diffusion coefficients of the alloys at 800 K using statistical model in the framework of quasi-chemical approximation. Surface properties have also been analysed using four different approaches. The theoretical study reveals that the ordering energy parameters are temperature dependent and all the observed thermodynamic parameters are in reasonable agreement with the observed values. The Cd–Zn liquid alloys at 800 K represent a segregating system with segregation of Cd-atoms at the surface. The values of surface tension obtained from different approaches have been found to be comparable with each other.

In the present work we have considered two alkali metals - sodium and potassium - at their molten stage near the melting point. For the purpose of this theoretical investigation we have used Harrison’s first principle (HFP) pseudopotential technique which is basically an orthogonalised plane wave method. The electrical resistivity has been computed through Ziman’s formula. Then the electrical conductivity of the present metals is found out just by taking the reciprocal of the values so obtained. Our computed results have been compared with the experimental data and a good agreement is obtained. A study of the existing literature reveals that the work with the magnetic property like Knight shift of metals is scarce. This has encouraged us to apply the said HFP technique to study the Knight shift of the present alkali metals. For this purpose we have used Knight’s formula. Our computed values of Knight shift are in reasonable agreement for the metals under investigation. DOI: http://dx.doi.org/10.3126/bibechana.v9i0.7181BIBECHANA 9 (2013) 92-95

We have studied the microscopic structure such as, concentration fluctuation in long wavelength limit (SCC(0)), Warren–Cowely short range order parameter (α 1), ratio of mutual and intrinsic diffusion coefficients (D M/D id) of molten Al–Si alloy at 1700 K using a statistical model of complex formation on the basis of quasi-lattice theory for weakly interacting systems. The approach used in this article reveals that molten Al–Si alloy at 1700 K is a weakly interacting heterocoordinating system and the alloy is more ordered in the Al-rich end.

Hydrogenated silicon films ranging from pure amorphous to those containing small crystallites in large crystalline fraction are prepared using the HWCVD technique without using any hydrogen dilution which is supposed to be necessary for the deposition of nanocrystalline Si films. The only parameter that is varied is Silane flow rate. The deposition rate ranges from 6–27 A/s. The band gap of the films (1.8–2.0 eV) is high compared to the regular films, which is attributed to the improved short and medium range order as well as the presence of low density amorphous tissues in the grain boundary regions. The films show improved stability under long term light exposure due to more ordered structure and presence of hydrogen mostly as strong Si―H bonds.

The thermodynamic properties such as, free energy of mixing ( G M ), heat of mixing ( H M ), entropy of mixing ( S M ) and microscopic properties such as, concentration fluctuation in long wavelength limit ( S CC (0)), Warren–Cowely short range ordering parameter (α 1 ), ratio of mutual and intrinsic diffusion coefficients ( D M / D id ) of two Cd-based liquid alloys have been studied by using two different models. The properties of Cd–Hg liquid alloy at 600 K have been studied on the basis of regular solution model, and the properties of Cd–Na liquid alloy at 673 K have been studied on the basis of quasi-chemical expression for weakly interacting system.

The alloying behaviour of Na–Sn liquid alloys at 773K has been studied by using regular associated solution model. This model has been utilized to determine the complex concentration in a regular associated solution of Na and Sn. We have then used the complex concentration to calculate the free energy of mixing (GM), enthalpy of mixing (HM), entropy of mixing (SM), concentration fluctuations in long wavelength limit (SCC(0)), the Warren Crowley short-range parameter (α1) and ratio of mutual and intrinsic diffusion coefficients (DM/Did). The analysis suggests that heterocoordination leading to the formation of complex Na3Sn is likely to exist in the liquid and is of a strongly interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend considerably on temperature and the alloys are more ordered towards intermediate region.

The mixing behaviour of two Na-based alloys has been studied in their liquid states. We have calculated free energy of mixing, activity, concentration fluctuation in long-wavelength limit and chemical short-range ordering parameter for the InNa alloy at 713 K and for the NaPb alloy at 700 K. This analysis shows that both the alloys show heterocoordinating interaction systems in liquid state.

The quasi-lattice model has been used to study the concentration dependant thermodynamic properties and microscopic structure of Fe–Si alloys in molten state. We have determined the free energy of mixing, excess entropy of mixing, the concentration–concentration structure factor in long wavelength limit [ S CC (0)] and the Warren–Cowley short range order parameter ( α 1 ) of Fe–Si liquid alloy at 1873 K. The observed asymmetry in the properties of mixing of Fe–Si alloy in molten state is successfully explained on the basis of the quasi-lattice model. The analysis suggests that the Fe 2 Si complexes are most likely to exist in the liquid state and are strongly interacting in nature. The theoretical analysis suggests that the pairwise interaction energies between the species depend considerably on temperature and the alloy is more ordered towards Fe rich region.

We have studied the thermodynamic properties and microscopic structures of HgNa liquid alloy at 673 K on the basis of regular associated solution model. The concentrations of ApB type complex in a regular associated solution of Hg and Na have been determined. We have then used the concentration of complex to calculate the free energy of mixing, enthalpy of mixing, entropy of mixing, activity, concentration fluctuations in long wavelength limit S CC (0) and the Warren–Cowley short-range parameter α 1 . The analysis suggests that heterocoordination leading to the formation of complex Hg 4 Na is likely to exist in the liquid and is of a strongly interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend considerably on temperature and the alloy is more ordered towards Hg-rich region.

The thermodynamic and microscopic structure of Ag–Al liquid alloy at 1273 K has been studied by using regular associated solution model. This model has been utilised to determine the complex concentration in a regular associated solution of Ag and Al. We have then used the complex concentration to calculate the free energy of mixing, enthalpy of mixing, entropy of mixing, activity and concentration fluctuations in long wavelength limit S CC(0) and the Warren–Cowley short-range parameter α 1. The analysis suggests that heterocoordination leading to the formation of complex Ag3Al is likely to exist in the liquid but is of a weakly interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend considerably on temperature and the alloy is more ordered towards Ag-rich region. The alloy behaves like a segregating system in Al-rich region.

The thermodynamic and microscopic structure of Cd – Na liquid alloy at 673 K has been studied by using regular associated solution model. This model has been utilized to determine the concentration of the complexes Cd 2 Na in Cd – Na alloys in molten state at 673 K. The concentration of the complexes is then used to find free energy of mixing, heat of mixing, entropy of mixing, activity, concentration fluctuations in long wavelength limit S cc (0) and the Warren Cowley short-range parameter α 1 . The analysis suggests that this alloy is of a weakly interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend considerably on temperature and the alloy is more ordered in Cd -rich region. The alloy behaves like a segregating system in Na -rich region. The observed asymmetry in the properties of mixing of Cd – Na alloy in molten state is successfully explained by assuming Cd 2 Na complex on the basis of regular associated solution model.

The regular associated solution model has been used to estimate the concentration of Ag3Sb type clusters in AgSb liquid alloys at 1250 K. The equilibrium constant for the dissociation of clusters and pairwire interaction energies between unassociated atoms and clusters have been evaluated using the concentrations of clusters. These enable estimation of thermodynamic and microscopic properties of the alloys at any desired concentration. The analysis suggests that the alloy is more ordered in Ag-rich region. The alloy behaves like a segregating system in Sb-rich end.

The thermodynamic properties and microscopic structure of liquid Fe–Si alloys at 1873 K were studied by using the regular associated solution model. The model was utilized to determine the complex concentration in a regular associated solution of Fe, Si and Fe2Si. The complex concentration was then used to calculate the integral excess free energy of mixing, activity, concentration fluctuations in the long-wavelength limit, SCC (0), and the Warren–Cowley short-range parameter α 1. The analysis suggests that heterocoordination leading to the formation of complex Fe2Si is likely to exist in the liquid and is of a strongly interacting nature. The theoretical analysis reveals that the alloy is more ordered towards the Fe-rich region. The observed asymmetry in the properties of mixing of Fe–Si alloys in the molten state is successfully explained on the basis of the regular associated solution model.

The observed asymmetry in the properties of mixing of Cu–Sn alloy in molten state is successfully explained on the basis of regular associated solution model. We have determined the free energy of mixing, heat of mixing, entropy of mixing, activity, concentration fluctuations in long wavelength limit SCC(0) and the Warren Crowley short-range parameter α1 of Cu–Sn alloys in molten state at 1400 K. The analysis suggests that heterocoordination leading to the formation of complex Cu3Sn is likely to exist in the liquid but is of a weakly interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend considerably on temperature and the alloy is more ordered towards Cu-rich region. Most of the thermodynamic parameters are found to be in good agreement with experimental values.

Thin films of hydrogenated silicon with band gap ranging from 2.0-2.34 eV are prepared at deposition rate 8-14 A/sec in an indigenously fabricated HWCVD system keeping all parameters except substrate temperature fixed. The films grown at Ts ≤ 150 °C are found to be pure amorphous, whereas the formation of nanocrystalline phase starts at Ts ≥ 200 °C. With increase in Ts, crystalline fraction increases along with the increase in the band gap whereas the hydrogen content in the films and the deposition rate decreases. The variation of microstructure by varying substrate temperature without a significant decrease in deposition rate is useful for various device applications. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Semi-relativistic calculations are carried out for the photoionization of neutral argon from its ground state 3s23p61S0 and the lowest three excited levels 3s23p5(2P0)4s3P02, 3s23p5(2P0)4s 3P01 and 3s23p5(2P0)4s 3P00, using the semi-relativistic Breit–Pauli approximation. Configuration interaction (CI) wavefunctions are used to represent the lowest 12 target states of the Ar II ion retained in the R-matrix expansion. The Rydberg series 3s3p6 2S1/2{np[1/2]1, np[3/2]1}, J=1° of autoionizing resonances formed in the photoionization process of ground state 3s23p61S0, just below 3s3p6 2S1/2 threshold of Ar II, are identified and their resonance positions and effective quantum numbers are reported. Excellent agreement with previously published resonance positions and effective quantum numbers is observed. Further, new results for photoionization cross-sections from excited states of Ar, involving clusters of Feshbach resonances converging to different thresholds of Ar II, are predicted.

Large-scale configuration interaction (CI) calculations are performed to evaluate the energy levels, oscillator strengths and transition probabilities for all the transitions in Co XI from ground-state level to those of 3s3p6, 3s23p43d, 3s23p44s and 3s23p44d states in LSJ coupling scheme. Lifetimes of the 3s3p6 and 3s23p43d levels are also determined. The calculations include the major correlation effects. We attempt to correct the inaccuracies in the CI coefficients in the wavefunctions, which would lead to inaccuracy in transition probabilities by applying a 'fine-tuning' technique. The relativistic effects are incorporated by adding mass correction, Darwin term and spin–orbit interaction terms to the non-relativistic Hamiltonian in the Breit–Pauli approximations. The calculated energy levels are in close agreement with the NIST results. We have predicted many new spectral lines, which are to be experimentally observed in the future.

Basic requirements of any agricultural implements are the desired combination of hardness and wear resistance properties. Heat treatment plays an important role in order to achieve these mechanical properties. Conventionally high carbon (∼0.70C) steel hardened by oil quenching (38–45 HRC) is being used but in desert areas and places having black soil higher hardness (45–52 HRC) is required. So for these applications medium carbon (∼0.30C) steels with microadditions of chromium or boron had been used. Present investigation characterized the mechanism of wear for these three experimental grades of steel. Preferred microstructures of the steel had been determined and the influence of surface hardness and other mechanical properties had been considered for their possible applications in the agricultural sector like tillage discs, soil-engaging components, etc. Predictions of the volume loss during progressive wear for any particular linear distance travelled was compared with the actual obtained by experiments. This in turn assessed the metallurgical life cycle of the agricultural implements made by particular grade of steel in desired soil conditions.

Anisotropy and the wave-vector dependence of the energy gap function determine many important properties of a superconductor. Starting from first principles, we present here a complete analysis of possible symmetries of the superconducting gap function E{sub g}({bold k}) at the Fermi surface in high-T{sub c} layered superconductors with either a simple orthorhombic or a tetragonal unit cell. This is done within the framework of Gorkov{close_quote}s mean-field theory of superconductivity in the so-called {open_quotes}layer representation{close_quotes} introduced by us earlier. For N conducting cuprate layers, J=1,2,{hor_ellipsis},N, in each unit cell, the spin-singlet order parameters {Delta}{sub JJ}({bold k}) can be expanded in terms of possible basis functions of all the irreducible representations relevant to layered crystals, which are obtained here. In layered materials, the symmetry is restricted to the translational lattice periodicity in the direction perpendicular to the layers and the residual point group and translational symmetries for the two-dimensional unit cell in each layer of the three-dimensional unit cell. We derive an exact general relation to determine different branches of the energy gap function E{sub g}({bold k}) at the Fermi surface in terms of {Delta}{sub JJ}({bold k}), which include both intralayer and interlayer order parameters. For N=2, we also obtain an exactmore » expression for quasiparticle energies E{sub p}({bold k}), p=1,2, in the superconducting state in the presence of intralayer and complex interlayer order parameters as well as complex tunneling matrix elements between the two layers in the unit cell, which need not be equivalent. The form of the possible basis functions are also listed in terms of cylindrical coordinates k{sub t},{phi},k{sub z} to take advantage of the orthogonality of functions with respect to {phi} integrations. (Abstract Truncated)« less

The wave-vector dependence of superconducting order parameters and the corresponding transition temperature in three-dimensional layered metals are investigated. It includes planar anisotropic {ital s}-wave-like as well as {ital d}-wave-like pairing contributions, but for simplicity only intralayer pairing of electrons has been considered for tetragonal and orthorhombic crystal structures, relevant to high-{ital T}{sub {ital c}} materials. It is shown that for the orthorhombic case order parameters are likely to have mixed symmetry, whereas in tetragonal structures it is possible to have only planar {ital d}-wave-like symmetry with a possible correction term with an additional wave-vector dependence in the direction perpendicular to the reciprocal layer plane. {copyright} {ital 1996 The American Physical Society.}

SrxCa1−xCu0.9957Fe0.01O2 was studied forx=0.13, 0.15, and 0.17. Mossbauer spectroscopy and magnetization measurements indicate magnetic ordering characteristic of spin glass systems withTf∼70K forx=0.15 and 0.13.

Mossbauer studies are reported on YBa2(Cu1-xFex)3O7- delta samples with x=0.02, 0.05, 0.15, and 0.25. Samples are studied in the untreated, fully oxygenated state, as O is progressively removed by vacuum annealing at 400, 500, 600, 700, and 800 degrees C, and after vacuum annealed samples are reoxygenated at low temperature. By following the sites as O is progressively removed at increasing annealing temperatures, we conclude that there is no evidence that Fe substitutes on Cu(2) sites. We interpret our results in terms of models based on neutron diffraction and recent EXAFS experiments. The general tendency at high annealing temperatures is to create sites with smaller quadrupole splittings, which are therefore more symmetric with respect to O coordination, at the expense of sites with less symmetric coordinations. We attribute this to clustering of the Fe atoms, and the increased coordination this creates. Observed magnetic sites are also attributed to clustering. Low-temperature reoxygenation of high-temperature-vacuum-annealed samples restores the original doublets, but with a higher population of symmetric sites, as has been reported in other studies. We conclude that this is evidence of the stability of the clusters to low-temperature reoxygenation. The present results and interpretation lead to consistency between Mossbauer and EXAFS. They also eliminate the problem created by the interpretation of previous Mossbauer experiments where thermal treatment resulted in a large population of Fe in Cu(2) sites without a deterioration in the superconducting transition temperature.

The large deviation from the ideal mixture behaviour and the concentration-dependent asymmetry in the thermodynamic properties of Mg-Sn liquid alloys is investigated within a simple theoretical model of heterocoordination (i.e. a model in which there is a preference for unlike atoms to be paired as nearest neighbours). This has been utilized to extract additional microscopic information such as concentration fluctuations and the chemical short-range order parameter. The analysis suggests that heterocoordination leading to the formation of chemical complexes Mg2Sn is likely to exist in the melt but is only of a weakly interacting nature. The interaction energies between the species of the melt are found to depend considerably on temperature and the alloy is chemically more ordered towards the Mg-rich end of the phase diagram.