Nanoindentation studies in NiTi films deposited on Si wafer

Nanoindentation tests were carried out at different locations in a Ti rich NiTi film deposited on a 3 `' silicon wafer by dc magnetron sputtering. The purpose of doing nanoindentation at different locations was to check the uniformity of the sample with respect to its mechanical behaviour and shape memory effect. The results showed that elastic modulus and hardness measured by nanoindentation was similar at different locations in the 3 `' wafer. Nanoindcntation coupled with depth profiling of residual indents using AFM also showed that the extent of shape memory recovery obtained by heating the film above its martensite to austcnite phase transformation temperature was also similar at different locations in the 3 `' wafer. However, the measured recovery ratio was lower than that predicted from theoretical calculations for indents made using Berkovich indenter. The results showed that the deposition process resulted in a NiTi film with uniform composition, mechanical properties and shape memory behaviour.

Ab initio studies of solvent effect on conformational equilibria and vibrational spectra of dipropionamide

Systematic ab initio molecular orbital studies of the conformational equilibria and vibrational spectra of dipropionamide using the basis sets 6-31g(d) and 6-31++G(d,p) have been carried out. The vibrational spectra of dipropionamide have been satisfactorily interpreted taking into account the agreement between the calculated frequencies, infrared and Raman band intensities and the shifts in the spectra of deuterated molecules with those observed. The previous assignments of most of the vibrational bands are well confirmed, a few bands need reassignment, however. The solvent effects were investigated by self-consistent reaction field theory using dipole and self-consistent isodensity polarized continuum model methods. The introduction of a dielectric medium has only a marginal effect on the conformational equilibria and vibrational spectra. However, the calculated changes in geometry and vibrational spectra on going from the gas phase to the solution phase are in accord with the increasing weight of the dipolar resonance structure in polar solvents. (C) 2002 Elsevier Science B.V. All rights reserved.

Electrocatalytic efficiency of polyaniline by cyclic voltammetry and electrochemical impedance spectroscopy studies

Electrochemical redox reactions of ferrous/ferric (Fe2+/Fe3+) and hydroquinone/quinone (H(2)Q/Q) were studied on Pt and polyaniline (PANI)-deposited Pt electrodes in 0.5 M H2SO4-supporting electrolyte by cyclic voltammetry and ac impedance spectroscopy. A comparison of the experimental data obtained with the Pt and PANI/Pt electrodes suggested that the reactions were catalyzed by the PANI. Based on a relative increase in peak currents of cyclic voltammograms, catalytic efficiency (gamma(cv)) of the PANI was defined. There was an increase in gamma(cv) with an increase of scan rate and a decrease of concentration of Fe2+/Fe3+ or H(2)Q. The complex plane impedance spectrum of the electrode consisted of a semicircle in high frequency range and a linear spike in low frequency range. The exchange current density (i(0)) calculated using the semicircle part of the impedance showed Butler-Volmer kinetics with respect to concentration dependence. From a relative increase of i(0) on the PANI/Pt electrode, catalytic efficiency (gamma(eis)) was evaluated. (C) 2002 Elsevier Science B.V. All rights reserved.

Hydrolytic degradation and diffusion studies on a polyphosphate ester

A polyphosphate ester was synthesized by interfacial polycondensation of bisphenol-A and phenylphosphorodichloridate. Accelerated hydrolytic degradation studies were conducted under alkaline conditions. The effect of concentration of alkali and temperature were monitored. The rate of degradation reached a maximum value at 6 molar sodium hydroxide solution and then reduced. The activation energy for hydrolytic degradation was found to be 45 kcal/mol. Diffusion of alkali into the polymer pellet was studied at various concentrations of alkali and at various temperatures. The rate of diffusion also attained a maximum at 6M NaOH and the activation energy for diffusion process was found to be 12 kcal/mol. (C) 2002 John Wiley Sons, Inc.

Real-time kinetic analysis of hCG-monoclonal antibody interaction using radiolabeled hCG probe: presence of two forms of Ag-mAb complex as revealed by solid phase dissociation studies

Real-time kinetics of ligand-ligate interaction has predominantly been studied by either fluorescence or surface plasmon resonance based methods. Almost all such studies are based on association between the ligand and the ligate. This paper reports our analysis of dissociation data of monoclonal antibody-antigen (hCG) system using radio-iodinated hCG as a probe and nitrocellulose as a solid support to immobilize mAb. The data was analyzed quantitatively for a one-step and a two-step model. The data fits well into the two-step model. We also found that a fraction of what is bound is non-dissociable (tight-binding portion (TBP)). The TBP was neither an artifact of immobilization nor does it interfere with analysis. It was present when the reaction was carried out in homogeneous solution in liquid phase. The rate constants obtained from the two methods were comparable. The work reported here shows that real-time kinetics of other ligand-ligate interaction can be studied using nitrocellulose as a solid support. (C) 2002 Elsevier Science B.V. All rights reserved.

Solid state structural and solution studies on the formation of a flexible cavity for anions by copper(I) and 1,2-bis(diphenylphosphino)ethane

Copper(l) complexes of 1,2-bis(diphenylphosphino)ethane (dppe) with a stoichiometry Cu-2(dppe)(3)(X)(2) [X- = CN- (1), SCN- (2), NO3- (3)] are obtained from direct reactions of CuX and dppe. The complexes are structurally and spectroscopically (NMR and IR) characterized. The structure of the [Cu-2(dPPe)(3)](2+) dication is similar to the structural motif observed in many other complexes with a chelating dppe and a bridging dppe connecting two copper centers. In complexes 1 -3, the anions are confined to the cavity formed by the phosphines which force a monodentate coordination mode despite the predominant bidentate/bridging character of the anions. The coordination angles rather than the thermochemical radii dictate the steric requirement of anions. While the solution behavior of 3, with nitrate, is similar to complexes studied earlier, complexes with pseudohalides exhibit new solution behavior. (C) 2002 Elsevier Science Ltd. All rights reserved.

Surface chemical studies on sphalerite and galena using extracellular polysaccharides isolated from Bacillus polymyxa

Adsorption, electrokinetic, microflotation, and flocculation studies have been carried out on sphalerite and galena minerals using extracellular polysaccharides (ECP) isolated from Bacillus polymyxa. The adsorption density of ECP onto galena is found to be higher than that onto sphalerite. The adsorption of ECP onto sphalerite is found to increase from pH 3 to about pH 7, where a maximum is attained, and thereafter continuously decreases. With respect to galena, the adsorption density of ECP steadily increases with increased pH. The addition of ECP correspondingly reduces the negative electrophoretic mobilities of sphalerite and galena in absolute magnitude without shifting their isoelectric points. However, the magnitude of the reduction in the electrophoretic mobility values is found to be greater for galena compared to that for sphalerite. Microflotation tests show that galena is depressed while sphalerite is floated using ECP in the entire pH range investigated. Selective flotation tests on a synthetic mixture of galena and sphalerite corroborate that sphalerite could be floated from galena at pH 9-9.5 using ECP as a depressant for galena. Flocculation tests reveal that in the pH range 9-11, sphalerite is dispersed and galena is flocculated in the presence of ECP. Dissolution tests indicate release of the lattice metal ions from galena and sphalerite, while co-precipitation tests confirm chemical interaction between lead or zinc ions and ECP. Fourier transform infrared spectroscopic studies provide evidence in support of hydrogen bonding and chemical interaction for the adsorption of ECP onto galena/sphalerite surfaces. (C) 2002 Elsevier Science (USA).

Thermal degradation studies of para-substituted poly(styrene peroxide)s

The thermal degradation of a series of para-substituted poly(styrene peroxide)s with electron-donating [CH3, C(CH3)(3)] and electron-attracting (Br) substitutents are investigated by thermogravimetric analysis (TGA). The results indicate that the Hammett relationship can describe quantitatively the trends in maximum rate of polymer decomposition (T-max) observed in TGA and thus thermostability of substituted poly(styrene peroxide)s depends only on the electronic nature of substituents and their ability to stabilize macroradicals formed during chain scission. The experimental results are also substantiated by thermochemical calculations. (C) 2002 Elsevier Science Ltd. All rights reserved.

Thermodynamic studies on NdFeO3(s)

The enthalpy increments and the standard molar Gibbs energy of formation of NdFeO3(s) have been measured using a hightemperature Calvet microcalorimeter and a solid oxide galvanic cell, respectively. A lambda-type transition, related to magnetic order-disorder transformation (antiferromagnetic to paramagnetic), is apparent from the heat capacity data at similar to 687 K. Enthalpy increments, except in the vicinity of transition, can be represented by a polynomial expression: {Hdegrees(m)(T)-Hdegrees(m) (298.15 K)} /J(.)mol(-1) (+/- 0.7%)=-53625.6+146.0(T/K) +1.150 X 10(-4)(T/K)(2) +3.007 x 10(6)(T/K)(-1); (298.15 less than or equal to T/K less than or equal to 1000). The heat capacity, the first differential of {Hdegrees(m)(T)-Hdegrees(m)(298.15 K)}with respect to temperature, is given by Cdegrees(pm)/J(.)K(-1.)mol(-1)=146.0+ 2.30x10(-4) (T/K) - 3.007 X 10(6)(T/K)(-2). The reversible emf's of the cell, (-) Pt/{NdFeO3(s) +Nd2O3(s)+Fe(s)}//YDT/CSZ// Fe(s)+'FeO'(s)}/Pt(+), were measured in the temperature range from 1004 to 1208 K. It can be represented within experimental error by a linear equation: E/V=(0.1418 +/- 0.0003)-(3.890 +/- 0.023) x 10(-5)(T/K). The Gibbs energy of formation of solid NdFeO, calculated by the least-squares regression analysis of the data obtained in the present study, and data for Fe0.95O and Nd2O3 from the literature, is given by Delta(f)Gdegrees(m)(NdFeO3 s)/kJ (.) mol(-1)( +/- 2.0)=1345.9+0.2542(T/K); (1000 less than or equal to T/K less than or equal to 1650). The error in Delta(f)Gdegrees(m)(NdFeO3, s, T) includes the standard deviation in emf and the uncertainty in the data taken from the literature. Values of Delta(f)Hdegrees(m)(NdFeO3, s, 298.15 K) and Sdegrees(m) (NdFeO3 s, 298.15 K) calculated by the second law method are - 1362.5 (+/-6) kJ (.) mol(-1) and 123.9 (+/-2.5) J (.) K-1 (.) mol(-1), respectively. Based on the thermodynamic information, an oxygen potential diagram for the system Nd-Fe-O was developed at 1350 K. (C) 2002 Elsevier Science (USA).

An economical method for direct numerical simulation studies of transitional round jets

A pseudo-spectral method based on Fourier expansions in a Cartesian coordinate system is shown to be an economical method for direct numerical simulation studies of transitional round jets, Several characteristics of the solutions are presented to establish the validity of the solutions in spite of the unnatural choices. We show that neither periodicity, nor the use of a Cartesian system have adversely affected the simulations, Instead, there are benefits in terms of ease of computing and lack of the usual restrictions due to grid structure near the jet axis. By computing the simultaneous evolution of passive scalers, the process of reaction in round jet burners, between a fuel-laden jet and an ambient oxidizer, was also simulated. Some typical solutions are shown and then the results of analysis of these data are summarized. (C) 2001 Elsevier Science Ltd, All rights reserved.

Optical and dielectric studies of gel grown alpha-hopeite single crystal

Single crystals of a-hopeite exhibiting high transparency were grown by single diffusion gel growth technique. Single crystal X-ray diffraction analysis reveals that the crystal belongs to orthorhombic system. The values of several structural and physical parameters have been determined for the grown crystal. The optical absorption study reveals the transparency of the crystal and is noticed in the entire visible region and the cut-off wavelength was found to be 230 nm. The optical band gap found to be at 3.25 eV. The dependence of extinction co-efficient (k) and the refractive index (n) on the wavelength was also shown. The dielectric constant and dielectric loss of the crystal was studied as a function of frequency and temperature. Transport properties of the grown crystal have been studied from the Cole-Cole plot. (C) 2010 Elsevier GmbH. All rights reserved.

Studies on compressive failure features in syntactic foam material

Syntactic foam made by mechanical mixing of glass hollow spheres in epoxy resin matrix is characterized for compressive properties in the present study. Volume fraction of hollow spheres in the syntactic foam under investigation is kept at 67.8%. Effect of specimen aspect ratio on failure behavior and stress-strain curve of the material is highlighted. Considerable differences are noted in the macroscopic fracture features of the specimen and the stress-strain curve with the variation in specimen aspect ratio, although compressive yield strength values were within a narrow range. Post compression test scanning electron microscopic observations coupled with the macroscopic observations taken during the test helped in explaining the deviation in specimen behavior and in gathering support for the proposed arguments.

Synthesis, structural characterization, thermal studies and chain dynamics of poly(methacrylonitrile peroxide) by NMR spectroscopy

Poly(methacrylonitrile peroxide) (PMNP) has been synthesized from methacrylonitrile by free radical initiated oxidative polymerization and characterized by different spectroscopic methods. NMR spectroscopy confirmed the alternating copolymer structure with labile peroxy bonds in the main chain. The extreme instability of PMNP was noted from FTIR spectroscopy. Thermal degradation studies by using differential scanning calorimetry and thermogravimetry have revealed that PMNP degrades highly exothermically and the heat of degradation, 42.5 kcal mol−1, is of the same order as that reported for other vinyl polyperoxides. Mass spectral fragmentation pattern under electron impact (EI) condition has also been investigated. The mechanism of the primary exothermic degradation has been substantiated by thermochemical calculations. The chain dynamics of the polyperoxide chain has been studied by means of 13C spin–lattice relaxation times (T1) of the main chain as well as the side chain carbons. The temperature dependence of the spin–lattice relaxation times shows that the PMNP is more flexible compared to the analogous poly(styrene peroxide).

Development and studies on microstrip detector

We report development of gas microstrip detectors using thin film and lithography techniques. The detectors were tested for their performance for X-rays (5.9 keV) and a maximum gas gain of similar to 13,000 and best resolution of similar to 12% was obtained. Factors affecting gain and resolution were investigated. The detectors were tested for their one-dimensional position sensitivity. Meandering resistive strips were used for charge division method. A position resolution of 0.48 mm was obtained.

Electrical switching studies on AS(40)Te(60-x)Se(x) and As35Te65-xSex glasses

The I-V characteristics of bulk As40Te60-xSex and As35Te65-xSex glasses have been studied with a current sweep of 0-18 mA-0, over a wide range of compositions (4 less than or equal to x less than or equal to 22). All the glasses studied showed a threshold electrical switching behaviour. The number of switching cycles withstood by the samples has been found to depend on the ON-state current. It is seen that the switching voltages increase with increase in selenium content. Further, the switching voltages are found to be almost independent of the thickness of the sample (d), in the range 0.18-0.3 mm. Also, the switching voltages and the number of switching cycles withstood by the samples are found to decrease with temperature.