K.C. Kalra

Anodic oxidation of tantalum in aqueous electrolytes

Abstract The formation and breakdown characteristics of anodic oxide films grown on tantalum, their dielectric properties and the effects of heating such films have been studied. The behaviour of such films formed in the presence of UV radiation is also reported. Steady state kinetic data obtained at different temperatures and current densities indicate a temperature-independent Tafel slope which rules out the applicability of the single-barrier theory of Cabrera and Mott. The data have been analysed in terms of Dignams equation. There is an appreciable (27%–37%) contribution of the quadratic term. The effects of temperature, current density and composition of the electrolytes on various parameters of Dignams equation have been examined. Single-barrier theories of ionic conduction do not explain the data satisfactorily.

Electrical breakdown of anodic films on titanium in aqueous electrolytes

Abstract Breakdown voltages and electronic current data (at constant voltage) for anodic titanium oxide films in contact with aqueous electrolytes of varying concentrations and compositions have been obtained at 308 K. Both breakdown voltage and electronic current depend on electrolyte concentration, resistivity and composition. A linear relation between breakdown voltage and logarithm of electronic current has been observed. The effect of electrolyte concentration, composition and resistivity on breakdown voltage has been discussed in terms of the Ikonopisov electron avalanche breakdown model and the theory of Di Quarto and coworkers. The major factor contributing to the decrease in breakdown voltage with increasing electrolyte concentration is the increasing primary electronic current j0.

Excess molar gibbs free energies of (1,2-dibromoethane+an aromatic hydrocarbon) at 308.15 K

Abstract Excess molar Gibbs free energies GmE for (1,2-dibromoethane + benzene or toluene or o-xylene or m-xylene or p-xylene) for the whole range of composition have been measured experimentally at 308.15 K from their measured vapour pressures. The values of GmE for these mixtures suggest the existence of weak specific interactions of electron donor-acceptor type in which the aromatic hydrocarbons behave as electron donors. The values of GmE have also been computed from the theory of Flory and his colleagues as well as from the theory of Sanchez and Lacombe; neither of these theories is able to predict the sign or magnitude of GmE.

Excess volumes of mixing and excess enthalpies of mixing of 1,2-dibromoethane with aromatic hydrocarbons at 298.15 K

Abstract The excess volumes and enthalpies of mixing of binary mixtures of 1,2-dibromoethane with benzene, toluene, o -xylene, m -xylene and p -xylene have been measured experimentally over the whole composition range at 298.15 K. Qualitatively, the data have been explained on the basis of electron donor/acceptor interactions between 1,2-dibromoethane and the aromatic hydrocarbons and also on the basis of the loss of favourable orientational order of the pure components. The Flory theory is not able to correctly predict the V E and H E values of the studied systems. However, the Sanchez and Lacombe theory correctly predicts the change of sign of the H E values with change of mole fraction. H E calculated by this theory is of the same order as the experimental H E The calculated values for V E are in poor agreement with the corresponding experimental values for V E .

Excess molar volumes and excess molar enthalpies of (1,2-dibromoethane + tetrachloromethane or cyclohexane)

Abstract Excess molar volumes V m E and excess molar enthalpies H m E for (1,2-dibromoethane + tetrachloromethane or cyclohexane) for the whole range of composition have been measured experimentally at 298.15 K. The values of V m E and H m E have also been computed from the theory of Flory and his colleagues which predicts the sign correctly and the magnitude of V m E or H m E reasonably well. The experimental values of V m E for these mixtures have also been obtained at 308.15 K.

Electrical breakdown and electronic current of tantalum-tantalum oxide-aqueous electrolyte systems

Abstract Breakdown voltage and electronic current data for barrier anodic tantalum oxide films in contact with aqueous electrolytes of various concentrations and compositions at 298 K have been obtained. The influence of electrolyte concentration on breakdown characteristics can be broadly explained in terms of the Ikonopisov electron avalanche breakdown model. Albella and coworkers theory explains the effect of electrolyte concentration for our results more explicitly. Various parameters of the Albella theory have been evaluated, and their dependence on electrolyte concentration has been studied. The dependence of breakdown voltage on electrolyte concentration has also been discussed in the light of the theory of Di Quarto and coworkers.

Thermodynamics of ethyl iodide + benzene mixtures

Abstract The values of the excess Gibbs free energy of mixing G E for ethyl iodide + benzene and ethyl iodide + cyclohexane at 298.15 K have been obtained from the measured vapour pressure data. Heats of mixing H E of ethyl iodide + cyclohexane at 298.15 K have been measured over the entire composition range. The H E and G E values for ethyl iodide + benzene are positive throughout the ethyl iodide concentration range, and H E > G E . The results have been analysed in terms of the Flory, Sanchez and Lacombe and the ideal associated solution model theory of non-electrolyte solutions. It has been observed that the ideal associated model approach, which assumes the presence of AB and A 2 B molecular species, describes well (within ±10 J mol −1 at the worst) the general dependence of H E on X A (mole fraction of ethyl iodide) over the whole composition range for ethyl iodide + benzene mixtures. The equilibrium constants for A + B ⇌ AB and 2A + B ⇌ A 2 B reactions, along with the enthalpies of formation of AB and A 2 B molecular species, have also been calculated.

Excess volume of mixing and excess enthalpies of mixing of ethyl iodide + aromatic hydrocarbons at 25° C

The excess volumes and enthalpies of mixing of binary mixtures of ethyl iodide with benzene, toluene, o-xylene, m-xylene and p-xylene have been measured experimentally over the whole composition range at 25°C. Qualitatively the data have been explained on the basis of electron donoracceptor interactions between the ethyl iodide and aromatic hydrocarbons and also on the loss of favorable orientational order of the pure components. Florys theory correctly predicts the sign and to some extent magnitude of the VE and HE values.

Ionic conduction in anodic oxide films on titanium in mixed solutions of aqueous electrolytes and diethylene glycol

Abstract Steady state kinetic data have been obtained for anodic growth of films on titanium in mixed solution (1:1 by volume) of 100 mol m −3 aqueous orthophosphoric acid with diethylene glycol (DEG), 100 mol m −3 aqueous sodium dihydrogen orthophosphate with DEG and 100 mol m −3 aqueous disodium hydrogen orthophosphate with DEG at different temperatures and current densities. The constant A in the Guntherschulze and Betz equation is temperature dependent while B is temperature independent. The constant A also depends on the nature of the electrolyte. The data indicate a temperature-independent Tafel slope which rules out the applicability of the single-barrier theory of Cabera and Mott. The data have been analysed in terms of Dignams equation. The effects of current density, temperature and composition of electrolyte on various parameters of Dignams equation have been examined.

Thermodynamics of molecular interactions in 1,2-dibromoethane + benzene or toluene mixtures

Abstract Kalra K.C., Singh K.C. and Spah, D.C., 1991. Thermodynamics of molecular interactions in 1,2-dibromoethane + benzene or toluene mixtures. Fluid Phase Equilibria , 66: 211-220. The excess Gibbs free energy of mixing data for 1,2-dibromoethane + benzene and 1,2-dibromoethane + toluene mixtures over the whole concentration range at 298.15 K have been obtained from their vapour pressure data. The results have been analysed in terms of the Flory theory and the ideal associated model approach. The ideal associated model which assumes the presence of 12-type molecular species explains reasonably well the dependence of the excess enthalpy of these systems on the mole fractions of the components. The equilibrium constant for the reaction 1 + 2 ⇌ 12, along with the enthalpy of formation of 12 molecular species, have also been calculated.