K. C. Singh

Topological aspects of the thermodynamics of binary mixtures of non-electrolytes

Abstract An approach based on the “graph” theory has been evolved to predict molar excess enthalpies, HE, and molar excess volumes, VE, for a number of binary mixtures of non-electrolytes. The calculated HE and VE values compare reasonably well with their corresponding experimental values. The limitations of this approach have also been discussed.

Topological aspect of the excess enthalpies of binary mixtures of non-electrolytes

Abstract An approach based on the graph theory has been evolved to predict molar excess enthalpies. H E of binary mixtures of non-electrolytes. The calculated H E values compare reasonably well with the corresponding experimental values. The approach has also been successful in predicting H E data for binary mixtures at other temperatures from H E data at two mole fractions at one temperature only.

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.

Thermodynamics of aniline + toluene mixtures

Abstract Heats of mixing, HE, of aniline + toluene at 298.15 and 308.15 K and that of aniline + cyclohexane at 308.15 K have been measured over the entire composition range. The excess Gibbs free energies of mixing, GE, for aniline + cyclohexane mixtures at 308.15 K have been obtained from the measured vapour pressure data. The HE and GE values are positive throughout the entire aniline concentration range and HE >GE. The results have been analysed in terms of the Barker and ideal associated model theory of non-electrolyte solutions. It has been observed that the ideal associated model approach which assumes the presence of AB, AB2, A2B2 and B molecular species describes well (within ±40 J mole−1 at the worst) the general dependence of HE on xB (mole fraction of aniline) over the whole composition range for aniline + toluene mixtures. The equilibrium constants for the various association reactions, along with the enthalpies of formation of various molecular species have also been calculated.

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 .

Speeds of Sound and Excess Isentropic Compressibilities of Butyl Acetate＋Aromatic Hydrocarbons

Abstract Speed of sound data for butyl acetate+benzene, or toluene, or o -xylene, or m -xylene, or p -xylene binary mixtures have been measured over the entire range of mole fraction at 308.15 K. The excess isentropic compressibilities (K E S ) were computed from speed of sound and density data, derived from molar excess volume data. The K E S values were analyzed by using graph theoretical approach. The K E S values evaluated by graph theory compared reasonably well with their corresponding experimental values. The K E S data were also expressed in terms of Redlich-Kister polynomial equation to derive the coefficients and the standard deviation.

Molar excess free energy of mixing of 1-propanol or 2-propanol with cyclohexane at 298.15 and 308.15 K in terms of association model with a Flory contribution term

Excess molar Gibbs free energies of mixing for 1-propanol or 2-propanol + cyclohexane over the whole composition range at 298.15 and 308.15 K have been calculated from vapour pressure data measured by static method. The data have been analysed in terms of a Mecke-Kempter association model with a Flory contribution term.

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.