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Excess molar volumnesVijkEand excess molar enthalpiesHijkEof {nitrobenzene (i) + benzene (j) + toluene, or +o-xylene, or +p-xylene (k)} ternary mixtures have been measured as a function of composition dilatometrically and calorimetrically at the temperature 308.15 K. The data obtained have been analysed in terms of the Flory theory. It has been observed that theHijkEvalues predicted by this theory compare reasonably well with the corresponding experimental values. TheVijkEvalues are of the same order and sign, however, the agreement with the predictions is not satisfactory for these ternary mixtures.

Excess molar enthalpies and excess molar volumes at 298.15 and 308.15 K are reported for 1-propanol or 2-propanol with cyclohexane. The analysis in terms of Mecke-Kempter association model with a Flory contribution term and generalized quasi-lattice model by Barker is described.

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.

Heat of mixing data for 1-propanol or 2-propanol with benzene, toluene, o-xylene, m-xylene and p-xylene at 308.15 K have been reported. The analysis in terms of the Mecke-Kempter association model with a Flory contribution term and generalized quasi-lattice model by Barker is described.

Molar excess Gibbs free energy of mixing values for 1-propanol or 2-propanol + benzene, toluene, o- m- or p-xylene at 298.15 K have been calculated by the Barker method from vapour pressure data measured by a static method. The free energies of mixing for these binary systems are also predicted in terms of the Mecke-Kempter type of association model with a Flory contribution term using two interaction parameters. The predicted values agree reasonably well with the experimental values.

Excess heat of mixing data at 298.15 K for 1-propanol or 2-propanol with benzene, toluene, o-xylene, m-xylene or p-xylene have been reported. Analysis in terms of the Mecke-Kempter association model with a Flory contribution term and generalized quasi-lattice model by Barker is described.

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.

The excess volumes for binary mixtures of 1-propanol or 2-propanol + benzene, + toluene, + o-xylene, + m-xylene, and + p-xylene have been measured over the entire range of composition at 298.15 K. The excess volume curves for 1-propanol + toluene, + o-xylene, and + p-xylene systems are sigmoids. For other mixtures, the V[sup E] values are positive over most of the concentration range, but are slightly negative at x[sub 1] > 0.8. The system 2-propanol + benzene is positive over the entire range of composition.

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 Dignam's equation. The effects of current density, temperature and composition of electrolyte on various parameters of Dignam's equation have been examined.

Excess volumes of (propanol or 1-methylethanol + benzene or toluene or o - or m- or p-xylene) over the whole range of composition have been measured dilatometrically at the temperature 308.15 K. The results indicate weak electron donor-acceptor interactions in these mixtures. The shape and size of the aromatic hydrocarbon are responsible for stretching or breaking of hydrogen in the alkanols.

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.

Breakdown voltages and electronic current data (at constant voltage) of anodic tantalum oxide films in contact with aqueous, as well as non-aqueous, electrolytes of varying concentrations and compositions have been obtained at 298 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 injecting avalanche model of electrical breakdown. The values of the parameters for impact ionization coefficient (α) and primary electronic current (j0) have been evaluated. The major factor contributing to the decrease in breakdown voltage with increasing electrolyte concentration is the increasing primary electronic current.

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.

The excess volumes and enthalpies of mixing of binary mixtures of n -butyl chloride with benzene, toluene, o -xylene, m -xylene and p -xylene have been measured experimentally over the whole composition range at 298.15 K. The data have been analysed qualitatively in terms of the specific interactions of electron donor-acceptor type and of the disruption of molecular order in the pure components. Flory's theory correctly predicts the sign and to an acceptable extent the magnitude of the H E values although the agreement for V E values is not good. However, the Graph theory correctly predicts the sign as well as the magnitude of the V E and H E values.

The excess Gibb's free energy of mixing, GE, for ethyl iodide+toluene at 25°C have been obtained from the measured vapor pressuure data. The HE and GE values for ethyl iodide+toluene are positive throughout the ethyl iodide concentration range and GE>HE. The results have been analyzed in terms of Flory and ideal associated model theory of nonelectrolyte solutions. It has been observed that the ideal associated model approach which assumes the presence of AN and A2B molecular species describes well (within±10 J-mol−1 in the worst case) the general dependence of HE on XA (mole fraction of ethyl iodide) over the whole composition range for ethyl iodide+toluene mixtures. The equilibrium constants for A+A⇆ AB and 2A+B⇆A2B reactions along with the enthalpies of formation of AB and A2B molecular species have been calculated.

The values of the excess molar Gibbs free energy of mixing for mixtures of 1,2-di-bromoethane with o -, m - and p -xylene over the whole concentration range at 298.15 K have been obtained from vapour pressure data. The results have been analysed in terms of the Flory theory, the Sanchez and Lacombe theory and the ideal associated model approach. The ideal associated model, which assumes the presence of AB type molecular species, explains reasonably well the dependence of excess enthalpy of these systems on the mole fraction of the components. The equilibrium constant for the reaction A + B ⇌ AB and the enthalpy of formation of AB molecular species have also been calculated.

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.

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 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.

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. Flory's theory correctly predicts the sign and to some extent magnitude of the VE and HE values.

Excess molar Gibbs free energies (GE) and ultrasonic speeds for 1,2-dibromoethane (1) + cyclohexane (2) or tetrachloromethane (2) over the whole composition range have been measured experimentally at 298.15 K. The values of isentropic compressibility (K[sub s]) and excess isentropic compressibility (K[sup E][sub s]) have been evaluated from ultrasonic speeds, and excess Gibbs free energies are calculated for the vapor pressure by using Barker's method.

Excess molar volumes V[sub m][sup E] and excess molar enthalpies H[sub m][sup E][sub m] for quinoline + benzene, toluene, o-xylene, or p-xylene for the whole range of compositions have been measured at 303.15 K. The values of H[sub m][sup E] and V[sub m][sup E] for these mixtures suggest that quinoline is partly self-associated and there is strong interaction (weak hydrogen bonding) between quinoline and aromatic hydrocarbons. The values of V[sub m][sup E] and H[sub m][sup E] have also been computed from the Flory and Abe theory and Sanchez and Lacombe theory as well as from the Graph theory. All the theories correctly predict the sign or magnitude of H[sub m][sup E]. Only the Graph theory is able to predict correctly the sign or magnitude of V[sub m][sup E]; the other theories give a poor estimate of V[sub m][sup E].

Chemistry Department, Maharshi Dayanand University, Rohtak-124 001 Manuscript received 2 July 1996, revised 4 March 1997, accepted 18 March 1997 Heat treatment of the oxide films in air makes them more conducting. This effect depends on the time and temperature. Capacitance of titanium oxide films as well as niobium oxide films increases on annealing. The conductivity patterns before and after beating show similar trends and are of two types, the one associated with high conductance and lower rate of change of capacitance with increase in temperature and the other associated with low conductance and changes capacitance more rapidly with increase in temperature.

Chemistry Department, Maharshi Dayanand University, Rohtak-124 001 Manuscript received 11 May 1993, revised 6 September 1993, accepted 12 October 1993 Kinetics of Growth of Anodic Oxide Films on Titanium in Mixed Solutions of Aqueous Electrolytes and Diethylene Glycol

Chemistry Department, Maharshi Dayanand University, Rohtak-124 001 Manuscript received 7 January 1991, revised 26 February 1992, accepted 6 March 1992 The viscosity data of binary mixtures of 1,2-dibromoethane (DBE) with benzene, \(o\)-, \(m\)- and \(p\)-xylenes have been experimen­tally obtained over the whole composition range at 298.15 K and the interactions existing between the components have been discussed. The excess viscosity data have been utilised io evaluate excess volume functions (VE) and there is a close agreement between the VE values calculated from the viscosity data and those obtained using a dilatometer. The values of excess Gibbs free energy of flow (GE*) have been calculated from the viscosities of the binary mixtures. \(\eta\)E , VE and GE values show the existence of weak specific interactions of electron donor-acceptor type between the components in which aromatic hydrocarbon behaves as electron donor.

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 Dignam's 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 Dignam's equation have been examined. Single-barrier theories of ionic conduction do not explain the data satisfactorily.

Ultrasonic speeds 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 298.15 K and values of the isentropic (κS) and excess isentropic (κSE) compressibilities have been evaluated. The values of κS and ϰSE have also been computed from Flory theory which predicts the sign correctly and the magnitude of κSE reasonably well.

Steady electronic current data through extremely thick films in contact with aqueous electrolytes have been obtained. The effects of field strength, temperature of the bath, composition, concentration and resistivity of the contacting electrolyte have been studied. The data show that the same relation between electronic current and field holds irrespective of the film thickness. The data also indicate a direct relation between electronic current and breakdown voltage. The effect of electrolyte concentration on breakdown voltage can be explained in terms of Ikonopisov's electron injecting avalanche model. The major factor contributing to a decrease of breakdown voltage with an increase in the concentration of the electrolyte has been found to be due to the increase in primary electronic current.

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 .

Department of Chemistry, Maharshi Dayanand University, Rohtak-124 001 Manuscript received 4 April 1989, revised 20 June 1989, accepted 20 July 1989 DC conduction studies have been made on Ta2O5, anodic oxide layers with vacuum deposited Sb, Bi, Ni and Sn contacts. The effect of thickness of Ta2O5, on current has also been studied. Current-voltage characteristics show ohmic conduction in the lower voltage range and space charge limited conductivity for the higher voltage levels. The slopes of the space charge limited log I vs log V characteristics are found to depend on metallic counter-electrode and the values vary from 3.28 to 3.57. The gap-state density N(EF) at the Fermi level was calculated by two alternative methods and the values yielded by different methods compare well.N(EF)has been found to vary inversely with the square of the oxide thickness

Department of Chemistry, Panjab University, Chandigarh. Received March 4, 1971 Charcoals and carbon blacks associated with CO2-complex can catalyse inversion of sucrose and hydrolysis of ethyl acetate. The rate constant of each reaction gives a measure of the H+ ion activity of the carbon used. The dissociation constant obtained from the data has about the same value irrespective of the nature of the carbon used or the type of the reaction studied. This shows that the same group or structure at carbon surface is responsible for surface acidity in charcoals and carbon blacks.