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DTA–TG techniques were applied to study the thermal decomposition and reactivity in intimately mixed powders of barium or strontium carbonate and titanium dioxide. The results showed that the temperature for the thermal decomposition of BaCO3–TiO2 mixtures precedes the decomposition of pure BaCO3 by about 250 °C, whereas the decomposition of SrCO3–TiO2 mixtures precedes the decomposition of pure SrCO3 by about 60 °C. Kinetic analysis of the isothermal data in view of various solid-state reaction models showed that the reaction is best described by the phase boundary models. The effects of 60Co γ irradiation and of doping the metal oxide with Li+ or Cu2+ ions on the thermal decomposition reactions were investigated. Keywords: titanates, thermal decomposition, doping, irradiation effects.

Several mixed ZnO-Al2O3 systems were prepared by the impregnation method and calcined for 5 h at 300, 600 and 1000 ° C. The crystal structure, surface acidity, surface basicity, surface area, catalytic decomposition of H2O2 and the electrical conductivity of the samples prepared were studied. It was found that the decomposition of H2O2 is catalysed by the acidic sites formed on the catalyst surface at composition less than 50 mol% ZnO and by basic sites for oxides having composition higher than 50 mol% ZnO. ZnAl2O4-spinel was found to be formed at temperatures ⩾ 600 ° C and it has a catalytic activity and electrical conductivity lower than each of the pure ZnO and the oxide mixtures. The results obtained were correlated together and discussed.

60Co-gamma radiolysis of 3-iodotyrosine and 3,5-diiodotyrosine in aqueous-ethanol solutions has shown that the chemical effects are mainly determined by the interaction of radicals from the radiolysis of solvent and controlled by the composition of the solution. The influence of varying solvent composition and radiation dose on the amount of iodoamino acid converted and on the yields of the radiolysis products (I2, I–, IO 3 – and H2O2) formed in aerated solutions at room termperature were investigated. The formation of I2 is dependent upon the acidity of the solution and is mainly produced as an after-effect due to the interaction of H2O2 with I– ions, both being radiolysis products. The variation of radiation-chemical yields with the solute and solvent composition, and the probable mechanisms for formation of the radiolysis products are discussed.

The kinetics of the alkaline decarboxylation of trichloroacetate ion in ethanol–water solutions have been studied over the temperature range 35.0 to 70.0 °C. The rate of reaction is first order with respect to the trichloroacetate ion and is independent of the concentration of the hydroxide ion. The reactivity is enhanced by increasing the concentration of ethanol in the water–ethanol solutions and the rate of reaction varies with ethanol addition in a nonlinear manner. The rate of reaction increases with the reciprocal of the dielectric constant of the medium and the plot of log k vs. 1/D is approximately linear for solvent mixtures with less than about 0.7 water mole fraction but is strongly curved towards the pure water end. The activation parameters for the reaction show a regular increase in the solvent composition range 0.3 to 1.0 water mole fraction. The results are discussed in terms of the influence of solvent internal pressure and polarity on reactivity and of the increased amount of hydrogen-bonded structure in the water-rich solutions.

The temperature dependence of the rate of alkaline solvolysis of monochloroacetate ion in water – tert-bulyl alcohol solutions has been determined. The rates of reaction were first order with respect to both the chloroacetate ion and to the total solvoxide ion concentrations. The reactivity is enhanced, first slowly, and then more rapidly, by increasing the concentration of tert-bulyl alcohol in the solvent mixtures. The rate of reaction increases with the reciprocal of the dielectric constant of the medium and the plot of log kvs. 1/D can best be represented by two lines intersecting at a point corresponding to 0.9 water mole fraction. The activation parameters ΔH*and ΔS* for the solvolysis reaction showed a minimum at about 0.9 water mole fraction. The significance of these results from the viewpoint of the electrostatic theory and the changing of solvent structure in such mixtures is discussed.

The chemical effects of cobalt neutron capture recoils produced in mixed crystals of the types K3Co/CN/6-K3Fe/CN/6 and K3Co/CN/6-K3Cr/CN/6 have been investigated. Analysis of the neutron irradiated samples was performed using solvent extraction and making use of a 512-channel analyzer for radioactivity measurements. It was found that the initial cobalt parent retentions vary linearly with parent mol fraction in the mixed crystals. The results are discussed in terms of retention and non-retention reactions in view of a mechanistic model involving metal-and ligand-vacancy exchanges, substitution and transfer reactions.

The Schiff base NN″-phenylenebis (salicylidineimine) H2FSN reacts with Cobalt, Nickel and Zinc(II) salts to give mono- and binuclear chelates. The first series reacts with coppric chloride to give heterobinuclear chelates. γ-Irradiation effects on the electrical conductivity of the different metal chelates were investigated. The changes in conductivity of solid compounds with temperature is characteristic of an intrinsic semiconductor with impurity centers. The annealing of electronic defects generated by γ-irradiation obeys a first order law. It was found that the conductivity increases with increasing temperature and decreasing radiation dose. However, the results showed that the rate constants of thermal annealing increase in the order mono-, homobi- and heterobinuclear chelates, but the activation energies decrease in the same order. Seebeck effect studies showed that electrons are the majority charge carriers in all irradiated and unirradiated complexes.

Gamma irradiation effects on the electrical conductivity behaviour of the double complexes [Co(NH 3 ) 6 ] [Co(CN) 6 ], [Co(NH 3 ) 6 ] [Al(CN) 6 ] and [Co(NH 3 ) 6 ] [Mn(CN) 6 ] were investigated. A comparison is made between the rates and activation energies of thermal annealing of electrical properties of pure and γ-irradiated samples. The conductivity of the solid double complexes increases with temperature, decreases with radiation dose, and remarkably increases when the transition metal of the negative component of the double complex changes from Al to Mn to Co. However, the results show that the rate constants and activation energies of thermal annealing of defects in these systems are not significantly affected by gamma irradiations.

The kinetics of the alkaline solvolysis of dichloroacetate ion in water–methanol solutions have been studied in the temperature range of 50.0 to 65.0 °C and the influence of solvent variation on reaction rate has been examined in terms of changes in the activation parameters. The activation parameters ΔH≠ and ΔS≠ for the solvolysis reaction showed a minimum at about 0.8 water mole fraction. The significance of the results was discussed in view of the electrostatic theory and the changing of solvent structure.

The rates of hydrolysis of phenylchloroformate were measured over the temperature range 30–55 °C in water-tetrahydrofuran and water-dioxane mixtures of different compositions. The influence of solvent variation on reaction rate was examined in terms of changes in the activation parameters. The activation parameters Δ H ★ and Δ S ★ for the solvolysis reaction showed minima at a water mole fraction of about 0.5 in water-tetrahydrofuran solvent mixtures, whereas these parameters increased continuously with increasing concentration of water in water-dioxane solvent mixtures. The results are discussed in terms of the polarity of the medium and the change in the solvent structure.

The effects of gamma radiations on the kinetic parameters of the three stages of isothermal decomposition of calcium oxalate monohydrate were investigated. Radiation did not modify the mechanism of thermal decomposition reactions and kinetic analysis of data showed that the random nucleation and the two-dimensional phase boundary reaction models give the best fit of the results. For the first two stages kinetic analysis showed progressive decrease in both activation energy and frequency factor with greater radiation dose due to the generation of more dislocations and surface etch pits. However, in the third stage, radiation has no effect at the higher doses due to the formation and accumulation of CO2 molecules and the self-generation of defects during the movement of the phase boundary.

The kinetics of the alkaline decarboxylation of trichloroacetate ion in water-methanol solutions covering the whole composition range have been studied over the temperature range 30.0–52.0 °C. The results indicate that the rate of reaction is independent of the concentration of the solvoxide ion and point to a mechanism in which the rate-determining step is formation of CCl3– carbanion. The rate of reaction varies with methanol concentration in the mixed solvent in a non-linear manner. The activation parameters, ΔH‡ and ΔS‡, showed a minimum at a water : methanol mole ratio of ca. 3:2.

High energy photonuclear reactions in 141 Pr were studied making use of the method of residual activity and gamma ray scintillation spectroscopy techniques. The yield values of 140 Nd produced in irradiations of praseodymium oxide target were determined with bremsstrahlung of maximum energy varying from 100 to 300 MeV. The observed 140 Nd yields indicate that there is significant contribution from secondary proton reactions.

The temperature dependence of the rate of alkaline solvolysis of monochloroacetate ion in water – tert-bulyl alcohol solutions has been determined. The rates of reaction were first order with respect to both the chloroacetate ion and to the total solvoxide ion concentrations. The reactivity is enhanced, first slowly, and then more rapidly, by increasing the concentration of tert-bulyl alcohol in the solvent mixtures. The rate of reaction increases with the reciprocal of the dielectric constant of the medium and the plot of log kvs. 1/D can best be represented by two lines intersecting at a point corresponding to 0.9 water mole fraction. The activation parameters ΔH*and ΔS* for the solvolysis reaction showed a minimum at about 0.9 water mole fraction. The significance of these results from the viewpoint of the electrostatic theory and the changing of solvent structure in such mixtures is discussed.