Diffusion studies of cobalt ions and their salts in agar gel medium: Obstruction effect and gel hydration

The obstruction effect in the electrolyte diffusion of cobalt halides and in tracer diffusion of Co²⁺ ions in the presence of different supporting electrolytes at various concentrations has been studied at 25 °C using the zone diffusion technique. It has been observed that obstruction effect expressed in terms of increases with concentration and is higher for electrolyte diffusion than in tracer diffusion. Further, for a given concentration it is found to decrease with increasing charge density of an anion. These observations are explained on the basis of competitive hydration between ions and agar molecules.     

Tracer-diffusion of Zn2+ ions in cobalt sulphate

Tracer-diffusion of Zn²⁺ ions in the presence of CoSO₄ is studied at 25°C in 1% agar gel over a concentration range of 10^–5 to 0.25M using a zone-diffusion technique. The deviations observed between experimental and theoretical values of diffusion coefficients are explained by considering different types of interactions occurring in the ion-gel-water system. Further, study of the obstruction, effect in the diffusion of Zn²⁺ ions at different concentrations of CoSO₄ reveals that the -value decreases with increasing concentration of the electrolyte. This observation is accounted on the basis of competitive hydration between ions and agar molecules.     

Polymerization of acrylamide initiated by Ce4+/L-cysteine redox system

Summary The polymerization of acrylamide initiated by Ce 4⁴⁺/L-cysteine redox system has been studied at 35 ± 0.2 °C in dark under nitrogen atmosphere. The effect of monomer,L-cysteine, Ce⁴⁺ and sulphuric acid concentration and temperature on the rate of polymerization has been studied. The rate may be expressed by the following equation:R _p [M] [Ce⁴⁺]^0.5 [Cysteine]^0.44 The overall energy of activation is 4.78 kcal/deg/mole in the investigated range of temperature 30–50 °C. Molecular weight of the polymer is independent of catalyst concentration but increases with increasing monomer concentration.     

Tracer diffusion of Co2+ ions in multielectrolyte systems: Activation energy and obstruction effect

The activation energy for the tracer diffusion of Co²⁺ ions in multielectrolyte systems containing alkali bromides has been determined in agar gel medium over the temperature range of 25–45°C. The decrease in the value of the Arrhenius parameters, E and D_o, with gel percentage is explained on the basis of the transition state theory. Further, studies of the influence of electrolyte concentration on activation energy and obstruction effect reveal that both parameters decrease with the former. The decrease in activation energy is explained by considering the changes in physical properties of the solution with concentration at microscopic level, while the decrease in the extent of obstruction effect is attributed to competitive hydration between ions and agar molecules in a diffusion system.     

Tracer-diffusion of Zn2+ ions in some transition metal sulphates

Tracer-diffusion of Zn²⁺ ions is studied in zinc, manganese and copper sulphates over a concentration range of 10^–4 to 0.25M using 1% agar gel medium at 25 °C. A comparison of the experimental and theoretical values of tracer-diffusion coefficients shows a deviation from the theory. This is explained in the light of different types of interactions occurring in the ion-gel-water system. The effect of supporting electrolytes and its concentration on the obstruction effect in the tracer-diffusion of zinc ions is also examined. The obstruction effect decreases with increasing charge density of the cation of the electrolytes at a given concentration and for a particular elecrolyte it decreases with its concentration. These observations are accounted on the basis of competitive hydration between ions and agar macromolecules.     

Diffusion of zinc sulphate in agar gel medium

The activation energy for the diffusion of ZnSO₄ as a function of electrolyte concentration is computed by least squares fitting of the diffusion coefficient data obtained at various temperatures in the Arrhenius equation. It is observed that the activation energy decreases with increasing concentration of the electrolyte. This observation is accounted for on the basis of Wang's model. Further, the obstruction effect caused by the agar macromolecules in the diffusion path of ZnSO₄ uis also determined at these concentrations by varying the gel concentration at 25°C., The obstruction effect expressed in terms of a found to decrease with ZnSO₄ concentration and explained on the basis of competitive hydration of diffusing ions and agar molecules.     

Thermodynamics of Copper Adsorption-Desorption by Ca-Kaolinite

The temperature effect on Cu adsorption and desorption on kaolinite has been investigated at four temperatures (8°C, 25°C, 30°C and 40°C). The clay sample was saturated with Ca. Copper was sorbed from solutions containing eleven Cu concentrations between 0.0010 and 0.0211 M, equilibrated for 2 days. Cu adsorption decreased, but desorption increased with increasing temperature, indicating that adsorption is an exothermic process while desorption is endothermic. These conclusions are confirmed by the values of H ⁰ estimated for adsorption and desorption.The initial copper concentration is a significant factor influencing mainly the adsorption process, which is spontaneous (G ⁰ < 0) only for low initial Cu concentrations. The desorption process is spontaneous for all Cu concentrations. S ⁰ values have also been calculated. Experimental adsorption data were successfully fitted to the Freundlich isotherm and to the Gouy-Chapman model in order to express the process quantitatively.     

Effect of the Measurement Temperature on the Dispersive Component of the Surface Free Energy of a Heat Treated SiO2 Xerogel

The surface free energy of a monolithic silica xerogel treated at 1000°C has been measured by inverse gas chromatography in the temperature range 25–150°C using n-alkanes. Values of the dispersive component, _S ^D, vary from 49.07 mJ·m^–2 at 25°C to 17.20 mJ·m^–2 at 150°C. The _S ^D value obtained at 25°C is lower than that found for amorphous and crystalline silicas but higher than that found for glass fibres meaning that the heat treatment at 1000°C changes drastically the structure of the silica xerogel showing a surface similar to a glass. However, the higher value of _S ^D in comparison to glass fibres can be attributed to the mesoporous structure present in the silica xerogel. In the temperature range of 60–90°C there exists an abrupt change of the _S ^D values as well as in the dispersive component of the surface enthalpy, h _S ^D. Such abrupt change can be attributed to an entropic contribution of the surface free energy.     

Conductance of tris(hydroxymethyl)-aminomethane hydrochloride (Tris·HCl) in water at 25 and 37°C

The conductances of aqueous solutions of tris(hydroxymethyl)aminomethane hydrochloride (Tris·HCl) at 25°C and 37°C have been measured. The concentration of salt varied from 4×10^–4 to 1.6×10^–2 mole-dm^–3. The data were analyzed by the full Pitts equation which yielded the following parameters: at 25°C, ° = 106.07 S-cm²-mole^–1, K_A=1.01; at 37°C, ° = 106.07 S-cm²-mole^–1, K_A=0.99. These values suggest that Tris·HCl is essentially completely dissociated in water. The mobility of the Tris·H⁺ ion was found to be considerably smaller than that of the alkali metal cations. This result is consistent with abnormal liquid-junction potentials for Tris buffer solutions at 25 and 37°C.     

Ionization constants of benzoic acid from 25 to 250°C and to 2000 bar

The ionization constant of benzoic acid has been determined by conductivity measurements of dilute aqueous solutions and found to vary from 6.27×10^–5 at 25°C to 0.39×10^–5 at 250°C. The pressure effect to 2000 bar has been measured, and the ratio of ionization constants K₂₀₀₀/K₁ is 2.26 at 25°C and 7.3 at 250°C. V°₁, the standard partial molar volume change for the ionization at 1 bar, varies from –11.7 cm³-mol^–1 at 25°C to –60 cm³-mol^–1 at 250°C. The volume changes are smaller at higher pressures.     

Ionization constants of aqueous ammonia from 25 to 250°C and to 2000 bar

The ionization constant of ammonia has been determined by conductivity measurements and found to vary from 1.77×10^–5 at 25°C to 1.3×10^–6mol-kg^–1 at 250°C. The pressure effect to 2000 bar has been measured and the ratio K₂₀₀₀/K₁ is 6.8 at 25°C and 11 at 250°C. The standard molar volume change for the ionization at 1 bar, V ₁ ^o , changes from –28.8 at 25°C to –67 cm³-mol^–1 at 250°C.     

Crystalline Inclusions Formed in C+N+BF2 Coimplanted on Silicon (111)

In the present work, high-doses (10¹⁷–10¹⁸cm^–2) of carbon, nitrogen, and boron (BF₂⁺) ions were coimplanted on silicon (111) substrates at 21, 25 and 77keV, respectively. Two series of samples have been implanted (series A and B) and subsequently annealed. Series A samples have been implanted at room temperature and treated one minute by rapid thermal annealing (RTA) and 3 hours at 1200°C. Series B samples have been implanted at 600°C and subsequently annealed at 1200°C during 3 hours. The annealing in both series has been carried out in N₂ at atmospheric pressures.The structure of the buried layers has been determined by conventional and high resolution transmission electron microscopy (CTEM and HRTEM). Polycrystalline silicon and new crystalline phases are observed by electron diffraction patterns. The polycrystalline silicon inclusions have been confirmed from analysis of HRTEM images.     

Limiting interdiffusion coefficients of Tris(acetylacetonato)cobalt(III) in water and in organic solvents

The diffusion coefficients of tris(acetylacetonato)-cobalt(III) in water (5, 15, 25, and 40°C), methanol (25°C), ethanol (15, 25, and 45°C), 1-propanol (25°C), 1-butanol (45°C), acetone (25 and 40°C), 2-butanone (25°C), acetonitrile (25°C), tetrahydrofuran (25°C), benzen (25°C), toluene (25°C), and carbon tetrachloride (25°C) have been measured at concentrations close to infinite dilution. The Stokes-Einstein coefficient (f=kT/Dr) has been calculated for Co(acac)₃ in each solvent and is found to be larger in water than in organic solvents. Furthermore, it increases as the temperature is lowered (or as the viscosity is increased) in water while it decreases with increasing viscosity of organic solvents. The differences are discussed in terms of the enhancement of the water structure by the solute.     

Carbon isotope effect studies in the mechanism of reactions of alkynes with formic acid

The¹³C fractionation has been studied in the reaction of phenylacetylene with the excess of liquid Merck formic acid at 30 and 40 °C to see the contribution of the¹³C fractionation in the formolysis of transient -formoxystyrene to the experimentally observed global¹³C fractionation. The¹³C fractionation has been investigated also in the hydration of 1 ml of PhCCH with 1 ml of formic acid in the temperature interval of 80–100°C. The¹³C KIE equal to 1.0168 at 91.75 °C and 1.0167 at 100°C indicate that the self-decomposition of formic acid in such experimental conditions is already largely suppressed. The isotope effect is discussed within the framework of the sequence of reaction steps leading to acetophenone and carbon monoxide production listed in part I.     

Tracer-diffusion of Co2+ ions in some transition metal chloride solutions

Tracer-diffusion coefficients of Co²⁺ ions have been determined in 1% agar gel containing transition metal chlorides, viz. ZnCl₂, NiCl₂ and MnCl₂ over the concentration range of 10^–6–0.15 M at 25°C using the zone-diffusion technique. The results are compared with calculated values on the basis of Onsager's theory and the deviations are accounted for on the basis of various types of interactions in the ion-gel water system. Further, activation energy for the tracer-diffusion of Co²⁺ ions in the above mentioned electrolytes has been obtained as a function of electrolyte concentration, using measurements in the temperature range of 25–50°C. The trend in activation energy is explained on the basis of the WANG's model.     

Applications of Inorganic Ion Exchangers: II—Adsorption of Some Heavy Metal Ions from Their Aqueous Waste Solution Using Synthetic Iron(III) Titanate

Adsorption of Zn²⁺ and Cd²⁺ ions from aqueous waste solutions on iron(III) titanate as inorganic ion exchange material was investigated to determine the effect of contact time, pH of solution and the reaction temperatures. Batch kinetic studies were carried out and showed that the time of equilibrium for both Zn²⁺ and Cd²⁺ ions was attained within three hours, and the order of kinetic reaction is the first order reaction. Batch distribution coefficients of Zn²⁺ and Cd²⁺ ions on iron(III) titanate as a function of pH have been studied at 25, 40 and 60 ± 1°C. From the obtained results we found that the K _d values decreased with increasing reaction temperatures. Enthalpy change (H) values for Zn²⁺ and Cd²⁺ ions were found to be –8.19 and –22.49 kJ/mol, respectively. The data of adsorption of Zn²⁺ and Cd²⁺ ions at various concentrations were fitted with the Freundlich isotherm. Finally, separation of the above mentioned cations on iron(III) titanate in a column was performed.     

Hydroxylamine Derivative in Purex Process III. The Kinetics of Oxidation-reduction Reaction Between N,N-diethylhydroxylamine and Neptunium(VI)

The kinetics of oxidation-reduction reaction between N,N-diethylhydroxylamine (DEHAN) and neptunium (VI) in nitric acid media has been studied by spectrophotometry at 25.2 °C. The rate equation is -d[Np(VI)/dt=k[Np(VI)][DEHAN]/[H⁺] found by investigating the influence of concentration, acidity, ionic strength and temperature on the reaction. The rate constant of the reaction k is 23.0±1.8 min^–1 for = 2.0 mol/l. A possible mechanism of reaction has been suggested according to the ESR spectra of nitroxide radical produced in the DEHAN+V(V) system.     

Aqueous polymerization of methacrylamide with potassium persulphate/thiomalic acid redox pair

Summary Methacrylamide was polymerized in aqueous medium at 35 ± 0.2 °C with the redox pair K₂S₂O₈/ thiomalic acid (mercaptosuccinic acid) in dark under nitrogen atmosphere. The effect of monomer, K₂S₂O₈ and thiomalic acid concentrations and temperature on the rate of polymerization was studied. The kinetics of polymerization was followed iodometrically.The role of the addition of complexing metal ions and a series of aliphatic alcohols was also investigated. The initial rate of polymerization was found to be independent of the concentration of thiomalic acid. Rate may be expressed by the following equation:R _p [M]^1.5[K₂S₂O₈]^0.76. The energy of activation was found to be 9.0 Kcal/deg/mole.With 4 figures     

Thermal diffusion of alkali bromides

The molar entropies (or heats) of transport of dilute aqueous alkali bromide solutions have been measured by the potentiometric method using the silver, silver bromide thermocell at a mean temperature of 25°C and over a concentration range of 5×10^–4 to 0.1M. Experimental results were extrapolated to infinite dilution to obtain the standard molar entropies of transport. The limiting behavior observed is compared with theory based on the electrostatic model.The standard transported entropy of Br^– was also derived by extrapolating the steady-state thermoelectric powers to infinite dilution. The absolute ionic entropies of transport of alkali metal ions have been estimated based on Gurney's scale. The results obtained are compared with that derived f¹/om the previous work on alkali chlorides.     

Heat capacities of concentrated multicomponent aqueous electrolyte solutions at various temperatures

The specific heat capacities of the aqueous multicomponent system NaCl +KCl+MgCl₂+CaCl₂ with ionic strength between 8.3 and 9.6 (resembling Dead Sea waters) were measured between 15°C and 45°C. The obtained data were fitted to an empirical equation as a function of concentration and temperature. The thermodynamic functions of the studied multicomponent system were found to be strongly influenced by changes in MgCl₂ concentrations. The application of Young's rule to such concentrated systems was checked at 25°C. The calculated (by Young's rule) specific heat capacitiesC _p and apparent molar heat capacities C_p, of these multicomponent electrolyte solutions were in reasonable agreement with the measured values (–0.008 J-g^–1-K^–1 and –2.6 J-mol^–1-K^–1, respectively).