Predicting points of zero charge of oxides and hydroxides

Pauling's electrostatic valence principle has been applied to describe the surface-charging mechanism of oxides in an aqueous environment. This approach has led to the development of an equation with which one can predict the points of zero charge (PZC) of oxides and hydroxides from crystallographic data. The equation proposed in the present work is an improved version of Parks' PZC equation. The improvements are the following: (i) The equation does not incorporate correction terms to take the cation coordination numbers into account; (ii) the PZC of a complex oxide can be predicted directly from crystallographic data instead of from “assumed” PZCs of its component oxides; and (iii) one can use the mean metal-oxygen bond distance of a crystal instead of the ionic radii tabulated by Parks, which are not consistent with the up-to-date values.     

Osmotic coefficients of polystyrenesulphonates in dioxane-water mixtures—II. Divalent counterions and mixtures of mono- and divalent counterions

The osmotic pressures of solutions of magnesium and calcium polystyrenesulphonate in water and in 25 wt % mixture of dioxane in water have been measured for concentrations from 0?002 to 0?06 molal in monomer units. The osmotic coefficient derived from these measurements is almost independent of concentration. Its values for solutions in dioxane-water mixtures are much lower than for aqueous solutions. The osmotic coefficients of solutions containing mixtures of polystyrenesulphonic acid and its calcium salt in 25 wt % dioxane have also been determined. The osmotic coefficient of these solutions has a distinct maximum at a certain value of the equivalent fraction of the acid. The experimental results are compared with the predictions of the cylindrical cell model and infinite line charge model. Satisfactory agreement between theory and experiment is found.     

Solid—liquid phase diagrams of mixtures containing substituted phenols and amine mixtures

The thermal decomposition of CaCO₃ was studied under high vacuum by means of both TG and the more recently developed constant decomposition rate thermal analysis (CRTA) which allows the monitoring of both reaction rate and the residual pressure over the sample. The reliability of the kinetic results seems to be much higher with the latter technique which actually allows the reduction of the reaction rate and therefore the heat and mass transfer effects over a broad range of sample size. For instance, it was necessary, by conventional TG started under a vacuum of 2 10^?6 torr with a heating rate of 0.5 K min^?1, to lower the amount of sample to 2 mg in order to obtain the same activation energy as that calculated from CRTA with various samples weighing up to 50 mg. The TG experimental conditions quoted above (and which are upper limits of mass and heating rate) are beyond the limit of sensitivity of most available conventional TG equipment.     

Synthesis of polymers containing tertiary phosphine oxides using complex bases

Tertiary phosphine oxides have been prepared in excellent yield from primary alkyl halides or aromatic halides and activated sodium phosphinates obtained by reaction of dialkyl phosphine oxides with complex bases (NaNH₂/tBuONa). This reaction has been successfully applied to soluble and cross-linked bromopolystyrenes and to macroporous polystyrenes with bromooctyl substituents giving polymers which contain pendant phosphine oxide groups.     

Thermodynamic studies of some binary mixtures containing a self-associated component. II. Excess volumes of some mixtures of tetrahydrofuran with alcohols

Excess volumes of mixing, V^E, for binary mixtures of tetrahydrofuran (THF) with methanol, ethanol, n-butanol, tert-butanol, 2-bromoethanol and ethylene glycol have been determined from the experimental density measurements at 298.15 K over the entire composition range. The V^E data follow the order: ethylene glycol < 2-bromoethanol < methanol < ethanol < n-butanol < tert-butanol. The results have been explained in terms of self-association and the hydrogen bond-donating abilities of alcohols.     

Thermodynamics of complex formation in ternary liquid mixtures containing acetonitrile

Vapor—liquid and liquid—liquid equilibria and excess enthalpies for ternary mixtures formed from acetonitrile, benzene, n-heptane, toluene, and carbon tetrachloride are successfully correlated with a modified version of the associated solution theory proposed by Lorimer and Jones in 1977, which assumes two types of self-association for acetonitrile and binary complexes between acetonitrile and unsaturated hydrocarbons and does not include any ternary parameters.     

Adsorption of adenine derivatives on a gold electrode studied by specular reflectivity measurement

The adsorption of adenine, deoxyadenosine, deoxyadenosine-5′-monophosphate,-diphosphate and-triphosphate on a gold electrode has been studied by specular reflectivity measurement in 0.1 M NaClO₄ solution. In the presence of these compounds, a marked decrease in reflectivity was found on reflectivity-potential curves in the potential region more positive than ?0.8 V vs. Ag/AgCl, the decrease being ascribed to the adsorption of them. The magnitude of change in reflectivity was dependent on both the concentration and the electrode potential. The reflectivity change observed in the negative potential region was analyzed quantitatively according to the procedure previously described. The results were elucidated on the basis of the same isotherm as used by Green and Dahms in their adsorption study of aromatic hydrocarbons, and the number of solvent molecules being replaced through the adsorption of one organic molecule and the free energy change of adsorption were obtained. The former is suggestive of a flat orientation of the adsorbed molecule in contact with its adenine moiety on the electrode surface. It is also suggested from the latter that the presence of phosphate groups leads to a decrease in ΔG_ad⁰ resulting from their hydrophilic properties and a repulsive interaction between these groups and the negative charges on the surface.     

The thermodynamic properties of binary mixtures containing carbon disulphide I. Phase diagrams and excess volumes

Phase diagrams and excess volumes at 298.15 K have been measured for the four binary mixtures carbon disulphide+cyclohexane, +n-hexane, +1,5-hexadiene, and +1,5-hexadiyne. The results are discussed qualitatively in the light of recent theoretical calculations of the structure and thermodynamic properties of mixtures containing anisotropic molecules.     

Relative stabilities of layered perovskite and pyrochlore structures in transition metal oxides containing trivalent bismuth

In order to investigate the factors determining the relative stabilities of layered perovskite and pyrochlore structures of transition metal oxides containing trivalent bismuth, several ternary and quaternary oxides have been investigated. While d⁰ cations stabilize the layered perovskite structure, cations containing partially-filled d orbitals (which suppress ferroelectric distortion of MO₆ octahedra) seem to favor pyrochlore-related structures. Thus, the vanadium analogue of the layered perovskite Bi₄Ti₃O₁₂ cannot be prepared; instead the composition consists of a mixture of pyrochlore-type Bi_1.33V₂O₆, Bi₂O₃, and Bi metal. The distortion of Bi_1.33V₂O₆ to orthorhombic symmetry is probably due to an ordering of anion vacancies in the pyrochlore structure. None of the other pyrochlores investigated, Bi₂NbCrO₇, Bi₂NbFeO₇, TlBiM₂O₇ (M = Nb, Ta), shows evidence for cation ordering in the X-Ray diffraction patterns, as indeed established by structure refinement of TlBiNb₂O₇.     

Bet nitrogen adsorption studies of iron oxides from natural and synthetic sources.

A vacuum microbalance technique has been used to obtain the surface areas and porosities of iron oxyhydroxides derived from Fe(III) and Fe(II) sources. The pore shape of the Fe(III)-derived material was of the wide-bodied, narrow-necked type, whereas the Fe(II)-derived precipitates were composed of parallel plates or slit-shaped pores. The surface area of the Fe(II)-derived material was found to be influenced by the temperature of the precipitate formation. These differences in surface character are discussed in relation to the adsorption of trace constituents at the iron oxyhydroxide-water interface.     

Further developments in the high-precision coulometric titration of uranium

An experimental study of the current efficiency in the coulometric generation of Ti(III), as a function of electrolyte composition, current density and electrode material, has been performed. The cathodes investigated include platinum, mercury and graphite. The first two are suitable for high-precision determination of uranium. The graphite surface is readily poisoned, rendering it useless for high-accuracy work. The use of mercury requires thorough removal of chloride from the system. The precision and error obtained are comparable for both the mercury and platinum cathodes, and are of the order of 50 ppm.     

Synthesis and properties of noncyclic polyether compounds. Part V : The influence of acid and concentration of cations on the uphill transport rates of cations and selectivities through liquid membranes by synthetic,noncyclic polyether ionophores

The effects of acid and cation concentration on the uphill transport rates of cations and selectivities through chloroform liquid membrane by noncyclic polyether ionophores, which are pentaethylene glycol derivatives containing both 8-quinolyt and o-carboxylphenyl terminal groups, have been demonstrated. Using sulfuric, oxalic, or polyphosphoric acid in aqueous solution, the initial transport rates and the amount of cation transported by the ionophores after two days were larger than those using hydrochloric or nitric acid. Using picric acid, the amount of cation transported decreased greatly. It was confirmed that it decreased where an acid could easily be counter-transported by the ionophore through liquid membranes. On the other hand, it was found that the rates, amounts of cation transported, and selectivities, change with the changing of the cation concentration in the aqueous solutions. When the cation concentration in both aqueous solutions is high enough compared with the pH gradient between the two aqueous solutions, the rate, amount, and selectivity of the ionophore for potassium ion increases compared with when the cation concentration is low.     

Determination of silver in dore metal by weight titration with equivalence-point detection by differential electrolytic potentiometry

Use of weight titrimetry, with differential electrolytic potentiometry for detection of the equivalence point, instead of gravimetry, has been critically tested for the determination of silver in doré metal. The electrode response in the presence of possible interferences (Sb, As, Se, Cu, Ni, Fe, Pb and Co) was studied by voltammetry. Titration curves for six different samples were obtained and their differences from those for pure silver were interpreted. Positive errors were found to occur in the presence of 0.1% Fe(III) and Se(IV) but not in the presence of 1% Cu(II). The results obtained by gravimetry and weight titrimetry were compared. The imprecision of the proposed method was between 0.03 and 0.05% (relative standard deviation); that of gravimetry was between 0.05 and 0.08%. The absolute difference from the gravimetric results was between + 0.05 and + 0.08%. The time for analysis of one sample was between 60 and 80 min.     

Determination of the zero point energy difference of trans- and cis-(NO)2 from the equilibrium constant of nitric oxide dimerization

Analysis of the equilibrium constant of NO radical dimerization taken as the result of two partial equilibria led to a value of ?301 ± 5 J/mol for the zero point energy difference of trans- and cis-(NO)₂. From a comparison of this value with recent ab initio calculations the difference between the correlation energies of the two isomers was estimated as 8 ± 3 kJ/mol.     

Vapor pressure measurements of ferrocene,mono- and 1,1′-di-acetyl ferrocene

By using different techniques the vapor pressure of ferrocene, mono-acetyl ferrocene and 1,1′-di-acetyl ferrocene was measured. The following pressure—temperature equations were derived ferrocene log P(kPa)= 9.78 ± 0.14 ? (3805 ± 46)/T mono-acetyl ferrocene log P(kPa) = 14.83 ± 0.14 ? (5916 ± 48)/T 1,1′-di-acetyl ferrocene log P(kPa) = 8.82 ± 0.11 ? (4289 ± 44)/T By second- and third-law treatment of the vapor data the ΔH⁰_sub,298 = 74.0 ± 2.0 kJ mole^?1 for the sublimation process of ferrocene was calculated and compared with the literature data. For the sublimation enthalpy of mono- and 1,1′-di-acetyl ferrocene the values ΔH⁰_sub,298 = 115.6 ± 2.5 kJ mole^?1 and ΔH⁰_sub,298 = 91.9 ± 2.5 kJ mole^?1 were derived by second-law treatment. Thermal functions of these compounds were also estimated.     

Transport of alkali metal cations across liquid membranes by crown ether carboxylic acids

Competitive alkali metal transport from an alkaline aqueous source phase through a chloroform phase to an acidic aqueous receiving phase facilitated by nine crown ethers with pendant carboxylic acid groups has been investigated. Transport selectivity is controlled by the size of the polyether cavity of the carrier. Increasing the lipophilicity of the carrier, while maintaining a constant polyether cavity size, enhances the total transport rate but does not affect the selectivity. There is poor agreement between the results of competitive transport and the behavior anticipated on the basis of single cation transport studies.     

Thermal decomposition of compounds containing the hydrazinium cation as a ligand

A thermal investigation of M(N₂H₅)₂(SO₄)₂, where M = Mn(II) or Co(II), has been carried out. On heating, the complexes become MSO₄ via an intermediate compound, M(N₂H₄)_0·5(HSO₄)(SO₄)_0·5. The intermediate compound has been isolated and characterised by elemental analyses, IR spectra, diffuse reflectance spectra, magnetic and conductance data. The intermediate compound seems to possess pseudo-tetrahedral coordination where one SO₄ group is tetradentate and bonded with four different metal ions which are surrounded by HSO₄ groups and hydrazines bridging two metal ions. The X-ray powder diffraction pattern of the intermediate derived from the cobalt(II) complex has been obtained and the d-values are reported. Activation energies (E^*) and enthalpy changes (ΔH) for each decomposition step have also been calculated. The probable mechanisms of decompositions are discussed.