Thermodynamics of ionic-association in aqueous solutions of Ca and Mg organic salts using ion-selective electrode technique—I. Formates, acetates, propionates and butyrates

The divalent selective electrode together with high precision solid state, digital pH -mv -meter makes broader application of potentiometry in physical and inorganic chemistry a certainty. The above set-up is used to determine the stoichiometric constants, K, for Ca and Mg ions association with formates, acetates, propionates and butyrates at 25°, 35° and 45°C in aqueous media. The K-values were converted to infinite dilution K_A values were found to be 8.4 LM⁻¹, 10.4 LM⁻¹, 19.1 LM⁻¹ and 19.3 LM⁻¹ for calcium salts of formate, acetate, propionate and butyrate respectively. Also K_A values for Mg salts of formate, acetate, propionate and butyrate were found to be 7.8 LM⁻¹, 9.5 LM⁻¹, 13.1 LM⁻¹ and 13.1 LM⁻¹ respectively. Other thermodynamic parameters such as ΔG°, ΔH° and ΔS° are also obtained from the variation of K_A with temperature for each salt. The data are interpreted relative to each other on basis of pK_a of the corresponding organic acid. Their temperature behaviour is similar to those salts derived from strong acids such as sulphates, rather than weak acids.     

Effect of electro-chemical properties of sodium salts of various anions on their diffusional parameters in symmetrical cellulose acetate membranes

A relation was obtained between electro-chemical properties of sodium salts (NaCl, NaBr, and Na₂SO₄), and the thermodynamic property of permeability in symmetrical cellulose acetate membranes, the distribution coefficient K and the kinetic property, the overall diffusion coefficients D. K and D were obtained by the method we proposed using measured unsteady- and steady-state dialysis data. The K values increase with the increase of water content and are in the range of 10⁻² for sodium halides and 10⁻³ for Na₂SO₄. D is found to increase with the increase of the solute concentration, and the extrapolated values of D to zero concentration D⁽⁰⁾ are obtained as 0.015–0.03 μm²/s and increase with the increase of water content in the membrane. D can be divided into the concentration independent diffusion coefficients in the dense part of the membrane D_d and in the porous D_p, applying a two-part (perfect or dense and imperfect or porous) model of the membrane. Contrary to D_d, D_p increases with the increase of W_w and can be correlated as D_p,c = _d exp (γ × W_w). It is shown that the averaged D_d, _D increases with the increase of the quantity of the ionic mobility u of the solutes at infinite dilution divided by valence, and that the parameter γ increases with the increase of the ionic mobility u. The value of K increases slightly with the increase of water content and decreases with the increase of the Flory—Huggins parameter χ. The Flory—Huggins parameter χ is calculated from the measured values of distribution coefficients and data obtained from the literature. And it was found that the gradient of linear decrease of χ (λ_cation) depends on equivalent ionic conductivity of anion of salt, λ_an.     

Mechanical behaviour of partially stabilized zirconia crystals with terbia and ceria additives

Mechanical behaviour of partially stabilized zirconia crystals (PSZC) with terbia and ceria additives was investigated under bending and indentation conditions. Test specimens were oriented along the [010] direction and along the axis of crystal growth. The PSZC bending strength (σ_b) was dependent on the crystallographic orientation of the specimens. The specimen volume subjected to stress influenced the PSZC strength. The highest mechanical characteristics were measured for ceria-doped crystals (σ_b = 1.9 GPa, K_lc = 11.4 MPa m^1/2, E_d = 366 GPa). The failure process was studied on the Vickers indentation, with special emphasis put on the development and propagation of lateral cracks. Anisotropy of lateral cracks in the (100) plane associated with that of the elastic moduli was revealed. At the same time anisotropy of radial cracks and hardness was not found. A new version of the equation to evaluate the fracture toughness (K_c^v) on the Vickers indentation was derived. The K_c^v values calculated by this equation correspond to those (K_lc) obtained by an SENB method.     

Microwave dielectric properties and co-firing with copper of (Bi1−xCux)(Nb1−xWx)O4 ceramics

Effect of substitution of CuO and WO₃ on the microwave dielectric properties of BiNbO₄ ceramics and the co-firing between ceramics and copper electrode were investigated. The (Bi_1−xCu_x)(Nb_1−xW_x)O₄ (x = 0.005, 0.01, 0.015, 0.02) composition can be densified between 900 and 990 °C. The microwave dielectric constants lie between 36 and 45 and the pores in ceramics were found to be the main influence. The Q values changes between 1400 and 2900 with different x values and sintering temperatures while Q_f values lie between 6000 and 16,000 GHz. The microwave dielectric losses, mainly affected by the grain size, pores, and the secondary phase, are discussed. The (Bi_1−xCu_x)(Nb_1−xW_x)O₄ ceramics and copper electrode was co-fired under N₂ atmosphere at 850 °C and the EDS analysis showed no reaction between the dielectrics and copper electrodes. This result presented the (Bi_1−xCu_x)(Nb_1−xW_x)O₄ dielectric materials to be good candidates for LTCC applications with copper electrode.     

Electrical resistivity and thermopower of (La1−xSrx)MnO3 and (La1−xSrx)CoO3 at elevated temperatures

Electrical resistivity and Seebeck (S) measurements were performed on (La_1−xSr_x)MnO₃ (0.02x0.50) and (La_1−xSr_x)CoO₃ (0x0.15) in air up to 1073 K. (La_1−xSr_x)MnO₃ (x0.35) showed a metal-to-semiconductor transition; the transition temperature almost linearly increased from 250 to 390 K with increasing Sr content. The semiconductor phase above the transition temperature showed negative values of S. (La_1−xSr_x)CoO₃ (0x0.10) showed a semiconductor-to-metal transition at 500 K. Dominant carriers were holes for the samples of x0.02 above room temperature. LaCoO₃ showed large negative values of S below ca. 400 K, indicative of the electron conduction in the semiconductor phase.     

DISPERSION OF MATTER IN FLOW OF A BINGHAM PLASTIC IN A TUBE

The paper is concerned with the dispersion of a solute in a Bingham plastic fluid flowing in a pipe or a parallel plate channel. For pipe flow, the dispersion coefficient K₂ first increases with ξ₀ (the dimensionless radius of the plug flow region), reaches a maximum and then decreases. But in a channel flow, K₂ decreases monotonically with increasing ξ₀. Further K₂ for channel flow is found to be larger than that for pipe flow for all values of ξ₀ except 0.8≤ξ₀≤1.     

Synthesis and properties of lanthanum hexaaluminate ceramic La1−xCaxAl11−y−zMgyTizO18

The aim of the present work is to obtain ceramic materials with a hexagonal structure and high density, hardness and mechanical strength at lower synthesis temperature. Ceramic samples with nominal composition La_1−xCa_xAl_11−y−zMg_yTi_zO₁₈ (x=0–1; y=0–3; z=0–3,5) are prepared. The samples are sintered at temperature 1500 °C by one-stage and two-stage ceramic technology. By X-ray diffraction and scanning electron microscopy, predominant phase LaAl₁₁O₁₈ and second phases LaAlO₃ and -Al₂O₃ are identified. Ceramic materials are characterized with high physico-mechanical properties and may be find application for production of mill bodies and materials for immobilization of nuclear waste.     

Ce1−xCuxO2−x/Al2O3/FeCrAl catalysts for catalytic combustion of methane

A series of the Ce_1−xCu_xO_2−x/Al₂O₃/FeCrAl catalysts (x = 0–1) were prepared. The structure of the catalysts was characterized using XRD, SEM and H₂-TPR. The catalytic activity of the catalysts for the combustion of methane was evaluated. The results indicated that in the Ce_1−xCu_xO_2−x/Al₂O₃/FeCrAl catalysts the surface phase structure were the Ce_1−xCu_xO_2−x solid solution, -Al₂O₃ and γ-Al₂O₃. The surface particle shape and size were different with the variety of the molar ratio of Ce to Cu in the Ce_1−xCu_xO_2−x solid solution. The Cu component of the Ce_1−xCu_xO_2−x/Al₂O₃/FeCrAl catalysts played an important role to the catalytic activity for the methane combustion. There were the stronger interaction among the Ce_1−xCu_xO_2−x solid solution and the Al₂O₃ washcoats and the FeCrAl support.     

Walden product, ion-solvent interactions and solvent structure in water-rich mixtures ionic conductances in water-sulfolane, water-acetonitrile and water-dimethylsulfoxide

Conductance measurements are reported for several salts in binary aqueous mixtures containing up to 60 mole % sulfolane, 20 mole % acetonitrile and 20 mole % dimethylsulfoxide. The variations of R = (λ^±₀η₀)_s/(λ^±₀η₀)_w with solvent composition have been compared with those observed in other water-rich mixtures. Alkali cations show R values greater than one with maxima in all the solvent mixtures. This behaviour has been discussed in terms of “sorting”, “averaging” and “steric” effects. Contrary to what happens to alkali cations, halide ions show R values greater or lesser than one according to whether the organic solvent respectively increases or decreases water structure. On these bases we suggest that conductometric behaviour of the halide ions may be indicative of the effect of the cosolvent on the water structure in water-rich mixtures and that DMSO is a water structure breaker.     

Polymerization of methyl methacrylate in the presence of molecular oxygen — a kinetic study

Methyl methacrylate was polymerized in aqueous medium initiated by a copper(II)-ascorbic acidoxygen system at 40°C and a kinetic study of the reaction is presented. The rate of polymerization, R_p showed an increase, constancy and then a decrease with increase in the [Cu²⁺]. The order with respect to [Cu²⁺] was 0.5 in the rate increase region. The order in monomer concentration changed gradually from 1.0 to 2.0 with increase in [Cu²⁺]. R_p became independent of ascorbic acid (AA) concentration and oxygen concentration at high concentrations. These results indicate that termination by mutual interaction of chain radicals predominates at low [Cu²⁺] while termination was exclusively by metal ions at high [Cu²⁺]. R_p was also observed to increase with temperature and ionic strength and to K_p/K_t^1/2 value was calculated and compared with literature values. Chain lengths were determined by viscometry for the polymers obtained under various experimental conditions.     

The glass temperature of polymer blends

The entropy theory of glasses is used to derive the glass temperature, T_g, of a binary polymer blend in terms of the glass temperatures of the two substituents. The formula is T_g = B₁T_g1 + B₂T_g2, where B_i is the fraction of flexible bonds of substituent i. A bond is flexible if rotation about it changes the shape of the molecule. Bonds in side groups as well as in the backbone are to be counted. This formula assumes that the free volume, taken here to be the volume fraction of empty lattice sites, is the same for each of the three materials. It has no parameters. The above equation expressed in weight fractions, W_i, is (T_g − T_g1)W₁(γ₁/ω₁) + (T_g − T_g2)W₂(γ₂/ω₂) = 0, where ω_i is the weight of a monomer unit and gg_i is the number of flexible bonds per monomer unit. A more general treatment is given. One variation of the more general treatment which expresses the properties of the blend in purely additive terms gives T_g = B₁T_g1 + B₂T_g2 + KB₁B₂(T_g1 − T_g2)(V₀₁ − V₀₂), where V_0i are the free volume fractions of the homopolymers at their glass temperatures and K is a constant. The added term is usually small. The most general form of the equation requires the energy of interaction between the two unlike molecules, which can be estimated by volume measurements on the blend.     

Catalytic behavior of La–Sr–Ce–Fe–O mixed oxidic/perovskitic systems for the NO+CO and NO+CH4+O2 (lean-NOx) reactions

Mixed oxides of the general formula La_0.5Sr_xCe_yFeO_z were prepared by using the nitrate method and characterized by XRD and Mössbauer techniques. The crystal phases detected were perovskites LaFeO₃ and SrFeO_3−x and oxides -Fe₂O₃ and CeO₂ depending on x and y values. The low surface area ceramic materials have been tested for the NO+CO and NO+CH₄+O₂ (“lean-NO_x”) reactions in the temperature range 250–550°C. A noticeable enhancement in NO conversion was achieved by the substitution of La³⁺ cation at A-site with divalent Sr⁺² and tetravalent Ce⁺⁴ cations. Comparison of the activity of the present and other perovskite-type materials has pointed out that the ability of the La_0.5Sr_xCe_yFeO_z materials to reduce NO by CO or by CH₄ under “lean-NO_x” conditions is very satisfying. In particular, for the NO+CO reaction estimation of turnover frequencies (TOFs, s⁻¹) at 300°C (based on NO chemisorption) revealed values comparable to Rh/-Al₂O₃ catalyst. This is an important result considering the current tendency for replacing the very active but expensive Rh and Pt metals. It was found that there is a direct correlation between the percentage of crystal phases containing iron in La_0.5Sr_xCe_yFeO_z solids and their catalytic activity. O₂ TPD (temperature-programmed desorption) and NO TPD studies confirmed that the catalytic activity for both tested reactions is related to the defect positions in the lattice of the catalysts (e.g., oxygen vacancies, cationic defects). Additionally, a remarkable oscillatory behavior during O₂ TPD studies was observed for the La_0.5Sr_0.2Ce_0.3FeO_z and La_0.5Sr_0.5FeO_z solids.     

Effect of macromolecular length on anisotropic scattering of light in an electric field

Light scattering by monodisperse solutions of rigid rod-like anisotropic macromolecules, with linear dimensions l of the order of incident wavelength λ, oriented in an external d.c. electric field, →E has been analysed. The relative variations δV^E_v, δH^E_v, δV^E_h, δH^E_h of the scattered light components are discussed for the three values [l/λ] = 1, 0·5, 2, and various reorientation parameters, p = [μE/kT] of the permanent dipole moment μ and q = [(₃ − ₁)E²/2kT] of the moment induced by the principal polarizabilities ₁ = ₂ ≠ ₃. The saturation orientation field strength has been calculated for certain macromolecules with the aim of determining their optical anisotropy numerically.     

Mass Transfer Studies in Stirred AirLift Reactor

In the present work, water and three phase compositions of Solka-Floc, a cellulose fiber for simulating the biomass in bacteria, yeast, and fungal fermentation were studied in a 1.4 m³ stirred airlift reactor. The fractional dispersed phase holdup and the overall volumetric mass transfer coefficients were measured. The dispersed phase riser gas holdup and overall volumetric mass transfer coefficients both increased with increasing riser superficial dispersed phase velocity (0.02-0.1 ms^-1) and agitator speed in the range of 0-5 rs^-1. An increase in the Solka-Floc concentration (1-3% w/v) was found to reduce ε_GR and K_La_L. Empirical correlations have been developed for fractional dispersed phase gas holdup and overall volumetric mass transfer coefficients.     

A data processing system for the Royco aerosol particle counter 225 and determination of the properties of the modified system

A data processing system, consisting of a peak detector, an AD-converter and a minicomputer was developed, which enables the simultaneous counting of particles with different diameters. A computer program was written to handle the output of data in groups of 1, 2, …, 1024 channels. The maximum number of particles that can be counted in a single channel (1024 mode) is 16777215. The resolving time of the system was determined from oscilloscope photographs of pulses generated by monodisperse PSL and DOP particles and amounts to about 15 μsec. The optical counter was calibrated for the size range 0.3–9 μm with monodisperse PSL and DOP aerosols. The response curve is non-singular in between 0.8 and 1.4 μm. The ratio between the standard deviation (σ_K) and the median (K_g) of the channel number distribution for monodisperse aerosols decreases continuously with increasing K_g from 0.7 (at 8) to 0.04 (at 922). Count losses due to coincidence and pulse processing were calculated. Completely ambiguous results have to be expected for concentrations higher than about 450 particle cm⁻³.     

Microwave dielectric properties of rutile (Zn1/3Nb2/3)0.40(Ti1−xSnx)0.60O2 (0.15 ≤ x ≤ 0.30) ceramics

Microwave dielectric properties of (Zn_1/3Nb_2/3)_0.40(Ti_1−xSn_x)_0.60O₂ ceramics were investigated as a function of SnO₂ content (0.15 ≤ x ≤ 0.30). A single phase with tetragonal rutile structure was obtained through the entire composition. The unit-cell volume of the specimens was increased with SnO₂ content, due to the larger ionic radius of Sn⁴⁺ (0.69 Å) than that of Ti⁴⁺ (0.605 Å) for octahedral site. Dielectric constant (K) of the sintered specimens was affected by the dielectric polarizability. Quality factor (Qf) was dependent on the degree of reduction of Ti⁴⁺ ion. With an increase of SnO₂ content, the temperature coefficient of resonant frequency (TCF) of the specimens decreased due to the decrease of the octahedral distortion of rutile structure.     

Mathematical modeling of gas evolution from flowing electrolytes on stable porous anodes of finite matrix phase conductivity

A mathematical model was developed to simulate the effects of the matrix phase conductivity on the behavior of flow-through porous anode operating for gas evolution reaction. The anode material was assumed to be stable and has a finite conductivity. The model accounts for the conductivities of the solution and the matrix phases, the electrode kinetics, hydrodynamics and gas bubble formation. The different ratios and values of the matrix conductivity group, K_σ (a measure of the matrix conductivity) and the electrolyte conductivity group, K_κ (a measure of the electrolyte conductivity) were found to have significant effects on the distributions of current, potential and gas void fraction. When K_σ was a finite value the reaction was pushed towards the back of the electrode and when K_κ was finite the reaction was pushed towards the front face. The effects of the bubble group, χ on the potential and current distributions were investigated under different impacts of K_σ and K_κ. When K_σ was limited the gas bubbles formed at the back of the electrode were forced to travel within the whole bed with the electrolyte streams, causing larger accumulation of the bubbles and hence higher polarization within the bed. The gas bubble formation limited the conductivity of the pore electrolyte resulting in potential and current distributions similar to the case of finite electrolyte conductivity.     

Relationships between crystal structure and microwave dielectric properties of (Zn1/3B2/3)xTi1 − xO2 (B = Nb, Ta) ceramics

Dependence of microwave dielectric properties on the crystal structure of (Zn_1/3B_2/3⁵⁺)_xTi_1 − xO₂ (B⁵⁺ = Nb, Ta) ceramics was investigated as a function of Zn_1/3B_2/3⁵⁺O₂ (B⁵⁺ = Nb, Ta) content (0.4 ≤ x ≤ 0.7). Dielectric constant (K) and the temperature coefficient of resonant frequency (TCF) of sintered specimens were strongly dependent on the structural characteristics of oxygen octahedra in rutile structure. Cation rattling and the distortion of oxygen octahedra were dependent on the bond length ratio of apical (d_apical)/equatorial (d_equatorial) of oxygen octahedra. The quality factor (Qf) was dependent on the reduction of Ti ion as well as the microstructure of the sintered specimens.     

Conductometric study of the ion association of hydrochloric acid in 80 weight per cent 2-methoxyethanol and 20 weight per cent water at temperatures from 20 to 50°C

The electrical conductance of solutions of hydrochloric acid in a mixture of 80 wt% 2-methoxy-ethanol and 20 wt% water has been studied at temperatures from 20 to 50°C. The results have been interpreted with the Fuoss Onsager theory for associated 1-1 types electrolytes. The values of the association constant K_A, the limiting conductivity and the distance parameters have been computed at each temperature.     

Electronic and structural properties of SnxTi1−xO2 solid solutions: a periodic DFT study

The structural and electronic properties of selected compositions of Sn_xTi_1−xO₂ solid solutions (x=0, 1/24, 1/16, 1/12, 1/8, 1/6, 1/4, 1/2, 3/4, 5/6, 7/8, 11/12, 15/16, 23/24 and 1) were investigated by means of periodic density functional theory (DFT) calculations at B3LYP level. The calculations show that the corresponding lattice parameters vary non-linearly with composition, supporting positive deviations from Vegard’s law in the Sn_xTi_1−xO₂ system. Our results also account for the fact that chemical decomposition in Sn_xTi_1−xO₂ system is dominated by composition fluctuations along [0 0 1] direction. A nearly continuous evolution of the direct band gap and the Fermi level with the growing value of x is predicted. Ti 3d states dominate the lower portion of the conduction band of Sn_xTi_1−xO₂ solid solutions. Sn substitution for Ti in TiO₂ increases the oxidation–reduction potential of the oxide as well as it renders the lowest energy transition to be indirect. These two effects can be the key factors controlling the rate for the photogenerated electron–hole recombination. These theoretical results are capable to explain the enhancement of photoactivity in Sn_xTi_1−xO₂ solid solutions.