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.     

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.     

Kinetics and equilibrium swelling of gelatine gels

The swelling features of gelatine gels in water (good solvent) were studied as a function of thermodynamic conditions of sol—gel transition and ripening. It is shown that the degree of equilibrium swelling Q_e varies with the volume fraction of the polymer in a casting solution φ_o in accordance with the prediction of the classic theory: Q_e φ_o^−0.4. Q_c, as a function of the gelation temperature T_g, the ripening time t_r and φ_o, can be rescaled and described by the single empirical equation: Q_e T_g^−x t_r^−yφ_o^−0.4, where x = 0.1, y = 0.15 for wet gels and X = −0.5, y = 0.04 for dried gels. The kinetics of macroscopic swelling is described by the equation of Peters and Candau, with values of collective diffusion coefficients being in good agreement with values obtained by other workers via photon correlation spectroscopy.     

Electrolyte—solvent interaction in the dipolar aprotic solvent dimethyl sulphoxide at 25°C

Conductance measurements are reported for s-alkylisothiouronium bromide, iodide and picrate salts in the dipolar aprotic solvent DMSO at 25°C. The data were analysed by Fuoss's equation (1975–1980) for 1:1 electrolytes, from which the values of Λ₀, the Gurney's cosphere diameter R and K_A are obtained. The results are discussed in the light of the recorded values of the constants K_R and K_S and the free energy term G_s.     

Analyzing indentation behavior of LaGaO3 single crystals using sharp indenters

In this work, the mechanical properties of (1 0 0) and (0 0 1) oriented LaGaO₃ single crystals have been studied using sharp indenters. Vickers hardness values for both the (1 0 0) and (0 0 1) samples were found to be in the same range (8 GPa). The values for the indentation fracture toughness (K_R) from Vickers indentation on the (1 0 0) samples were determined to be 0.8 ± 0.2 MPa m^1/2. Different crack lengths, implying a strong anisotropy in the indentation fracture toughness values, were observed in the two mutually perpendicular directions in the indentations on the (0 0 1) samples. These measurements led to estimates of 0.5 ± 0.1 and 1.3 ± 0.3 MPa m^1/2 for the two different sets of cracks on the (0 0 1) samples. In situ nanoindentation inside the SEM using a cube-corner indenter has also been used for studying the indentation fracture response of these samples.     

Aerosol classification by electric mobility: apparatus, theory, and applications

An improved version of the Hewitt (differential) electric mobility analyzer was developed and its classifying characteristics were determined theoretically. The central mobility of the classified aerosol was found to be (q_c + q_m)/4πΛV, where q_c and q_m are the clean air and main outlet flows, respectively, Λ is a geometric factor, and Λ is the center rod voltage. The half-width of the mobility band was found to be (q_a + q_s)/4πΛV, where q_a and q_s are the aerosol and sampling outlet flows, respectively. These expressions were verified by the tests with a monodisperse aerosol of known size and low charge.

A major advantage of this device is that the classified aerosol fraction remains airborne, ready for further use or analysis. Thus, one application of the device is the production of monodisperse test aerosols of known size, charge, and concentration by classification of a polydisperse aerosol. Other current applications include accurate measurement of particle electric mobility moments and high-resolution particle size analysis for polydisperse aerosols in the 0.005–1.0 μm size range.     

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.     

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.     

Direct Correlation Between Adhesion Promotion and Coupling Reaction at Immiscible Polymer-Polymer Interfaces

Hugh Brown has shown that interfacial entanglements govern adhesion between two polymers. We demonstrate this for three systems by adding interfacial chains via chemical coupling. The adhesion between polypropylene (PP)/amorphous polyamide (aPA) was reinforced by the coupling reaction of maleic anhydride grafted PP (PP-g-MA) and the primary amine groups on aPA; huge increases in adhesion were observed. A good correlation between critical fracture toughness, G_c, and PP-g-MA concentration squared follows Brown's crazing mechanism. For a polystyrene (PS)/aPA interface reinforced by the coupling reaction of poly(styrene-r-maleic anhydride) (PS-r-MA)/aPA only modest adhesion increases in G_c were observed through the whole PS-r-MA concentration range. This different behavior of G_c vs. functional polymer concentration is believed to be caused by segregation of the formed graft copolymers at the interface. The relationship between G_c and the extent of coupling was studied quantitatively with a model PS/PMMA system. The interface was reinforced by the coupling reaction of 0-10% PS-NH₂/PMMA-anh. G_c was measured with the asymmetric dual cantilever beam test (ADCB) and the amount of copolymer formed at the interface was determined by a fluorescence labeling technique. G_c is low and is linear in block copolymer interfacial coverage (Σ), indicating a chain scission mechanism. Reasonable agreement was achieved between experiment and theoretical prediction based on the energy to break C-C bonds.     

Einfluss der säurekonzentration auf die anodische auflosung des indiumamalgams

The effect of HClO₄ concentration on the rate of electrode processes on a stationary indium amalgam electrode in stirred In(ClO₄)₃ solutions at constant ionic strength (3 M NaClO₄) has been investigated. Alongside with the measurement of polarization curves, the exchange current and the true rate of the anodic process of amalgam dissolution (i_a at different potentials (φ) were determined by a radiochemical method. With an increase in the HClO₄ concentration, a sharp decrease in the exchange current is observed; at HClO₄ concentrations below 0.2 M at constant φ, the i_a values are inversely proportional to the HClO₄ concentration. The experimental results are expressed by the equation p] i_a = k[In][H⁺]⁻¹ exp (βφF|RT),

where [In] is the concentration of the indium amalgam. The rate of the cathodic process at constant φ also decreases with a decrease in pH. A hypothesis is advanced according to which partially hydrolysed In(H₂O)₅OH²⁺ ions, rather than In(H₂O)₆³⁺ which are predominant in the solution, participate in the electrode process. The OH⁻ ions, like some other anions, appear to be capable of facilitating the transfer of electrons between the electrode surface and the reacting particle. An analysis of the results obtained (and of data in the literature) shows that partially hydrolysed metal ions play an essential role in electrode processes.     

AFeO3 (A=La, Nd, Sm) and LaFe1−xMgxO3 perovskites as methane combustion and CO oxidation catalysts: structural, redox and catalytic properties

Catalytic methane combustion and CO oxidation were investigated over AFeO₃ (A=La, Nd, Sm) and LaFe_1−xMg_xO₃ (x=0.1, 0.2, 0.3, 0.4, 0.5) perovskites prepared by citrate method and calcined at 1073 K. The catalysts were characterized by X-ray diffraction (XRD). Redox properties and the content of Fe⁴⁺ were derived from temperature programmed reduction (TPR). Specific surface areas (SA) of perovskites were in 2.3–9.7 m² g⁻¹ range. XRD analysis showed that LaFeO₃, NdFeO₃, SmFeO₃ and LaFe_1−xMg_xO₃ (x·0.3) are single phase perovskite-type oxides. Traces of La₂O₃, in addition to the perovskite phase, were detected in the LaFe_1−xMg_xO₃ catalysts with x=0.4 and 0.5. TPR gave evidence of the presence in AFeO₃ of a very small fraction of Fe⁴⁺ which reduces to Fe³⁺. The fraction of Fe⁴⁺ in the LaFe_1−xMg_xO₃ samples increased with increasing magnesium content up to x=0.2, then it remained nearly constant. Catalytic activity tests showed that all samples gave methane and CO complete conversion with 100% selectivity to CO₂ below 973 and 773 K, respectively. For the AFeO₃ materials the order of activity towards methane combustion is La>Nd>Sm, whereas the activity, per unit SA, of the LaFe_1−xMg_xO₃ catalysts decreases with the amount of Mg at least for the catalysts showing a single perovskite phase (x=0.3). Concerning the CO oxidation, the order of activity for the AFeO₃ materials is Nd>La>Sm, while the activity (per unit SA) of the LaFe_1−xMg_xO₃ catalysts decreases at high magnesium content.     

Microhardness and Fracture Toughness Anisotropy in Cubic Zirconium Oxide Single Crystals

Vickers and Knoop indentation tests have been used to study the fracture and deformation characteristics of 9.4-mol%-Y₂O₃-stabilized ZrO₂ single crystals. K_c is anisotropic, with values of 1.9 and 1.1 MPa·m^1/2 for radial cracks propagating along (100) and (110), respectively. The toughness for these two orientations was also determined using the single-edge notched-beam geometry, and yielded values of 1.9 and 1.5 MPa·m^1/2.     

The Strength of an Adhesive Weak Boundary Layer

The strength of model adhesive joints composed of different thicknesses of low (10,300 narrow distribution) molecular weight polystyrene sandwiched between high molecular weight poly(methyl methacrylate) has been studied. The joints model a polymer-to-polymer adhesive bond across a low-strength boundary layer. As an appraisal of strength, the fracture toughness was measured by driving a cleavage wedge into the specimens along the polystyrene layer and analyzing the results with Kanninen's equation. The fracture toughness for both crack growth initiation K_Ic and arrest K_Ia was essentially that for bulk poly(methyl methacrylate) until the polystyrene layer exceeded 1 μm, at which K_Ic and K_Ia fell by approximately 85%. Examination of the fracture surfaces of specimens with polystyrene layers less than 1 μm thick revealed that the fracture path was predominantly in the poly(methyl methacrylate). Possible reasons for this are discussed.     

On mass transfer effect due to electrolytically evolved gas

Based on the Ibl penetration model mass transfer equations for gas-evolving electrodes were derived and compared to the effect of forced convection. Experimental studies were conducted in a rectangular flow channel with the working electrode facing downward. The variables were linear bubble velocity, linear electrolyte velocity, nature of the gas and electrode position. Up to bubble velocities (U_x) of 2 and 6 cm s⁻¹ for O₂ and H₂ gases respectively, the thickness of the Nernst diffusion layer (δ_av) was described well by the equation δ_av = [Dd_eL/(U_x)_av]^1/3. Intermediate slopes between − 1/3 and − 1 were observed for O₂ bubble velocities between 2 and 6 cm s⁻¹. A theoretical derivation suggests that in the absence of bubble coalescence, the mass transfer effect due to laminar flow induced by electrolytically evolved gas exceeds that due to forced external laminar flow for all practical channel designs.     

Electrosorption and inhibition properties of p-norborn2-yl phenolate ions at the mercury/solution interface

The electrosorption properties of p-norborn-2-yl phenolate ions in alkaline solutions were investigated by ac polarographic and electrocapillary measurements.

Two adsorption regions were found. At low bulk surfactant concentrations the adsorption at the positively charged electrode (−0.2 E −0.6 V) is predominant while at higher surfactant concentrations the adsorption at the negatively charged electrode (−0.6 E −1.0 V) is more pronounced. At E = −0.40 V the adsorption parameters were determined (a ≈ 2; ΔG°_A = −32.5 ± 1 kJ mol⁻¹. Between −0.6 E −1.0 V one potential of maximum adsorption for all concentrations does not exist and therefore the adsorption parameters could not be calculated.

At E = −0.40 V progressive two-dimensional nucleation with a nucleation order of 3 was observed which corresponds well with the high attraction constant.

The electrode reaction S₂O²⁻₈ + 2e⁻ → 2 SO²⁻₄ is inhibited by norborn-2-yl phenolate ions in the potential range −0.2 E −0.6 V. In the second potential range of capacity decrease the electrode process is much less retarded. At E = −0.40 V, in a similar manner as described for neutral molecules, a linear dependence of the log k_s (k_s apparent rate constant) on ln c_A and π (π = surface film pressure), respectively, has been found.     

Dissociation constant of bibenzyl measured by e.s.r.

The equilibrium constant for the dissociation of bibenzyl to form benzyl radicals has been measured in dilute solutions of bibenzyl in toluene at 605°C and at 20.7 MPa (200 atm) and 13.8 MPa (133 atm) using electron spin resonance to assay the concentration of the benzyl radical. The value for K_c, the equilibrium constant expressed in terms of concentrations, was found to be 0.75×10⁻¹⁰ moll⁻¹ within a factor of 1.7 at both pressures.     

Grain growth in TiO2-added ZnO–Bi2O3–CoO–MnO ceramics prepared by chemical processing

The effect of TiO₂ on the grain growth of the ZnO–Bi₂O₃–CoO–MnO ceramic system prepared by chemical coprecipitation, was studied between 1150 and 1300 °C in air. Bi₂O₃ melts during firing, and then TiO₂ dissolves into Bi₂O₃-rich liquid. TiO₂ initially reacts with Bi₂O₃ to form Bi₄Ti₃O₁₂. Above ≈1050 °C, Bi₄Ti₃O₁₂ reacts with ZnO to form Zn₂TiO₄ spinel phase. The kinetic study of grain growth carried out using the expression Gⁿ–G_oⁿ=K_o·t·exp(−Q/RT) gave grain exponent (n) value as 6 and the apparent activation energy (Q) as 226.46 kJ/mol. 1.00 mol% TiO₂ addition increased the grain growth exponent value from 6 to 7 and apparent activation energy with 1.00 mol% TiO₂ addition was found to be 197.10 kJ/mol. The ZnO grain size gradually increases with increasing TiO₂ content. Addition of TiO₂ may increase the reactivity of the Bi₂O₃-rich liquid towards the ZnO grain, thus affecting the ZnO grain growth.     

Cr/V/Sb mixed oxide catalysts for the ammoxidation of propane to acrylonitrile: Part I: Nature of the V species

Rutile-type Cr/V/Sb mixed oxides, catalysts for the ammoxidation of propane to acrylonitrile, were prepared and characterized. For atomic ratios between components equal to Cr/V/Sb 1/x/1 and 1/x/2 the systems were monophasic, but different types of compounds formed depending on the ratio between the three metals. The compositional parameter which most affected the nature of the compound formed was the (Cr+V)/Sb atomic ratio. When this ratio was between 2 and ≈1, a rutile Cr³⁺/V⁴⁺/Sb⁵⁺ mixed oxide of composition Cr₁V_xSb₁O_4+2x developed (0<x<1), which in practice corresponds to a solid solution between 1 CrSbO₄ and x VO₂. When the (Cr+V)/Sb ratio was between 0.5 and ≈1, a rutile Cr³⁺/V³⁺/Sb³⁺/Sb⁵⁺ mixed oxide of composition CrV_xSb_1+x+2zO_4+4x+4z developed (0<x<1), which corresponds to a solid solution between 1 Cr³⁺Sb_z³⁺Sb_1+z⁵⁺O_4+4z and x VSbO₄. The distinction between the two classes of compounds was not clear-cut, and when the (Cr+V)/Sb atomic ratio was around 1, mixed oxides containing both V³⁺ and V⁴⁺ formed. Values of the (Cr+V)/Sb atomic ratio lower than ≈0.5 led to the additional formation of antimony oxide.     

Indentation resistance of zirconia ceramics and crystals

Special features of resistance to Vickers indentation exhibited by ZrO₂ ceramics and crystals are investigated. The relation between their behavior in indentation and deformation in static bending is investigated. The anisotropy of lateral cracks in the (001) plane in partially stabilized ZrO₂ crystals is shown to correspond to the anisotropy of their elasticity moduli. New variants of the formulas for evaluating the crack resistance in indentation of zirconia materials, which obey Hooke's law until the moment of failure, are presented. Translated from Ogneupory, No. 3, pp. 2 – 12, March, 1996.     

Small-angle neutron scattering from branched epoxide resins

Small-angle neutron scattering experiments in the range of q² from 0.01 to 25 nm⁻² have been carried out on branched epoxide resins based on bisphenol-A at the Institute Laue—Langevin (I.L.L) in Grenoble (q=(4π/λ) sin(θ/2)). Measurements were made with six samples in the range of M_W from 1500 to 19 000 and four concentrations between 1.3 and 10% (w/w) in deuterated diglyme. The results are as follows: (i) The mean square radius of gyration follows a relationship S²_z=4.69×10⁻⁴M^1.20_W (nm²). (ii) In all cases fairly large second virial coefficients A₂ are obtained which, however, decrease strongly with molecular weight. Above M_W=2500, the virial coefficient follows the relationship A₂=1.6M^−0.85_W (mol cm³g⁻²). (ii) The reciprocal particle scattering factor as a function of q² exhibits only a slight upturn and otherwise shows the behaviour of a randomly branched polycondensate. The slight upturn is discussed as being caused by the finite volume of the monomeric unit. Possible reasons for the high exponent in the S²_z versus M_W dependence are briefly discussed.