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.     

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.     

Fracture toughness of (Ce) stabilized ZrO2/Al2O3 composites

Three techniques for the determination of K_Ic in Ce-stabilized ZrO₂/Al₂O₃ composites have been evaluated: the single-edge-notched beam (SENB); the indentation strength in bending (ISB) and the indentation fracture (IF). Comparative measurements, performed on samples prepared by sintering uniaxially pressed powders obtained by a chemical route, showed that whatever the technique used, K_Ic increased as the Al₂O₃ grain size decreased.

The three methods give similar results if some procedural improvements are introduced, namely: (i) the polished samples are annealed prior to testing: (ii) a more reproducible notching technique would be developed for the SENB method; and (iii) the crack shape and length are known exactly in the IF technique.

In the IF test, the crack shape profile is of Palmquist type at low indentation loads while a transition to a half-penny-shaped crack occurs at higher loads.     

Experimental studies of air-blast atomization on the CO2 capture with aqueous alkali solutions

In this work, an air-blast atomizing column was used to study the CO₂ capture performance with aqueous MEA (mono-ethanol-amine) and NaOH solutions. The effects of gas flow rate, the liquid to gas ratio (L/G), the CO₂ concentration on the CO₂ removal efficiency (η) and the volumetric overall mass transfer coefficient (K_Ga_v) were investigated. The air-blast atomizing column was also compared with the pressure spray tower on the studies of the CO₂ capture performance. For the aqueous MEA and NaOH solutions, the experimental results show that the η decreases with increasing gas flow rate and CO₂ concentration while it increases with increasing L/G. The effects on K_Ga_v are more complicated than those for η. When the CO₂ concentration is low (3 vol%), K_Ga_v increases with increasing gas flow rate while decreases with increasing L/G. However, when the CO₂ concentration is high (9.5 vol%), as the gas flow rate and L/G increases, K_Ga_v increases first and then decreases. The aqueous MEA solution achieves higher η and K_Ga_v than the aqueous NaOH solution. The air-blast atomizing column shows a good performance on CO₂ capture.     

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.     

Insight into solute-solute and solute-solvent interactions of semicarbazide hydrochloride in water and D-glucose/D-sucrose+water solutions at temperatures (293.15 to 318.15) K

The solute-solute and solute-solvent interactions of drug semicarbazide hydrochloride with carbohydrates (D-glucose/D-sucrose) are investigated by using volumetric, viscometric and acoustic properties. The measurements of the densities ρ, ultrasonic speeds u, and viscosities η. of semicarbazide hydrochloride in 5% and 10% D-glucose/D-sucrose+water (w/w) solutions were carried out at temperatures (293.15-318.15) K and at pressure, p=101 kPa. The apparent molar volumes, V_ϕ, limiting apparent molar volumes,V_ϕ°, apparent molar compressibilities, K_{s, ϕ}, limiting apparent molar compressibilities, K_s,ϕ°, partial molar expansibilities, E_ϕ°, transfer volumes, V_ϕ,tr° and transfer compressibilities, K_s,ϕ,tr° have been calculated from the experimental data. The viscosity data were examined by using the Jones-Dole equation and the viscosity A and B coefficients were evaluated. The results are discussed in terms of solute-solute and solute-solvent interactions in these solutions. The structure making/breaking ability of semicarbazide hydrochloride is examined using the sign of temperature derivative of B-coefficient, dB/dT.     

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.     

The fracture behaviour of a PXE/HIPS polyblend

As part of an overall examination of the fatigue crack propagation (FCP) behaviour of impact-modified polymers, a study of the fracture morphology of a PXE/HIPS polyblend polymer subjected to monotonic and cyclic loading conditions is reported. The HIPS rubbery-phase particles are found to fail by particle rupture in both fatigue and fast fracture. Another impact modifying addition, PE, is found to fail by a combination of interfacial rupture and tearing, the balance depending on the prevailing stress intensity value and the strain rate. Matrix failure is via multiple crazing at low fatigue crack growth rates, but shear yielding is believed to become a major fracture mechanism with increasing K. The degree of plastic deformation of the matrix increases with increasing strain rate. This fact is manifested by the increasing void size associated with the interfacial separation of the PE particles.     

The correlation of slow crack growth in linear polyethylene by the J-integral

The fracture of a polyethylene (PE) homopolymer by slow crack growth was measured with a three point bending (TPB) specimen and a single edge notch tension (SENT) specimen. The crack growth rate correlated with the stress intensity for each type of specimen. However, for a given K, SENT specimens exhibited a faster crack growth rate than TPB specimens. Since PE is non-linear, the J-integral is more appropriate than K and it was found that J does correlate the SENT and TPB results. In addition, the degree of non-linearity of the PE was increased by quenching. For the quenched state it was also found that J correlated the SENT and TPB results in accordance with the dependence of J on the degree of non-linearity of the material.     

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.     

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.     

Fracture Toughness of a Partially Stabilized ZrO2 in the System CaO-ZrO2

The room-temperature fracture behavior of partially stabilized ZrO₃ (PSZ) in the system CaO-ZrO₂ was investigated. Fracture energy was measured using standard single-edge-crack and work-of-fracture techniques. Attempts were made to relate the fracture toughness parameters to the microstructure of the material. Stable crack propagation was always observed; a model is proposed to explain these observations on the basis of the formation of a microcrack zone at the tip of a propagating crack. The occurrence of initial stable crack propagation is explained in terms of an increase in microcrack zone size. The possibility that crack stability results from testing geometry superimposed on the microcracking stability is also discussed.     

Compared imbibitions of ordinary and high performance concrete with null or positive water pressure head

A method to simultaneously measure the moisture diffusion coefficient, D_θ, of unsaturated concrete, and the saturated concrete hydraulic conductivity, K_l, was developed for cylindrical specimens placed on a container filled with water that could be maintained at a given hydraulic pressure. Ordinary Portland cement Concrete (OPC) with a moderate and High Performance Concrete (HPC) with a low water to cement ratio were tested. The time dependent distribution of water content in the specimens was measured using a non-intrusive method based on gamma-ray attenuation. The measurements were conducted with varying hydraulic head (positive or null). Boltzmann's transformation was used to analyze the experimental results obtained at different hydraulic pressures and the difference between the null (or atmospheric) and positive pressure results is used to accurately determine K_l and also D_θ . This paper will present the results obtained using this original method, possible interpretations and future research.     

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.     

Effect of Microstructure on Strength of Si3N4-SiC Composite System

The Si₃N₄-SiC composite system was investigated to better understand the effect of microstructure on the strength-controlling factors, i.e. fracture energy, elastic modulus, and crack size. Silicon carbide dispersions with average particle sizes of 5, 9, and 32 μm were used to form 3 composite series within this system, each containing 0.10, 0.20, 0.30, and 0.40 vol fraction of the dispersed phase. These composites were fabricated by hot-pressing. Fracture energy and strength values were measured for each composite. A linear relation between the elastic modulus of the two phases was assumed. The crack size was calculated for each composite using the appropriate property values. The strength behavior of the 9- and 32-μm series was controlled by the crack size, which, in turn, was controlled by the particle size and volume fraction of the SiC phase. Particle size and volume fraction did not affect the crack size of the 5-μm series, in which strength was controlled by both fracture energy and elastic modulus. Strengths measured at 1400°C and thermal conductivity measurements indicate that several of these composites are promising as high-temperature structural materials.     

Size effect on dielectric properties of fine-grained BaTiO3 ceramics

The effect of grain size on the dielectric behavior of high-purity, fine-grained BaTiO₃ ceramic has been investigated. It was found that the dielectric constant and dissipation factor changed much with the decreasing of average grain size. The specimen with grain size of 280 nm had a high dielectric constant at room temperature, and the _r-T and tanδ-T curves remarkably changed with the grain size. Part of the grains remaining ferroelectric structure was ascribed to the high value of dielectric constant. ©     

K R -Curve Behavior of Duplex Ceramics

The fracture toughness behavior during crack growth ( K ^R -curve behavior) of duplex ceramics is investigated. Different types of K ^R -curves can be distinguished depending on the microstructural designs of these materials which are characterized by the volume fraction and size of the dispersed pressure zones, and by their effective volume expansion. According to their K ^R -curve behavior, duplex ceramics can be subdivided into two groups consisting of "short-range" and "long-range" toughened materials. The experimental results are discussed regarding the appearance of different toughening mechanisms which are documented by crack path micrographs. An unusual toughening effect, a "crackbranching chain reaction," is documented by in situ observations. The critical stress to nucleate the observed process zone development is calculated and compared with the internal stress intensity factor K _i which has been previously proposed for these materials and with the material strength.     

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.     

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.