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.     

Computations of the Mie scattering coefficient corrected for the forward scattering

Computations of the actual Mie scattering coefficient (K_a) have been performed by taking into account the acceptance angle (₀) of the optical receiving system. Results show that in problems concerning the determination of the aerosol particle parameters through scattering methods, the total scattering coefficient (K_r) computed by taking ₀ = 0 has to be substituted by K_a. Tables of K_a have been arranged for the following values of the particle refractive index (m), size parameter (x) and ₀: M = 1·33, X = 0·1 (0·1) 200 and m = 1·55, X = 0·1 (0·1) 100, for ₀ = 0·1° (0·1°) 1·0°.     

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.     

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.     

RESIDENCE TIMES OF TWO- AND THREE-COMPONENT MIXTURES IN CASCADING ROTARY DRYERS

The residence times of the components of two- and three-component mixtures of fine (195 µm), coarse (1315 µm) and very coarse (5040 µm) sands were measured in a pilot-scale cascading rotary dryer. The effects of mixture composition and air velocity (0-5.4 m s^-1) were determined. With no air flowing through the drum, the residence times of the individual components were almost the same as that of the overall mixture. Increasing the gas velocity caused a large decrease in residence time. In contrast, particle size had very little effect. The spread of residence times increased with air velocity, peaking between 2 and 4 m s^-1; composition had very little effect on the spread. The residence time of the overall mixture could be calculated using the particle transport model of Matchett and Baker if both the modified drag coefficient Φ_d and the particle Reynolds number Re_p were based on the superficial air velocity and the mass-average particle diameter.     

Mass transfer at cylindrical gas evolving electrodes

Mass transfer coefficients at cylindrical, H₂ evolving electrodes, were measured by determining the reduction rate of K₃Fe(CN)₆. The variables studied were: gas discharge rate V, diameter of the cylinder D, height and position of the cylinder. The diameters ranged from 0·2–2·5 cm, the cd from 25-380 mA/cm². For horizontal cylinders, the following correlation was found: log K = a + 2·17 log(V^0·11/D^0·08). The application of gas evolving cylindrical electrodes in industrial electrolysis is discussed in comparison with rotating electrodes.     

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.     

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.     

NOx removal from the flue gas of oil-fired boiler using a multistage plasma-catalyst hybrid system

The study on removal of NO_x from the flue gas of oil-fired boiler has been carried out using non-thermal plasma cum catalyst hybrid reactor at 150 °C. Propylene (C₃H₆) was used as a reducing agent. A multistage plasma-catalyst hybrid reactor was newly designed and successfully operated to clean up the flue gas stream having a flow rate of 30 Nm³/h. TiO₂ and Pd/ZrO₂ wash-coated on cordierite honeycomb were used as catalysts in the present study. Though the plasma-catalyst hybrid reactor with TiO₂ showed good activity on the removal of NO yet it removed only 50–60% of NO_x because a significant portion of NO oxidized to NO₂. On the contrary, the plasma-catalyst hybrid reactor with Pd/ZrO₂ removed about 50% of inlet NO with a negligible amount of NO oxidation into NO₂. The plasma/dual-catalysts hybrid system (front two units of plasma-Pd/ZrO₂ + rear two units of plasma/TiO₂) proved to be very promising in NO_x removal in the presence of C₃H₆. DeNO_x efficiency of about 74% has been achieved at a space velocity of 3300/h at 150 °C.     

Thermoelectric characterization of NaxMx/2Ti1−x/2O2 (M=Co, Ni and Fe) polycrystalline materials

Layered -titanate materials, Na_xM_x/2Ti_1−x/2O₂ (M=Co, Ni and Fe, x=0.2–0.4), were synthesized by flux reactions, and electrical properties of polycrystalline products were measured at 300–800 °C. After sintering at 1250 °C in Ar, all products show n-type thermoelectric behavior. The values of both d.c. conductivity and Seebeck coefficient of polycrystalline Na_0.4Ni_0.2Ti_0.8O₂ were ca. 7×10³ S/m and ca. −193 μV/K around 700 °C, respectively. The measured thermal conductivity of layered -titanate materials has lower value than conductive oxide materials. It was ca. 1.5 Wm⁻¹ K⁻¹ at 800 °C. The estimated thermoelectric figure-of-merit, Z, of Na_0.4Ni_0.2Ti_0.8O₂ and Na_0.4Co_0.2Ti_0.8O₂ was about 1.9×10⁻⁴ and 1.2×10⁻⁴ K⁻¹ around 700 °C, respectively.     

PHOTOCATALYTIC OXIDATION OF ALDEHYDES/PCE USING POROUS ANATASE TITANIA AND VISIBLE-LIGHT-RESPONSIVE BROOKITE TITANIA

We have synthesized an annealed porous aerogel titania (LUAG2), which demonstrates a very high photocatalytic activity for aldehydes and perchloroethylene (PCE) photocatalytic oxidation (PCO) in gas phase under blacklight and fluorescent light irradiation. LUAG2 has a BET surface area of 237 m²/g and a porosity of 0.31 (volume fraction). X-ray diffraction (XRD) analysis shows LUAG2 is nearly pure anatase. It has improved the destruction of PCE and aldehydes as a group by 10-34% with black light compared to Degussa P-25. The optimum water vapor to butyraldehyde molar ratio is around 1/3. LUAG2 also shows better mineralization to CO₂ than Degussa P-25 TiO₂ does. Under irradiation of a 4 W fluorescent lamp LUAG2 gives a consistently higher conversion than that of Degussa P-25. The highly active photocatalyst indicates potential applications in indoor and outdoor environmental pollution control. A visible-light-responsive TiO₂, NTB 200, is also investigated for comparison purposes.     

TERNARY NaCl+LiCl+H2O MIXED ELECTROLYTE SYSTEM: DETERMINATION OF ACTIVITY COEFFICIENTS BASED ON POTENTIOMETRIC METHOD

The mean activity coefficients for NaCl in a ternary electrolyte system were determined by the potentiometric method, at 25°C, using a solvent polymeric (PVC) sodium-selective membrane electrode (Na⁺ ISE), containing N,N'-dibenzyl-N,N'-diphenyl-1,2-phenylenedioxydiacetamide as ionophore, and combined with an Ag/AgCl electrode. The potentiometric measurements were performed at the same ionic strengths in different series of mixed salt solutions, each characterized by a fixed salt molal ratio r (where r = m₁/m₂ = 1, 10, 50, 100). The nonideal behavior of the ternary NaCl(m₁) + LiCl(m₂) + H₂O electrolyte system was described based on the Pitzer ion-interaction model for mixed salts over the ionic strength ranging from 0.01 up to about 4 mol/kg. Two- and three-particle Pitzer interaction parameters for a mixed electrolyte system were determined based on potentiometric data, and the critical role of potentiometric selectivity coefficient (K₁₂) of ISE as limiting factor in the potentiometric measurements was analyzed.     

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.     

UNSTEADY CONVECTIVE DIFFUSION IN BLOOD FLOW THROUGH A TUBE

The paper presents an exact analysis of unsteady convective dispersion of a solute in a Casson fluid (assumed as the non-Newtonian behaviour of blood) flowing in a tube. Using a generalized dispersion model, which is valid for all time after the injection of the solute in the flow, we evaluate the axial dispersion coefficients as functions of time. The variation of the asymptotic dispersion coefficient K₂* with y₀ (the dimensionless radius of the plug flow region) shows that K₂* first increases with y₀, reaches a maximum and then decreases. The behaviour of the dimensionless dispersion coefficient K₂(T) - Pe^-2 with time T is also shown graphically.     

Catalytic decomposition and mass transfer of aqueous ozone promoted by Fe-Mn-Cu/γ-Al2O3 in a rotating packed bed

This study investigated catalytic decomposition and mass transfer of aqueous ozone promoted by Fe-Mn-Cu/γ-Al₂O₃ (Cat) in a rotating packed bed (RPB) for the first time. The results showed that the value of the overall decomposition rate constant of ozone (K_c) and overall volumetric mass transfer coefficient (K_La) are 4.28×10^-3 s^-1 and 11.60×10^-3 s^-1 respectively at an initial pH of 6, β of 40, of 60 mg·L^-1 and Q_L of 85 L·h^-1 in deionized water, respectively. Meanwhile, the K_c and K_La values of Fenhe water are 0.88×10^-3 s^-1 and 2.51×10^-3 s^-1 lower than deionized water, respectively. In addition, the K_c and K_La values in deionized water for the Cat/O₃-RPB system are 44.86% and 47.41% higher than that for the Cat/O₃-BR (bubbling reactor) system, respectively, indicating that the high gravity technology can facilitate the decomposition and mass transfer of ozone in heterogeneous catalytic ozonation and provide some insights into the industrial wastewater.     

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.     

AN ARTIFICIAL NEURAL NETWORK APPROACH TO CAPILLARY RISE IN POROUS MEDIA

An artificial neural network (ANN) was used to analyze the capillary rise in porous media. Wetting experiments were performed with 15 liquids and 15 different powders. The liquids covered a wide range of surface tension (15.45-71.99 mJ/m²) and viscosity (0.25-21 mPa.s). The powders also provided an acceptable range of particle size (0.012-45 μm) and surface free energy (25.5-62.2 mJ/m²). An artificial neural network was employed to predict the time of capillary rise for a known given height. The network's inputs were density, surface tension, and viscosity for the liquids and particle size, bulk density, packing density, and surface free energy for the powders. Two statistical parameters, the product moment correlation coefficient (r²) and the performance factor (PF/3), were used to correlate the actual experimentally obtained times of capillary rise to: (i) their equivalent values as predicted by a designed and trained artificial neural network; and (ii) their corresponding values as calculated by the Lucas-Washburn equation as well as the equivalent values as calculated by its various other modified versions. It must be noted that for a perfect correlation r² = 1 and PF/3 = 0. The results showed that only the present ANN approach was able to predict with superior accuracy (i.e., r² = 0.92, PF/3 = 51) the time of capillary rise. The Lucas-Washburn calculations gave the worst correlations (r² = 0.15, PF/3 = 1002). Furthermore, some of the modifications of this equation as proposed by different workers did not seem to conspicuously improve the relationships, giving a range of inferior correlations between the calculated and experimentally determined times of capillary rise (i.e., r² = 0.27 to 0.48, PF/3 = 112 to 285).     

GAS PERMEANCE BEHAVIOR AT ELEVATED TEMPERATURE IN MESOPOROUS ANODIC OXIDIZED ALUMINA SYNTHESIZED BY PULSE-SEQUENTIAL VOLTAGE METHOD

Mesoporous anodic oxidized alumina (MAOA) capillary tubes with and without a barrier layer have been synthesized by applying a pulse-sequential voltage. The single gas permeances at an elevated temperature and the thermal and hydrothermal stabilities of MAOA were investigated. A highly oriented radial mesopore channel with pore sizes from 40 to 4 nm was formed in the MAOA tubes. Micropores with sizes from 0.4 to 0.8 nm were formed in the barrier layer. The H₂ permeance of MAOA with a barrier layer (barrier type) was approximately 540 times lower than that of MAOA without a barrier layer (block type) at 773 K. The H₂/N₂ permselectivity of the barrier type in the temperature range from 333 to 673 K was 3.4; those of the barrier type at 773 and 823 K were 4.4 and 11, respectively. On the other hand, the H₂/N₂ permselectivities of the block type were from 3.1 to 3.6 in the temperature range from 333 to 773 K. The H₂ permeance and the H₂/N₂ permselectivity of the amorphous silica membrane on the block type were 1.1 × 10^-7 mol/m² · s · Pa and 40 at 773 K, respectively. MAOA synthesized by the pulse-sequential voltage method can be applied to the mesoporous support of the gas separation membrane at elevated temperatures.     

Alkali/Chloride release during refuse incineration on a grate: Full-scale experimental findings

Waste to energy (WtE) plants are utilised for the production of heat and electricity. However, due to corrosion at super heater surfaces a relatively low 25% of the waste lower heating value can with the present technology be converted to electricity. High contents of Cl, Na, K, Zn, Pb and S in waste cause relatively high super heater corrosion rates. The Cl-content in waste is one of the key-factors for volatilisation of alkali and heavy metals in WtE plants. Little is known about the release of Cl, Na, K, Zn, Pb, and S along grate of waste incineration plants. The 26 t h^− 1 WtE plant Vestforbrænding unit 5 in Denmark was used for measurements of temperature, gas-concentration (O₂/CO/CO₂), and sampling of gas phase Cl, Na, K, Pb, Zn, and S. Unit 5 has 6 ports distributed along the 13 m long grate between 1.5–1.8 m above the grate. Five of these ports were used for measurements. Two aqueous absorption systems containing a solution of NH₃ or a solution of H₂O₂/HNO₃ were used to collect the gaseous samples. Tar was found to condense in the sampling system at the ports near the fuel inlet. The experiments showed the majority of Cl, Na, and K to be volatilised during the early stages of combustion. The maximum release of Cl, Na, and K was measured in port 2 as 177 ppm_v, 71 ppm_v, and 44 ppm_v respectively. The maximum average gas temperature of 1140 was measured in port 3 compared to the temperatures at ports 2 and 4 of 816 and 551 respectively. It has been suggested to use flue gas from the area of the grate near port 3 with a high temperature, that contains relatively low amounts of corrosive elements, and lead to a separate high temperature super heater and thus increase the electrical efficiency.     

Low-temperature sintering of 0.85CaWO4–0.15LaNbO4 ceramics

Microwave dielectric properties of 0.85CaWO₄–0.15LaNbO₄ (CWLN) ceramics were investigated as a function of H₃BO₃, Li₂CO₃ content and sintering temperature. With the co-addition of 3.0 wt.% H₃BO₃–1.0 wt.% Li₂CO₃, the sintering temperature could be effectively reduced from 1150 °C for pure CWLN ceramics to 900 °C without any degradation of dielectric properties. These results are due to the enhancement of the sinterability of CWLN by liquid phase sintering. For the specimens with H₃BO₃–Li₂CO₃ sintered at 900 °C for 3 h, the dielectric constant (K) did not changed remarkably. However, the quality factor (Qf) and the temperature coefficient of resonant frequency (TCF) increased up to y = 1.0 of 3.0 wt.% H₃BO₃–y wt.% Li₂CO₃, and then decreased due to the formation of the secondary phases. Typically, K of 11.8, Qf of 45,200 GHz and TCF of −23.1 ppm/°C were obtained for the specimens of CWLN with 3.0 wt.% H₃BO₃–1.0 wt.% Li₂CO₃ sintered at 900 °C for 3 h.