La—Ni system porous anode in an alkaline fuel cell

La—Ni system alloys in fine powder form were used to make the hydrogen electrode for an alkaline fuel cell. LaNi₅ electrodes were found to have the highest electrode performance among the La—Ni system electrodes. Using LaNi₅ powder of mean particle size 3.4 μm for the electrode, the limiting current density was 180 mA/cm². However mixing the same size powder (mean particle size 3.4 μm) with powder of mean particle size 40.5 μm in a ratio of 4:1, the limiting current density of the new electrode was 250 mA/cm². The electrode was found to have both relatively fine pores in the range 0.01–0.2 μm and relatively large pores in the ranges 0.5–1 μm and 4–5 μm. Thus, it was found that not only relatively fine pores but relatively large pores had an important effect upon the LaNi₅ electrode characteristics.     

High temperature lithium/sulphur batteries: a preliminary investigation of a zeolite—sulphur cathode

A reversible lithium/sulphur high temperature cell is described in which the cathode consists of elemental sulphur absorbed in a zeolite 4A matrix. A lithium—aluminium alloy is used for the anode and the electrolyte is a molten ionic salt consisting of a LiI-KI eutectic (m.p. 260°). The cell was operated at 300° and underwent more than 70 continuous charge/discharge cycles (800 h) without significant loss in efficiency. The coulombic efficiency was more than 90% and the energy density 404 Wh/kg (based on the masses of active electrode materials, viz lithium metal and zeolite 4A—sulphur). The cell showed an open circuit voltage of 1.80 V, a short-circuit cd of about 1.1 A/cm² and a maximum power of about 0.5 W/cm². The internal resistance was 0.54 Ω (cathode surface area ～ 3 cm²).     

Determination of concentration of surface states at the illuminated semiconductor—electrolyte interface

Surface states at the semiconductor—electrolyte interface under illumination have been determined. The faradaic reaction involved at the (CdTe and GaP) interface is the photo-electrochemical reduction of carbon dioxide to carbon monoxide in dimethylformamide—water mixtures. A new equivalent circuit has been proposed to account for the impedance data. Surface states act as faradaic mediators for the reduction of carbon dioxide. Surface state density at a given bias potential has been calculated to be of the order of 10¹⁴ cm⁻². Adsorbed ions induce surface states. Surface state density induced by tetraalkylammonium ions decrease with increase of alkyl chain length. The number of surface states increases with water concentration. The resistance for the surface states in the Tafel region is larger than the resistance of those in the space—charge region indicating that the rate determining step lies on the solution side of the interface. However, in the limiting current density region, the space charge resistance is larger than the surface state resistance.     

Properties of structural insulation ceramic materials from a mixture of intershale clay and anthracite flotation wastes

The use of anthracite flotation wastes in ceramic masses based on waste fused rock—intershale clay—without the application of traditional natural materials makes it possible to obtain structural insulation materials with thermal conductivity and density of <0.20 W m^?1 K^?1 and 1200 kg/m³, respectively.     

Development and Fabrication of a New Concept Planar‐tubular Solid Oxide Fuel Cell (PT‐SOFC)

The paper reports a new concept of planar‐tubular solid oxide fuel cell (PT‐SOFC). Emphasis is on the fabrication of the required complex configuration of Ni‐yttria‐stabilised zirconia (YSZ) porous anode support by tert‐butyl alcohol (TBA) based gelcasting, particularly the effects of solid loading, amounts of monomers and dispersant on the rheological behaviour of suspension, the shrinkage of a wet gelcast green body upon drying, and the properties of final sample after sintering at 1350 °C and reduction from NiO‐YSZ to Ni‐YSZ. The results show that the gelcasting is a powerful method for preparation of the required complex configuration anode support. The anode support resulted from an optimised suspension with the solid loading of 25 vol% has uniform microstructure with 37% porosity, bending strength of 44 MPa and conductivity of 300 S cm^—1 at 700 °C, meeting the requirements for an anode support of SOFC. Based on the as‐prepared anode support, PT‐SOFC single cell of Ni‐YSZ/YSZ/LSCF has been fabricated by slurry coating and co‐sintering technique. The cell peak power density reaches 63, 106 and 141 mW cm^—2 at 700, 750 and 800 °C, respectively, using hydrogen as fuel and ambient air as oxidant.     

Layer-chain carbons

Studying the behaviour of the abnormal reflection of d = 336.0 pm in a number of carbon substances, the authors come to the conclusion that there exists a new structural polytype of polymeric carbon, the layer chain carbon, where atomic layers and carbon chains are mutually linked. The notation given by the authors to this hypothetical carbon modification is LC2. This new structural type of carbon differs from graphite by having covalent bonds between the layers, and from diamond in having two long C—C bond links between the layers. The calculated density of LC2 = 3.24 g/cm², the cell parameters of the two layer polytype ((2LC2) are: a ≅ 252 pm, c ≅ 672 pm; and of the three layer polytype (3LC2); a ≅ 252 pm, c ≅ 1008 pm.     

The cathodic behavior of microwave-treated manganese dioxide in lithium nonaqueous cells

The cathodic behavior of microwave-treated manganese dioxide (MnO₂) was studied in lithium nonaqueous cells. Two types of discharge tests, low rate continuous discharge at current densities of 0.1–5 mA cm^?2 and high rate pulse-discharge at current densities of 10–25 mA cm^?2 were carried out in 1 M LiClO₄—propylene carbonate—50% tetrahydrofuran—50% electrolyte, and it was found that the Li—microwave-treated MnO₂ cell exhibited good characteristics in both types of discharge tests. A stability test of microwave-treated MnO₂ in a cell was also carried out, and it was shown to have no problems with gassing and to provide long shelf life.     

Extrusion of polystyrene nanocomposite foams with supercritical CO2

Intercalated and exfoliated polystyrene/nano‐clay composites were prepared by mechanical blending and in situ polymerization respectively. The composites were then foamed by using CO₂ as the foaming agent in an extrusion foaming process. The resulting foam structure is compared with that of pure polystyrene and polystyrene/talc composite. At a screw rotation speed of 10 rpm and a die temperature of 200°C, the addition of a small amount (i.e., 5 wt%) of intercalated nano‐clay greatly reduces cell size from 25.3 to 11.1 μm and increases cell density from 2.7 × 10⁷ to 2.8 × 10⁸ cells/cm³. Once exfoliated, the nanocomposite exhibits the highest cell density (1.5 × 10⁹ cells/cm³) and smallest cell size (4.9 μm) at the same particle concentration. Compared with polystyrene foams, the nanocomposite foams exhibit higher tensile modulus, improved fire retardance, and better barrier property. Combining nanocomposites and the extrusion foaming process provides a new technique for the design and control of cell structure in microcellular foams.     

Recycling of FGD gypsum to calcium carbonate and elemental sulfur using mixed sulfate-reducing bacteria with sewage digest as a carbon source

A combined chemical and biological process for the recycling of flue gas desulfurization (FGD) gypsum into calcium carbonate and elemental sulfur is demonstrated. In this process, a mixed culture of sulfate-reducing bacteria (SRB) utilizes sewage digest as its carbon source to reduce FGD gypsum to hydrogen sulfide. The sulfide is then oxidized to elemental sulfur via reaction with ferric sulfate, and accumulating calcium ions are precipitated to calcium carbonate using carbon dioxide. Employing anaerobically digested-municipal sewage sludge (AD-MSS) medium as a carbon source, SRB in serum bottles demonstrated an FGD gypsum reduction rate of 8 mg dm⁻³ h⁻¹ (10⁹ cells)⁻¹. A chemostat with continuous addition of both AD-MSS medium and gypsum exhibited sulfate reduction rates as high as 1·3kg FGD gypsumm⁻³ day⁻¹. The increased biocatalyst density afforded by cell immobilization in a columnar reactor allowed a productivity of 152 mg SO₄ dm⁻³ h⁻¹ or 6·6kg FGD gypsum m⁻³ day⁻¹. Both reactors demonstrated 100% conversion of sulfate, with 75–100% recovery of elemental sulfur and as high as 70% COD utilization. Calcium carbonate was recovered from the reactor effluent upon precipitation using carbon dioxide. The formation of two marketable products—elemental sulfur and calcium carbonate—from FGD gypsum sludge, combined with the use of a low-cost carbon source and further improvements in reactor design, promises to offer an attractive alternative to the landfilling of FGD gypsum.     

Ab initio molecular dynamics: Propagating the density matrix with gaussian orbitals. IV. Formal analysis of the deviations from born-oppenheimer dynamics

In the context of the recently developed Atom-centered Density Matrix Propagation (ADMP) approach to ab initio molecular dynamics, a formal analysis of the deviations from the Born—Oppenheimer surface is conducted. These deviations depend on the fictitious mass and on the magnitude of the commutator of the Fock and density matrices. These quantities are found to be closely interrelated and the choice of the fictitious mass provides a lower bound on the deviations from the Born—Oppenheimer surface. The relations are illustrated with an example calculation for the Cl⁻(H₂O)₂₅ cluster. We also show that there exists a direct one-to-one correspondence between approximate Born—Oppenheimer dynamics, where SCF convergence is restricted by a chosen threshold value for the commutator of the Fock and density matrices, and extended Lagrangian dynamics performed using a finite value for the fictitious mass. The analysis is extended to the nuclear forces used in the ADMP approximation. The forces are shown to be more general than those standardly used in Born—Oppenheimer dynamics, with the addition terms in the nuclear forces depending on the commutator mentioned above.     

Electrocatalytic and thermal activation of anodic oxygen- and cathodic hydrogen-evolution in alkaline water electrolysis

In micro-electrolysis cells (4 cm² electrode area) which possess a sandwich-configuration as used in advanced water electrolysis[1] different anodic and cathodic electrocatalysts, which did not contain noble metals were investigated over the current density range from 10^?4 to 1.0 A cm^?2 and a temperature range from 30 to 130°C (electrolyte: 50 wt% caustic potash). Mechanically activated nickel electrodes, RuO₂ doped anodes and Pt-black covered cathodes served as comparison standards for H₂ and O₂ evolution.IR-drop connections were not applied. Nonetheless the measuring-method used allowed to keep IR-induced mistakes in voltage-reading in single-electrode voltages below 40 mV even at the highest current densities of 1.0 A cm^?2.Plots of voltage vs log current densities for anodic oxygen evolution possess slopes between 40 and 70 mV (100°C) dec^?1 of current density which in some cases—especially at low temperatures—increased up to a value of 2 RT/F at higher current densities. By increasing the temperature these steeper parts of the anodic current—voltage curves very often disappear.The current-voltage curves of anodic oxygen evolution for different temperatures unexpectedly run nearly parallel to each other ie with a slope which is nearly independent of temperature and thus cannot be described according to the Butler—Volmer equation with a constant value of the formal charge-transfer coefficient βⁱ.The effective activation energies obtained from dln i_o/d(1/T) range from 70 to 100 kJ mole^?1.O₂ overpotentials at current densities around 1 A cm^?2 are most efficiently decreased by (i) application of mixed oxides containing cobalt in at least two different valency states (Co^II/Co^III or Co^III/Co^IV) and (ii) by use of higher working temperatures; roughened surfaces, however, are only of limited value in this respect.Voltage vs log current curves for cathodic hydrogen evolution show a pattern which is in agreement with the Butler—Volmer equation. The effective charge-transfer coefficient is close to 0.5 and increases slightly above this value for Raney-metal activated cathodes.The effective activation energies lie between the limits of 40 and 55 kJ mol^?1. Hydrogen evolution overpotentials are most efficiently decreased by (i) preparation of cathode surfaces with high roughness factors, (ii) using Ni, Co or Fe as cathode material and (iii) by increasing the working temperatures.     

Effect of Contact between Electrode and Interconnect on Performance of SOFC Stacks

This work investigates the effect of contact between electrodes and alloy interconnects on output performance of solid oxide fuel cell (SOFC) stacks. The measured maximum output power density (p_max) of the unit cell increases from 0.07 to 0.1 W cm^–2 by increasing the tip area of the interconnect from 40 to 60 cm². The p_max increases from 0.07 to 0.15 W cm^–2 upon the addition of nickel foam and Ag mesh on the anode and cathode side, respectively. An additional (La_0.75Sr_0.25)_0.95MO_3–σ cathode current collecting layer is re‐printed on the original cathode current collecting layer, which aims to further improve the performance of the stack and individual cell. The performance of a 3‐cell short stack assembled by the cells with a new cathode current collecting layer is evaluated by measuring the current–voltage curve. The results indicate that the p_max values of the stack and individual cells are enhanced from 0.07 to 0.37 W cm^–2 and 0.15 to 0.5 W cm^–2 at 850 °C, respectively. The performance of the whole stack and individual cells is greatly improved due to the interconnect embedded in the re‐printed new cathode current collecting layer.     

Low density microcellular foam processing in extrusion using CO2

A continuous extrusion process for the manufacture of low-density microcellular polymers is presented. Microcellular polymers are foamed plastics characterized by a cell density greater than 10⁹ cells/cm³ and a fully grown cell size on the order of 10 μm. Previous research on continuous processing of microcellular polymers has focused on control of microcell nucleation in extrusion. This paper presents an effective means for control of cell growth to achieve a desired expansion ratio with CO₂ as a blowing agent in microcellular foam processing. Also, a strategy to prevent deterioration of the cell-population density via cell coalescence during expansion is presented. Promotion of a desired volume expansion ratio and prevention of cell coalescence in microcellular foam processing were experimentally verified. By tailoring the extrusion processing parameters, microcellular HIPS foams with a cell density of 10¹⁰ cells/cm³ and a controlled expansion ratio in the range of 1.5 to 23 were obtained.     

Ébullition par Convection Forcée des Mélanges Eau‐Ammoniac dans un Tube Vertical

An experimental study has been conducted on the forced convective boiling heat transfer of ammonia‐water mixtures flowing inside a 6 mm inner diameter vertical smooth tube. Using a water‐heated double pipe type generator, the local heat transfer coefficients are measured inside the inner tube for a range of heat flux density (29.93 — 99.79 kW/m²), mass flux density (35.36 — 99.04 kg/m²·s), mass flow rate (0.001 — 0.03 kg/s) and ammonia mass concentration (49%, 55% and 61%). The effect of the experimental parameters on the heat transfer coefficients is analysed. Three methods are used to predict the boiling heat transfer coefficients. Experimental data were compared with the available correlations. The obtained results confirm the good performance of the Mishra et al. (1981) and Bennett‐Chen's (1980) correlations in predicting the convective boiling heat transfer coefficient of NH₃‐H₂O mixtures. These methods are able to predict the boiling heat transfer data within an average accuracy of ± 20 %.     

Investigation on the cell nucleation and cell growth in microcellular foaming by means of temperature quenching

The cell nucleation and real‐time cell growth with increasing cell growth time in microcellular foaming were investigated by means of temperature quenching in a supercritical CO₂ pressure‐quench process. Samples of uniform size and shape were saturated in a vessel under conditions of 100–180°C and 30 MPa, and then depressurized to the atmosphere in 10 s. After depressurization, these samples were removed from the vessel at prescribed intervals, and immediately immersed in an ice‐water slurry to obtain foamed samples with various cell growth times. It was found that the nucleation density is closely correlated to the gas absorption capacity of the polymer matrix, so that the final cell density should not be adopted as the nucleation density, as done commonly. The change of cell structure and mass density with increasing cell growth time was dominated by gas diffusion behavior, which was strongly influenced by the temperature. The final cell structure was mainly determined by the cell growth step, where gas diffusion played a key role. The final cell density was in direct proportion to the gas remaining in the substrate, which ranged from 6.0 × 10⁹ to 4.7 × 10⁶ cells/cm³. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 163–171, 2004     

The effect of heat treatment and carbon content on the corrosion behaviour of iron—chromium steels in sulphuric acid solutions

In this study the corrosion behaviour of iron—chromium steels was investigated. The samples were subjected to heat treatment. The current density—potential curves were obtained in 1 N H₂SO₄ by electrochemical, potentiodynamic (1 mV min^?1), potentiostatic and galvanostatic methods. Corrosion rates were obtained from the extrapolation of anodic and cathodic Tafel lines and using potentiodynamic, potentiostatic and galvanostatic linear polarization techniques with the Stern—Geary equation. It was seen that the effect of chromium on the rate of corrosion varies with the heat treatment method applied and the amount of carbon content.     

High speed zinc electrowinning using a hydrogen gas-diffusion electrode

The feasibility of a high speed zinc electrowinning cell using a Pt catalyzed hydrogen gas-diffusion electrode as an anode is investigated. This new type of zinc-winning cell is operated at a current density of 1.0 A cm^–2, which is 20 times higher than usually employed in conventional methods. Current efficiency is 86% at 0.5 A cm^–2 in an electrolyte containing 60 gl^–1 Zn+270 gl^–1 H₂SO₄, the zinc purity being at least 99.999%. The energy usage of the system is 1400 kWh and 380 m³ H₂ gas per ton of zinc.     

Phenolic wastewater treatment in a three‐phase fluidised bed bioreactor containing low density particles

The treatment of phenolic wastewater was investigated in a gas–liquid–solid fluidised bed bioreactor containing polypropylene particles of density 910 kg m^?3. Measurements of chemical oxygen demand (COD) versus residence time (t) were performed for various ratios of settled bed volume to bioreactor volume (V_b/V_R) and air velocities (u) to determine the values of (V_b/V_R) and u for which the largest reduction in COD occurred. Optimal operation, corresponding to the largest COD removal, was attained when the bioreactor was controlled at the ratio (V_b/V_R) = 0.55 and an air velocity u = 0.036 m s^?1. Under these conditions, the value of COD was practically at steady state for times greater than 50 h. At this steady state, only about 50% COD removal was achieved in the treatment of a ‘raw’ wastewater (no mineral salts added), whereas in the operation with wastewater enriched in nutrient salts approximately 90% COD removal was attained. The following amount of mineral salts (mg dm^?3): (NH₄)₂SO₄—500; KH₂PO₄—200; MgCl₂—30; NaCl—30; CaCl₂—20; and FeCl₃—7, when added to wastewater before treatment, was sufficient for biomass growth. The application of low density particles (used as biomass support) in a bioreactor allowed the control of biomass loading in the apparatus. In the cultures conducted after change in (V_b/V_R) at a set u, the steady state mass of cells grown on the particles was achieved after approximately 6 days of operation. With change in u at a set (V_b/V_R), the new steady state biomass loading occurred after culturing for about 2 days. Phenolic wastewater was successfully treated in a bioreactor. In the operation conducted in a bioreactor optimally controlled at (V_b/V_R) = 0.55, u = 0.036 m s^?1 and t = 50 h, conversions greater than 99% were achieved for all phenolic constituents of the wastewater. Conversions of about 90% were attained for other hydrocarbons. Copyright © 2005 Society of Chemical Industry     

Improvements of anode properties of aluminium alloys for aluminium primary cell: heat treatment and corrosion inhibitors

Improvements of anode properties of aluminium alloys were attempted for application to a primary dry cell. Heat treatments were investigated chiefly for the alloy A1—3.0Zn—0.13Sn—0.01Ga—0.07Bi(% w/w) derived from high purity aluminium (99.999%). The solution heat treatment (homogenization) of the alloy at 400°C for 4 h presented the best anode properties, ie the faradaic efficiency and the rate of corrosion in 1 M AlCl₃ aqueous solution as the electrolyte. The average grain size diameters of the alloy specimens were also measured after heat treatment at various temperatures. The electrochemical properties were discussed in connection with the structures of alloy. Corrosion inhibitors were investigated for suppression of corrosion rates. Addition of agar and α-amilase to 1 M AlCl₃ significantly reduced the current loss (100 — faradaic efficiency, %) and the rate of corrosion. The alloy mentioned above treated at 400°C (homogenization) combined with agar (2 g l⁻¹) as a corrosion inhibitor gave the best electrochemical properties; the faradaic efficiency 99.8% and the average rate of corrosion 0.008 mg cm⁻² h⁻¹ (short term) and 0.005 mg cm⁻² h⁻¹ (long term).