A new magnesium-air cell for long-life applications

A novel type of magnesium-air primary cell has been evolved which employs non-polluting and abundantly available materials. The cell is based on the scheme Mg/Mg(NO3)2, NaNO2, H20/Q(C). The magnesium anode utilization is about 90% at a current density of 20 mAcm -2. The anode has been shown to exhibit a low open-circuit corrosion, a relatively uniform pattern of corrosion and a low negative difference effect in the electrolyte developed above as compared to the conventional halide or perchlorate electrolytes. In the usual air-depolarized mode of operation, the cell has been found to be capable of continuous discharge over several months at a constant cell voltage of about 1 V and a current density of 1 mAcm -2 at the cathode. The long service-life capability arises from the formation of a protective film on the porous carbon cathode and fast sedimentation of the anodic product (magnesium hydroxide) in the electrolyte. The cell has a shelf-life in the activated state of about a year due to the low open-circuit corrosion of the anode. These favourable features suggest the practical feasibility of developing economical, long-life, non-reserve magnesium-air ceils for diverse applications using magnesium anodes with a high surface area and porous carbon-air electrodes.

Phase relations and Gibbs energies of spinel phases and solid solutions in the system Mg-Rh-O

Pure stoichiometric MgRh(2)O(4) could not be prepared by solid state reaction from an equimolar mixture of MgO and Rh(2)O(3) in air. The spinel phase formed always contained excess of Mg and traces of Rh or Rh(2)O(3). The spinel phase can be considered as a solid solution of Mg(2)RhO(4) in MgRh(2)O(4). The compositions of the spinel solid solution in equilibrium with different phases in the ternary system Mg-Rh-O were determined by electron probe microanalysis. The oxygen potential established by the equilibrium between Rh + MgO + Mg(1+x)Rh(2-x)O(4) was measured as a function of temperature using a solid-state cell incorporating yttria-stabilized zirconia as an electrolyte and pure oxygen at 0.1 MPa as the reference electrode. To avoid polarization of the working electrode during the measurements, an improved design of the cell with a buffer electrode was used. The standard Gibbs energies of formation of MgRh(2)O(4) and Mg(2)RhO(4) were deduced from the measured electromotive force (e.m.f.) by invoking a model for the spinel solid solution. The parameters of the model were optimized using the measured composition of the spinel solid solution in different phase fields and imposed oxygen partial pressures. The results can be summarized by the equations: MgO + beta -Rh(2)O(3) -> MgRh(2)O(4); Delta G degrees (+ 1010)/J mol(-1) = -32239 + 7.534T; 2MgO + RhO(2) -> Mg(2)RhO(4); Delta G degrees(+/- 1270)/J mol(-1) = 36427 -4.163T; Delta G(M)/J mol(-1) = 2RT(xInx + (1-x)In(1-x)) + 4650x(1-x), where Delta G degrees is the standard Gibbs free energy change for the reaction and G(M) is the free energy of mixing of the spinel solid solution Mg(1+x)Rh(2-x)O(4). (C) 2011 Elsevier B. V. All rights reserved.

Effect of pouring temperature on cooling slope casting of semi-solid Al-Si-Mg alloy

Present trend of semi-solid processing is directed towards rheocasting route which allows manufacturing of near-net-shape cast components directly from the prepared semi-solid slurry. Generation of globular equi-axed grains during solidification of rheocast components, compared to the columnar dendritic structure of conventional casting routes, facilitates the manufacturing of components with improved mechanical properties and structural integrity. In the present investigation, a cooling slope has been designed and indigenously fabricated to produce semi solid slurry of Al-Si-Mg (A356) alloy and successively cast in a metallic mould. The scope of the present work discusses about development of a numerical model to simulate the liquid metal flow through cooling slope using Eulerian two-phase flow approach and to investigate the effect of pouring temperature on cooling slope semi-solid slurry generation process. The two phases considered in the present model are liquid metal and air. Solid fraction evolution of the solidifying melt is tracked at different locations of the cooling slope, following Schiel's equation. The continuity equation, momentum equation and energy equation are solved considering thin wall boundary condition approach. During solidification of the liquid metal, a modified temperature recovery scheme has been employed taking care of the latent heat release and change of fraction of liquid. The results obtained from simulations are compared with experimental findings and good agreement has been found.

Time-temperature histories of spherical food products during bulk forced-air precooling

A general mathematical model for forced air precooling of spherical food products in bulk is developed. The food products are arranged inline to form a rectangular parallelepiped. Chilled air is blown along the height of the package. The governing equations for the transient two-dimensional conduction with internal heat generation in the product, simultaneous heat and mass transfer at the product-air interface and one-dimensional transient energy and species conservation equations for the moist air are solved numerically using finite difference methods. Results are presented in the form of time-temperature histories. Experiments are conducted with model foods in a laboratory scale air precooling tunnel. The agreement between the theoretical and experimental results is found to be good. In general, a single product analysis fails to predict the precooling characteristics of bulk loads of food products. In the range of values investigated, the respiration heat is found to have a negligible effect.

Interaction of Co, Mn, Mg and AI with d(GCGTACGC): a spectroscopic study

Spectroscopic study on the interactions of trace elements Co, Mn, Mg and Al with d(GCGTACGC) indicated the following: Al and Mg did not alter T-m values. Mn enhanced T-m at lower concentration and decreased it at higher concentrations. Interestingly Co at higher concentration elevated the T-m. These studies also showed lower concentrations of Mn displaced EtBr, whereas Al could displace it at higher ionic strength. Mg and Co displaced EtBr fluorescence at moderate concentrations. The binding constant values and CD spectra clearly indicated strong binding of these elements to DNA.

Formative time lags in nitrogen, oxygen and dry air In crossed electric and magnetic fields

Formative time lags in nitrogen, oxygen, and dry air are measured with and without a magnetic field over a range of gas pressures (0.05 ' p ' 20.2 torr 5 kPa to 2 MPa, electric field strengths (1.8xO14 EEs 60xlO V m l) and magnetic field strengths (85xl0-4 < B ' 16x10-2 Tesla). For experiments below the Paschen minimum, the electrodes are designed to ensure that breakdown occurs over longer gaps and for experiments above the Paschen minimum, a coaxial cylindrical system is employed. The experimental technique consists of applying pulse voltages to the gap at various constant values of E/p and B/p and measuring the time lags from which the formative time lags are separated. In the gases studed, formative time lags decrease on application of a magnetic field at a given pressure for conditions below the Paschen minimum. The voltages at which the formative time lags remain the same without and with magnetic fields are determined, and electron molecule collision frequencies (v/p) are determined using the Effective Reduced Electric Field [EREF] concept. With increasing ratio of E/p in crossed fields, v/p decreases in all the three gases. Measurements above the Paschen minimum yield formative time lags which increase on application of a magnetic field. Formative time lags in nitrogen in ExB fields are calculated assuming an average collision frequency of 8.5x109 sec-1 torr 1. It is concluded that the EREF concept can be applied to explain formative time lags in ExB fields.

Preparation, structure, and magnetic properties of isostructural La3MAlS7 and La3MFeS7 (M = Mg, Mn, Fe, Co, Ni, or Zn)

A series of quaternary metal sulfides of the general formula La3MM′S7 (M = Mn, Fe, Co; M′ = Al and M = Mg, Mn, Fe, Co, Ni; M′ = Fe) consisting of linear chains of face shared MS6 octahedra and isolated M′S4 tetrahedra has been prepared and studied. The aluminium compounds La3MAlS7 (M = Mn, Fe, Co) exhibit linear chain antiferromagnetism. Magnetic behavior of other La3MFeS7 sulfides has been examined in detail. The magnetic susceptibility of La3MgFeS7 shows that tetrahedral site Fe3+ undergoes a transition from Image to S = 2 spin state around 150 K.

Analysis of Paschen Curves for air, N2 and SF6 Using the Townsend Breakdown Equation

It has been shown that it is possible to extend the validity of the Townsend breakdown criterion for evaluating the breakdown voltages in the complete pd range in which Paschen curves are available. Evaluation of the breakdown voltages for air (pd=0.0133 to 1400 kPa · cm), N2(pd=0.0313 to 1400 kPa · cm) and SF6 (pd=0.3000 to 1200 kPa · cm) has been done and in most cases the computed values are accurate to ±3% of the measured values. The computations show that it is also possible to estimate the secondary ionization coefficient ¿ in the pd ranges mentioned above.

Novel Self-Supported Natural and Synthetic Polymer Membranes for Air Humidification

Novel self-supported natural and synthetic polymer membranes of chitosan-hydroxy ethyl Cellulose-montmorillonite (CS-HEC-MMT) and polyvinyl alcohol (PVA)-polystyrene sulfonic acid (PSSA) are prepared by solution casting method followed by crosslinking. These membranes are employed for air humidification at varying temperatures between 30 degrees C and 70 degrees C and their performances are compared with commercial Nafion membranes. High hater fluxes with desired humidified-air output have been achieved for CS-HEC-MMT and PVA-PSSA hybrid membranes at air-flow rates of 1-10 slpm. Variation in the air/water mixing ratio, dew point, and relative humidity that ultimately results in desired water flux With respect to air-flow rates are also quantified for all the membranes. Water flux values for CS-HEC-MMT are less than those for Nafion (R) and PVA-PSSA membranes, but the operational Stability of CS-HEC-MMT membrane is higher than PVA-PSSA and comparable with Nafion (R) both of which can operate up to 70 degrees C at repetitive cycles of humidification.

Interfacial area measurement in a gas - liquid ejector for a sodium chloride - air system

Interfacial area measurement has been carried out experimentally by measuring the bubble size and holdup for air-sodium chloride solution system. The size of the bubble is predominantly established by the air hold up. High speed photography technique for bubble size measurement and gamma ray attenuation method for holdup measurements are followed. The measured values are compared with the theoretically predicted values. Interracial area as a function of the liquid flow rate and also its distance from the nozzle of the ejector has been reported in this paper. The results obtained for this non-reactive system are also compared with those of air-water system.

D-MG Tradeoff and Optimal Codes for a Class of AF and DF Cooperative Communication Protocols

Cooperative relay communication in a fading channel environment under the orthogonal amplify-and-forward (OAF), nonorthogonal and orthogonal selection decode-and-forward (NSDF and OSDF) protocols is considered here. The diversity-multiplexing gain tradeoff (DMT) of the three protocols is determined and DMT-optimal distributed space-time (ST) code constructions are provided. The codes constructed are sphere decodable and in some instances incur minimum possible delay. Included in our results is the perhaps surprising finding that the orthogonal and the nonorthogonal amplify-and-forward (NAF) protocols have identical DMT when the time durations of the broadcast and cooperative phases are optimally chosen to suit the respective protocol. Moreover our code construction for the OAF protocol incurs less delay. Two variants of the NSDF protocol are considered: fixed-NSDF and variable-NSDF protocol. In the variable-NSDF protocol, the fraction of time occupied by the broadcast phase is allowed to vary with multiplexing gain. The variable-NSDF protocol is shown to improve on the DMT of the best previously known static protocol when the number of relays is greater than two. Also included is a DMT optimal code construction for the NAF protocol.

Cuprous oxide catalyzed air oxidation of thiosulfate and tetrathionate

Thiosulfate (S2O32−) and tetrathionate (S4O62−)are oxidized to sulfate by air at atmospheric pressure and 50–70°C in the presence of cuprous oxide (Cu2O) as catalyst. Sulfate is produced from S2O32− by series-parallel reaction paths involving S4O62− as an intermediate. The rate data obtained for air oxidation of S2O32− on Cu2O agree well with a pseudo-homogeneous first order kinetic scheme, yielding values of rate constants for series parallel reaction paths which have been used in modelling the catalyzed air oxidation of S2O32−. Air oxidation of S4O62− on Cu2O proceeds at a higher rate in the presence of S2O32− than in its absence. Cu2O is less active than Cu2S for the air oxidation of S2O32−, as shown by the rate constant values which for Cu2O catalyzed oxidation are an order of magnitude smaller than those for the Cu2S catalyzed oxidation.

Low-temperature preparation of fine-particle cobaltites

A novel solid-solution precursor method for the preparation of fine-particle cobaltites at low temperatures has been described. The precursors, hydrazinium metal hydrazine carboxylate hydrates, N2H5M1/3Co2/3(N2H3COO)3 · H2O, where M = Mg, Mn, Fe, Co, Ni, and Zn, decompose in air <250°C to yield corresponding metal cobaltites, MCo2O4. Formation of cobaltites has been confirmed by thermogravimetry (TG) weight loss, IR, and X-ray diffraction. Combustion of the precursor in air yields fine-particle cobaltites with surface areas in the range of 12–115 m2g−1 and particle sizes of 1–40 μm. Low decomposition temperatures of the precursors accompanied by the evolution of large amounts of gases appear to control the particle size of the cobaltites.

Vapour composition and activities in Mg-Zn liquid alloy at 923 K

Vapour species effusing from a magnesia Knudsen cell containing Mg-Zn alloy at 923 K were condensed on a water cooled copper plate. The equilibrium composition of the vapour phase over the alloy was determined from chemical analysis of the condensate. The activity coefficients of both components in the alloy have been derived from the data using a modified Gibbs-Duhem relation. The ratio of saturation vapour pressures of pure Zn and Mg obtained from the analysis of alloy data agree well with values from the literature, providing an internal check on the accuracy of data obtained in this study. Both components of the alloy exhibit negative deviations from Raoult's law. The concentration-concentration structure factor of Bhatia and Thomton at zero wave vector, evaluated from the measurements, indicate the presence of MgZn2 type complex in the liquid state. The associated regular solution model has been used for the thermodynamic description of liquid Mg-Zn alloys.

Oxides supported carbon air-electrodes for alkaline solution power devices

Porous carbon oxygen-reducing electrodes incorporated with perovskite oxide catalysts are reported. It has been possible to fabricate high-performance oxygen-reducing electrodes by introducing La0.5Sr0.5CoO3 and La0.99Sr0.01NiO3 with the activated coconut-shell charcoal; these electrodes could sustain load currents as high as 1 A cm−2 without serious degradation. A model to explain oxygen-reducing activity of these oxides has been proposed.