High-temperature stabilities of YCuO2, BaCu2O2 and Ba2CuO3 from oxide electrolyte e.m.f. measurements

The oxygen potentials in the system YCuO₂/Y₂O₃/Cu and Y₂O₃/YCuO₂/CuO were measured over the ranges 1113–1255 K and 782–1122 K by employing oxide electrolyte galvanic cells with air/platinum as the reference electrode, and the expression $$\Delta G_{f, ox}^o (YCuO_2 )( \pm 0.19)(kJ mol^{ - 1} ) = - 5.346 + 0.00384{\text{ }}T (K)$$ was determined. Similar e.m.f. measurements were carried out on the electrodes BaCuO₂/BaCu₂O₂/Cu₂O and Ba₂CuO₃/BaCuO₂/BaCu₂O₂ were measured over the ranges 1003–1132 K and 1175–1235 K and from the results, the ΔG _f,ox ^o of BaCu₂O₂ and Ba₂CuO₃ were determined to be $$\begin{gathered} \Delta G_{f, ox}^o (BaCu_2 O_2 )(kJ mol^{ - 1} ) = - 25.09 + 0.01548{\text{ }}T (K) \hfill \\ \Delta G_{f, ox}^o (BaCu_2 O_3 )(kJ mol^{ - 1} ) = - 5.79 - 0.07492{\text{ }}T (K) \hfill \\ \end{gathered} $$      

Standard Gibbs' energies of formation of BaCuO2, Y2Cu2O5 and Y2BaCuO5

The Gibbs' energies of formation of BaCuO₂, Y₂Cu₂O₅ and Y₂BaCuO₅ from component oxides have been measured using solid state galvanic cells incorporating CaF₂ as the solid electrolyte under pure oxygen at a pressure of 1.01×10⁵ Pa BaO + CuO BaCuO₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=–63.4–0.0525T(K) Y₂O₃ + 2CuO Y₂Cu₂O₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=18.47–0.0219T(K) Y₂O₃ + BaO + CuO Y₂BaCuO₅ G _f,ox ^o (± 0.7) (kJ mol^–1)=–72.5–0.0793T(K) Because the superconducting compound YBa₂Cu₃O_7– coexists with any two of the phases CuO, BaCuO₂ and Y₂BaCuO₅, the data on BaCuO₂ and Y₂BaCuO₅ obtained in this study provide the basis for the evaluation of the Gibbs' energy of formation of the 1-2-3 compound at high temperatures.     

Design implementation of ATM switch with input priority anddistributed output buffers

A switch architecture for ATM is described which uses a simple priority module to resolve input contention and a distributed design to permit transfer of input cells to the first free output buffer. The switch has been synthesised using VHDL software and a target generic library and can operate at speeds >400 Mbit/s     

TG/DTA-based techniques for the determination of equilibrium vapour pressures of N,N′-propylenebis(2,4-pentanedion-iminoato)nickel(II) for CVD applications

The Schiff’s base complexes of nickel(II) prepared by condensing 1,2-diaminopropane (pn), 1,3-diaminopropane (trien), 1,4-diaminobutane (tren) or 1,2-diaminobenzene (opdn) with 2,4-pentanedione (acac) in a 1:2 mole ratio followed by chelation with nickel(II) were examined for their volatility/decomposition behaviour for CVD applications. Among the complexes screened, only one complex namely N,N′-propylenebis (2,4-pentanedion-iminoato) nickel(II) (designated as [Ni(acac)₂pn], Ni′) exhibited a single stepped volatilisation commencing from above its melting point (T_o) of 431.9 K and ending up with nil residue at about 570 K. Fast Atom Bombardment Mass Spectrometry was employed to determine the molecular mass of the vapour species to be 295 in accordance with the molecular mass for the monomeric Ni(C₁₃H₂₀O₂N₂). The equilibrium vapour pressure (p_e) of Ni′ over the range of 434–498 K was determined to be log p_e/Pa = 13.771 (±0.574)–4925.4 (±258.2) K/T by employing a TG-based transpiration technique, which yielded a value of 94.3±5.0 kJ mol⁻¹ for its standard enthalpy of vapourisation . The DTA-based melting point depression (T_o–T) studies were carried out on four mixtures of Ni′ (as a volatile solvent) with bis(2,4-pentanedionato)nickel(II) (designated as Ni(acac)₂ or Ni″) as the non-volatile solute. The dependence of log X_Ni′ against 1/T(K) for the four mixtures with the solvent mole fraction X_Ni′ = 0.910, 0.897, 0.881 or 0.849 exhibited near constant slope leading to an average value of 19.4±1.6 kJ mol⁻¹ for the standard enthalpy of fusion . Combining and , a value of 113.7 ± 6.6 kJ mol⁻¹ for standard enthalpy of sublimation was derived to facilitate the estimation of vapour pressures for solid/vapour equilibrium below the melting point.     

Mathematical model and analysis of self-excitation in compensated lines

The paper deals with the generalized study of self-excited oscillations and hunting phenomena of synchronous machines connected to series-compensated EHV lines of inherent low resistance. The effect and the necessity of considering the rotor motion in the mathematical model have been highlighted. The application and the superiority of the D-partition technique for the analysis and demarcation of the stability zones in the parametric plane for a typical case are demonstrated. An equivalent circuit based on the frequency characteristics of the alternator has been developed in order to study the self-excited electrical oscillations in the practical range of series compensation.     

A mechanical study of the deterioration of coconut leaf thatch under natural and accelerated environmental conditions

The deterioration of coconut leaf thatch, a cheap roofing material, has been studied by following the changes in strength on its exposure to both natural and accelerated environmental conditions such as natural weathering, accelerated conditions of rain and alternate wet and dry climate and micro-organisms such as fungus. Strength was found to decrease with time during deterioration. Scanning electron and stereo-optical microscopes were also used to study the fracture phenomena and surface changes during deterioration. It has been found that the major factors contributing to the deterioration of coconut leaf thatch are identified as rain, alternate wet and dry weather, decay by fungus and the brittle nature of the leaf itself. It appears from the present study that the deterioration of coconut leaf thatch occurs as a result of progressive embrittlement with possible contributions from environmental stress-cracking.     

Comparative e.m.f. study of CaF2 and β-alumina cells with Ni/NiF2 and Fe/FeF2 or Cr/CrF2 electrodes

The reliability of employing beta-alumina as electrolyte for fluorine potential measurement is examined by measuring the e.m.f.s of the galvanic cells with metal/metal fluoride electrodes and comparing with those obtained by using CaF₂ as electrolyte under identical conditions. The results from both types of galvanic cell can be superimposed to give the following standard Gibbs energy of formation, ΔG _f ⁰ , of FeF₂ and CrF₂ over extended ranges of temperature: $$\begin{gathered} \Delta G_f^0 (FeF_2 ) = - 702.0 + 0.125 20T (K) ( \pm 0.70) kJ mol^{ - 1} (506 - 1063K) \hfill \\ \Delta G_f^0 (CrF_2 ) = - 732.8 + 0.087 90T (K) ( \pm 0.64) kJ mol^{ - 1} (497 - 1063K) \hfill \\ \end{gathered} $$ The absence of significant temperature-dependent errors in both these measurements are verified by a third law treatment of the data yielding values of ?716.8 and ?777.4 kJ mol^?1 for ΔH _f.298 ⁰ of FeF₂ and CrF₂, respectively. The feasibility of using beta-alumina electrolyte cells for e.m.f. measurements on other metal/metal fluoride systems is discussed in the light of the existence of a useful potential domain of beta-alumina. High sodium potential in the electrode system can lead to sodium depletion. Likewise, low sodium potential may result in oxidation of the metals in the electrodes. Both these limiting factors are also examined.     

Tuning mesoporous molecular sieve SBA-15 for the immobilization of α-amylase

The present work describes the immobilization of α-amylase over well ordered mesoporous molecular sieve SBA-15 with different pore diameters synthesized by post synthesis treatment (PST) hydrothermally after reaction at 40°C. The materials were characterized by N₂ adsorption–desorption studies, small angle X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy. Since α-amylase obtained from Bacillus subtilis has dimensions of 35 × 40 × 70 Å it is expected that the protein have access to the pore of SBA-15 (PST-120°C) with diameter 74 Å. The pore dimension is appropriate to prevent considerable leaching. The rate of adsorption of the enzyme on silica of various pore sizes revealed the influence of morphology, pore diameter, pore volume and pH.