Electrical conduction of partially stabilized zirconia Zr0.94Ca0.06O1.94 as a function of temperature and oxygen partial pressure

Partially stabilized zirconia (PSZ), Zr_0.94Ca_0.06O_1.94was prepared by a hot kerosene drying method and a conventional oxide wet-mixing method. The total d.c. conductivities of these zirconia specimens were measured by the three-terminal technique as a function of temperature in the range 1088 to 1285 K and oxygen partial pressure in the range 1 to 10^–24 bar. The specimen prepared by the hot kerosene drying method showed near oxygen ion conduction with four times higher conductivity than the specimen prepared by the conventional mixing method at T=1088–1285 K and bar. The higher oxygen pressure conductivity tended approximately towards a to dependence, indicative of p-type conduction, whereas the lower oxygen pressure conductivity tended to be virtually independent of oxygen pressure, indicative of oxygenion conduction. The activation energy was found to be 130 kJ mol^–1 at T=1088–1285 K, bar (air) for pure electron-hole conduction and 153kJ mol^–1 at T=1088–1285 K for ionic conduction.     

Chemical diffusion of (La,Sr)CoO3 and (La,Sr)FeO3

The present work reports equilibration kinetics for (La_0.8,Sr_0.2)CoO₃(LSC) and (La_0.72,Sr_0.18)FeO₃(LSF) in the temperature range 876–1114 K using a gravimetric method. Chemical diffusion determined in this way that depends on oxygen partial pressure, can be expressed by the following temperature dependence at low and high O₂), respectively, for LSC:

Rheological behaviour and modelling of semi-solid Sn-15% Pb alloy

The rheological behaviour and modelling of a semi-solid, Sn-15% Pb alloy characterized by a special coaxial-cylinder rheometer over a wide range of process conditions is reported. In particular, the effect of shear rate , volume fraction of solid (f _s), and cooling rate on the apparent viscosity () of the semi-solid Sn-15% Pb alloy under isothermal and various cooling conditions was studied. Based on the experimental data, the shear rate used in preparing the semi-solid alloy as well as the volume fraction of solid have the most dominant effects on the rheological properties of the semi-solid Sn-15% Pb alloy. A viscosity model expressed as is proposed in which f _s ^* is the critical solid fraction at which the apparent viscosity goes to infinity, (F _s) corresponds to the asymptotic viscosity at infinity shear rate, and characterizes the transition shear rate between the power-law and Newtonian regions. finally, measurements with a differential scanning calorimeter were made and used to correlate the temperature and volume fraction of solid which, in turn, was corroborated with available data from the literature.     

Estimation of oxygen pressures for the formation of superconducting phases based on La-Cu-O and Y-Cu-O systems

The use of thermodynamic data in the calculation of limiting oxygen pressures for the existence of ternary oxides is demonstrated in the case of LaMO₃ and La₂MO₄ (M=Mn, Fe, Co, Ni or Cu) compounds using the literature data on the relevant chemical equilibria. The standard Gibbs' energy of formation, G _f ⁰ , of LaCuO₃ is estimated from the values of G _f ⁰ of the other LaMO₃ compounds calculated from the literature and is given as (kJ mol^–1)= –1095.0+0.2351 T (K). The validity of this expression is qualitatively verified with the help of experimental conditions reported in the literature for the synthesis of this compound. Similar considerations are used to predict values of 0.03 and 30 atm to be the oxygen pressure range for the existence of a quarternary compound, YBa₂Cu₃O_9–y at 1273 K. The superconducting transition temperature, T _c, is qualitatively predicted to show a maximum for the sample annealed under an oxygen pressure in the range 1 to 30 atm at 1273 K.     

A second order accurate,positive scheme for singularly perturbed boundary value problems

We give a novel finite difference method for singularly perturbed boundary value problems in . The method is of positive type in 1–D with errors of O(h ² + h) in regions a few meshpoints away from possible layers, where is the small parameter in the differential equation. Global and local error estimates are proven for the method and numerical experiments are presented. Possible extension to 2–D as a monotone scheme is considered, but more questons are unsolved than solved in 2–D.     

Defect structure of acceptor-doped calcium titanate at elevated temperatures

The defect structure of acceptor (Al or Cr)-doped polycrystalline calcium titanate was investigated by measuring the oxygen partial pressure dependence (at 10° to 10–18 atm) of the electrical conductivity at 1000 and 1050° C. The observed electrical conductivity data were proportional to for the oxygen pressure range < 10^–10 atm and proportional to for the oxygen pressure range ( 10^–7 atm. The conductivity values were observed to increase with the acceptor concentration in the p-type region with the shift in the conductivity minima towards lower oxygen partial pressure. The absolute value of the electrical conductivity in the acceptor-doped samples were lower in the n-type region compared to the values in the undoped CaTiO₃. Aluminium and chromium were found to be equally effective in acting as acceptor impurities in CaTiO₃. The defect chemistry of CaTiO₃ is dominated by the added acceptor impurities for the entire oxygen partial pressure range used in this investigation.     

Heat flux measurement from the temperature field of a heated surface. 2. Inhomogeneous flux

Based on the previously obtained analytical solutions of the three-dimensional space-time problem of recalculating boundary conditions, algorithms are developed and a computational experiment is carried out to reconstruct the heat flux with arbitrary spatial distribution of the temperature field of the heated surface.Notation T(t, ) temperature over the plate surface - q(t ) heat flux to the plate surface - ={x,y} transverse coordinate - t time - k thermal conductivity - a ² thermal diffusivity - L plate thickness - Jacobi theta-function [4] - Fourier parameter - Jacobi theta-function [4] - transversal Laplacian Institute of Atmospheric Optics, Siberian Division, Russian Academy of Sciences, Tomsk, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 4, pp. 622–628, July–August, 1995.     

Photocatalytic membrane for removal of organic contaminants during ultra-purification of water

Experiments were performed using a photocatalytic membrane fabricated by embedding titanium dioxide particles within a polymer matrix. Catalyst particles were activated by ultraviolet illumination of the membrane. Experimental results demonstrated the feasibility of the photocatalytic process for elimination from water of trace organic solute concentrations. A mathematical model is proposed that aided in the estimation of kinetic parameters associated with the process. The process simulation is based upon a mechanism whereby the primary organic solvent is mineralized via a series of reactions that involve not less than two organic solute intermediates. The reaction rate parameter associated with 254-nm illumination is estimated to be directly proportional to light intensity. Where 185-nm light and 254-nm light were used together, their catalytic effects were shown to be comparable, but the oxidative effect of 185-nm illumination had the added benefit of noncatalytic oxidation. Catalyst and support system improvements are indicated to increase the photocatalytic effect.Abbreviations C _i TOC present as solute i within membrane volume, spatially dependent (ppb solute in water) - TOC present as solute i exiting the "downstream" side of the membrane chamber (ppb solute in water) - TOC present as solute i entering the "upstream" side of the membrane chamber (ppb solute in water) - intensity of illumination, frequency specific and spatially dependent (mW cm^–2) - incident intensity of illumination, frequency specific (mW cm^–2) - intensity of 185-nm illumination incident upon the membrane surface (mW cm^–2) - intensity of 254-nm illumination incident upon the membrane surface (mW cm^–2) - overall surface reaction rate constant for solute i, incorporating both illumination intensity and reaction energetics (s^–1) - bulk reaction rate constant for solute i attributed to 185-nm illumination of CSTR volume (cm² mW^–1 s^–1) - surface reaction rate constant for solute i attributed to 185-nm illumination (cm² mW^–1 s^–1) - surface reaction rate constant for solute i attributed to 254-nm illumination (cm² mW^–1 s^–1) - L membrane thickness (cm) - m modified Beer's law exponent - q TOC analyzer consumption volumetric flow rate (cm³ s^–1) - Q recirculation volumetric flow rate (cm³ s^–1) - S membrane diametral area (cm²) - u _x linear velocity of fluid (cm s^–1) - initial reservoir volume (cm³) - V ^b membrane chamber CSTR volume "upstream" of the membrane (cm³) - V ^p membrane pore volume (cm³) - x spatial coordinate across membrane (cm) - modified Beer's law coefficient (cm^–m ) - membrane porosity (cm³ fluid (cm³ total)^–1) - illumination wavelength (nm)     

On unbiased Lehmann-estimators of a variance of an exponential distribution with quadratic loss function

Summary Lehmann in [4] has generalised the notion of the unbiased estimator with respect to the assumed loss function. In [5] Singh considered admissible estimators of function λ^-r of unknown parameter λ of gamma distribution with density ,x> 0, whereb-known parameter, for loss function . Goodmann in [1] choosing three loss functions of different shape found unbiased Lehmann-estimators, of the variance σ² of the normal distribution. In particular for quadratic loss function he took weight of the formK(σ²)=C andK(σ²)=(σ²)^-2 only. In this work we obtained the class of all unbiased Lehmanns-estimators of the variance λ² of the exponential distribution, among estimators of the form functions of the sufficient statistics-with quadratic loss function with weight of the form ,C>0.

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Resumen Lehmann en su trabajo [4] generalizó la idea del estimador sin vías en relación a la aceptación de la función de pérdidas. En el trabajo [5] Singh considera de estimadores admisibles para la función λ^-r parámetro desconocido λ de la distribución de gamma, de densidad ,x>0,b>0 parámetro conocido, de la función de pérdidas resulta . Goodman en su trabajo [1] acumulando 3 formas diferentes de funciones de pérdidas encontró estimadores sin biases en el sentido de Lehmann de la variancia de σ² de una distribución normal, en particular para la función de pérdidas con los pesos, solo de la formaK(σ²)=C,K(σ²)=(σ²)^-2. En su trabajo distinguida la clase de todos los estimadores sin biases obtenidos en el sentido de Lehmann de la variancia λ² en la distribución exponencial, entre los estimadores de forma así pues de la función estadística suficiente— por una función de pérdidas al cuadrado con los pesos de la forma ,C>0. Palabras y frases. Estimador sin vías en el sentido de Lehmann, función de pérdidas, riesgo mínimo, suficiente estadística.

     

Annealing effects on electrical characteristics of 100 MeV 28Si implantation in GaAs

Electrical characteristics of single crystal 100 orientation n-GaAs substrates implanted at room temperature with 100 MeV ²⁸Si ions to a dose of 1 × 10¹⁴ ions cm^-2 are reported. The room temperature electrical chracteristics of as-implanted samples and samples annealed in the temperature range of 100–1000 °C arc studied. The I–V curves show a complex behavior with annealing treatment. To understand this complex behavior, the resistance–temperature measurements for each annealing stage were carried out in the temperature range of 113 K–433 K. In the low temperature range from 113 K to 270 K, it is observed that the resistance of the as-implanted sample and samples annealed at and below 450 °C follows the relation . This suggests that the conduction mechanism for these samples is governed by variable range hopping. In the high temperature range of 300 K to 433 K, it is observed that the resistance of samples annealed at 450–550 °C follows the relation which is characteristic of a conduction mechanism due to carriers in the extended states.     

Diffusivity and solubility of oxygen in solid palladium

The solid solubility c _O of oxygen in palladium in equilibrium with gaseous oxygen has been determined from absorption-desorption experiments for temperatures T of 1123 and 1173 K and oxygen partial pressures between 2.7 × 10³ and 4.0 × 10⁴ Pa. The relationship between c _O, and T is given by , where R = 8.314 JK⁻¹ mol⁻¹ is the universal gas constant, ΔH _s = −13.55 kJ/mol denotes the heat of solution of oxygen in palladium and the constant a amounts to or . The diffusion coefficient D _O of oxygen in solid palladium has been determined by incomplete isothermal internal oxidation of Pd–Fe alloys using the data on the oxygen solubility in palladium. The temperature dependence of D _O obeys the Arrhenius equation D _O = D ⁰ exp(−E _d/RT) with pre-exponential factor D ⁰ = 2.33 × 10⁻⁷ m²/s and activation energy of diffusion of oxygen in palladium, E _d = 102.76 kJ/mol     

High-temperature properties of rapidly solidified Al-Be alloys

Rapidly solidified Al-Be binary alloys (10%, 20%, and 40%, Be by weight) have been produced by melt-spinning techniques. The microstructures have been evaluated and the elevated temperature mechanical properties have been characterized over a range of strain rates. Despite the fact that the materials exhibited duplex microstructures resulting from high-temperature processing, they showed behaviour typical of dispersion strengthened alloys. The mechanical properties at elevated temperature can accurately b8 described by the equation exp (–120 kJ mol^–1/RT), where is the deformation rate, is the stress,E is the modulus,A is 8 material constant, andRT has its usual meaning. A direct comparison of the deformation properties was made between binary Al-Be composition and pure aluminium as baseline, as well as between Al-Be and some high temperature aluminium alloys. The Al-Be alloys do not exhibit good high-temperature strength when compared with other high-temperature aluminium alloys, e.g. Al-Fe-Co alloys. This is a result of particle coarsening and agglomeration during processing and testing.     

Mass transport of cobalt and nickel in Incoloy-800

Lattice diffusion of cobalt and nickel in Incoloy-800 has been studied in the temperature range 1070 to 1500K by serial sectioning and residual activity techniques using radioactive tracers⁶⁰Co and⁶³Ni. The lattice diffusion coefficient can be expressed by the relation:

A local-global matching method for the single fiber pullout problem with perfectly bonded interface

This paper presents a local-global matching method to effectively determine the detail spatial structure and magnitude of the locally singular stress field as well as the complete global stress distribution in the single fiber pullout model. The motivation to solve for the local stress field is the belief that these accentuated stresses, strains and energy are likely to induce damage. The local-global matching method consists of three components: a local analysis, a global analysis, and proper matching of the local asymptotic field to the global complete stress field. The method as developed is applicable for various fiber-matrix interfacial conditions: namely perfectly bonded interface, partially debonded interface with interfacial crack, or debonded interface with frictional interfacial sliding. In this paper, results for perfectly bonded fiber-matrix interface are presented to illustrate key features of the local-global matching method. For this problem, the local stress field is asymptotically singular at the location where the fiber protrudes from the matrix. A local analysis at the fiber protrusion point reveals that, when the fiber is stiffer than the matrix, the most dominant singular stresses are of the from: where the exponent is real-valued and <0. The local analysis can solve for the spatial structure of the local field: its radial dependence and angular variations . The actual magnitude of the local stress field is scaled by the amplitude factor K which depends upon externally applied load and global boundary conditions. The global analysis, performed using a finite element model, can be subjected to arbitrary fiber-pulling load and/or thermal load. With solutions from both the local analysis and global analysis, a local-global matching method based on angular variation of stresses is developed to accurately determine K. In local-global matching, a proper region is selected in which the angular variation of stresses of the local field is scaled to match the angular variation of the finite-element computed full-field stresses. Several monitoring parameters are developed to measure the quality of the matching and to determine the region of dominance of the local asymptotic field. The local analysis shows that in many composite material systems, there are two singular terms in the local field: . Hence, local-global matching procedures have been developed for both one-term field and two-term field. The matching method is further generalized to determine complex-valued K for composites having complex-valued . The local-global matching method may also be applied to problems with material nonlinearity.This work was partially supported by a grant from the Air Force Office of Scientific research and by Drexel University. The finite element analyses were performed using ABAQUS made available through an academic license by Hibbitt, Karlsson and Sorensen, Inc. The authors gratefully acknowledge these support     

Effect of superplastic deformation on the grain size and tensile properties of Al-6.2Zn-2.5Mg-1.7Cu (7010) alloy sheet

An Al-Zn-Mg alloy (7010) was cold-rolled and annealed to produce a small recrystallized grain size, and superplastically deformed in the temperature range 475 to 520° C at strain rates to 2.8×10^–3 sec^–1. At 500° C and sec^–1 superplastic elongations up to 350% were obtained, but above about 60% elongation the residual room-temperature tensile properties after heat treatment decreased due to increasing grain-boundary cavitation. Grain growth rates were increased by superplastic strain.     

Nuclear relaxation in bcc3He for large molar volumes

We report the results of measurements of longitudinal and transverse nuclear relaxation timesT ₁ andT ₂ in bcc³He at 300 mK and at a Larmor frequency of 3 MHz for molar volumes 22.6V24.9 cm³. It is found, even in this extended range of molar volumes, that the relaxation times increase withV as , with ₁=19±1 and ₂=18±1.5. This molar volume dependence has also been found in various thermodynamic data, including recent results of pressure measurements through the nuclear ordering temperature. This universality in molar volume dependence remains unexplained within the context of the present models of multiple exchange.     

Grain growth behaviour of the Al-Cu eutectic alloy during superplastic deformation

Grain growth behaviour of the Al-Cu eutectic alloy was investigated as a function of strain (ε), strain rate and deformation temperature (T) over = 10⁻² s⁻¹ and T=400 to 540°C. The grain size increases with increase in strain and temperature. Upon deformation to a fixed strain, the grain growth is generally seen to be more at lower strain rates. The rates of overall grain growth and due to deformation alone , however, increase with increasing strain rate according to and , respectively. The increase in the grain growth rate with strain rate is attributed primarily to the shorter time involved at higher strain rate for reaching a fixed strain. The activation energy for grain growth under superplastic conditions is estimated to be 79 kJ mol⁻¹.     

Zr surface diffusion in tetragonal yttria stabilized zirconia

The value for surface diffusivity of Zr tetragonal ZrO₂–3mol% Y₂O₃ has been calculated from measurements of surface area reduction and pore growth in powder compacts during sintering. The surface diffusivity thereby obtained can be described by D =5.52×10⁵ exp[–531(kJ mol^-1)/RT] m²/s, which is in reasonable agreement with values calculated by prior researchers from direct TEM observation of neck growth between touching particles.     

Electrical conductivity in non-stoichiometric titanium dioxide at elevated temperatures

The electrical conductivity of polycrystalline titanium dioxide prepared by a liquid mix technique was measured for the oxygen partial pressure range of 10° to 10^–19 atm and temperature range of 850 to 1050° C. The data were found to be proportional to the –1/6 power of oxygen partial pressure for the oxygen pressure range 10^–19 to 10^–15 atm, and proportional to for the oxygen pressure range >10^–15 atm. The region of linearity where the electrical conductivity varied as the –1/4 power of increased as the temperature was decreased. There was evidence of p-type behaviour for 10^{ - 2}$$ " align="middle" border="0"> atm in the temperature range 950 to 850° C, although the measured data were insufficient to assign a pressure dependence. Electrical conductivity minima in the log against log plot moved to lower as the temperature was decreased in the range 950 to 850° C. The measured oxygen pressure dependence of electrical conductivity in the lowest region supports the oxygen vacancy defect model. The observed data are consistent with the presence of very small amounts of acceptor impurities. A binding energy of 0.67 eV between the acceptor impurity and its compensating oxygen vacancy was also determined.     

Stress-strain rate relations for high-temperature deformation of two-phase Al-Cu alloys

Al-Cu alloys containing 6, 11, 17, 24 and 33 wt% Cu, annealed for 0.5–100 h, were deformed by the differential strain-rate test technique over a strain-rate range of 4×10^–6 to 3×10^–2s^–1 at temperatures ranging from 460–540°C. Superplastic behaviour, with strain-rate sensitivity, m0.5, and activation energy, Q=171.5 kJ mol^–1, is shown by the Al-24Cu and Al-33Cu alloys at lower strain rates and higher temperatures. All the alloys show m0.20 at higher strain rates, but the average activation energy for deformation of the Al-6Cu, Al-11Cu, and Al-17Cu alloys is evaluated to be 480.7 kJ mol^–1, in contrast to a lower value of 211 kJ mol^–1 for the Al-24Cu and Al-33Cu alloys. Instead of grain size, the mean free path between particles is suggested to be a more appropriate microstructural parameter for the constitutive relationship for deformation of the Al-Cu alloys.