Zr-Hf interdiffusion in polycrystalline Y2O3-(Zr+Hf)O2

Lattice and grain-boundary interdiffusion coefficients were calculated from the concentration distributions determined for Zr-Hf interdiffusion in polycrystalline 16Y₂O₃·84(Zr_1–x Hf _x )O₂ withx=0.020 and 0.100. The lattice interdiffusion coefficients were described byD=0.031 exp [–391 (kJ mol^–1)/RT] cm² sec^–1 and the grain-boundary diffusion parameters byD=1.5×10^–6exp [–309(kJ mol^–1)/RT] cm³ sec^–1 in the temperature range 1584–2116° C. Comparison of the results with those for the systems CaO-(Zr+Hf)O₂ and MgO-(Zr+Hf)O₂ indicated that the Zr self-diffusion coefficient was insensitive to the dopants in the fluorite-cubic ZrO₂ solid solutions.     

Thermal conductivity of D2O vapor

Results are shown of an experiment in which the thermal conductivity of D₂O vapor was measured and the ratio was determined at temperatures up to 760°C under a pressure of about 1 bar.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 2, pp. 336–340, August, 1973.     

Isochoric Heat Capacity Measurements for 0.5 H2O+0.5 D2O Mixture in the Critical Region

The isochoric heat capacity C _V of an equimolar H₂O+D₂O mixture was measured in the temperature range from 391 to 655 K, at near-critical liquid and vapor densities between 274.05 and 385.36 kgm^–3. A high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter was used. The measurements were performed in the one- and two-phase regions including the coexistence curve. The uncertainty of the heat-capacity measurement is estimated to be ±2%. The liquid and vapor one- and two-phase isochoric heat capacities, temperatures, and densities at saturation were extracted from the experimental data for each measured isochore. The critical temperature and the critical density for the equimolar H₂O+D₂O mixture were obtained from isochoric heat capacity measurements using the method of quasi-static thermograms. The measurements were compared with a crossover equation of state for H₂O+D₂O mixtures. The near-critical isochoric heat capacity behavior for the 0.5 H₂O+0.5 D₂O mixture was studied using the principle of isomorphism of critical phenomena. The experimental isochoric heat capacity data for the 0.5 H₂O+0.5 D₂O mixture exhibit a weak singularity, like that of both pure components. The reliability of the experimental method was confirmed with measurements on pure light water, for which the isochoric heat capacity was measured on the critical isochore (321.96 kgm^–3) in both the one- and two-phase regions. The result for the phase-transition temperature (the critical temperature, T _{C, this work}=647.104±0.003 K) agreed, within experimental uncertainty, with the critical temperature (T _{C, IAPWS}=647.096 K) adopted by IAPWS.     

Static recrystallization kinetics of 304 stainless steels

Static restoration mechanism during hot interrupted deformation of 304 stainless steel was studied in the temperature range from 900 to 1100°C, various strain rate from 0.05 to 5/sec and pass strain of 0.25–3 times peak strain. It was clarified that the static recrystallization was happened after 3–10 seconds at first deformation. The static restoration was depended on the pass strain, deformation temperature and strain rate and fractional softening (FS) values increased with increasing strain rate, deformation temperature and pass strain. Recystallization kinetics was explained with Avrami equation and Avrami constant was 1.113. This value was independent of deformation variables significantly. The time of 5, 50, 95% recrystallization was evaluated using such equations: t _0.05 = 2.9 × 10^{–12 –1.17 –0.94} D exp(222000 J/mol/RT), t _0.5 = 2.0 × 10^{–10 –1.56 –0.81} D exp(197000 J/mol/RT), t _0.95 = 1.9 × 10^{–8–1.63 –0.76} D exp(173000J/mol/RT). The predicted values by use of upper equations had a good agreement with a measurement.     

The surface diffusion coefficients of MgO and Al2O3

From the measurement of neck size and neck curvature during the sintering of two spheres the surface diffusion coefficients of MgO and Al₂O₃ were determined. The spheres of both materials were machined from single crystals. The following values of surface diffusion coefficients were found: for MgO,D _{s s} = 3.7 × 10^–4 exp (407.8 kJ mol^–1/RT m³ sec^–1; for Al₂O₃,D _{s s} = 1.5 × 10^–2 exp (518.7 kJ mol^–1/RT) m³ sec^–1.     

Diffusion coefficients of tetrazolium blue in homogeneous and micellar solutions

Diffusion coefficients of the electron acceptor dye tetrazolium blue were measured by the Taylor dispersion method, with an accuracy better than 4%, in two solvents: (i) a homogeneous one-aqueous phosphate buffer, 0.1 M, pH=7.0 (medium I); and (ii) a heterogeneous one-nonionic micelles of Triton X-100, 2.0 mM (where M stands for mol·dm^–3), in the same aqueous phosphate buffer (medium II). The values obtained were D ₁₂ ^I =3.64×10^–10m²·s^–1 and D ₁₂ ^II =3.01×10^–10m²·s^–1·D ₁₂ ^II has the meaning of a macroscopird or average diffusion coefficient, in which the partition coefficient of tetrazolium blue between micelles and water, as well as the diffusion coefficients of this dye and of the micelles in the aqueous phase, are involved.     

Metadynamic recrystallization of austenitic stainless steel

Interrupted torsion tests were performed in the temperature range of 900–1100°C, strain rate range of 5.0 × 10^–2–5.0 × 10⁰/sec and interpass time range of 0.5–100 seconds to study the characteristics of metadynamic recrystallization (MDRX) for austenitic stainless steel. To compare the MDRX with static recrystallization (SRX), the pass strain was applied above the critical strain (_c) (_c = 2.2 × 10^–3 D^1/2 ₀ Z ^0.089, where Z is Zener-Hollomon parameter, Z = exp((380000 J/mol)/RT) and D ₀ is as-received grain size) to obtain the MDRX during interpass time. It was found that the kinetics of MDRX were dependent of the strain rate and deformation temperature but were nearly independent of the change in pass strain after the peak strain. The time for 50% metadynamic softening, t ₅₀, was determined as follows: t ₅₀ = 1.33 × 10^{–11 –0.41} D ₀ exp((230000 J/mol)/RT) and this calculated value was consistent with the measured value. The Zener-Hollomon parameter was impossible to evaluate the MDRX fraction, because the fractional softening values were different at the same Z values. The new parameter (MDRX parameter) considering deformation temperature, strain rate and interpass time was proposed to evaluate the MDRX fraction. The MDRX-parameter was determined as 3.25 × 10^{–19 0.3} t _i ^0.6 T ¹².     

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.     

Preparation and photovoltaic properties of anodically grown Ag2O films

The semiconducting and photovoltaic properties of p-type Ag₂O films grown anodically on silver electrodes were studied, in view of possible applications in solar energy conversion. Films were grown in different alkaline solutions; the best results were obtained for 0.02M Ag₂SO₄ + 0.17M NH₄OH + 5.7 × 10^–3M Ba(OH)₂ saturated with Ag₂O powder, stirred mechanically at room temperature. Film thicknesses of up to 10m were thus obtained for the first time in anodically grown Ag₂O. Photovoltaic spectra taken at 300 K give a bandgap ofEg = 1.42 ± 0.04 eV. Evaporated gold on Ag₂O appears to be ohmic while aluminium and platinum are rectifying. The barrier height of Ag/Ag₂O is 0.90 ± 0.02 eV, that of Al/Ag₂O is 0.93 ± 0.02 eV, and that of platinum 0.94 ± 0.02 eV. The best cells give an open-circuit voltage,V _oc, of over 150 mV, and a short circuit current,I _sc = 100A cm^–2 under 50 mW cm^–2 illumination.     

Oxygen self-diffusion in a potassium strontium silicate glass using proton activation analysis

Oxygen self-diffusion coefficients were measured in a 20K₂O-20SrO-60SiO₂ (wt%) glass above and below the glass transition temperature using the single spectrum proton activation analysis of oxygen-18 using the nuclear reaction ¹⁸O(p, )¹⁵N. The -particle spectrum recorded during proton irradiation is used to determine the ¹⁸O concentration profile. The self-diffusion coefficients, D, determined for the three diffusion times of about 22 h, 3 1/2 and 7 1/2 days were in good agreement within experimental error, except for the two lowest temperatures of the short-time run possibly because of the shallow depths of diffusion and surface exchange. In the temperature range 600 to 1000 K, D values with the relations, above the glass transition temperature D=7.6×10¹⁴ exp(–119 kcal/RT) cm²sec^–1, and below the glass transition temperature D=1×10^–12 exp(–10 kcal/RT) cm²sec^–1, were obtained.     

Non-stoichiometric disorder in α-Nb2O5 at elevated temperatures

The electrical conductivity of polycrystalline-Nb₂O₅ was determined for the oxygen partial pressure range of 10⁰ to 10^–20 atm and temperature range 700 to 1150 ° C. The data were found to be proportional to the –1/6th power of the oxygen partial pressure for the oxygen pressure range 10^–20 to 10^–9 atm, and proportional toPO ₂ ^–1/4 for oxygen pressures greater than 10^–9 atm. The region of linearity where electrical conductivity varies as the –1/4th power of increased as the temperature was decreased. Thermogravimetric measurements were carried out in the temperature range 950 to 1250 ° C. The deviation from stoichiometry in-Nb₂O₅ (x in Nb₂O_5–x ) as a function of partial pressure of oxygen showed two distinct regions, namely a region with an approximately –1/6th dependence on and a region where the deviation was nearly independent of oxygen partial pressure. The electrical conductivity and thermogravimetric data are consistent with the presence of small amounts of acceptor impurities in-Nb₂O₅.     

Anomalous Depression of the Debye-Waller Factor and Observations of the Laue Spots Only at Forward X-ray Diffraction in the Light Atom Crystals as Quantum Solid

The ratio of 6·(1/2m)·(E ₀/c)² of 12.9 meV at E ₀=4 keV to k _{B D} of 2.27 meV for hcp-⁴He in the exponent 2M=[6·(1/2m)·(E ₀/c)²/k _{B D} ]·(t)sin² _B of the Debye-Waller factor D=exp(–2M) becomes 5.7, because of the small atomic mass m and the low Debye temperature _D . Conversely that of the heavy atom crystals becomes smaller than 1. An experiment on hcp-⁴He as an example of a light atom crystal at low temperature limit of (t)1 reveals that not only the maximum value of D is significantly reduced below 0.249 (=e ^–1.395) but also the values of D for all other Laue spots except the following observed six spots are crowded into a range of D<0.05. Therefore, only the six Laue spots of at 11.2 keV, (0002) at 20.3 keV, and at 14.4 keV and and at 23.9 keV in a low angular range of _B10.22° were observed over low values of e ^–1.395>De ^–3. At high angle of _B 45°, the values of E ₀ for the above six Laue spots are assigned to the region below 4.07 keV from the Bragg condition under constant values of D. Therefore, detection of them over the higher angular range of _B 45° is not impossible but quite difficult at low temperature X-ray diffraction, considering X-ray absorption by multi-thermal shields of the refrigerator, the thick sample holder as a pressure vessel and massive air in space. Generally this means that the large reduction of the Debye-Waller factor of hydrogen and helium drastically encloses the diffraction intensity and the number of observable Laue spots within lower bounds. This is the reason why definite Laue spots in the light atom crystals of hcp-⁴He could be observed only by forward X-ray diffraction. Conversely the recoil fraction of the diffuse scattering expressed by 1–D concomitantly increases as a major part of the total scattering. A proposal to measure thermal diffuse scattering as well as pressure experiments will provide insight into the wave-like character of constituent atom in solid helium.     

Phonon Vibration and Conduction of La2 ? xSrxCuO4 ? δ and La1.85 ? xSr0.15 + xCu1 ? xCoxO4 ? δ

Polycrystalline samples La_{2 – x} Sr _x CuO_{4 –} (0.06 x 0.5) and La_{1.85 – x} Sr_{0.15 + x} Cu_{1 – x} Co _x O_{4 –} (0 x 1) were synthesized by a conventional solid state reaction method. The structure, phonon vibration, and conduction were investigated by means of XRD, infrared (IR) spectra, and resistance. It is found that the increase of itinerant hole carriers could mask the in-plane stretching vibration mode (689 cm^–1). The softening of the phonon vibration mode gives an index of the weakening of hybridization. The distortion of CuO₆ octahedron and the microstructural inhomogeneity induced by Co doping lead to the widening of the IR absorption peaks.     

Domain Walls Due to Anisotropic Diffusion in 3.8% 3He-4He Solutions

Nonlinear anisotropic spin diffusion is considered in ³He-⁴He solutions at the ³He concentration 3.8% where spin-rotation effects are absent. For large anisotropy D _∥ D _⊥ it is shown that a long-lived domain wall solution exists in which transverse magnetization is confined in a tube between two reservoirs of up and down spins, as in a longitudinal spin diffusion experiment. This is possible when D _∥ D _⊥ because diffusion of the transverse magnetization away from the domain wall is balanced by longitudinal diffusion toward the wall. Furthermore, the spin current between the up- and down-spin reservoirs is reduced because the spins must diffuse through the domain wall via transverse diffusion. The decay rate of the wall due to small external and demagnetizing field gradients is also calculated.     

Convective heat transfer in the entrance region of a rectangular duct with two indented sides

This study presents a numerical solution to convective heat transfer in laminar flow in the thermal entrance region of a rectangular duct with two indented sides. The flow is considered to be hydrodynamically fully developed and thermally developing laminar flow of incompressible, Newtonian fluids with constant thermal properties. The ducts are subjected to a constant wall temperature. An algebraic technique is used to discretize the solution domain and a boundary-fitted coordinate system is numerically developed. The governing equations in the boundary-fitted coordinates are solved by the control volume-based finite difference method. Distribution of the bulk temperature and the Nusselt number along the direction of flow is calculated and presented graphically. Also calculated is the thermal entrance length of the rectangular ducts with two indented sides. The parameters, such as the friction factor times the Reynolds number, and the Nusselt number for the fully developed flow and thermally developing flow are obtained.List of symbols a half-width of duct [m] - A cross-sectional area [m²] - b half-height of duct [m] - C _p specific heat [kJ kg^-1 K^-1] - D _h hydraulic diameter [m] - f skin friction factor = - h _z local heat transfer coefficient [Wm^–2 K^–1] - h _T asymptotic heat transfer coefficient [Wm^–2 K^–1] - J Jacobian matrix of transformation, Eq. (20) - k thermal conductivity [Wm^–1 K^–1] - L thermal entrance length [m] - L ^* dimensionless thermal entrance length =L/D _h RePr - L1 maximum number of grids in direction - M1 maximum number of grids in direction - Nu _T asymptotic Nusselt number =h _T D _h /k - p pressure [n m^–2] - P circumferential length [m] - Pr Prandtl number = /_T - Re Reynolds number =w _m D _h / - T temperature [K] - T _b bulk temperature [K] - T _i inlet temperature - T _w circumferential duct wall temperature [K] - w velocity [ms^–1] - w _m mean velocity [ms^–1] - W dimensionless velocity = – - W _m dimensionless mean velocity - x, y transveral coordinates [m] - X,Y dimensionless transversal coordinates =      

Gibbs energy of formation of Cu2 Ln 2O5 (Ln = Yb,Tm, Er,Ho, Dy) and CuGd2O4 compounds by the e.m.f. method

Employing electrochemical cells with the solid zirconia electrolyte Cu₂O, Cu₂ Ln ₂0₅, Ln ₂O₃O^2– air and Cu₂O, CuGd₂O₄, Gd₂O₃O^2– air the Gibbs free energy of formation of the solid Cu₂ Ln ₂O₅ (Ln=Yb,Tm, Er, Ho, Dy) and CuGd₂O₄ phases was determined. The results obtained were used to derive Gibbs free energy change of reactions of formation of these compounds from the respective oxides in the following form G _oxides ⁰ (Cu₂Yb₂O₅)=19 429-22.02TJmol^–1 G _oxides ⁰ (Cu₂Tm₂O₅)=35 275-34.09TJmol^–1 G _oxides ⁰ (Cu₂Er₂O₅)=17 427-19.61TJmol^–1 G _oxides ⁰ (Cu₂Ho₂0₅)=18 165-19.49TJmol^–1 G _oxides ⁰ (Cu₂Dy₂O₅)=16 648-17.58TJmol^–1 G _oxides ⁰ (CuGd₂O₄)=9562-12.29TJmol^–1     

Glassy behavior of low-temperature energy relaxation in YBa2Cu3O7 and YBa2Cu3O6

Measuring the power release after rapid cooling a YBa₂Cu₃O₇ sample (m=42.85 g, T_c=91 K) from the equilibrium temperature T₁ (2.35 KT₁15.1 K) to T₀=1.5 K, we observed a time dependence typical of a glass: is proportional to t^–1. The results allow us to determine the linear term of the heat capacity (0.8 mJ/mole · K²) due to the two-level systems. While the low-temperature heat capacity anomaly noticeably decreases, the power release is essentially unchanged after oxygen reduction of the sample.     

Some effects of copper-oxide additions to Co0.6Zn0.4Fe2O4

A series of samples of the system Co_0.6Zn_0.4Cu _x Fe_{2 –x} O₄ (x=0, 0.2, 0.4, 0.6 and 0.8) were prepared by the usual ceramic technique, X-ray analysis showed that the samples were cubic spinels (single phase). The lattice parameter, the theoretical density,D _x, the bulk density,D, and the porosity, p, were measured for the samples. The lattice parameter increased with the increase in Cu. Increases in the population of Fe²⁺ ions in octahedral sites with the introduction of Cu²⁺ resulted in increases in the lattice parameter. Differential thermal analysis (DTA) traces showed that there were exothermic peaks for the samples in the temperature range 120–190 C.     

Seebeck coefficient of V2O5-R2O3-TeO2 (R = Sb or Bi) glasses

The thermoelectric power of glasses in the systems V₂O₅-Sb₂O₃-TeO₂ and V₂O₅-Bi₂O₃-TeO₂ was measured at temperatures in the range 373–473 K. The glasses in both systems were found to be n-type semiconductors. The Seebeck coefficient, Q, at 473 K was determined as –192 to –151 VK^–1 for V₂O₅-Sb₂O₃-TeO₂ glasses, and –391 to –202 VK^–1 for V₂O₅-Bi₂O₃-TeO₂ glasses. For these glasses in both systems, Heikes' formula was satisfied adequately for the relationship between Q and In [C _v/(1-C_v)] (C _v = V⁴⁺/V_total, C _v is the ratio of the concentration of reduced vanadium ions), and discussions confirmed small polaron hopping conduction of the glasses in both systems. Mackenzie's formula relating to Q and V⁵⁺/V⁴⁺ was also applicable to the glasses in both systems, and it was concluded that the dominant factor determining Q was C _v.     

Growth and Properties of K2TiNb2P2O13Crystals

K₂TiNb₂P₂O₁₃single crystals (monoclinic structure, a= 13.788 Å, b= 6.418 Å, c= 16.927 Å, = 97°) were grown from off-stoichiometric K₂O–TiO₂–Nb₂O₅–P₂O₅melts, and their habit was described. The 300°C electrical conductivity of the crystals was determined to be 5 × 10^–4S/cm.