Thermal Characterization of PZT Ceramics Obtained by Mechanically Activated Mixed Oxides Using Different Pb Sources

In this study, three sets of PZT samples with compositions 57/43 and 55/45 (rhombohedral phase), 53/47 and 51/49 (tetragonal phase) prepared by mechanochemical activation of powder mixtures (during 4?h of milling) and thermal treatment (sintered at 1200?°C for 4?h) were thermally characterized. The three sets of compositions were prepared using different Pb sources (A-PbO, B-PbO₂, and C-Pb₃O₄). The thermal characterization of sintered samples was carried out by photoacoustic spectroscopy and differential scanning calorimetry, to obtain the thermal diffusivity and specific heat (c _p ). The DSC thermograms also allowed the determination of the Curie temperature, and the thermal conductivity was calculated combining the results of the thermal diffusivity, specific heat, and density. The samples obtained with Pb₃O₄ showed a theoretical density higher than 95?%, whereas those obtained from PbO₂ precursors showed a lower densification rate (around 89?%). The samples obtained with Pb₃O₄ with compositions 53/47 and 51/49 also showed the highest values of thermal diffusivity (7.3 ± 0.4)?× 10^?7m²· s^?1 and (6.6 ± 0.3)?× 10^?7m²· s^?1, respectively.     

Effet Hall dans les films d'argent déposés par voie chimique

Study of the Hall effect on silver films prepared by chemical reduction shows an electronic conductivity. At 25°C the Hall coefficient R_H is ?(12 ± 1) × 10^?11 m³ C^?1 and the number of conduction electrons n = 0.89 electrons per atom agrees within 10% of the result obtained from measurement of the conductivity.The mobility of the electron transport in the annealed films, μ_Hr(25°C) = 4.85 × 10^?3 m²V^?1s^?1 is six to seven time greater than that of the same unannealed films, μ_Hi(25°C) = 0.75 × 10^?3 m² V^?1 s^?1.     

Thermomechanical properties of iron: viscoplasticity of ferrite and of austenite—ferrite mixtures

The available data on secondary creep in creep tests and on maximum stress in hot deformation tests obtained for δ and α ferrite have been reviewed and expressed in the form of the equation ? = K(σ/E)^P_c sinh(Vσ/RT) exp(—Q_c/RT) with p_c = 2·5, V = 0·0013 m³ mol^?1, and K = 2·6 × 10¹⁷ s^?1, E and Q_c being temperature dependent functions. The approximate range of validity is Z = ? exp (Q_c/RT) ≈ 10¹—10¹¹ s^?1. Together with the corresponding equation for austenite the data can be used to predict the viscoplastic behaviour of austenite—ferrite mixtures.

MST/1538     

Densities and Excess,Apparent, and Partial Molar Volumes of Binary Mixtures of BMIMBF<Subscript>4</Subscript> + Ethanol as a Function of Temperature,Pressure, and Concentration

The densities of five BMIMBF₄ (1-butyl-3-methylimidazolium tetrafluoroborate) + ethanol binary mixtures with compositions of (0.0701, 0.3147, 0.5384, 0.7452, and 0.9152) mole fraction BMIMBF₄ and of pure BMIMBF₄ have been measured with a vibrating-tube densimeter. Measurements were performed at temperatures from 298 K to 398 K and at pressures up to 40 MPa. The total uncertainty of density, temperature, pressure, and concentration measurements were estimated to be less than 0.1 kg · m⁻³, 15 mK, 5 kPa, and 10⁻⁴, respectively. The uncertainties reported in this article are expanded uncertainties at the 95% confidence level with a coverage factor of k = 2. The measured densities were used to study derived volumetric properties such as excess, apparent, and partial molar volumes. It is shown that the values of excess molar volume for BMIMBF₄ + ethanol mixtures are negative at all measured temperatures and pressures over the whole concentration range. The effect of water content on the measured values of density is discussed. The volumetric (excess, apparent, and partial molar volumes) and structural (direct and total correlation integrals, cluster size) properties of dilute BMIMBF₄ + ethanol mixtures were studied in terms of the Krichevskii parameter. The measured densities were used to develop a Tait-type equation of state.     

High strain rate superplasticity of TiNP/2014Al composite

Superplasticity of the TiN_p/2014AI composite prepared by powder metallurgy method was investigated by tensile tests conducted at different temperatures (773, 798, 818 and 838 K) with different strain rates range from 1·7×10° to 1·7×10^?3s^?1. Results show that a maximum elongation of 351% is achieved at 818 K and 3·3·10^?1s^?1. At different deformation temperatures, the curves of m value can be divided into two stages with the variation of strain rate and the critical strain rate is 10^?1 s^?1. Superplastic deformation activation energy in the TiN_p/2014AI composite is 417 kJ mol^?1, which is related to liquid phase formation at triple points of grain boundaries and interfaces between the matrix and the reinforcement. Superplastic deformation mechanism of the TiN_p/2014AI composite is grain boundary sliding accommodate mechanism when the strain rate is lower than 10^?1 s^?1, and transfers to grain boundary sliding accommodation mechanism plus liquid phase helper accommodation mechanism when the strain rate is higher than 10^?1 s^?1     

Progress Toward Redetermining the Boltzmann Constant with a Fixed-Path-Length Cylindrical Resonator

A single, fixed-path-length cylindrical-cavity resonator was used to measure c ₀ = (307.825 2 ± 0.001 2) m · s^?1, the zero-density limit of the speed of sound in pure argon at the temperature of the triple point of water. Three even and three odd longitudinal modes were used in this measurement. Based on the ratio M/?? ₀ = (23.968 644 ± 0.000 033) g · mol^?1, determined from an impurity and isotopic analysis of the argon used in this measurement and the measured c ₀, the value k _B = 1.380 650 6 × 10^?23J · K^?1 was obtained for the Boltzmann constant. This value of k _B has a relative uncertainty u _r(k _B) = 7.9 × 10^?6 and is fractionally, (0.12 ± 8.1) × 10^?6 larger than the value recommended by CODATA in 2006. (The uncertainty is one standard uncertainty.) Several, comparatively large imperfections of our prototype cavity affect the even longitudinal modes more than the odd modes. The models for these imperfections are approximate, but they suggest that an improved cavity will significantly reduce the uncertainty of c ₀.     

Measurement of the Diffusion Coefficient of Water in RP-3 and RP-5 Jet Fuels Using Digital Holography Interferometry

The diffusion coefficient of water in jet fuel was measured employing double-exposure digital holographic interferometry to clarify the diffusion process and make the aircraft fuel system safe. The experimental method and apparatus are introduced in detail, and the digital image processing program is coded in MATLAB according to the theory of the Fourier transform. At temperatures ranging from 278.15 K to 333.15 K in intervals of 5 K, the diffusion coefficient of water in RP-3 and RP-5 jet fuels ranges from 2.6967?×?10 ^?10 m²·s^?1 to 8.7332?×?10 ^?10 m²·s^?1 and from 2.3517?×?10 ^?10 m²·s^?1 to 8.0099?×?10^?10 m²·s^?1, respectively. The relationship between the measured diffusion coefficient and temperature can be well fitted by the Arrhenius law. The diffusion coefficient of water in RP-3 jet fuel is higher than that of water in RP-5 jet fuel at the same temperature. Furthermore, the viscosities of the two jet fuels were measured and found to be expressible in the form of the Arrhenius equation. The relationship among the diffusion coefficient, viscosity and temperature is analyzed according to the classic prediction model, namely the Stokes–Einstein correlation, and this correlation is further revised via experimental data to obtain a more accurate predication result.     

Serrated yielding in Nb–V dual phase steel

Abstract

The characteristics of serrated yielding (the Portevin–Le Chatelier effect) in a Nb–V dual phase steel have been studied in the temperature range 85–210°C at strain rates between 1·2 × 10^?5 and 1·2 × 10^?2 s^?1. Serrated yielding was found to initiate only after a critical strain ?_c was reached. The strain between two successive serrations ??_s increases almost linearly with strain, while the stress drop ?σ_c increases with strain up to ?σ_max, then decreases. The exponent β in the mobile dislocation density–plastic strain relationship (ρ_m= ?^β) is 1·09 in the temperature range 85–140°C and 1·34 in the temperature range 140–210°C. The results also indicate that in the same temperature ranges there are two values of activation energy for type A serrations, i.e. 79 and 119 kJ mol^?1 respectively. The results are discussed in terms of substitutional–interstitial solute atom interaction and changes of concentration of interstitial atoms.

MST/934     

Supercapacitive performance of hydrous ruthenium oxide (RuO2 · nH2O) thin films synthesized by chemical route at low temperature

In the present investigation, we report the synthesis of ruthenium oxide (RuO₂ · nH₂O) thin films by simple chemical bath deposition (CBD) method at low temperature on the stainless steel substrate. The prepared thin films are characterized for their structural and morphological properties by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT–IR) and scanning electron microscopy (SEM). The structural study revealed that the ruthenium oxide thin films are amorphous. Scanning electron microscopy study shows compact morphology with small overgrown particles on the surface of the substrate. FT–IR study confirms the formation of RuO₂ · nH₂O material. The supercapacitor behaviour of RuO₂ · nH₂O thin film was studied using cyclic voltammetry (CV) technique in 0 · 5 M H₂SO₄electrolyte. RuO₂ · nH₂O film showed maximum specific capacitance of 192 F · g^{? 1}at a scan rate of 20 mV · s^{? 1}. The charge–discharge studies of RuO₂ · nH₂O carried out at 300 μA · cm^{? 2}current density revealed the specific power of 1 · 5 kW.kg^{? 1}and specific energy of 41 · 6 Wh.kg^{? 1}with 95% coulombic efficiency.     

Microstructure and thermoelectric properties of tungsten trioxide ceramics doped with a low amount of terbium dioxide

The effect of the nonstoichiometric compound terbium dioxide (Tb₄O₇) on the thermoelectric properties of tungsten trioxide (WO₃) ceramics was investigated. Among the sintered ceramics, the sample doped with 0.1 mol% Tb₄O₇ showed the maximum grain size and density. Doping with Tb₄O₇ also increased the electrical conductivity (σ) of the ceramics by about two orders of magnitude, and the sample doped with 0.1 mol% Tb₄O₇ showed the highest electrical conductivity. The absolute value of Seebeck coefficient (|S|) of the doped samples increased as well. Consequently, the power factor (σs ²) markedly increased. The sample doped with 2.0 mol% Tb₄O₇ demonstrated the maximum σs ² of 2.88 μW m^?1 K^?2 at 973 K, which was larger than the highest recorded σs ² for WO₃ ceramics (2.71 μW m^?1 K^?2 at 1,023 K). In addition, the low-doped sample (0.1 mol%) exhibited excellent thermoelectric properties.     

Simultaneous Absorptance and Thermal-Diffusivity Determination of Optical Components with Laser Calorimetry Technique

The laser calorimetry (LCA) technique is used to determine simultaneously the absorptances and thermal diffusivities of optical components. An accurate temperature model, in which both the finite thermal conductivity and the finite sample size are taken into account, is employed to fit the experimental temperature data measured with an LCA apparatus for a precise determination of the absorptance and thermal diffusivity via a multiparameter fitting procedure. The uniqueness issue of the multiparameter fitting is discussed in detail. Experimentally, highly reflective (HR) samples prepared with electron-beam evaporation on different substrates (BK7, fused silica, and Ge) are measured with LCA. For the HR-coated sample on a fused silica substrate, the absorptance is determined to be 15.4?ppm, which is close to the value of 17.6?ppm, determined with a simplified temperature model recommended in the international standard ISO11551. The thermal diffusivity is simultaneously determined via multiparameter fitting to be approximately 6.63?×?10^?7?m² · s^?1 with a corresponding square variance of 4.8?×?10^?4. The fitted thermal diffusivity is in reasonably good agreement with the literature value (7.5?×?10^?7?m² · s ^?1). Good agreement is also obtained for samples with BK7 and Ge substrates.     

Compressed Liquid Densities of 1-Pentanol and 2-Pentanol from 313 to 363 K at Pressures to 25 MPa

Compressed liquid densities of 1-pentanol and 2-pentanol have been measured from 313 to 363 K at pressures to 25 MPa. Measurements have been achieved using a vibrating tube densimeter. Water and nitrogen are the reference fluids to calibrate the densimeter. Measurements uncertainties are estimated to be ±0.03 K for temperatures, ±0.008 MPa for pressures and ±0.20 kg·m⁻³ for densities. Two volume-explicit equations with five and six parameters and the 11-parameter BWRS equation of state are used to correlate the experimental densities of 1-pentanol and 2-pentanol reported in this work. Statistical values for the evaluation of the correlations are reported. Comparisons with literature data are performed for the temperature and pressure ranges of the measurements.     

Constant-Volume Gas Thermometry with Different Helium-3 Gas Densities at NMIJ/AIST

Constant-volume gas thermometer (CVGT) measurements are conducted using ³He of three different densities as the working gas to obtain the thermodynamic temperature T _CVGT and the second virial coefficient of ³He, B, at temperatures down to 3 K, using the triple point of Ne as a reference temperature. Densities of 127 mol ?? m^?3 and 278 mol ?? m^?3 are used in addition to the density of 168 mol ?? m^?3 used in the measurement reported previously, where T _CVGT was obtained using the virial coefficient adopted by the International Temperature Scale of 1990 (ITS-90), B _ITS-90. T _CVGT is obtained by two methods, by the single- and multi-isotherm fitting of B to the three densities and by the method used in the previous work using one of the three densities and B _ITS-90. B obtained from the isotherm fitting agrees with B _ITS-90 within the uncertainty of the data used to derive B _ITS-90. Moreover, B obtained from a multi-isotherm fit agrees with that of recent theoretical ab initio calculations within 0.05?cm³ ?? mol^?1 at 5 K and above, and within 0.3?cm³ ?? mol^?1 down to 3 K. The values of T _CVGT obtained from the multi-isotherm fits assuming different forms for the temperature dependence of B agree with each other within 0.1?mK. T _CVGT obtained from the multi-isotherm fitting agrees with that obtained from the method in the previous report within 0.22?mK. The tendency of the difference between T _CVGT and the ITS-90 temperature reported in the previous work is confirmed in the present work.     

Multiple implantation of29Si+ in semi-insulating GaAs and its characterisation

Formation of a uniformn-layer by multiple²⁹Si⁺ implantation on LEC grown semi-insulating GaAs 〈100〉 substrate and its characterisation by differential Hall measurement at room temperature is reported. The implantation energies are 60, 160 and 260 keV with corresponding doses of 1 × 10¹², 2·55 × 10¹² and 3 × 10¹² cm⁻². Asimplanted, uncapped substrates were furnace-annealed with face-to-face configuration in an N₂ ambient at 850°C with arsenic overpressure. After annealing, the samples were subjected to Hall measurements using Van der Pauw configuration. Experimental and theoretical (LSS) profiles are compared. Electrical activation of the dopant atoms was found to range from 65–90% with average mobility values lying between 2000–2300 cm² V⁻¹ s⁻¹. Uniform concentration of then-layer ∼ 10¹⁷ cm⁻³ up to a depth of 0·3 μm has been achieved. These layers are used for the fabrication of power MESFETs.     

Structural relaxation and electrical conductivity of molybdovanadate glass

⁵⁷Fe Mössbauer spectrum of conductive barium iron vanadate glass with a composition of 20BaO·10Fe₂O₃·70V₂O₅ (in mol%) showed paramagnetic doublet peak due to distorted Fe^IIIO₄ tetrahedra with isomer shift (δ) value of 0.37 (±?0.01) mm s^?1. Mössbauer spectra of 20BaO·10Fe₂O₃·xMoO₃·(70???x)V₂O₅ glasses (x?=?20–50) showed paramagnetic doublet peaks due to distorted Fe^IIIO₆ octahedra with δ’s of 0.40–0.41 (±?0.01) mm s^?1. These results evidently show a composition-dependent change of the 3D-skeleton structure from “vanadate glass” phase, composed of distorted VO₄ tetrahedra and VO₅ pyramids, to “molybdate glass” composed of distorted MoO₆ octahedra. After isothermal annealing at 500 °C for 60 min, Mössbauer spectra also showed a marked decrease in the quadrupole splitting (Δ) of Fe^III from 0.70 to 0.77 to 0.58–0.62 (±?0.02) mm s^?1, which proved “structural relaxation” of distorted VO₄ tetrahedra which were randomly connected to FeO₄, VO₅, MoO₆, FeO₆ and MoO₄ units by sharing corner oxygen atoms or edges. DC-conductivity (σ) of barium iron vanadate glass (x?=?0) measured at room temperature was 3.2?×?10^?6 S cm^?1, which increased to 3.4?×?10^?1 S cm^?1 after the annealing at 500 °C for 60 min. The σ’s of as-cast molybdovanadate glasses with x’s of 20–50 were ca. 1.1?×?10^?7 or 1.2?×?10^?7S cm^?1, which increased to 2.1?×?10^?2 (x?=?20), 6.7?×?10^?3 (x?=?35) and 1.9?×?10^?4 S cm^?1 (x?=?50) after the annealing at 500 °C for 60 min. It was concluded that the structural relaxation of distorted VO₄ tetrahedra was directly related to the marked increase in the σ, as generally observed in several vanadate glasses.     

An excimer emitter with pumping by barrier discharge in mixtures of zink diiodide vapors with inert gases

An experimental investigation is performed of the output characteristics of an excimer lamp utilizing mixtures of zinc diiodide vapors with inert gases and excited by a barrier discharge (BD) with the repetition rate of sine voltage pulses f ≤ 130 kHz. Radiation spectra of BD plasma in the range of 200–900 nm with resolution of 0.05 nm are studied, as well as the time characteristics of voltage and current and the dependence of radiation intensity on the composition of mixtures. The radiation of ZnI(B–X) excimer molecules is revealed with a maximum at λ = 602 nm, as well as of I ₂ ^* excimer molecules, lines of inert gases, and, in mixtures with xenon, of XeI* excimer molecules. The composition and pressure of gas components of mixture are optimized. It is found that the most intense radiation of ZnI* in binary mixtures is observed when helium or neon is used as buffer gas. The specific average radiation power in the visible range is 23 mW/cm².     

Hydrodynamic behavior of binary mixture of solids in a triple-bed combined circulating fluidized bed with high mass flux

Flow behaviors of binary mixture of silica sand and nylonshot (coal char substitute) were investigated in a triple-bed circulating fluidized bed (TBCFB) as a cold model of coal gasifier. The TBCFB consisted of a downer (ϕ 0.1 m × 6.5 m), a bubbling fluidized bed (0.75 m × 0.27 m × 1.9 m), a riser (ϕ 0.1 m × 16.6 m) and a gas-sealing bed (GSB, ϕ 0.158 m × 5 m). The initial fraction of the nylonshot in the solid mixture (X_nylon,i) was 15.4 and 30% on mass and volume bases, respectively, or otherwise, 30.7 and 50%. The maximum solids mass flux (G_s) at X_nylon,i of 15.4 and 30.7 wt% were 394 and 349 kg/m² s, respectively, when the gas velocity in the riser (U_gr) was 10 m/s. Apparent solids holdups of silica sand and nylonshot were calculated separately from the static pressure gradient across the riser and the downer. The results showed possibility of large-mass-flux circulation of char in the gasifier, which plays a significant role in decomposition of tar from pyrolysis as the primary step of gasification. A newly developed pressure balance model successfully predicted G_s of the binary mixtures in TBCFB.     

High strain rate superplasticity of ultrafined Ti–10V–2Fe–3Al compact prepared by sintering and isothermal forging

Abstract

High strain rate superplasticity was obtained for powder Ti–10V–2Fe–3Al (Ti-1023) alloy prepared by powder sintering and isothermal forging technology. The selected powder was cold isostatic pressed, sintered and isothermal forged to prepare this powder alloy. Tensile testing was conducted at optimum superplastic temperaure of 1023 K with different initial strain rate, and the elongation to failure, the flow stress and the microstructure were analysed. The experiment results exhibited that the microstructure of this powder alloy is extraordinary uniform and fine, resulted in considerable enhancement of optimum initial strain rate increased from 3·3×10^?4 s^?1 of conventional cast and wrought Ti-1023 alloy to 3·3×10^?3 s^?1 of this powder alloy. The elongation to failure increased first and then decreased with initial strain rate from 3·3×10^?4 to 3·3×10^?2 s^?1. The strain rate sensitivity m is about 0·46 near initial strain rate of 3·3×10^?3 s^?1, larger than conventional cast and wrought Ti-1023 alloy. Microstructure observations showed that dynamic recrystallisation and grain growth were present during superplastic deforming.     

Design of a Calibration System for Heat Flux Meters

Accurate heat flux measurements are needed to gain a better knowledge of the thermal performance of buildings and to evaluate the heat exchange among various parts of a building envelope. Heat flux meters (HFMs) are commonly used both in laboratory applications and in situ for measuring one-dimensional heat fluxes and, thus, estimating the thermal transmittance of material samples and existing buildings components. Building applications often requires heat flux measurements below 100 W · m^?2. However, a standard reference system generating such a low heat flux is available only in a few national metrology institutes (NMIs). In this work, a numerical study aimed at designing an HFM calibration apparatus operating in the heat flux range from 5 W·m^?2 to 100 W · m^?2 is presented. Predictions about the metrological performance of such a calibration system were estimated by numerical modeling exploiting a commercial FEM code (COMSOL^®). On the basis of the modeling results, an engineered design of such an apparatus was developed and discussed in detail. The system was designed for two different purposes: (i) for measuring the thermal conductivity of insulators and (ii) for calibrating an HFM with an absolute method (i.e., by measuring the applied power from the heater and its active cross section) or by a relative method (i.e., by measuring the temperature drop across a reference material of known thickness and thermal conductivity). The numerical investigations show that in order to minimize the uncertainty of the generated heat flux, a fine temperature control on the thermal guard is needed. The predicted standard uncertainty is within 2% at 10W·m^?2 and within 0.5% at 100 W · m^?2.     

Viscosity-Entropy Ratio of the Unitary Fermi Gas from Zero-Temperature Elementary Excitations

We investigate the low-temperature behavior of the ratio between the shear viscosity ?? and the entropy density s in the unitary Fermi gas by using a model based on the zero-temperature spectra of both bosonic collective modes and fermonic single-particle excitations. Our theoretical curve of ??/s as a function of the temperature T is in qualitative agreement with the experimental data of trapped ultracold ⁶Li atomic gases. We find the minimum value ??/s?0.44 (in units of ?/k _B ) at the temperature T/T _F ?0.27, with T _F the Fermi temperature.