Investigation of thermal conductivity and thermal diffusivity of liquid bismuth within the temperature range of 545–970 K

Thermal conductivity and thermal diffusivity of liquid bismuth within the temperature range from 545 K up to 970 K are investigated by the laser flash method. The measurement errors are equal to (3.5–4.5)%. Approximating equations are obtained, and the reference tables are presented for the temperature dependencies of the properties. The measurement results are compared to the published data available. The temperature dependence of the Lorentz number is calculated up to 970 K.     

Oxidation of ion-implanted niobium in the 300–700°C temperature range

Ion implantation of different species was shown to have a beneficial influence on the thermal oxidation kinetics of niobium in pure oxygen at temperatures below 500°C. The implants were chosen with regard to their affinity for oxygen compared to that of niobium and their solubility in niobium. The effects of the treatment was to delay the appearence of the linear catastrophic kinetics. The mechanisms involved are discussed.     

Determination of the thermal conductivity of polypyrrole over the temperature range 280–335 K

Samples of polypyrrole were synthesised under galvanostatic conditions to produce films possessing a range of electrical conductivity from 10^–3 to 10 S cm^–1. The electrical and thermal conductivity of these films has been determined between 280 and 335 K. The electrical conductivity was measured using a four probe technique calibrated against ASTM D4496-87. Thermal conductivity was determined from measurements of thermal diffusivity, specific heat and density. Thermal diffusivity was determined using a modified a.c. calorimetry technique, while differential scanning calorimetry (DSC) was used to determine specific heat. The polymer's density was measured using Archimedes' principle. The results were used to calculate the Lorenz number of polypyrrole. A comparison of the predicted behaviour and experimental results was made. Thermal conductivity is found to be large compared to that predicted from the electrical conductivity measurements on low conductivity films. Molecular vibration effects are found to be non-trivial and experimental means for measuring their contribution are mentioned. While polypyrrole has been regarded as a synthetic metal the thermal conductivity results show this classification is wrong.     

Experimental studies of the heat capacity of liquid octene-1 in the temperature range 282–368 K

Results are presented on the heat capacity c_p of octene-1 in the temperature range 282–368 K. The present experimental data are compared with results in the literature.Academic Scientific Complex A. V. Luikov Heat and Mass Transfer Institute, Academy of Sciences of Belarus, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 4, pp. 490–491, April, 1994.     

Thermal conductivity and electrical resistivity of pure polycrystalline cobalt in the temperature range 2.5–30 K

Thermal conductivity and electrical resistivity of 99.99% pure Co sample were measured in the temperature range 2.5–30 K. The annealing, procedure of the sample (either above or below Curie temperature), followed by cooling it down to room temperature at a slow cooling rate, caused an unexpected increase in its thermal resistivity and residual electrical resistivity, contrary to the results obtained for most pure metals. Co samples either not thermally treated or annealed consist only of a HI phase as proved by X-ray and electron diffraction analyses. The result, led to the conclusion that changes of grain structure and physical defects appearing in the Co at Curie temperature and at 690 K, when phase transitions take place, should be taken into account. The electron-magnon scattering, is significant in electrical conductivity but the electron-physical defect and impurity scattering plays a dominant role in thermal conductivity. The electron-physical defect and impurity scattering is elastic (validity of the Wiedemann Franz law)) as demonstrated by the value of _{th el} = 1.0, obtained in this work.     

Thermal diffusivity of gadolinium in the temperature range of 287–1277 K

New experimental data on the thermal diffusivity of gadolinium in the temperature interval from 287 to 1277 K obtained by the laser flash method with an error of 3–4% are presented. Results are compared with the available literature data. Reference tables on the heat transfer coefficients of gadolinium for scientific and practical use are developed. Critical indices for the thermal diffusivity of gadolinium above the Curie point are determined. The limitations of the laser flash method during measurement in the region of phase transformations are briefly discussed.     

Measurement of liquid tin heat transfer coefficients within the temperature range of 506–1170 K

The thermal conductivity and thermal diffusivity coefficients of liquid tin within the temperature range of 506–1170 K were measured by the laser flash technique. The measurement errors for the heat transfer coefficients were equal to ±(2.5–3.5)%. Approximation equations and the reference data tables were obtained for the temperature dependency of the properties. The measurement results were compared with the available literature data. The Lorentz number temperature dependence was calculated up to 1000 K.     

The influence of neutron irradiation on the thermal conductivity of aluminum in the range 5–50 K

Measurements of thermal conductivity of 6N to 3N pure aluminum in the temperature range 5–50 K subjected to fast neutron irradiation, with exposures of 10¹³ and 10¹⁶ n · cm^–2, are reported. The thermal conductivity maximum was found to shift towards higher temperatures with an increase in the fast neutron irradiation exposure. At high temperatures, a departure from Wilson's theory was observed, which may be attributed to the existence of additional electron scattering mechanisms. An increase in both ideal and residual thermal resistivity components with an increase in the radiation exposure was noted.Nomenclature I ₅ (/t) Debye integral of the fifth order - –m slope of the straight line that crosses maximum thermal conductivity values - n exponent in ideal thermal resistivity component - T _m temperature corresponding to maximum thermal conductivity - W _e total electronic thermal resistivity - W _i ideal thermal resistivity - W ₀ residual thermal resistivity - ideal thermal resistivity coefficient in Eq. (4) - ideal thermal resistivity coefficient in Eq. (1) - constant related to the ideal part of thermal resistivity in Eq. (2) - () ideal thermal resistivity coefficient depending on irradiation exposure - () residual thermal resistivity coefficient depending on irradiation exposure - thermal conductivity - _m maximum thermal conductivity - Debye characteristic temperature - irradiation exposure     

Stress-strain behaviour of nitrogen bearing austenitic stainless steels in the temperature range 298–473 K

The stress-strain behaviour of three nitrogen-bearing low-nickel austenitic stainless steels has been investigated via a series of tensile tests in the temperature range 298–473 K at an initial strain rate of 1.6×10^–5s^–1. Experimental stress-strain data were analysed employing Rosenbrock's minimization technique in terms of constitutive equations proposed by Hollomon, Ludwik, Voce and Ludwigson. Ludwigson's equation has been found to describe the flow behaviour accurately, followed by Voce's equation. The resultant strain-hardening parameters were analysed in terms of variations in temperature. A linear relationship between ultimate tensile stress and the Ludwigson parameters has been established. The influence of nitrogen on the Ludwigson modelling parameters has also been explained.Nomenclature True stress - _t True strain - _f True fracture strain - Strain rate - T Temperature - K _H, n _H Hollomon parameters - K _L, n _L Ludwik parameters - K _1L, k _2L, n _1L, n _2L Ludwigson parameters - _s, K _V, n _V Voce parameters - _{u relation} Uniform strain computed from a particular relation - _L Transient strain - ₀ Flow stress at zero plastic strain (Ludwik) - _L Transient stress - _y Yield stress - _u Ultimate tensile stress     

Generalization of experimental specific heat data for synthetic corundum in the temperature range 80–300°k

The results of an experimental investigation of the specific heat of corundum on state standard GÉT 70–75 are given. The possibility of generalizing the most accurate data to expanded batches of corundum is discussed.Notation c specific heat - T absolute temperature - c_calc calculated values of specific heat - c_exp experimental values - c=[(c_exp–C_calc)/c_exp]·100% relative deviations of experimental values of specific heat - f theoretical normal curve of relative errors Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 4, pp. 664–670, October, 1980.     

Synthesis of Pr2CuO4 and its heat capacity in the range 364–1064 K

The heat capacity of Pr₂CuO₄ has been determined by differential scanning calorimetry in the temperature range 364–1064 K. The experimental C _p (T) data have been used to evaluate the thermodynamic functions of praseodymium cuprate: enthalpy increment H ⁰(T)–H ⁰(364 K) and entropy change S ⁰(T)–S ⁰(364 K).     

Thermal conductivity of five normal alkanes in the temperature range 283–373 k at pressures up to 250 MPa

Experimental data on the thermal conductivity of five liquid n-alkanes-hexane, heptane, octane, decane, and dodecane-are presented in the temperature range from 283 to 373 K at pressures up to 250 MPa or the freezing pressures. The measurements were performed on an absolute basis by an automated transient hot-wire apparatus. The uncertainty of the reported data is estimated to be within ±1%. The thermal conductivity of each alkane decreases almost linearly with rising temperature at a constant pressure and increases with increasing pressure at a constant temperature. Both the temperature coefficient of the thermal conductivity ¦(/T) _p¦ and the pressure coefficient (/P) _T decrease with increasing carbon number of alkanes. The experimental results were correlated with temperature and pressure by a similar expression to the Tait equation. It is also found that both the dense hard-sphere model presented by Menashe et al. and the modified significant structure theory proposed by Prabhuram and Saksena provide good representations of the present experimental results.     

Influence of strain rate on the temperature rise of specimens in static tests of a titanium alloy in the 293–4.2 K range

The influence of two strain rates, 1.10^–1 and 2.10^–2 sec^–1, on the temperature rise of specimens of -titanium alloys in static tests in the 290- 4.2 K range is investigated. It is established that at room temperature conditions (290 K) the temperature rise of the specimens is nonuniform over the length and is 14 K, in liquid nitrogen (77 K) it is more than 0.5 K, and in liquid helium (4.2 K) the temperature depends upon the strain rate and reaches 46 K. It is shown that the temperature rise of the specimens in liquid helium in strain at a rate of 2.10^–2 sec^–1 reduces the tensile strength but does not influence the yield strength of the material.Translated from Problemy Prochnosti, No. 12, pp. 70–78, December, 1992.     

Heat capacity of rare-earth stannates in the range 350–1000 K

R₂Sn₂O₇ (R = Pr–Lu) rare-earth stannates with the pyrochlore structure have been synthesized by solid-state reactions, by firing stoichiometric mixtures of SnO₂ and R₂O₃ in air at 1473 K. The high-temperature heat capacity of the rare-earth stannates has been determined by differential scanning calorimetry in the temperature range 350 to 1000 K, and the Raman spectra of polycrystalline Tb₂Sn₂O₇ and Dy₂Sn₂O₇ samples have been measured.     

Investigation of ignition of hydrogen–oxygen mixtures within the range of temperatures from 700 to 2500 K

The results of numerical modeling of the ignition process of hydrogen–oxygen mixtures diluted with argon at temperatures of 700–2500 K within wide ranges of the initial gas parameters are presented. The time evolutions of the concentration of the electron-excited radical OH* and other components, as well as the strength of the radical total radiation on wavelengths about λ = 306.4 nm, are calculated. Their peculiarities are described and the correspondence between the measured radiation strength scans obtained in the experiments by the emission method and those calculated in the process of modeling is determined. The temperatures upon which the mixtures ignite are determined. The dependences of the time delay of the ignition of the mixture on the pressure and component composition are found. The relationships are used to obtain the temperature dependence of the ignition time delay reduced to a preliminarily chosen pressure and gas composition.