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.     

Investigation of the heat conductivity of niobium in the temperature range 0.05–23 K

We report thermal conductivity measurements on a single-crystal niobium specimen of resistivity ratio 33,000 over the temperature range 0.05–23 K in the superconducting state and above 9.1 K in the normal state. The axis of the niobium rod was [110] oriented. The surface roughness was varied by sandblasting of the sample. The values of the thermal conductivity in the range from the lowest temperatures up to the maximal value covered a range of six orders of magnitude (=2×10^–5 W cm^–1 K^–1 at 50 mK to =22 W cm^–1 K^–1 at 9 K). Above 2 K the results for the untreated and the sandblasted sample are in accord, whereas below 2 K the influence of the sample surface is discernible. The various conduction and scattering mechanisms are discussed.     

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.     

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.     

Differences in the relation between resistance and temperature of several grades of platinum in the range of 10.8 to 273.16°K

Conclusions The resistivity characteristic of platinum thermometers of different origins (1.39178W_100°C 1.39251) was studied in the range of 10.8–273.16°K and it was established that Nernst's reduction formula holds in the range of 273-50°K with an error of 0.01° and does not hold at temperatures lower than 50°.The applicability of Matthiessen's rulemade it possible to suggest a simple method for calibrating and computing temperature, which extends the range of platinum thermometers [1, 2] down to the nitrogen boiling point with an error not larger than the one guaranteed by the ITS calibration method.The inapplicability of Matthiessen's rule at temperatures below 50°K makes it necessary to adopt a critical approach to various reduction methods [3–8].     

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     

Engineering the magnetic structure of Fe clusters by Mn alloying

We propose to tailor the magnetic structure of atomic clusters by suitable doping, which produces the nanometric equivalent to alloying. As a proof of principle, we perform a theoretical analysis of Fe(6-x)Mn(x) clusters (x = 0-5), which shows a modulation of the magnetic moment of the clusters as a function of Mn doping and, more importantly, a collinear to noncollinear transition at x = 4.     

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.     

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.     

Determination of the Thermal Diffusivity of Electrically Non-Conductive Solids in the Temperature Range from 80 K to 300 K by Laser-Flash Measurement

The adoption of the popular laser-flash method at temperatures far below 300 K is restricted by the weak signal-to-noise ratio and the limited spectral bandwidth of the commonly used mercury cadmium tellurite (MCT) infrared (IR) detector used as a non-contacting temperature probe. In this work, a different approach to measure the temperature rise in pulse heating experiments is described and evaluated. This method utilizes the change of the temperature-dependent electrical resistance of a thin strip of sputtered gold for the detection of a temperature rise as it was proposed by Kogure et al. The main advantage of this method at lower temperatures is the significantly higher signal-to-noise ratio compared to the commonly used IR detectors. A newly developed laser-flash apparatus using this detection method for the determination of the thermal diffusivity in the temperature range from 80 K to 300 K is presented. To test the accuracy of the new detection method, the thermal diffusivity of a borosilicate crown glass (BK7) specimen at 300 K was determined and compared to results derived with a MCT detector. Good agreement of the derived thermal diffusivity values within 3 % was found. The thermal diffusivity of BK7 and polycrystalline aluminum nitride (AlN) was measured at temperatures between 80 K and 300 K by a laser-flash method to test the functionality of the apparatus. Finally, the thermal conductivity was calculated using values for the specific heat capacity determined by temperature modulated differential scanning calorimetry (MDSC). Comparisons with literature data confirm the reliability of the experimental setup.     

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.     

Thermal expansion of tungsten in the range 1500–3600 K by a transient interferometric technique

The linear thermal expansion of tungsten has been measured in the temperature range 1500–3600 K by means of a transient (subsecond) interferometric technique. The tungsten selected for these measurements was the standard reference material SRM 737 (a standard for thermal expansion measurements at temperatures up to 1800 K). The basic method involved rapidly heating the specimen from room temperature up to and through the temperature range of interest in less than 1 s by passing an electrical current pulse through it and simultaneously measuring the specimen temperature by means of a high-speed photoelectric pyrometer and the shift in the fringe pattern produced by a Michelson-type interferometer. The linear thermal expansion was determined from the cumulative shift corresponding to each measured temperature. The results for tungsten may be expressed by the relation $$\begin{gathered} (l - l_0 )/l_0 = 1.3896 \times 10^{ - 3} - 8.2797 \times 10^{ - 7} T + 4.0557 \times 10^{ - 9} T^2 \hfill \\ - 1.2164 \times 10^{ - 12} T^3 + 1.7034 \times 10^{ - 16} T^4 \hfill \\ \end{gathered} $$ whereT is in K andl ₀ is the specimen length at 20°C. The maximum error in the reported values of thermal expansion is estimated to be about 1% at 2000 K and approximately 2% at 3600 K.     

Thermal expansion of molybdenum in the range 1500–2800 K by a transient interferometric technique

The linear thermal expansion of molybdenum has been measured in the temperature range 1500–2800 K by means of a transient (subsecond) interferometric technique. The molybdenum selected for these measurements was the Standard Reference Material SRM 781 (a high-temperature enthalpy and heat capacity standard). The results are expressed by the relation where T is in K and l ₀ is the specimen length at 20°C. The maximum error in the reported values of thermal expansion is estimated to be about 1% at 2000 K and not more than 2% at 2800 K.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

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.     

Impact toughness of ternary Al-Zn-Mg alloys in as cast and homogenized condition measured in the temperature range 263–673 K

Impact toughness of six Al-Zn-Mg ternary alloys are compared with two Al-Zn binary alloys and one CP aluminium metal at eight different temperatures of 263, 268, 273, 300, 373, 473, 573 and 673 K. The effects of alloying and temperature on toughness have been compared and analysed. The influence of alloying is more pronounced than that of temperature in reducing the toughness.     

The temperature dependence of the resistivity of ohmic contacts based on gallium arsenide and indium phosphide in the 4.2–300 K range

Technical Physics Letters - Resistivity ρc of InP- and GaAs-based ohmic contacts has been measured in a temperature range of 4.2–300 K. Both temperature dependences are nonmonotonic and...