Elevated-temperature strengthening in carbide (Al4C3)-dispersed aluminium

The effect of strain rate on the compressive flow behaviour of DISPAL 2 is investigated in the temperature range 473–823 K. The stress exponent, n, was 28 in the temperature range 473–623 K, while it increased to 59 above 673 K. The activation volume and energy for deformation were 70 b ³ and 100–200 kJ mol^–1, respectively, in the temperature range 473–623 K. In the higher range, 673–823 K, the observed activation volume of 300–500 b ³ and the activation energy of ~ 1086 kJ mol^–1 cannot be reconciled with any of the deformation mechanisms. A new model-based creep equation for dispersion-strengthened materials proposed by Rosler and Arzt has been applied to the flow data from 673–823 K. Its predictions are in agreement with the experimental data in the temperature range 673–723 K. The predictions of the model, however, differ from the experimental data at 773 and 823 K.     

Pressure-pulsed chemical vapour infiltration of pyrolytic carbon into porous carbon or two-dimensional-carbon/SiC particulate preforms from C6H6–H2–N2

Pyrolytic carbon was infiltrated into porous carbon or two-dimensionally woven carbon fibre (2D-C)/SiC particulate preforms using pressure-pulsed chemical vapour infiltration from C6H6 (3–16%)–H2–N2 at 1273–1373 K. Residual porosity of porous carbon decreased from 29 to 10% after 1×104 pulses at 1323 K, and that of 2D-C/SiC particulate preform decreased from 30 to 7.5% after 4×104 pulses at 1273 K. Flexural strength of 2D-C/SiC preform reached about 150 MPa.     

Calorimetric Study of Rubidium Hexafluoroarsenate at Elevated Temperatures

The heat capacity of rubidium hexafluoroarsenate, RbAsF₆, was measured from 300 to 700 K by differential scanning calorimetry. The results indicate that the structural transformation from the rhombohedral to the cubic phase occurs in the range 305–436 K through an intermediate stable phase and reaches isothermal completion in a narrow temperature range of 407–409 K. The enthalpy of the transformation is 10.90 ± 0.03 kJ/mol, and its entropy is 26.39 ± 0.08 J/(K mol) = Rln24, which suggests that this structural transition is of the order–disorder type. The heat capacity data are used to evaluate the thermodynamic properties of RbAsF₆ in the range 300–700 K.     

Calculation of the density of solutions (sunflower oil +n-hexane) over a wide range of temperatures and pressure

We present the results from an experimental investigation of the density of the sunflower oil system as a function of the mass concentration of n-hexane in the ranges of temperatures T=290–520 K and pressures P=0.101–98.1 MPa. A method of hydrostatic weighing was used to measure the density of the solutions under study.K. Dzhuraev Dushanbe State Pedagogical University, Tadzhikistan. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 5, pp. 789–792, September–October, 1995.     

Removal of phosphorus by the solidification refining with Si–Al melts

To discuss the possibility of phosphorus removal from silicon by the solidification refining with Si–Al melts, the distribution of phosphorus between solid silicon and the liquid Si–Al alloy at 1173–1373 K was investigated. In the present study, the distribution of phosphorus was examined by the temperature gradient zone melting method, where a phosphorus containing molten Si–Al zone was passed through a single crystalline silicon phase. The segregation ratio of phosphorus at its infinite dilution was obtained as 0.12 (1373 K), 0.085 (1273 K) and 0.061 (1173 K), respectively, and the solidification refining with the Si–Al melts was found to be effective for the removal of phosphorus at lower temperature.     

The Density of Liquid Sodium–Potassium Eutectic

The experimental investigations of the density of molten sodium–potassium alloys of eutectic composition, described in the literature, are briefly reviewed. This review is used to estimate the confidence error of the measurement results. The least squares method is used to simultaneously process the entire body of the experimental data on the density of the liquid Na–K eutectic. An approximating equation is derived for the temperature range from the melting point of the sodium–potassium eutectic to 1300 K. The mean-square error of the calculated values of the density of Na–K eutectic melt in the given temperature range is determined.     

The Activity of the Components of a Na–K–Cs System at High Temperatures

The activity coefficients of the components of a Na–K–Cs ternary system in a temperature range of 773–1200 K are determined using the previously calculated thermodynamic properties, in particular, the activity of the components of binary alloys of alkali metals such as Na–K, Na-Cs, and K–Cs, at high temperatures [1–3]. The sides of the triangle of the phase diagram of this system are constituted by the binary Na–K, Na–Cs, and K–Cs binary alloys. The results obtained are used to calculate the saturated vapor pressure of the sodium–potassium-cesium eutectic (22.1 wt % K and 73.8 wt % Cs [4, 5]) in the same temperature range. The calculated data are in good agreement with the recommended reference data [6].     

Thermal expansion of irradiated polypropylene from 10–340 K

The coefficient of thermal expansion of gamma-irradiated polypropylene (PP) has been measured from 10–340 K by using the three-terminal capacitance technique. The samples were irradiated to 500 Mrad in air at room temperature with gamma rays from a⁶⁰Co source at a dose rate of 0.26 Mrad h^–1. The crystallinity of the sample was measured by X-ray diffraction technique. The crystallinity was found to decrease with radiation dose from 55% at 0 Mrad to 44.7% at 500 Mrad. The thermal expansion coefficient was found to be almost constant with radiation dose from 10–125 K and decreases with radiation dose from 125–340 K.     

Thermophysical properties of scandium-titanium alloys

We present the results of measurements of the specific heat capacity of scandium-titanium alloys in the 4.2–12°K range and their electrical resistivity in the 4.2–300°K range.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 4, pp. 587–592, April, 1980.     

Viscosity of diallyl ether within the temperature range 291.7–626.6 K and within the pressure range 0.101–58.86 MPa

Results of an experimental investigation of the dynamic viscosity of liquid diallyl ether within the temperature range 291.7–525.6 K and pressure range 0.101–58.86 MPa are presented along with equations describing the relationship between the dynamic viscosity and the density of the substance at various temperatures and pressures.K. Dzhuraev State Pedagogical University, Dushanbe, Tadjikistan. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 4, pp. 619–621, July–August 1995.     

Density of isoamyl and heptyl alcohols at various temperatures and pressures

The hydrostatic weighing method is used to determine the density of isoamyl alcohol at T=273.15-587.37°K and the density of heptyl alcohol at T=273.15–575.07°K at pressures of 10.86–491.4 bar. An equation of state is presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 2, pp. 313–318, February, 1981.     

Speeds of Sound and Isentropic Compressibilities of Binary Mixtures Containing Cyclic Ethers and Haloalkanes at 298.15 and 313.15 K

Speeds of sound of binary mixtures formed by either 1,3-dioxolane or 1,4-dioxane and isomeric chlorobutanes at 298.15 and 313.15 K are reported in this paper. Isentropic compressibilities and isentropic compressibility deviations have been calculated from experimental measurements. Isentropic compressibility deviations have been fitted to a Redlich–Kister equation, and the results have been discussed in terms of molecular interactions and structural effects. Isentropic compressibilities have been estimated at 298.15 K using the Prigogine–Flory–Patterson theory.     

Absolute thermal expansion measurements of single-crystal silicon in the range 300–1300 K with an interferometric dilatometer

The thermal expansion coefficient of single-crystal silicon has been measured in the range 300–1300 K using an interferometric dilatometer. The measurement system consists of a double-path optical heterodyne interferometer and a radiant image furnace with a quartz vacuum tube, which provides both accuracy and rapidity of measurement. The uncertainties in length and temperature determination are within 4 nm and 0.4 K, respectively. A high-purity dislocation-free FZ silicon single crystal was used in the study. Thermal expansion coefficients of silicon oriented in the [111] direction have been determined over the temperature range from 300 to 1300 K. The standard deviation of the measurement data from the best fitting for the fifth-order polynomial in temperature is 2.1×10^–8 K^–1. The present value for the thermal expansion coefficient agrees within 9×10^–8K^–1 with the interferometric measurement of polycrystalline pure silicon by Roberts (1981) between 300 and 800 K and within 1.2 × 10^–7 K^–1 with the single-crystal X-ray diffractometric measurement by Okada and Tokumaru (1984) between 300 and 1300 K.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Viscosity and thermal conductivity of alkali metal vapors at temperatures up to 2000 K

New experimental data were obtained on transport coefficients of alkali metals in gaseous phase at high temperatures and within the pressure range from about 10 to about 100 kPa: lithium—thermal conductivity, T= 1400–1800 K, and viscosity, T=1600–2000 K; sodium-viscosity, T= 1100–1500 K; and cesiumviscosity, T=900–1250 K. Viscosity of the alkali metal vapors has been measured using a stationary-technique viscometer with an annular gap. Thermal conductivity was measured by the method of the nonstationary monotonous heating. Experimental data were used as a basis for computing effective atomatom and atom-molecule collision cross section, the values obtained from data on viscosity being in good agreement with those derived from thermal conductivity data. In the case of lithium, the atom-atom cross sections yielded by experiments are fairly consistent with the results of calculations with exact formulae of kinetic theory on the basis of quantum-mechanical potential curves for atom-atom interactions. This has enabled the authors to compile consistent tables of viscosities and thermal conductivities for lithium in a gaseous phase within the temperature range from 800 to 2500 K and pressures from 0.5 to 800 kPa, including the saturation curve.     

High-temperature thermal conductivity of neon at temperatures up to 5000°K and argon up to 6000°K

We fit the experimental data on the thermal conductivity of neon at temperatures of T=600–5000°K and of argon for T=500–6000°K.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 3, pp. 473–481, March, 1981.     

Olefin-vapor conductivities below 0.1 MPa at 220–680 K

A curve has been fitted to measurements on the thermal conductivities of olefin vapors at 220–680 K, which is based on the corresponding-state theory. Measurements have been made on the thermal conductivity of non-1-ene at 303–372 K.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 3, pp. 480–485, September, 1989.     

High-Resolution Thermal Expansion of MgB2

The thermal expansion of polycrystalline MgB₂ from 5–300 K is studied using high-resolution capacitance dilatometry. The thermal expansivity exhibits a small jump of –5.8×10^–8 K^–1 at T _c (in accord with expectations from the Ehrenfest relationship and published specific heat and pressure data) and a negative peak-like feature close to 5 K. No indications of any structural instabilities are observed.     

Mass-Spectrometric Study of the Temperature Variation in the Dimer-to-Monomer Ratio in the Free-Surface Vaporization Fluxes from Alkali Halide Single Crystals

A mass-spectrometric method is used to investigate the kinetics of the vaporization of LiF (970–1070 K), NaCl (722–889 K), KCl (780–900 K), KBr (724–918 K), and CsI (656–838 K) single crystals. A dimer-to-monomer ratio, J_D/J_M, in the fluxes vaporizing from free surfaces of these crystals are calculated, using the currents of M⁺, MX⁺, and M₂X⁺ ions formed via electron impact ionization of the molecules MX and M₂X₂ (M is the alkali atom; X is the halogen). It is found that the dimer-to-monomer ratio increases with temperature at a continually increasing rate in the LiF and NaCl cases. In the KCl, KBr, and CsI cases, this rate passes through a maximum. Such a specific temperature variation in J_D/J_M is discussed through the analysis of proposed mechanisms of dimer formation in light of the terrace–ledge–kink and surface charge models.     

The dielectric relaxation time of collagen over a wide temperature range

The dielectric properties of collagen were measured at two hydration levels over a frequency range of 10¹–10⁵ Hz and at temperatures from 298–470 K. In the low-frequency range, dielectric dispersion was observed which results from Maxwell-Wagner-Sillars polarization. The relaxation times for a collagen sample containing loosely bound water were shorter than for a collagen sample containing only structural water in the temperature range 298–390 K. Above 390 K, continuous decrease in the relaxation times was observed for both samples.     

Effect of nitrogen on the dynamic strain ageing behaviour of type 316L stainless steel

The dynamic strain ageing (DSA) behaviours of type 316L stainless steels containing different nitrogen contents (0.01–0.15 wt% N) were studied in tension under varying strain rates (1 × 10^–2–2 × 10^–4s^–1) and the test temperatures (R.T.–1023 K). The temperature range for DSA was moved to higher temperature for increasing nitrogen contents. The critical strain, _c for the onset of serration increased with nitrogen content at 773 K and then became almost constant at 873 K. Type A and B serrations were observed at 873 K with the value of the strain required to effect the transition from type A to type B serration increasing for nitrogen contents upto 0.1 wt% and then becoming saturated. The activation energy for DSA was 23.4–26.2 kcal mol^–1 (97.8–109.5 kJ mol^–1) at the onset and 65.0–76.6 kcal mol^–1 (271–320.2 kJ mol^–1) at the end of serration. The lower activation energy was related to vacancy diffusion and the higher activation energy was attributed to the diffusion of chromium to dislocations. The activation energy for DSA was slightly increased with nitrogen addition. DSA was retarded by an increase in the nitrogen content since nitrogen reduced the chromium diffusion to dislocations due to a strong interaction between the nitrogen and chromium.