Thermal conductivity of neutron-irradiated MgO

The thermal conductivity of pure and neutron-irradiated MgO has been measured in the temperature range 0.4–80 K and for neutron doses up to 2×10 ¹⁹ n·cm^–2 . Resonance dips in the thermal conductivity vs. temperature curves are observed at 1 and 20 K. It is suggested that the high-temperature dip, which becomes more pronounced with increasing radiation dose, may be a quasilocalized mode resulting from the production ofF-type centers. The low-temperature dip, which fades with increasing neutron dose, may result from the presence of small aggregate centers which give rise to another set of quasilocalized modes. The experimental data for the pure and irradiated crystals are in agreement with calculated curves based on the Debye model of solids. A combined relaxation time for the calculated curves of the irradiated specimens includes a term for the defect scattering rate consisting of two resonance expressions of the Lorentzian form.Supported by the U. S. Atomic Energy Commission.     

Thermal stability of MgO nanoparticles

Thermal stability of nanocrystalline MgO particles with average diameter of 11 nm was investigated by annealing of the cold isostatically pressed compacts between 600 °C and 900 °C for various durations. Sintering time versus grain radius at 800 °C demonstrated a linear line with the slope of ∼ 4 similar to that expected for surface diffusion. High resolution scanning electron microscope images from different specimens showed a porous microstructure of interconnected particles typical for initial sintering. Arrhenius plot of the grain size data revealed the activation energy of 161 ± 11 kJ mol^− 1 for the growth process in agreement with those reported for grain boundary grooving experiments. It was found that MgO particles undergo coarsening already at temperatures as low as 0.31 of the MgO melting point (3125 K). Increase in the particle diameter and decrease in the surface area were associated with surface diffusion mechanism that leads to initial sintering between the particles.     

Thermal conductivity of methane

This paper reports thermal conductivity data for methane measured in the temperature range 120–400 K and pressure range 25–700 bar with a maximum uncertainty of ± 1%. A simple correlation of these data accurate to within about 3% is obtained and used to prepare a table of recommended values.Nomenclature a _k ,b _ij ,b _k Parameters of the regression model, k= 0 to n; i =0 to m; j =0 to n - P Pressure (MPa or bar) - Q _kl Heat flux per unit length (mW · m^–1) - t time (s) - T Temperature (K) - T _cr Critical temperature (K) - T _r reduced temperature (= T/T _cr) - T _w Temperature rise of wire between times t ₁ and t ₂ (deg K) - T ^* Reduced temperature difference (TT _cr)/T _cr - Thermal conductivity (mW · m^–1 · K^–1) - ₁ Thermal conductivity at 1 bar (mW · m^–1 · K^–1) - _bg Background thermal conductivity (mW · m^–1 · K^–1) - _cr Anomalous thermal conductivity (mW · m^–1 · K^–1) - _e Excess thermal conductivity (mW · m^–1 · K^–1) - Density (g · cm^–3) - _cr Critical density (g · cm^–3) - _r Reduced density (= / _cr) - ^* Reduced density difference (– _cr )/ _cr      

Thermal conductivity of composites

A general expression for the effective thermal conductivity of inhomogeneous media in terms of the Fourier components of the spatial variation of the conductivity is applied to composites consisting of inclusions in a continuous matrix. It is reformulated in terms of the mean square fluctuations of the conductivity. Specific cases treated are spherical inclusions and long cylinders, both random and with preferred directions. The results hold provided the difference in thermal conductivities is small or provided the concentration of inclusions is not too large. The theory fails if the thermal conductivity of the matrix is much smaller than that of the inclusions. The same considerations also apply to electrical conductivity.     

Thermal stability of additively manufactured austenitic 304L ODS alloy

Thermal stability and high-temperature mechanical properties of a 304L austenitic oxide dispersion strengthened(ODS)alloy manufactured via laser powder bed fusion(LPBF)are examined in this work.Additively manufactured 304LODS alloy samples were aged at temperatures of 1000,1100,and 1200℃for 100h in an argon atmosphere.Microstructure characterization of LPBF 304L ODS alloy before and after the thermal stability experiments revealed that despite the annihilation of dislocations,induced cellular substructure by the LPBF process was partially retained in the ODS alloy even after aging at 1200℃.The size of Y-Si-O nanoparticles after aging at 1200℃increased from 25 to 50 nm.EBSD analysis revealed that nanoparticles retained the microstructure of LPBF 304L ODS and hindered recrystallization and further grain growth.At 600℃and 800℃,the yield stress of the 290 and 145 MPa were measured,respectively,which are substantially higher than 113 MPa,and 68 MPa for 304L at the same temperatures.Furthermore,the creep properties of LPBF 304L ODS alloy were evaluated at a temperature of 700℃under three applied stresses of 70,85,and 100 MPa yielding a stress exponent(n)of～7.7;the minimum creep rate at 100 MPa was found to be about two orders of magnitude lower than found in the literature for wrought 304L stainless steel.     

Thermal conductivity of solutions

The results of an experimental and theoretical study of the thermal conductivity of binary, ternary, and multicomponent solutions are presented. A probable mechanism of heat conduction in solutions is proposed and calculation formulas are obtained.     

Thermal conductivity of consolidated systems

A structural model and method for calculating the effective thermal conductivity of consolidated granular materials are proposed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 27, No. 1, pp. 55–62, July, 1974.     

Thermal conductivity of organic liquids

A new instrument and technique for determining the thermal conductivity of liquids by the coaxial cylinder method are described. Experimental values of the thermal conductivity, obtained over a broad temperature interval, are compared with the results of other investigators.     

Thermal conductivity of sulfur hexafluoride

This paper reports new measurements of the thermal conductivity of sulfur hexafluoride at the nominal temperature of 27.5°C as a function of density in the range up to 200 kg · m^–3. The measurements were performed in a transient, hot-wire instrument. When combined with earlier measurements of the viscosity of the gas, they allow us to calculate the rather large contribution stemming from the internal degrees of freedom. The present measurements compare well with those in the literature. All of them suggest that the excess thermal conductivity is a unique function of density in the present range of states. An empirical correlation of our measurements can serve users in the ranges 0 < t< 100°C and 0 < < 200 kg · m^–3.     

Thermal conductivity of multicomponent mixtures

The authors propose a method of calculating the effective thermal conductivity of multicomponent mixtures as a function of their structure, the thermal conductivities of the components, their concentrations, and other parameters.     

Thermal conductivity of glass-fiber systems

Heat transfer in glass-fiber materials is considered. The effect of scattering on heat transfer is investigated, and the results of calculations are compared with published data.Inzhenerno-Fizicheskii Zhurnal, Vol. 21, No.5, pp. 797–803, November, 1971.     

Thermal conductivity of polyester-amide-imide film

Thermal conductivity measurements were performed on polyester-amide-imide film from 4 to 323 K. The specimen was in the form of a stack of aluminium discs coated on both sides with film. The results exhibit a temperature dependence similar to varnish, but are about half as large in conductivity. The results, based on nineteen data points, are estimated to be accurate to about 10%.     

Thermal conductivity of Freon-218

The thermal conductivity of Freon-218 is investigated experimentally in a wide region of the parameters. Reference tables of thermal conductivity are compiled.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 2, pp. 244–248, February, 1980.     

Thermal conductivity of copper films

The thermal conductivity of thin films of copper (400–8000 Å) has been measured in the temperature range 100–500 K. It decreases with decreasing film thickness. An electrical-thermal transport analogy has been used to calculate the size-dependent thermal conductivity of the thin copper films. The decrease of the thermal conductivity with thickness is attributed partly to the scattering of the conduction electrons from the film surfaces and partly to the scattering by lattice impurities and frozen-in structural defects in the films. The variation of the thermal conductivity with temperature agrees with the variation for bulk copper. The Lorentz ratio has been determined and is found to vary from 2.4 × 10^-8 to $\text{2.0 × 10}{}^{-8}\text{W}\text{Ω/}\text{deg}{}^2$ for film thicknesses ranging from 400 to 8000 Å.     

Thermal conductivity of epoxy resin-aluminium

Journal of Materials Science -     

Thermal conductivity of liquid tetrachlorides

The thermal conductivity of liquid carbon, silicon, titanium, germanium, and tin tetrachlorides overthe-20 to +60°C temperature range was measured by the transient relative null method with a hot wire.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 23, No. 5, pp. 835–841, November, 1972.     

Thermal conductivity of fibrous systems

The process of heat transfer in fibrous materials with a random structure is examined and a method is proposed for calculating the effective thermal conductivity as a function of the characteristic parameters of the system (thermal conductivities of the components, their volume concentration, temperature, pressure of the interstitial gas, etc.).     

Thermal conductivity of inhomogeneous materials

The effective thermal conductivity is calculated from the rate of entropy production per unit volume. Thermal conductivity and the temperature field are expressed in terms of Fourier components and these are related. The rate of entropy production is then obtained in terms of the volume-averaged thermal conductivity and the Fourier components of thermal conductivity. A simple expression for the effective thermal conductivity is found. In the case of striations it leads to well-known results. The formalism is applied to solids with inhomogeneously distributed solutes. It is shown that the thermal conductivity is less than the volume-averaged thermal conductivity and that homogenization by diffusion increases the thermal conductivity. Similar results would apply to the electrical conductivity of inhomogeneous alloys.