Specific Heat Of Alloys Research Articles

Evaluation of thermal conductivity for liquid lead lithium alloys at various Li concentrations based on measurement and evaluation of density, thermal diffusivity and specific heat of alloys

The thermophysical properties of lead lithium alloy (Pb–Li) are essential for the design of liquid Pb–Li blanket system. The purpose of the present study is to make clear the density, the thermal diffusivity and the heat conductivity of the alloys as functions of temperature and Li concentration. The densities of the solid alloys were measured by means of the Archimedean method. The densities of the alloys at 300K as a function of Li concentration (0at%<χLi<28at%) were obtained in the equation as ρ(300K)[g/cm3]=−6.02×10−2×χLi+11.3. The density of the liquid alloys was formulated as functions of temperature and Li concentration (0at%<χLi<30at%), and expressed in the equation as ρ[g/cm3]=(9.00×10−6×T−7.01×10−2)×χLi+11.4−1.19×10−3T. The thermal diffusivity of Pb, Pb–5Li, Pb–11Li and Pb–17Li were measured by means of laser flash method. The thermal diffusivity of Pb–17Li was obtained in the equation as αPb–17Li[cm2/s]=3.46×10−4T+1.05×10−1 for the temperature range between 573K and 773K. The thermal conductivity of the Pb–17Li at the temperature of 773K was newly obtained and expressed in the equation as λ[W/mK]=4.47×10−2χLi2−0.08χLi+14.9. The dependence of Li concentration on the thermal diffusivities of the alloys was larger at higher temperature. The temperature dependence of the thermal conductivities of the alloys was larger when the Li concentration in the alloys was higher.

Lattice specific heat and local density of states of Ni-based dilute alloys at low temperature

A detailed theoretical study of the low-temperature lattice specific heat of Ni-based dilute alloys has been carried out. Lattice Green’s function method has been used to calculate the local density of states of substitutional impurities and lattice specific heat in different alloys. The resonance condition has been investigated for possible occurrence of resonance modes. Except in NiCr and NiMn, low-frequency resonance modes have been obtained in all the alloys. However, no localized mode was obtained. The impurity-induced increase in lattice specific heat is explained on the basis of the obtained resonance modes. The calculation shows an excellent agreement with the measured lattice specific heat in these alloys

Specific heats of fast-quenched Au-Ni alloys

The low-temperature specific heats of liquid-quenched Au-Ni alloys containing between 20 and 52 at % Ni have been measured using ac calorimetry techniques. The specific heats of alloys near the critical composition for ferromagnetism (42–44 at % Ni) contain an anomalous contribution, similar to that observed in Cu-Ni alloys, seen as a significant upturn below 6 K in plots ofC/T vs.T2. The anomalous contribution can be interpreted in terms of a magnetic cluster contribution, which is independent of temperature above 2 K. The magnitude of the cluster contribution is greatest at the critical composition, and is 2–3 times larger than the cluster contribution for Cu-Ni alloys. This suggests that these liquid-quenched Au-Ni alloys contain a greater concentration of magnetic clusters than the Cu-Ni alloys. The average cluster moment is therefore smaller, since the saturation magnetizations are comparable.

Entropies of mixing of liquid metals A hard-sphere description

Abstract The entropies of mixing of liquid metals are well explained on the basis of a hard-sphere model in which (i) the total ionic volumes are supposed not to change on alloying and (ii) the observed excess volumes are incorporated into the calculation. The above propositions are illustrated by the consideration of 31 binary alloys in the middle of their composition ranges and of seven such systems across their whole ranges. The formalism also yields a qualitatively correct description of specific heats of alloys in so far as the limited experimental information permits us to judge.

Contribution of giant spin clusters to the resistivity, neutron-scattering cross section, and specific heat in alloys: Application to Ni-Cu

A simple model for a nondilute alloy containing giant spin clusters is used to calculate the spin contribution to the resistivity, the neutron cross section, and the specific heat ${C}_{V}$. The model is expected to be applicable to Ni-Cu alloys near the critical concentration for ferromagnetism. Intracluster interactions are treated exactly using a near-neighbor Heisenberg exchange interaction. Intercluster interactions are treated within the molecular-field approximation. It is assumed that in paramagnets there is a weak local field, which derives from the magnetic-anisotropy energy. Reasonable semiquantitative agreement with resistivity, elastic neutron scattering, and low-temperature specific-heat measurements on Ni-Cu for a range of concentrations and temperatures is obtained if the average cluster contains 50 Ni spins and if a Ni atom has a spin when eight or more of its near neighbors are also Ni. It is found that the anomalous temperature dependence of the resistivity, which behavior is common to a variety of alloy systems, can be accounted for using the present theory if the Fermi wave vector times the lattice spacing is less than \ensuremath{\cong}2. The previously unexplained behavior of the elastic neutron cross section in paramagnetic alloys can also be understood within this theoretical framework. In contrast to earlier discussions, it is shown that the spin contribution to ${C}_{V}$ is not temperature independent; in ferromagnetic alloys this contribution is found to increase with increasing temperature and in paramagnetic alloys it decreases with temperature. It is believed that this temperature dependence has, in the past, been incorrectly attributed to the electronic contribution to the specific heat. The validity of previous suggestions that the specific-heat and neutron-scattering measurements on these alloys probe different spin clusters is also questioned.

Low-Temperature Specific Heats of Alloys Based on the Noble Metals, Cu, Ag, Au:ζ-Phase Ag-Sn Alloys

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Deviations of the specific heats of the alkali metals from harmonic behaviour. A possible dependence on isotopic composition of the anharmonic contribution to specific heat

Abstract An analysis of the ‘high temperature‘ specific heats of all the alkali metals shows that positive departures from harmonic lattice theory predictions occur at temperatures in the range θ/3 to θ, suggesting the onset of appreciable anharmonic contributions to the specific heat in this temperature range. A further positive anomaly is observed starting at temperatures of about 50 °K below the melting point (except possibly in lithium) and is believed to correspond to the thermal generation of lattice vacancies. Recent measurements have shown that at low temperatures the specific heats of alloys of the two isotopes of lithium are intermediate between the specific heats of the separated isotopes. However, as the temperature is increased the specific heats of the alloys increase more rapidly than do the specific heats of the separated isotopes. As a result by 300 °K (where the lattice constants of the alloys and pure isotopes are probably all the same) the specific heats of alloys containing more than about 50 per cent 7Li exceed the specific heat of pure 7Li (which is itself greater than the specific heat of pure 6Li). These results suggest that the anharmonic contribution to the specific heat may depend on isotopic composition. However, the observed effect is rather small (less than 1 per cent of the total specific heat) and an independent set of measurements is desirable to confirm its existence and magnitude.

Effect of Magnetic Clusters on the Specific Heat of Ni-Cu and Fe-V Alloys

Recent experiments with Ni-Cu and Fe-V alloys indicate that the specific heat at low temperature cannot be described by electronic and lattice terms alone. An attempt is made to explain an additional term in the specific heat of these alloys on the basis of ferromagnetic clusters.

The specific heat of metals and alloys at low temperatures

The effect of thermal excitation of the conduction electrons on the elastic shear constants is investigated in a metal in which the Fermi surface lies close to the Brillouin-zone boundaries. It is shown that in these circumstances electron-lattice interaction leads to an addi­tional term in the specific heat, linear in the temperature in the liquid-helium range, which, therefore, augments the pure electronic specific heat. The variation in magnitude of this linear term is considered in the α-brasses. It is suggested that this is the physical effect underlying the peculiarities of the ‘electronic’ specific heat of these alloys.