Determination Of Specific Heat Research Articles

Accurate determination of specific heat at high temperatures using the flash diffusivity method

The flash diffusivity method can be extended, very simply, to measuring simultaneously thermal diffusivity and specific heat and thus obtaining the thermal conductivity directly. This was accomplished by determining the amount of heat absorbed by a sample with a well-known specific heat and then using this to determine the specific heat of any other sample. The key to using this technique was to have identically reproducible surfaces on the standard and the unknowns. This was achieved earlier by sputtering the surfaces of the samples with a thin layer of graphite. However, the accuracy in determining the specific heat was within ±10% and there was considerable scatter in the data. Several improvements in the technique have been made which have improved the accuracy to ±3% and increased the precision. The most important of these changes has been the introduction of a method enabling the samples to be placed in exactly the same position in front of the light source. Also, the control of the thickness and the application of the graphite coating have turned out to be very important. A comparison of specific heats obtained with this improved technique and with results obtained using other techniques has been made for two materials.

Determination of specific heats of some edible oils and fats by differential scanning calorimetry

Measurements of specific heat as a function of temperature were carried out with a differential scanning calorimeter on rape-seed, soybean, sunflower and corn oils and on lard.

Determination of Thermal Conductivity and Estimation of Specific Heat for High-Temperature Oxides

A new method is proposed for the simultaneous determination of thermal conductivity, thermal diffusivity and specific heat for high-temperature materials by use of a hot strip.The principle of this method is based on the two solutions of the Fourier’s partial differential equation solved under the different conditions of time. The temperature increase with time is proportional to logarithm of time for a long-time measurement. The slope of this straight line gives thermal conductivity (λ). On the other hand, the response-curve by a short time measurement is proportional to square root of time. The slope of this straight line offers thermal diffusivity (κ). The specific heat (Cp) can be estimated by virtue of ρCp=λ⁄κ (ρ: density).By using this method, thermal conductivity, thermal diffusivity and specific heat of 30(mol%)Na2O–70SiO2 sample have been determined over the wide temperature range of 300 to 1500 K in liquid and glassy states. The thermal conductivity is in good agreement with that obtained by the hot wire method. The thermal diffusivity is nearly constant at low temperatures but decreases with increasing temperature. The specific heat increases with increasing temperature but the absolute values are 1.1–1.2 times higher than those by the laser-flash method.The hot-strip method can be used for a simultaneous determination of thermal conductivity, thermal diffusivity and specific heat for materials at high temperatures.

Experimental Determination of the Specific Heats of Liquid Li7Pb2 and LiPb Alloys*

Experimental Determination of the Specific Heats of Liquid Li₇Pb₂ and LiPb Alloys*

New measurement method of thermal properties by means of flux calorimetry

The equations for the heat that has passed through each plane from one steady state to another are obtained from the Laplace transform of the differential equation of heat conduction in a solid bounded by two parallel planes. From these equations for the heat flow, a method for the simultaneous determination of specific heat and thermal conductivity of a solid is deduced. This determination is carried out by measuring quantities of heat, and neither measurement of temperature gradient nor comparison with a sample of known thermophysical properties is needed.

Simultaneous DSC-TG up to 1700 K

A DSC-TG-sample carrier up to 1700 K employs plate-type thermocouples as heat flux sensors. Flat bottomed sample pans ensure an almost ideal thermal contact with these sensors, resulting in high sensitivity and peak resolution. Its performance was tested with standard materials and some polymeric samples. The construction of the sample carrier permits quantitative determinations of specific heat at high temperatures. Results are shown with sapphire, aluminium oxide, graphite and glass samples.

Thermal analysis by photoacoustic phase measurements: Effect of sample thickness

The phase of the photoacoustic signal is measured as a function of chopping frequency for different thicknesses of Pb resting on a water backing. Analysis of the results is in agreement with the theory of Rosencwaig and Gersho [J. Appl. Phys. 47, 64 (1976)] and leads to a simultaneous determination of thermal conductivity and specific heat of the sample.

Electronic properties and stability of the ordered Pd-Y alloys

The Pd-Y system belongs to the family of binary transition metal systems with a large valence difference ΔN characterized by the existence of numerous ordered intermetallic compounds of narrow solid solution range. We present a revised phase diagram and discuss the degree of stability of the existing ordered structures. Since the stability of ordered structures is intimately correlated with their electronic structure we present experimental data for the density of states at the Fermi level obtained from electronic specific heat determinations. None of the ordered Pd-Y alloys show magnetic ordering. Good agreement is obtained with the results of existing density of states calculations showing the electronic structure of these compounds to be of the split-band-type regime. The importance of the position of the Fermi level E F with respect to the typical pseudogap of ordered structures with large ΔN is pointed out. In particular, E F is shown to lie in the gap for Pd 3Y which, from the high temperature of formation, is expected to be very stable, in contrast with PdY 3, where E F lies outside the gap, which is not expected to be very stable.

Determination of the thermal conductivity of graphite and high-temperature alloys by the laser-flash method

Thermal conductivity measurements at very high temperatures (above 1000°C) are difficult, particularly because of the heat loss by radiation which is hard to avoid when using all the steady-state methods. But, in many cases, the experimental problems can be overcome by measuring the thermal diffusivity and calculating the conductivity data after additional determinations of specific heat and density have been made. For some high-temperature materials (graphite and metallic alloys), this procedure was chosen to determine the thermal conductivities. Therefore an apparatus was designed based on the known method, but with some special adaptations. Standard materials were tested in this way to show its advantages. The laser-flash apparatus is described, and the results obtained are reported and discussed.

Thermodynamics of superconducting lanthanum

We have calculated the thermodynamics of superconducting lanthanum from numerical solutions of the finite-temperature Eliashberg equations, written on the imaginary frequency axis, with electron-phonon kernel taken from the available tunneling data. We compare the theory with a recent specific heat determination of the thermodynamics. Also, we study several possible changes in the spectral density chosen to improve agreement with experiment. Our favored spectrum is obtained by a constant scaling of the tunneling spectral density chosen to increase the mass enhancement parameter from 0.79 to approximately 1.0.

DTA determination of specific heats of liquids

A method is described for conversion of the experimentally measured total heat capacity of a sample of low-boiling liquid, heated in a closed, pressure-proof pan, to its specific heat.

Specific heat of high-purity solid gallium close to the melting point

Abstract We report on specific heat determinations of 99·9999% pure gallium applying an optical A.C. method. Data were taken with a temperature resolution, relative to the melting point T M, of 2 mK, starting from 1·5 K below T M and proceeding across the melting transition. The specific heat which was derived from amplitude and phase measurements, increases below the nominal melting point. The implication of these findings is discussed.

The thermal properties of thin films at low temperatures using an improved heat-pulse method

A heat-pulse technique for the simultaneous determination of specific heats and thermal diffusivities of thin-film samples at low temperatures is discussed. In addition, correction formulae are provided to account in the analyses for various departures from ideal experimental conditions. An analysis of the limits of the technique suggests that heat capacities as small as 10-11 J K-1 can be measured.

Programmable temperature control system for biological materials.

A system was constructed which allows programmable temperature-time control for a 5 cm3 sample volume of arbitrary biological material. The system also measures the parameters necessary for the determination of the sample volume specific heat and thermal conductivity as a function of temperature, and provides a detailed measurement of the temperature during phase change and a means of calculating the heat of the phase change.

Specific heats of polymer powders by differential scanning calorimetry

The specific heats of five polymers were determined by differential scanning calorimetry (DSC) in the temperature range of 300 to 360 K. The measurements were performed with polymers in the form of films, powders, and granules to clarify whether or not DSC specific heat values are dependent on the diminution of the sample. It was found that the specific heats for the bulk and powdered form of the polymer samples are indistinguishable within the error limits, justifying the determination of specific heats of powders by means of DSC.

Determination of specific heats of coal powders by differential scanning calorimetry

Specific heats ( C p ) of bituminous and subbituminous coals were investigated in the temperature range 300–360K by differential scanning calorimetry (DSC). To establish the validity of the procedure, specific heats of glass beads and graphites in powdered and bulk form were determined. Good agreement was obtained with the values for the specific heats of glass and graphites in the literature, and it was established that the specific heats were not dependent on the degree of diminution of these materials. Specific heats of coal samples were found to depend upon mesh size, temperature, rank, moisture content and whether the coal powder was wet- or dry-screened. However, there were only minor differences in C p between bituminous and subbituminous coals.

Determination of specific heat of polystyrene by d.s.c.: 2

Determination of specific heat of polystyrene by d.s.c.: 2

The use of a continuous-flow helium cryostat in low-temperature calorimetry

For experimental investigation of the temperature-dependences of specific heat and thermal conductivity in the range 4–300 K a continuous-flow helium cryostat has been developed. Its adaptation for low-temperature calorimetry and its use for measurement of the temperature-dependences of the specific heats of bulk samples of metals and insulators are described in this note. The phase transition from the normal to the superconductive state has been measured on NbTi and its critical temperature determined. Two methods of determination of the temperature-dependences of the specific heats of metals and insulators have been developed. The inaccuracy of specific heat determination did not exceed 2 % with metal materials and 5 % with insulating materials.

Determination of specific heat of phenol formaldehyde resol resins by differential scanning calorimetry

AbstractThe specific heat, Cp, was determined by DSC on a series of resol‐type phenol formaldehyde resins with varying phenol formaldehyde molar ratio. The extrapolated Cp values at 25°C vary between 1.181‐1.206 kJ · kg−1 K−1 and the dCp/dT ratio was found to be 0.0042kJ · kg−1K−2 in the temperature range of 70–125°C.

Determination of specific heat by differential scanning calorimetry at low temperature

Determination of specific heat by differential scanning calorimetry at low temperature