Determination of Thermal Diffusivity

Generally, thermal diffusivity measurement has many advantages, such as small sample size, short measuring period and wide temperature range. On this account, it is an important method for obtaining thermal conductivity data. There 

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Frez C, Diebold GJ, Tran C et al. (2006) Determination of thermal diffusivities, thermal conductivities, and sound speeds of room temperature ionic liquids by the transient grating technique. J Chem Eng Data 51 1250-1255... 

Nix, G.H., Lowery, G.W., Vachan, R.I., and Tanger, G.E., Direct determinations of thermal diffusivity and conductivity with a refined line-source technique, in Progress in Aeronautics and Astronautics Therrrwphysics of Spacecraft and Planetary Bodies, Vol. 20, Heller, G. (ed.). Academic Press, New York, 1967, pp. 865-878. 

THE DETERMINATION OF THERMAL DIFFUSIVITY OF SOLID STATE MATERIALS BY A SIMPLIFIED PERIODIC HEATING METHOD. M.S. THESIS. 

DIRECT DETERMINATION OF THERMAL DIFFUSIVITY AND CONDUCTIVITY WITH A REFINED LINE-SOURCE TECHNIQUE. FROM THERMOPHYSICS OF SPACECRAFT AND PLANETARY BODIES. PROGRESS IN ASTRONAUTICS AND AERONAUTICS-VOL. 20. 

DETERMINATION OF THERMAL DIFFUSIVITY OF POLYMERS BY DIFFERENTIAL THERMAL ANALYSIS. 

Nguyen, M. Beckett, R. Determination of thermal diffusion coefficients using thermal field-flow fractionation and Mark-Houwink constants. Anal. Chem. 2004, 76, 2382-2386. 

Bernini U, Bernini R, Maddalena P, Massera E, Rucco P (2005) Determination of thermal diffusivity of suspended porous silicon films by thermal lens teehnique. Appl Phys A 81 399-404... 

Photoacoustics is also widely used for numerous non-spectroscopic applications, such as the determination of thermal diffusivity, non-destructive testing of materials (in particular probing of sub-surface... 

DIN EN 821-2. Monolithic ceramics - thermo-physical properties - Part 2 Determination of thermal diffusivity by the laser flash (or heat pulse) method. 

ISO 18755 2005. Fine ceramics (advanced ceramics, advanced technical ceramics) - determination of thermal diffusivity of monolithic ceramics by laser flash method. 

PA and PT phenomena are widely used for numerous non-spectroscopic applications such as the determination of thermal diffusivity, non-destructive testing of materials (in particular the probing of sub-surface defects) by thermal wave imaging, time-resolved studies of de-excitation processes or on biological photoreceptors, studies of phase transitions, etc. Here, only spectroscopic applications are considered that demonstrate the main characteristics and the potential of photoacoustic spectroscopy (PAS). In the following, illustrative examples are presented for solids, liquids, gases, biological and medical samples. 

Various forms of diffusion coefficients are used to establish the proportionality between the gradients and the mass flux. Details on determination of the diffusion coefficients and thermal diffusion coefficients is found in Chapter 12. Here, however, it is appropriate to summarize a few salient aspects. In the case of ordinary diffusion (proportional to concentration gradients), the ordinary multicomponent diffusion coefficients Dkj must be determined from the binary diffusion coefficients T>,kj. The binary diffusion coefficients for each species pair, which may be determined from kinetic theory or by measurement, are essentially independent of the species composition field. Calculation of the ordinary multicomponent diffusion coefficients requires the computation of the inverse or a matrix that depends on the binary diffusion coefficients and the species mole fractions (Chapter 12). Thus, while the binary diffusion coefficients are independent of the species field, it is important to note that ordinary multicomponent diffusion coefficients depend on the concentration field. Computing a flow field therefore requires that the Dkj be evaluated locally and temporally as the solution evolves. 

In 1972, Miller made a detailed analysis of the data on the influence of electron acceptor additives on the yield of ionic products during radiolysis of organic matrices and showed this to agree quantitatively with the electron tunneling mechanism of the formation and annihilation of these particles [7], In particular, the annihilation of et) in MTHF glass containing naphthalene (Nh) as the additive was found to be accompanied by simultaneous formation of the Nh anion radical (via the reaction etj. + Nh - Nh ). The kinetic curves for this reaction at 77 and 87 K coincided, which ruled out the possibility of the reaction rate being determined by thermal diffusion. 

Since there had not been any measurements of thermal diffusion and Soret coefficients in polymer blends, the first task was the investigation of the Soret effect in the model polymer blend poly(dimethyl siloxane) (PDMS) and poly(ethyl-methyl siloxane) (PEMS). This polymer system has been chosen because of its conveniently located lower miscibility gap with a critical temperature that can easily be adjusted within the experimentally interesting range between room temperature and 100 °C by a suitable choice of the molar masses [81, 82], Furthermore, extensive characterization work has already been done for PDMS/PEMS blends, including the determination of activation energies and Flory-Huggins interaction parameters [7, 8, 83, 84],... 

T. Log, Transient Hot-Strip Method for Simultaneous Determination of Thermal Conductivity and Thermal Diffusivity of Refractory Materials , Journal of the American Ceramic Society, 74 (3) 650-653 (1991). 

The dependence of retention in Th-FFF on chemical composition of the polymers and solvent [84] also opens a wide field of application for Th-FFF, especially for copolymers. According to Eq. (42), retention in Th-FFF can be used to determine the thermal diffusion factor aT which was demonstrated for polystyrene in toluene [209]. Eater, this study was extended to other solvents (ethyl acetate, 2-butanone, p-dioxane, cyclohexane, dimethylformamide, chloroform, and ethylbenzene) [204]. 

Recent studies [111,214] indicate that Th-FFF can even be used to determine the relative chemical composition of two components in random copolymer and linear block copolymers whose monomers do not segregate due to solvent effects. However, this application is limited by the unpredictable nature of thermal diffusion. Nevertheless, combining information from Th-FFF with those derived on fractions by independent detectors selective to composition (such as an IR spectrometer) can yield further insight into the dependence of DT on the chemical composition. Even more powerful is the combination of Th-FFF with SEC as, here, the chemical composition (from Th-FFF) can be studied as a function of the molar mass (from SEC). This was demonstrated by van Asten et al. by cross fractionating copolymers and polymer blends with SEC and Th-FFF [358]. 

Consider a 2-cin-diameter cylindrical rod made of a sample material whose density and specific heat are 3700 kg/m- and 920 Jfkg C, respectively. The sample is initially at a uniform temperatuce of 25°C, In order to measure the temperatures of the sample at its surface and its center, a thermocouple is inserted to the center of the sample along the centerline, and another thermocouple is welded into a small, hole drilled on the surface. The sample is dropped into boiling water at I00°C. After 3 min, the surface and the center iemperaturc.s are recorded to be 93 C and 75°C, respectively. Determine the thermal diffusivity and the thermal conductivity of the material. 

The thermal effect after the photoexcitation was detected by Mack [65], Pohl [21], Scarlet [22], and Key et al. [66] as the TG signal. Soon after that, it was applied to the measurements of thermal diffusivities in solutions [67-69], liquid crystals [70], solids [71-73], gases [74,75] and supercritical fluids [76], Measurements of the energy deposition quantum yield and the thermal diffusion rate were performed by Andrew and Hochstrasser [77] for iron(III)tetra-phenylporphyrin chloride. They determined the quantum yield of nonradiative transitions to be 0.93 + 0.07 using azulene as a reference molecule. 

Measurement of steady-state compositions y and y after thermal diffusion equilibrium has been established between temperatures T and T" is the most accurate way of determining the thermal diffusion constant. The next-to-the-last column of Table 14.26 pves values of the measured thermal diffusion constant for several binary isotopic mixtures. In all these cases, 7 is positive, which means that the light isotope concentrates at the higher temperature under the experimental conditions listed. 

The goal of these experimental investigations is the determination of the diffusion coefficient D as a function of the temperature. In the typical molecular crystals naphthalene or anthracene, the diffusion is thermally activated ... 

In-pile self-diffusion of uranium in stoichiometric UO2 and UC has been measured by Hoh and Matzke 3J6). The diffusion coefficients obtained at a nominal irradiation temperature of 900°C and a fission rate of 1 x 10 //cm indicated that radiation-enhanced diffusion was higher by a factor of 10 to lO than determined by extrapolation of thermal diffusion coefficients. They suggested that the data are of immediate relevance to the understanding and the prediction of such quantities as in-pile sintering and densification, diffusion-controlled creep, and fission gas behavior in the outer zones of the fuel. 

For selected values of 0J0o obtained from the experiments, the values of z can be obtained, and with the measured values of time, t, and x the diffusivity is calculated from Equation 27.21. The values of the thermal diffusivities can also be determined for seeds by solving the Fourier equation for either an infinite cylinder [60], or a sphere [59]. Table 27.13 gives values of thermal diffusivities for selected seed types obtained with the direct or indirect method. 

For gases, the kinetic gas theory is able to derive relationships for the diffusion coefficient as well as it does for viscosity and thermal conductivity (44). It depends both on temperature and pressure, but not on the composition. At pressures lower than 1 MPa, it is proportional to the reciprocal value of the pressure. At low pressures, it can be accurately estimated according to Fuller et al. (91). The equation for the determination of vapor diffusion coefficients is... 

In addition, the free volume increases with NR content and vulcanization temperature. Goyanes et al. [124] obtained NR-SBR blends by using sulfur vulcanization and Af-tert-butyl-2-benzothiazolesulfenamide accelerator at 160°C and studied their thermal properties in terms of thermal diffusion and by determining the glass transition temperatures of each blend. 

Various other methods have been described for the determination of thermal conductivity. Capillarity has been used to measure the thermal conductivity of LDPE, HOPE and PP at various temperatures and pressures [30]. A transient plane source technique has been applied in a study of the dependence of the effective thermal conductivity and thermal diffusivity of polymer composites [31]. 

Thermal diffusivity was determined for samples where x = 0.2 and 0.5. Acceptable values of thermal diffusivity at temperatures below 600°C were difficult to obtain, likely owing to the very low thermal diffusivity of the samples and the resultant nonlinear heat flow. Measured bulk densities of the samples were approximately 80% theoretical. 

Any particular fuel cycle might employ some, or all of these features, as needed. In addition, advanced characterization techniques will help to elucidate the relationship between fuel properties and fuel performance for advanced fuels. Examples of such innovative techniques include the measurement of thermal diffusivity, porosity, density, or the oxygen potential of irradiated fuel, use of advanced techniques for measuring the diffusion coefficient of fission gases (Hocking et al. 1998), and methods to accurately determine plutonium distribution in MOX fuel. 

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