The three-phonon scattering relaxation rates and their temperature exponents have been analysed in the frame of Guthrie's classification of the phonon-phonon scattering events as class I and class II events and as a result of this, a new expressionτ 3ph -1=(B N,I+B U,Ie-θ/αT) g(w)T m I (T)+(B N,II+B U,IIe-θ/αT)g(w)T mII(T) for the three phonon scattering relaxation rates has been proposed for the first time to calculate the lattice thermal conductivity of a sample. Using the expression proposed above, the lattice thermal conductivity of Ge has been analysed in the temperature range 2–1000K and result obtained shows a very good agreement with the experimental data. The percentage contributions due to three-phonon normal and umklapp processes are also reported. The role of four phonon processes is also included at high temperatures. To estimate an approximate value of the scattering strength and the phonon conductivity, the analytical expression is also obtained in the frame of the expression proposed above forτ 3ph -1.
): 1267 – 1277 . Karawacki , E. , Suleiman , B. M. , Ul-Hang , I. , Nhi , B. T. ( 1992 ). An extension to the dynamic plane source technique for measuring thermal conductivity
agent is of great importance to achieve the product with the required technical properties [ 9 ]. The glass-ceramic foams normally possess fascinating characteristics, including high durability, low thermal conductivity, lightweight, high corrosion
The method of determining the thermal conductivity depends upon a relation between the maximum temperature (θ m ) attained for a given current and potential difference (V) in a current carrying specimen. Heat is assumed to enter and leave specimen only through the surfaces through which electric current enters and leaves, other surfaces being insulated against flow of both heat and electricity. The plane ends of the rod were taken to be isothermal and equipotential surfaces held at a constant temperature.
The lattice thermal conductivities of Mg2Si and Mg2Sn have been analyzed in the entire temperature range 2–1000 K in the frame of the expression for the three-phonon scattering relaxation rate recently proposed by Dubey and Misho, and a very good agreement is found between the calculated and the experimental values of the lattice thermal conductivity in the entire temperature range of the study. The separate contributions due to transverse and longitudinal phonons towards the total lattice thermal conductivity have also been studied by calculating their percentage contributions. The percentage contributions of the three-phonon normal and umklapp process scattering relaxation rates towards the three-phonon scattering relaxation rate have been studied for both Mg2Si and Mg2Sn. The percentage contribution of the three-phonon scattering relaxation rate towards the combined scattering relaxation rate has also been studied for transverse as well as for longitudinal phonons, for four different values of the phonon frequencies. The role of the four-phonon processes is. also included in the present analysis.
The thermal diffusivity and the thermal conductivity of polypropylene-based composite polymer were simultaneously measured with a temperature wave analysis method. We can measure the thermal properties under cooling process which are important to consider the polymer processing. The effect of filler in the composite was analyzed by thermal diffusivity and thermal conductivity as a function of temperature. The thermal conductivity of particle dispersed composite was confirmed as a reasonable value and was explained with a series model.
An intermediate range (50–1000°C) self-referencing differential scanning calorimeter (SR-DSC) has been built and its performance evaluated. The SR-DSC measures heat flow across a heat flow metal plate, and any changes to the heat flow caused by a thermal transition occurring in a centrally placed sample is monitored by a temperature difference across the plate. The criteria for high sensitivity are that the circular plate should be as thin as possible and have a low thermal conductivity. The best sensitivity conducive with robust behaviour was achieved with an inconel thermal plate of uniform thickness, 75 m, this gave reproducible results, and the enthalpy of the thermal transition was proportional to sample mass. Calorimeter sensitivity decreased with increasing temperature and a sloped baseline was observed. Both of these effects can be corrected mathematically. An example of the use of the SR-DSC in polymer characterisation was limited to a study of the physical ageing of PET.
Films ≈350 μm of poly(vinyl-alcohol) composites, containing copper (Cu), aluminium (Al) and iron (Fe), metallic powder very fine, were prepared by a casting method. Thermal conductivity, phonon velocity, mean free path and specific heat were studied. The pure sample of PVA has a lower values of thermal conductivity than that which are doped with metals. For all samples the thermal conductivityK increases up to a certain temperatureT gg (120–160°C) and then decreases with temperature. The specific heat increase with temperature up to ≈120°C and above 120°C is nearly independent on temperature. The pure sample of PVA has small values of mean free path (L)≈0.2 Å at room temperature, but for PVA+ metalsL≈2.0 Å. The phonon velocity of pure PVA is larger than that of PVA containing metals.
Lignin-and molasses-based polyurethane (PU) foams with various lignin/molasses mixing ratios were prepared. The hydroxyl group in molasses and lignin is used as the reaction site and PU foams with various isocyanate (NCO)/the hydroxyl group (OH) ratios were obtained. Thermal properties of PU foams were investigated by differential scanning calorimetry (DSC), thermogravimetry (TG) and thermal conductivity measurement. Glass transition temperature (T g) was observed depending on NCO/OH ratio in a temperature range from ca. 80 to 120°C and thermal decomposition temperature (T d) from ca. 280 to 295°C. Mixing ratio of molasses and lignin polyol scarcely affected the T g and T d. Thermal conductivity of PU foams was in a range from 0.030 to 0.040 Wm−1 K−1 depending on mixing ratio of lignin and molasses.