Laser-flash method

In the laser flash method, the heat is put in by laser flash instead of electric current in the stepwise heating method mentioned above. Thus this method may be classified as a stepwise heating method. A two-layered laser flash method was developed by Tada et al. " The experimental method and the data analysis, including a case involving radiative heat flow, are described in detail in the review article by Waseda and Ohta. A thin metal plate is placed at the surface of a melt. A laser pulse is irradiated onto a metal plate of thickness / having high thermal conductivity. The sample liquid under the metal plate and the inert gas above the plate are designated as the third and first layers, respectively. The temperature of the second layer becomes uniform in a short time" and the response thereafter is expressed by... 

The two-layered laser flash method has been applied to some molten systems above 1000 K. In Fig. 30 an example of curve fitting is shown for molten calcium aluminosilicate at 1723 K. An analysis in which the radiative component is taken into account gives a good fit. The thermal conductivity and the radiative component parameter can be determined simultaneously by a curve-fitting procedure. 

In the laser flash method, a melt of interest is placed between two parallel plates. The upper plate is heated stepwise and the thermal diffusiv-ity is measured from the rise in temperature. The specific design for molten materials and especially slags employed by Ohta et al. is based on the differential three-layer technique utihzing a special cell that can be accommodated in the system. A schematic diagram of the principle of the measurement section is shown in Fig. 31. A laser pulse irradiates the upper (platinum) crucible and the temperature response of the surface of the lower platinum crucible is observed, a liquid specimen being sandwiched between the two. 

There are no ISO standards at present for polymers. However, a series of methods are being developed in TC 61 for conductivity and diffusivity of plastics. At the time of writing there are drafts for general principles, laser flash method, temperature wave analysis method and the Gustafsson method. The general principles draft is a bit misleading as it appears to deal only with transient methods, and the specific procedures so far drafted appear to have been selected at random from the many transient methods available. 

The laser flash method has been used by Foreman36 and by Agari et al60, the latter considering the effect of test conditions and sample size on accuracy. Papa et al61 developed a prototype apparatus that operated with step-down temperature perturbations and could be used with molten samples. 

High pressure grown single crystals of GaN [15] were used in the determination of thermal conductivity. The measurement was made using the laser-flash method. The result of these measurements was k = 1.7 W/(cm K), which is in agreement with the theoretical estimate of Slack [12]. 

InN single crystals of a size suitable for thermal conductivity measurements have not been obtained. The only measurement of the thermal conductivity has been made using InN ceramics [20], InN microcrystals obtained by microwave plasma were sintered under a pressure of 70 kbar at 700°C. The room temperature thermal conductivity was measured by the laser-flash method giving k = 0.45 W/(cm K) [20], This value is much below the estimate by Slack which gives k = 0.8 W/(cm K). This result indicates that the InN ceramic has a high impurity content and consists of small size grains. 

In the case of FeSi2, Fe and Si are melted at 1803 K (1530°C) and annealed in vacuum to form the /1-crystal of FeSi2. Then, we need to form the n- and p-type FeSi adding Co and Mn to the /> crystal of FeSi2, respectively. Another type of furnace (ULVAC Co. Ltd., Yokohama) is utilized to measure the Seebeck coefficient and the electrical resistivity in He atmosphere by increasing the temperature up to 900 K. The thermal conductivity is measured with the laser flash method (ULVAC Co. Ltd., Yokohama). 

Alkyl enol ethers polymerize under these conditions, and their reactivity, as that of other strong nucleophiles, has been determined with the LASER flash method (Table 7). Because this method of carbocation generation produces the nucleophilic counterions CL, eventual polymeriza-... 

As FGM interlayer, eleven kinds of sintered compacts in which the mixing ratio of beryllium powder and oxygen free copper powder was different, were manufactured by powder metallurgical method, that is, HP and HIP. In this study, to estimate thermal stress at joining interface, thermal conductivity and thermal expansion coefficient of Be/Cu sintered compacts were measured by laser flash method and laser interferometry method, respectively. The characterization on these compacts was performed by using SEM (Scanning Electron Microscope) to investigate distribution of intermetallic phases on these compacts. 

In this study, thermal diffusivity and specific heat of Be/Cu sintered compacts were measured by laser flash method. In those measurement, specimens were loaded with laser which had constant energy under vacuum. The degree of vacuum was less than 1X lO Pa in order to avoid the oxidation of specimens. Themial diffusivity and specific heat of these compacts were... 

Thermal conductivity was evaluated by the product of the density, specific heat, and thermal diffusivity. Thermal diffusivity was measured by the Laser Flash method. 

Thermal diffusivity of oxidation-resistant SiC/C compositionally graded graphite materials has been measured by using the laser flash method. In order to study the effect of the SiC/C graded layer on the diffusivity, the thickness of the graded layer and the SiC content were changed. In addition, the specific surface areas of the SiC/C materials have been measured. It is shown that the effect of the SiC/C graded layer on thermal diffusivity was small within SiC contents (0.27-8.52 mass%) used in this study. 

The thermal diffusivities of each composite were measured at 673K, 1073K, 1273K, 1373K and 1473K by laser-flash method. The thermal conductivity coefficient, the product of thermal diffusivity, specific heat and density, are plotted as a function of the concentration of PSZ and test temperature in Fig. 2 and Fig.3. In Fig. 2, the thermal conductivity coefficient at room temperature is plotted simultaneously. From... 

The Seebeck coefficient were calculated from measurement of electromotive force with temperature difference of lOK. The electrical resistivity and Hall measurement were performed by van der Pauw method. The thermal conductivity were calculated from the thermal diffusivity, the specific heat and the density. The thermal diffusivity and the specific heat were measured by laser flash method and differential scanning calorimeter (DSC), respectively. 

The microstructure of the samples was examined by the x-ray diffraction (XRD), the scanning electron microscope (SEM), and the electron probe microanalysis (EPMA). The electrical conductivity and Seebeck coefficient were measured from 300 to 1200 K. The thermal conductivity was measured by the laser-flash method at room temperature. 

The thermal conductivity was determined by laser-flash method (LFA447, Netzsch, German) with billets dimension of (pl2.7mmx2.5mm. The dielectric loss (land) was measured at IMHz by the perturbation meth(xl using a cavity resonator and a vector network analyzer (HP-4294A). 

For high thermal-conductivity adhesives, such as the silver-glass compositions whose thermal conductivities are greater than 20 W/m K, the indirect laser-flash method is used. Unlike the steady-state methods, the flash method does not measure thermal conductivity directly, but measures thermal diffusivity, from which thermal conductivity is calculated as follows ... 

FIGURE 34.5 Schematic of the laser flash method used for measuring thermal conductivity of ceramics. 

Thermal Diffusivity - The thermal diffusivity [D = k/(pCp)] of S10C-N312 BN 2-D composites was determined by the laser flash method in which a laser is used as a heat source and the thermal pulse transmission speed is measured in the desired orientation. Thermal diffusivity measurements were made both in-plane and through-plane ofthe 2-D composite. The specimen size was 9x9x2 mm square. The thermal diffusivity was calculated from solution of the diffusion equation for heat flow with the known boundary conditions. Details of this procedure are found in ASTM Standard Test Method E37.05 (Thermal Diffusivity by the Flash Method). 

High thermal composites from PPS and boron nitride have been prepared by melt compounding [62]. The thermal conductivity was measured by a laser flash method. Sample with a sufficient concentration of boron nitride exhibits an enhanced breakdown strength in comparison to neat PPS. 

The thermal conductivities A of the composites were calculated by equation A = a Cp />, where a, C, and p are the thermal diffusivity, specific heat, and density of the composites, respectively, a of the composites was measured by laser flash method (TC-7000, Sinku-Riko, Japan) p was calculated by the density of AIN of 3.26 g cm" and the measured density of the polymer matrix (1.31 g cm ) was... 

Specimens with a dimension of 10 mm in diameter and 2-3 mm in thickness were cut from the CS-SPSed discs, and were polished using emery paper until No. 1200. Prior to measurement, a thick layer of colloidal graphite was sputter-coated to the surface of the specimen to enhance absorption of the flash energy. The thermal diffusivity and specific heat capacity were measured by the laser-flash method... 

The thermal conductivity was measured by a laser flash method. Disk-type samples (12.7 mm in diameter and 1mm in thickness) were set in an electric furnace. Specific heat capacities were measured with a differential scanning calorimeter. Thermal diffusivity (X, Wm K ) was calculated from thermal diffusivity (a, m s ), density (p, g/cm ) and specific heat capacity (C, J g K ) at each temperature using the following ... 

C848- 76. Young s mouutus was also determined at room temperature by strain gaging a four-point bend specimen. Thermal expansion was measured as a function of temperature with a differential transformer. Thermal conductivity and specific heat were determined as a function of temperature via the laser flash method. ... 

The laser flash method is used for thermal diffusivity measurements. In this technique, a laser is used to pulse one side of a test specimen uniformly. The temperature rise of the other side is measured using an infrared detector. This transient is then used to calculate the thermal diffusivity. While the technique is simple in concept, nonidealities such as heat loss from the front and back surfaces complicate the resulting data analysis, so that fairly complex models need to be used to extract the thermal dilfu-sivity. These calculations can be easily performed by the computers used to run the instruments. 

Thermal difihsivity data are still not commonly available even though this is the ultimate property used in heat transfer calculations and simulations. The lack of data is attributed to the difficulty in making these measurements over a wide range of test conditions. With the availability of modern refinements to the laser flash method, it is anticipated that this situation will change and that our understanding of this important property will improve. 

---