Development of a System for Measuring Thermal Diffusivity of Thin Films by Laser Flash Method Based on a New Principle.

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A laser flash method for measuring thermal diffusivity in the direction parallel or perpendicular to the sample surface of film has been developed. On measurement of parallel direction of a sample, a pulsed laser beam which has narrow line-shaped cross section is flashed onto the front surface of the sample. The temperature response at the back surface at a certain distance away fro the line-shaped illuminated area of a laser beam is measured by the infrared detector and the thermal diffusivity value can be dete mined by comparing measured temperature response curve with theoretical one. On the other hand, the measurement of thermal diffusivity in the direction perpendicular to the sample surface of a film, a pulsed laser beam whose diameter is about 10 mm, is flashed onto the front surface of the sample. The temperature response at the back surface is measured by the infrared detector. The thermal diffusivity value can be determined by comparing with the theoretical solution including … More a pulse duration. The usefulness the present method has been demonstrated by measuring successfully thermal diffusivities of metallic foil samples of platinum (25 mum copper (18 mum), SUS304 stainles s steel (50 mum) and nickel (130 mum).Ruby lasers usually employed in the laser flash method for measuring thermal diffusivity of various inorganic substances a known to have the inhomogeneous energy distribution and their particular spatial intensity structure significantly effects the quantitative accuracy of the resultant thermal diffusivity data in some cases. Random packed fiber bundle made of plastic optical fiber wi plastic optical guiding rod has been developed for homogenizing the energy distribution in a laser beam on the specimen surface. T usefulness of this new device has been well approved by measuring the energy distribution and the thermal diffusivity of nickel disc.A simple cell and easy data processing have been proposed for measuring the thermal diffusivity of a liquid sample at high temperatures using the laser flash method. A cell consists of a liquid sample sandwiched by two metallic plates. The front surface one metallic plate is exposed to a single pulse of beam laser and the resulting temperature rise of the back surface of the other metal plate is measured. The logarithmic analysis proposed by James using the initial time region of the temperature response curve of a two layered cell system has been extended to apply to the present three layered cell system in order to estimate the thermal diffusivity value of a liquid sample. Measurements of distilled water and methanol were made first and the results were found to be in good agreement with the reference data. Then, the thermal diffusivities of molten NaNO_3 at 593-660 K and of molten KNO_3 at 621-694 were determined and the results also appear to agree reasonably well with those reported in the literature. Less