Thermal Properties Laboratory

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Thermal Diffusivity Testing

The centerpiece of the Thermal Properties Laboratory is a well-established laser flash thermal diffusivity measurement capability.

Two diffusivity test units are available, a low-temperature apparatus for testing from room temperature to 400°C in air, and a high-temperature unit (shown at right) for testing from 300 to 1500°C in vacuum or inert gas. The low-temperature unit utilizes an aluminum-block box furnace, while the high-temperature system uses a tungsten-mesh tube furnace. Temperature control is facilitated by the use of thermocouples located near, but not touching, the test samples.

Thermal diffusivity can be measured on either monolithic, isotropic composites, or layered materials. Samples can vary in size from 6 to 10 mm in diameter, and typical sample thicknesses range from 1 to 3 mm (optimum sample thickness is determined separately for each material based on its expected thermal diffusivity). Square or other cross-sections can be accommodated with custom fixturing. Ideally, the samples should be rigid and opaque, although the use of metallic or carbon coatings to render translucent samples opaque is possible. The high-temperature unit tests one sample at a time, while the low-temperature apparatus tests up to six samples simultaneously.

Data acquisition, reduction, and analysis in both systems is performed computationally in near-real-time using software tailored to specific customer needs. Both systems can accommodate either unirradiated or irradiated materials. The units are maintained and operated such that they remain uncontaminated, and they may be used for unirradiated materials without risk of cross-contamination.

Materials tested in the two systems include depleted-UO2 experimental light water reactor fuels, stainless steels, precious metals, refractory metal alloys, aluminum metal-matrix composites, alumina, zirconia, zirconium carbide, silicon nitride, silicon carbide, alumina particulate-reinforced alumina-matrix composites, silicon carbide particulate- and whisker-reinforced silicon carbide composites, and SiC-based fiber-reinforced SiC-matrix composites. In addition to measuring thermal diffusivity for determination of engineering properties, the systems also have been used to elucidate irradiation damage mechanisms and defect structures via isochronal annealing and in-situ measurement of thermal diffusivity on irradiated materials. The systems also have been used to evaluate the nature of fiber-matrix bonding in fiber-reinforced ceramic-matrix composites in order to optimize the composition and fiber architecture of these materials.

Project Contact: D. Senor