Facilities & Laboratories
Thermal Properties Laboratory
The Thermal Properties Laboratory is a state-of-the-art facility for integrated thermal properties measurements on unirradiated or irradiated materials. The laboratory offers thermal diffusivity and thermal expansion test capabilities, as well as a variety of metrology and sample preparation capabilities. Thermal properties testing of classified materials can also be accommodated.
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 for testing from 300 to 1500°C in vacuum or inert gas. The low-temperature unit uses 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.
Thermal Expansion Testing
A complementary thermal expansion testing capability also exists in the Thermal Properties Laboratory. Thermal expansion tests are performed in inert gas over a temperature range from room temperature to 1500 °C. Thermal expansion is measured using a horizontal dual alumina-pushrod dilatometer that utilizes absolute displacement transducers for simplicity of operation and increased reliability. Standard thermal expansion tests can be conducted with any combination of heating and cooling rates. The furnace can also hold temperatures to within a few degrees for any length of time to allow equilibrium thermal expansion tests or in-situ sintering or annealing studies.
The system is completely automated and can accommodate testing of two samples simultaneously. Samples may be tested individually or they may be tested in comparison to a standard for more precise thermal expansion measurements. The standard sample length is 38 mm, but lengths from 13 to 65 mm can be accommodated with custom fixturing. Samples can have round, rectangular, or other irregular cross-sections up to a maximum diameter of 10 mm. Irradiated or unirradiated samples may be tested in this system without risk of cross-contamination.
Previous testing experience includes thermal expansion measurements on monolithic ceramics, ceramic composites, metals, alloys, and metal-matrix composites. In addition, the system has been used for isochronal annealing tests on irradiated high purity silicon carbide specimens for the purpose of determining irradiation temperature. Used in conjunction with the thermal diffusivity systems, the isochronal annealing tests on irradiated materials offers complementary data that can help to determine irradiation damage mechanisms and irradiation-induced defect structures. The system also has been used to measure, in-situ, the shrinkage of pre-ceramic polymer joints in SiC during curing and pyrolysis.
Radioactive Materials Characterization and Handling
The Thermal Properties Laboratory provides other capabilities that are necessary to support the thermal properties testing activities. Principal among these is an extensive metrology capability for precise dimensional measurements on unirradiated and irradiated materials.
This capability has been used extensively for measuring irradiation-induced swelling in ceramics, ceramic composites, and ceramic fibers. A radioactive-material glovebox is available for activities such as preparing metallography samples and metrology of dispersible radioactive materials. A large fume hood is available for work with chemicals or less-dispersible radioactive materials. Two lead-shielded caves are available for safe and secure storage of radioactive materials.