Thermal conductivity data of carbon-carbon composite materials (2)

All the materials were initially prepared by prepregging the fabric/3D preforms with a phenolic resin and molding into carbon-phenolic composites. The phenolic resin was then converted into the carbon matrix by inert-environment pyrolysis. A variety of densification methods was used to increase the densities of these composites to desired levels. Phenolic resin was the matrix for about one-third the materials. CVI-deposited pyrolytic carbon was the matrix for another third. Two Tohr, Inc., densification processes, designated by them as Low-pressure Pitch impregnation and carbonization (LoPIC) and hybrid, were used on the remaining third of the materials. In the LoPIC process, both phenolic resin and pitch are used as matrix material. The hybrid process is a combination of using CVI and LoPIC processes.

The fiber heat treatment temperature and maximum composite fabrication temperature are also given in the table. For material specimens 1 through 18, the fabric had heat treatment temperatures of 2273K except the three made by the Boeing company and Rohr which were heat treated at 2423K. The maximum composite fabrication temperature was either 1173 K or 1923K except for specimen 15; this material had been coated at a temperature of about 2033K. In order to get a more direct comparison of results between the uncoated materials in the original set of 18, the decision was made that the finished composite materials (1-10 and 16-18) should all be conditioned to the same final temperature. The finished composites were heated to the fiber heat treatment temperature of 2273K. None of the commercial materials (11-15) were conditioned, since the thermophysical property data would not be representative of off-the-shelve commercial material. The fiber heat treatment temperature for material specimens 19 through 26 was 2623K and the CVI densification was done at 1323K. The fibers in both material specimens 27 and 28 were heat treated to 2273K. Material 27 had a maximum composite fabrication temperature of 2373K, whereas material 28 had a maximum composite fabrication temperature of 2973K.

The tenth column in table 1 indicates whether the material contained inhibitors and/or had been coated. The three Boeing/Rohr materials are the only ones to have inhibitors. The nomenclature of 0.2 FAW designates 20 percent by fabric areal weight. Two of the Boeing/Rohr materials (12 and 13) and material 15 are the only three coated materials. The next to last column lists the direction in which the thermophysical properties were measured. Coated materials were only measured in the through-the-thickness direction for reasons discussed in the next paragraph. The last column gives additional information on the construction of the 3-D and stitched materials.

The thermal diffusivity was measured by the flash diffusivity method, which basically consists of subjecting one side of a sample to a single laser flash and then monitoring the transient temperature response on the other side. A round specimen, 0.45 inch in diameter, was used for through-the-thickness direction measurements. For in-plane measurements, a square specimen was used. This square specimen was fabricated by cutting rectangular pieces 0.118 inch wide by 0.340 inch high and then stacking sufficient pieces together in the thickness direction to make the stack approximately 0.340 inch thick. In-plane diffusivity measurements were not made on the three coated materials because the stacking of the rectangular pieces required for the in-plane specimen would have left column of coating within the stacked thickness and thus would have invalidated the measurement. Data were taken in increments of approximately 373K from room temperature to 1938K for material specimens 1 through 26 and to 2448K for material specimens 27 and 28. The data reported by Hasselman to LaRC were temperature and thermal diffusivity.


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