impregnation, carbonization and graphitization. (heat treating) of the preform. The impregnant used for this composite was Ashland Petroleum. Company's A-240 ...
CONF-910645—2 INVESTIGATION INTO THE EFFECT OF HEAT TREATMENT ON THE THERMAL CONDUCTIVITY OF 3-D CARBON/CARBON FIBER COMPOSITES
DE91 010388
Ralph B. Dinwiddie, Timothy D. Burchell, Oak Ridge National Laboratory*, Oak Ridge, TN 37831-6064 Clifford F. Baker, Fiber Materials, Inc., Biddeford Industrial Park, Biddeford, ME 04005
INTRODUCTION The material used in this study was a ci'boncarbon fiber composite manufactured from precursor yarn and petroleum based pitch through a process of repetitive densification of a woven preform. The resultant high temperature-high strength material exhibits relatively high thermal conductivity and is thus of interest to the fusion energy, plasma materials interactions (PMI) and plasma facing components (PFC) communities. Carbon-carbon fiber composite manufacture involves two distinct p r o c e s s e s , preform weaving and component densification. The carbon fiber preform was woven using 2000 filament bundles of P-55 pitch precursor fibers, manufactured by Amoco Performance Products, Incorporated. The longitudinal thermal conductivity of these fibers is reported by the manufacturer to be 120 W/m K. The preform was woven in an orthogonal structure with each unit cell consisting of one fiber bundle in each of the three directions X, Y and Z. The center to center spacing between fiber bundles in the Z direction was 1.22 mm. The Z fiber bundles are spaced 0.889 mm apart (center to center) in both the X and Y directions. The total fiber volume in the preform was approximately 48%. Forty percent of ine fibers were in the Z direction, 30% in the X direction and 30% in the Y direction. The dry woven preform was converted to a d e n s i f i e d c o m p o s i t e by r e p e t i t i v e pitch impregnation, carbonization and graphitization (heat treating) of the preform. The impregnant used for this composite was Ashland Petroleum Company's A-240 petroleum based pitch. The preform was impregnated with molten pitch and heated to 700°C to convert the organic pitch to carbon. The carbonized preform was then heated to 2400°C to graphitize the carbon. During carbonization at standard pressure.
approximately 50% of the pitch is driven off as volatile material, creating porosity which must be filled by repetition of the densification cycle. The preform becomes rigid after one densification cycle and may be subjected to high p r e s s u r e . Therefore, subsequent densification c y c l e s consisted of vacuum impregnation, high pressure (15,000 psi) impregnation and carbonization (HiPIC), which yields 85% carbon rather than the 50% of a standard p r e s s u r e c a r b o n i z a t i o n and grapiiitization to 2400°C. Four HiPIC cycles are used to bring the final composite density above 1.96 g/cm^. In this study three samples were subjected fo an additional heat treatment of 2550. 2750 or 3000°C at Oak Ridge National Laboratory (ORNL) subsequent to their fourih graphitization at 2400°C. It should be noted that no effort was made to optimize the composite for thermal conductivity, but rather only to provide a material with which to evaluate the effect of the final heat treatment temperature on the thermal conductivity. The fiber is the primary source of heat conduction in the composite. Consequently, increasing the fiber volume fraction, and/or the fiber thermal c o n d u c t i v i t y is expected to increase the composite thermal conductivity. EXPERIMENTAL Thermal diffusivity measurements were made using a Holometrix automated laser flash thermal d i f f u s i v i t y (LFTD) system. This technique, first described by Parker et al. [I], employs a high power infrared pulse laser to deliver a short burst of energy to one face of a disk shaped s p e c i m e n . The resulting temperature rise on the opposite face is monitored by an infrared detector and recorded as a function of time by a computerized data acquisition system. The thermal diffusivity may then be calculated from an analysis of this temperature rise
* Research sponsored by the U.S. Department of Energy, Assistant Secretary for Conservation and Renewable Energy, Office of Fusion Energy and Office of Transportation Technologies, as part of the High Temperature Materials Laboratory User Program, under contract DE-AC05-84OR21400 managed by Martin Marietta Energy Systems, Inc. -Th» mbmitiK) m»nu»cnot • * • b—n
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DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United Stales Government or any agency thereof.
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