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Title: High-Thermal-Conductivity Densified Graphitic Foams as Novel Bearing Materials

Abstract

The high-thermal-conductivity graphitic foams (foam-reinforced carbon-carbon composites) developed at ORNL have been mainly used for thermal management, as in heat sinks for electronic circuit boards and highly-efficient automotive radiators. However, recent studies in our laboratory have rather unexpectedly revealed their potential as novel bearing materials. In addition to their low density and potential for weight savings, there are three primary tribological advantages of the graphitic foam materials: (1) their graphitic structures provide self-lubricating qualities, (2) their extraordinarily high thermal conductivity aids in the efficient removal of frictionally-generated heat, and (3) the pores in the foam serve both as wear debris traps and lubricant reservoirs. Previous studies on the densified graphitic foam (DGF) sliding against steel and alumina at relatively low speed (1 m/s) and low load (10 N), revealed their encouraging self-lubricating behavior, comparable to solid graphite while much better than bronze and polytetrafluoroethylene (Teflon{trademark}). In this study, pin-on-disk tests with higher speeds (2, 6, and 10 m/s) and higher loads (322 N) were conducted on DGF and graphite disks sliding against a DGF pin. The surface temperature on the graphite disk increased rapidly due to frictional heating and the friction coefficient increased proportionally with surface temperature when it wasmore » higher than 40 C. The DGF disk, however, ran much cooler due to the higher thermal conductivity, and more impressively, the friction coefficient remained low and constant even at elevated disk temperatures. This suggests high potential for the graphitic foam material in weight-sensitive, high-speed, and elevated temperature bearing applications.« less

Authors:
 [1];  [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1003288
DOE Contract Number:
AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Journal Volume: 27; Conference: the 30th International Conference & Exposition on Advanced Ceramics & Composites, Cocoa Beach, FL, USA, 20060122, 20060127
Country of Publication:
United States
Language:
English

Citation Formats

Qu, Jun, Blau, Peter Julian, Klett, James William, and Jolly, Brian C. High-Thermal-Conductivity Densified Graphitic Foams as Novel Bearing Materials. United States: N. p., 2006. Web. doi:10.1002/9780470291313.ch66.
Qu, Jun, Blau, Peter Julian, Klett, James William, & Jolly, Brian C. High-Thermal-Conductivity Densified Graphitic Foams as Novel Bearing Materials. United States. doi:10.1002/9780470291313.ch66.
Qu, Jun, Blau, Peter Julian, Klett, James William, and Jolly, Brian C. Sun . "High-Thermal-Conductivity Densified Graphitic Foams as Novel Bearing Materials". United States. doi:10.1002/9780470291313.ch66.
@article{osti_1003288,
title = {High-Thermal-Conductivity Densified Graphitic Foams as Novel Bearing Materials},
author = {Qu, Jun and Blau, Peter Julian and Klett, James William and Jolly, Brian C},
abstractNote = {The high-thermal-conductivity graphitic foams (foam-reinforced carbon-carbon composites) developed at ORNL have been mainly used for thermal management, as in heat sinks for electronic circuit boards and highly-efficient automotive radiators. However, recent studies in our laboratory have rather unexpectedly revealed their potential as novel bearing materials. In addition to their low density and potential for weight savings, there are three primary tribological advantages of the graphitic foam materials: (1) their graphitic structures provide self-lubricating qualities, (2) their extraordinarily high thermal conductivity aids in the efficient removal of frictionally-generated heat, and (3) the pores in the foam serve both as wear debris traps and lubricant reservoirs. Previous studies on the densified graphitic foam (DGF) sliding against steel and alumina at relatively low speed (1 m/s) and low load (10 N), revealed their encouraging self-lubricating behavior, comparable to solid graphite while much better than bronze and polytetrafluoroethylene (Teflon{trademark}). In this study, pin-on-disk tests with higher speeds (2, 6, and 10 m/s) and higher loads (322 N) were conducted on DGF and graphite disks sliding against a DGF pin. The surface temperature on the graphite disk increased rapidly due to frictional heating and the friction coefficient increased proportionally with surface temperature when it was higher than 40 C. The DGF disk, however, ran much cooler due to the higher thermal conductivity, and more impressively, the friction coefficient remained low and constant even at elevated disk temperatures. This suggests high potential for the graphitic foam material in weight-sensitive, high-speed, and elevated temperature bearing applications.},
doi = {10.1002/9780470291313.ch66},
journal = {},
number = ,
volume = 27,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}

Conference:
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  • Approximately two thirds of the world's energy consumption is wasted as heat. In an attempt to reduce heat losses, heat exchangers are utilized to recover some of the energy. A unique graphite foam developed at the Oak Ridge National Laboratory (ORNL) and licensed to Poco Graphite, Inc., promises to allow for novel, more efficient heat exchanger designs. This graphite foam, Figure 1, has a density between 0.2 and 0.6 g/cm 3 and a bulk thermal conductivity between 40 and 187 W/m{center_dot}K. Because the foam has a very accessible surface area (> 4 m 2 /g) and is open celled, themore » overall heat transfer coefficients of foam-based heat exchangers can be up to two orders of magnitude greater than conventional heat exchangers. As a result, foam-based heat exchangers could be dramatically smaller and lighter.« less
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  • Means to characterize and measure morphology which affects the solid and radiative contributions in closed cell foams have been developed. From measured two-dimensional intercept area distributions, the actual cell size distribution is calculated. For each of the small-celled polyurethane foams examined, the distribution is narrow, close to the mean cell diameter. From numerical analysis of extreme cell segregation, less than 13% error in the extinction coefficient and the radiative contribution calculated from the mean cell diameter is expected due to cell size distribution. A means to measure the fraction of solid in the strut from strut cross sectional areas ismore » derived. For the small-celled foams analyzed, the fraction of solid in the strut decreases from 0.67 to 0.34 as mean cell diameter decreases from 0.363 mm to 0.109 mm. Smaller celled foams which show a redistribution of polymer from the struts to the cell walls as cell size decreases will exhibit a larger solid conductivity which may counterbalance the decrease in radiation which accompanies the small cell size.« less