Thermal conductivity of individual carbon nanofibers Eric Mayhew, Vikas Prakash * Department of Mechanical Engineering, Case Western Reserve University, 2123 Martin Luther King Jr. Drive, Glennan Building, Cleveland, OH 44106, USA ARTICLE INFO Article history: Received 8 November 2012 Accepted 17 June 2013 Available online 24 June 2013 ABSTRACT In the present paper, we present results of thermal conductivity measurements in commer- cially-available, chemical vapor deposition grown, heat-treated and non-heat-treated indi- vidual carbon nanofibers (CNFs). The thermal conductivity measurements are made using the T-type probe experimental configuration using a Wollaston wire probe inside a high res- olution scanning electron microscope. The results show a significant increase in the ther- mal conductivity of CNFs that are annealed at 2800 °C for 20 h when compared with the non-heat-treated CNF samples. When adjusted for thermal contact resistance, the highest measured thermal conductivity is 449 ± 39 W/m-K. The average thermal conductivity of the heat-treated samples is 163 W/m-K, while the average thermal conductivity of the non- heat-treated samples is 4.6 W/m-K. The results demonstrate the importance of the quality of the CNFs, in particular their heat treatment (high temperature annealing), in controlling their thermal conductivity for thermal management applications. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Although a relatively large body of literature exists for ther- mal conductivity measurements in large diameter carbon fi- bers (CFs) [1–6], only a few measurements of thermal conductivity have been reported in individual carbon nanofi- bers (CNFs) [7]. The individual CFs for which thermal conduc- tivity measurements are available in the literature have outer diameters ranging from 4 to 71.4 lm [1,2], and their room temperature thermal conductivities range from 12 to 1950 W/m-K [1–6]. This relatively large variation in the mea- sured thermal conductivity of CFs can be attributed to the dif- ferences in sample diameter, synthesis method employed, resultant defect structure, and heat treatment [1,2,7]. Here- mans and Beetz [2] were the first to show that heat-treatment of CFs (at 3000 °C) significantly improved their room tempera- ture thermal conductivity. The high thermal conductivity of the heat-treated CFs suggest the potential use of CFs and per- haps CNFs as thermal interface materials [3,4,8]. Most CFs and CNFs are synthesized in any one of the fol- lowing three ways: (1) carbonization of spun polyacrylonitrile (PAN-based fibers), (2) carbonization of spun petroleum pitch (pitch-based fibers), and (3) carbon chemical vapor deposition (CVD), usually using methane or benzene [1]. The simplicity of the CVD process suggests that the production of vapor grown CFs and CNFs can be much less expensive than for their PAN-based and pitch-based counterparts [8]. The oppor- tunity for wide-spread use of CVD grown CNFs along with their potential for dramatic improvement in thermal conduc- tivity by heat treatment provide the motivation for the pres- ent study. While a number of thermal conductivity measurements have been made on heat-treated and non-heat-treated CFs, to the best of authors’ knowledge only one previous study 0008-6223/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2013.06.048 * Corresponding author: Fax: +1 216 368 6440. E-mail address: [email protected](V. Prakash). CARBON 62 (2013) 493 – 500 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon
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