Thermal conductivity of nanocomposites based on diamonds and nanodiamonds S.V. Kidalov ⁎ , F.M. Shakhov, A.Ya. Vul' Ioffe Physico-Technical Institute of the Russian Academy of Sciences, Russia, 26 Polytechnicheskaya str., St.Petersburg, 194021 Russia Received 24 October 2006; received in revised form 27 June 2007; accepted 9 July 2007 Available online 14 July 2007 Abstract The thermal conductivity of composites sintered from natural microdiamond (5–7 and 10–14 μm) and nanodiamond powders under pressure of ∼ 6.0 to 6.5 GPa at the temperature ∼ 1000 to 2000 °C for 6–20 s was measured in a steady heat flow in the temperature range of 50–200 °C. It was found that the thermal conductivity of nanodiamond composites produced in these conditions was less than 10 W/(m ⁎ К) while that of natural microdiamonds was as high as 500 W/(m ⁎ К). © 2007 Elsevier B.V. All rights reserved. Keywords: Nanodiamond; Thermal conductivity; Diamond composite 1. Introduction Natural diamond is known to have the highest thermal conductivity. For single crystal diamond of the IIa type, it is as high as 2200 W/m ⁎ К. This parameter, however, strongly depends on the crystallinity and the concentration of impurities such as nitrogen [1]. The characteristic value for single crystal diamond appears to be 1200 W/(m ⁎ К), which is over three times greater than that of copper at 20 °С, about 390 W/(m ⁎ К). According to available data, the conductivity of diamond- copper composites does not exceed 600 W/(m ⁎ К) with the thermal expansion coefficient about 3 ppm/K. There are reports of diamond-copper composites with the thermal conductivity of 700 W/(m ⁎ К) and more [2]. Diamond sintering occurs under milder conditions than in direct graphite-diamond transition, namely, at ∼ 7 GPa and ∼ 2000 °C. When the sintering is carried out at 8.5 GPa and 2170 °С for 3 min, the composite density is found to be 3.48 g/cm 3 , i.e. 99% of diamond density [3]. At the same time sintering of 20 μm diamonds with high nitrogen content at 770–1800 °C and 8 GPa can produce samples with 160 W/(m ⁎ K) and low composite density 3.3 g/cm 3 and 3.5 g/ cm 3 after 25 h chloric acid etching of sp 2 -phase at 100 °C [4]. Samples density doesn't depend on sintering conditions in a very wide temperature range [4]. It was reported in [5] that nanodiamonds sintered at high static pressure and temperature produce composites with a high hardness, 55–65 GPa, and density of 2.5–2.7 g/cm 3 . It was reported in [6] that nanodiamonds sintered at 8 GPa and 1550 °C produce composites with density of 2.45–2.8 g/cm 3 . At the highest value of density equal to 2.86 g/cm 3 the hardness was 28 GPa. The authors of [7] studied the thermal conductivity of diamond-carbon composites containing 6 nm diamond grains embedded into an sp 2 -bonded carbon matrix formed in a CVD process. The composite density was found to be 1.0–1.55 g/cm 3 and the thermal conductivity varied from 0.3 to 1.7 W/(m ⁎ К), depending on the sp 2 /sp 3 phase ratio. The aim of the present work was to sintered nanodiamond composites with a high thermal conductivity. 1.1. Experimental techniques The sintering was carried out in a high pressure toroid-type chamber of 0.26 cm 3 in volume, using a press with the axial force of 5 MN. AC current at 50 Hz in the electric power Available online at www.sciencedirect.com Diamond & Related Materials 16 (2007) 2063 – 2066 www.elsevier.com/locate/diamond ⁎ Corresponding author. Tel.: +7 812 2927377; fax: +7 812 2970073. E-mail address: Kidalov@mail.ioffe.ru (S.V. Kidalov). 0925-9635/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2007.07.010