Thermal conductivity of diamond

The thermal conductivity of diamond at 300 K is higher than that of any other material, and its thermal expansion coefficient at 300 K is 0.8 x 10". lower than that of Invar (an Fe-Ni alloy). Diamond is a very widc-band gap semiconductor Eg = 5.5 eV), has a high breakdown voltage (I07V cm-1), and its saturation velocity of 2.7 x I01 cm s-1 is considerably greater than that of silicon, gallium arsenide, or indium phosphide. 

Che, J., T. Qagin, W. Deng, and W.A. Goddard, Thermal Conductivity of Diamond and Related Materials from Molecular Dynamics Simulations. Journal of Chemical Physics, 2000. 113(16) p. 6888-6900. 

FIGURE 8.3 Thermal conductivity of diamond as a function of temperature [5]. The solid line represents the T3 behavior. 

The record-high thermal conductivity of diamond makes it an obvious choice for consideration as a substrate for high power electronic devices. One method that has been successful in producing diamond films is chemical vapor deposition (CVD). The CVD diamond films are polycrystalline, but can still have k > 2000Wm" K . The high cost of diamond films still precludes their widespread use. 

Berman, R. (1979) in The Properties of Diamond, edited by J.E. Field, Academic Press, London, p. 3. Discusses the thermal conductivity of diamond and the effect different impurities have on this property. Kingery, W.D., Bowen, H.K., and Uhlmann, D.R. (1976) Introduction to Ceramics, 2nd edition, Wiley, New York, pp. 583-645. A very detailed chapter on thermal properties. The discussion of photon conductivity and the thermal properties of glasses are covered in more depth than we do. 

Returning to diamonds, the high thermal conductivity of diamonds is certairrly mysterious. In physics, a rale called the Wiedemann-Franz law states that the electric conductivity of a substance is proportiorral to the thermal conductivity. Briefly put, this law says that good thermal condrrctors are good electrical conductors attire same time. Strictly speaking, this is orrly true for metals. The best coimteiexarrrple... 

The flank wear s tool-life curve of in dry turning of diamond tool for Al-20 mass% Si alloy is presented in Figure 11.2.12 1191. In comparison with the cemented carbide, the diamond tool shows superior cutting performance. This is due to extremely high hardness and superior thermal conductivity of diamond. The diamond is suitable material for machining such non-ferrous alloys. 

IB-SB The thermal conductance of diamond is very high. Would you suspect that its electrical conductance would also be high Briefly explain your answer. 

By the same token, as the ambient temperature increases, the number of collisions increases, and the thermal conductivity of most materials decreases. A plot of the thermal conductivity versus temperature for several materials is shown in Fig. 4.9 One material not plotted in this graph is diamond. The thermal conductivity of diamond varies widely with composition and the method of preparation, and is much higher than those materials listed. Diamond will be discussed in detail in a later section. Selected data from Fig. 4.9 was analyzed and extrapolated into binomial equations that quantitatively describe the thermal conductivity versus temperature relationship. The data are summarized in Table 4.3. 

The classical approach of conduction does not include the above time lag concept or the wavelike response. It expects a delta function-like response of temperature without any time lag with respect to the applied heat pulse. In the classical approach, we use phenomenological models which do not require any knowledge of the mechanism of energy transport or the microstructure of the solids. Fourier s law of heat conduction uses thermal conductivity as a material property which is a function of temperature. This thermal conductivity depends on the microstructure of the solids, which the thermal conductivity data does not show. For example, thermal conductivity of diamond can span an order of magnitude depending on the type of microstructure obtained by chemical vapor deposition. Thermal conductivity of natural... 

Thermal conductivity data is presented in Figure 3. At 70% diamond content the thermal conductivity was measured at 447 W/m K. The reference used for the thermal conductivity of diamond in Table I lists pure diamond at 2200 W/m K. Examining the theoretical mr el, Equation 1, developed by Hasselman and Johnson, it is clear that the diameter of the particles and the thermal boundary conductance both have a large influence on the composite thermal conductivity. 

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