Diamond thermal conductivity value

CNTs are great heat conductors in the direction of their axis, but are poor thermal conductors in the transverse axis. Measurements indicate thermal conductivity values between 1,000 and 6,000 Wm k [65, 66], comparable to diamond (2,000 Wm k ). The thermal stability of carbon nanotubes is extremely high in non-oxidizing atmospheres MWNTs can withstand up to 2,800 °C [67]. 

Thermal Conductivity. The value of 2000 W/(m-K) at room temperature for Type Ila natural stones is about five times that of Cu, and recent data on 99.9% isotopicaHy pure Type Ila synthesized crystals ate in the range of 3300—3500 W/(m-K) (35). This property combined with the high electrical resistance makes diamond an attractive material for heat sinks for electronic devices. 

In diamond C, it is the fact that the structure consists of sp covalent bonds only that accounts for its unique physical properties, such as the highest hardness of any material (Mohs hardness 10), small compressibility (1.7X10 cm /l ), the highest elasticity among any known material (4 6 X10 dynes/cm, bulk elasticity), large thermal conductivity (9 26 W/(deg cm)), and small thermal expansion coefficient (0.8 0.1 X10 at 20 °C, comparable to the value of invar). As a result. 

The transmission of heat is favored by the presence of ordered crystalline lattices and covalently bonded atoms. Thus graphite, quartz, and diamond are good thermal conductors, while less-ordered forms of quartz such as glass have lower thermal conductivities. Table 7.3 contains a brief listing of thermal conductivities for a number of materials. Most polymeric materials have X values between 10 and 10° W m- K"1. 

Fig. 24. Magnetic field dependence of the electronic thermal conductivity at T - 0, normalized to its value at Hc2- Circles are for LuNi2B2C, squares for UPt3 and diamonds for Nb. Note the qualitative difference between the activated thermal conductivity of the s-wave superconductor Nb and the roughly linear growth seen in UPt3, a superconductor with a line of nodes (Boaknin et al. 2001).

Diamond Hints, although not approaching bulk diamond, are harder than most refractory nitride and carbide thin films, which makes them attractive for tribological coatings. Transparency in the visible and infrared regions of the optical spectrum can be maintained and index-of-refraction values approaching that of bulk diamond have been measured. Electrical resistivities of diamond films have been produced within the full range of bulk diamond, and thermal conductivities equivalent to those of bulk diamond also have been achieved. As substrates for semiconductor electronic devices, diamond films can be produced by both the PACVD and IBRD techniques. 

When determined from the physical constants, the values of the time constant are found to vary because of the appreciable change of the specific heat with temperature. The precision is limited by the uncertainties in the values of the thermal conductivity of powders. Large single diamond crystals have a high thermal conductivity (see Table I), being of the same order of magnitude as for silver... 

It has been known for long that diamond is the material with the largest thermal conductivity (although CNTs in axial direction show even higher values, Section... 

Even good heat conductors such as silver or copper come off badly when compared to diamond. The thermal conductivity of the latter passes through a maximum of 175 W cm" K" at 65 K (about 1 /30 of the Debye temperature). In the range of temperatures about 300 K as relevant for practical applications, the value is still 15-30Wcm" K". ... 

Grayish-white, lustrous, brittle metalloid. Diamond-cubic structure when cryst. Poor conductor of electricity. dj 5.323. Reported melting points range from 925-975 best value 937.2 (Hassion). Vol smaller by a few % when molten, bp 2700. Thermal expansion coefficient (at 25 ) 6.1 X 10 / C. Thermal conductivity (at 25 ) 0.14 cal/sec... 

What makes diamond so attractive, and in many cases unique, is not only the extreme value of some of the above properties such as hardness, thermal conductivity or the Young modulus, but the combination of two or more of these properties in a high performance product, as will be discussed later in this chapter. 

The phase or optical path length variation — (d x /) is a function of radial position in the ZnSe and CVD diamond windows and is shown in Fig. 20. The variation for CVD diamond over the effective beam width is over a factor of 250 smaller. Three factors combine to yield this large difference the smaller temperature rise in CVD diamond due to the higher thermal conductivity (AT a factor of more than 7 smaller in CVD diamond), the smaller value of dn/df for diamond (a factor of 5.8), and the thickness of the window, which for CVD diamond is only l/6th of that in ZnSe. For an example similar to that shown in Fig. 18 the thermal lensing effect in the ZnSe window was found to be equivalent to a lens of 3-5 m focal length, whereas for the CVD diamond window the effect was negligible [27,34]. 

Numerical simulations of the junction temperature increase of a laser diode array have been performed for a package configuration as illustrated in Fig. 33. Calculations have been performed with and without a CVD diamond heat-spreader. The decrease in thermal resistance has been calculated for different values of the heat-spreader thickness, depth and thermal conductivity. The simulations have been performed for an array of laser diodes which are individually 200 pm wide... 

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