2.12.2.2.1 Thermal conductivity

It is reasonable to assume that the single-crystal form of SiC, compared to the other varieties, exhibits the highest thermal conductivity. However, high-purity and dense polycrystalline CVD SiC exhibits practi­cally the same conductivity as the single-crystal material. It is worth noting that the impurity content of the very high thermal conductivity CVD SiC mate­rials is negligibly small, and this material has near theoretical density (~3.21 gcm—3). The curve-fitting to the single-crystal SiC data above 300 K yields an upper limit of the thermal conductivity of SiC (in Wm—3K—3):

Kp = (-0.0003 + 1.05 x 10—5T)—1 [7]

2.12.2.2.2 Specific heat

The temperature dependence of the specific heat can be treated in two temperature regions: a rapid increase at low temperatures (below 200 K), and a gradual increase at higher temperatures. No system­atic difference can be distinguished between the struc­tural types. The specific heat, Cp (in J kg-1 K), over the temperature range 200-2400 K can be approximately expressed as

Cp = 925.65 + 0.3772T — 7.9259 x 10—5T2

— 3.1946 x 107/T2 [8]

The specific heat of SiC at room temperature is taken as 671 ± 47Jkg~1K.

2.12.2.2.3 Thermal expansion

The coefficient of thermal expansion for p-SiC has been reported over a wide temperature range. The average value in the interval from room temperature to 1700 K is a = 4.4 x 10~6K~

At higher temperatures (T> 1273 K), a = 5 x 10~6K_1

At lower temperatures (550 < T< 1273 K), a = 2.08 + 4.51 x 10~3T