Physical and chemical indicators of carbon materials ：Thermal properties

Thermal properties of graphite materials:

The thermal properties of solid materials are essentially the performance of lattice thermal vibrations in all respects. The specific heat capacity, thermal expansion, and heat transfer of solid materials are directly related to this. The thermal properties of graphite materials include heat capacity, entropy, vapor pressure, thermal conductivity, thermal expansion coefficient, and thermal shock resistance. We mainly introduce three factors: thermal conductivity, thermal expansion coefficient, and thermal shock resistance.

A, thermal conductivity:

In general, thermal conductivity is the efficiency with which a material conducts heat. Graphite is a good thermal conductor. Its thermal conductivity is comparable to that of some metals, but other carbon materials (such as porous carbon, carbon cloth, carbon felt, etc.) are high temperature insulation.

The thermal conductivity of graphite is anisotropic and decreases with increasing temperature, roughly inversely proportional to absolute temperature. The thermal conductivity of carbon graphite materials is related to the degree of graphitization. The higher the degree of graphitization, the higher the thermal conductivity. The thermal conductivity of graphite materials is from several to several dozen times higher than that of carbon materials.

The unit of thermal conductivity is W/mK.

B, coefficient of thermal expansion (CTE):

???The phenomenon that the length of a solid material increases as the temperature increases is called linear thermal expansion. The linear thermal expansion coefficient characterizes the size change of the material under high temperature conditions. The linear thermal expansion coefficient of carbon material is much smaller than that of metal, and the higher the degree of graphitization, the smaller the linear thermal expansion coefficient. Since the dimensional change is small at high temperatures, the carbon graphite material is suitable for use as a high temperature resistant structural material in a high temperature environment.

The unit of coefficient of thermal expansion (CTE) is 10^-6/°C.

C, thermal shock resistance:

???When the material is used at high temperatures, the ability to withstand rapid changes in temperature without damage is called thermal shock resistance (or thermal stability). When the temperature changes drastically, if the material cannot pass the heat away in time, the temperature gradient occurs on the surface and inside of the material, and their expansion and contraction are different to produce internal stress. When the stress reaches the ultimate strength, the material is destroyed. The thermal shock resistance of carbon materials is strong, and the thermal shock resistance coefficient of graphite is much larger than other materials.

Thermal Shock Resistance = Thermal Conductivity × Tensile Strength / Linear Thermal Expansion Coefficient × Young’s Modulus of Elasticity

In order to improve the thermal shock resistance of the product, it should be considered from the aspects of reducing the generation of thermal stress, the development of buffering thermal stress and the ability to enhance the resistance to thermal stress.