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Carbon and Graphite have the following unique characteristics

  • Carbon and Graphite have the following unique characteristics

DATA1 HAVE THE FOLLOWING UNIQUE CHARACTERISTICS

  1. Good electrical conductivity and high thermal conductivity
  2. Low thermal expansion resulting in high thermal shock resistance
  3. Strength at high temperatures
  4. Chemical inertness and non-wetting to glass and most metals
  5. Self lubricity
  6. Appropriate machinability

1.Specific Resistance vs Temperature

Relative specific resistance

One of the most useful characteristics of graphite is its ability to carry electric current. Its resistivity alightly decreases when temperature rises up to 400 to 600°C but increases, though slightly, over this temperature range. The resistivity of graphite can be controlled by modifying raw materials and manufacturing process to meet broad requirements.

Graphite has an exceptionally conductivity. Roughly it is one-third that of copper, half that of aluminum and twice that of steel at room temperature.

2.Comparison of Thermal Expansion Coefficient

The expansion of graphite is considerably lower than that of practically all other materials. The high thermal shock resistance of graphite results principally from the low coefficient of thermal expansion and good thermal conductivity. The thermal shock resistance is shown in the following formula.

R=K.S/αE

K: Thermal conductivity (W/mK)

S: Tensile strength (MPa)

α: Coefficient of thermal expansion ( ×10-6 /°C)

E: Young's modulus (GPa)

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3.Temperature Dependence of Strength

The mechanical strength of increases as temperature rises and the strength will be approximately double from room temperature to about 2,500°C.

compressive strength

=2×flexural strength

The flexural strength and compressive strength have roughly the above correlations.

4.Reaction Temperature of Graphite

Graphite is resistant to most acids and alkali except for strong oxidizing media like concentrated nitric acid, etc and media to create lamellar compound like concentrated sulfuric acid, strong alkali and bromine etc.

Graphite is chemically stable under normal conditions. But at high temperatures, it will react with some atmosphere and metals as shown in the left.

Graphite does not ordinarily adhere to molten glass and most molten metals.

Atmosphere/Metals Temperature State of graphite
Air 400 Oxidation
Steam 700 Oxidation
Hydrogen 1,100 CH4 gas
Vacuum 2,200 Vaporization
Nitrogen 2,500 C2N2
Al 800 Al4C3
B 1,600 B4C
Fe 600-800 Fe3C
W 1,400 W2 C, WC

(Cu, Mg, PB and Sn do not react.)

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