Properties of isotropic pyrolytic carbon

As mentioned above, the structure of pyrolytic carbon is essentially isotropic and so are its properties. These are summarized in Table 7.3.

Hardness: Being composed of minute crystallites with essentially random orientation, isotropic pyrolytic carbon lacks the easy interlayer slippage which is characteristic of the well-oriented laminar or columnar structures of pyrolytic graphite. As a result, it is considerably harder. This makes it easy to polish and the material can be given a high gloss. The wear resistance is usually superior to that of the columnar and laminar deposits of vitreous carbon.

Mechanical properties: Isotropic pyrolytic carbon is stronger than the oriented pyrolytic graphites and vitreous carbon and can ba considered as a reasonable structural material, comparing favorably with some of the more brittle ceramic materials.

Table 7.3: Properties of isotropic pyrolytic carbon at 25C.

Density, g/cm3 2.1
Vickers DPH hardness, kg/mm2 240-370
Flexural stength, Mpa 350
Young’s modulus, Gpa 28
Strain to failure, % 1.2
DPH: diamond pyramid hardness

Gas permeability: Isotropic pyrolytic carbon provides a better barrier to gases than the more crystalline pyrolytic graphites. The permeability, K, is as follows:

Isotropic pyrolytic carbon: 10-6 to 10-15 cm2.s

Pyrolytic graphite: 10-2 to about 10 cm2.s

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