handbook of carbon, graphite, diamond and fullerenes

4.2 Chemical Properties
Vitreous Carbon 133
In most cases, the chemical properties of vitreous carbon are similar
to those of the graphite crystal, reviewed in Ch. 3, Sec. 7. Since the material
has low permeability, is essentially non-porous and free of surface defects,
and can be made with very low impurities, its resistance to chemical attack
is generally excellent and is one of its outstanding characteristics. In many
instances, it is far more chemically resistant than other forms of carbon,
such as molded or pyrolytic graphites.
The presence of impurities (ashes) is very critical. For instance, the
rate of oxidation increases by approximately an order of magnitude when
the amount of impurities increases by the same ratio, as shown in Fig. 6.7.E 7 !
Thisfigure also shows thatthe oxidation of vitreous carbon is much Iessthan
that of molded graphite.
Vitreous carbon does not react with nitric, sulfuric, hydrofluoric, and
chromic acids. It is not attacked by halogens such as bromine, even at high
temperatures, as opposed to other graphitic materials which are attacked
rapidly.t 8 ' Its rate of reaction with various reagents is shown in Table 6.3.
Temperature °C
800 750 700 650 600
a) Vitreous carbon,20 ppm impurities
b) Vitreous carbon, 200 ppm impurities
c) Fine-grain graphite
d) Baked carbon
Figure 6.7. Oxidation rate of vitreous carbon and other carbon products.t 7 '