Expanded applications of graphite material are expected in the
nuclear and aerospace fields. Such applications result from the
excellence of the chemical, physical, and nuclear properties of
the material. Graphite material, however, has a significant undesirable
property, it gasifies in an oxidizing atmosphere at high temperatures.
There are two methods to improve this undesirable property of
graphite: one is to strengthen the oxidation-resistance of the
graphite crystals and the other is to coat graphite materials
with a high-temperature melting material that has good oxidation-resistance.
In JAERI, the oxidation-resistance of graphite material was improved
with a unique coating of silicon monocarbide (SiC). The coating
is applied by an exchange reaction between the C of the graphite
and the Si of gasified silicon monoxide (SiO). SiO is a volatile
material at elevated temperatures, which enables sufficient Si
to be fed to the reaction. We used 1300 degrees cent. as the temperature
for vaporization of SiO and about 1400 degrees cent. for the reaction.
The SiC formed by this method has a concentration gradient that
decreases from the surface of the graphite. As the gradient of
SiC depends on the reaction temperature, a designed profile of
SiC/C in the coating can be obtained by controlling the temperature.
The coating also shows excellent resistance against thermal and
mechanical shocks as well as the oxidation-resistance. This method
can be applied to graphite material in various sizes when there
is a furnace large enough. |
