Variations in orientation of etch pits on graphite surfaces

A study has been made of the dependence of etch-pit shape upon oxidizing temperature for oxygen and for nitric oxide. For nitric oxide it has been established that, at 873°c, rates of oxidation in <100> and in <110> directions are comparable since dodecagonal pits are obtained on the {0001} surfaces. Below and above this temperature the etch pits are hexagonal, being respectively [parallel] and [perpendicular] to the twin lamellae (sides of pits are in <100> and <110> directions respectively). For oxygen [parallel] and [perpendicular] pits have also been observed, and the temperature at which the rates of oxidation in <100> and in <110> directions are comparable lies beyond 900°c.