It is therefore suggested that the increased erosion of mica in air can best be explained
by nitric acid, formed in the discharge environment, causing surface erosion by an
acid reaction mechanism on the mica. This mechanism would also account for the
presence of metallic elements from the electrode at the degraded surface, found during
the experimental programme, as the electrode too would suffer similar erosion.
As damage was observed in both gaseous environments, however, a second degradation mechanism had to be postulated to account for degradation in nitrogen. Given