Oxidation (and also oxidization) is what my dictionary carries. That must be right because in Italian is ossidazione, the formation of an ossido an oxyde a compound containing oxygen. When something already underwent the chemical process, you say it is oxidized.
Forming oxidization from oxidized sounds a bit clumsy, a bit like saying "the developization of a roll of film" re-forming the noun from the past participle of the connected verb. So Oxidation is the way to go, and in any case it sounds better