Abstract: A method for generating highly concentrated ozone gas by adsorbing ozone gas generated by an ozonizer with an absorbent within an adsorption column and then separating highly concentrated ozone gas from the adsorption column. Three adsorption columns are arranged in parallel. Each of the adsorption columns is controlled to repeat four steps of an ozone gas adsorbing step, a stabilizing and pressurizing step, an ozone gas desorbing step and a cooling down step. Each of the ozone gas adsorbing step and the ozone gas desorbing step has operation time set twice the operation time of each of the stabilizing and pressurizing step and the cooling down step. An ozone gas concentrating unit comprises three adsorption columns which are set to operate one after another by ⅓ cycle lag. Highly concentrated ozone gas separated at the desorbing step of each adsorption column is once stored in an ozone gas storage vessel.

Abstract: A high-concentration ozone gas having a concentration of at least 50 VOL % of ozone in the ozone-oxygen system is acted within the temperature range of a normal temperature to 60.degree. C. on an ultrapurity-gas piping system for use in a semiconductor manufacturing apparatus and the like or on a metal component part for use in an ultrahigh-vacuum apparatus to form a passivation film on the interior metal surface thereof.