Process for making an oxide-layer

Claim 1

A process of producing an oxide layer consisting predominantly of Fe 3 0 4 on an iron surface in an oxidizing atmosphere and at a temperature between 500° to 600° C. whereby the oxidizing atmosphere of combustion gases is produced by understoichiometrically burnt natural fuel gas or other fuel gases producing CO when burnt, comprising the following process steps: (a) controlling the combustion of the fuel gases by cooling the combustion chamber to maintain an apparent reaction temperature of from 500° to 800°C. in the combustion chamber to form the combustion gases; (b) without cooling to remove water from said combustion gases subsequently conveying the latter into a heated blackening chamber while maintaining constant the mass of the combustion gases and maintaining the temperature substantially above the dew point of the combustion gases; (c) producing a blackened oxide layer on the iron surface in the blackening chamber by contacting the iron surface with the combustion gases; and (d) monitoring the proportion of CO in the combustion gases after burning of the gases producing CO with a sensing means and controlling the air and fuel supplies by a control means in accordance with the measured values of the CO concentration.