Patent ID: 6524402
Filing Date: 2003-02-25
Classification: B01J,C10G,C23C

Abstract:
A passivation method for the metallic surface of a nickel and iron based superalloy with an expansion coefficient of about 10Ã—10âˆ’6 to about 25Ã—10âˆ’6Kâˆ’1 containing less than 0.5% by weight of aluminum used as a constituent material for the walls of a reactor or furnace, which comprises coating at least one of the surfaces of the superalloy which comes into contact with a corrosive atmosphere containing either hydrocarbons at high temperature or containing oxidizing gases at high temperature, with at least two different successive layers superposed directly on one another,said layers comprising: an external layer which comes into direct contact with the corrosive atmosphere having an expansion coefficient of about 2Ã—10âˆ’6 to about 10Ã—10âˆ’6Kâˆ’1 deposited by chemical vapor deposition of at least one silicon compound and an intermediate layer positioned between the superalloy surface and said external layer, having an expansion coefficient of about 4Ã—10âˆ’6 to about 12Ã—10âˆ’6Kâˆ’1 deposited by chemical vapor deposition of at least one compound of a metal or metalloid, the layer(s) being selected such that the value of the expansion coefficients of the layers decreases from that of the superalloy to that of the expansion coefficient of the external layer.