Kinetics and mechanism of reaction between water vapor, carbon monoxide and a chromia-forming nickel base alloy

Abstract

The kinetic aspects of the competitive reaction of CO and H 2 O in the formation of chromia layer on a nickel base alloy at high temperature were studied by thermogravimetry combined to gas phase chromatography. It was shown that competitive adsorption occurred between both molecules and that whatever P CO /P H2O ratio, CO mainly reacted in the first instants of oxidation and H 2 O became the main long-term oxidant species. After an interfacial and diffusion mixed kinetic regime, the long-term oxidation rate was parabolic and did not depend on the water vapour content in the gas phase. The oxidation kinetics was well described by considering that the rate limiting step was the outwards diffusion of interstitial chromium cations in the oxide layer.

Preparation of Inconel 740 superalloy by electron beam smelting

“…The metal-deficit oxides such as Cr, and Ti oxides grow outward by the outward diffusion of metal cations to react with the oxygen, therefore, they mostly concentrate on the above and within the very top portion of the surface [18]. On the other hand, the oxygendeficit oxides such as Al and W oxides grow at the expense of oxygen anions diffused from the surface to the interface [19].…”

Oxidation behavior of GTD111 Ni-based superalloy at 900 °C in air

“…The resultant relative charge difference in the oxide becomes the driving force for oxidation, and controls the kinetics of the oxidation process. The metal-deficit oxides such as Ni, Cr and Ti oxides grows outward from the surface of the component by the outward diffusion of metal cations to react with oxygen at the oxide / gas interface [28]. On the other hand, the oxygen-deficit or n-type oxides such as Al ,W and Ta oxides grows inward from the surface by the diffusion of oxygen anions to react with metal cations at the oxide / metal interface [20].…”

Oxidation Behavior of the Nickel-Based Superalloy DZ125 at 980 °C

“…The resultant relative charge difference in the oxide becomes the driving force for oxidation and controls the kinetics of the oxidation process. Accordingly, the metaldeficit oxides such as Ni, Cr oxides grew outward from the surface of the alloy by the outward diffusion of metal cations to react with oxygen at the oxide/gas interface [13,17,21]. While the oxygen-deficit or n-type oxides such as Al, Ta oxides grow inward from the surface by the diffusion of oxygen anions to react with metal cations at the oxide/metal interface [14,17,22].…”