Oxidative Vaporization Kinetics of Cr[sub 2]O[sub 3] in Oxygen from 1000° to 1300°C

Abstract

Rates of oxidative vaporization of Cr208 on preoxidized resistively heated chromium were determined in flowing oxygen at a pressure of 0.115 Torr for temperatures from 1000 ~ to 1300~ Reaction controlled rates were obtained from experimental rates by a gold calibration technique, and these rates were shown to agree with those predicted by thermochemical analysis. The activation energy obtained for the oxidative vaporization reaction corresponded numerically with the thermochemical enthalpy of the reaction. A theoretical equation is given for calculating the rate from thermodynamic data using boundary-layer theory. Grimley et al. (11) subsequently identified this mole-) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.129.120.3 Downloaded on 2015-05-30 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.129.120.3 Downloaded on 2015-05-30 to IP I T h e r m o d y n a m i c data for Cr(g), CrO(g), and e r o s ( g ) w e r e taken from Schlck (24). Data for Cr2Oa(s) w e r e calculated f r o m h G ' f values given by Wicks and ]]lock (31). T h e r m o d y n a m i c data for CrO~(g) and the " n e w " chromium-oxygen molecules are given in the following paper (16).) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.129.120.3 Downloaded on 2015-05-30 to IP

Influence of Chromium Carbides on the High Temperature Oxidation Behavior and on Chromium Diffusion in Nickel-Base Alloys

“…Second, the values obtained for K v , are of the same order of magnitude as volatilization constants previously measured by other techniques directly on Cr 2 O 3 , 37 · 10 À10 g cm À2 s À1 (1,1008C) and 124 · 10 À10 g cm À2 s À1 (1,2008C) [16], and 83 · 10 À10 g cm À2 s À1 (1,1008C) and 280 · 10 À10 g cm À2 s À1 (1,2008C) [17].…”

Chromium Volatilization Rates from Cr2O3 Scales into Flowing Gases Containing Water Vapor

“…Conventional boilers operate at maximum steam pressures of 120-150 atm (12)(13)(14)(15) in their superheaters. Supercritical boilers have superheater pressures of $240 atm (24 MPa).…”

“…One suggested explanation is the doping of Cr 2 O 3 by hydrogen species deriving from the gas. 8,9 Another suggestion is that of volatile Cr-bearing species, such as CrO 3 (g), or CrO 2 (OH) 2 (g) being formed [10][11][12] at high temperature, and depleting the scale in Cr. More recently, it has been discovered that water vapor has adverse effects on chromia formers at much lower temperatures, [5][6][7]13 where the oxy-hydroxide is the predominant volatile species.…”

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“…Jianian et al 8 investigated the mechanism of breakaway oxidation in Fe-Cr alloys at 1173 K in wet oxygen, and they suggested that microchannels or microcracks in the initially formed Cr 2 O 3 scale enabled [9][10][11][12][13][14][15] . Asteman et al [14][15] reported that evaporation of chromia occurred during oxidation of Type 304L at 873 K in humid oxygen.…”