THE MECHANISM OF OXIDATION OF IRON AND COBALT IN CARBON MONOXIDE-CARBON DIOXIDE MIXTURES (thesis)

Technical Report · Tue May 01 04:00:00 EDT 1962

OSTI ID:4829140

Pettit, F S

The oxidation of iron and cobalt in carbon monoxidecarbon dioxide mixtures was studied in the temperature ranges 700 to 1100 deg C and 920 to 1200 deg C, respectively. The kinetics of oxidation were determined through use of an automatic recording vacuum balance. The mechanism of oxidation was ascertained through the analysis of kinetics and by marker studies, x-ray analysis and metallographic examination of oxidized specimens. The oxidation kinetics of iron were linear for oxide thicknesses less than 2 x 10/sup -2/ cm and parabolic for larger oxide thicknesses. The linear oxidation rate was found to be a linear function of the mole fraction of CO/sub 2/ in the gas phase and the sum of the partial pressures of CO and C0/sub 2/ between 0.4 and 1.0 atmosphere pressure. These data confirmed the rate-determining step for the linear kinetics to be the dissociation of carbon dioxide into carbon monoxide and adsorbed oxygen atoms or ions in accordance with a mechanism proposed by C. Wagner. Linear kinetics were eventually replaced by parabolic kinetics because the rate of diffusion of iron ions across the oxide became slower than the rate of dissociation and adsorption of the gas phase. The oxidation kinetics of cobalt were linear for oxide thicknesses less than 7 x 10/sup -4/ cm and parabolic for larger oxide thicknesses. The linear oxidation rate, for oxide thicknesses between 4 x 10/sup -6/ and 7.3 x 10/sup -5/ cm was found to be a linear function of the mole fraction of CO/sub 2/ in the gas phase for temperatures between 1000 to 1200 deg C and 1 atm pressure. These data are in accordance with the mechanism proposed by C. Wagner. Parabolic kinetics were observed at oxide thicknesses greater than 7 x 10/sup -4/ cm since diffusion of cobalt ions across the oxide becomes slower than the phase boundary reaction. Oxygen ion diffusion was found not to occur in the oxidation of cobalt. The linear kinetics which are observed for the oxidation of iron in CO- CO/sub 2/ mixtures, were found to be dependent upon the size and orientation of grains in the oxide. For thin oxides, the size and orientation of oxide grains were controlled by the metal substrate. For thick oxides, a textured oxide surface was formed as a resuit of lateral growth of fast growing oxide grains. (auth)

• Research Organization: Yale Univ., New Haven
• NSA Number: NSA-16-020360
• OSTI ID: 4829140
• Report Number(s): NYO-10289
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

CARBON DIOXIDE
CARBON MONOXIDE
CHEMISTRY
COBALT
COBALT OXIDES
DECOMPOSITION
DIFFUSION
EXPANSION
GRAIN SIZE
HIGH TEMPERATURE
INSTRUMENTS
IRON
IRON OXIDES
METALLOGRAPHY
MIXING
OXIDATION
PRESSURE
REACTION KINETICS
RECORDING SYSTEMS
VACUUM
WEIGHT
X RADIATION