THE PRESSURE DEPENDENCE OF THE LINEAR OXIDATION OF NIOBIUM IN THE TEMPERATURE RANGE 450-1050 C

Journal Article · Sat Jun 01 04:00:00 EDT 1963 · J. Less-Common Metals

DOI:https://doi.org/10.1016/0022-5088(63)90033-X· OSTI ID:4712894

McLintock, C H; Stringer, J

The pressure dependence of the linear oxidation of niobium was studied using both constant-pressure and varyingpressure techniques in the temperature range 450 to 1050 deg C, for pressures in the range 10 to 760 mm Hg of oxygen. Below 600 deg C there is an initial slow linear rate during which a continuous oxide layer forms. After a time, a powdery oxide nucleates on the metal surface bursting through the continuous layer and the reaction accelerates to a faster linear rate. The breakaway time is very variable, but decreases as the temperature is raised, and above 560 deg C is too short to be detectable. The pre-breakaway rate is shown to involve an equilibrium adsorption step, with a low- pressure rate depending on the square root of the pressure. The post-breakaway rate depends on pressure to the power 0.7 to 0.8, and the activation energy of this step is about 17 kcal mole/sup -1/. In the range 600 to 650 deg C the shape of the rate curves changes, the overall rate diminishing. This decrease is shown to be due to a third linear rate appearing at increasingly early times in this range, with a rate depending on the square root of the oxygen pressure and an associated activation energy of 28.0 kcal mole/sup -1/. Above 850 deg C a fourth linear rate appears, depending on pressure to the power 0.7 to 0.9. The pressure dependence increases linearly with temperature. The temperature dependence of the overall reaction is small and is a function of pressure. The inapplicability of the Arrhenius equation to this process is demonstrated. (auth)

• Research Organization: Univ. of Liverpool
• NSA Number: NSA-17-028863
• OSTI ID: 4712894
• Journal Information: J. Less-Common Metals, Journal Name: J. Less-Common Metals Vol. Vol: 5
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ADSORPTION
ARRHENIUS EQUATION
CATALYSIS
CHEMICAL REACTIONS
CHEMISTRY
CRYSTALLIZATION
DIAGRAMS
ENERGY
EXCITATION
LAYERS
NIOBIUM
NUCLEATE BOILING
OXIDATION
OXYGEN
POWDERS
PRESSURE
STABILITY
TEMPERATURE