Oxidation of Tantalum at 300-550 deg C
Abstract
The oxidation behaviour of tantalum at 300 deg to 550 deg C has been studied. The work comprises gravimetric oxidation rate measurements and x-ray diffraction, electron diffraction, electron microscopy, metallographic and microindentation hardness studies of oxidized specimen. Direct x-ray diffraction and metallographic observations have also been made on specimens during oxidation. The oxidation constitutes oxygen dissolution in the metal, formation of the metallic oxide phases TaOY and TaOz, and formation of Ta2O5. The relative importance of the various part-processes involved in the oxidation is a function of temperature, oxygen pressure, and time of oxidation. Initial oxidation below 450 deg C conforms with a logarithmic oxidation. This is interpreted in terms of a rate-determining nucleation and formation of the metallic oxide phases. Over longer periods and during initial oxidation at higher temperatures the oxidation is approximated by a parabolic oxidation behaviour which mainly constitutes a rate-determining oxygen dissolution in the metal and associated metallic oxide formation. Above 450 deg C the initial approximate parabolic oxidation is followed by a breakaway oxidation which is associated with Ta2O5-formation. The breakaway oxidation is interpreted in terms of an oxygen chemisorption equilibrium followed by a rate-determining reaction governed by nucleation and growth of Ta2O5-nuclei(exp 1).
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1961
- Accession Number
- AD0273214
Entities
People
- Per Kofstad