Effects of Pt Surface Coverage on Oxidation of Zr and Other Materials
2009 (English)In: ZIRCONIUM IN THE NUCLEAR INDUSTRY: 15TH INTERNATIONAL SYMPOSIUM, 2009, Vol. 1505, 285-302 p.Conference paper (Refereed)
Certain elements, including noble metals, are identified to influence corrosion behavior of many metals in high-temperature water/steam and O-2. We have previously reported effects of porous Pt coatings on the thermal oxidation of Zr, Fe, Ni, Cr, and GaAs in O-2. Effects of Pt on oxidation of Zircaloy-2 in H2O have also been observed at temperatures near 400 degrees C. An enhanced oxidation rate is observed in all of the studied systems upon a sufficiently high surface Pt-particle density. Even more interesting, low Pt-particle density in most cases leads to a decreased oxidation rate. In the case of Zr and Zircaloy-2 the beneficial effect of Pt is stronger when hydrogen is present in the metal substrate and in the oxide layer. From O-18/SIMS experiments it is concluded that, for a sufficiently high Pt-particle density on the surface, enhanced transport of dissociated oxygen, On- (n=0; 2), towards the oxide/metal interface occurs in all of the studied systems. An oxygen spillover from Pt particles to the adjacent surface is a known phenomenon in catalysis and partly explains the results observed also in the current study of oxidation of Zr-based materials. Such a spillover involves a high surface diffusivity of dissociated oxygen, On-, which results in an increased gradient of On- across the oxide scale. In turn, the high oxygen gradient enhances the transport of oxygen towards the substrate/oxide-interface, This shows that not only diffusivity but also an effective activity of dissociated oxygen at the external oxide surface influences the oxidation rate. Naturally, the effects of Pt are maximized when small (nm-sized) and evenly distributed Pt particles are present on the surface. In our presentation a summary of obtained results of Pt additions on different materials will be given with suggested interpretations. Especially, the observed beneficial combination of Pt and hydrogen in the oxidation of Zr-based materials is discussed with a possible mechanistic explanation. Parallels are also drawn to the potential effect of Noble Metal Chemical Application (NMCA), used in a large traction of the U.S. BWRs, on the corrosion resistance of Zr-based claddings.
Place, publisher, year, edition, pages
2009. Vol. 1505, 285-302 p.
, American Society for Testing and Materials Special Technical Publications, ISSN 1040-1695 ; 1505
Pt particle coverage, Zircaloy-2, oxide growth, spillover, Noble Metal Chemical Application (NMCA)
Engineering and Technology
IdentifiersURN: urn:nbn:se:kth:diva-30760DOI: 10.1520/STP48142SISI: 000268223100016ScopusID: 2-s2.0-70449806025ISBN: 978-0-8031-4514-6OAI: oai:DiVA.org:kth-30760DiVA: diva2:401811
15th International Symposium on Zirconium in the Nuclear Industry, Sunriver, OR, JUN 24-28, 2007
QC 201103042011-03-042011-03-042011-03-04Bibliographically approved