| AVS 55th International Symposium & Exhibition | |
| Surface Science | Thursday Sessions |
| Session SS2-ThA |
| Session: | Novel Reactive Surfaces |
| Presenter: | J.L. Sacedon, Instituto de Ciencia de Materiales de Madrid, Spanish National Research Council |
| Authors: | M. Diaz, Instituto de Ciencia de Materiales de Madrid, Spanish National Research Council, Spain B. Remartinez, Iberdrola, S. A., Spain S. Perez, Iberdrola, S. A., Spain J.L. Sacedon, Instituto de Ciencia de Materiales de Madrid, Spanish National Research Council |
| Correspondent: | Click to Email |
In these Zirconium based materials, when the H2 dissociation at a surface is enough efficient, a continuous and compact hydride layer is formed, increasing in thickness with time. Using a UHV equipment and method, specifically developed to compare the resistance to hydriding of tubular nuclear fuel claddings,1 the propagation kinetics of the Hydride/metal interface through the cladding thickness is obtained. It results in a hydride thickness vs time dependence th =K ta, where a is close to 1/2 and a rate dependence on the thickness dth /dt =C thb where b is close to -1. They are near to the expected values from an H ideal diffusion through the Hydride layer, and differ from the linear kinetics (a =1) and other fractional a exponents obtained from thermo-gravimetric methods. At difference, in our method the sample is directly heated in an UHV environment, which allows a fast control of the local temperature where the hydriding reaction takes place. At the same time, pure H2flows inside the tube, starting the hydriding from the inner tube surface. The method allows determining the formation enthalpy of ZrH 1.5 (Zircaloy2) H=-117±8 kJ/mol at 295.5 K, giving the second determination of this value in the literature.2 Being the Hydride composition determinate by X ray diffraction methods, mass spectrometry allows to follow the H2 desorption produced by the surface reaction Hs+Hs = H23 at the external surface of the tube, opposite to surface where the hydriding begins. A kinetic model and expression that explain the H2 desorption curves is presented. In this model the H desorption rate, is proportional to a fractional surface Hydride coverage. This coverage increase in time by the excess of H precipitated from the H oversaturated metal. The Hydride/ metal interface acts as a very weak H source feeding the metal over saturation. The ratio between the of H flux precipitated at the external metal surface to that precipitated at the Hydride / metal interface is determinate to be ≤10-6.
1J. L. Sacedón, M. Díaz, J.S. Moya, B. Remartínez and J. Izquierdo, Journal of Nuclear Materials. 327 (2004) 11.
2P. Dantzer, W.L., T. B. Flanagan and J. D. Clewley, Metall. Transact. A. 24 (1993) 1471.
3D. E. Sheleifman, D. Shaltiel and I. T. Steinberger, J. Alloys and Compounds. 223 1995) 81.