Wyniki 1-1 spośród 1 dla zapytania: authorDesc:"Bartłomiej Trybuś"

Oxidation kinetics of Zircaloy-4 alloy at 673 K determined by GDOES technique DOI:10.15199/28.2019.2.1

  1. INTRODUCTION Oxygen can form solid zirconium solution of α-Zr to 28.6% of atomic oxygen content at 473 K, and its solubility increases with increasing temperature reaching its maximum of 35% at 2338 K. When the limit of solubility of oxygen in the zirconium is reached, the ZrO2 zirconium oxide appears on the metal surface. The increase in mass during oxidation is divided into two stages, determined by phase transformation of oxide: pre-transition and post-transition period [1÷5]. The change in the structure of the crystalline oxide layer from β-ZrO2 to α-ZrO2 involves a change in the morphology of grains from columnar to equiaxed, accumulation of stresses caused by change in the volume of oxide, and formation of cracks and porosity [6÷8]. Many reports [1, 2, 9÷11] described the mass increase of oxide during the pre-transition according to the parabolic law. However, some authors [3, 12] found a cubic law. The kinetics described by cubic law is argued in that the diffusion process of oxygen atoms, which determined the rate of oxide build-up, is not a homogeneous process taking place in a perfect solid body, but is located mainly at the grain boundary. The grain boundary surface decreases with increasing oxide thickness. The thin layer contains many small, equiaxial crystallites, however, as the layer thickness increases, the crystallites have the columnar structure in the direction normal to the surface. The reason for this change in the geometry of crystallites is the increasing compressive stress created as a result of the difference in the volume of oxide and metal (~1.56) on which it is formed [3]. Part of the research groups analysing the pre-transformation phase considered the difference in the kinetics between parabolic and cubic related on the oxidation temperature [4]. Below the temperature of 1173 K, the increase in the oxide layer is described by the cubic law, while above this temperature the parab[...]

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