Abstract
Considerable numbers of studies have been done on the peculiar oxidation of zirconium and its alloys, mostly by measuring the weight increase during oxidation and the oxygen concentration gradient in the substrate. In order to obtain a better understanding of the oxidation of zirconium and its alloys, it is more adequate to separate the total weight increase into the formation of oxide scales and the oxygen solution into the substrate. The growth of oxide scales is estimated from the measurement of the electric capacity. The relative importance of the oxide scale formation in the total oxidation is investigated and a consideration is given to the substantial function of oxygen solution into the substrate.
Main results of this study are as follows: (1) The oxidation of zircaloy-2 at 600°∼800°C is proportional to the cubic root of oxidation time until the breakaway occurs. (2) According to the electric capacity measurement of specimens, the increase of the oxide scale thickness is also neatly proportional to the cubic root of oxidation. (3) The higher the oxidation temperature, the more oxygen dissolves into the substrate. (4) According to the radio-chemical analysis of the amount of oxygen dissolved in the substrate at 800°C, the contribution of the oxide scale formation to the total weight gain is 93 to 95% in the initial period of oxidation (within 70∼100 min). Thereafter, the contribution of the dissolved oxygen increases rapidly and that of the oxide scale formation does not increase so much.
