Comportement du graphite nucleaire purifie au cours d'une succession de traitements dans l'oxygene a 620°C et de degazages sous vide

Abstract

The sample is oxidized in oxygen at 620°C, then degassed under vacuum in the same apparatus, in successive steps from 250 to 1700°C. 1. (a) If the oxidation rate measurement is preceded by a degassing above 1000°C, an initial transitory period is observed during which this rate is at first considerably lower than normal, after which it increases rapidly and, when dry oxygen is used, passes through a high maximum. After a certain time the oxidation rate regains the value it would have attained without degassing. 2. (b) As with oxidation in air, oxidation in oxygen to a 10 per cent weight loss will not eliminate the gases fixed on the graphite before oxidation. On the other hand, by degassing under vacuum up to 1700°C after oxidation the greater part of these gases can be eliminated, giving a sample suitable for the study of the effect of humidity on oxidation. 3. (c) The presence of water in the oxygen leads to an excess quantity of CO and H 2 during desorption. The carbon monoxide is mainly given off below 1000°C and the hydrogen between 1000 and 1300°C. The total composition of this gas is generally higher in CO than in H 2, by comparison with that of water gas. Even if the concentration of water present during oxidation is varied within wide limits, the excess quantity of gases desorbed is found to be of the same order. This effect must be related to the inhibiting action of water on the oxidation rate of the same graphite.