Degazage du graphite nucleaire avant et apres purification —influence de l'oxydation a l'air a 620°C

Abstract

Three apparatuses were used to de-gas the graphite samples over different temperature ranges: 1. (a) from 25 to 900°C in a current of argon, CO and CO 2 being analysed by infra-red absorption, 2. (b) up to 1700°C, heating by high frequency under vacuum; the gases being analysed by chromatography, 3. (c) above 2200°C, the presence of very troublesome carbon vapours made it necessary to use an auxiliary field concentrator. Heating was continued up to 2500°C, at which temperature sublimation leads to complete opening of the closed pore structure. It was found that: 1. (a) as a result of their manufacturing or storage conditions, nuclear graphites can release hydrogen or a gas corresponding stoichiometrically to water gas; 40 per cent of these gases come from the closed pores and are given off at temperatures above 1750°C. Heat treating the sample in a bed of carbon black can lead to a substitution of CO by H 2, 2. (b) oxidation by air opens up a large proportion of the closed pores and leads to the formation of surface oxides in proportion to the available surface. These surface oxides are not greatly influenced by inorganic impurities. The gas production by degassing after oxidation is at a maximum between 600 and 800°C and almost finished at 1000°C, but a further small increase occurs when the graphite sublimes, 3. (c) an oxidation to 10 per cent weight loss is not sufficient to eliminate entirely the substances adsorbed by the graphite before oxidation at 620°C; they appear to be profoundly in the carbon.