The effect of microstructure on air oxidation resistance of nuclear graphite

• Published in: Carbon (New York) Vol. 50; no. 9; pp. 3354 - 3366
• Main Authors: Contescu, Cristian I., Guldan, Tyler, Wang, Peng, Burchell, Timothy D.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.08.2012; Elsevier
• Subjects: ACTIVATION ENERGY; AIR; Carbon; CHEMISORPTION; Chemistry; Colloidal state and disperse state; Cross-disciplinary physics: materials science; rheology; DISTRIBUTION; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; General and physical chemistry; GRAIN SIZE; GRAPHITE; MATERIALS SCIENCE; MICROSTRUCTURE; nuclear graphite; optical microscopy; oxidant penetration; OXIDATION; Oxidation resistance; OXIDIZERS; OXYGEN; OXYGEN COMPLEXES; PENETRATION DEPTH; Physics; POROSITY; Porous materials; SHAPE; Specific materials; SURFACE AREA; Surface chemistry; Surface physical chemistry; Grain size; Chemisorption; Surface complex; Oxygen; Shape; Thermodesorption; Air; High temperature; Oxidizers; Penetration depth; Characterization; Resistance; Reactors; Distribution; Graphite; Oxidation; Porosity; Surface area; Microstructure; Structure; Activation energy; Low temperature
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2012.01.040

Oxidation resistance in air of three grades of nuclear graphite with different structures was compared using a standard thermogravimetric method. Differences in the oxidation behavior have been identified with respect to both (i) the rate of oxidation in identical conditions and the derived apparent activation energy and pre-exponential factor and (ii) the penetration depth of the oxidant and the development of the oxidized layer. These differences were ascribed to structural differences between the three graphite grades, in particular the grain size and shape of the graphite filler, and the associated textural properties, such as total BET surface area and porosity distribution in the un-oxidized material. It was also found that the amount of strongly bonded surface oxygen complexes measured by thermodesorption significantly exceeds the amount afforded by the low BET surface area, and therefore low temperature oxygen chemisorption is not a reliable method for determining the amount of surface sites (re)active during air oxidation. The relationship between nuclear graphite microstructure and its oxidation resistance demonstrated in this work underlines the importance of performing comprehensive oxidation characterization studies of the new grades of nuclear graphite considered as candidates for very high temperature gas-cooled reactors.