Effect of microstructure and temperature on nuclear graphite oxidation using the 3D Random Pore Model

• Published in: Carbon (New York) Vol. 191; no. C; pp. 132 - 145
• Main Authors: Paul, Ryan M., Arregui-Mena, Jose D., Contescu, Cristian I., Gallego, Nidia C.
• Format: Journal Article
• Language: English
• Published: New York Elsevier Ltd 01.05.2022; Elsevier BV; Elsevier
• Subjects: Bulk density; Graphite; High temperature; Microstructure; Nuclear graphite; Oxidation; Porosity; Random pore model; Reactivity; Spatial distribution; Temperature dependence; Temperature effects; Three dimensional models; Weight loss; Oxidation; Nuclear graphite; Reactivity; Porosity; Microstructure
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2022.01.041

This work compared the 3D Random Pore Model (3D-RPM) with experimental and characterization data to systematically study the effect of nuclear graphite microstructure and air oxidation temperature. It is well known that oxidation-induced weight loss at elevated temperatures degrades graphite structure and properties; however, a fundamental understanding of the role of graphite microstructure is still unclear. In this work, three diverse grades of nuclear graphite—IG-110, NBG-18, and PCEA—were examined and tested at air oxidation temperatures of 600, 650, 700, and 750 °C following ASTM D7542. The 3D-RPM reproduced the microstructure and temperature dependence of mass loss curves for these grades. For the first time, measurements and modeling were combined to show how bulk density and the amount and spatial distribution of open and closed porosity affects oxidation. IG-110 was less dense and had an open pore network that is finer and more uniformly spread, and showed fastest oxidation. PCEA porosity was less uniform and showed less oxidation, while NBG-18 was more dense, had the least fine and uniform porosity, and showed the slowest oxidation. In general, oxidation proceeds faster if open porosity is more uniformly distributed and can incrementally access closed pore surface area with more ease. [Display omitted] •3D microstructural model reproduced the oxidation mass loss of three grades at four different oxidation temperatures.•In the microstructure, the amount of open and closed pores and their proximity to each other are important factors.•Intrinsic reactivity of high-purity graphite is independent of grade and follows expected temperature scaling.•Even in kinetic regime oxidation, there can be a density gradient due to spatial distribution of porosity and sample size.