Determination of impurity distribution in IG-11/110 nuclear graphite using TOF-SIMS

Abstract

Graphite serves as moderator and structural material in various type of graphite-based reactors. The presence of impurities within the graphite matrix can lead to adverse consequences, including diminished fuel efficiency, heightened radionuclide production, and catalytic oxidation. High-purity graphite materials also find essential applications in diverse industries, such as semiconductor manufacturing and chemical analysis. In this study, we conducted an investigation into IG-11 graphite, which has an ash content of 347 ppm, and its purified version, IG-110 nuclear grade graphite, which has an ash content of 12.7 ppm, to understand the purification mechanism of polycrystalline graphite. The analysis of Time-of-flight secondary ion mass spectrometry spectra revealed that metallic impurities in IG-11 were primarily segregated within graphite porosities or appeared as discrete point inclusions, rather than uniformly distributed throughout the graphite matrix. IG-110 demonstrated a significant reduction in impurities such as Na, K, Ca, and Al compared to IG-11, but Ti was still present within its porosity. Notably, impurities residing on the walls of these porosities can accelerate graphite oxidation. The establishment of the theory on impurity segregation in porosities help to develop innovative graphite purification techniques that produce graphite with even greater purity and stronger oxidation resistance.