Abstract
In previous studies, the oxidation reaction of nuclear graphite could be divided into three regimes and the increase of oxidation rate subjected to heating was up to Regime III (about 1000-1200°C).However; our study finds that the oxidation rate increases again above 1200°C.This phenomenon has not been reported by other authors up to now. Therefore, we focus on the oxidation behavior of nuclear graphite oxidized at very high temperature range (700-1600°C). Petroleum-based coke IG-110 and pitch-based coke NBG-18 are the materials selected in this study. The sample size is 10 mm diameter x 15 mm height. The 3-zone furnace and mass flow controller were used to oxidize these samples under 700 to 1600°C and 2L/min dry air. The weight loss of these specimens were measured and they were characterized by Scanning Electron Microscope (SEM). As we know, the nuclear graphite was composed of filler and binder. Due to higher activation energy and greater crystallinity, filler oxidized slower than binder. From SEM cross section images result showed that the surface roughness increased with temperatures. The increasing roughness implied more exposed area that can react with air which led the oxidation rate to increase again above 1200°C. And, this increasing trend terminated when the testing temperature finally reached 1600°C. In view of this, we finally concluded that the oxidation rate would increase again above 1200°C because of different oxidation behavior of filler and binder on the surface. In other words, the oxidation mechanism above 1200°C was different from the oxidation reaction between 1000°C to 1200°C.