核石墨氧化后微观结构观测与分析
Observation and Analysis on Micro-structure of Oxidized Nuclear Graphite
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摘要: 针对高温气冷堆中石墨材料在可能出现的事故中的氧化问题，开展了不同氧化程度下IG-11石墨的表面二维电镜扫描观测和三维CT扫描观测实验，分析了石墨氧化后的表面形态特征和内部微结构分布特点。通过试样氧化前后表面灰度概率分布图可知，石墨氧化后由于内部大孔隙的出现，灰度概率分布图由单峰变为双峰。通过分析灰度平均值以及试样分层密度随深度的变化可知，氧化主要发生在距离石墨试样表面1 mm的区域内；当氧化失重率较小时，在浅层区域损失的质量所占比重相对更大，而氧化程度较高后反应形成的开孔孔隙网络才逐步深入材料内部。Abstract: In the possible accidents, the nuclear graphite used in high-temperature gas-cooled reactor may be oxidized. 2-D scanning electron microscope observation and 3-D CT scanning analysis on the oxidized graphite were conducted to study the surface and inner micro-structure of the graphite. After the oxidation, there appear big voids inside the graphite, which makes the probability distribution of grayscale change from single-peak to double-peak. By analyzing the mean grayscale and the mean density of layered graphite versus the depth of the graphite, it is found that the oxidized zone of the graphite is mainly within 1 mm under the surface. When the total mass loss is small, the superficial zone suffers more oxidizing mass loss, and the crack network caused by oxidation grows into the graphite when oxidizing process continues.
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Keywords:
- graphite ,
- oxidation ,
- CT scanning ,
- micro-structure
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