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Insights into thermal reduction of the oxidized graphite from the electro-oxidation processing of nuclear graphite matrix

机译：核石墨基体的电氧化处理对氧化石墨进行热还原的见解

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Electro-oxidation disintegration is a potential technology pathway to detach graphite waste from high-level radioactive wastes in the spent fuel reprocessing of high temperature gas cooled reactors (HTGR). But this electrochemical treatment can introduce oxygen functional groups into the graphite lattice. Further disposal will require the development of safe and cost-effective methods to achieve the reduction and deoxygenation of the oxidized graphite wastes. In general, oxygen species can be removed from oxidized graphite directly in an easy-to-operate way by thermal annealing. In this paper, the thermal reduction process of oxidized graphite from the electro-oxidation processing of graphite matrix from simulative element of HTGR was researched. The thermodynamic state and kinetic process of the deoxygenation reaction of electrolytic graphite oxide (EGO) have also been investigated for better understanding of the reduction mechanism. According to thermal analysis results, the oxygen functional groups were removed mostly between 160 °C and 250 °C, and the main weight loss of EGO during thermal annealing was caused by evolved volatile gases (CO2, CO and H2O). The activation energy of deoxygenation reaction for EGO is calculated to be 115.6 kJ mol?1 (1.20 eV per atom). And the persistent residual oxygen species on reduced EGO (REGO) is determined to be from two parts, i.e. the stubborn built-in oxygen species of pristine nuclear graphite and the newly formed C–O moieties on the basal plane of graphite sheet during thermal annealing process. In addition, an attempt was also made to elucidate how the thermal treatment acted on the electronic structure of EGO. Meanwhile, the mechanism of dissociation of oxygen species (–OH, C–O–C, CO, –COOH) on the thermal reduction of oxidized graphite has been suggested in this paper.
机译：电氧化分解是在高温气冷反应堆（HTGR）的乏燃料后处理中将石墨废物与高放射性废物分离的潜在技术途径。但是这种电化学处理可以将氧官能团引入石墨晶格中。进一步的处置将需要开发安全且具有成本效益的方法，以实现氧化石墨废料的还原和脱氧。通常，可以通过易于操作的方式通过热退火直接从氧化石墨中除去氧。本文研究了用高温气冷堆模拟元件对石墨基体进行电氧化处理后，氧化石墨的热还原过程。为了更好地理解还原机理，还研究了电解氧化石墨（EGO）的脱氧反应的热力学状态和动力学过程。根据热分析结果，在160°C和250°C之间大部分除去了氧官能团，热退火过程中EGO的主要重量损失是由挥发的气体（CO 2 ，CO和H 2 O）。 EGO的脱氧反应的活化能经计算为115.6 kJ mol ？1 （每个原子1.20 eV）。并确定还原EGO（REGO）上的持久残留氧物种来自两个部分，即原始核石墨的顽固内置氧物种和基体上新形成的C-O部分热退火过程中石墨片的平面。另外，还试图阐明热处理如何作用于EGO的电子结构。同时，本文提出了氧物种（–OH，C–OC–C，CO，–COOH）的解离机理对氧化石墨的热还原作用。

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