Wang Honglong, Sun Yaping, Chu Jian, Wang Xu, Zhang Ming
Institute of Materials, China Academy of Engineering Physics Jiangyou 621908 China
RSC Adv. 2019 Feb 20;9(11):6199-6210. doi: 10.1039/c8ra08565j. eCollection 2019 Feb 18.
The evaluation of radiation stability of clay is important for the disposal of high-level radioactive waste (HLRW). In this study, phlogopite single crystals were irradiated by Co-60 γ-rays in air at a dose rate of 3.254 kGy h with doses up to 1000 kGy. Subsequently, the radiation stability and mechanism of radiation damage were explored by RS, FT-ATR, XRD, TGA, CA, and SEM techniques. In general, phlogopite single crystals show worthwhile radiation resistance toward their chemical structure but poor radiation stability toward their crystalline structure. Upon irradiation, their chemical structure changed slightly, while their crystalline structure varied obviously. For the 1000 kGy-irradiated sample, the interlayer space of the (001) lattice plane increased by more than 1% with a value close to 0.13 Å, showing expansion. This could be mainly ascribed to HO radiolysis and framework breakage: the former seems more important. These variations had a considerable impact on surface hydrophilicity, while they had marginal impacts on thermal stability and morphology: the effect on surface hydrophilicity is dose-dependent. A lower dose of irradiation sufficiently reduced the hydrophilicity, while a higher dose recovered the hydrophilicity. For instance, the CA increased from 14° to 28° with dose increases from 0 kGy to 200 kGy and then decreased to approximately 20° as the dose continued to increase to 1000 kGy. In general, the crystalline structure is more sensitive toward γ-ray irradiation and phlogopites could be regarded as poorly radiation-resistant. In this procedure, HO radiolysis occupies a crucial role and seems to be the dominant factor. This finding is meaningful to evaluate the radiation stability of clay matrixes and to understand the microscopic property variations in clays used in practice when they are under irradiation.
黏土辐射稳定性的评估对于高放废物处置至关重要。本研究中，金云母单晶在空气中以3.254 kGy/h的剂量率用Co-60 γ射线辐照，剂量高达1000 kGy。随后，通过拉曼光谱（RS）、傅里叶变换衰减全反射红外光谱（FT-ATR）、X射线衍射（XRD）、热重分析（TGA）、接触角（CA）和扫描电子显微镜（SEM）技术探究了其辐射稳定性及辐射损伤机制。总体而言，金云母单晶对其化学结构表现出值得关注的抗辐射性，但对其晶体结构的辐射稳定性较差。辐照后，其化学结构变化较小，而晶体结构变化明显。对于1000 kGy辐照的样品，（001）晶格面的层间间距增加超过1%，值接近0.13 Å，呈现出膨胀。这主要可归因于羟基（HO）的辐射分解和骨架断裂：前者似乎更为重要。这些变化对表面亲水性有相当大的影响，而对热稳定性和形态的影响较小：对表面亲水性的影响与剂量有关。较低剂量的辐照能充分降低亲水性，而较高剂量则使亲水性恢复。例如，随着剂量从0 kGy增加到200 kGy，接触角从14°增加到28°，然后随着剂量继续增加到1000 kGy，接触角又降至约20°。一般来说，晶体结构对γ射线辐照更敏感，金云母可被视为抗辐射性较差。在此过程中，羟基辐射分解起着关键作用，似乎是主导因素。这一发现对于评估黏土基体的辐射稳定性以及理解实际应用中黏土在辐照下的微观性质变化具有重要意义。
