Chemical structure and dissolution behaviour of CaO and ZnO containing alkali-borosilicate glass
Chemical structure and dissolution behaviour of CaO and ZnO containing alkali-borosilicate glass
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含CaO和ZnO碱硼硅酸盐玻璃的化学结构和溶解行为
DOI：
10.1039/d1ma01029h
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发表时间：
2022
影响因子：
5
通讯作者：
Fisher A
中科院分区：
文献类型：
--
作者：
Fisher A
在英国的放射性废物玻璃化方案，利用改性的锂钠硼硅酸盐玻璃与CaO和ZnO固定高水平的核废料的背景下，进行了调查，以评估改变CaO ZnO的比例对结构和化学耐久性的影响。使用6组分简化的碱金属铝硼硅酸盐玻璃，用ZnO替换CaO，即使是中等量，对玻璃结构也有显著影响。锌K-边EXAFS确定，锌存在于两个不同的环境中，都含有锌的四面体协调。在高CaO含量下，Zn在“类硬硅钙石”（Ca 2 ZnSi 2 O 7）环境中配位，而较高的ZnO含量导致失稳和纳米级相分离，在“类硅锌矿”（Zn 2SiO 4）环境中形成离散的Si/Al-O-Zn三簇。热分析和29 Si MAS NMR数据证实了这些环境的存在。尽管存在这种相分离，但发现具有较高ZnO含量的玻璃在稀释条件下表现出最低的归一化溶解速率，如使用单程流通方法测定的。化学结构分析表明，这样的行为是一个结果，增强聚合的玻璃网络中存在的锌，和减少的倾向Si-O-Zn键水解在水中，解决了长期运行的文献争论的作用，锌的溶解玻璃的前进速度。证据表明，相分离的区域溶解在有些不同的速率。这些结果增强了对含CaO：ZnO玻璃行为的理解，这对于评估放射性废物管理和处置策略的长期安全性非常重要。
Within the context of the UK's radioactive waste vitrification programme, which utilises a lithium-sodium borosilicate glass modified with CaO and ZnO to immobilise high level nuclear waste, an investigation was undertaken to evaluate the effects on the structure and chemical durability of altering the CaO to ZnO ratio. Using a 6-component simplified alkali aluminoborosilicate glass, replacement of CaO by ZnO, even in moderate amounts, had a marked effect on the glass structure. Zn K-edge EXAFS identified that Zn existed within two distinct environments, both containing Zn in tetrahedral coordination. At high CaO content, Zn was coordinated in a “hardystonite-like” (Ca2ZnSi2O7) environment, while higher ZnO content induced destabilization and nano-scale phase separation occurred, forming discrete tri-clusters of Si/Al–O–Zn in a “willemite-like” (Zn2SiO4) environment. The presence of these environments was corroborated by thermal analysis and 29Si MAS NMR data. Despite this phase separation, glasses with higher ZnO content were found to exhibit the lowest normalized dissolution rates under dilute conditions, as determined using the Single-Pass Flow-Through methodology. Chemical structure analysis indicates that such behaviour is a result of enhanced polymerization of the glass network in the presence of Zn, and a reduced propensity for Si–O–Zn bond hydrolysis in water, resolving a long-running literature debate on the role of Zn on the dissolution of glass in the forward rate. Evidence is presented that indicates the phase-separated regions dissolve at somewhat different rates. These results enhance understanding of CaO : ZnO-containing glass behaviour, important to assess the long-term safety of radioactive waste management and disposal strategies.