Department of Materials Engineering, Center for Research, Technology and Education in Vitreous Materials, Federal University of São Carlos, São Carlos, SP, Brazil.
Sci Rep. 2017 Feb 27;7:43022. doi: 10.1038/srep43022.
Understanding the conditions that favour crystallisation and vitrification has been a longstanding scientific endeavour. Here we demonstrate that the extremely high glass-forming ability of unseeded supercooled NaO·AlO·6SiO (Albite) and BO-known for decades as "crystallisation anomaly"-is caused by insufficient crystal nucleation. The predicted temperatures of the maximum homogeneous nucleation rates are located well below their glass transition temperatures (T), in a region of very high viscosity, which leads to extremely long nucleation time-lags and low nucleation rates. This behaviour is due to the remarkably small supercoolings where the glass transition occurs for these liquids, which correspond to a very small driving force for crystallisation at and above the T, where crystallisation is normally observed. This meagre nucleation ability is caused by the significant difference in the structures of the supercooled liquids and their isochemical crystals. These findings elucidate the cause behind the crystallisation anomaly, and could be used for the design of other oxide glasses that are extremely stable against crystallisation.
长期以来，人们一直致力于研究有利于结晶和玻璃化的条件。在这里，我们证明了未成核过冷 NaO·AlO·6SiO（钠长石）和 BO 的极高玻璃形成能力——几十年来被称为“结晶异常”——是由于结晶核形成不足引起的。预测的最大均匀成核速率的温度远低于其玻璃化转变温度 (T)，处于极高粘度的区域，这导致成核时间延迟非常长且成核速率非常低。这种行为归因于这些液体在玻璃化转变时发生的非常小的过冷度，这对应于在 T 及以上温度下结晶的很小驱动力，在该温度下通常观察到结晶。这种微薄的成核能力是由过冷液体与其等化学晶体结构的显著差异引起的。这些发现阐明了结晶异常的原因，并可用于设计其他对结晶极为稳定的氧化物玻璃。
