Cheng Shangcong
Molecular Foundry of Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Materials (Basel). 2023 Sep 15;16(18):6218. doi: 10.3390/ma16186218.
The anomalous density-temperature relationship of vitreous silica with low hydroxyl content is explained by the formation of medium-range ordering structure in the glass transition process. The ordered medium-range structure has the shape of a "nanoflake" and consists of two layers of SiO tetrahedra, bonded by O atoms located in the middle of the structure. The nanoflakes interact with their surrounding structures through both covalent chemical bonds and van der Waals bonds. In the formation of the van der Waals bonds, the orientation of SiO tetrahedra can change, which results in an increase in distance between the nanoflakes and their surrounding structures. Thus, there is a slight volume enlargement associated with the formation of nanoflakes. Since the nanoflakes' formation starts at a temperature near 1480 °C, and the population of the nanoflakes grows continuously as temperature decreases until about 950 °C, the bulk volume of silica glass increases in the temperature range from about 1480 °C to 950 °C. Therefore, the density anomaly of silica glass can be explained as a byproduct of forming of medium-range ordering structure in the silica glass transition.
低羟基含量的石英玻璃密度-温度关系异常，这是由玻璃转变过程中形成的中程有序结构所导致的。这种有序的中程结构呈“纳米片”形状，由两层SiO四面体组成，通过位于结构中间的O原子相连。纳米片通过共价化学键和范德华键与周围结构相互作用。在形成范德华键的过程中，SiO四面体的取向会发生变化，这导致纳米片与其周围结构之间的距离增加。因此，纳米片的形成会伴随着轻微的体积增大。由于纳米片的形成始于接近1480°C的温度，并且随着温度降低，纳米片的数量持续增加，直至约950°C，石英玻璃的总体积在约1480°C至950°C的温度范围内增大。所以，石英玻璃的密度异常现象可以解释为石英玻璃转变过程中形成中程有序结构的一个副产品。
