Salt expansion in sulfate saline soils that are widely distributed in northwestern China causes serious infrastructural damages under low-temperature conditions. However, the mechanism of salt expansion under low temp...Salt expansion in sulfate saline soils that are widely distributed in northwestern China causes serious infrastructural damages under low-temperature conditions. However, the mechanism of salt expansion under low temperatures is not clear. In this study, we conducted a series of cooling experiments combined with salt crystallization to study this mechanism, and employed an ionic model to calculate the supersaturation ratio of the solution. During the experiments, the strength and the process of salt expansion were examined under different cooling rates and various crystal morphologies. The relationship between temperature and supersaturation ratio under transient conditions was also considered. Results indicate that the initial supersaturation ratio of a sodium sulfate solution is closely related to environmental conditions, and that this ratio decreases with slowing the cooling rates and stabilizing the crystal forms. Higher initial supersaturation ratios lead to an increased non-steady-state zone, resulting in less salt expansion. On the other hand, chloride ion content has a distinct influence on the crystallization supersaturation ratio of the sodium sulfate solution, and higher chloride ion content can inhibit salt expansion in sodium saline soils. These findings help explain salt expansion mechanisms in complex conditions such as seasonally frozen soils, and thus help search for improved methods of preventing salt expansion in sulfate saline soils.展开更多
Carbon forms a variety of compounds with single, double, triple and the intermediate resonance bonds with atoms of its own or other kinds. This paper is concerned with graphite, a very useful material, which is a stac...Carbon forms a variety of compounds with single, double, triple and the intermediate resonance bonds with atoms of its own or other kinds. This paper is concerned with graphite, a very useful material, which is a stack of electrically conducting graphene layers held together by weak van der Waals (vdW) bonds. It crystallizes in hexagonal and rhombohedral forms, in which the hexagon inter-planar bond distance is 0.34 nm. Here a new and simple approach accounts for this bond length and shows the coulombic nature of the vdW bond.展开更多
基金supported by the National Natural Science Foundation of China (41601068, 31602001, 41230630)the Young Scholars Development Fund of Southwest Petroleum University (201599010104)the Scientific Research Starting Project of Southwest Petroleum University (2015QHZ025)
文摘Salt expansion in sulfate saline soils that are widely distributed in northwestern China causes serious infrastructural damages under low-temperature conditions. However, the mechanism of salt expansion under low temperatures is not clear. In this study, we conducted a series of cooling experiments combined with salt crystallization to study this mechanism, and employed an ionic model to calculate the supersaturation ratio of the solution. During the experiments, the strength and the process of salt expansion were examined under different cooling rates and various crystal morphologies. The relationship between temperature and supersaturation ratio under transient conditions was also considered. Results indicate that the initial supersaturation ratio of a sodium sulfate solution is closely related to environmental conditions, and that this ratio decreases with slowing the cooling rates and stabilizing the crystal forms. Higher initial supersaturation ratios lead to an increased non-steady-state zone, resulting in less salt expansion. On the other hand, chloride ion content has a distinct influence on the crystallization supersaturation ratio of the sodium sulfate solution, and higher chloride ion content can inhibit salt expansion in sodium saline soils. These findings help explain salt expansion mechanisms in complex conditions such as seasonally frozen soils, and thus help search for improved methods of preventing salt expansion in sulfate saline soils.
文摘Carbon forms a variety of compounds with single, double, triple and the intermediate resonance bonds with atoms of its own or other kinds. This paper is concerned with graphite, a very useful material, which is a stack of electrically conducting graphene layers held together by weak van der Waals (vdW) bonds. It crystallizes in hexagonal and rhombohedral forms, in which the hexagon inter-planar bond distance is 0.34 nm. Here a new and simple approach accounts for this bond length and shows the coulombic nature of the vdW bond.
