Preparation of Thermally Stable Bulk Amorphous Sulfur with Additive by Rapid Compression
|School||Southwest Jiaotong University|
|Course||Condensed Matter Physics|
|Keywords||rapid compression additive amorphous thermal stabiity|
The preparation and thermal stability of amorphous are important leading issues. A new method about rapid compression was researched in our lab. We have prepared successfully bulk amorphous element sulfur and some other amorphous materials by the method. It is found, however that the amorphous sulfur is unstable and easy to crystallization under room temperature after 75min and get to 26% when times get to 168min.In this work, author studied the preparation and thermal stability of the amorphous sulfur doped additive by using rapid compression. We conducted six separate experiments, using the mixture of sulfur with lmol% selenium, phosphorus, iodine, KC1, KBr additive respectively. These samples were first pre-pressed to 0.17 GPa and melted at 430 K,but 473K for that with KC1. Holding at the temperature the melt was solidified through a rapid compression from 0.17 to 2 GPa in 20 ms, then cooled down naturally to room temperature under 2 GPa and decompressed slowly to atmospheric pressure. The same process was also conducted for pure sulfur as a comparative experiment. Recovered samples are bulk homogeneous solids, translucent, elastic and flexible. All samples were characterized by X-ray diffraction, Differential scanning calorimetry analysis, in situ wide angle X-ray scattering under room temperature.X-ray diffraction results showed that all samples doped additives have typical amorphous structure as same as the pure amorphous sulfur except that doped KCl, which has partially crystalline structure.Differential scanning calorimetry analysis results showed the exothermic crystallization process obviously started about 370K for all samples. The crystallization heat 39.15J/g in the amorphous sulfur doping iodine is much more than that in the pure amorphous sulfur and other impure amorphous samples. There is an endothermic peak at about 438K in the pure amorphous sulfur and most samples, which is thought that the Sg changed to long-chain. The peak in the sample doped phosphorus is more smooth than that in the pure sample; but there is no endothermic peak in the sample doped iodine in the test range. It is indicated that the crystalline mesophase doped iodine has higher stability.Recovered samples were further analyzed in situ wide angle X-ray scattering at room temperature. The results showed that a spontaneous crystallization started after one hour in the samples doping selenium and phosphorus, and speed of the crystallization is more fast than pure amorphous sulfur. Nevertheless, there is no crystallization in the sample doping iodine as far as 191min. It is showed the amorphous sulfur doped iodine is much more stable than pure one and other samples.The results indicated that the rapid compression is an effective method to prepare amorphous sulfur with above additives. There are different influences by different impurites. Obviously the element iodine plays important role for improving the thermal stability of amorphous sulfur.In last chapter author suggested there were lots of clusters composed by one iodine atom and twelve Sg in the amorphous sulfur doping iodine and gave a further explanation about the change of thermal stability of the amorphous sulfur with iodine additive by the hypothetical model.