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由于在高温下缺乏实验检测方法,反应的中间产物寿命短、浓度低,很难通过实验手段获得准确的分析数据,本文采用从头算分子动力学模拟方法对氟磷酸钙真空碳热还原的反应机理进行研究。结果表明:在1723K下,Ca_5(PO_4)_3F与C摩尔比为1∶12时,Ca_5(PO_4)_3F中的P原子态密度(PDOS)比较接近单个P原子态密度,C原子与O原子具有明显的共价键特征,还原效果最好;PDOS结果显示在费米能级附近,Ca原子与P原子、C原子没有形成共价键,故没有出现中间产物Ca_3P_2和CaC_2;由此推测氟磷酸钙碳热还原反应机理,首先C与Ca5(PO4)3F中PO3-4反应,不断脱去PO3-4中的O原子,PO3-4→PO_3~(2-)→PO_2~-→PO→P,然后C与O~(2-)结合生成CO,Ca~(2+)分别与O~(2-)、F~-结合生成CaO、CaF_2。
Due to the lack of experimental detection method at high temperature, the intermediate product of the reaction has a short life span and a low concentration, and it is very difficult to obtain accurate analytical data by experimental means. In this paper, the reaction mechanism of ab initio molecular dynamics simulation on the vacuum carbothermal reduction of fluorophosphate research. The results show that the P atom density (PDOS) in Ca_5 (PO_4) _3F is close to the density of single P atom at 1723K, the molar ratio of Ca_5 (PO_4) _3F to C is 1:12, and the C atom and O atom have Obvious covalent bond characteristics, the best reduction effect; PDOS results show that near the Fermi level, Ca atoms and P atoms and C atoms did not form a covalent bond, so there is no intermediate products Ca_3P_2 and CaC_2; speculated that fluorophosphate First, C reacts with PO3-4 in Ca5 (PO4) 3F to continuously remove O atoms in PO3-4. PO3-4 → PO3 → (2-) → PO2 → → → PO → P , Then C combines with O ~ (2-) to form CO, and Ca ~ (2+) combines with O ~ (2-) and F ~ - respectively to form CaO and CaF_2.