氟磷酸钙真空碳热还原反应机理的分子动力学研究
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摘要
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。
The carbon thermal reduction of Ca_5(PO_4)_3Fin vacuum wasmodeled and simulated by ab initio molecular dynamics simulation with software Material Studio,to understand the reduction mechanisms. The influence of the reduction temperature and molar ratio of Ca_5(PO_4)_3F/C on the P-extraction was investigated. The simulatedresults show that the optimized reduction occurs at 1723 K and a molar ratio of 1∶ 12,because the atomic P's partial density of state(PDOS) is fairly close to that of P-atom in Ca_5(PO_4)_3F,favorable for C-P co-valence bond formation; no Ca_3P_2 and CaC_2 intermediates emerge because Ca,P,and C atoms fail to form co-valence bonds near Fermi level. We suggest that the mechanisms may be:C atom forms CO by continuously depriving PO3-4in Ca_5(PO_4)_3Fof O~(2-) in the reaction path of PO_4~(3-)→PO_3~(2-)→PO_2~-→PO→P; while the Ca~(2+) form Ca O and CaF_2 compounds with O~(2-) and F-1ions,respectively.
The carbon thermal reduction of Ca_5(PO_4)_3Fin vacuum wasmodeled and simulated by ab initio molecular dynamics simulation with software Material Studio,to understand the reduction mechanisms. The influence of the reduction temperature and molar ratio of Ca_5(PO_4)_3F/C on the P-extraction was investigated. The simulatedresults show that the optimized reduction occurs at 1723 K and a molar ratio of 1∶ 12,because the atomic P's partial density of state(PDOS) is fairly close to that of P-atom in Ca_5(PO_4)_3F,favorable for C-P co-valence bond formation; no Ca_3P_2 and CaC_2 intermediates emerge because Ca,P,and C atoms fail to form co-valence bonds near Fermi level. We suggest that the mechanisms may be:C atom forms CO by continuously depriving PO3-4in Ca_5(PO_4)_3Fof O~(2-) in the reaction path of PO_4~(3-)→PO_3~(2-)→PO_2~-→PO→P; while the Ca~(2+) form Ca O and CaF_2 compounds with O~(2-) and F-1ions,respectively.
引文
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[2]龙涛,余斌,胡建军.磷矿开采对粮食安全的保障及其对策分析[J].中国矿业,2009,18(5):88-90
[3]刘代俊,蒋绍志,罗洪波,等.中国磷矿资源贫化危机与挑战[J].无机盐工业,2005,3-7(5):1-4
[4]刘艳飞,张艳,于汶加,等.资源与环境约束下的中国磷矿资源需求形势[J].中国矿业,2014,23(9):1-8
[5]钟本和,方为茂,唐艳,等.发展磷化工需重点研究的几个内容[J].磷肥与复肥,2009,24(3):1-5
[6]燕春培,郁青春,刘大春,等.真空碳热还原分解硫酸钙热力学分析及实验探究[J].真空科学与技术学报,2014,34(5):517-521
[7]袁海滨,朱富龙,杨斌,等.氧化铝真空碳热还原-氯化法炼铝的工艺研究[J].真空科学与技术学报,2010,30(6):582-587
[8]刘予成,李秋霞,邱臻哲,等.Si O2对氟磷酸钙真空碳热还原反应的影响[J].真空科学与技术学报,2013,33(3):293-296
[9]李秋霞,林倩宇,荆碧.氟磷酸钙和碳反应生成Ca O、CO、Ca F2和PO(g)的热力学计算[J].真空,2013,50(6):68-71