摘要
以氢氧化锂、磷酸二氢铵和醋酸钴为原料,首先经低热固相反应合成得到前驱体NH4CoPO4,再经高温固相反应制备得到LiCoPO4纳米晶。应用XRD、FT-IR、SEM等方法对产物进行表征。研究表明:前驱体NH4CoPO4在高温下很快就发生反应或变为非晶态。固相合成LiCoPO4是多个反应共存且相互关联的复杂过程,样品中共生Co2P2O7杂质。Li3PO4和LiCoPO4、Co2P2O7经历了不同的反应历程;Li3PO4转化反应遵循指数成核反应机理,活化能为41.8kJ·mol-1,是固相反应的控制步骤;LiCoPO4和Co2P2O7的生成反应可用幂律机理模型来描述,而且LiCoPO4和Co2P2O7之间存在转化反应;Co2P2O7转化为LiCoPO4的反应符合级数n=3的恒速成核、二维核生长的相界面反应控制的Avrami-erofeev机理模型。高温反应有利于Co2P2O7的转化,但样品颗粒也随之增大,又阻碍反应的进一步进行。
The precursor NH4CoPO4 was synthesized firstly via the solid-state reaction at low-heating temperature with lithium hydroxide,ammonium dihydrogen phosphate and cobalt acetate as raw materials in the present of PEG-400.Then the nano-crystallite LiCoPO4 powder was successfully obtained via the solid-state reaction of the prepared precursor at high temperature.The products were characterized with XRD,FT-IR and SEM,and the results show that,in the high temperature solid-state reaction,the precursor NH4CoPO4 is quickly reacted to form amorphous intermediates.The formation of LiCoPO4 via solid phase reaction undergoes a series of complex kinetic competitive process.The Co2P2O7,Li3PO4 and LiCoPO4 accrete in the products,and the transform reaction of Li3PO4 follows the index nucleation reaction mechanism with the active energy of 41.8 kJ·mol-1 which is the control step of the solid-state reaction.The formation reactions of LiCoPO4 and Co2P2O7 can be described by power law mechanism model,and there exists a transform reaction transforming Co2P2O7 to LiCoPO4.The above transforming reaction agrees with the Avrami-erofeev mechanism model of reaction controlled by the phase-boundary reaction of constant rate nucleation and two-dimensional nuclear growth with the reaction order n=3.Furthermore,the transform reaction from Co2P2O7 to LiCoPO4 is promoted by high temperature,but the size of the sample particles increases,which will impede further proceeding of the reaction.
出处
《高校化学工程学报》
EI
CAS
CSCD
北大核心
2010年第6期967-973,共7页
Journal of Chemical Engineering of Chinese Universities
基金
国家自然科学基金(20766001)
广西青年科学基金(0728101)
广西教育厅基金(200505083)
