纤维状氧化亚钴前驱体制备热力学分析

Thermodynamic Analysis for Preparation of the Precursor of Fibrous CoO Powders

根据同时平衡原理和质量平衡原理,从理论上推导出了常温常压下Co(Ⅱ)-C2O42--NH3-NH4+-H2O体系中金属钴离子和草酸盐在水溶液中的热力学平衡数学模型,计算并绘制出体系的lg[Me2+]T～pH图,热力学分析表明,当pH<5.5时,游离的钴离子是溶液当中的主导离子,pH>5.5时,大部分钴离子主要以钴氨配合离子的形式存在,沉淀反应为钴氨配合离子与草酸根离子之间的反应。在此基础上,利用氨为配位剂,通过配位沉淀法制备了纤维状复杂前驱体,并采用X射线衍射、红外光谱和扫描电镜研究了前驱体粉末的物相、成分与形貌。结果表明:纤维状前驱体为含氨草酸钴复盐,氨与钴离子配合并生成含氨草酸钴复盐是纤维状形貌形成的内在机制。通过控制热分解温度和热分解气氛,最终得到了纤维状CoO粉末。

A mmhematic model of thermodynamic equilibrium between cobalt ions and oxalates in Co（Ⅱ）-C2O4^2.NH3-NH4^＋-H2Osystem at ambient temperature is deduced according to the principles of simultaneous equilibrium and mass equilibrium. The diagrams of lg[ Co^2＋]T -pH at different solution compositions are drawn. The results of thermodynamic analysis show that free cobalt ions are dominant in the solution when pH 〈 5.5, and cobalt-ammonia complex ions pre- dominate and the precipitation reaction slowly proceeds between the cobalt ammonia complex ions and oxalate ions when pH 〉 5.5. The complicated precursor of fibrous CoO powders has been synthesized by coordination-precipitation process using ammonia as complex agent. The phase, composition and morphology of the novel precursor are characterized by X-ray diffraction, infrared spectrum and scanning electron microscope. The results indicate that the fibrous precursor, a complex salt of cobalt oxalate containing ammonia, is formed by coordination and reaction of ammonia with cobalt ions, which is the internal mechanism of the formation of fibrous morphology. The fibrous CoO powders are produced by controlling the temperature and atmosphere of thermal decomposition.