Thermodynamics analysis of Ni2+-C2H8N2- -H2O system and preparation of Ni microfiber
(School of Metallurgy and Environment, Central South University, Changsha 410083, China)
Abstract: According to the principles of simultaneous equilibrium and mass equilibrium, the thermodynamics model of the precipitation-coordination equilibrium of Ni2+-C2H8N2- -H2O system was established, and calculation for the relationships between concentration of each substance in solution and parameters was carried out, including pH value, concentrations of ethylenediamine and oxalate by MATLAB program. The results show that Ni exists as Ni2+ and [Ni(C2O4)n]2-2n mainly at pH<1 and pH=1-6, respectively. When pH> 6, the complex between Ni2+ and ethylenediamine is predominant. The precursor of Ni microfiber was prepared by an oxalate precipitation process using ethylenediamine as a coordination agent, and the role of ethylenediamine in the growth of the precursor fiber was discussed. The Ni microfiber can be obtained by a thermal decomposition-reduction process of the precursor in N2 and H2 mixed atmosphere. The diameters and aspect ratios of the obtained Ni microfibers are 0.2-1 μm and 20-30, respectively.
Key words: thermodynamics analysis; Ni microfiber; precursor; thermal decomposition; reduction