아연 도금욕 내 초기 Fe 함량이 Fe 용출속도에 미치는 영향

Abstract

The mechanism of iron dissolution and the effect of initial Fe content in a Zn bath on the dissolution rate of iron was investigated using a finger rotating method (FRM). When the initial iron content, [Fe]o, in the zinc bath was less than the solubility limit, the iron content in the zinc bath showed a rapid increase, whereas a creeping increase was observed when [Fe]o was close to the solubility limit. Based on Eisenberg’s kinetic model, the mass transfer coefficient of iron in the present experimental condition was calculated to be kM=1.2×10-5 m/s, which was similar to the results derived by Toussaint et al. and Tang under industrial practice conditions. A dissolution of iron occurred even when the initial iron content in the zinc bath was greater than the solubility limit, which was explained by the interfacial thermodynamics in conjunction with the morphology of the surface coating layer. By analyzing the diffraction patterns using TEM, the outermost dendritic-structured coating layer was confirmed as FeZn13 (ζ). In order to satisfy the local equilibrium based on the Gibbs-Thomson equation, iron in the dendrite-structured phase spontaneously dissolved into the zinc bath, resulting in the enrichment of iron in front of the dendrite tip. Through the diffusion boundary layer in front of the dendritic structured layer, dissolved Fe atoms diffused out and reacted with Zn and small amounts of Al, resulting in the formation of dross particles such as FeZn10Alx (δ). It was experimentally confirmed that the smaller the difference between the initial iron content in the zinc bath and the iron solubility limit at a given temperature, the lower the number of formed dross particles.