Hansson E B, Odziemkowski M S, Gillham R W
Department of Earth Sciences, University of Waterloo, Waterloo, ON, Canada N2L 3G1.
J Contam Hydrol. 2008 Jun 6;98(3-4):128-34. doi: 10.1016/j.jconhyd.2008.02.003. Epub 2008 Feb 29.
This paper presents the results of kinetic studies to investigate the effect of FeS film formation on the degradation rate of CCl(4) by 99.99% pure metallic iron. The film was formed by submersing metallic iron grains in an oxygen free HCO(3)(-)/CO(3)(2-) electrolyte solution. When the grains had reached a quasi steady-state value of the corrosion potential, Na(2)S((aq)) was injected. Upon injection, a microm thick poorly crystalline FeS film formed immediately on the iron surface. Over time, the iron became strongly corroded and both the FeS film and the metallic iron grains began to crack leading to exposure of bare metallic iron to the solution. The effect of the surface film on the degradation rate of CCl(4) was investigated following four periods of aging, 1, 10, 30, and 60 days. Relative to the controls, the 1-day sulfide-aged iron showed a substantial decrease in rate of degradation of CCl(4.) However, over time, the rate of degradation increased and surpassed the degradation rate obtained in the controls. It has been proposed that CCl(4) is reduced to HCCl(3) by metallic iron by electron transfer. The FeS film is substantially less conducting than the bulk iron metal or non-stoichiometric magnetite and from the results of this study, greatly decreases the rate of CCl(4) degradation relative to iron that has not been exposed to Na(2)S. However, continued aging of the FeS film results in breakdown and stress-induced cracking of the film, followed by dissolution and cracking of the iron itself. The cracking of the bulk iron is believed to be a consequence of hydrogen embrittlement, which is promoted by sulfide. The increase in CCl(4) degradation rate, as the FeS films age, suggests that the process of hydrogen cracking increases the surface area available for charge transfer.
本文介绍了动力学研究的结果，旨在探究FeS膜的形成对99.99%纯金属铁降解CCl₄速率的影响。该膜是通过将金属铁颗粒浸没在无氧的HCO₃⁻/CO₃²⁻电解质溶液中形成的。当颗粒达到腐蚀电位的准稳态值时，注入Na₂S(aq)。注入后，在铁表面立即形成了微米厚的微晶FeS膜。随着时间的推移，铁被强烈腐蚀，FeS膜和金属铁颗粒都开始开裂，导致裸露的金属铁暴露于溶液中。在1天、10天、30天和60天这四个老化阶段后，研究了表面膜对CCl₄降解速率的影响。相对于对照组，1天硫化老化的铁对CCl₄的降解速率大幅下降。然而，随着时间的推移，降解速率增加并超过了对照组的降解速率。有人提出，CCl₄通过电子转移被金属铁还原为HCCl₃。FeS膜的导电性远低于块状铁金属或非化学计量磁铁矿，并且从本研究结果来看，相对于未暴露于Na₂S的铁，它大大降低了CCl₄的降解速率。然而，FeS膜的持续老化会导致膜的破裂和应力诱导开裂，随后铁本身也会溶解和开裂。块状铁的开裂被认为是氢脆的结果，而硫化物会促进氢脆。随着FeS膜老化，CCl₄降解速率的增加表明，氢开裂过程增加了可用于电荷转移的表面积。
