Estudo da influência dos aditivos manitol, EDTA e NTA no processo de eletrodeposição de zinco sobre aço 1010 e na morfologia dos eletrodepósitos

Abstract

In this paper the effects of adding mannitol, EDTA or NTA to an alkaline deposition bath on the electrodeposition of zinc on to AISI 1010 steel substrate were evaluated. Voltammetric curves of 1010 steel in deposition bath with mannitol or EDTA additives showed similar profiles. However, for NTA it was different. These experiments indicated that the current density (j) of zinc electrodeposition increased due to hydrogen evolution reaction (HER) from H2O reduction occurring in parallel to this process. The voltammograms of 1010 steel substrate in deposition bath with and without mannitol or EDTA showed two regions c0 and c1, due to iron oxide reduction/HER/initial zinc bulk deposition and secondary zinc bulk deposition, respectively. These regions were called b0 and b1, as NTA was present in deposition bath. In the region c1, for deposition bath with and without mannitol or EDTA, the j was similar, suggesting that the area of zinc electrodeposit did not differ significantly, unlike the plating bath with NTA (region b1). From cyclic voltammograms with lowerlimit potential, can be seen that the initial zinc bulk deposition occurred at - 1.45 V in cathodic sweep to deposition bath with and without mannitol or EDTA and this potential was shifted 100 mV in the positive direction (- 1.35 V) in the presence of NTA. When the sweep was reversed at - 1.60 V all the deposition bath showed, in the anodic sweep, a zinc dissolution peak. The current efficiency (e) was always lower than 100%, due to HER occurring in parallel to the zinc electrodeposition. It was verified that in the presence of NTA additive, higher values of e (55.8%) was obtained and also, zinc electrodeposits were thicker (2.65 μm) for charge density (qd) 10.0 C cm-2. For qd = 2.0 C cm-2, irrespective the additives, the values of e and thickness () were comparable. The morphological studies of zinc electrodeposits showed that all the additives work as a brightener, since refining of the zinc grains. The EDX analysis showed that for qd = 2.0 C cm-2 the oxygen incorporation did not occur for 0.20 mol L- 1NTA or 0.20 mol L-1EDTA, but was below detection limit for the 0.20 mol L-1 mannitol. For qd = 10.0 C cm-2, it can be seen that as plating bath containing 0.20 mol L-1 EDTA the oxygen incorporation was hindered in the zinc electrodeposits.