Abstract
The aim of this investigation is to evaluate the influence of glycerol (a nontoxic additive) on Zn-Mn coatings formed by electrochemical deposition. The influence of glycerol (GLY) on the electrodeposition of Zn-Mn alloys on Pt from acid baths was studied by cyclic voltammetry. The coatings were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The Zn-Mn alloys prepared in the absence or presence of this additive showed similar voltammograms except when using GLY and boric acid (BA) concentrations at 0.63 and 0.24 M, respectively. The current efficiency of the Zn-Mn electrodeposition process ranged from 5 to 41%, due to the lowest and highest concentrations of GLY and BA, respectively. SEM images of deposits obtained at -1.53 V from baths containing 0.08-0.48 M GLY were dendritic, while those formed in the presence of 0.63 M GLY showed that GLY acted as a brightener at this concentration. The XRD analysis showed that the electrodeposits contained Zn, Mn, oxides as well as alloys of various compositions. GLY acted as a grain refiner and inhibited the codeposition of Zn with Mn and the formation of oxides.
Highlights
IntroductionThis is considerably more negative than that of zinc, -0.76 V (vs NHE) (Brenner, 1963)
To investigate the process of electroplating, the Zn-Mn voltammograms were recorded on a Pt substrate in deposition baths containing salts of Mn and Zn with boric acid (BA) and glycerol (GLY) at various concentrations
A reddish-brown coloration was seen in the film while at the end of region a2, which may be due to manganese oxide (MnO2) (Pourbaix, 1966)
Summary
This is considerably more negative than that of zinc, -0.76 V (vs NHE) (Brenner, 1963) This higher electronegativity of Mn confers two types of protection on the steel: it dissolves prior to Zn (Boshkov, Petrov, & Vitkova, 2002; Boshkov, Petrov, Vitkova, & Raichevsky, 2005; Díaz-Arista et al, 2009; Chen & Hussey, 2007) and it ensures better protective ability with low solubility products (Wykpis et al, 2014). This Mn electronegativity leads to significant but low efficiency hydrogen evolution reaction (HER) (Bozzini et al, 1999; Díaz-Arista et al, 2009). According to Ananth and Parthasaradhy (1996), the ZnMn system is so complex that the Mn content in the alloy can range from 0 to 100%
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