Electrodeposition of nanocrystalline zinc‑tin alloy from aqueous electrolyte containing gluconate in the presence of polyethylene glycol and hexadecyltrimethylammonium bromide

Abstract

Electrodeposition of nanocrystalline Zn-Sn alloy was investigated in aqueous acidic electrolyte containing gluconate in the absence and presence of additives. Distribution diagrams of Zn (II) and Sn (II) species in acidic gluconate electrolyte showed that ZnSO4 and Sn(GH4)+ were the main species over the pH range of 2 to 5. The surface morphology of the Zn-Sn alloy deposited under various plating conditions showed that the production of nanocrystalline structure was not possible in the absence of additives. Additions of hexadecyltrimethylammonium bromide (CTAB) and polyethylene glycol (PEG) with various molecular weight (M¯n = 400 and 2050 g mole−1) were found to assist the formation of nanocrystalline structure. In the presence of CTAB and equal concentrations of PEG, the surface morphology of deposits exhibited a finer and more uniform structure with PEG 2050 than PEG 400. Nanocrystalline Zn-Sn alloy coating was produced from the bath containing 1 mM of CTAB and 1 g/L of PEG 2050. All zinc‑tin alloy deposits exhibited a low tin content (<35 wt%) as identified by EDS. X-ray diffraction patterns of deposits showed peaks of hexagonal zinc and tetragonal tin and confirmed the production of a co-deposited alloy coating, akin to a mechanical type zinc‑tin plating.