Abstract
β-naphthol was one of the first additives introduced for smooth and homogeneous tin electrodeposition. Although it can be oxidized under the plating conditions, forming either 1,2-napthoquinone or polymeric materials based on naphthioxides, it is still in use. In this work, an investigation of its more stable form, alkoxylated β-naphthol (ABN), on tin plating is undertaken. For this purpose, chloride based (pH ~5) and methane sulfonic acid (MSA, pH ~0.5) electrolytes, including ABN, were prepared. Reaction kinetics were studied by polarization, Tafel measurements, and cyclic voltammetry. Tin electrodeposits were obtained on flat brass substrates. Surface morphology and preferred crystal orientation were studied by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). In both studied electrolytes ABN acts as an inhibitor but in the case of the chloride electrolyte it is more pronounced. In the MSA electrolyte this effect was overlaid by the presence of tin-citrate complexes. In the chloride-based electrolyte, ABN has a grain refining effect, while in the MSA electrolyte an increase of ABN concentration leads to a slight enlargement of the average grain size. X-ray analysis shows a constant decrease of the (101) intensity with increasing concentration of ABN for the sample deposited from both baths.
Highlights
The electrochemistry of tin in an acidic electrolyte has been studied for several decades.both the role of organic additives for optimized brightness, gloss and hardness, and their effect on the electrochemical mechanism is still an open field of research
Results from the Tafel measurements confirm the observation that the ABN additive acts as Results from the Tafel measurements confirm the observation that the ABN additive acts as an inhibitor in the methane sulfonic acid (MSA) electrolyte
A significant decrease of exchange current exchange current density, j0, which indicates slower electron transfer across the tin-electrolyte density, j, which indicates slower electron transfer across the tin-electrolyte interface, is reached with interface,0 is reached with the ABN concentration of 4.37 mg/L
Summary
The electrochemistry of tin in an acidic electrolyte has been studied for several decades Both the role of organic additives for optimized brightness, gloss and hardness, and their effect on the electrochemical mechanism is still an open field of research. Due to their solderability and chemical inertness, tin electrodeposits are industrially used in several applications. Alkaline electrolytes are based on sodium [4] or potassium stannate [5,6] They have excellent throwing power and simple compositions, and satisfactory deposits can be obtained from a wide range of tin concentrations. Due to the stannate form of Coatings 2018, 8, 79; doi:10.3390/coatings8020079 www.mdpi.com/journal/coatings
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