The Correlation of Texture and Microstructure to the Corrosion Resistance of Tin Coatings

Abstract

The influence of current density and temperature on the macrotexture, the orientation and size of grains, and the corrosion resistance of tin deposits was studied. Tin coatings with two different textures, (100) and (301) fiber textures were produced by electrodeposition at 20°C by varying current density. At a lower current density of 100A/m2, (301) fibre was obtained. At the current densities of 100 and up to 400 A/m2, only (100) fibre texture was observed. An increase in current density leads to a decrease in grain size. At the same current density, the grain size of tin coatings increases with increased temperature. The influence of temperature (20, 40, 60 and 80 °C) on texture is relatively negligible. The corrosion resistance of tin coatings increases with a decrease in grain size. The corrosion resistance of tin coating with (301) fibre is higher than that of tin coating with (100) fibre texture. The results suggest that texture and microstructure play an important role in controlling corrosion rate of tin based coatings.

Kinetics and Initial Stages of Bismuth Telluride Electrodeposition

“…Proton diffusion is fast and Reaction 5 is essentially controlled by kinetics. Reaction 12 is controlled by diffusion due to a low diffusivity of telluryl ions ͑HTeO 2 + ͒, resulting in the second plateau at −0.6 V. As contrasted to the literature reports, 13,20,[22][23][24][25] our experimental results show that the reaction between HTeO 2 + and H 2 Te is an electrochemical reaction rather than a chemical reaction. The third plateau is due to hydrogen coevolution.…”

“…The assignment is consistent with other literature reports. 12,[20][21][22][23][24][25] Peak B is related to the consequence of hydrogen telluride evolution; it is due to the dissolution of the tellurium formed from Reaction 6. The tellurium deposited in this way is slightly more difficult to oxidize than through Reaction 4.…”

“…19 It is not surprising that controversy exists in the literature. 13,[20][21][22][23][24][25] Danaher and Lyons 20 have suggested that the mechanism of tellurium deposition is dependent on the concentration of telluryl ions ͑HTeO 2 + ͒: at low concentration ͑Ͻ1 mM͒, tellurium deposition occurs through a six-electron reduction of HTeO 2 + + 5H + + 6e − → H 2 Te, followed by a reaction between H 2 Te and HTeO 2 + to yield Te͑0͒; at HTeO 2 + concentrations higher than 1 mM, the overall reaction behaves as a four-electron reduction of HTeO 2 + to Te͑0͒. Tradore et al 22 and Mori et al 23,24 have concluded that the reduction of Te͑IV͒ occurs via a four-electron process, leading to Te͑0͒.…”

“…For kinetic studies, the potential step method is frequently used; while for industrial coatings preparation, the current step method ͑galvanostatic electrolysis͒ is usually applied. 25 The most important benefit of using the galvanostatic method is that the thickness or weight of deposits can be readily controlled according to Faraday's law of electrolysis. The potential-time method ͑chronopotentiometry͒ at constant current and the Sand equation can be used to calculate diffusion coefficients.…”

The corrosion characteristics and solderability of immersion tin coatings on copper

“…A better corrosion resistance of Sn rich alloys with coarser structure was observed in Ref. 33, however, the opposite relation was also reported 34. Contrary, a gradual increase of the corrosion resistance for thicker coatings (Table 2) can be explained by an increase in grain size with coating thickness 4.…”