Hello reseacrchers
I work on the mechanical properties of Ni-Co coatings elaborated by electrodeposition ,so I have two problems with the deposited coatings: the first problem is the presence of small pits in the surface, I think it's due to hydrogen out, then I have worked on the diminishing of them using several solutions: bath temperature variation, current density variation, pH variation, etc ..., I have succeeded in reducing them, but they still exists. The second problem is concerning the adhesion of hight cobalt content coatings that show poor adhesion to the substrate, I hope you can help me solving these problems, if possible.
notes:
bath contents :
Current Density: 3-5 A/dm2
NiSO4(200g/l) , NiCl2 (30g/l),CoSO4.
boric acid (30g/l), Saccharine(0.5 g/l),
Please help me, if possible
Best regards
Mohamed
You can check the following steps
1) If you have clean substrates/surfaces
2) check if there impurities in the coating bath.
3) Check in literature if others are also using similar deposition as you are and if they report same type of problem. If not then you need to optimize the coating process parameters.
4) Sometimes it also deposits on the coating methodology. Like coating defects are always expected in ARC magnetron sputtering.
I hope it helps in some way.
I have worked with Ni-Co alloy electrodeposition and it forms solid solutions rather than alloy. Moreover it follows anomalous codeposition and hence naturally Cobalt content is larger than Nickel, though cobalt reduction is more cathodic than nickel reduction. The formation of pits primarily due to H2 liberation followed by nickel hydroxide formation via anomalous codeposition, as you know nickel codeposition hindered by diffusion control and activation overpotential. Competitive adsorption of hydroxide followed after H2 liberation with Ni(OH)2 may lead to such pits. One possible solution may be,... codeposition carried out at moderate pH ~6 and at low current density 0.5-2 Adm-2. I hope this doesn't virtually eliminate the pits, but relatively reduces the H2 liberation (and hence pits), since H2 liberation followed by nickel hydroxide adsorption is the primary cause for poor adhesion.
See the paper: http://www.sciencedirect.com/science/article/pii/S0257897213004349
Dr M Kanagasabapathy
Thank you very much Dear M. Kanagasabapathy for your answer, 'll try to implement solutions, which advised me out. I hope that it succeeds .
Best regards
Mohamed
Thank you very much Dear Stefan Svetsky for your answer ,I wish you could tell me more about the way of filtrate the bath through activated carbon,please help me if possible
Best regards
Mohamed
thank you very very match dear Stefan Svetsky for your Important information,
Accept my thanks
Best regards
Mohamed
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