Pitting in Watt's dull nickel plating
I use a Watt's dull Ni plating bath and find the Ni surface plated with so many pits. There are two kinds of pits:
- - The pits look shiny when viewed by unaided eye. But under microscope, it is a small dark hole, the Ni around the dark hole is also dark in color.
- - Much smaller hole (compared with the one mentioned above.The Ni plated around the hole is normal.
Both types of pits are caused by the same reason?
- Concentration of Ni I use = 95 g/L of Ni without additive.
- Concentration of boric acid used = 55 g/L
- With current density about 2.8 ASD
I have tried to use hydrogen peroxide and carbon filter to clean the bath over 7 days... but no improvement...
I have also tried to add wetting agent in the tank, but no improvement is observed.
Is that using active carbon powder to clean the tank is the only method to solve this problem?
Sometimes. even I have tried to make-up a new bath, the problem still exists for the new bath.
But some baths (for the same composition and process parameters), no pitting problems observed even after using in production for over 1 months. Please advise me.
Thanks for your kindly help.Kelvin YU
- Hong Kong
If the pits you observe are semi-hemispherical, they are almost surely "gas" pits (hydrogen pits) that develop because a hydrogen bubble starts forming on the surface, and does not become dislodged until too late in the plating process.
You need a wetting agent, and a means of measuring the viscosity. But you also need agitation and you did not mention any facts about that. Air agitation would probably be best if there is nothing about your situation that would preclude it.
You did not mention what the substrate is, and it is possible that the defects are related to the substrate condition. Zinc or aluminum diecastings will generate pits if the castings are porous, even if you have good agitation and wetting agent. Almost any foreign ingredient left on the surface will cause pits too.
I was once told by a very competent plater that it is even possible to ruin a surface by being overzealous in Scotchbrite polishing, such that very tiny, invisible, amounts of the Scotchbrite melt onto the surface and cause pitting. Unfortunately I've never had the opportunity to actually prove or disprove that contention.
Ted Mooney, P.E.
Pine Beach, New Jersey
Dear Mr. Mooney,
Thanks for your advise.
I have already tried wetting agent with air stirring but no improvement is observed. And you said that I should measure the viscosity, viscosity of plating solution? Please advise.
I use copper as substrate for the nickel plating.Kelvin YU
- Hong Kong
What is the base Metal? If it is steel, too Strong a pickling solution can cause pitting.Gary Patigler
Forming co. - Richmond Ca. USA
August 27, 2009
I have also observe this pitting problem Semi bright Nickel plating on MS, in this case foreign substrate on surface may create this pitting. This foreign substrate (particle)is removable with air agitation or jet water spray on the surface on the part, I think this foreign substrate develop in pre treatment process only.
Thanks & regards
- Hosur, Tamil nadu, India
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