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Acid Zinc plating problems


 

Hi Everybody,

1. I have a problem in ammonium chloride zinc plating bath of not getting desired current. I am passing 10-16 volts but getting 500 amps, where it should be 1000 amps. What could be the reason.

2. Also if I process 33.6 sq.m. surface area in one barrel by passing 500 amps current, the what time it should take to get the 3-5 microns coating. Our supplier has given following spec. -

0.5 to 1.0 amp current per one Sq.Decimeter
time - 1 hour
coating thickness - 13 micron.

3. Also please let me know, for high carbon containing compounds which process is suitable, alkaline zinc (non-cyanide) or acid zinc, keeping in the mind that no loss of production rate.

Regards,

Santosh Zope
DWP - Dubai


 

1). It should be 1000 Amps based on? Wanting it to be 1000 Amps so you can plate twice as fast is one thing, and having a valid reason to expect 1000 Amps may be another thing :-(

2). The Metal Finishing Guidebook has an "Electrochemical Equivalents" shortcut table which factors metal densities and valences into Faraday's Law so that you can directly read that it takes 14.3 A-hr/ft2 to deposit a 0.001" thickness of zinc, assuming 100 percent efficiency. Converting square feet to square decimeters, it should take 1.544 A-hr/dm2 to deposit 0.001". Converting mils to microns, it should take 0.0608 A-hr/dm2 to deposit a micron at 100 percent efficiency. Your supplier's numbers say you'll need 0.038 to 0.077; so let's go with the 0.077 A-hr/dm2 to deposit a micron. So 3 to 5 microns will take you .23 to .39 A-hr/dm2 to get your thickness. I hope there is a typo in your question because 33.6 square meters is several times too large of a load and would take 773 to 1290 Amp-hours to deposit 3-5 mils. You want to be plating 20-30 minutes, not 1-1/2 to 2-1/2 hours.

3). For high carbon, you need acid zinc. Because of hydrogen overpotential you can't plate them in an alkaline bath.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



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