Acid Zinc plating problems
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.
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, P.E. RET
Pine Beach, New Jersey
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