Re: copper plating - Electrode Tips

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Hollmike-at-aol-dot-com>

Brent wrote: 

>Yes, proper pH is critical to a successful plating job. Too much acidity 
>and you oxidize the surfaces and also the plating layer - hence that 
>spongy stuff. Not enough and the plating layer doesn't bond with the 
>material being plated. 

There is a wide range of acceptable acid concentration for copper plating.    
I have not previously suggested any additives because I did not realize this 
was going to get this much interest, but here goes: 

  Copper Sulfate pentahydrate  - 190 - 250 g/L 
  Sulfuric acid                         -  10 - 75 g/L 
  Chloride                               - 50 - 120 PPM (mg/L is close 
enough here) 
  Thiourea                               - approx 0.01 g/L 

Now for other additives for "bright copper" (which I think is quite 
unnessesary for our purposes, but will list them anyway) 
    
   wetting agent (could be a flocculent or even a drop or two of detergent)   
0.2 g/L 
    Dextrin   0.01g/L 
    Mollases(as an alternative to Dextrin)  0.75 g/L 

also, I have heard reference to using guar gum for similar purposes here, but 
my 
book here does not list it.  I think a drop of old fasion horse glue can even 
be used here.   

>That guy at work with the copper desktop is right -- one chemical used 
>in electroplating is urea. (Likely derived as uric acid from human pee.) 
>Also goes by the name thiurea (if I remember my spelling.) I use to do 
>my own tin-plating on copper printed circuits that I'd make in my 
>garage, and the system won't work without the urea. (Never tried peeing 
i>nto it though. *grin*) 

(close - thiourea) 

>Current density is also critical so as to form a slowly building layer. 

YES!! current density is a major factor.  typical is 20 - 100 amps/ sq. ft   
cathode area(or about 140 - 700 ma/ sq. in.) I would suggest the low end 
particulary in the beginning to minimize the formation of nodules etc.  the 
thiourea and other 'leveling agents help this greatly.  I think one of 
Terry's biggest difficulties is due to excessive current.  Gotta calculate 
the area of the little skinny tungsten rods. 
   Last night,  I plated one of my tungsten induction furnace gaps.  These 
are 3/4 in. diameter and 1.5 inches long.  I only plated half of it to see 
how it would come out.  I knew that if I did not like it, I can simply 
dissolve the copper off with nitric acid.  Anyway, I used the most crude 
simplist setup imaginable.  I used electrical tape to attach two lengths of 
wire with alligator clips to a D cell battery.  I discovered right away that 
too much current was passing through the solution.  I then put a 3 ohm 
resistor in series and let it go overnight.  It came out very nice in spite 
of the fact that I had NOTHING in the solution except copper sulfate and 
sulfuric acid.  I see that some really tiny nodules did start forming, but 
nothing that a quick sanding with 400 grit paper won't take care of.  This, 
to me, would be fine for the purpose of soldering to the tungsten if one 
wishes to. 
  
I think I will put some sugar(or mannitol) into by plating bath to see about 
making a nice bright  plating, but this is really just for aesthetics and has 
no practical value for what we are doing.   
Should I open a new can of worms and ask why no one has yet mentioned silver 
plating?  lol.   Most of the silver plating baths I know of use cyanide, so I 
doubt too many people would really care to try this.   
Cheers, 
Mike