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Re: Toroid Material

In a message dated 4/24/99 11:15:23 PM Mountain Daylight Time, 
tesla-at-pupman-dot-com writes:

>    <snip>                                       I had an idea a while ago 
about 
>  electroplating a Al duct toroid w/ copper until it was smooth.  In 
>  addition to a smooth toroid ( if that realy matters) you wouldn't 
>  have to worry about dents so much.  Pro: nice looking smooth shiney 
>  toroid made in your basement Cons: It would be heavy, take lots copper
>  (how much does copper cost), it would take forever, and might not work
>  (might still be bumpy). Any input?

   I would have some concerns about trying to plate an aluminum duct toroid 
with copper(aside from trying to immerse the thing if it is well sealed).   
The copper cost would be the least of concerns.  

  1)  The aluminum has an oxide coating that would make plating difficult.  
If that coating is removed, then the aluminum becomes very reactive and would 
possibly dissolve spontaneously in the electrolyte(aluminum in amphoteric and 
will dissolve in either acidic or caustic solutions-once the oxide coating is 
broken).  It would also spontaneously reduce the copper while it undergoes 
oxidation.  This would be very difficult to control to get a decent plating . 
 You would likely get a grainy, crystallized copper deposit that would not 
adhere well if at all.
   2)   To get a smooth plating of copper onto any substrate, certain 
additives must be used (such as guar gum, eg.).  It would take a number of 
experiments to get the additives and the proper concentrations just right.  
You would also need to determine the right current density( probably in the 
range of 50 to 100 amps per sq. meter).  
   3)  The ridges of the aluminum duct present areas of localized high 
current density.  This would tend to cause the metal that is being plated to 
be deposited at a greater rate on the ridges vs. the rate of deposition in 
the "valleys".   This would tend to exaggerate the ridges rather that 
smoothing them out.  The additives mentioned above could help somewhat in 
reducing this effect, but may not be enough.  I can envision a lot of sanding 
and several platings to get the valleys filled in before a smooth surface 
could be obtained.  I would expect that one would want to spin the cathode in 
the plating bath to prevent uneven plating as well over the whole surface.

   I am not saying that this couldn't be done(this is all just off the top of 
my head), but it would be quite a lot of work and the benefits may not 
justify this amount of work.  It may work if you first put a coating of 
nickel onto the aluminum and then copper plate onto the nickel.   I have 
deposited nickel onto aluminum with decent results(but not with aluminum 
ducting).  I dissolved nickel sulfate hexahydrate and then added ammonium 
hydroxide to complex the nickel(pretty blue solution) and simply immersed the 
aluminum substrate.  I would guess some multistep method similar to this 
would be the way to go.
  
Mike