http://www.pfonline.com/articles/pfd0603.html
Cyanide Silver Solutions
Typical general purpose cyanide silver plating solutions consist simply of
about 90-120 grams of free alkali cyanide per liter, together with about
25-40 grams metallic silver per liter, added in the form of the
corresponding alkali silver cyanide, or as Ag CN. At one time the use of
sodium cyanide was the norm, but this was largely superseded by potassium
cyanide because of the higher solubility of most potassium salts. As a
result of hydrolysis, carbonate gradually forms in alkaline cyanide
systems, and at concentrations greater than about 90 grams per liter,
sometimes less, impedes dissolution of the anode and causes deposit
roughness. Excess carbonate can be frozen outfrom sodium cyanide-based
solutions by chilling the solution to 3oC or so and filtering. This is not
possible in potassium-based solutions, which require treatment with calcium
cyanide or barium cyanide. Additionally, some brightener systems,
particularly selenium or sulfur-based, are more effective in sodium-based
solutions. ............................................
Noncyanide Silver Plating
Of the various soluble noncyanide forms of silver, only two have achieved
commercial success in electroplating applications. These include
organosilver complexes, of which the complex with succinimide is best
known; and the alkaline thiosulfate, to which succinimide is added as an
anode activator.
The design of electrolytes for noncyanide silver plating is constrained by
the requirement to maintain the anodes in an active and film-free condition
as a source of silver for replenishment. Nitrate, lactate, and sulfamate
are suitable for this purpose, and various combinations have been employed.
A further consideration is that succinimide hydrolyzes slowly at the
operating pH (generally from about 7.5-9) and has to be periodically
replenished, regardless of whether or not the plating solution is actually
being used. Since the hydrolysis process consumes hydroxyl ions, the
solution pH falls slowly as well, and must be periodically adjusted.
For all these considerations, however, deposits from the succinimide
solutions are semibright, with good conductivity and above-average
resistance to wear. In the as-plated condition they are harder (120-130
Knoop) and more stressed than corresponding deposits from cyanide solution;
but as with cyanide deposits, they show relaxation with time at ambient
conditions, and can be annealed by post-baking. In the as-plated condition
they are more easily subject to tarnishing than are deposits from cyanide,
but this can be largely overcome by chemical treatment and stress-relief,
even by immersion in hot water.
More recently, a series of silver complexes with hydantoin and substituted
hydantoins have been prepared, and are coming into use. These promise
improved pH stability and solution control, as well as higher brightness
and greater resistance to tarnishing.
..also, control the current to avoid "burning" the edges.
Ode
At 02:06 PM 3/25/2006 -0800, you wrote:
I would like to plate some small items with silver. Can our EIS system,
or some simple variation be used to apply a very thin coating? I believe
industrial plating solutions use an acid bath, but that is about all I
know. Since this is limited use, I don't need great speed and quantity of
items.
note: I am still considering, or rather interested, in the cast iron
plating concept.....but this is not that.
Maz
Acmeair <[email protected]> wrote:
doing the vitc/salt protocol, can you use potassium instead of salt?
need a good source of vit c, potassium,
thanks, jim
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