You have a satuaration point at a given temperature.
When the saturation point is exceeded, you get crystal formation.
Crystals like to form around impurities and tend to get bigger and bigger when they do. [The string hanging in the jar of cooling sugar water]
The more sugar that's dissolved, the bigger the crystal, or the more of them.
In CS making, without stirring, there are high ion concentration zones where crystals will form first.
As the water is supersaturated, more and more crystals form. [The stronger you make it, the more ions are packed together to make more crystals which want to become bigger if they can...ion to particle ratio eventually equalizes and particle size 'wants' to be larger]
A rough surface has more exposed area than a smooth one.
Ions like to discharge from edges and points..like any electrical arc.
A rough pitted electrode has many many small discharge points around the edges of the pits.
Eventually the pits expand till they meet, making points which will turn into new pits.
A coin only has edges, no points. Points are the preferred discharge point, edges, second preferred.
An ion high concentration zone will be more dense around a point, less dense around an edge, less dense than that around a curve and least dense near a flat discharge surface with virtually no discharge on the other side of a flat surface decreasing towards the center of the other side.
Modern electroplating electrodes are "D" shaped in cross section for that reason, with the rounded part of the "D" facing away from the object to be plated. Vigerous random agitation of the electrolyte is used to help prevent hot spots on the object being plated..mostly corners and edges.
Edges and points work the same way on the other end of the process, attracting ions.
Projecting edges and points are sometimes fitted with bleed-off wires and holes will sometimes have 'bleed -on'? wires centered in them if getting a good thick coating is important..or bleed-off wires to prevent buildup on the edges of the holes. Placing a sharp point in strategic locations guides the ions towards it and away from other areas.
Reversing electrodes in the CS maker amounts to a reverse current cleaning tank used to preclean an object to be plated by removing some of its surface electrically.
Ode [Once a photo etch and electroplate technician..electroless and electrical plating of copper, zinc, tin/lead and gold..making circuit boards and computer hardware for Terminal Communications Inc]
At 12:34 PM 8/18/2004 -0400, you wrote:
>>>>
The $5 Maple makes a very nice electrode. Another<<<<
reason I prefer a bullion coin like the Maple to wire is
that it is rigid enough to change the surface texture.
I like to impart a satiny texture, using the brass-
bristled detailing brush. Silver loss from abrasion is
no big deal, since I have a spare electrode and more
than enough for a lifetime supply. In the long run, DW
is more expensive and presents more problems.
A satiny finish on an electrode may, or may not,
have an effect on the ratio of ion to particulate in the
EIS. I still wonder if there is a dynamic equilibrium
between the two species leading to a constancy of
that ratio.
Matthew
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