OT: tin whiskers (sort of)

A beautiful example (originally from 1895!) of what happens on modern Pb-free soldered PCBs that are exposed to certain types of moisture...

John :-#(#

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Fun (and short) I wonder how much current was flowing? I've always wanted to do an electroplating measurement to determine Avogadro's number. (so much charge gives so much mass.)

George H.

More precisely, Faraday's constant, N_A * e. (You'd have to do a seperate test to find e, to get N_A truly from scratch.)

I used that a bunch, back in high school when I did electrochemistry experiments. Disappointingly slow, but hey, electricity is cheap, and you can leave a lot of experiments to run unattended.

Downsides: side reactions and surface effects. Different materials have different overpotentials for different reactions, and small amounts of additives have large effects on reaction kinetics, or morphology (for plating -- levelers and such). Copper plating turns out to be pretty simple, but something as seemingly simple as electrolysis of sodium chloride is actually quite complex (because of the pH dependency between Cl-, Cl2, HOCl, OCl-, ClO3-, HClO3, ClO2, oxidation of the anode material, and reduction of them at the cathode).

Tim

Here's a whiskered, probably tin plated, d-sub connector shell:

Right, Faraday's constant. I was thinking of electroplating copper. I did a bunch of that in college, but never thought to measure the mass/ total charge.

George H.