John, Thanks for your insights, I believe we are in agreement. Possibly the reason the table was never revisited is because either the potentials listed were taken from an undocumented source or some sort of an ad hoc test method was used and never documented. No one today wants to risk upsetting years of usage based on this table. I see no reference for the data source, although I have not tried going back through earlier editions. I am currently viewing IEC 60950-1: 2005 and 2001. The two errant points indicate 0.5 V. Unfortunately, this table is normative. Interesting that silver, gold and platinum are listed in elemental form. When used as plating on another base metal, I am not so certain these potentials will be the same.
I also noticed, the way the numbers are set up there are no negative potentials as you would find in a anode-cathode system referenced to hydrogen. In reality electrochemical potentials, or more correctly, electrode potentials must have a standardized point of reference. In the 60950 table it is apparent the reference was reassigned as the negative electrode of every combination. My guess is someone did an experiment with commonly available metallic samples of the day and placed them in an aqueous solution. Simple measurements of galvanic potentials of every combination were taken. My hope was to reproduce the experiment that generated these numbers and expand the table to include other alloys commonly used in today's world. The problem of course is all the unknowns: ambient temperature, atmospheric pressure, electrode profile, instrumentation, and number of samples averaged. Thanks, - doug Douglas Powell http://www.linkedin.com/in/dougp01 Original Message From: John Woodgate Sent: Tuesday, March 25, 2014 12:47 AM To: [email protected] Reply To: John Woodgate Subject: Re: [PSES] electrochemical potentials In message <cabyvtvpn92qzq49yjff2pfdholb8ycpxpvpjuquw4hfavfo...@mail.gmail.com>, dated Mon, 24 Mar 2014, Doug Powell <[email protected]> writes: >s anyone aware of some resource which expands on the electrochemical >potentials table found in IEC 60950 Annex J? Sorry, can't help with that. > >I am attempting to correlate this table to other resources and include >metals which are not found on the IEC version. It is obvious this >table had not seen recent committee review in a very long time and >there are a number of modern metals and alloys which really should be >added. I've had problems with this table for a very long time. It tends to be treated by the committee as a 'sacred cow', but in fact it's not useful and is positively misleading. > >Additionally I have noticed what appears to be a couple of errors in >the table where the listed potential apparently has a misplaced decimal >point. > >1) Intersection of "Cr on steel, soft solder" and "Lead" >2) Intersection of "Rh on Ag on Cu, silver/gold alloy" and "Silver" What numbers do you see? In the latest edition, EN 60950-1:2006+A12:2011, the values are 0.05 V. I don't think either 0.005 V or 0.5 V would be correct. You can check the numbers by making a triangular circuit from any three of the materials. The voltages around the circuit must sum to zero, otherwise the circuit would be a perpetual generator. Care is needed to get the signs of the voltages correct. > >Also, when I try to correlate the potentials in this table to other >resources the numbers do not match up very well. Apparently the test >method used in the original IEC 60950 table was somehow different than >the CRC Handbook of Chemistry and Physics. Very likely: the original source seems unknown, but relates to tests under laboratory conditions with no contamination from such ubiquitous ions as chlorides. I asked some connector manufacturers, who make connectors for aerospace that have to withstand all sorts of contaminants, and they regarded the table as near useless for predicting corrosion effects. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Nondum ex silvis sumus John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
