I read in !emc-pstc that Jan Vercammen <jan.vercamm...@agfa.com> wrote (in <ofdcf4c49e.94e1a38a-onc1256e76.004f83c3-c1256e76.004fc...@agfa.com> ) about 'zincor EMI contact' on Wed, 14 Apr 2004:
>Because it is lower in the electrochemical table zinc oxide will protect >the iron. No, it doesn't work like that. Zinc is a 'sacrificial coating', unlike nickel, chromium etc. The zinc dissolves in the oxygenated water, instead of the iron being converted to rust. >The steel is coated with a thickness of 2.5 to 5 microns (data from >manufacturers). > >The question is about a zincor chassis which we want to contact with Be Cu >fingers. Do the fingers penetrate the zinc oxide in a reproducible and >consistent >manner? There is no *hard* oxide layer on zinc, unlike on some other metals. The fingers will rather easily contact the zinc metal itself. The electrochemical table Annex J in IEC/EN 60950 shows that zinc in contact with copper or copper alloys is above the critical line, so corrosion will occur in the presence of moisture and oxygen. This means that contact will not necessarily be reliable. Having said that, the electrochemical potentials are NOT a safe guide to avoiding electrochemical corrosion, because they are determined under laboratory conditions with no impurities present. But 'real life' conditions (especially where chlorine ions are present, which is almost everywhere) are usually less favourable that the table indicates, i.e. even combinations below the line can suffer from corrosion. -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
