url: http://escribe.com/health/thesilverlist/m61852.html Re: CS>PWT & its Limits From: Robert Berger Date: Fri, 8 Aug 2003 13:25:54
> In fact just stopping for a minute and restarting without doing > anything and the current readings will drop. > "Ole Bob" You are seeing the effects of the Nerst diffusion layer. Nernst and Einstein discussed this in 1906, which resulted in the partial differential equations that bear their names and describe the concentration of ions close to the electrodes. The important things to remember are 1) the density of the ion cloud depends on the current density at the electrode, and 2) the ion concentration reaches a maximum at the surface of the electrode. I have described how this influences the formation of silver oxide in previous posts, and why the current density at either electrode is the major influence on particle formation. A high current density at either electrode promotes the formation of silver hydroxide, which then decomposes to silver oxide. This grows by agglomeration to form particles large enough to absorb blue from tha spectrum, leaving the yellow color we are so familiar with. I also showed how to visualize the high concentration of silver ions at the anode with ordinary cabbage juice, and also with plain salt. The Nernst-Einstein diffusion layer is real, and readily visible to anyone who wants to see it. Of course, modern depictions give an asymptotically-changing concentration in the diffusion layer instead of straight-line, but that's OK. The basic idea still holds. Here are some references that may be helpful: 3.1 The Nernst Equation The Nernst equation describes the fundamental relationship between the potential applied to an electrode and the concentration of the redox species at the electrode surface. http://www.phattimes.com/myoglobin/chapter3.htm Diffusion Controlled Electrode Processes http://www.chem.uoa.gr/Applets/AppletDiffus/Text_Diffus2.htm Mapping Concentration Profiles within the Diffusion Layer of an Electrode http://www.chimie.ens.fr/w3amatore/themes/ume/carto_angl.htm CHM 3120C Introduction to Analytical Chemistry LECTURE NOTES Week #10 X. Coulometry and Voltammetry A. Principles of Electrolysis http://www.chem.fsu.edu/cooper/chm3120f00/Notes-Week10.htm Current equations - mass transport http://www.tannerm.com/mass_transport.htm The Tafel equation http://www.tannerm.com/Tafel.htm Butler-Volmer equation http://www.tannerm.com/Butler-Volmer_1.htm Current equations 1 http://www.tannerm.com/current.htm Current equations 2 http://www.tannerm.com/current_equations_2.htm Current density http://www.tannerm.com/current_density.htm Diffusion and conductivity: the Nernst-Einstein equation http://www.tannerm.com/diffus_conduct.htm Ion speeds and conductivity-the Einstein and Stokes-Einstein equations http://www.tannerm.com/IonSpeeds.htm Limiting current http://www.tannerm.com/limiting_current.htm And thousands more... Best Regards, Mike Monett -- The silver-list is a moderated forum for discussion of colloidal silver. Instructions for unsubscribing may be found at: http://silverlist.org To post, address your message to: [email protected] Silver-list archive: http://escribe.com/health/thesilverlist/index.html List maintainer: Mike Devour <[email protected]>
