Hi Arnold, Nice to talk to you again! Happy to repost, but not quite sure of the particular ones you had in mind. I have two (see below) which explain the rational behind current limiting, and I shall try to find my calculations of the current density.
Kind regards Ivan. "Hi Arnold, I think we need to start on common ground, so I will go through the process as I understand it...you probably know all this anyway. The power supply and the electrolysis cell form a circuit. The cell consists of an electrolyte and 2 electrodes. Current is able to flow in the circuit when cations are able to leave one electrode and anions contact the other. Electrons cannot flow in a liquid and so travel via the power supply connections. In the case of a silver anode (positive electrode), at a certain potential a single electrons will be removed from silver atoms creating Ag+ silver ions. These cations, as they are known, enter the liquid electrolyte and drift towards (and some will eventually contact) the cathode where they are supplied with the electron they need to become metallic silver once more. The current able to flow in the circuit is wholly dependent upon the conductivity of the electrolyte, that is the number of ions that are able to complete the circuit. Distilled water is a very poor electrolyte but above 0.71V hydrogen will reduce (gain electrons) at the cathode while silver requires 0.80V to oxidise (lose electrons) at the anode. This is what drives the reaction at start up. Silver is oxidised at the anode, supplying electrons, and hydrogen gas is generated at the cathode receiving electrons. The limiting factor at this time is the number of hydrogen ions able to be ripped from the water molecules, and this is a function of the current flow and so of the applied potential. As silver ions enter the solution and ultimately reach the cathode they are also reduced as the reduction potentials of hydrogen and silver are similar, and reducing hydrogen leaves a charged hydroxyl anions in solution which adds to the accumulation of charged species, hence the current increases. The reason that silver accumulates in the solution at all, even though the same number of electrons oxidised at the anode must be reduced at the cathode, is that the later is shared between hydrogen and silver, that is more silver ions enter the system than leave it. What I am leading to Arnold, is that to achieve an acceptable concentration of silver ions (10 -20 ppm in my opinion) one must accept a certain amount of plating out on the cathode, and that the process is not futile past this point as silver keeps accumulating as long as hydrogen gas is evolved at the cathode. Now, in order to generate a product that is of the smallest particle size one must allow the silver ions to hydrate, to become surrounded by water molecules so that they resist the attractive forces that are generated between like ions and limit the aggregation that otherwise occurs. Limiting the current limits the amount of ions generated at any moment, increasing the chance of quick hydration and dispersion. There is a certain current density at the electrode that when exceeded leads to an inferior product. The trouble with limiting the current of course is, as the resistance of the cell decreases so does the voltage. It is the voltage which determines the type of electrolysis that will proceed (it is possible to remove more than one electron from a silver atom if the voltage is high enough). I feel that being able to control the voltage across the electrodes will eventually lead to a better product. The only way I can think of to do this is by PWM which although, as you rightly note, is a method of controlling power input, it does so at a particular voltage (yes?) and is also a method of limiting current. PWM would also have the advantage of the pulse - drift movement of the silver ions, further increasing the chance of better hydration and dispersal." and "In anticipation of your question, let me give a little more information. The velocity of an ion in an electric field is the product of the field strength E(Vcm^-1) and its electrophoretic mobility U(cm^2 V^-1 s^-1). The ion is instantly accelerated to the velocity where the resistive forces (viscosity of medium etc.) equal the attractive forces, where upon the ion travels at a constant rate. v = EU(cm s^-1) For silver ions (effective radius of 0.15nm) U = 6.4 x 10^-6. Larger ions = slower speeds. Higher charge = higher speeds. So at a field strength of 1Vcm^-1 the velocity = 6.4 x 10^-6 cm s^-1 which is very slow unless you are an ion. Obviously it is not the voltage that is the main diffusion factor in CS production but thermal or mechanically induced currents. The link below (part of a marvellous body of work) gives a gentle insight into the world of electrode dynamics, and the treatment of the electrolyte solution as a resistive and capacitive load. http://diana.oce.orst.edu/cmoweb/micro/glennthesis/AppendA.htm > -----Original Message----- > From: Arnold Beland [mailto:abel...@tampabay.rr.com] > Sent: Tuesday, 26 March 2002 12:21 a.m. > To: *Silver-List* (E-mail) > Subject: CS>Hi Ivan > > > Would you be so kind as to re-post your rational and calculations for > surface area versus current versus particle size?. Glad to > see you are > still around. > > Arnold -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: silver-list-requ...@eskimo.com -or- silver-digest-requ...@eskimo.com with the word subscribe or unsubscribe in the SUBJECT line. To post, address your message to: silver-list@eskimo.com Silver-list archive: http://escribe.com/health/thesilverlist/index.html List maintainer: Mike Devour <mdev...@eskimo.com>
