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Effects of Voltage on Colloidal Silver Production


Effect of Voltage on Colloidal Silver Production
Copyright 2011

Most amateur colloidal silver producers know of connecting 3 nine volt batteries together to get 27 volts, and most have heard that 30 volts is the best voltage to make colloidal silver.  But is this correct?  The answer is not necessarily.  Voltage is important, but the exact amount depends on other factors.   

To understand why, it is necessary to understand some background:

1 ) Some definitions and terms:

    a) The Anode is the positively charged silver electrode, where oxidation of silver occurs producing silver free radicals.
    b) The Cathode is the negatively charged electrode (doesn't have to be silver).
    c) Positively charged ions are atoms or groups of atoms which have fewer electrons than protons, while negatively charged ions are atoms or groups of atoms which have more electrons than protons.
    d) Electric field strength is determined by the voltage between the anode and cathode divided by the distance between them.
    e) Ag is the chemical symbol for silver

2 ) The battery creates an electric field between the Cathode and Anode.   It does this by removing some electrons from the Anode, and adding the exact same amount of extra electrons to the Cathode (initial current flow).  Electrons move to or from the electrodes until their electric field exactly cancels out the battery voltage.  Changing the distance or voltage between the electrodes changes the amount of electron surplus or deficit on the electrodes.  Initially, the electrodes behave like and actually are a charging capacitor.

If you want a formula, it would be: e = kV/d
where e= field strength, k = a constant, V = voltage, and d = distance.

3 )  The shortage of electrons on the surface of the anode facing the cathode effectively causes silver metal ions at the surface of the anode to be formed1.  These Ag+ ions are called silver free radicals and are very reactive, meaning they want to chemically combine with something else which will restore their missing electrons.  Initially, the only negative ion which should be in distilled water is the hydroxide ion (OH-).

4 )  The electric field propels negatively charged ions in the water toward the Anode, and positively charged ions to the Cathode.  This allows a compatible negatively charged ion (the OH- in this case) to react easily with the silver atom to produce a molecule of silver hydroxide (AgOH) which dissolves and floats free into the water.  When I say compatible, I mean it must react with the silver anode to produce a compound which is to some degree water soluble and ionizable. 

When the OH- ion touches a silver atom on the anode, it allows the battery to remove one more electron from the Anode thus creating another silver free radical ion.

The electrical current then depends upon the number of OH- ions available and also the number of electrons removed from the Anode by the battery. This in turn depends on the voltage applied,  the distance between the electrodes and how many OH- ions have already been produced.  (It also depends upon the surface area of the electrodes, but I am assuming here that electrode size is fixed.)

5 ) If only distilled water is used, a very tiny amount of water molecules dissociate to provide H+ and OH- ions.  This is why the colloidal silver process starts so slowly.  In 1 liter of pure water, less  than 2 millionths of a milliliter actually dissociate into  H+ and OH- ions.

6 ) When an OH is removed from the water by combining with an Ag+ free radical, another water molecule disassociates producing a new OH.  When the AgOH enters the solution, it dissociates again into Ag+ and OH- ions.  So each OH- removed produces two new OH- ions, causing the conductivity of the water to increase.  This is why the process speeds up as it goes along.

7 ) The Ag+ ions are now no longer electrically neutral and thus are attracted to the Cathode while the OH- ions are again attracted to the Anode where they can liberate another Ag.  Some of the Ag ions reach the Cathode where they pick up an electron reverting the Silver ion to metallic silver.  This is what creates the silver residue on the Cathode.  It is the basic electroplating system and obeys electroplating laws unless it is prevented.

8 ) There is a minimum voltage necessary to create colloidal silver, but it is very low,  3.5 volts when using a sodium based electrolyte.  However, in practice, the applied voltage must be several times higher than this minimum to maintain reasonable current levels.

9 ) A higher voltage produces more efficient scavenging of the silver hydroxide from the boundary layer between the silver anode and the bulk fluid.  This helps keep the concentration of silver hydroxide below its solubility limit close to the anode, causing less precipitated silver oxide in the solution.  Electrode voltages below 10 volts are not as effective at scavenging, but the positive effect is not linear.   IE: doubling the voltage does not halve the deposition of silver oxide on the anode.  Vigorous stirring allows lower voltage to be used, as the stirring motion also scavenges the silver oxide from the anode.

10)  The voltage across the electrolysis cell is the sum of three separate voltages:
  A)  The voltage drop across the anode boundary layer of 0.8 volts
  B)  The voltage drop across the cathode boundary layer of 2.7 volts (when using electrolyte)
  C)  The voltage drop across the bulk fluid between the electrodes.
This sets the minimum voltage of 3.5 volts plus the voltage loss of the bulk fluid.  To account for the bulk fluid the minimum voltage must be substantially higher and depends on the amount of electrolyte, and the electrode geometries.

14) Doubling the distance between the electrodes halves the electric field which reduces the mobility of the ions resulting in less anode scavenging.  It also increases the electrical resistance between the electrodes which necessitates higher voltage to maintain the same current. 

The general rule is: required minimum voltage to keep same results is:
Vr = 3.5 + (New spacing) * (Old voltage - 3.5)  / (Old Spacing)

An electrode spacing of 1.5 inches is a reasonable distance for voltages up to 40 volts with 2 millimoles of sodium per liter of water (1 ml of 1 Molar sodium carbonate solution)


Voltage causes surface atoms of the silver anode to oxidize losing an electron and become a silver ion.
Voltage is the motive force which moves positive ions toward the cathode, and negative ions toward the anode.
Minimum of 3.5 volts is required to assure plateout protection and silver ion generation but practical minimum is 10 volts.
Higher voltage is helpful with high current to anode size ratios or without mechanical stirring.
Voltage does not directly determine speed of production. (IE: when using constant current source)

1)  This formation of metal ions on the positive terminal is the same effect that causes the copper wires on the positive post of a car battery to corrode over time, but not the negative one.  The corrosion on the positive terminal of a car battery is always a blue or blue-green color which indicates a copper compound or a reddish brown color if the battery clamp is steel.  Lead does not react readily with most anions (negative ions) but copper or iron does.

2) Good sodium based electrolytes are sodium carbonate, or sodium hydroxide.  Potassium carbonate is also a good choice.


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