WHAT IS ELECTROLYSIS
The following is a very basic explanation of how electrolysis works, but it is enough to give the average person a working understanding of what is happening to the coins you are cleaning.
Electrolysis is used around the world in the electro-chemical industry to produce gases and purify chemicals. Gases such as Chlorine and Hydrogen are produced as well as chemicals such as Sodium metal and Sodium Hydroxide. The principles of electrolysis are also used in industry to plate a base metal with a dissimilar metal such as silver plating a brass ring or chrome plating a car bumper. This will be discussed further.
As coin cleaners we are not interested in the production of chemicals, but rather blasting the concrete hard encrustations of dirt and metal off the coin. These encrustations have attached themselves to the coins over centuries of time, and if conventional methods of cleaning don’t work, electrolysis will.
Electrolysis works by passing direct current (DC) through an electrolyte. An electrolyte can be any solution that has free electrons. A simple electrolyte is tap water. Tap water is slightly conductive because it contains a certain amount of minerals, where as distilled water is almost a perfect insulator. Electrodes are inserted into the electrolyte and one is attached to the positive source (anode) and the other is attached to negative source (cathode). Electrodes can be made from many materials, iron, stainless steel and carbon are just some of the materials that can be used for electrodes. Some materials make better electrodes than others, for instance platinum will last much longer than titanium. Electrodes are sacrificial, meaning that they will eventually be used up, they disappear in the electrolyte solution. Electrons flow from the negative source to the cathode then through the electrolyte to the anode and back to the positive source.
Electrons move from
negative to positive as
shown by the arrows.
Providing that the voltage is above approximately 1.5VDC current will flow in tap water and electrolysis will begin. The electron flow begins to split the water molecules into positive Hydrogen ions (H) and negative Hydroxide ions (OH).
The positively charged Hydrogen ion is attracted to the negative cathode where it regains an electron to become neutral again. This Hydrogen atom joins up with another Hydrogen atom and becomes a Hydrogen molecule (H2), and this molecule bubbles to the surface.
H + H ---> H2
The negatively charged Hydroxide ion is attracted to the anode where it gives up its extra electron and becomes neutral again. The Hydroxide molecule combines with three others to form one Oxygen molecule (O2)and two water molecules(H2O). The Oxygen molecule bubbles to the surface.
4OH ---> O2 + 2H2O
So we now know that Hydrogen gas forms at the cathode and Oxygen gas at the anode. The amount of gas produced is proportional to the amount of current . Assuming the voltage was around 1.5VDC the amount of gas would be minimal.
Now lets add just a pinch of table salt to the water. The table salt which is called sodium chloride (NaCl) makes the water more conductive and aids in current flow. The more current flow the more gasses we will produce and the quicker a piece of metal or coin will be cleaned. With just a touch of salt added to the water, nothing much changes in the electrolysis process, except it will happen faster. Hydrogen is produced at the cathode and Oxygen is produced at the anode.
If we keep adding table salt until no more will dissolve in the water we will have a saturated salt solution. We have made the solution as conductive as possible with table salt. This will give us the maximum amount of current possible given the 1.5VDC source and the saturated salt solution. With the saturated salt solution the electrolysis process changes. In a saturated solution of salt water it is easier to oxidize the chlorine than the oxygen, so while we still produce hydrogen at the cathode, chlorine gas is now produced at the anode. Hydrogen and oxygen are very insoluble gases in water and will immediately bubble to the surface, while chlorine will dissolve into the water. Once the water is saturated with chlorine, then the gas will start to form bubbles and rise to the surface. If you use table salt in your electrolysis setup you will eventually start to smell the chlorine gas.
How should we make our electrolytic solution? One can use many different chemicals to make an electrolytic solution. Table salt, baking soda, and various strong/weak acids and bases. Since we don't want to damage the kitchen counters or blind ourselves we won't consider the acids and bases. Baking soda or sodium bicarbonate (NaHCO3) makes a good electrolytic solution, everyone has some on hand and it won't make chlorine gas. I find that the baking soda solution is less conductive than the salt solution so the electrolysis process is somewhat slower. People have also told me that they don't like to use table salt because it can be corrosive to the coin being cleaned.