Tag Archives: Electroplating

The Road to Gold: Producing Olympic Medals

The Olympic Gold medal is possibly the most iconic symbol of athletic achievement and excellence in today’s society. However, it may be surprising to learn that they are not, in fact, made of pure gold;. Sure, the bronze is made of pure bronze, an alloy made up of tin and copper, and the silver is 92.5% pure. But the gold medal is in fact identical to the silver, only with a 6-gram coating of gold. the process by which this coating is made and applied to the otherwise second-place medal is called electroplating.

Electroplating is achieved through electrodeposition. As the name implies, a coating, most often a metal, is adhered to a surface by an electric current.

As seen in the figure above, the two metals are hooked up to some form of power supply: the recipient metal is negatively charged to act as the cathode, and the donor metal is positively charged to act as the anode. For Olympic medals, the cathode is the silver base, and the anode is pure gold. These metals are then immersed in an acidic solution, usually sulfuric acid in the case of Olympic medals, which also contains a salt of the metal to be deposited. The positively charged portion of the dissolved salt, the metal, is attracted to the cathode and receives electrons, losing its ionic nature and reverting back to its metallic form. The gold anode, meanwhile, is slowly oxidized and dissolves into the solution, replaces those cations being attracted to the cathode.

In order to make this possible, these equations must be taken into account:

Q = m n Na Qe , the amount of charge “Q” required to reduce the depository metal is equal to the number of moles “m” of metal times the number of electrons “n” times Avagadro’s number “Na” times the charge of an electron “Qe“. Avagadro’s number times the charge of an electron is referred to as the Faraday constant “F”.

If the number of moles deposited must be known, and assuming constant current flow, the charge “Q” can be determined with the equation  Q = It , where “I” is the current and “t” is the number of seconds the current is applied.

To determine the weight of the deposition, simply mulitply the number of moles by the molar weight of the metal. Finally, the determine the thickness of the deposit, we use the equation T = w / AD , where “T” is the thickness, “w” is the weight determined, “A” is the area of the recipient metal, and “D” is the diameter of the recipient metal (AD is the volume of the cathode).

Therefore, to determine how thick the layer of gold will be, we can combine the above equations thusly:

T = w/AD = Mw It/nFAD

After the proper amount of gold is applied, the design for the medal heated to 750 degrees to soften the metal, and the desired design is impressed at extreme pressure with a die press. However, there is still more equations and factors in this long and difficult process. Such a lengthy effort for so small object: the result, however, is well worth the effort.

 

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