Randy Crawford, age 14, of Rochester, New York, for his question:
What is electroplating?
Plated spoons and such have silver coating, perhaps no thicker than 1/1,OOOth of an inch. The idea of spreading this thin, even layer of metal sounds downright impossible. So it is at least for clumsy human fingers. But the delicate job can be done with perfect precision by electroplating. It is a chemical electric process called electrolysis.
The secret lies in knowing what an electric current does to certain atoms. The trick is in using its energy to transfer atoms from one metal and deposit them one by one .to plate an object made from another metal. Tableware is plated with silver for shiny show. Steel food cans are plated with a layer of non corrosive tin. A double layer of nickel and then chromium is added to give a hard, bright corrosion resistant surface to automobile parts.
This electroplating process is powered by DC current from a battery or generator. The energy supply must be steady and uniform to deposit an even layer. The two terminals from the power source are connected to two electrodes. These are dunked into a chemical solution called the plating bath. When the current is turned on, the bath acts as an electrolyte, which transports atoms from one electrode to the other.
The negative terminal may be connected to a spoon made of nickel, tin or some other base metal. When submerged in the right kind of chemical bath, it becomes a cathode, or negative electrode. The other electrode may be a rod of silver, which becomes a positively charged anode. In this case, the liquid chemical electrolyte may be a solution of silver cyanide.
When the current passes through the chemical bath, it dissolves atoms from the silver rod. They are robbed of electrons and become positive ions. These positive charges are attracted to the negative cathode. There they gain back their lost electrons and deposit themselves as silver atoms on the metal spoon. Atom by atom they cover its base metal with a layer of silver. The plating, may be 1/1,000 of an inch thick. A thicker layer is deposited by a stronger current or a longer period in the chemical bath, or both.
Each metallic plating requires the right anode and chemical solution. Gold plating is done with a gold anode and the electrolyte bath may be a solution of gold cyanide. Copper plating may be done with a copper anode and a copper cyanide.
The process for electroplating sounds simple enough. But several things can go sarong. Impurities on the cathode may prevent atoms from adhering to its surface. An alkaline solution is used to rinse away greasy dirt and an acid dunking removes chemical oxides. During, the process, the anode or cathode may lose or gain atoms too fast or too slowly. Hence, the electrolyte must be tested from time to time. Water or metallic chemicals are added to adjust it to the precise chemical mixture required to do a perfect job.