in which articles is electroplating used
Answers
First, you have to choose the right electrodes and electrolyte by figuring out the chemical reaction or reactions you want to happen when the electric current is switched on. The metal atoms that plate your object come from out of the electrolyte, so if you want to copper plate something you need an electrolyte made from a solution of a copper salt, while for gold plating you need a gold-based electrolyte—and so on.
Next, you have to ensure the electrode you want to plate is completely clean. Otherwise, when metal atoms from the electrolyte are deposited onto it, they won't form a good bond and they may simply rub off again. Generally, cleaning is done by dipping the electrode into a strong acid or alkaline solution or by (briefly) connecting the electroplating circuit in reverse. If the electrode is really clean, atoms from the plating metal bond to it effectively by joining very strongly onto the outside edges of its crystalline structure.
Artwork: Copper-plating brass: You need a copper electrode (gray, left), a brass electrode (yellow, right), and some copper sulfate solution (blue). The brass electrode becomes negatively charged and attracts positively charged copper ions from the solution, which cling to it and form an outer coating of copper plate.
Now we're ready for the main part of electroplating. We need two electrodes made from different conducting materials, an electrolyte, and an electricity supply. Generally, one of the electrodes is made from the metal we're trying to plate and the electrolyte is a solution of a salt of the same metal. So, for example, if we're copper plating some brass, we need a copper electrode, a brass electrode, and a solution of a copper-based compound such as copper sulfate solution. Metals such as gold and silver don't easily dissolve so have to be made into solutions using strong and dangerously unpleasant cyanide-based chemicals. The electrode that will be plated is generally made from a cheaper metal or a nonmetal coated with a conducting material such as graphite. Either way, it has to conduct electricity or no electric current will flow and no plating will occur.
We dip the two electrodes into the solution and connect them up into a circuit so the copper becomes the positive electrode (or anode) and the brass becomes the negative electrode (or cathode). When we switch on the power, the copper sulfate solution splits into ions (atoms with too few or too many electrons). Copper ions (which are positively charged) are attracted to the negatively charged brass electrode and slowly deposit on it—producing a thin later of copper plate. Meanwhile, sulfate ions (which are negatively charged) arrive at the positively charged copper anode, releasing electrons that move through the battery toward the negative, brass electrode.
It takes time for electroplated atoms to build up on the surface of the negative electrode. How long exactly depends on the strength of the electric current you use and the concentration of the electrolyte. Increasing either of these increases the speed at which ions and electrons move through the circuit and the speed of the plating process. As long as ions and electrons keep moving, current keeps flowing and the plating process continues.