This coating, unlike the metal itself, can take dyes. When aluminum is anodized in this way, an aluminum oxide coating builds up on its surface. Galvanized iron is widely used in garbage cans, pails, and chain-link fencing.Īnodizing is a process in which a piece of metal is made the anode in an electrolytic cell to oxidize it deliberately. The zinc oxidizes in preference to the iron. Galvanized iron has been coated with zinc so that it can be used outdoors or in the ground without rusting.

For the same reason, a zinc cable was buried alongside the Alaskan oil pipeline, the huge steel pipe that transports petroleum from the Alaskan oil fields to the lower United States. It is said to be “sacrificed ” because it gradually gets eaten away by oxidation instead of the iron. Because zinc oxidizes more easily than iron, the zinc acts as the anode and is preferentially oxidized. The iron and zinc in the moist soil constitute the two electrodes of a galvanic cell. For example, to keep iron or steel from oxidizing (rusting) when in contact with air and moisture, such as when it is being used as a fence post, the post can be connected to a piece of zinc that is buried in the ground next to it. Anodes in practical useĪ sacrificial anode is a piece of metal that acts as an anode, and is therefore oxidized, to protect another piece of metal from being oxidized.

The cathode, then, is the electrode at which the corresponding reduction reaction is taking place. The anode is the electrode at which an oxidation reaction is taking place in the cell. The confusion can be cleared up by defining the anode and cathode in terms of the actual chemical reactions -the oxidation and reduction reactions - that take place inside the cell, whether it is generating electricity as a galvanic cell or consuming it as an electrolytic cell. This has led to a variety of conflicting definitions of anodes in various textbooks and reference works. Furthermore, even chemists have been confused because negative charge flows away from one of the electrodes inside the cell, but in the external circuit negative charge flows toward that same electrode. Chemists and physicists correctly consider electricity to be a flow of negative electrons, but for historical reasons, engineers have considered electricity to be a flow of positive charge in the opposite direction. Unfortunately, there has been much confusion about which electrode is to be called the anode in each type of cell. In either case, there are an anode and a cathode in each cell. An example of a galvanic cell is a flashlight battery, and an example of an electrolytic cell is a cell used for electroplating silver or gold. There are two kinds of electrochemical cells: those in which chemical reactions produce electricity -called galvanic cells or voltaic cells -and those in which electricity produces chemical reactions -called electrolytic cells. In an x-ray tube, the kind of metal that the anode is made of determines the kind of x rays (i.e., the x-ray energy) that the tube emits. The positive electrode is called the anode the negative electrode is called the cathode.Ĭommon examples of vacuum tubes in which electrons flow from a cathode to an anode are cathode ray tubes, such as those in television tubes, computer monitors, and x-ray tubes. Electrons, being negatively charged, are repelled out of the negative electrode and fly through the vacuum toward the positive electrode, to which they are simultaneously attracted.

Vacuum tubesĪ vacuum tube is a tube (usually made of glass) with most of the air pumped out, which usually contains two electrodes -two pieces of metal with a potential difference (a voltage difference) applied between them. The word anode is used in two different sets of circumstances: with respect to vacuum tubes and with respect to electrochemical cells.

Anode cathode pic