Electrode . It is an electrical conductor used to make contact with a non-metallic part of a circuit, for example a semiconductor, an electrolyte, a vacuum (in a thermionic valve), a gas (in a neon lamp ) , etc.
Summary
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- 1 Operation
- 2 electrochemical cells
- 1 Primary cell
- 2 Secondary cell
- 3 Other anodes and cathodes
- 4 welding electrodes
- 1 Alternating current electrodes
- 5 external links
- 6 Fountains
Functioning
An electrode is a surface where oxidation-reduction reactions occur. Therefore, the processes that take place at the metal-solution interface of any metal in contact with an electrolyte (aggressive medium) cannot be measured in an absolute way (it has to be only relative). The metal in contact with the electrolyte has, on the one hand, a tendency to dissolve, thus remaining negatively charged, and, on the other hand, for ions from the electrolyte to be deposited on the metal, thus reaching equilibrium in a Certain moment. Thus, a potential difference has been created between the metal and the electrolyte. In order to measure this potential difference, a standard electrode was adopted, which is the normal hydrogen electrode , to which, by convention and at anytemperature , it was assigned the value zero.
electrochemical cells
An electrode in an electrochemical cell. It refers to either of the two concepts, either anode or cathode, which were also coined by Faraday . The anode is defined as the electrode at which electrons leave the cell and oxidation occurs, and the cathode is defined as the electrode at which electrons enter the cell and reduction occurs. Each electrode can become an anode or a cathode depending on the voltage applied to the cell. A bipolar electrode is an electrode that functions as the anode in one cell and the cathode in another.
primary cell
A primary cell is a special type of electrochemical cell in which the reaction cannot be reversed, and the identities of the anode and cathode are therefore fixed. The cathode is always the positive electrode. The cell can be discharged but not recharged.
secondary cell
A secondary cell, a rechargeable battery for example, is a cell in which the reaction is reversible. When the cell is being charged, the anode becomes the positive (+) electrode and the cathode the negative (-). This also applies for the electrolytic cell. When the cell is being discharged, it behaves like a primary or voltaic cell, with the anode as the negative electrode and the cathode as the positive.
Other anodes and cathodes
In a vacuum tube or a biased semiconductor (diodes, electrolytic capacitors) the anode is the positive (+) electrode and the cathode is the negative (-). Electrons enter the device at the cathode and leave at the anode.
In a three-electrode cell, an auxiliary electrode is used only to make the connection to the electrolyte so that a current can be applied to the current electrode. The auxiliary electrode is usually made of an inert material, such as a noble metal or graphite .
welding electrodes
In arc welding, an electrode is used as the pole of the circuit and the electric arc is generated at its end. In some cases, it also serves as a flux material. The metal electrode or rod is usually covered by a combination of different materials depending on its use. The functions of the coatings can be: electrical to achieve good ionization, physical to facilitate good formation of the weld bead and metallurgical to achieve anti-oxidation properties and other characteristics.
electrode welding
Those in charge of everything related to welding worldwide, as well as the components and types of electrodes, are the members of the American Welding Society. Electrode welding is performed in both alternating and direct current. In alternating current it is possible to use electrodes with larger diameters than usual, while in direct current it is not feasible to weld thick elements, although it produces a more stable arc that is easier to ignite. As far as welding with covered electrode is concerned, it is only carried out on a small scale, since it is known that its application is entirely manual, and its automation is not possible.
In all welding, it is necessary to achieve a joint that meets the characteristics of the metal that serves as the base, otherwise it is very likely that the weld will have a porous finish and be brittle, because the oxygen and nitrogen will have been absorbed by the metal in the molten state. TIG (Tungsten Inert Gas) welding, or welding by non-consumable electrode, is characterized by the use of a fixed electrode that is usually tungsten, in which process the metal that will constitute the welding bead must be added on the outside, although it might not be necessary, if it is the case that the parts to be welded are specifically thin. The most used gases are argon, helium, and mixtures of both. helium _, noble gas, is more used in the United States , since they obtain it cheaper in natural gas deposits. This gas leaves a more flattened cord with little penetration, as is the case with argon. A combination of helium and argon will provide a weld bead with qualities referring to both. This welding can be treated both in alternating and direct current.
In the second, current intensities are of the order of 50 to 500 amps. With this polarization obtaining more depth and longer duration of the electrode. In this gaseous protection welding, clean and uniform welds are produced due to the scarcity of fumes and projections, therefore the mobility of the gas allows the welder to clearly see what he is doing at all times, which has a favorable effect on the quality of the welding. .
Similar to the above is the welding by protected consumable electrode although in this the protected consumable electrode is the food of the welding bead. The electric arc is maintained as in the previous one by a continuous flow of gas that provides a clean joint in good condition. The two types that derive from this welding are: MIG (Metal Inert Gas) and MAG (Metal Active Gas).
- MIG welding, the gas is inert; does not participate in any way in the welding reaction.
- MAG welding, the gas used actively participates in the welding.
What both processes have in common is the use of a continuous consumable electrode. This electrode is in the form of a wire, it is at the same time the material from which the welding bead will be generated, and it reaches the application area by the same path as the gas or the feed. Generally, this process works with direct current and current intensities vary between 20 and 500 amps with direct current and direct polarity, 5 and 60 with reverse polarity, and 40 and 300 amps with alternating current. In industry, the use of MIG and MAG welding methods is common and periodic. Gas protection guarantees a continuous and uniform welding bead, as well as free of impurities and slag. Nevertheless,
alternating current electrodes
For electrical systems using alternating current, the electrodes are circuit connections to the object that will act under the electrical current, but are not designated anode or cathode because the direction of electron flow changes periodically, many times per second. An exception to this are systems in which the alternating current that is applied is of low amplitude (for example 10 mV) in such a way that the properties such as anode or cathode are not altered, since the system is maintained in a constant state. pseudo-stationary.
Electrodes are also considered metal rods covered with substances appropriate to the type of welding. The most used electrode measurement is 2.50 x 350 and 3.25 x 350 mm. The first number indicates the diameter of the electrode (1.5-2.5, etc.) and the second number the total length of the electrode.
