WeldingThe phenomenon described as either plasma formation or arcing that occurs between contacts may be an intentional effect, as is the case in processes such as arc welding and coating by means of physical vapour deposition (PVD). On the other hand, there are also situations in which this effect may occur when it is not intended, and this can result in damage to electrical components, such as relays, switches, and circuit breakers. Should an unexpected arc occur near an inflammable gas source, for instance, this could trigger a fire or an explosion.

There are, however, a variety of techniques in use to supress the tendency for arcing to occur between contacts. One approach makes use of a “snubber”, a device consisting of a small resistor and capacitor connected in series that acts to prevent the rapid rise in voltage that can lead to the formation of an arc. Other methods act by surrounding the potentially troublesome source with a vacuum, or immersing it in a dielectric gas or transformer oil to prevent any conduction, or arcing, across an intervening air gap.

By contrast, in the case of a welding or coating operation, where it is required to promote the formation of an arc, steps must be taken to prolong the life of the arcing contacts. When it is desired to create a tough and stable joint between sections of high-alloy steels or aluminium alloys, tungsten inert gas (TIG) welding is the method of choice. To survive the temperatures required, the electrodes used need to be made from a refractory metal. With a melting point of 3422 °C, tungsten is the ideal material from which to manufacture the non-consumable electrodes for this process.

In the PVD coating process, however, the principle is to vaporise a refractory metal and allow it to condense on a target object to form a coating with protective properties, such as resistance to abrasion or corrosion. In this process, the metal source is gradually consumed and, in time, will need to be replaced.