Silver is the best electrical conductor of all metals and is hence used in many electrical applications, particularly in conductors, switches, contacts and fuses. Contacts, a junction between two conductors that can be separated and through which a current can flow, account for the largest proportion of electrical demand.
Ordinary household wall switches, which normally carry high electric current for electrical appliances from irons to refrigerators, use silver. Silver is the metal of choice for switch contacts because it does not corrode, which would result in overheating, which could lead to fire. Today switch manufacturers play it safe by using high-performance silver for ordinary household switch and circuit breaker contacts. Less expensive metal contacts have high resistance which can overheat and cause a fire, says a major supplier of switch contacts. It is this consideration of liability that assures the public of continued preference for silver in switch contacts. With an increasing concern for quality, warranties become more important, and extended warranties mean that industry cannot chance even one failure in a million; that level of performance requires silver.
From the very beginning of electricity, silver has been the metal of choice for switch contacts because of its low contact resistance, high thermal conductivity, mechanical wear resistance, chemical stability (it does not corrode), low polymer formation (the build-up of an insulating carbon-polymer film over the contact as a consequence of arcing), and cost-effectiveness (it provides the longest functional life).
Films on other metals like copper, even when the corrosion is barely visible, cannot be tolerated. Over 50 categories of electrical components incorporating silver as the contact material are listed by The National Electrical Manufacturers Association, Washington, D.C. These range from silver thick films that are used to make membrane switches which carry 5 volts or less for electronic systems, to large circuit breaker contacts required to interrupt or close the circuits of 75,000-volt power distribution lines.
The use of silver for motor control switches is universal. In the home, wall switches, timing devices, thermostats, sump pumps, and virtually all electrical appliances use silver contacts. A typical washing machine requires 16 silver contacts to control its electric motor, pump, and gear clutch. A fully-equipped automobile may have over 40 silver-tipped switches to start the engine,activate power steering, brakes, windows, mirrors, locks, and other electrical accessories.
Relays are another important market for silver contacts. Relays are used when low voltage switches (such as membrane switches) are used to activate considerably higher voltage or amperage switches. The increasing use of automated appliances has increased the number of silver contacts manufactured.
Electric motor control switches use the largest amount of silver for each contact. The range of applications is enormous, covering: washing machines, dryers, automobile accessories, vacuum cleaners, electric drills, elevators, escalators, machine tools, and so on up to railway locomotives and marine diesel engines. Silver contacts start motors, set them to run forward or reverse, or at partial or full power. The silver contacts carry electrical power ranging from a fraction of an ampere, for small appliances, to 600- ampere loads required for oil-well drilling motors; their performance is required to be flawless.
The circuit breaker is the second major user of silver for contacts. For circuit breakers, silver combines the highest heat conductivity and the highest electrical conductivity of all metals, with almost unlimited performance. Circuit breakers are used to interrupt loads ranging from 10 amperes (small household lines) to 4000 amperes (high-tension power lines).
The circuit breaker is the most demanding use of silver contacts because the temperature of the arc generated by the interruption of high electrical power often exceeds the melting point of silver. As a consequence, silver is alloyed or infiltrated into other metals such as Tungsten to provide long-term performance.
Silver is the best electrical and thermal conductor of all metals and is hence used in many electrical applications, particularly in conductors, switches, contacts and fuses. Contacts provide junctions between two conductors that can be separated and through which a current can flow, and account for the largest proportion of electrical demand.
The most significant uses of silver in electronics are in the preparation of thick-film pastes, typically silver-palladium for use as silk-screened circuit paths, in multi-layer ceramic capacitors, in the manufacture of membrane switches, silvered film in electrically heated automobile windshields, and in conductive adhesives.
The ease of electro-deposition of silver from a double-alkali metal cyanide, such as potassium silver cyanide, or by using silver anodes accounts for its widespread use in coating. Silver solutions are made up of a cyanide, a carbonate, silver and a brightener. The silver is usually added as the single salt, silver cyanide, or the double salt, potassium silver cyanide. Various forms of silver are used as anodes and may be in the form of plates, bars, rods, grain or in custom designed shapes. Silver is used as a coating material for compact disks, whilst in 2002 digital video disks also switched to a silver coating. The unique optical reflectivity of silver, and its property of being virtually 100% reflective after polishing, allows it to be used both in mirrors and glass coatings, cellophane or metals.
The plating thickness of some items, such as fuse caps, is less than one micron although the silver then tarnishes more easily, and coatings of two to seven microns are normal for heavy duty electrical equipment.
Many batteries, both rechargeable and non-rechargeable, are manufactured with silver alloys as the cathode. Although expensive, silver cells have superior power-to-weight characteristics than their competitors.
The joining of materials (called brazing if done at temperatures above 600º Celsius and soldering when below) is facilitated by silver’s fluidity and strength. Silver brazing alloys are used widely in applications ranging from air-conditioning and refrigeration equipment to power distribution equipment in the electrical engineering sector. It is also used in the automobile and aerospace industries.
Steel bearings electroplated with high purity silver have greater fatigue strength and load carrying capacity than any other type and are hence used in various hi-tech and heavy-duty applications.
It was a layer of silver on main shaft bearings of the 9,000 horsepower reciprocating engines of the World War II Superfortress that resolved the unacceptable failure rate of its giant engines. Silver, with its superior fatigue resistance, lubricity, corrosion resistance, and thermal conductivity came to the rescue.
Today's commercial and military jet engines deliver 35,000 to 100,000 pound thrusts under high temperature conditions. Despite the far higher power and a far more rigorous internal environment, silver coated bearings continue to provide the superior performance and critical margin of safety for today's jet engines.
The fan/compressor/turbine rotating components that push the air through the jet engine are all attached to the main shaft. This main shaft rotates on steel ball bearings that roll within steel retaining rings, called cages. Similar bearings are required for the connecting gear boxes that drive accessories such as hydraulic pumps and fuel pumps; all rotate at much higher speeds than ground-based machinery. Steel has a poor coefficient of friction, but placing a layer of silver between the steel ball and the steel cage reduces the friction between the two to a minimum, increasing the performance of the engine and its accessories.
But silver also plays another critical role. Safety in jet engines is a paramount consideration. Failure of any one of the jet engine bearings would be catastrophic. Rolling contact bearings are lubricated and cooled with synthetic engine oil. In the event of an oil interruption, such as a pump failure, the silver plated bearings provide adequate lubricity to allow a safe engine shut-down before more serious damage can occur. To prepare for such a possibility, the U.S. Federal Aviation Authority (FAA) and airplane manufacturers require fail-safe engine testing for the bearings. The test requires stopping the lubricating oil system for 15 seconds with the engine running at full power and then turning on the lubricating system, then turning off lubrication again for 15 seconds, and repeat for four successive cycles. The dry lubricity of silver always allows jet engines to pass the tests.
The use of silver in high-performance bearings provides the wide margin of safety demanded by Pratt & Whitney, General Electric, Rolls Royce, and all other producers of jet engines that power modern aircraft.