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Incandescent lamp. History of invention and production
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An incandescent lamp is an artificial light source in which light is emitted by an incandescent body heated by an electric current to a high temperature.
As a heating body, a spiral made of refractory metal (most often tungsten) or a carbon filament is most often used. To prevent oxidation of the heating body upon contact with air, it is placed in an evacuated flask, or a flask filled with inert gases or halogen vapors.
The design of a modern lamp. In the diagram: 1 - flask; 2 - the cavity of the flask (vacuum or filled with gas); 3 - glow body; 4, 5 - electrodes (current inputs); 6 - hooks-holders of the body of heat; 7 - lamp leg; 8 - external link of the current lead, fuse; 9 - base case; 10 - base insulator (glass); 11 - contact of the bottom of the base.
The incandescent lamp is familiar to almost every modern person. Its main element is a tungsten filament, which, when heated by current, becomes hot and begins to shine, flooding the surrounding space with soft warm light. It wasn't always like that. Edison's light bulb at the time of its invention (in 1878) was far from perfect. Charred paper filament often burned out, and in 1882 Lewis Latimer patented a process for making filaments from charred cotton filaments, which increased lamp life. But this was not enough.
The idea to increase energy efficiency using a thread of refractory metals was put forward by our compatriot Alexander Lodygin. In an application filed with the US Patent Office in 1892, he described in detail how to make a filament from platinum, chromium, and also mentioned tungsten as the most suitable material, although he noted the difficulties in processing it. As a result, tungsten still found its place in lamps, despite its low ductility. Tungsten powder was mixed with an organic paste (usually starch), the resulting mass was squeezed out through a spinneret, and then a thin thread was calcined, removing the organic binder.
However, organic residues led to the appearance of a layer of carbon on the walls of the flask, and the lamp quickly "darkened". In 1905, this problem was tackled by a new employee of the General Electric research laboratory in the town of Schenectady, New York, William Coolidge, a graduate of the Massachusetts Institute of Technology, who received a doctorate in 1899 from the University of Leipzig. He was given the seemingly impossible task of developing a carbon-free binder.
The decision came unexpectedly. Sitting in the dentist's chair, Coolidge watched as the doctor mixed silver with mercury, making a plastic mass - silver amalgam, which was then filled with diseased teeth. According to the physicist, he was amazed at the plasticity of the resulting mass: "I immediately thought about whether it was possible to use an amalgam of some metal as a temporary binder for tungsten."
After many experiments with various metals, a solution was found: tungsten was mixed with cadmium amalgam, a wire was made from the resulting plastic mass, and when it was calcined in a vacuum, first cadmium and then mercury completely evaporated, leaving a thin thread of sintered pure tungsten, which, moreover, amenable to further processing. The process was soon modified to avoid mercury, but, as Coolidge himself recalled in the 1960s, "without the first step, there would be no second."
As a result, Coolidge received recognition (he later rose to vice president of GE), and the world - cheap and energy-efficient electric lighting.
Author: S.Apresov
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