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Coolidge’s cool trick with tungsten

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William David Coolidge received a patent on December 30, 1913 for a method of making ductile tungsten. Even though this patent was later invalidated, the process developed by Coolidge helped in brightening the world. A.S.Ganesh throws light upon Coolidge, the man who helped utilise the ductility of tungsten…

You’ve seen incandescent light bulbs, haven’t you? A device wherein a wire filament is heated to such a high temperature that it glows with visible light, the incandescent light bulb is one of the earliest forms of electric light that still remains relevant to this day. If you had looked at these bulbs close enough, you surely would have noticed the wire filament. That filament is generally made of tungsten and it was William David Coolidge who made that possible.

A liking for electrical devices

Born in a small farm in Hudson, Massachusetts, the U.S. in 1873, Coolidge was drawn towards electrical devices from a very young age and spent a considerable amount of time in the town’s machine shop. He excelled at school right from the beginning and went to the Massachusetts Institute of Technology in 1891, specialising in physical chemistry and electrical engineering.

Even though he had to borrow money to complete his course work and graduated with a debt, he won a scholarship to the University of Leipzig, Germany, where he received his Ph.D. in Physics in 1899. He returned to teach at MIT, conducting research at the same time into the electrical conductivity of aqueous solutions at high temperatures.

Whitney’s welcome

It was during this time, in 1905, when Willis R. Whitney, American chemist and founder of the General Electric Research Laboratory, approached Coolidge and offered him a position in his laboratory. The laboratory was devoted to original research to discover profitable fields, but had been drawing blanks and was failing in its mission. Coolidge accepted the offer and would eventually help them turn a corner.

As GE’s lighting business depended on the Edison high-resistance carbon-filament lamp, Whitney and the management were tasked to ward off the competition from ceramic-filament lamp and mercury-vapour lamp, which were gaining prominence. Coolidge, who first got into the lamp filament problem through tantalum, soon switched to tungsten and was left to explore its possibilities.

Years of toil

Through years of toil, Coolidge observed that sintered (coalesced into a solid or porous mass by heating without liquefaction) tungsten filaments lost some of their extreme brittleness when passed through a rolling mill with heated rolls. This proved to be a foot in the door and further years of research allowed them to come up with a process that made tungsten sufficiently ductile (the ability to be drawn out into a thin wire) at room temperatures.

Using close control of the working temperatures and through trace metal additions, the process was perfected. GE scrapped all its previous lamp-making equipment and started selling lamps with the ductile tungsten filaments by early 1911. Considering that these bulbs went on to dominate the lighting industry, it proved to be a shrewd move from the company.

Not a patentable invention

The ductile tungsten thus obtained even came to be known as “Coolidge metal” and Coolidge received a patent for this process on December 30, 1913. This patent, however, was invalidated in the 1920s on the grounds that ductility was a property inherent to metallic tungsten. The courts ruled that Coolidge metal was essentially a discovery and not a patentable invention.

Apart from his contribution towards lighting, Coolidge also had a hand in various other achievements. He invented the Coolidge tube, capable of producing highly predictable amounts of radiation, that became the prototype of the modern X-ray tube. He also worked on the construction of X-ray machines for cancer treatment and ably steered GE’s Research Laboratory to safety during the Great Depression. By the time Coolidge passed away aged 101, he had amassed innumerable patents, awards and honorary degrees, not to mention the goodwill of the countless lives that he had impacted.

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Printable version | Jan 26, 2020 11:45:54 AM | https://www.thehindu.com/children/coolidges-cool-trick-with-tungsten/article25869974.ece

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