Thursday, July 01, 2010

A Note on Carborundum

Certain naturally-occurring minerals can be used to detect radio signals, including galena, zincite, silicon, bornite and others. Carborundum was unique among the early crystals because it was synthetic. It was durable, and at 9 mohs much harder than most available crystals. More here. Also interestingly it requires it requires a negative potential of 1 volt to be used as a diode. Carborundum was not created with this purpose in mind. It was created in the early search for artificial diamonds. How it got into radio is truly arcane.

If you look at the Arlington Cemetery Website, they refer to General Henry Harrison Chase Dunwoody as "The inventor of Heart Of Radio."  He was once the Chief Signal officer of the United States Navy.  The website doesn't explain what the "heart" is it at all.  So I turned to his patents. In 1906 he patented a detector using silicon carbide aka Carborundum.  I can see calling that the heart of radio. It was none other than Lee DeForest who first marketed the invention commercially. DeForest installed it at 120 of his telegraph stations. At the time there were only 145 telegraph stations in the whole of the United States, and 130 of them switched to Carborundum by the end of 1907.  This is because of two things, it really was more durable, and it was a drop in component that could be used with existing hardware. The voltage it required could be applied by a battery. All this thanks to Dunwoody. But Dunwoody didn't invent Carborundum, he just figured out how to use it as a detector. So how did that end up in his hands?

The invention of the light-emitting diode (LED) is usually credited to Nick Holonyak in 1962. This is wrong. The real credit should go to Captain Henry Joseph Round at Marconi Labs.  Henry was a personal assistant to Marconi, but he racked up 117 patents on his own. In 1907 he applied voltage to a crystal of silicon carbide (Carborundum) and a cat's-whisker detector that it glowed. We call it electroluminescence. That diode he was using was General Henry Harrison Chase Dunwoody's detector (or something else nearly identical). Henry was so excited he wrote a letter to the editors of Electrical world. the published it February 9th 1907. I quote most of it below:
"During an investigation of the unsymmetrical passage of current through a contact of carborundum and other substances a curious phenomenon was noted. On applying a potential of 10 volts between two points on a crystal of carborundum, the crystal gave out a yellowish light. Only one of two specimens could be found which gave a bright glow on such a low voltage, but with 110 volts a large number could be found to glow. In some crystals only edges gave the light and others gave instead of a yellow light green, orange or blue. In all cases tested the glow appears to come from the negative pole, a bright blue-green spark appearing at the positive pole. In a single crystal, if contact is made near the center with the negative pole, and the positive pole is put in contact at any other place, only one section of the crystal will glow and that same section wherever the positive pole is placed.  There seems to be some connection between the above effect and the e.m.f. produced by a junction of carborundum and another conductor when heated by a direct or alternating current..."
This was huge. More interesting to me is that since it's a diode it naturally goes that it could be used as a crystal detector. Dunwoody later made that leap.  Back in 1907 an issue of Mineral Industry reveals that the Carborundum Company of Niagara Falls NY as the sole producer of carborundum in America. It then goes on to list the quantity of carborundum produced each year in the United States all the way back to the year 1891, all by the Carborundum Company. Let me list that off.
1891 - 50 lbs
1892 - 2,145 lbs (1 ton)
1893 - 15,200 lbs (7 tons)
1894 - 52,190 lbs (24 tons)
1895 - 225,930 lbs (102 tons)
1896 - 1,190,600 lbs (540 tons)
1897 - 1,242,929 lbs (564 tons)
1898 - 1,594,152 lbs (724 tons)
1899 - 1,741,245 lbs (791 tons)
1900 - 2,401,000 lbs (1,089 tons)
1901 - 3,838,175 lbs (1,742 tons)
1902 - 3,741,599 lbs (1,698 tons)
1903 - 4,760,000 lbs (2,160 tons)
1904 - 7,060,380 lbs (3,203 tons)
1905 - 5,596,280 lbs (2,539 tons)
1906 - 6,225,280 lbs (2,824 tons)
1907 - 7,532,670 lbs (3,418 tons)

What's interesting is that the invention of the carborundum detector by Dunwoody in 1906 barely produces a blip in the volume of carborundum being produced. What were we doing with all this carborundum? They were used to make grinding wheels and sharpening stones. Sharpening things was way more common than radio.

Carborundum was created accidentally by Edward Acheson during what is usually described as "attempts to create artificial diamonds."  It's not exactly accurate. Mr. Acheson was born march 9th 1856 in Washington, PA.  His dad was a grocer and later became the manager of a furnace in Monticello, PA. In 1873, his father died and the furnace shut down.  At the age of 17 he had to work to support the family.  He worked for the oil companies as it was booming in western PA at the time. In 1880 he managed to get a job working for Thomas Edison at Menlo park. He later worked for Westinghouse, and the Standard Underground Cable Company.

A stone cutter working for the Tiffany Company named George Kuntz by chance told Acheson about his need for a better abrasive to cut, shape and work stones. Acheson  already knew that some carbon minerals were very hard, specifically diamond. In his electric work Acheson had already noticed that on some carbons were naturally-occurring tiny dark crystals. Acheson began to save these and sell them as an abrasive powder. But he didn't know how to produce it deliberately. He did know that an electrical arc between two carbon elements produced a lot of heat. So he mixed coke, sand, sawdust and salt and applied tremendous voltage. When the mixture vaporized it cooled and formed carborundum.  It was 1891.

He also noticed that in the uneven heating the hottest parts of the mixture had become graphite.  He then devised that applying additional current to heat the carbide produced graphite. He went on to also make a graphite lubricant with a similar method.  He patented the furnace, those methods and the products. US patent numbers 492,767 and 615,648 etc. In 1894 he incorporated the Carborundum Company, and relocated it to Niagara Falls in 1895 because he needed more power to make more Carborundum. Acheson died in New York City,1931.


  1. Jose, good stuff about carborundum. I knew this was something that Deforest worked on, but I didn't know all the connections.

  2. The connection between Dunwoody and deforest went deeper. Some years before he retired, Colonel Dunwoody (he was promoted to General shortly before retiring in 1906) apparently helped deForest secure contracts with the Army to install radio stations at some of their east coast forts. Earlier he and deForest had worked with Alexander Graham Bell conducting some long distance radio tests using Bell’s kites to raise the aerial wire. They apparently got along well; Dunwoody was made a deforest vice president shortly after retiring. This was around the time deForest was being sued over the “spade” detector, and he had not quite perfected his audion tube. Conveniently, along comes Dunwoody and his carborundum detector.

    It is possible deForest actually came up with the idea; he was an avid reader of the technical journals of the day and likely would have noticed articles mentioning the electrical properties of carborundum. Dunwoody was more of a telegraph kind of guy. Whichever one of them did actually invent it, neither of them could get it to work properly, and they eventually called in G. W. Pickard as a consultant to get it working. He did, was never paid for his trouble, and the deForest company was saved. For the moment. Eventually deForest was sued again by American Marconi, losing all assets, including the carborundum detector. All except the one the court viewed most valueless – the audion.

    Dunwoody spent his later years running a small copper mining company. He died in 1933. He left an impressive legacy: his son, grandson, and great granddaughter all held the rank of General; his Great Granddaughter, Ann Dunwoody, is the first American four star officer in US history.

  3. AH HA! I was looking for a link like that but didn't find anything. That would better explain how it got from Dunwoody's hands into the deForest wireless stations.

    Thanks for the detail. Can you cite a source for further reading?

  4. I've been researching Dunwoody and some of the other early Army radio guys for a while so I'll have to pull together some sources for you. There isn't much at all written about Dunwoody, in fact DeForest barely mentions him. Most of what I know about him is pieced together from old newspaper articles etc. I've spoken with his grandson, also General Dunwoody, retired, who knew him but didn't remember his ever keeping a journal or notebooks, but he did remember building a crystal radio with him as a child.

  5. There's nothing like original research. You'd best publish it at some point!