Saturday, September 30, 2006

Silicon Carbide for Rock Tumbling & Polishing

Silicon carbide is man-made for use as an abrasive or more recently as a semiconductor and the gemstone moissanite The simple manufacturing process is to combine silica sand and carbon at temperature between 1600 °C and 2500 °C.

Gem crystals of silicon carbide can be made up to one inch. This material is called moissanite. It is very cheap to produce and is very close to diamonds in its properties, making it a great and cheap gemstone.

Natural occurring silicon carbide is only found in meteorites, making it extremely rare. It was first discovered in the Canyon Diablo meteorite, Meteor Crater and vicinity, Coconino Co., in Arizona.

Why does silicon carbide work as an abrasive? It has some very unique properties that man has found very important. It is extremely hard. On the Moh's hardness scale it is a 9.5, making diamonds the only thing harder than silicon carbide.

It works well as an abrasive for grinding and polishing rocks because of another property it has. It always breaks, fractures, and chips at very sharp angles. Unlike most materials, it doesn't round off on the corners when it is used. This means that when it is ground from a coarse grit to
a fine grit it still works just as well for abrading.

The material was discovered by Edward G. Acheson around 1893. He also developed the electric batch furnace by which SiC is still made today. He also formed "The Carborundum Company" to manufacture it in bulk as an abrasive.

Acheson was trying to dissolve carbon in liquid alumina (corundum) and found that all he got were hard black crystals of a new compound. He named it "carborundum" (carbon + corundum from the two materials he was working with).

A new thing on the market today is recycled grit. Many dealers selling grit for tumbling are selling recycled grit. It is much cheaper (It's used!) and will not work as well on grinding rocks. This is because used 60/90 grit has been broken down to a finer grit and will not work as a coarse grit. There is also the problem of contamination. You may be buying fine grit that has a lot of coarse grit mixed into it. This makes it not such a good deal when you are trying to polish in your fine stage.

When you are buying grit make sure you are purchasing "new" grit and not recycled. You never know what you are going to get with recycled. For the price difference it is well worth it as it will save time in the long run and you will get a better result.

We sell a variety of grit at www.rocks4u.com (click on the "Shop" tab). All of our grit is NEW!

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