Historical Note
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Abrasives
vania, Edward Goodrich Acheson was the first to use the electric furnace to produce crystals of silicon carbide. Acheson heated silica and coke in an electric furnace. He found that the resulting intergrown mass of greenish black crystals could scratch glass. He named the new material "carborundum." It was first commercially used for polishing gemstones. Synthetically produced carborundum crystals are superior to natural corundum and emery in hardness, toughness, and fracture strength. Carborundum remains the hardest common manmade abrasive, second only to diamond. The introduction of general-purpose grinding wheels made with carborundum greatly improved manufacturing operations. Though relatively friable, carborundum is widely used in grinding cast iron, nonferrous metals, and nonmetallic substances like ceramics, rubber, and leather. In 1897 at the Ampere ElectroChemical Company in Ampere, New Jersey, Charles Jacobs manufactured fused aluminum oxide using a new tempering technique and rock bauxite. Hard enough and strong enough to be used as an industrial abrasive, the fused aluminum oxide was first sold on a commercial scale in 1901. It is so uniform and efficient that it has replaced carborundum in many applications. Manmade diamonds—with all the desirable properties of natural diamonds—became widely available in 1955 through a high-pressure, high-temperature process developed by the General Electric Co. Synthetic diamonds are now extensively bonded in thin layers to metal or resinoid wheels as abrasive grains. Though still expensive, synthetic diamonds are among the most widely used abrasives. Other abrasive materials include glass pellets and steel in several forms. Steel wool is good for removing corrosion from metal surfaces and smoothing them. Steel shot and glass pellets are used for peening or work hardening a surface. Steel grit is used for blasting and as a roughing abrasive for finishing granite and other stone.
Besides more usual applications, abrasives have been used to grind animal-gut sutures and guitar strings to a uniform thickness, saw frozen fish into fish sticks, and round off toothpicks. Since the beginnings of civilization, abrasive materials have been used to grind, cut, polish, or smooth surfaces. Abrasives are harder than the materials they abrade and work by a fracturing or shearing action to erode the softer substance. As early as 25,000 to 15,000 B.C., weapons and utensils were shaped and polished by rubbing them with sand or against harder stone. Iron Age workers fashioned iron or bronze implements by rubbing stone against them. Ancient Egyptian tomb drawings show vases and jewelry being polished with powdered abrasives. Natural abrasive stones (such as sandstone) were later shaped into wheels for grindstones and millwheels, and into smaller blocks for sharpening knives, axes, scythes, and woodworking tools. Abrasives were also often crushed into a powder and mixed with a liquid or a paste, then pressed into wheels or blocks, or glued to paper, cloth, or other soft materi
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