boron nitride allotrope, is the fourth hardest substance, after aggregated diamond nanorods, ultrahard fullerite, and diamond, and the third hardest artificial material. Borazon is a crystalcreated by heating equal quantities of boronand nitrogenat temperatures greater than 1800 °C (3300 °F) at 7 GPa (1 millionlbf/in²). Borazon is the only substance other than those listed above that can scratch a diamond [http://biotsavart.tripod.com/bci.htm] (although laserscan cut diamond). A diamond will also scratch Borazon.
Borazon was first produced in
1957by Robert H. Wentorf, Jr., a physical chemist working for the General Electric Company. In 1969, General Electric adopted the name Borazon as its trademarkfor the crystal.
Uses and production
Prior to the production of Borazon, also referred to as cubic boron nitride or CBN,
diamondwas the preferred abrasive used for grinding very hard superalloysbut it could not be used effectively on steels because of its carbon solubility potential. Aluminium oxidewas the conventional abrasive used on hardened steel tools. [http://www.patentstorm.us/patents/5308367-description.html Description of Borazon and Borozon as prior art in patent from 31 December 1969] ]
Borazon replaced aluminium oxide for grinding hardened steels due to its far superior abrasive properties, comparable to that of diamond. Borazon is used in industrial applications to shape tools, as it can withstand temperatures greater than 2000 °C (3500 °F), much higher than that of a pure diamond at 871 °C (1600 °F).Fact|date=April 2008 Other uses include
jewellerydesigning, glasscutting and laceration of diamonds.Fact|date=April 2008
CBN-coated grinding wheels, referred to as Borozon wheels, are routinely used in the machining of hard ferrous metals, cast irons, and nickel-base and cobalt-base superalloys. They can grind more material, to a higher degree of accuracy, than any other abrasive. The limiting factor in the life of such tools is typically determined not by wear on the cutting surface but by its break-down and separation from the metal core resulting from failure of the bonding layer.
* [http://www.winstonbrill.com/bril001/html/article_index/articles/51-100/article61_body.html Discovering a Material That's Harder Than Diamond] by
Robert H. Wentorf, Jr.
* [http://biotsavart.tripod.com/bci.htm Boron in Materials Technology]
* [http://www.abrasivesnet.com/en/product/mbs/cbn/index.htm Borazon-CBN]
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