Cubic boron nitride. (Technology Spotlight).

Diamonds may be the hardest substance on earth, but not necessarily the most durable. When it comes to grinding applications, this super-hard form of carbon tends to dissolve in iron at high temperatures. In comes thermally-stable boron nitride, which, in cubic form, is the second hardest substance. Norton, Co, Worcester, MA, manufactures cubic boron nitride (CBN) grinding wheels for use in high-volume, tight-tolerance applications. Compared to aluminum oxide abrasive wheels with typical cost of $150, these super-abrasive CBN grinding wheels can run around $5,000--but as productive as 40 conventional wheels. The extraordinary temperatures and pressures--up to 2000 [degrees]C and 500,000 atmospheres--required for making CBN contribute to its high cost. However, researchers at Shandong University in Jinan, China, have recently synthesized 3Onm-wide BN crystals at only 480[degrees]C in atmospheric pressure, using boron tribromide and lithium nitride within a benzene solvent. The next challenge will be to increas e the crystals to industrial size with these methods. A paper detailing the research is available at Circle 182--Chemistry of Materials, or connect directly at www.RSLeads.com/?111df-182. Circle 183--Norton Co, or connect at www.RSLeads.com/?111df-183