From Magnetic to Bioactive Materials by Rainer Pöttgen Thomas Jüstel Cristian A. Strassert

Author:Rainer Pöttgen, Thomas Jüstel, Cristian A. Strassert
Language: eng
Format: epub
Publisher: De Gruyter
Published: 2022-04-27T10:58:31.663000+00:00

10.4.4.6 Boron nitride

α-Boron nitride is structurally comparable to graphite (therefore, also called white graphite), and consists of a planar, hexagonal crystal structure in layers. In powder form or as a surface coating, hexagonal boron nitride α-BN is often used as a release agent and lubricant in foundry technology due to its poor wettability with molten metals. In its cubic modification β-BN, it is used as cutting ceramic due to its high hardness, thermal conductivity and thermal stability [36]. The industrially used name CBN is derived from the initial letters in “Cubic Boron Nitride”. CBN was first synthesized in 1957 and has been available on the European market since 1969. The ceramic bonds, which have been in use since 1982, made it possible for the first time to dress grinding tools economically. With a Knoop hardness of 45 GPa at room temperature, CBN is the second hardest known material after diamond (88 GPa). Due to the graphitization of diamond, which begins at 700 °C, it can only be used up to a maximum of 900 °C. CBN, on the other hand, can be used up to 1400 °C and is therefore the hardest known material above 900 °C. Since CBN does not contain carbon, it is suitable – unlike diamond – for machining hardened and unhardened steels containing carbon [35, 37].

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