Ceramics-Silikáty 47 (4) 135-140 (2003)

IMPROVEMENT IN BORON NITRIDE CERAMICS PREPARED BY ELECTROCONSOLIDATION

V. Brožek, V. Dufek, V. Harok, P. Rohan

The contribution brings an analytical assessment of thermal expansion for ceramic parts on boron nitride base prepared by a new pressure-sintering method registered by Superior Graphite Company, USA known as Electroconsolidation^®. The prepared samples were compared with common hot pressed ceramics. Together with usual starting BN powder two additionally modified powders were prepared: a special type purified by deoxidative chlorination and a mixture with B₄C in order to prove the changes in BN sinterability. Further noteworthy properties of these products are discussed. Thermal expansion of electroconsolidated samples has an average value of 4.56 x 10^-6 K^-1 and its course is linear up to 1470 K. Above this temperature the course is influenced by oxygen traces and/or B₄C addition. Measurement of flexural strength using the four-point bending method showed a 30 % increase for electroconsolidated samples compared to values of samples prepared by conventional hot pressing in graphite dies. Young modulus values were higher as well, but they are strongly dependent on structural anisotropy. The compressive strength measurement indicated the priority of electroconsolidation too.

Keywords: Hexagonal boron nitride, Turbostratic structure, Hexagonalisation, Nonoxide ceramics.