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M. V. NIKISHINA and P. P. ITSENKO
«Stability of Pyrolytic BN Structure under Thermobaric Action »
PACS numbers: 07.35.+k, 61.48.De, 61.50.Ks, 62.50.-p, 81.07.Bc, 81.40.Vw, 81.70.Pg
Thermal stability of quasi-crystalline nanostructure of pyrolytic boron nitride (pBN) with a density ????2 g/cm3 is studied under pressure of 7.7 GPa in the temperature range from 1000 to 1900?C simultaneously with compact samples of highly-crystalline carbothermal BN powder (? ? 1.83 g/cm3). As revealed, the onset temperature of the pBN transformation into the dense cubic phase (cBN) is 1600?C that is higher than that of carbothermal BN by 300?C. During the phase transformation, heterogeneous ordering of the pBN structure is observed. Below 1600?C, pBN is structurally stable, and its density is practically unchanged at thermobaric action that makes it possible to use pBN as a matrix material in studying the processes of its infiltration by non-reactive melts under high pressure and a temperature between 300?C and 1600?C.