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B x O: Phases Present at High Pressure and Temperature
Author(s) -
Srikanth Varanasi,
Roy Rustum,
Graham Earl K.,
Voigt Donald E.
Publication year - 1991
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1991.tb04316.x
Subject(s) - boron , materials science , analytical chemistry (journal) , amorphous solid , boric acid , hydrostatic pressure , crystallography , mineralogy , metallurgy , chemistry , thermodynamics , physics , organic chemistry , chromatography
Boron suboxide compounds are of interest because of their low densities coupled with high hardness. In the present study, we have attempted to determine the nature of the B x O phases that occur in the field defined by pressures of zero to 1.5 GPa, temperature between 1200° and 1700°C, and the compositional range 2/3 x 24. Amorphous boron powder and boric acid B 2 O 3 were the starting reactants for all the runs. The processing of the specimens was carried out in a controlled atmosphere furnace, a hot‐pressing assembly, and in a piston—cylinder high‐pressure apparatus within quasi‐hydrostatic and inductively heated cell assemblies. After processing at elevated temperature and pressure, for compositions over the range 2/3 x 6, B 2 O 3 (identical to the hexagonal starting material) and B 6 O ( R 3¯ m ) were the dominant phases present. For the compositions 6 x 24, B 6 O and rhombohedral B were the primary phases identified. In general, the hardness of the processed composites was dominated by the occurrence of B 6 O (approximately equivalent to B 4 C). However, there is some suggestion of particularly high values of hardness on a very localized scale in specimens near the B 22 O composition.