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Title: Thermal stability of hexagonal OsB{sub 2}

The synthesis of novel hexagonal ReB{sub 2}-type OsB{sub 2} ceramic powder was performed by high energy ball milling of elemental Os and B powders. Two different sources of B powder have been used for this mechanochemical synthesis. One B powder consisted of a mixture of amorphous and crystalline phases and a mixture of {sup 10}B and {sup 11}B isotopes with a fine particle size, while another B powder was a purely crystalline (rhombohedral) material consisting of enriched {sup 11}B isotope with coarse particle size. The same Os powder was used for the synthesis in both cases. It was established that, in the first case, the hexagonal OsB{sub 2} phase was the main product of synthesis with a small quantity of Os{sub 2}B{sub 3} phase present after synthesis as an intermediate product. In the second case, where coarse crystalline {sup 11}B powder was used as a raw material, only Os{sub 2}B{sub 3} boride was synthesized mechanochemically. The thermal stability of hexagonal OsB{sub 2} powder was studied by heating under argon up to 876 °C and cooling in vacuo down to −225 °C. During the heating, the sacrificial reaction 2OsB{sub 2}+3O{sub 2}→2Os+2B{sub 2}O{sub 3} took place due to presence of O{sub 2}/watermore » vapor molecules in the heating chamber, resulting in the oxidation of B atoms and formation of B{sub 2}O{sub 3} and precipitation of Os metal out of the OsB{sub 2} lattice. As a result of such phase changes during heating, the lattice parameters of hexagonal OsB{sub 2} changed significantly. The shrinkage of the a lattice parameter was recorded in 276–426 °C temperature range upon heating, which was attributed to the removal of B atoms from the OsB{sub 2} lattice due to oxidation followed by the precipitation of Os atoms and formation of Os metal. While significant structural changes occurred upon heating due to presence of O{sub 2}, the hexagonal OsB{sub 2} ceramic demonstrated good phase stability upon cooling in vacuo with linear shrinkage of the lattice parameters and no phase changes detected during cooling. - Graphical abstract: The in situ high temperature XRD contour plot (A) and XRD patterns (B) of h-OsB{sub 2} upon heating and cooling under an argon atmosphere. - Highlights: • Different boron sources were compared for the synthesis of h-OsB{sub 2}. • The phase stability and thermal behavior of h-OsB{sub 2} were studied by in situ XRD. • Shrinkage of the a lattice parameter was observed from 276 °C to 426 °C upon heating. • Oxidation of OsB{sub 2} produced B vacancies led to the shrinkage of a lattice parameter.« less
Authors:
 [1] ;  [1] ;  [2] ;  [1] ;  [3] ;  [4]
  1. Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States)
  2. (United States)
  3. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States)
  4. Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States)
Publication Date:
OSTI Identifier:
22443461
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 219; Other Information: Copyright (c) 2014 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ARGON; BORON 10; BORON 11; BORON OXIDES; COMPARATIVE EVALUATIONS; COOLING; FINE PARTICLES; HEATING; LATTICE PARAMETERS; MIXTURES; OSMIUM; OXIDATION; PHASE STABILITY; POWDERS; PRECIPITATION; RAW MATERIALS; SHRINKAGE; SYNTHESIS; TRIGONAL LATTICES; X-RAY DIFFRACTION