"Nanomaterials and nanocomposites"

Lightweight boron-based ceramic composites
Barvitskyi P.P.1, Prikhna T.O.1, Karpets M.V.2, Muratov V.B.2, Moshchil` V.E.1, Vasiliev O.O.2, Lokatkina A.S.1 Prysiazhna O.V.1
1 Institute for Superhard Materials of the National Academy of Sciences of Ukraine, 2, Avtozavodska Str., Kyiv, 04074, Ukraine. 
E-mail: barvitskp@gmail.com 
2 Institute for Problems in Material Science of the National Academy of Sciences of Ukraine, 3, Krzhizhanovsky Str., 03680, Kyiv, Ukraine.
E-mail: vasalexandr@gmail.com 

The work is devoted to the study correlations between consolidation conditions, structures, mechanical, chemical and damping characteristics of -AlB12-, AlB12C2-[1], B4C-Al(AlB40C4 [2])- based lightweight, dense ceramics and composites synthesized or sintered under by hot pressing (at 30 MPa, 1500-2200 C) quasi-isostatic high pressures (at 2-4.5 GPa, 1100-1800 C) conditions from the nanosized AlB12 powders with the additives of different amounts of C (carbon), TiC, SiC and AlN. Temperature, pressure, exposure time and composition of the starting powders were optimized to obtain sintered bodies with desired overall dimensions with high mechanical characteristics.
Relatively cheap nanopowders (50…150 nm, with a specific surface area of 21-15 m2/g) -AlB12 (three types with different content of amorphous carbon impurities from the graphite crucible during powder synthesis) and AlB12C2, synthesized by ph.Dr V.B. Muratov (IPM NAS of Ukraine) from h-BN, Al and C in graphite crucibles [3].
One of the best materials was a sample in which the additions of TiC to -AlB12 resulted in the formation of 74 wt.% AlB12C222 wt.% TiB24 wt.% Al2O3 composition (according x-ray) which contained Al0.17B4.55C2O0.04N0.21, TiB2.58C0.8Al0.02 and Al2O3.79B2.04C0.8 (according SEM EDX) havin Rcs=1143 MPa compression and Rbs=646 MPa bendin strengths, HV(49 N-load)=37.7 GPa hardness K1C(49 N-load)=6.9 MPa·m0.5 fracture toughnes and =3.2 g/m3 density. The effect of TiC, SiC and C additions on the properties of the resultant composites and the particularities of the ceramics destruction under shock loading are discussed [4].
The use of source nanopowders allows to intensify consolidation processes, reduce synthesis and sintering temperatures, ie reduce the cost and simplify production technologies, as well as improve the mechanical properties of materials. Features of the structure of aluminum dodecaborides and decarbododecaborides (similar to boron carbide), namely the presence of the same structural elements - almost correct icosahedrons of boron atoms, high dispersion and reactivity allows to modify the structure and properties of such materials by adding additives. It was the reason for research in this area, aimed at creating new composites based on them, in particular, with improved damping and construction characteristics 
The developed lightweight dodecaboride dicarbododecaboride -based ceramic composites hold great potential for a wide range of applications in extreme conditions: for the manufacture of abrasive nozzles, friction pairs for pumping oil and other aggressive liquids, constructional ceramics for nuclear power plants, as a personal protection or for armored defense of ground military equipment and vehicles, etc [5].
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