12007-16-8Relevant articles and documents
Interaction of oxides of 3d transition metals with boron
Solov'ev,Makarov,Meshchaninova,Ugai
, p. 131 - 138 (1992)
Differential thermal analysis and X-ray phase analysis were used to investigate the preparation conditions and composition of products of the borothermal reduction of oxides of 3d transition metals (titanium, vanadium, chromium, manganese, iron, cobalt, n
Crystal structure refinement and bonding patterns of CrB4: A boron-rich boride with a framework of tetrahedrally coordinated B atoms
Knappschneider, Arno,Litterscheid, Christian,Kurzman, Joshua,Seshadri, Ram,Albert, Barbara
, p. 10540 - 10542 (2011)
Crystals of chromium tetraboride, a recently proposed candidate superhard material, have been grown for the first time to allow for a first structure refinement of the compound [orthorhombic, space group Immm (No. 71), a = 474.82(8) pm, b = 548.56(8) pm, and c = 287.17(4) pm, R value (all data) = 0.018]. The previously proposed structure model is confirmed, and accurate interatomic distances are presented for the first time. First-principles electronic structure calculations emphasize the unique framework of three-dimensionally linked B atoms that are tetrahedrally coordinated and carry a slightly negative charge. All B-B bonding is of the 2-center 2-electron type. CrB4 is metallic with a pseudogap at the Fermi level.
Preparation of borides in Nb-B and Cr-B systems by combustion synthesis involving borothermic reduction of Nb2O5 and Cr2O3
Yeh,Wang
, p. 366 - 371 (2010)
An experimental study on the preparation of metal borides in the Nb-B and Cr-B systems was conducted by self-propagating high-temperature synthesis (SHS) involving the reduction of Nb2O5 and Cr2O3 by amorphous boron. The starting stoichiometry of the reactant compact was shown to make a great impact on the combustion behavior and the phase composition of the final product. For the powder compacts of Nb2O5 and boron, self-sustaining combustion was performed under a molar ratio of B/Nb2O5 between 5 and 10, but complete reduction of Nb2O5 was achieved when B/Nb2O5 ≥ 8. Partial reduction of Nb2O5 caused a decrease in the combustion temperature and velocity, and was responsible for the presence of NbO2 in the final products. For the samples with stoichiometry of 6 ≤ B/Nb2O5 ≤ 8, three boride phases NbB, Nb3B4, and NbB2 were synthesized. An increase in the boron content up to B/Nb2O5 = 8.5-10 resulted in not only full reduction of Nb2O5, but also formation of single-phase NbB2. On the other hand, the SHS process involving Cr2O3 and boron was feasible for the powder compacts of 4 ≤ B/Cr2O3 ≤ 9, wherein the highest combustion temperature and the fastest reaction front were observed in the compact with B/Cr2O3 = 6. During combustion Cr2O3 was fully reduced, leading to the formation of three borides Cr5B3, CrB, and CrB2 in either monolithic or composite form. With a boron content more than the stoichiometric amount, the powder compacts of B/Cr2O3 = 4, 5, and 9 yielded single-phase Cr5B3, CrB, and CrB2, respectively.
Syntheses and Sinterings of Chromium Borides via Solid-State Reactions and Mechanochemical Processes of Chromium-Amorphous
Iizumi, Kiyokata,Kudaka, Katsuya
, (2008/10/08)
As a basic study for the development of chromium boride materials which are expected as refractory materials or hard materials, syntheses and sinterings of the chromium borides via solid state reactions and mechanochemical processes of chromium-amorphous boron mixed powders were studied.The single phases of Cr2B, CrB and CrB2 were obtained by the solid stat e reaction in the temperatures of 1400-1500°C. These borides wereso unsinterable that could be consolidated by pressure sintering only. The chromium boride of the highest relative density and hardness among t he ceramics obtained was CrB2. By mechanochemical processes, the single phases of CrB2 and CrB were obtained by milling of Cr-B(molar ratio,1:2)and Cr-B(1:1) mixed powders by using a planetary ball mill for 20-40 h, followed by annealing at 900 and 1000°C, respectively. As-milled Cr-B(1:1) mixed powders were consolidated by both of pressureless and p ressure sinterings. These are a reaction sintering because the sinterings are accelerated by the exothermic reaction heat of the unreacted Cr-B in the as-milled mixed powders. The unsinterable powder could be consolidated by pressureless sintering via mechanochemical process. At pressuresintering via mechanochemical process, the sintering temperature lowere d and the hardness of ceramics obtained increased.
