Boron powder

Fine and ultra-fine BN is used for lubricants and toners and can be produced by combustion of boron powder at 5500 °C in a nitrogen-plasma [91-93]. 

Metals and amorphous boron powder are mixed and then heated and reacted under vacuum or inert gas,... 

In some cases, several refractory compounds can result from two or more parallel reactions occurring simultaneously in the combustion wave. A typical example of this type is the Ti-C-B system, where both the Ti+C and Ti-I-2B reactions affect the combustion synthesis and structure formation processes (Shcherbakov and Pityulin, 1983). By adjusting the contents of carbon and boron powders in the reactant mixture, either carbide- or boride-based ceramics can be obtained. 

The direct reaction between elemental boron and Hj gas has limited utility e.g., MgjBj, which contains elemental boron, does not react with Hj at high T. However the reaction between boron and Hj at 840 C forms only traces of B H, and Hj reacts little with boron powder. Thermodynamic calculations based on free energy minimization for the chemical-vapor deposition of boron from BXj-H mixtures (X = Cl, Br) at 1000-1900 K and 0.101 MPa indicate low borane (BHj) cone at equilibrium, but traces of HBXj are predicted in these T ranges. ... 

Fig. 7.2S. XRD pattern and TEM images of the BP samples prepared by reduction of PCI3 in the presence of amorphous boron powders at 350 °C (a) and (b) and by Na co-reduction of PCI3 and BBrj at 300 °C in benzene (c).

The mixtures of silicon and boron powder in a boron content range of 80 to 94mol% were pressed into disk-shaped pellets (10 mm thickness and 20 mm diameter) and then arc-melted in an argon atmosphere. The arc-melted samples were then heat-treated in argon atmosphere at temperatures of 1400 to 1700K. 

I. Slynthesis via fusion of the elements entails such high heats of formation that the reaction temperatures become veiy high. As a result, there is interaction with the material of the vessel and the product boride becomes contaminated. On the other hand, all borides may be prepared by sintering the appropriate metal with amorphous boron powder, which should be as pure as possible (commercial grades now available contain 97-99% B). The reaction mixtures should be heated in alumina crucibles (W or Mo crucibles or boats may also be used) in vacuum (an argon atmosphere is occasionally also used). The reaction, which is always exothermic, starts at temperatimes of 700-1200 C the highest temperature may lie above 2000°C. In some cases, sintering under pressure in carbon tubes (mentioned as a possible method of synthesis for silicides—see p. 1796) can be used. 

Hafnium-like boron is known to be a neutron absorber or neutron moderator element, and, therefore, composites of boron carbide, B4C, and hafnium diboride, HfB2, can be considered as nuclear materials. These boron compounds after sintering and °B/"B isotopic ratio adapting are found to be heterogeneous polyphone cermets useful for nuclear applications (Beauvy et al. 1999). Boron acid obtained from the °B enriched boron trifluoride also was used in nuclear reactors (Shalamberidze et al. 2005). Amorphous boron powders enriched both in °B and "B, boron carbide, and zirconium diboride (ZrB2) powders and pallets labeled with °B isotope And applications in nuclear engineering too. The °B enriched Fe-B and Ni-B alloys are useful for the production of casks for spent nuclear fuel transfer and storage. 

As it was mentioned, boron carbide containing enriched elemental boron ( B 65 at%) can serve as the control rod material in fast breeder nuclear reactors. Because boron carbide is fabricated by reacting elemental boron with carbon and the elemental boron in turn is produced by electro-winning process, Jain et al. (2011) have carried out studies to explore the viability of a high-temperature molten salt electro-winning process for the large-scale production of °B isotopically enriched elemental boron. It was established that elemental boron powder with a purity of better than 95 wt% could be produced. 

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