Boron crystallization

The B-B bond lengths in borides is close to that in pure boron crystals, and the latter are quite hard (=3000kg/mm2). Furthermore, the relative bond lengths in the borides are different from the carbides. For example, in TiB2 the... 

Figure 1. The a-rhombohedral unit cell of boron crystal (Fig. la) and the corresponding density of states DOS (Fig. lb).

We would like to remind that all tubular structures are composed of 96 boron atoms, the same number of atoms in the elemental a-boron unit cell of boron crystals. The purpose is simply having clusters of the same size, in order to be energetically comparable. On one hand, a-boron is a real component existing in nature, and on the other hand, single-wall nanotubes so far have been predicted and also synthesized [15]. In this case we calculated the total B3LYP energies and determined the structure stability as follows = (nEi - E ) / n = Ei - E / n, where E is the... 

The significance of the icosahedron to molecular architecture is illustrated by the discussion of the tetragonal boron crystal, the dodecabo-rohydride ion, the decaborane molecule, and the tetraborane molecule on the following pages. 

The bond length for a normal boron-boron bond estimated from the observed values for other single bonds is 1.62 A. The larger value 1.80 A found in the tetragonal boron crystal is reasonable for a half-bond. 

Bom, E. 1973. Helium release from neutron irradiated boron crystals. Radiochim. Acta 19 41-42. 

Kimura, K., H. Hyodo, A. Sumiyoshi, T. Nagatochi, F. Esaka, S. Yamamoto, K. Kirihara, Y. Shimizu, T. Sasaki, N. Koshizaki, H. Yamamoto, and S. Shamoto. 2011. Carrier doping into boron crystals and their nanostructures by Li ion implantation and neutron transmutation. In Abstracts of the 17th International Symposium on Boron, Borides and Related Materials, Istanbul, Turkey, p. 282. 

RHR suction line is used as SIS hot leg injection. This approach is made possible because SIS hot injection is manually actuated after 90 minutes in case of a loss of coolant accident to avoid boron crystallization. With such a design, a big pipe and its associated valves together with the injection nozzle could be deleted. This contributes to a certain gain in safety (reduction of the number of nozzles on the primary coolant lines) and in investment costs. 

The basic boron structural element is the icosahedron, i.e., a polyhedron having twenty faces, twelve equivalent vertices and I2J, symmetry, forming a cage of twelve atoms shown in Fig. 7.7.P1 To form a boron crystal, diese icosahedra combine in a ihombohedral configuration, i.e., a geom cal pattern with axes of equal length and equal axial angles (but not 90 ) (Fig. 7.8). 

SS 7 Boron crystallization and dilution in tfie core in case of LOCAs... 

For the systems containing boron of high concentration, the following measures are taken to minimize the possibility of boron crystalization ... 

Modifications are being implemented in all units to allow water injection simultaneously in hot and cold legs of the reactor coolant system. This results in the long term operation of the emergency core cooling system eliminating the risk of boron crystallization and without repeated valve operations. 

Because the solubility coefficients of carbon in the solid and the liquid phase are almost the same, zone melting, which is used to prepare high-purity crystals of many other elements, is not suitable in the case of boron. Technical boron, which is often taken as the ingredient for the preparation of boron compounds, contains up to about 0.5% carbon. However, in several preparative methods for boron compounds the carbon content may be reduced by secondary chemical or physical reactions. The purest P-rhombohedral boron crystals that have become available up to now were produced by Wacker-Chemie, Munich, FRG. Despite the claimed purity of 99.9999% with respect to other elements, even this high-purity boron contains carbon in concentrations of typically 30 to 80 ppm. Therefore, apart from boron carbide containing carbon as a determining bonding partner, in the assessment of the properties of boron and boron compounds attention must be paid to the fact that a certain, usually unknown carbon content could have influenced the properties determined. 

The thermoelectric power of the boron films obtained shows a small peak at a higher temperature, compared with those for bulk boron. This may be attributed to the fact that the concentration of the acceptors in amorphous boron films is higher than that in boron crystals. 

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