Group metal borides

Borides of Group Via. As with the borides of Group Va, the incorporation of free metal in the Group Via borides is difficult to avoid. Both tungsten and molybdenum borides are obtained at high temperature by the hydrogen reduction of the mixed bromides.Bonding appears a more effective method to form these borides in thin layers (see Sec. 2.2 above). 

Figure 1 presents a scheme for the formation of B—B bonds in binary metal borides, i.e., the occurrence of one-, two- and three-dimensional B aggregates as a function of the periodic group of the metal constituent. 

The compressibility of group-IVA and -VIA transition-metal boride powders is measured by the dimensions and weights of the blanks, by measuring the stroke of the punches with a cathetometer, or alternatively by electrical conductivity (based upon the metallic conductivity of most borides). The process of densiheation by pressing is defined by ... 

Table 1. Hot-Pressing Characteristics of Group-VIA Metal Borides...

Another important group of metal borides has the composition M3B4 and features the geometry of Ta3B4 shown in Fig. 5-2, with boron double chains sandwiched between layers of metal atoms.2... 

In the fifteen years since publication of the first edition of Comprehensive Coordination Chemistry (CCC, 1987), group 5 chemistry has been part of the intensive development of ceramic, optical, and magnetic materials based upon metal borides, nitrides, phosphides, oxides, and sulfides. A major impetus came from the discovery of the high-temperature superconducting oxides. In addition, the search for new routes to these materials via sol-gel or chemical vapor deposition techniques has spurred growth in metal amido, oxo, alkoxo, thio, and carboxylato chemistry. 

Boron Nitride, Metal Borides, and Related Spedes.— Alo.o6BeB3 05, Le. BeB3 belongs to the space group P6/mmm, and contains B12 icosahedra and other polyhedral units of Be and B atoms. The linkages between the polyhedra resemble those in /3-rhombohedral boron. Aluminium atoms occupy interstitial... 

In this section and the next three, the properties and characteristics of the interstitial carbides of Group IV are reviewed and compared with those of the host metals, the corresponding interstitial nitrides, as well as those of another refractory group the borides of the Group IV metals. The values given are those for composition as close to stoichiometry as possible. 

Boron carbide is chemically inert, although it reacts with oxygen at elevated temperatures and with white hot or molten metals of the iron group, and certain transition metals. B4C reacts with halogens to form boron halides—precursors for the manufacture of most nonoxide boron chemicals. B4C also is used in some reaction schemes to produce transition metal borides. Boronizing packings containing B4C are used to form hard boride surface layers on metal parts. 

We note that the three structure types which we correlated here are also found in transition metal borides not containing rare earth elements. In this case, the rare earth elements (R) are replaced by earlier transition elements (T ), the late transition elements (T) by boron atoms, and the main group elements (M) by late transition elements (T). The formulae of these compounds are compared in table 5. 

The present status of information about phase equilibria and formation of ternary metal borides with R elements (R = Sc, Y, and the lanthanides) is summarized in fig. 1. Only a small number of the possible ternary combinations R-M-B have been investigated by now and for a larger number only a few compounds have been identified. Little information is available involving main group elements. 

Ued] Ueda, M., Hayakawa, H., Mukaida, M., Imai, Y, Seebeck Coef eients of Iron Group Elements Borides , Intermetallics, 12(1), 155-58 (2004) (Electr. Prop., Experimental, 8) [2006Now] Nowacki, J., Polyphase Sintering and Properties of Metal Matrix Composites , J. Mat. 

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