Transition metal diborides

Boron-based ternary phase diagrams with two transition metals have been investigated for exploitation of the diborides with an AIB2 structure, which have high hardness and a high melting point. Due to the identical crystal structure, most of the transition metal diborides have been considered of high mutual solubility... 

Boron Carbide-Transition Metal Diboride Ceramics... 

A further improvement of both hot-pressing cycles and additives, in particular concerning the transition metal diborides resulted in a microstructural optimization with in-situ grown W2B5 particles. After annealing, the average of the diameter of the W2B5 particles was about 4.5-7 pm (Fig. 59). 

The densification of single-phase and pure ceramics of transition metal diborides is complicated by two characteristics of these compounds, the high melting point and the comparatively high vapor pressure of the constituents. As a rule, sintering temperatures exceeding 70% of the absolute melting temperature have to be applied. 

The electric resistivity in the solid solution system TiB2-ZrB2 was studied by Rahman et al. [273]. Billehaug and 0ye [274] present a study of several transition metal diborides for cathode materials in Hall-Herould cells and come to the conclusion that TiB2 should be an excellent candidate because of its stability against the... 

Combinations of diborides of different transition metal borides have been studied, especially in the TiB2/CrB2 and TiB2/W2B5 systems, for wear applications and to a minor extent for eleetrodes in Hall-Herould cells [135,139,140,293-295], Since the transition metal diborides crystallize in the same structure type, namely the AIB2... 

TABLE 1. Observed phase stability of transition metal diborides of the AIB2 structure. 

Guillermet, A. F. and Grimvall, G. Phase Stability Properties of Transition Metal Diborides, Am. InsL Phy. Conf. PiDc., [231] 423 31 (1991). 

The metal diborides, MB2, have two-dimensional networks of boron atoms in a hexagonal crystal symmetry. They are very hard, brittle, metallic conductors, and are chemically inert (especially TiB2 and ZrB2). Transition metal diborides are resistant against carbon at lOOO C and are therefore used to passivate steel in coal liquefaction equipment. The diboride alloys Zro.13Moo.87B2 (Tc=10K) and SC0.1Nb1.9B2 (7 = 6.6K) are superconductors. 

Tantalum Diboride (TaB2) hexagonal, AIB2 structure (C-32 type) isomorphous with other transition metal diborides a=3.078-3.088A c=3.241-3.265A c/a= 1.06-1.074... 

The objective of this work was to study and to develop a method for high-temperature electrochemical synthesis (HTES) of transition metal diboride coating from chloro-fluoride melts. 

The HTES of all the Titanium-group transition metal diborides fi om chloro-fluoride melts was possible at a wide range of current densities, using more positive potentials than those for deposition of boron, or transition metal fi om the same melt. 

Devyatkin, S.V., Kaptay, G., Shapoval, V.I., and Berecz, E. Electrochemical synthesis of transition metal diborides from molten salts (1993), in Proc. of the Int. Symp. on Molten Salts Chemistry and Technology, The Electrochemical Society Proceedings Series, Pennington, NJ 93-9, 584-599,... 

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