Diboride systems

Chemical vapor deposition processes are complex. Chemical thermodynamics, mass transfer, reaction kinetics and crystal growth all play important roles. Equilibrium thermodynamic analysis is the first step in understanding any CVD process. Thermodynamic calculations are useful in predicting limiting deposition rates and condensed phases in the systems which can deposit under the limiting equilibrium state. These calculations are made for CVD of titanium - - and tantalum diborides, but in dynamic CVD systems equilibrium is rarely achieved and kinetic factors often govern the deposition rate behavior. 

Borides and Tetrahydroborate Compounds.—ZrB2, HfB2, and the mixed diboride TiB2-ZrB2 have been prepared by heating a stoicheiometric mixture of boron and the metal dioxides (1600—1900 C 10 mmHg). The phases of the Hf-B and I f-M-B (M = Mo or W) systems have been studied by X-ray diffraction techniques. 

The Lifshitz parameter z as a function of x in the case of the A1 and Sc substitutions for Mg in the Mgi xAlxB2, and Mgi xScxB2 systems and for the C for B substitution in the MgB2.xCx system has been calculated by R. De Coss et al. by band structure calculations described elsewhere [204] therefore it has been possible to convert the variation of the critical temperature as a function of the number density of substituted ions x to the variation of Tc versus the universal reduced Lifshitz parameter z for all doped magnesium diborides. 

Although few applications have so far been found for ceramic matrix composites, they have shown considerable promise for certain military applications, especially in the manufacture of armor for personnel protection and military vehicles. Historically, monolithic ("pure") ceramics such as aluminum oxide (Al203), boron carbide (B4C), silicon carbide (SiC), tungsten carbide (WC), and titanium diboride (TiB2) have been used as basic components of armor systems. Research has now shown that embedding some type of reinforcement, such as silicon boride (SiBg) or silicon carbide (SiC), can improve the mechanical properties of any of these ceramics. 

From the physico-chemical properties of the melts of the system KF-KCl-KBF4-K2T1F6, it follows that the most characteristic feature of these melts is the formation of the thermodynamically less stable ionic species TiFy and TiFeCl " with lowered symmetry of the coordination sphere in the melt. The presence of these anions in the melt facilitates most probably the electro-reduction of titanium and thus the formation of titanium diboride on the cathode. 

Among the systems of alkali metal fluorides containing boron oxide, the melts of the system LiF-KF-B203-Ti02 were tested as possible electrolytes in the electro-chemical synthesis of titanium diboride, especially when well-dispersed powders should be... 

The system (LiF-NaF-KF)eut-KBF4-B203 is a part of the (LiF-NaF-KF)eut-K2TaFy-KBF4-B203-Ta205 system, where melts were proposed as electrolytes in the electrochemical synthesis of tantalum diboride by Polyakova et al (1998, 1999). 

As an example, the coupled analysis of the thermodynamic and phase diagram data of the KF-KCl-KBF4-K2TiF6 system performed by Chrenkova et al. (2001) is presented. This system is important because of its potential use as an electrolyte for electro-deposition of titanium diboride. 

EINECS 234-963-5 Zirconium boride Zirconium boride (ZrB2) Zirconium diboride Zirconium diboride (ZrB2). Refractory for aircraft and rocket applications, thermocouple protection tubes, high-temp, electrical conductor, cutting-tool component, coating tantalum, cathode in high-temp, electrochemical systems oxidation-resistant composites. Atomergic Chemetals Cerac Noah Cham. 

The occurrence of the binary borides of the alkaline, alkaline earth, aluminum, and transition elements has been collected in Table 1, together with boron compounds of the right main group elements (carbides, etc.). Only relatively well-established phases have been included. Noncorroborated and/or badly characterized borides lacking precise composition and structure data are not included. The reader is referred to other sources for references. There are no binary borides among the Cu, Zn, Ga, and Ge group elements with the exception of a noncorroborated early report on diborides in the Ag-B and Au-B systems. Two silicon borides have been established, namely, SiB3 4 and SiBe. 

Joining of Zirconium Diboride-Based Ceramic Composites to Metallic Systems... 

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... 

A.L. Chamberlain, W.G. Fahrenholtz, G.E. Hilmas and D.T. Ellerby, Characterization of Zirconium Diboride for Thermal Protection Systems, Key Engineering Materials. 264-268 493-496 (2004)... 

On the basis of the measurements of the phase equilibria, density and viscosity of the melts of the system KF-KCl-KBF4 K2TiF6, using the complex thermodynamic and physicochemical analysis, the structure or ionic composition was studied. It was found that in this electrolyte complex anions TiF7 and TiFeCl with lowered symmetry of co-ordination sphere and different stability are present. The electrodeposition of titanium and titanium diboride from the K2TiF6 based electrolytes is enhanced by the formation of these anions. 

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