Titanium diboride deposition

The deposition of a binary compound can be achieved by a coreduction reaction. In this manner, ceramic materials such as oxides, carbides, nitrides, borides, and silicides can be produced readily and usually more readily than the parent metal. A common example is the deposition of titanium diboride ... 

Another candidate material for high temperature fiber is titanium diboride. It has a melting point of around 3000°C. Diefendorf and Mazlout (1994) used a gas mixture of titanium tetrachloride boron trichloride, hydrogen, and hydrochloride to make titanium diboride fibers by chemical vapor deposition (CVD) in a cold wall reactor at atmospheric pressure. 

Different methods used to prepare titanium diboride have been reviewed by Samsonov et al. (1975). At present, it is mainly produced as a powder by thermochemical reduction of boron and titanium oxides followed by hot pressing and sintering to process the final product. The less costly alternative appears to be to coat suitable substrate materials with TiB2 or TiB2-based composites by hot pressing, plasma spraying, chemical vapor deposition, etc. 

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. 

The source can be heated by a variety of techniques. Resistance heating can be used, employing W, Mo, or Ta heater wire or tape. These have the advantage that their low vapour pressures do not cause contamination of the deposit. The source can be contained in a crucible made of boron nitride or titanium diboride. Induction heating can also be used to heat a susceptor source contained in a nonsusceptor crucible. Electric-arc and laser-beam sources can also be used to heat the evaporant. 

Wendt H, Dermetiek S. Erosion of sintered titanium diboride cathodes during cathodic aluminium deposition from lithium chloride/aluminium chloride melts. J Appl Electrochem. 

CS Choi, GC Xing, GA Ruggles, CM Osburn. The effect of annealing on resistivity of low pressure chemical vapor deposited titanium diboride. J Appl Phys 69 7853, 1991. 

Ceramic Matrix Composites (CMC) performed by a hybrid process is described in this paper. This process is based on (i) the chemical vapor deposition of carbon interphase on the fiber surface, (ii) the introduction of mineral powders inside the multidirectional continuous fiber preform and (Hi) the densification of the matrix by Spark Plasma Sintering (SPS). To prevent carbon fibers and interphase from oxidation in service, a self-healing matrix made of silicon nitride and titanium diboride was processed. A thermal treatment of 3 minutes at 1500 C allows to fully consolidate by SPS the composite without fiber degradation. The ceramic matrix composites obtained have an ultimate bending stress at room temperature around 300 MPa and show a self-healing behaviour in oxidizing conditions. 

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. 

Apart from the reactions described above for the formation of thin films of metals and compounds by the use of a solid source of the material, a very important industrial application of vapour phase transport involves the preparation of gas mixtures at room temperature which are then submitted to thermal decomposition in a high temperature furnace to produce a thin film at this temperature. Many of the molecular species and reactions which were considered earlier are used in this procedure, and so the conclusions which were drawn regarding choice and optimal performance apply again. For example, instead of using a solid source to prepare refractory compounds, as in the case of silicon carbide discussed above, a similar reaction has been used to prepare titanium boride coatings on silicon carbide and hafnium diboride coatings on carbon by means of a gaseous input to the deposition furnace (Choy and Derby, 1993) (Shinavski and Diefendorf, 1993). 

However, among all of the above mentioned compounds, the technologically most important are the K2TiF6 and K2ZrF6, because of their frequent use in the electrochemical deposition of titanium and zirconium and the electrochemical synthesis of titanium and zirconium diborides. 

DEPOSITION OF TITANIUM, ZIRCONIUM AND HAFNIUM DIBORIDE COATINGS BY HIGH-TEMPERATURE ELECTROCHEMICAL SYNTHESIS 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. 

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