Titanium carbide diffusion

Titanium Carbide. TiC, with its great hardness and wear resistance, is particularly suitable to reducing mechanical and abrasive wear. However, it is susceptible to chemical attack and is not a good diffusion barrier. 

DL Kohlstedt, WS Williams, JB Woodhouse. Chemical diffusion in titanium carbide crystals. J Appl Phys 41 4476, 1970. 

J Bethin, WS Williams. Ambipolar diffusion contribution to high-temperature thermal conductivity of titanium carbide. J Am Ceram Soc 60 424, 1977. 

Petrii and Entin [54, 57, 78, 150, 180, 243] investigated the adsorption and electrochemical characteristics of platinum and ruthenium alloys in detail. The optimum alloy compositions for oxidation of methanol at various temperatures were determined, the anodic oxidation reactions of various compounds of the alloys were investigated, the stability of the alloys after prolonged use was investigated, and the characteristics of platinum— ruthenium alloys prepared by various methods (skeletal electrodes, electro-lytically mixed deposits on a platinum and titanium carbide bases, powders deposited by sodium borohydride, smooth alloys) were compared. It was found that heat treatment of platinum - ruthenium alloys at 800 C in an atmosphere of inert gas led to loss of their high catalytic properties and formation of catalysts which behave similarly to platinum. This phenomenon is explained by diffusion of ruthenium atoms from the surface layer into the volume. 

In the case of TiC, preferential evaporation of titanium leads to a change in the stoichiometry of the compound towards the carbon-rich end, the excess carbon being left diffuses into the carbide phase, and so the flux ratio of the two elements changes widi time until congruent vaporization is achieved. 

Many CVD reactions are being investigated for the deposition of carbides and nitrides, particularly for titanium nitride for semiconductor applications, such as diffusion barrier. The following is a summary of the metallo-organic precursors and deposition condition presently used in development or production of these materials. 

However, unlike for boron carbide and nitride, the kinetics becomes parabolic again at higher temperatures (>1200°C). This can be explained by the fact that when B2O3 is completely evaporated the process is controlled by the diffusion through the titanium dioxide film. 

The early transition metal nitrides of titanium, zirconium, hafnium, tantalum, and tungsten as well as titanium and tantalum carbide are effective diffusion... 

Titanium Nitride. TiN a special refractory material m.p. approx. 3000°C thermal expansion (25-1400°C) 9 x lO- . It can readily be produced from TiC and NH3. TiN coatings on metal cutting tools act as a diffusion barrier to impurities. They have higher electrical conductivity and better adhesion than alumina, and are used as an undercoat for AI2O3 coatings on tungsten carbide. Thin TiN films show iridescent interference effects, and are used as decorative hard surfacing for watches and jewelry. 

The diffusion problems can be partially overcome by applying a barrier coating such as titanium, boron, nickel, copper, or niobium carbide over the fiber priorto processing the composite. The latter material, NbC, has shown excellent diffusion-barrier characteristics in a laminate composed of P-100 fibers (43 vol.%) and a copper matrix.P f A cross-section of the composite after isothermal exposure at 815°C for 240 hours is shown in Fig. 9.6. 

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