The synthesis of titanium nitride and titanium carbonitride by self-propagating combustion

Abstract

The self-propagating high-temperature synthesis of titanium nitride (TiN)_1−x and titanium carbonitride (TiC _x N_1−x ) from Ti metal is investigated to provide insight into the mechanism of the reaction. For the synthesis of TiN, the extent of reaction, expressed as percent conversion or nitrogen uptake, is strongly dependent on the composition and porosity of the reacting pellets and the pressure of nitrogen gas. The total nitrogen uptake at 1 bar pressure is a maximum at about 58% relative density. X-ray diffraction (XRD) analysis shows that regardless of porosity, the surface of the samples is titanium nitride (TiN_1−x ) of rock salt structure. The effects of nitrogen gas pressure and diluent (TiN) content on the synthesis of titanium nitride is investigated in the pressure range of 0.1 to 1.4 MPa. For the pure titanium samples, increasing the pressure of nitrogen leads to a decrease in nitrogen uptake. An increase in the conversion can only be achieved if the amount of diluent is above 40 wt%, with full conversion attained at 60 wt% diluent at nitrogen pressures of 0.5 MPa.

In the combustion synthesis of titanium carbonitride from a mixture of pressed titanium and carbon powders the nitrogen uptake of the undiluted samples is only about 40% of the maximum theoretical uptake. Addition of TiN as diluent increases the nitrogen uptake to 100% at 0.5 MPa nitrogen. XRD analysis demonstrates that the structure of all the products regardless of dilution or nitrogen pressure is the rock salt phase. SEM of the reacted samples reveals that the porosity of the samples increases with increasing carbon content. Analysis shows that if the amount of carbon is less than 0.4 mol/mol of the reactant, then carbon causes no significant effect on nitrogen uptake. At higher carbon contents the nitrogen uptake increases to about 80% of its theoretical maximum value.