Controlling Surface Area of Titanium Nitride Using Metathesis Reactions

A metathesis (exchange) reaction between TiCl 3 and Ca 3 N 2 produces phase-pure titanium nitride, TiN, after washing away the CaCl 2 byproduct salt. With use of in situ thermocouples, a maximum reaction temperature ( T max ) of 1665 °C is measured for a reaction producing 1.0 g of TiN 0.6 s after initiating the reaction with a resistively heated Nichrome filament. Scanning electron microscopy indicates the formation of micrometer-size TiN particles. Reduction of the reaction size and addition of 3 mol of NH 4 Cl lowers the reaction temperature to 965 °C and decreases the time the CaCl 2 byproduct remains in a molten state from 9 to 0.6 s. This suppresses Ostwald ripening of the TiN, decreasing the crystallite size and increasing its surface area. Line broadening of X-ray diffraction peaks shows a decrease in the average crystallite size from >200 to 30.8 nm, consistent with 20−30-nm-size particles observed using transmission electron microscopy. Nitrogen gas absorption (BET) indicates that the surface area of the TiN increases from 16.0 to 71.3 m 2 /g. Higher surface area TiN can be used to improve the performance of electrodes in supercapacitors. Experiments with 26 m 2 /g TiN result in a capacitance of >100 F/g and a Coulombic efficiency near 100% even after 10 6 cycles of charging and discharging.