Controlling surface area of titanium nitride using metathesis reactions

A metathesis (exchange) reaction between TiCl3 and Ca3N2 produces phase-pure titanium nitride, TiN, after washing away the CaCl2 byproduct salt. With use of in situ thermocouples, a maximum reaction temperature (T-max) of 1665 degreesC 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 NH4Cl lowers the reaction temperature to 965 degreesC and decreases the time the CaCl2 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.