Kinetics of high-temperature reaction in titanium-nitrogen system: nonisothermal conditions

The kinetics of rapid high-temperature reaction in titanium-nitrogen (Ti-N-2) system, when it occurs under essentially nonisothermal conditions, are investigated. For this purpose, we utilized a computer-assisted electrothermography (CAE) set-up built in our laboratory. It is shown that under certain conditions, overshooting occurs where the reaction temperature exceeds the setpoint value. This phenomenon may be considered as self-ignition of the metal in nitrogen and its characteristics (e.g, rate of heat release, maximum temperature, etc.) depend strongly on preheating rate. This effect is explained by change in surface area of the solid reactant during preheating period: lower preheating rates to the setpoint temperature provide more change in the metal reactant microstructure (primarily reduction of specific surface area), which decreases the rate of subsequent chemical interaction. Also, it is found that activation energy, E-a, measured under nonisothermal conditions (E-a = 330 W/mol) is significantly higher than that obtained from isothermal experiments (E-a = 210 kJ/mol). The conclusion is made that isothermal kinetics may in general not be applicable for the nonisothermal case. (C) 2001 Elsevier Science B.V. All rights reserved.