Thermal explosions in (Ti, Zr, Hf, Nb, Ta) carbon mixtures

Abstract

This research focuses on investigating the ignition and thermal explosion behavior of (Ti, Zr, Hf, Nb, Ta) + 5C mixtures that have been mechanically activated. First, we mechanically activated the metal powder mixtures to produce composite particles consisting of Ti, Zr, Hf, Nb, and Ta, followed by the addition of carbon, and re-activation. An activation time of 120 min at 347 rpm resulted in the formation of solid solutions from the metals in the mixture, while large tantalum particles were preserved. The resulting mixtures were then pressed into pellets, which were heated in argon until ignition occurred. The ignition process involves multiple phases, with the first being inert heating, followed by progressive heating at t = 420÷450 °C, and a  subsequent endothermic phase transformation at 750–770 °C. The temperature then rises rapidly, resulting in a thermal explosion that forms complex carbides, leaving some unreacted tantalum behind. The (Ti, Zr, Hf, Nb, Ta)C5 activated mixtures and high entropy solid solution are unstable and  release titanium and zirconium carbides when heated above 1300 °C, causing changes to the composition of the (Ti, Zr, Hf, Nb, Ta)C5 final product. When diluted by adding 25 and 50 % of the final product, the effective activation energy Ea for the (Ti, Zr, Hf, Nb, Ta) + 5C reaction in the 1100–1580 °C temperature range was found to be 34 kJ/mol.