Exothermic behavior of several elemental powder mixes

A study of the exothermic nature of the reactions that occur within elemental powder mixtures with compositions of Ni–24Al; Fe–29Al and Ti–50Ni during heating has been carried out. The experimental procedure consisted of heating and reacting powder compacts in vacuum (4×10−3 Pa), and the temperature of the compacts was monitored in situ. Temperature variations of specimens sealed or unsealed in a stainless steel sheath were compared and analyzed. It was observed that the maximum temperature of Ni–Al compact was effectively depressed due to an absorption of the exothermic heat by the near equal-weight sealing sheath, and the reacted phase structures changed. Neither significant variation of the maximum temperature nor modification of the reacted phase was found in the Fe–Al compact when it came into contact with the sealing stainless steel sheath. It is suggested from the observed results that the reaction between Fe–Al particles is more violent and faster than that of Ni–Al particles, although the exothermic heat is less. In addition, a tremendous exothermic heat was released once the Ti–Ni mixture was heated up to 1100 °C. The sealing stainless steel sheath could not resist the maximum temperature of the mixture, so it melted down. The exothermic behavior of the three powder compacts is difficult to investigate with the common thermal analysis instruments and calorimetric measurement.