The influence of compression conditions on the peculiarities of self-propagating exothermal reaction in Al-Ni powder reactive materials

The paper deals with the effect of the compression conditions on the propagation front velocity of exothermal reaction and the specific heat release in Al-Ni powder reactive materials with mean particle sizes of 70-110 nm. It was shown that the velocity increases from 2.7 to 8 cm s(-1) and comes to saturation with the lowering of the porosity (eta) from 0.91 to 0.34, while the dependence of the specific heat release has its maximum for eta = 0.5. The results of the X-ray diffraction analysis obtained in situ during the sample heating suggest that the sequence of phase transformations in the system does not depend on the porosity. In all cases, first in the temperature range of similar to 500-540 degrees C the NiAl compound is formed. With the further heating up to similar to 640 degrees C, the Ni3Al, Ni2Al3 and NiAl3 compounds are additionally formed. The calculation of kinetic parameters was performed using the obtained curves of the differential scanning calorimetry: activation energy, pre-exponential factor and reaction model. The comparison of the calculated results and the scanning electron microscopy data has shown that such behavior of the Al-Ni system with the porosity lowering occurs due to the growth of the transformation degree and is associated with the presence in the final powder mixture of mutually non-contacting Al and Ni agglomerates with the dimensions of over 10 mu m.