The kinetics of growth and consumption of Ni-rich phases is determined from in situ X-ray diffraction measurements performed during isothermal annealing. The results show that the life time of theta-Ni2Si depends on the initial Ni thickness. A slow kinetic of consumption of theta-Ni2Si is observed during the reaction of 50 nm Ni with Si substrate, while a fast rate of consumption of theta-Ni2Si is observed when theta-Ni2Si is a transient phase. A qualitative model has been proposed to explain the obtained results. (C) 2017 Elsevier Ltd. All rights reserved.