Formation of transition metal silicides by solid-gas reactions: thermodynamic and kinetic considerations

Alternative synthesis routes to nickel silicides are discussed. Results of the reactions of Ni with a SiCl4/H-2 gas mixture (1), of NiSi with NiCl2 (2 ) as well as of Si with nickel halides (3) are presented. Kinetics of the r eactions (1) and (2) were studied in detail by in situ electrical resistanc e measurements and isothermal X-ray powder diffraction, respectively. Kinet ic evaluation of the electrical resistance measurement data points to islan d and layered silicide growth in process (1). XRD data analysis leads to th e conclusion that process (2) proceeds via transient metastable nickel sili cide phases, which are interrelated with the thermodynamically stable silic ide phases Ni2Si, Ni3Si2 and NiSi. (C) 2001 Elsevier Science B.V. All right s reserved.