Studying the Formation of Ni3C from CO and Metallic Ni at T=265 °C in Situ Using Ni K-Edge X-ray Absorption Spectroscopy

Metallic Ni nanopowder (Ni-0) was monitored during 23 h of carburization (2CO + 3Ni(0) - Ni3C + CO2, T = 265 degrees C) using Ni K-edge X-ray absorption spectroscopy. X-ray diffraction analysis made afterward at room temperature revealed 28 +/- 3% Ni3C among 72% unreacted Ni-0. The chi(k) data recorded during carburization showed small changes at low k indicative of carbon backscattering. The identification of carbon was possible with wavelet transform analysis after eliminating the integral contribution from the unreacted Ni-0 phase using experimental chi(k) data collected during methanation (CO + 3H(2) -> CH4 + H2O) at T = 265 degrees C. The Fourier-transformed chi(k) data recorded during carburization revealed destructive interference between signals from Ni atoms in slightly different (Ni-0, Ni3C) environments. The interference effect mainly lowered the peak amplitude of the first two Ni-Ni coordination shells compared to metallic Ni at T = 265 degrees C and it propagated very slowly with increasing carburization run time. In simulation of the amplitude lowering of the first Ni-Ni peak by destructive interference as a function of the carburization run time, it followed that the carbon atoms migrate into the Ni-0 particle lattice according to the diffusion-induccd grain boundary motion advocated in the literature.