Preparation and crystal structure of ζ-Cr2(C,N) powders

In this work, the influence parameters, including synthesis temperature, nitrogen pressure, and isothermal dwell time, were systematically investigated during carbothermal preparation of ζ-Cr2(C,N) solid solution powders by using thermogravimetry differential scanning calorimetry, X-ray diffraction, scanning electron microscope, and composition analysis. The results showed that Cr2O3 began to be carbonized at ~ 1000 °C firstly and then was nitrided with the formation of Cr2(C,N) at elevated temperature, and finally ζ-phase Cr2(C,N) particles were obtained at the optimal condition of 1200 °C for 1 h under the N2 pressure of 0.02 MPa, which showed lowest oxygen (0.82 wt%) and highest nitrogen (6.25 wt%) content with the diameter of ~ 3 μm. Increasing temperature, N2 pressure, and dwell time facilitates the reduction of oxygen. However, these parameters must be carefully controlled under reasonable ranges to preventing quality deterioration. In addition, the crystal structure of ζ-Cr2(C,N) was characterized by transmission electron microscope and neutron powder diffraction (NPD). Based on the selected area diffraction and NPD patterns, the crystal structure of Cr2(C,N), prepared in this work, was confirmed to be orthorhombic (Pbcn) as well as the interstitial atoms (C and N) were ζ-type occupational ordering.