Effect of incorporation of nitrogen on calcium hexaaluminate

Ions doping is regarded as an efficient approach to improve the density of calcium hexaaluminate (CA(6)). In this work, different amounts of N-3(-) have been tried to dope into CA(6) (CaAl12O(19-1.5x)Nx, x = 0-0.8) by pressureless sintering under N-2 at 1750 degrees C using CaO, Al2O3 and Al fine powder as the raw materials. The results of the synthesized specimens characterized by XRD in combination with SEM and EDS show that a small amount of N-3 up to x = 0.30 can be incorporated into CA(6), increasing the thickness of the CA(6) grains. Besides, first-principle calculation and structure refinement analysis suggest that the structure formula of the N-doped CA(6) is CaAl12O18.58N0.28, and it is preferential for N-3- to substitute O(3) ions near Al(2) in the spinel block. Such a substitution occurs in the Al-O (Al2-O3) bond parallel to c axis, and the bond lengths for tetrahedral Al-N bonds are larger than those of Al-O bonds, showing a promising potential of N-3- for increasing the c-axis crystallization thickness of CA(6).