Reaction Mechanism of Al and N in Diamond Growth from a FeNiCo-C System

It is significant to investigate the action of nitrogen getters, which are used to synthesize type-IIa large diamond single crystals under high pressure and high temperature (HPHT). The reaction mechanism of Al as a nitrogen getter and N in the HPHT alloy solvent is still indeterminate at present. In order to investigate the reaction of Al and N in the HPHT alloy solvent, Al and AlN are respectively added to the system of Fe₅₅Ni₂₉Co₁₆−C (wt%, abbr. FeNiCo-C) for the synthesis of diamonds at about 5.5 GPa and 1600 K. The concentration of nitrogen in the diamonds is characterized by a micro Fourier transform infrared (micro-FTIR) spectrometer. The experimental results show that c_N decreases when Al is added to the FeNiCo-C system. However, it increases when AlN is added. A reversible reaction confirms that Al and N can react and form AlN, simultaneously AlN can be decomposed into Al and N in the HPHT alloy solvent. Therefore the mechanism of eliminating the nitrogen of nitrogen getter Al is realized in detail.