Preparation and crystallization of nanosized amorphous nickel sulfide by using gamma-irradiation

Nano-sized amorphous nickel sulfide has been prepared in a mixed aqueous solution of Na2S2O3 and Ni2SO4 compounds using gamma-irradiation at room temperature, The obtained precipitate after gamma-irradiation was washed and dried at 60 degrees C, It was then crystallized by calcination in a flow of argon at 160 - 500 degrees C, respectively, All these samples were characterized by X-ray diffraction and extended X-ray absorption fine structure (EXAFS) spectroscope. No peak is detected in the X-ray diffraction patterns of 60 degrees C dried and 160 degrees C calcined samples, it reveals that particles in these two samples are in amorphous states with high level of disorder, Several weak peaks are found in the pattern of 300 degrees C calcined sample and they become stronger in that of 400 degrees C and 500 degrees C calcined samples. All these peaks are due to NiS compound, EXAFS results demonstrate that the nickel sulfide particles in 60 degrees C dried sample are present in a tetrahetral structure with an average Ni - S coordination distance of 0.221nm and a Ni - S coordination number of 4.4, which are changed to octahedral structures with Ni - S coordination distances of about 0.238nm and Ni - S coordination numbers of near 6.0 after calcined at above 300 degrees C, Both the tetrahedral species and the octahedral species exist in 160 degrees C calcined sample.