Quasi-Elastic Neutron Scattering Study of Aqueous Solutions of FeCl3, NiCl2 and MgCl2

Quasi-elastic neutron scattering experiment was performed on FeCl 3 , NiCl 2 and MgCl 2 aqueous solutions. The whole shape of energy spectra of incoherently scattered neutrons was analyzed. The hydration number of Fe 3+ ion was estimated to be 2.6, being independent of solute concentration. Based on a jump diffusion model, the diffusion constant and the rest time for the water molecules bound to Ni 2+ ion in the NiCl 2 solution were estimated as 0.2×10 -5 cm 2 sec -1 and 3.0×10 -12 sec at 25°C, and 0.6×10 -5 cm 2 sec -1 and 2.0×10 -12 sec at 55°C, respectively. Those to Mg 2+ ion in the MgCl 2 solution were estimated as 0.8×10 -5 cm 2 sce -1 and 3.0×10 -12 sec at 25°C, respectively. The present results justify the structure model proposed by Brady et al . for the FeCl 3 solution and the simplified “hard sphere model” originally proposed by Quirke et al . for the NiCl 2 solution. The diffusion process of Mg 2+ ion in the MgCl 2 solution is discussed.