The effects of temperature on the hydration structure around Ni2+ in concentrated aqueous solution

A preliminary investigation has been made of the effects of temperature on the hydration structure around Ni2+ in a concentrated (nominally 4 m) aqueous solution of nickel (II) chloride using the technique of neutron diffraction with isotope substitution. The scattering from two heavy water solutions containing, respectively, nickel in natural abundance and enriched in the Ni-62 isotope, were measured at temperatures of 90, 175, and 230 degreesC using the general liquids and amorphous materials diffractometer at the intense pulsed neutron source, Argonne National Laboratory. The Ni2+ hydration structure was seen to become progressively weaker and broader with increasing temperature, consistent with the findings of previous experiments. A more subtle effect of temperature on hydration structure has also been highlighted for the first time, namely, gradual shifts in the first hydration peak positions in the real-space difference function. Our findings point to the importance of following changes in hydration structure closely by measuring as many state points as possible, and the desirability of complementary approaches such as EXAFS (extended x-ray absorption fine structure) and quasielastic neutron scattering. Our initial study has also demonstrated the successful performance of a new sample cell designed at Oak Ridge National Laboratory for handling corrosive aqueous solutions under conditions of elevated temperatures and pressures. (C) 2003 American Institute of Physics.