Evaluation of the dissolution behavior of zircon using high-resolution phase-shift interferometry microscope

Abstract

The dissolution behavior of the (101) plane of zircon mineral in ultrapure water, 1 M HCl (aq), and 1 M NaOH (aq), under room temperature and nearly atmospheric pressure was evaluated by in situ measurement of the change in the surface height. A high-resolution phase-shift interferometry microscope (HR-PSI) was employed to evaluate the velocity of the change in the surface height of zircon in different solutions, and the application of this method in evaluating the dissolution behavior of nuclear materials was examined. In all cases, the measured surface height decreased linearly with small variations. Although the measured change in height of zircon in 1 M NaOH (aq) was the smallest under these conditions, the concentration of dissolved Zr in NaOH (aq) was two orders of magnitude higher than that in ultrapure water. This indicates that a high amount of dissolved Zr in 1 M NaOH (aq) was immediately precipitated on the zircon surface as a secondary phase, and the surface shape was almost retained. On the other hand, the precipitation on the reference of the surface height was confirmed while measuring the zircon in 1 M HCl (aq). This shows that the precipitation in 1 M HCl (aq) occurred far from the dissolution points, and the surface shape changed. As a result, the velocity of surface change and the precipitation behavior of zircon, which is one of the extremely durable minerals, was successfully evaluated using HR-PSI. This relatively quick method would be useful for evaluating the detailed surface change behaviors of nuclear materials, such as fuel debris, ceramic waste forms, and UO 2 , during the reaction with various solutions, since it minimises radiation exposure times and also the amount of radioactive waste generation during measurement.