Following ion diffusion in solution.

An x-ray projection microscope equipped with a charge-coupled device camera allows direct observation of zinc (Zn(2+)) ions diffusing in aqueous hydrochloric acid solution during the corrosion of zinc foil and pellets. Time series of microradiographic images with a lateral resolution on the order of 10 micrometers allow observation of the time and spatial evolution of the colorless Zn(2+) ions in solution without any previous treatment. The concentration distribution of the ions can be quantified from these images. This technique should find applications in the biology, chemistry, and electrochemistry of aqueous solutions, allowing direct observation of the behavior and concentration fluctuations of medium or heavy ions moving in a weakly absorbing medium.