Fabrication, characterization, and leach testing of hollandite, (Ba,Cs)(Al,Ti)₂Ti₆O₁₆

The dissolution in de-ionized water (DIW) at 90 and 150 °C of Cs and Ba from mechanically polished Cs-doped Ba hollandite samples is essentially congruent. The normalized Ba and Cs release rates were <0.001 g/m²/day after 56 days in DIW at 90 °C, and the Ba normalized release rate of a Cs-free sample was 0.01 g/m²/day after 56 days in DIW at 150 °C. Varying the pH between approximately 2.5 and 12.9 affected only the Ba dissolution rates of hollandite by half an order of magnitude. The dissolution rates of all species decrease with increasing leaching time due to the formation of partly impervious surface coatings of Al- and Ti-rich species. These surface coatings were investigated by scanning electron microscopy, and in some cases by cross-sectional transmission electron microscopy and x-ray photoelectron spectroscopy.