Chemical durability and crystalline surface film formation of nanocrystalline Gd2Zr2O7-based ceramics

Dense nanocrystalline ceramics exhibit excellent chemical durability comparable to coarse-grained counterparts. • A unique crystalline, multilayered surface film was observed on nanocrystalline surfaces for the first time. • Sharp interfacial chemical gradients confirm the leaching mechanism is governed by coupled dissolution-reprecipitation. Introducing a high density of grain boundaries into ceramic waste forms has been shown to significantly enhance their irradiation resistance. However, this strategy is likely to compromise their leaching resistance. To date, this view still lacks experimental verification. Furthermore, the corrosion behavior and nuclide leaching mechanisms of nanocrystalline ceramic waste forms remain unclear. Herein, x TRPO-(1- x )Gd 2 Zr 2 O 7 ( x  = 0.3 and 0.5) ceramics with grain sizes ranging from the nanoscale (53.6 nm) to the micron scale (13.4 µm) were synthesized, and their chemical durability was investigated via semi-dynamic leaching tests. The normalized leaching rates ( LR i ) for both micron- and nanograined ceramics fell within the range of 10 -5 ∼10 -6 g·m -2 ·d -1 after 42 days, indicating good chemical durability, although the nano-grained ceramics exhibited slightly higher release rates. We demonstrate distinct surface alteration behaviors for the first time: an amorphous film formed on the micron-grained samples, whereas a crystalline, multilayered structure developed on the nano-grained samples after leaching. Both alteration layers can act as protective barriers against aqueous corrosion, contributing to reduced long-term release rates. These findings provide valuable insights into performance prediction and material design for next-generation ceramic waste forms.