Assessing the Long‐Term Aqueous Durability and Structural Stability of Pyrochlore (Gd ₂ Ti ₂ O ₇ ) and Glass‐Pyrochlore (Fe‐Al‐BG‐Gd ₂ Ti ₂ O ₇ ) Composite Materials

ABSTRACT Understanding the corrosion behavior of glass–ceramic composite materials such as Fe‐Al‐BG‐Gd 2 Ti 2 O 7 as potential nuclear wasteform candidates has attracted considerable attention due to their high loading of actinide elements and fission products compared to current borosilicate glass nuclear wasteforms. The result of long‐term corrosion studies on the Fe‐Al‐BG‐Gd 2 Ti 2 O 7 composite material indicated that the Fe‐Al‐BG matrix had higher solubility in deionized water compared to the Gd 2 Ti 2 O 7 phase. This is an important property for composite materials as actinide elements can be incorporated into the Gd 2 Ti 2 O 7 phase. Furthermore, the corrosion resistance of the Fe‐Al‐BG matrix of the Fe‐Al‐BG‐Gd 2 Ti 2 O 7 composite material was found to be comparable to that of borosilicate glass nuclear wasteform on its own. Comprehensive surface analysis of Gd 2 Ti 2 O 7 and Fe‐Al‐BG‐Gd 2 Ti 2 O 7 composite materials demonstrated that the surface composition and chemistry of these materials were affected by aqueous corrosion. However, the results of bulk analysis showed that the bulk structure of these materials remained stable over 365 days of exposure to deionized water. The analysis of XPS data from the Fe‐Al‐BG‐Gd 2 Ti 2 O 7 composite material demonstrated that a precipitated metal‐hydroxide layer has been formed on the surface of the composite material after exposure to water and remained likely unchanged between 270 and 365 days of exposure to water. The stability of the surface layer during this time frame could potentially protect the surface of the Fe‐Al‐BG‐Gd 2 Ti 2 O 7 composite material from further corrosion and suggest this composite material could be considered as a potential alternative substitute to borosilicate glass wasteforms.