Kinetics of Structural and Microstructural Changes at the Solid/Solution Interface during Dissolution of Cerium(IV)鈥揘eodymium(III) Oxides

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• 作者：St茅phanie Szenknect ; Adel Mesbah ; Denis Horlait ; Nicolas Clavier ; Sandrine Dourdain ; Johann Ravaux ; Nicolas Dacheux
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：June 7, 2012
• 年：2012
• 卷：116
• 期：22
• 页码：12027-12037
• 全文大小：652K
• 年卷期：v.116,no.22(June 7, 2012)
• ISSN：1932-7455

文摘

Improving the understanding of dissolution mechanisms at the solid/solution interface of mixed Ce^IV_1鈥?i>xNd^III_xO_2鈥?i>x/2 dioxides is a critical step in the frame of generation IV (Gen IV) nuclear fuel elements that integrates minor actinides recycling. In order to give significant insight into the dissolution kinetics of Ce_0.4Nd_0.6O_1.7 sintered samples prepared from the thermal conversion of oxalate precursors, X-ray reflectivity (XRR) and grazing incidence X-ray diffraction (GI-XRD) were used to characterize the microstructural and structural changes of the solid/solution interface and were coupled with solution analysis. The dissolution mechanism occurred in three steps. After a short period of dissolution in which no Nd release was observed, GI-XRD revealed the existence of a 200 nm depth chemical gradient below the surface formed during the early times of the dissolution. A Nd-enriched zone was located at the surface of a Nd-depleted zone. Simultaneously, XRR data showed the development of a surface layer of 40 脜 of low electron density. Both results fit well with the presence of a Nd-based thin surface layer phase. Then, the Nd-based surface layer dissolved and developed microporosity, leading to a strong increase of the surface of this layer. Thus, during the initial times, the Nd-based layer mainly contributed to dissolution, which played a crucial role in the kinetics of dissolution and explained why incongruent dissolution was first observed as a transient stage to congruent dissolution. From almost 3% of mass loss, a steady state was reached, corresponding to a congruent dissolution mechanism. The duration of the transient steps depended on the alteration conditions.