On the structural destabilization of Ce-based alloys by reactive milling in the Ce-3Ni system

A.AVALOS; E. ZELAYA; M.R ESQUIVEL.

Bariloche, Rio Negro, Argentina

Congreso; XXIII Latin American Symposium on Solid State Physics; 2018

Universidad de Rio Negro-Comisión Nacional de Energía Atomica

The Ce-3Ni system is a novel precursor for the synthesisof CeO2-Ni composites used in the selective captureof O2 (g) in high-purity Ar or He supply. Themetal constituents are milled to achieve an intimatemixture and then selectively oxidized under controlledconditions. At the rst step, the system is milled up toreach the intermediate stage [1]. At the second step,it is temperature-assisted to produce the desired cermet.But milling of Ce-based alloys in Ar=O2 mixturesin the presence of Ni induces a destabilization andfurther phase transformation which eventually favorsthe CeNi3 intermetallic formation. The process evolvesby an in-series exothermal process as analyzed bydierential scanning calorimetry (DSC). The structureand microstructure of the phases is studied by HTXRD.The nanostructure is analyzed by transmissionelectron microscopy (TEM). Starting Ce-based alloyconsists of a mixture of two phases reported for Ce: anhexagonal structure equivalent to a -dhcp and a cubicone equivalent to a -cc. The cubic phase is onlyobserved at temp. higher than 200 C in the binaryCe-Ni phase diagrams. After processing the system for5 h, a complete  to phase transformation is observed.This process occurs in parallel to the renementof the Ni structure. The cubic structure is stabilizedby temperature treatment between 100 C and 600 Cand no signicant composition changes are observedbetween both Ce-based and Ni cubic phases. Millingalso induces an extension of the solubility limits inthe Ce-Ni system. The CeNi3 intermetallic is obtainedat 900 C under Ar atmosphere treated for 5h. Afterthat, the system is oxidized in O2. The nal oxideshave crystalline habits according to the Fm3m spacegroup. The composite is reduced under H2 ( g)-Arto obtain a CeO2 -based-Ni mixture. The rst resultsof selective capture of O2 impurities in in Ar(g) arepromising and currently under way.[1] S. A. Obregon, J. Andrade, M.R. Esquivel, InternationalJournal of Hydrogen Energy, 37, 14972 (2012).