Characterization of phases and structures in composites by TEM and SEM

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

CABA

Congreso; XV CIASEM CONGRESS; 2019

Asociación Argentina de Microscopia - Sociedad Interamicana de Microscopia

The composites based on cerium dioxide (CeO2) and nickel are widely demanded in different researchfields including energy and environmental applications 1,2. These required composites need to fulfillat least two common requirements. One is to use the nickel as a catalyst in the composite and the other isto use the cerium based dioxide as both a support and a conductive structure. Both requirements aresomehow complex because a strong structure should also be compatible with a porous 3-D distributionof Ni. A large number of synthesis methods developed to obtain these composites are found in thebibliography. The variety of methods includes mechanical alloying in different atmospheres, sol-gelsynthesis from the nitrate precursor, sequential impregnation and solution combustion synthesis. But thisvariety of methods is developed according to the application selected. In this work, a method of additivemanufacture is done to obtain a Ce0.52La0.25Nd0.17Pr0.06O2-Ni mixture. The manufacture method isdesigned to obtain a porous stable structure with properly distributed Ni. In a first step, a 3-D mold isfabricated with poly-lactic acid (PLA). The method used is molten deposition modeling using a 3-Dprinter. The mold is filled with a Ce-based alloy (Ce0.52La0.25Nd0.17Pr0.06) -3Ni mixture previously milledin a high energy mill (Retsch M100 mill). Then, the alloy-metal mixture is pressed at low pressure in adie within the mold. The sample is withdrawn and thermally treated in air and hydrogen. The finalsample is shaped according to the mold. The sample nanostructure is analyzed by Transmission ElectronMicroscopy (TEM - FEI Tecnai G20 operated at 200 kV) and associated techniques. The TEMtechnique is used to study the composite at nano-scale to determine the individual features of eachcomponent.. The morphology, habit and forms of structures at micro-scale are studied by ScanningElectron Microscopy (SEM - FEI Inspect S50 operated at 30 kV). These features are observed inFigures 1 and 2. The Figure 1 shows TEM micrographs of a Ce0.52La0.25Nd0.17Pr0.06O2 particle of theCe0.52La0.25Nd0.17Pr0.06O2-Ni mixture. Figure 1.a shows the bright field. Note the straight cuts thatindicate a structure evolving in equilibrium after temperature treatment. Figure 1.b shows the dark field.Notice the two different sizes on the crystalline domains. The Figure 2 b shows SEM micrographs of theCe0.52La0.25Nd0.17Pr0.06O2-Ni composite. The Figure 2.a shows the micrograph in the emissive mode. Theselected particle presents a porous structure of the mixture. The Figure 2.b shows the same micrographon the reflective mode. The atomic contrast is evidenced. The white color is assigned toCe0.52La0.25Nd0.17Pr0.06 in the oxide and the grey color to Ni. The particle boundaries are well defined inthe Ce0.52La0.25Nd0.17Pr0.06O2-based component. The micrograph also shows the Ni distribution withinthe Ce0.52La0.25Nd0.17Pr0.06O2 matrix. These images indicate that the synthesis method combiningadditive manufacture, mechanical milling and thermal treatment lead to the formation of the desiredstructure. The samples obtained in this work are used to capture oxygen to purify argon /nitrogen gases.References:[1] M. Li, A. Van Veen. App. Catal. B: Environm. 237 (2018) p. 641.[2] S. Kasturibai, G.P. Kalaignan. Mat. Chem. Phys. 147 (2014) p. 1042.