Characterization of phases and structures in composites by TEM and SEM

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

CABA

Congreso; XV CIASEM CONGRESS; 2019

Asociación Argentina de Microscopía

Thecomposites based on cerium dioxide (CeO2) and nickel are widelydemanded in different research fields including energy and environmentalapplications [1,2]. These required composites need to fulfill at least two common requirements.One is to use the nickel as a catalyst in the composite and the other is to usethe cerium based dioxide as both a support and a conductive structure. Both requirementsare somehow complex because a strong structure should also be compatible with aporous 3-D distribution of Ni. A large number of synthesis methods developed toobtain these composites are found in the bibliography. The variety of methodsincludes mechanical alloying in different atmospheres, sol-gel synthesis fromthe nitrate precursor, sequential impregnation and solution combustionsynthesis. But this variety of methods is developed according to theapplication selected. In this work, a method of additive manufacture is done toobtain a Ce0.52La0.25Nd0.17Pr0.06O2-Nimixture.   The manufacture method isdesigned to obtain a porous stable structure with properly distributed Ni. In afirst step, a 3-D mold is fabricated with poly-lactic acid (PLA). The methodused is molten deposition modeling using a 3-D printer. The mold is filled witha Ce-based alloy (Ce0.52La0.25Nd0.17Pr0.06)-3Ni mixture previously milled in a high energy mill (Retsch M100 mill). Then,the alloy-metal mixture is pressed at low pressure in a die within the mold.The sample is withdrawn and thermally treated in air and hydrogen.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 byTransmission Electron Microscopy (TEM - FEI Tecnai G20 operated at 200 kV) andassociated techniques. The TEM technique is used to study the composite atnano-scale to determine the individual features of each component.. Themorphology, habit and forms of structures at micro-scale are studied byScanning Electron Microscopy (SEM - FEI Inspect S50 operated at 30 kV).  These features are observe in Figures 1 and 2.The Figure 1 shows TEM micrographs of a Ce0.52La0.25Nd0.17Pr0.06O2particle of the Ce0.52La0.25Nd0.17Pr0.06O2-Nimixture. 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 thecrystalline domains. The Figure 2 b shows SEM micrographs of the Ce0.52La0.25Nd0.17Pr0.06O2-Nicomposite. The Figure 2.a shows the micrograph in the emissive mode. The selectedparticle presents a porous structure of the mixture. The Figure 2.b shows thesame micrograph on the reflective mode. The atomic contrast is evidenced. Thewhite color is assigned to Ce0.52La0.25Nd0.17Pr0.06in the oxide and the grey color to Ni.  Theparticle boundaries are well defined in the Ce0.52La0.25Nd0.17Pr0.06O2-basedcomponent. The micrograph also shows the Ni distribution within the Ce0.52La0.25Nd0.17Pr0.06O2matrix. These images indicate that the synthesis method combining additivemanufacture, mechanical milling and thermal treatment lead to the formation ofthe desired structure. The samples obtained in this work are used to captureoxygen to purify argon /nitrogen gases. References:[1] M. Li, A. Van Veen.App. Catal. B: Environm. 237 (2018),641-648.[2] S. Kasturibai, G.P. Kalaignan. Mat. Chem. Phys.47 (2014), 1042-1048.