Publications

Publications

Ferroelastic mechanical behavior of LaCoO3 was investigated by the impression test and compared with the conventional compression test using digital image correlation technique for deformation measurement. The results show that the coercive stress for ferroelastic deformation can be detected by impression test, which is less than critical stress for such deformation in the compression test. Room temperature ferroelastic impression creep characterization showed different equilibrium penetration of flat-end punch at different constant stresses, which can be characterized by Prony series.

https://doi.org/10.1016/j.jeurceramsoc.2018.11.008

Abstract

Structural and mechanical Characterizations of La1.8M0.2NiO4+δ (M: Sr and Ba) prepared by low frequency ultra-sound assisted synthesis technique and sintered at different temperatures were studied. HRTEM and XRD analyses showed the uniform shape of calcined nanocrystalline powders with the particle size of less than 100 nm with mixed phases, which were refined by Rietveld method using orthorhombic (Fmmm) and tetragonal (F4/mmm) structures. Sintering La1.8Sr0.2NiO4+δ and La1.8Ba0.2NiO4+δ compacted discs at temperatures higher than 1300 °C and 1250 °C, respectively, resulted in appearance of extra peaks close to a monoclinic phase. Doping La2NiO4+δ with Sr2+ and Ba2+ did not affect its sinterability and average grain size significantly, however, Ba2+ improved the elastic modulus and microhardness, while Sr2+ improved the fracture toughness.

https://doi.org/10.1016/j.ceramint.2018.03.077

Abstract

In this work, we present the synthesis of Ag doped TiO2 materials. The products are characterized by powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption, and hydrogen adsorption. The Ag/TiO2materials exhibit 3.65 times higher in hydrogen adsorption capability compared with the non-doped TiO2 materials thank to the existence of Ti3+ species, which are Kubas-type hydrogen adsorption centers, and the Ag nanoparticles which provide spillover effects. We believe that this is the first time that both Kubas-type adsorption and spillover are exploited in the design of novel hydrogen storage materials.

https://doi.org/10.1016/j.ijhydene.2017.12.080

The effect of molecular weights and hydrolysis degrees (HD) of polyvinyl alcohol (PVA) on thermal and mechanical properties and crystallinity of polylactic acid (PLA)/PVA blends was investigated. Blends were prepared by the melt blending method using PLA/PVA ratios: 80/20, 90/10 and 97/3 wt. %. A single glass transition temperatures was observed for all PLA/PVA blends, suggesting the formation of binary compatible blends at concentration range studied. Thermogravimetric analysis results showed a better thermal stability for PLA/PVA blends containing PVA of higher Mw and HD. According to mechanical properties, low quantities of PVA (3 wt. %) do not affect the tensile strength of blends (irrespective of Mw and HD). However, as the PVA content increases, tensile strength tends to lower values, especially for blends with 20 wt.% of PVA, with 98% of HD.

DOI: 10.1590/0104-1428.03117

Abstract

Flash sintering technique was applied to Ce0.9Gd0.1O1.95 (10GDC) electrolyte fabricated by tape-casting at different temperatures under various electric fields. Densification of the electrolyte at constant electric field depended mainly on the current passing through the sample. The applied electric field influenced the temperature at which the flash sintering occurred. To achieve the microstructure with high densification, a suitable current density must be selected. The temperature for flash sintering varies with the materials and the contact area between the particles, which changes with the particle size, the porosity and the inhomogeneity.

https://doi.org/10.1016/j.matlet.2017.07.129

Abstract

Nanopowders of Ce0.9RE0.1O1.95 (RE=Nd, Y, Pr and Er) were synthesized by nitrate-fuel combustion method and calcinated at 700 °C for 2 h to obtain completely crystalline structures. The effect of RE dopants on the crystalline nature, lattice parameters, and microstructural parameters such as microstrain, stress, and deformation energy density of ceria was evaluated through uniform deformation model (UDM), uniform deformation stress model (UDSM) and uniform deformation energy density model (UDEDM) by using the X-ray diffraction (XRD) data. The results revealed that the microstructural parameters were considerably altered with respect to the dopants. The transmission electron microscope (TEM) graphs and their corresponding selected area diffraction (SAED) patterns of ceria nanoparticles confirmed that all doped ceria powders are crystalline with the wide range of particle size distributions aligned in all the directions. The optical diffuse reflectance spectroscopy (DRS) measurements showed a band at around 340 nm attributed to the transitions of charge-transfer between O 2p and Ce 4f orbitals in cerium oxide and RE doped CeO2 exhibited the reflectance band in the visible regions due to the transition of 4f energy levels of RE ions. Photoluminescence (PL) spectra of RE doped ceria showed the blue-green emission bands.

https://doi.org/10.1016/j.ceramint.2017.01.046

Abstract

La0.6Sr0.4M0.1Fe0.9O3-δ (M: Co, Ni and Cu) perovskite nanostructures were synthesized using low frequency ultrasound assisted synthesis technique and effect of substitution of Fe by Co, Ni and Cu on crystal structure and mechanical properties in La0.6Sr0.4FeO3-δ perovskite was studied. The HRTEM and Rietveld refinement analyses revealed the uniform equi-axial shape of the obtained nanostructures with the existence of La0.6Sr0.4M0.1Fe0.9O3−δ with mixed rhombohedral and orthorhombic structures. Substitution by Cu decreases the melting point of La0.6Sr0.4FeO3-δ. The results of mechanical characterizations show that La0.6Sr0.4Co0.1Fe0.9O3−δ and La0.6Sr0.4Ni0.1Fe0.9O3−δ have ferroelastic behavior and comparable elastic moduli, however, substitution by Ni shows higher hardness and lower fracture toughness than Co in B-site doping.

https://doi.org/10.1016/j.ceramint.2016.10.185

Molybdenum-doped ceria (CMO) is a promising material for the fabrication of anodes for carbon-air fuel cells. In this work, Ce0.9Mo0.1O2+δ was synthesized by the combustion method, which reports lower synthesis times than the solid-state reaction and Pechini methods. The material obtained does not present impurities (determined by EDS analysis) and forms Fm-3m (225 space group) single phase fluorite-type structures with a cell parameter of ca.5.419 Å (determined by Rietveld refinement). The mechanical properties of this material were studied using dense pellets produced by pressing the powders (pressure of ca. 105 MPa) and sintering the tablets obtained at 1000°C for 24 hours. The Young’s modulus (291.7 GPa) and Vickers microhardness (between 4694 and 2474.4 MPa) were determined by using the resonant frequency method and Struers microhardness tester, respectively. Future work considers the complete characterization of mechanical and electrical properties of CMO with different amounts of dopant.

DOI: 10.1149/07801.1427ecst

Abstract

Structural characteristics of combustion synthesized, calcined and densified pure and doped nanoceria with tri-valent cations of Er, Y, Gd, Sm and Nd were analyzed by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The results showed that the as-synthesized and calcined nanopowders were mesoporous and calculated lattice parameters were close to theoretical ion-packing model. The effect of dopants on elastic modulus, microhardness and fracture toughness of sintered pure and doped ceria were investigated. It was observed that tri-valent cation dopants increased the hardness of the ceria, whereas the fracture toughness and elastic modulus were decreased.

https://doi.org/10.1016/j.msea.2015.09.125

Abstract

In the present work, the pure CeO2 and yttrium doped CeO2 nanopowders were synthesized by the nitrate-fuel self-sustaining combustion method and calcined at 700 °C for 2 h. X-ray diffraction (XRD) and high resolution electron transmission microscopy (HRTEM) results demonstrated a cubic fluorite with high purity and the crystallite sizes less than 20 nm calculated from Scherrer’s formula. The BET specific surface area of yttrium doped CeO2 samples showed high values than those of pure CeO2. The photocatalytic activity of yttrium doped CeO2 showed high degradation of Rhodamine B solution under visible light illumination.

https://doi.org/10.1016/j.jscs.2015.06.003

Abstract

La0.6Sr0.4Co0.2Fe0.8O3 − δ (LSCF) perovskite nanostructures were synthesised using a 42 kHz ultrasound assisted synthesis technique for the fabrication of electrodes in the intermediate and/or low temperature solid oxide fuel and electrolysis cells (SOFCs/SOECs). The obtained nanomaterials were dried at 110 °C followed by calcination in a normal atmosphere at various temperatures from 400 to 1000 °C for 2 h. Powder characteristics such as crystal structure, thermal decomposition, particle size and morphology were analysed. The transmission electron microscopy (TEM) study revealed the uniform equi-axial shape and growth of the obtained nanostructures with respect to the calcination temperature till 800 °C. The structural and chemical analyses confirmed the existence of LSCF and CoFe2O4 phases.

https://doi.org/10.1016/j.powtec.2015.02.043