Scientific Papers in SCI

2012


Title: Chemical–physical characterization of isolated plant cuticles subjected to low-dose γ-irradiation
Author(s): Heredia-Guerrero, Jose A; de Lara, Rocio; Dominguez, Eva; Heredia, Antonio; Benavente, Juana; Benitez, Jose J
Source: Chemistry and physics of lipids, 165 (2012) 803-808

abstract | fulltext

Isolated tomato fruit cuticles were subjected to low dose (80 Gy) γ-irradiation, as a potential methodology to prevent harvested fruit and vegetables spoilage. Both irradiated and non-irradiated samples have been morphologically and chemically characterized by scanning electron (SEM), atomic force (AFM), attenuated total reflectance Fourier transform infrared (ATR-FTIR) and X-ray photoelectron (XPS) spectroscopies. Additionally, electrochemical measurements comprising membrane potential and diffusive permeability were carried out to detect modifications in transport properties of the cuticle as the fruit primary protective membrane. It has been found that low dose γ-irradiation causes some textural changes on the surface but no significant chemical modification. Texture modification is found to be due to a partial removal of outermost (epicuticular) waxes which is accompanied by mild changes of electrochemical parameters such as the membrane fixed charge, cation transport number and salt permeability. The modification of such parameters indicates a slight reduction of the barrier properties of the cuticle upon low dose γ-irradiation.

December, 2012 | DOI: 10.1016/j.chemphyslip.2012.10.003

Title: Spark plasma sintering of Ti yNb 1-yC xN 1-x monolithic ceramics obtained by mechanically induced self-sustaining reaction
Author(s): Borrell, A; Salvador, MD; Garcia-Rocha, V; Fernandez, A; Chicardi, E; Gotor, FJ
Source: Materials Science and Engineering A, 543 (2012) 173-179

abstract | fulltext

Nanometer-sized titanium-niobium carbonitride powders (Ti yNb 1-yC xN 1-x) with different Ti/Nb atomic ratios were obtained by a mechanically induced self-sustaining reaction, and sintered by spark plasma sintering technique at 1500°C for 1min in a vacuum atmosphere. Mechanical properties such as hardness and Young's modulus were determined by nanoindentation technique and friction and wear coefficients assessed by ball-on-disk testing using alumina ball in dry sliding conditions. The fracture surface and wear tracks of samples were examined by scanning electron microscopy. Results showed that it is possible to obtain dense monolithic ceramics from the solid solution (Ti yNb 1-yC xN 1-x) with good mechanical properties and excellent wear resistance. The optimum values of nanomechanical properties were found for the Ti 0.3Nb 0.7C 0.5N 0.5 ceramic composition, which exhibited a high hardness over 26.0GPa and Young's modulus around 400GPa.

May, 2012 | DOI: 10.1016/j.msea.2012.02.071

Title: Residual stresses in Al2O3-ZrO 2 (3mol.% Y2O3) directionally solidified eutectic ceramics as a function of temperature
Author(s): Ramirez-Rico, J; Martinez-Fernandez, J; Pena, JI; Singh, D; Routbort, J
Source: Materials Science and Engineering A, 541 (2012) 61-66

abstract | fulltext

Directionally solidified eutectics are in situ composites grown from the melt. Due to the differences in the thermoelastic properties of the different phases present in the material, these composites often exhibit residual stresses that can affect their mechanical properties. In this work we use neutron diffraction to investigate residual stresses in Al 2O 3-ZrO 2 eutectic composites as a function of temperature, for samples processed at two different growth rates, 10mm/h and 750mm/h. Our results show that the stress-free temperature is in the range of 1200±200°C. We explain the experimental observations based on the thermoelastic properties of the phases in the material and confirm our measurements using a simple, self-consistent model.

April, 2012 | DOI: 10.1016/j.msea.2012.02.001

Title: Effect of oxidation on the compressive strength of sintered SiC-fiber bonded ceramics
Author(s): Ramirez-Rico, J; Martinez-Fernandez, J; Singh, M
Source: Materials Science and Engineering A, 534 (2012) 394-399

abstract | fulltext

The compressive strength of SiC-fiber bonded ceramics obtained from hot-pressed amorphous Si-Al-C-O fibers and its degradation by high temperature exposure to an oxidizing environment was studied. Compressive strength was measured at room temperature as a function of strain rate, orientation, and oxidation temperature. Weight loss was monitored as a function of exposure time in atmospheric air at temperatures ranging from 800 to 1600°C, for times ranging from 0.5 to 5. h. Room-temperature compressive strength had a moderate decrease after exposures at 800°C associated to carbon burnout; increased for exposures in the range 1000-1500°C due to a defect-blunting action of the silica scale; and decreased significantly at 1600°C due to extensive surface recession.

February, 2012 | DOI: 10.1016/j.msea.2011.11.085

Title: Microcalorimetric study of the annealing hardening mechanism of a Cu–2.8Ni–1.4Si (at%) alloy
Author(s): Donoso, E; Espinoza, R; Dianez, MJ; Criado, JM
Source: Materials Science and Engineering: A, 556 (2012) 612-616

abstract | fulltext

The precipitation processes in a Cu–2.8 at% Ni–1.4 at% Si alloy were studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and microhardeness measurements. The analysis of the calorimetric curves from room temperature to 900 K shows the presence of one exothermic reaction attributed to the formation of δ-Ni2Si particles in the copper matrix that was confirmed by Transmission Electron Microscopy (TEM) and EDS microanalysis. The activation energies calculated for the precipitation of δ-Ni2Si was lower than the ones corresponding to diffusion of nickel and silicon in copper. A correlation between of microhardness of the alloy and the formation of δ-Ni2Si particles has been found.

October, 2012 | DOI: 10.1016/j.msea.2012.07.035

Title: In Situ Synthesis of Ceramic Composite Materials in the Ti-B-C-N System by a Mechanically Induced Self-Sustaining Reaction
Author(s): Aviles, MA; Chicardi, E; Cordoba, JM; Sayagues, MJ; Gotor, FJ
Source: Journal of the American Ceramic Society, 95 (2012) 2133-2139

abstract | fulltext

The synthesis of multicomponent ceramic materials in the titanium-diboride-carbide-nitride-carbonitride system by the mechanochemical process known as the mechanically induced self-sustaining reaction (MSR) was investigated. Ceramic composite powders containing TiB 2and TiC, TiN or TiC xN 1-xwere prepared from a blended mixture of the elements by exploiting the highly exothermic nature of the formation reactions. The synthesis of the composite materials was made possible by the ability of the MSR to simultaneously induce independent self-sustaining reactions, generating a mixture of ceramic phases. The composition of the ceramic composites was designed using the initial atomic ratio of the reactants, and the achieved microstructure was characterized by TiB 2particles in the micrometric range, surrounded by submicrometric and nanometric TiC, TiN, or TiC xN 1-xcrystals.

July, 2012 | DOI: 10.1111/j.1551-2916.2012.05174.x

Title: Nanostructured Spark Plasma Sintered Ce-TZP Ceramics
Author(s): Cruz, SA; Poyato, R; Cumbrera, FL; Odriozola, JA
Source: Journal of the American Ceramic Society, 95 (2012) 901-906

abstract | fulltext

In this work, spark plasma sintering (SPS) of 10 mol% CeO 2-doped ZrO 2 nanocrystalline powders, obtained by a two-step synthesis procedure, allows the preparation of fully densified nanostructured ceramics. The CeO 2-ZrO 2 powders with particle size below 100 nm are obtained after CeO 2 deposition on hydrothermally synthesized ZrO 2 particles by the impregnation method. Tetragonal CeO 2-ZrO 2 ceramics are obtained when sintering at 1200°C without holding time. A graded material containing tetragonal, monoclinic, and pyrochlore phases are obtained when sintering at 1200°C and for 5 min holding time. This is explained in terms of the gradual reduction of Ce 4+ to Ce 3+ species by carbon in the graphite environment during SPS. With the successful combination of the stabilizer coating technique and SPS, we achieve not only the stabilization of the tetragonal phase in the ceramics, but also good control of the grain size, by producing nanostructured ceramics with 40-70 nm grain sizes.

March, 2012 | DOI: 10.1111/j.1551-2916.2011.04978.x

Title: Creep strength of nickel oxide/zirconia composites under different environmental atmospheres
Author(s): M. Jiménez-Melendo; F.A. Huamán-Mamani
Source: Solid State Ionics, 225 (2012) 471-475

abstract | fulltext

NiO/8YSZ (8 mol% Y2O3-stabilized cubic ZrO2) and NiO/3YTZP (3 mol% Y2O3-stabilized tetragonal ZrO2) composites with different NiO contents have been fabricated by a conventional route of mechanical mixing of NiO and zirconia powders and sintering at 1500 °C for 10 h in air. The resulting microstructures have been characterized by electron microscopy. The composites show a duplex microstructure formed by equiaxed grains of NiO and ZrO2, without any intermediate phase. Compressive mechanical tests at constant strain rate were carried out at temperatures between 1150 and 1350 °C under different environments: air, inert (Ar) and reducing (5% H2/95% Ar) atmospheres. The overall creep behavior of the composites is essentially controlled by the zirconia matrix, due to the softness of the NiO phase in the experimental conditions used in this study. The creep strength is not affected by oxygen partial pressure. However, a large decrease in creep resistance under reducing conditions was observed in samples submitted to in situ redox cycling.

October, 2012 | DOI: 10.1016/j.ssi.2012.02.011

Title: High-temperature plastic deformation mechanisms of ytterbium-doped barium cerate proton conductor
Author(s): M. Jiménez-Melendo
Source: Solid State Ionics, 225 (2012) 286-290

abstract | fulltext

The enhanced proton conductivity exhibited by trivalent cation-doped barium cerate perovskites makes these materials excellent candidates for electrochemical applications, in particular as electrolytes for solid oxide fuel cells. These devices operate at elevated temperatures, where creep and other deformation processes influence the overall efficiency and lifetime. In this work, the high-temperature plastic deformation mechanisms of fine-grained 5 at.% Yb-doped BaCeO3 polycrystals produced by conventional solid-state reaction has been investigated by means of compressive tests at constant load between 1150 and 1250 °C in air. The creep curves show an unusual sigmoidal behavior, followed by extended steady states of deformation. Grain boundary sliding is the main deformation mechanism, characterized by a stress exponent n of 2, as found in other fine-grained superplastic ceramics and metals.

October, 2012 | DOI: 10.1016/j.ssi.2012.03.031

Title: Chromium incorporation into TiO2 at high pressure
Author(s): Escudero, A; Langenhorst, F
Source: Journal of Solid State Chemistry, 190 (2012) 61-67

abstract | fulltext

Chromium incorporation into TiO 2 up to 3 GPa at 1300 °C and 900 °C has been studied by XRD as well as TEM. A CaCl 2 type TiO 2 polymorph has been observed in the quenched samples from high pressure. Two different mechanisms of solubility occur in the recovered samples. Chromium replaces titanium on normal octahedral sites but it also occupies interstitial octahedral sites, especially in the samples recovered from higher pressures. Interstitial chromium is responsible for an orthorhombic distortion of the TiO 2 rutile structure in the quenched samples and gives rise to a (1 1 0) twinned CaCl 2-structured polymorph. This phase is very likely the result of temperature quench at high pressure. The formation of this phase is directly related to the chromium content of the TiO 2 grains. Chromium solubility in TiO 2 increases with increasing the synthesis pressure. TiO 2 is able to accommodate up to 15.3 wt% Cr 2O 3 at 3 GPa and 1300 °C, compared to 5.7 wt% at atmospheric pressure at the same temperature.

June, 2012 | DOI: 10.1016/j.jssc.2012.01.041

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