Scientific Papers in SCI


Title: Inverse core-rim microstructure in (Ti,Ta)(C,N)-based cermets developed by a mechanically induced self-sustaining reaction
Author(s): Chicardi, E; Cordoba, JM; Sayagues, MJ; Gotor, FJ
Source: International Journal of Refractory Metals & Hard Materials, 31 (2012) 39-46

abstract | fulltext

Cermets with a nominal composition (Tia(0.8)Ta(0.2)C(0.5)N(0.5)-20 wt.% Co) were synthesised by a mechanically induced self-sustaining reaction (MSR) process from stoichiometric elemental powder blends. The MSR allowed the production of a complex (Ti,Ta)(C,N) solid solution, which was the raw material used for the sintering process. The pressureless sintering process was performed at temperatures between 1400 degrees C and 1600 degrees C in an inert atmosphere. The microstructural characterisation showed a complex microstructure composed of a ceramic phase with an unusual inverse core-rim structure and a Ti-Ta-Co intermetallic phase that acted as the binder.

March, 2012 | DOI: 10.1016/j.ijrmhm.2011.09.003

Title: Attenuation lengths of high energy photoelectrons in compact and mesoporous SiO2 films
Author(s): Ferrer, FJ; Gil-Rostra, J; Gonzalez-Garcia, L; Rubio-Zuazo, J; Romero-Gomez, P; Lopez-Santos, MC; Yubero, F
Source: Surface Science, 606 (2012) 820-824

abstract | fulltext

We have experimentally evaluated attenuation lengths (AL) of photoelectrons traveling in compact and micro and mesoporous (∼ 45% voids) SiO 2 thin films with high (8.2-13.2 keV) kinetic energies. The films were grown on polished Si(100) wafers. ALs were deduced from the intensity ratio of the Si 1s signal from the SiO 2 film and Si substrate using the two-peaks overlayer method. We obtain ALs of 15-22 nm and 23-32 nm for the compact and porous SiO 2 films for the range of kinetic energies considered. The observed AL values follow a power law dependence on the kinetic energy of the electrons where the exponent takes the values 0.81 ± 0.13 and 0.72 ± 0.12 for compact and porous materials, respectively.

May, 2012 | DOI: 10.1016/j.susc.2012.01.017

Title: Influence of PVP in magnetic properties of NiSn nanoparticles prepared by polyol method
Author(s): Bobadilla, LF; Garcia, C; Delgado, JJ; Sanz, O; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Source: Journal of Magnetism and Magnetic Materials, 324 (2012) 4011-4018

abstract | fulltext

The influence of PVP on the magnetic properties of NiSn nanoparticles prepared by polyol method has been studied. NiSn nanoparticles exhibit superparamagnetic behavior although there is a ferromagnetic contribution due to particles agglomerated below the blocking temperature. The particle size is controlled by the addiction of PVP in varying amounts. The addition of PVP also favours the particles isolation, narrow the particle size distribution and decrease the interparticle interaction strength increasing the superparamagnetic contribution.

November, 2012 | DOI: 10.1016/j.jmmm.2012.07.005

Title: Interfacial characterization of silicon nitride/silicon nitride joints brazed using Cu-base active metal interlayers
Author(s): Singh, M; Fernandez, JM; Asthana, R; Rico, JR
Source: Ceramics Intenational, 38 (2012) 2793-2802

abstract | fulltext

Silicon nitride/silicon nitride joints were vacuum brazed at 1317 K for 5 min and 30 min using ductile Cu-base active metal interlayers. The joints were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron back scattered diffraction (EBSD), and transmission electron microscopy (TEM). An inhomogeneous Ti-rich reaction layer (similar to 2-3 mu m thick) formed in 5 min at the Si3N4/braze interface. The inhomogeneity disappeared after brazing for 30 min and was replaced with a compact and featureless reaction zone. TEM studies revealed fine grains in the reaction layer, and larger grains in the inner part of the joint interfaces. The joints were crack-free and presented features associated with plastic deformation, which indicated accommodation of strain associated with CTE mismatch. Electron Backscatter diffraction (EBSD) revealed a highly textured braze alloy interlayer and its crystallographic orientation was determined. The formation of additional phases at the joint interface during brazing is discussed.

May, 2012 | DOI: 10.1016/j.ceramint.2011.11.050

Title: Characterisation of ternary TixV1-xNy nitride prepared by mechanosynthesis
Author(s): Roldan, MA; Alcala, MD; Real, C
Source: Ceramics Intenational, 38 (2012) 687-693

abstract | fulltext

In the present manuscript the authors have systematically investigated the composition and microstructure of a series of ternary nitrides (TixV1-xNy) (0.0 <= x <= 1.0) prepared by mechanosynthesis, using XRD, SEM, EELS, XAS and TGA. The ternary titanium-vanadium nitride (TixV1-xNy) has been obtained in all range of compositions by the mechanical treatment of the two metals under nitrogen pressure in a planetary mill with a maximum milling time of 3 h and without any post-heating treatment. The materials' microhardnesses were measured after sinterisation and compared to those reported in the literature for these types of materials. When compared with the previously reported data for bulk samples, these values are similar or higher for compositions within the range x = 0.5 to x = 0.77 (TixV1-xN).

January, 2012 | DOI: 10.1016/j.ceramint.2011.07.057

Title: Preparation of nanostructured nickel aluminate spinel powder from spent NiO/Al2O3 catalyst by mechano-chemical synthesis
Author(s): Nazemi, M. K.; Sheibani, S.; Rashchi, F.; Gonzalez-DelaCruz, V. M.; Caballero, A.
Source: Advanced Powder Technology, 23 (2012) 833-838

abstract | fulltext

In this paper, the possibility of mechano-chemical synthesis, as a single step process for preparation of nanostructured nickel aluminate spinel powder from NiO/Al2O3 spent catalyst was investigated. Powder samples were characterized in terms of composition, morphology, structure, particle size and surface area using complementary techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential thermal analysis (DTA) and volumetric adsorption of nitrogen. It was found that formation of spinel was possible after 60 h of milling with no heat treatment. Additionally, influence of mechanical activation on the heat treatment temperature was discussed. It was observed that heat treatment of 15 h milled sample at 1100 °C is enough to produce nickel aluminate spinel. A product of direct mechanical milling showed higher value of surface area (42.3 m2/g) and smaller crystallite size (12 nm) as compared to the heat treated product.

November, 2012 | DOI: 10.1016/j.apt.2011.11.004

Title: Characterization of highly crosslinked polyethylenes by colorimetry
Author(s): Martinez-Morlanes, MJ; Terriza, A; Yubero, F; Puertolas, JA
Source: Polymer Testing, 31 (2012) 841-847

abstract | fulltext

Colour analysis appears to be a robust technique for characterizing vitamin E doping and gamma irradiation of medical grade polyethylene samples. The analysis procedure described in this paper is of great interest because it can easily distinguish between polyethylene samples with differences in vitamin E (α-tocopherol) doping of about 0.1 wt% and gamma irradiation doses of 30 kGy. It is found that the colour differences (with respect to untreated samples) induced by gamma irradiation and/or vitamin E doping add-up linearly. This method for detecting the presence of vitamin E is fast, simple and non-destructive.

September, 2012 | DOI: 10.1016/j.polymertesting.2012.06.005

Title: Wall slip phenomena in concentrated ionic liquid-based magnetorheological fluids
Author(s): Gomez-Ramirez, A; Lopez-Lopez, MT; Gonzalez-Caballero, F; Duran, JDG
Source: Rheologica Acta, 51 (2012) 793-803

abstract | fulltext

Ionic liquids (ILs) have been recently proposed as carrier for magnetorheological (MR) fluids. Their special properties, such as very low vapor pressure and high thermal stability, make ILs highly suitable dispersion media to increase the broad range of technological applications that magnetorheological fluids already have. It has been just reported that using ILs as carriers in MR fluids an improvement in the colloidal stability and suspension redispersibility is obtained. In this work, the magnetorheological behavior of highly concentrated suspensions in ILs is studied. Two kinds of suspensions were analyzed: using an ionic liquid of low conductivity and a mineral oil as carriers. In both cases, silica-coated iron microparticles were used as solid phase, being the solid volume concentration of 50% vol. A complete magnetorheological analysis focused on the wall slip phenomenon was performed. Steady-state and oscillatory experiments were carried out. In order to study wall slip effects, all experiments were performed with a plate-plate system, using both smooth and rough measuring surfaces. A significant effect of wall slip was observed when the experiments were performed using smooth surfaces. The novelty of this paper is mainly based on (1) the use of an ionic liquid as carrier to prepare magnetic suspensions, and (2) the analysis of wall slip phenomena in MR fluids with a particle content close to the maximum packing fraction.

September, 2012 | DOI: 10.1007/s00397-012-0639-5

Title: Mechanochemical synthesis and characterization of nanocrystalline BiSe, Bi 2Se 3 semiconductors
Author(s): Achimovicova, M; Gotor, FJ; Real, C; Daneu, N
Source: Journal of Materials Science: Materials in Electronics, 23 (2012) 1844-1850

abstract | fulltext

Mechanochemical synthesis of bismuth selenides (BiSe, Bi 2Se 3) was performed by high-energy milling of bismuth and selenium powders in a planetary ball mill. The particle size distribution and the specific surface area of Bi/Se and 2Bi/3Se powder mixtures were analysed at increasing milling time. The products were characterized by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The presence of bismuth selenide phases was observed after only 1 min of milling and full conversion into hexagonal BiSe phase (nevskite) and rhombohedral Bi 2Se 3 phase (paraguanajuatite) was reached after 10 min of milling. The nanocrystalline nature of both mechanochemically synthesised bismuth selenides was confirmed and their optical band gap energies were obtained on the basis of the recorded absorption spectra in UV-Vis spectral region.

October, 2012 | DOI: 10.1007/s10854-012-0672-2

Title: Microstructure, composition and P-T conditions of rutile from diamondiferous gneiss of the Saxonian Erzgebirge, Germany
Author(s): Escudero, A; Miyajima, N; Langenhorst, F
Source: Chemie der erde-geochemistry, 72 (2012) 25-30

abstract | fulltext

The chemical composition and microstructure of rutile grains in a ultra-high pressure metamorphic gneiss of the Saxonian Erzgebirge, Germany have been studied by Raman spectroscopy, SEM, EMPA and TEM. Rutile inclusions in garnet contain free dislocations, iron-enriched dislocations and exsolved ilmenite lamellae, while subgrain boundaries are observed in rutile grains of the rock matrix. The previously reported alpha-PbO2 type TiO2 phase could not be confirmed by our TEM observations. On the basis of Zr solubility in the rutile and the presence of microdiamonds, minimum metamorphic peak conditions of 3.95 GPa and 915 degrees C are estimated.

January, 2012 | DOI: 10.1016/j.chemer.2011.11.001

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