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2008


"in situ" XPS studies of laser induced surface cleaning and nitridation of Ti


Lahoz, R; Espinos, JP; de la Fuente, GF; Gonzalez-Elipe, AR
Surface & Coatings Technology, 202 (2008) 1486-1492
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

A titanium foil has been subjected to laser irradiation "in situ" in a pre-chamber of an X-ray photoemission spectrometer under different atmospheres (vacuum, Ar, 02, air, N-2 and H-2). As a result of these treatments, a high amount of the carbon contamination layer was removed and other changes in composition were induced. Nitridation was achieved by laser irradiation under nitrogen. The most effective treatment protocol included an initial cleaning procedure induced by irradiation in vacuum, followed by a second irradiation process performed under nitrogen. Partial nitridation is also observed when irradiating under synthetic air. Lateral and depth analysis of the nitrogen concentration around the laser spot has been also carried out. It is found that the outermost layers present a similar concentration of nitrogen. In addition, the measured nitrogen profile indicates that the amount of nitrogen within the laser spot region is relatively lower than within the immediately surrounding area. Almost no nitrogen remains in the spot area after sputtering for 30 min. A model is proposed to account for the observed titanium surface nitridation processes.


Enero, 2008 | DOI: 10.1016/j.surfcoat.2007.06.061

Apatite and Portland/apatite composite cements obtained using a hydrothermal method for retaining heavy metals


Dominguez, MI; Carpena, J; Borschnek, D; Centeno, MA; Odriozola, JA; Rose, J
Journal of Hazardous Materials, 150 (2008) 99-108
Química de Superficies y Catálisis

ABSTRACT ▼

Apatite and Portland/apatite composite cements containing steelwork dusts have been prepared using a low temperature hydrothermal method (200° C, 48 h). The produced solids were characterized by means of XRD, IR, and SEM-EDX, and the remaining liquid was analyzed by ICP. The results clearly show the capability of these cements to inertise the heavy metals contained in steelwork dusts, that is Fe, Pb, Mo, Cr, Mn, Ni, and Zn. In the case of apatitic cements, Fe, Mg, Cr, Mn, and Pb coming from steel dust replaced Ca in the divalent cation position of the apatite structure, while Si and Mo replaced P in tetrahedral position. The average crystal size of the apatite-containing dust is smaller than in pure apatite synthesized using the same procedure, which is related to the magnesium content of the dust, since magnesium seems to inhibit the crystal growth. XRD diagrams of composite cements show only peaks corresponding to phases observed in the single cements, and in that no new phases are found. However, EDX analysis reveals the introduction of cations coming from Portland cement into the apatite structure. From the results of water analysis it could be concluded that the capability of retention is higher in composite matrices than in the pure apatite one. In conclusion, the obtained data allow stating that the proposed method, the hydrothermal synthesis of steelwork dust containing cement, is a reliable one for immobilization of toxic residues containing heavy leachable cations.


Enero, 2008 | DOI: 10.1016/j.jhazmat.2007.04.091

Microstructural and chemical characterisation techniques for nanostructured and amorphous coatings


Godinho, V; Fernandez-Ramos, C; Martinez-Martinez, D; Garcia-Lopez, J; Sanchez-Lopez, JC; Fernandez, A
European Physical Journal-Applied Physics, 43 (2008) 333-341
Materiales Nanoestructurados y Microestructura - Tribología y Protección de Superficies

ABSTRACT ▼

A full characterization of amorphous or nanostructured coatings at the microstructural level has some intrinsic difficulties associated with the lack of long range order and reference compounds, which often make difficult their study. Only by the combination of different characterization techniques is possible in many cases to achieve valuable chemical and structural information. In this paper, three different systems were used to illustrate how the combination of characterization techniques, as TEM associated to ED or EELS, EFTEM, SEM, XPS, RBS and XRD was determinant to correlate microstructure with deposition parameters and properties in such complex systems. The coatings were deposited on silicon and AISI M2 steel substrates by magnetron sputtering under different Ar/N-2 gas mixtures from Ti and C targets (system 1 and 2) or a Si target (system 3). In each case, the performed characterization allowed to get a deeper understanding of the whole system and explain their mechanical response. The studied systems are: (i) Ti-TiN-CNx multilayered coatings: the chemical and structural analysis shows that a gradual enrichment in nitrogen and nitride phases from the metallic substrate to the CNx top layer is responsible for the improvement of the adhesion properties. (ii) Ti-C-N: the existence of a nanocrystalline TiC phase embedded in an amorphous carbon matrix is demonstrated by the microstructural and chemical analysis for samples prepared under pure Ar. When N-2 is introduced in the gas phase, the nanocrystalline structure is not seen and the chemical composition is enriched in amorphous non-stoichiometric CNx. (iii) SiOxNy: although the coatings present similar composition, small differences in microstructure are observed, which can be responsible for different mechanical properties.


Septiembre, 2008 | DOI: 10.1051/epjap:2008114

Degradation of phenylmercury compounds by heterogeneous photocatalysis over alpha-Fe2O3


Navio, JA; Cerrillos, C; Macias, M; Pradera, MA
Journal of Advanced Oxidation Technologies, 11 (2008) 411-416
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT ▼

We report here on the degradation of diphenylmercury and monophenylmercury chloride in air-equilibrated aqueous solutions by heterogeneous photocatalysis over alpha-Fe2O3. Photocatalysis proceeded via sequential de-phenylation leaving inorganic mercury. GC-MS analysis of the products revealed that photocatalytic degradation involved hydroxylation of the phenyl rings. Mechanistic features and photocatalytic activity were also studied and are reported upon.


Julio, 2008 | DOI:

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