Naida El Habra

New calcium alkoxides for consolidation of carbonate rocks. Influence of precursors' characteristics on morphology, crystalline phase and consolidation effects

New ambient temperature liquid calcium alkoxides, [Ca(O(CH2CH2O)3CH3)2] (1) and [Ca(O(CH2CH2O)3CH2CH3)2] (2), together with [Ca(OCH2C(CH3)3)2] (3), were synthesised by reaction of ammonia-activated calcium with the appropriate alcohol. Their potentiality as stone consolidant products was investigated and compared with those of other alkoxides: [Ca(OCH2CH3)2(CH3CH2OH)4] (4), [Ca(OCH3)2] (5), [{Ca(OCH2CH2OCH3)2}9] (6), already described in the literature. Reaction of 1–3 with the atmosphere was studied, final products analysed and kinetic pathways investigated. The reaction produces CaCO3 and the vaterite/calcite ratios observed in the coatings generated from isopropyl alcohol solutions of 1–6 were found to considerably vary with the alkoxide precursor, which has a strong influence also on the morphology of the produced films. Furthermore, their efficiency as stone consolidants was tested by ultrasound measurements.

Fe2O3-TiO2 systems grown by MOCVD: an XPS study

The present work was devoted to the X-ray photoelectron spectroscopy (XPS) investigation of the principal core levels of a Fe2O3-TiO2 system. The sample was synthesized on a glass substrate at 430 °C in N2/O2 atmospheres by low-pressure metal organic chemical vapor deposition (MOCVD) co-evaporating the precursors titanium(IV)isopropoxide [Ti(OiPr)4] and bis-(methylcyclopentadienyl)Fe(II) [Fe(MeCp)2] through independent sources. Beside the wide scan spectrum, detailed spectra for O 1s, Fe 2p and Ti 2p regions and related data are presented and discussed. XPS analysis revealed the presence of iron(III) and titanium(IV) oxides as the main phases, with a possible Fe2O3 segregation on the specimen surface.

MOCVD Growth and Characterization of Cobalt Phosphide Thin Films on InP Substrates

Cobalt phosphide thin films were grown by metal-organic chemical vapor deposition (MOCVD) in H 2 atmospheres on InP(001) substrates using bis(η-methylcyclopentadienyl)Co(II)[Co(Cp Me ) 2 ] and phophine (PH 3 ) precursors at 550°C. Film microstructure, composition, and morphology were investigated in detail by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Rutherford backscattering (RBS), and atomic force microscopy. Films were crystalline and consisted mainly of the orthorhombic CoP phase and some amount of the CoP 2 phase. XPS measurements indicate an oxidation state (III) for Co, while the P/Co ratio was found by RBS to lie in the range 1-2. The coatings were highly textured with (202), (103) CoP, and (-311) CoP 2 crystal planes parallel to the substrate surface. The root mean square surface roughness was below 10 A for thicknesses smaller than 20 nm and increased to a maxiumum of 70 A for a 35 nm thick film. Cobalt and In intermixing was investigated by XPS depth profiles.

Effective and Low-Cost Synthesis of Sulphur-Modified TiO 2 Nanopowder with Improved Photocatalytic Performances in Water Treatment Applications

In the present paper, sulphur-modified titanium dioxide (S-TiO2) is prepared as nanopowder in mixed rutile-anatase phase by an unprecedented simple, reproducible and cheap synthetic procedure, directly employing elemental sulphur powder as sulphur source. TiO2 and several reference TiO2 samples obtained in pure rutile or anatase phase were also prepared with nanometric size and compared to S-TiO2 as well as Degussa P25. The prepared samples and the reference benchmark were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), BET specific surface area and X-ray photoelectron spectroscopy (XPS) techniques, while their photoactivity was determined with respect to methyl red degradation as typical probe reaction. The results from the characterisation and photocatalytic measurements were discussed and inter-correlated, thus providing a complete and consistent analysis of the samples performances. The prepared sulphur-modified titanium dioxide appeared as a very efficient and long-lasting photocatalyst with respect to the unmodified TiO2 and to the benchmark Degussa P25 (S-TiO2 appears to be two times faster than P25) for the methyl red removal under UV lighting, also in repeated cycles.

Stabilized Zirconia-Based Materials for Solid Oxide Fuel Cells (SOFC) obtained by MOCVD and Aerosol-CVD

Zirconium dioxide is one of the most studied ceramic materials under various forms (film, powder, bulk, etc.). Pure ZrO2 is monoclinic at room temperature and it undergoes phase transitions to the tetragonal and cubic structures above 1170 and 2370 °C, respectively. The introduction of MgO, CaO, Sc2O3, Y2O3 and other aliovalent oxides in the ZrO2 structure allows the ZrO2 stabilization in the cubic fluorite structure from room temperature to its melting point (2680 °C), thus enabling the production of materials for high temperature applications. At the same time, the doping of ZrO2 increases oxygen ion vacancies with a significant rise of the ZrO2 ionic conductivity. In fact, stabilized ZrO2 is used in oxygen sensors and in Solid Oxide Fuel Cells (SOFC) as electrolyte and anode support. Nowadays almost all SOFC use an yttria-stabilized zirconia (YSZ) electrolyte, strontium lanthanum manganite cathode, a mixed nickel/YSZ cermet anode and a doped lanthanum chromite as the interconnect. The Metal Organic Chemical Vapor Deposition (MOCVD) process, thanks to its high number of tuning chemical and physical parameters, represents a suitable and versatile tool to realize thin films of all the materials for SOFC. In fact, thin films of nanostructured and dense electrolyte can be conveniently obtained by MOCVD, while the porous cermet anode could be deposited by liquid injection or aerosol-CVD systems, by using the same reaction chamber employed for the deposition of the electrolyte mixed oxide materials. Herein we report the results of two processes to obtain thin film of nanostructured stabilized ZrO2: the former corresponds to a MOCVD deposition of ZrO2 stabilized with aliovalent metal oxides such as CaO, MgO, Y2O3, Sc2O3, and to be used as SOFC electrolyte; the latter consists of an Aerosol-CVD process to produce porous films of stabilized ZrO2 and Ni/c-ZrO2 for SOFC anode applications. MOCVD depositions of stabilized ZrO2 were carried out in a cold wall reactor at 670 °C and 10 mbar by using Si(100) as substrates and Zr(tmhd)4, Ca(tmhd)2, Mg(tmhd)2·H2O, Y(tmhd)3 and Sc(tmhd)3 as metal precursors. The used carrier gas was N2, while the coreagent gas was a mixture of O2/H2O. Aerosol-CVD depositions were performed by using an air blast spray system for the precursor feeding and a substrate heating element working at 350-500 °C for the precursor thermal decomposition. An aqueous solution of metal nitrates was sprayed at atmospheric pressure on the hot substrate surface. Here, the nitrates pyrolised to oxides releasing gaseous nitrogen oxides and forming porous films suitable as catalyst with high specific surface area. All samples have been characterized by XRD, FEG-ESEM and EDS analyses. XRD measurements showed that films deposited on Si(100) by MOCVD were polycrystalline. Moreover, the Lotgering factor, higher than 0.7 for all differently doped samples, ultimately indicated a cubic-fluorite ZrO2 phase with a significant (200) preferred orientation. In this regard, it is noteworthy that a not complete ZrO2 stabilization was limited to the Sc2O3-ZrO2 system, as demonstrated by the co-existence of both the distorted fluorite tetragonal and cubic phases. Deposits obtained by Aerosol-CVD were amorphous, and they became polycrystalline, with ZrO2 stabilized in the cubic phase without preferential orientation, after an annealing treatment in air at 800 °C. The Ni/c-ZrO2 system was obtained by firstly exposing all the as grown deposits to a thermal treatment in air at 800 °C (to get the NiO/c-ZrO2 mixed oxide) and, afterwards, by annealing NiO/c-ZrO2 in H2 atmosphere to reduce all the NiO to Ni to obtain the cermet. This behaviour was confirmed by X-ray diffraction. EDS data were consistent with a good compositional control of the stabilizing oxides, as required for SOFC applications, even if a slight CaO excess was always revealed. All samples were uniform, crack-free and well adherent to the substrate. The comparison between the FEG-ESEM micrographs of the films deposited with the two methods highlighted a different surface morphology (Figure 1). ZrO2 obtained by MOCVD was colorless, dense, as desired for SOFC electrolyte, with a lenticular texture, while the one deposited by Aerosol-CVD was highly porous with a sponge-like morphology, suitable for SOFC anode or catalyst support.