O. de Sanctis

Electrochemical behaviour of SiO2 sol-gel coatings on stainless steel

SiO2 coatings onto stainless steel substrates have been prepared by sol-gel in order to study the performance and mechanism of attack in different corrosive solutions. The electrochemical behaviour of the samples has been evaluated by Electrochemical Impedance Spectroscopy using NaCl and HCl as electrolytes. Comparative tests have been performed on samples with one and two silica layers as well as on uncoated ones. SiO2 coatings produce no important protection of stainless steels subjected to electrochemical corrosion. This behaviour may be explained by micropores and microcracks produced during the coating sintering.

Synthesis of precursors for chemical solution deposition of PZT thin films

Abstract Lead zirconate titanate precursors involved in the sol–gel synthesis of PZT thin films were prepared from alkoxides of Pb, Zr and Ti, with the same alcoholic radical (methoxyethoxide), obtained by dehydration and alcoholysis of lead acetate, and by alcoholic exchange of zirconium n-propoxide and titanium ethoxide. In this investigation, 1H and 13C NMR spectroscopic techniques and FTIR analysis have been used to study the reaction mechanisms and identify the compounds obtained. The titanium and zirconium precursors present a complete alkoxy group exchange, whereas lead acetate is partially alkoxylated. A precursor solution of PZT has been obtained with minimal quantity of acetate groups and residual water. The molecular structures for the Zr, Ti, and Pb precursors and for the PZT precursor have been proposed.

Fabrication of PbS Nanoparticles Embedded in Silica Gel by Reverse Micelles and Sol-Gel Routes

PbS doped-silica gels showing a visible absorption onset were prepared by the sol-gel method. PbS nanoparticles with strong quantum-confinement effect were obtained from sodium sulfide and lead nitrate by the reverse micelle method. Chemical parameters such as the water/surfactant and the [Pb2+]/[S2−] ratios play a very important role in the PbS particle size and in their absorption threshold. The PbS nanoparticles were dispersed in a hydrolyzed solution of TEOS and converted to homogeneous gels after heating. The absorption threshold of PbS doped-gel is blue shifted compared to the one of the as-prepared PbS particles. The non-linear optical properties of the PbS nanoparticle solution were measured by degenerate four-wave mixing and theX(3) value was estimated to be 1.95 10−11 esu.

ZrO2 phase structure in coating films and powders obtained by sol-gel process

Zirconia coating film and powder obtained by the sol-gel route using zirconium n-propoxide as starting material and acid catalyst were investigated by the Perturbed Angular Correlations method, X-Ray Diffraction and Differential Scanning Calorimetry and Differential Thermal Analyses. The hyperfine interaction, measured after annealing the samples at increasing temperatures up to 1100°C, allowed to distinguish five different zirconium neighborhoods. Two of them describe rather disordered material which, on heating, crystallizes to the tetragonal phase and end finally in monoclinic zirconia. As compared with the powder, the film exhibits a minor fraction of an unidentified ordered form and a higher and more stable fraction of tetragonal phase. In addition, the tetragonal to monoclinic conversion takes place at higher temperatures and with a larger activation energy.

Preparation and microstructure study of borosilicate coatings produced by sol-gel: Code: EP5

Borosilicate coatings in the systems (100−x)SiO2−xB2O3 (x=20, 30) and 75SiO2-20B2O3-5Na2O have been obtained using the dip-coating procedure. Stable solutions were prepared from TEOS and trimethylborate, H2O/TEOS ratios being changed from 2 to 6. Sodium acetate in aqueous solution was used as Na2O precursor. Coatings were prepared in an airtight glove-chamber with humidity and temperature control. Good and transparent films were obtained only for RH<20%. Microstructure evolution and phase separation phenomena were investigated by TEM studying their dependence on the water content of the solution, temperature and time of the heat treatment and thickness of the coatings. A comparison with similar melted glasses and bulk glasses prepared by sol-gel has been also established.

Preparation and Characterization of Mn-Doped (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 Ceramics

MnO2-doped lead free 0.5[Ba(Zr0.2Ti0.8)O3]-0.5[(Ba0.7Ca0.3)TiO3] ceramics were synthesized by a high-energy ball milling process. We studied the phase formation process along different steps of the mechanical milling. We show that the addition of a small amount of MnO2 (x < 0.5 mol.%) improves the dielectric and ferroelectric properties of the ceramics. It is found that the doping with manganese increases the dielectric constant and reduces the loss, which decreases considerably as the Mn content increases. The remnant polarization of the doped ceramics is increased by 10%.

Thermal evolution of CaO-doped HfO2 films and powders

Solid solutions of ZrO2 and HfO2 are potential electrolyte materials for intermediate-temperature SOFC because both are oxygen-ion conductors. The main challenge for these compounds is to reduce the relatively high value of the activation energies vacancies diffusion, which is influenced by several factors. In this work the thermal evolution of CaO-HfO2 materials have been investigated. (CaO)y-Hf(1-y)O(2-y) (y = 0.06, 0.14 y 0.2) coatings and powders were synthesized by chemical solution deposition (CSD). Films were deposited onto alumina substrates by Dip Coating technique, the burning of organic waste was carried out at 500 ?C under normal atmosphere and then the films were thermally treated at intervals of temperature rising to a maximum temperature of 1250 ?C. By means Glazing Incidence X-ray Diffraction (?-2? configuration) the phases were studied in the annealed films. On the other hand, the thermal evolution and crystallization process of powders were analyzed in-situ by HT-XRD. The phenomena crystallization occurred in films and powders were analyzed. The activation energies of diffusion of oxygen vacancies of HfO2-14 mole% CaO and HfO2-20 mole% CaO films were measured from the thermal evolution of the relaxation constant measured by Perturbed Angular Correlation Technique.

Preparation of YBa2Cu3O7−x superconducting films: influence of the chemical composition on the sintering

Abstract The influence of the cationic ratio Y:Ba:Cu on the kinetics of densification of the YBa 2 Cu 3 O 7− x (YBCO) superconductor ceramic was studied. The powders were prepared from organic precursors and the nominal compositions were: (A) stoichiometric composition YBa 2 Cu 3 O 7− x , (B) composition on the tie line joining YBa 2 Cu 3 O 7− x –BaCuO 2 phases, and (C) composition in the triangle YBa 2 Cu 3 O 7− x –Y 2 BaCuO 5 –CuO. The phases present in these powders heated to 890°C were detected by X-ray diffraction (XRD), while the ratio Y:Ba:Cu was measured by neutronic activation analysis (NAA). The reactions between 900°C and 1070°C under O 2 atmosphere were determined by differential thermal analysis (DTA) at a heating rate of 10°C/min. Compacts of different powders were obtained by uniaxial pressing and were then studied by dilatometric experiments under similar conditions as established in DTA measurements. The dilatometric curves were applied to different sintering models to obtain the validity ranges and activation energies corresponding to the different densification mechanisms that operate in the initial and intermediate stages of sintering.

Parameter Optimization in the Synthesis of BZT Ceramics to Achieve Good Dielectric Properties

The powder synthesis of barium zirconate titanate (BZT) (BaZrTiO3) from the mechanochemical activation of BaCO3, ZrO2, and TiO2 was studied. The grinding effect, by using a planetary ball milling, on the crystallization temperature of BZT powders was analyzed. X-ray diffractometry, differential thermal analysis, thermogravimetric analysis, and scanning electronic microscopy (SEM) were used as characterization methods. The crystallization behavior of powders activated by high-energy grinding and the effect of grinding time on the BZT crystallization were analyzed. After grinding by 4 h, the BaZr(0.05)Ti(0.95)O3 sample was almost fully crystallized at . The results of dielectric and ferroelectric properties show that high-energy ball milling is a practical and promising way to prepare BZT ceramics.

Chemical solution technique to prepare perovskite PZT and PLZT thin films and powders

Abstract PbZr0.65Ti0.35O3 and Pb0.91La0.09Zr0.65Ti0.35O3 thin films with thickness of around 100 nm were prepared by the chemical solution deposition technique on Si (100) substrate. Complex metal alkoxide precursors were synthesized by alcoholisis and alcohol exchange reactions starting from metallorganics compounds. NMR spectroscopic techniques, 1H and 13C, and FTIR analysis were used to study the arrangement of the metals and oxygen in the precursor molecules. The films were deposited on Si (100) by spin coating technique and thermal treated by Rapid Thermal Processing for film crystallization. The thermal evolution and structural characterization were performed by DTA-TG/FTIR and by glazing incidence XRD and XRD powder. A PLZT powder with a well-crystallized perovskite structure was obtained at 700°C free of pyrochlore phase whereas the PLZT film exhibits a distorted perovskite structure and residual pyrochlore. The PZT films were less crystallized. The silicon substrate affects the crystal structure of the film. The residual acetylacetonate groups in the precursor of PLZT, would reduce the clustering of Zirconium species.