The main aim of this work was to study and understand the influence of SiC particles on the corro... more The main aim of this work was to study and understand the influence of SiC particles on the corrosion and tribocorrosion of Al-matrix composite materials. For that, Al-SiCp functionally graded composites were produced by centrifugal casting and different SiCp contents were achieved. Their mechanical properties were improved by age-hardening heat treatments. The tribocorrosion behaviour was studied in 0.05M NaCl solutions using a reciprocating motion tribometer involving an alumina ball sliding against the Al-based samples. Above critical SiC particles' content the matrix alloy surface was found to be protected against wear by SiC particles protruding from the surface. Below this threshold content, the SiC reinforcement was inefficient and the wear rate of the composite was the same as the non-reinforced alloy.
... Appl. Catal. B: Environ., 30 (2001), p. 277. [34] MJ Van Bommel and TNM Bernards. J. Sol–Gel ... more ... Appl. Catal. B: Environ., 30 (2001), p. 277. [34] MJ Van Bommel and TNM Bernards. J. Sol–Gel Sci. Technol., 8 (1997), p. 459. ... J. Non-Cryst. Solids, 261 (2000), p. 9. [38] J. Jon, S. Sakida, T. Yoko and M. Nogami. J. Non-Cryst. Solids, 262 (2000), p. 183.
In this work, we report the synthesis and the photoluminescence features of Eu(III)-doped yttrium... more In this work, we report the synthesis and the photoluminescence features of Eu(III)-doped yttrium-aluminium oxide obtained by non-hydrolytic sol-gel routes. After heating the powders above 600 ºC the XRD patterns show the presence of the Y4Al2O9 (YAM) and Y3Al5O12 (YAG) phases. At 800 and at 1500 ºC the PL spectra display the Eu(III) lines characteristic of the YAM monoclinic phase. The 5D0®7F2 transition is favored relatively to the 5D0®7F1 lines. However, at 1100 ºC the cubic YAG is the preferential phase and the 5D0®7F1 transition dominates the spectrum. The Eu(III) ions lie in a centrosymmetrical site. The different solvents used in the sol-gel synthesis also change the relative proportion between these two phases. This is monitored analyzing the modifications in the relative intensity between the 5D0®7F2 and the 5D0®7F1 transitions.
The thermal stability of vegetable oils is an important factor that affects their quality. In thi... more The thermal stability of vegetable oils is an important factor that affects their quality. In this study, we investigated the thermal stability of oil and lecithin extracted from soybeans by two distinct processes: mechanical extraction (pressing) and physical extraction (solvent). Thermal analysis was used to obtain information about different methodologies of extraction. The physically extracted products proved more stable than those extracted mechanically. Raman and UV-Vis techniques were applied to underpin the discussion of process differences.
Titania oxide films doped with europium were prepared by the sol–gel process and deposited on gla... more Titania oxide films doped with europium were prepared by the sol–gel process and deposited on glass substrates by the dip-coating technique. The fluorescence and excitation spectra of the Eu (III) in the films changed as the calcination temperature rose. TiO2:Eu thin films were heat-treated at various temperatures (100, 200, 300, 400 and 500 °C), resulting in transparent films. Excitation spectra presented a change in the charge transfer band (CTB) with increasing temperature. Eu (III) emission spectra exhibited transitions arising mainly from the 5D0 level to the 7FJ (J = 0–4) manifolds. The lifetime of the 5D0 → 7F2 transition of the Eu (III) ion increased in the samples heated-treated up to 400 °C, while the lifetime of the sample treated at 500 °C decreased, probably due to a change in the crystalline structure of the TiO2.
In this work we studied the preparation of titania thin films by sol–gel process and analyzed the... more In this work we studied the preparation of titania thin films by sol–gel process and analyzed the influence of parameters such as deposition speed (100, 200 and 300 mm min−1) and stirring type (magnetic or ultrasound) during the homogenization of the sol used for deposition. Europium III was incorporated into the titania thin films and used as a structural probe. The prepared films present good transparency. Excitation spectrum presents a large band with maximum in 309 nm. This band can be attributed to charge transfer band (CTB). The emission spectra presented the correspondent bands to the transitions of the excited state of the ion for the fundamental (). The thickness films depend on deposition speed, we observed a large enhanced when the deposition speed increase of the 100–200 mm min−1 (0.1562–0.4552 nm) and less to 200–300 mm min−1 (0.4552–0.5364 nm). The refractive index for samples obtained in the deposition speed 200 and 300 mm min−1, are respectively 1.9798 and 1.9803. Both are different from the film deposited at 100 mm min−1 (2.3635).
Colloids and Surfaces A-physicochemical and Engineering Aspects, 2006
This work describes the synthesis of a first-generation iron porphyrin catalyst entrapped in a si... more This work describes the synthesis of a first-generation iron porphyrin catalyst entrapped in a silica matrix by the sol–gel route, leading to spherical particles. The catalyst was synthesized by the method of Stober, through hydrolysis and condensation of the alkoxysilane TEOS in a mixture of alcohol, water and ammonia, in the presence of the iron porphyrin Fe(TPP)Cl. The relation between particle morphology and catalytic activity of the different Fe(TPP)–SiO2, obtained using different H2O/silane molar ratios and ammonia concentrations in the xerogel syntheses, was studied.The obtained catalysts were characterized by UV–vis spectroscopy, NMR 29Si, thermogravimetric analysis and transmission electron microscopy. Their ability to catalyze (Z)-cyclooctene epoxidation and cyclohexane oxidation was tested using iodosylbenzene as oxygen donor; the oxidation products were analyzed by gas chromatography and the catalysts obtained in a form of particles spherical and monodispersed showed to be a promising catalytic system for selective oxidation.
Materials Research-ibero-american Journal of Materials, 2005
In this work titanium sol was prepared from tetraethylorthotitanate (TEOT) in ethanol, stabilized... more In this work titanium sol was prepared from tetraethylorthotitanate (TEOT) in ethanol, stabilized with beta-diketonate 2,4 pentanedione in molar ratio 1:1 homogenized by magnetic stirring, europium ion was add as structural probe. The xerogels were heat treated at 500, 750 and 1000 °C and the characterization was realized by x-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA/DSC) and photoluminescence (PL). The excitation spectra of Eu (III) ion present maximum in 394 nm correspondent to 5L6 level and emission spectra present bands characteristic transitions arising from the 5 D0 ® 7FJ (J = 0, 1, 2, 3, 4) manifolds to samples treat at 500 and 750 °C. The Eu (III) emission disappear, when heated at 1000 °C, probably due to phase transition anatase to rutile and migrations of ions to the external surface that was proved by x-ray diffraction, transmission electronic microscopy and the thermogravimetric analyses of xerogels.
This work describes optimized conditions for preparation of a cobalt complex entrapped in alumina... more This work describes optimized conditions for preparation of a cobalt complex entrapped in alumina amorphous materials in the form of powder. The hybrid materials, CoNHG, were obtained by a nonhydrolytic sol–gel route through condensation of aluminum chloride with diisopropylether in the presence of cobalt chloride. The materials were calcined at various temperatures. The presence of cobalt entrapped in the alumina matrix is confirmed by ultraviolet visible spectroscopy. The materials have been characterized by X-ray diffraction (XRD), surface area analysis, thermogravimetric analysis (TGA), differential thermal analyses (DTA) and transmission electron microscopy (TEM). The prepared alumina matrix materials are amorphous, even after heat treatment up to 750 °C. The XRD, TGA/DTA and TEM data support the increase of sample crystallization with increasing temperature. The specific surface area, pore size and pore diameter changed as a function of the heat treatment temperature employed. Different heat treatment temperatures result in materials with different compositions and structures, and influence their catalytic activity. The entrapped cobalt materials calcined at 750 °C efficiently catalyzed the epoxidation of (Z)-cyclooctene using iodozylbenzene as the oxygen donor.
The main aim of this work was to study and understand the influence of SiC particles on the corro... more The main aim of this work was to study and understand the influence of SiC particles on the corrosion and tribocorrosion of Al-matrix composite materials. For that, Al-SiCp functionally graded composites were produced by centrifugal casting and different SiCp contents were achieved. Their mechanical properties were improved by age-hardening heat treatments. The tribocorrosion behaviour was studied in 0.05M NaCl solutions using a reciprocating motion tribometer involving an alumina ball sliding against the Al-based samples. Above critical SiC particles' content the matrix alloy surface was found to be protected against wear by SiC particles protruding from the surface. Below this threshold content, the SiC reinforcement was inefficient and the wear rate of the composite was the same as the non-reinforced alloy.
... Appl. Catal. B: Environ., 30 (2001), p. 277. [34] MJ Van Bommel and TNM Bernards. J. Sol–Gel ... more ... Appl. Catal. B: Environ., 30 (2001), p. 277. [34] MJ Van Bommel and TNM Bernards. J. Sol–Gel Sci. Technol., 8 (1997), p. 459. ... J. Non-Cryst. Solids, 261 (2000), p. 9. [38] J. Jon, S. Sakida, T. Yoko and M. Nogami. J. Non-Cryst. Solids, 262 (2000), p. 183.
In this work, we report the synthesis and the photoluminescence features of Eu(III)-doped yttrium... more In this work, we report the synthesis and the photoluminescence features of Eu(III)-doped yttrium-aluminium oxide obtained by non-hydrolytic sol-gel routes. After heating the powders above 600 ºC the XRD patterns show the presence of the Y4Al2O9 (YAM) and Y3Al5O12 (YAG) phases. At 800 and at 1500 ºC the PL spectra display the Eu(III) lines characteristic of the YAM monoclinic phase. The 5D0®7F2 transition is favored relatively to the 5D0®7F1 lines. However, at 1100 ºC the cubic YAG is the preferential phase and the 5D0®7F1 transition dominates the spectrum. The Eu(III) ions lie in a centrosymmetrical site. The different solvents used in the sol-gel synthesis also change the relative proportion between these two phases. This is monitored analyzing the modifications in the relative intensity between the 5D0®7F2 and the 5D0®7F1 transitions.
The thermal stability of vegetable oils is an important factor that affects their quality. In thi... more The thermal stability of vegetable oils is an important factor that affects their quality. In this study, we investigated the thermal stability of oil and lecithin extracted from soybeans by two distinct processes: mechanical extraction (pressing) and physical extraction (solvent). Thermal analysis was used to obtain information about different methodologies of extraction. The physically extracted products proved more stable than those extracted mechanically. Raman and UV-Vis techniques were applied to underpin the discussion of process differences.
Titania oxide films doped with europium were prepared by the sol–gel process and deposited on gla... more Titania oxide films doped with europium were prepared by the sol–gel process and deposited on glass substrates by the dip-coating technique. The fluorescence and excitation spectra of the Eu (III) in the films changed as the calcination temperature rose. TiO2:Eu thin films were heat-treated at various temperatures (100, 200, 300, 400 and 500 °C), resulting in transparent films. Excitation spectra presented a change in the charge transfer band (CTB) with increasing temperature. Eu (III) emission spectra exhibited transitions arising mainly from the 5D0 level to the 7FJ (J = 0–4) manifolds. The lifetime of the 5D0 → 7F2 transition of the Eu (III) ion increased in the samples heated-treated up to 400 °C, while the lifetime of the sample treated at 500 °C decreased, probably due to a change in the crystalline structure of the TiO2.
In this work we studied the preparation of titania thin films by sol–gel process and analyzed the... more In this work we studied the preparation of titania thin films by sol–gel process and analyzed the influence of parameters such as deposition speed (100, 200 and 300 mm min−1) and stirring type (magnetic or ultrasound) during the homogenization of the sol used for deposition. Europium III was incorporated into the titania thin films and used as a structural probe. The prepared films present good transparency. Excitation spectrum presents a large band with maximum in 309 nm. This band can be attributed to charge transfer band (CTB). The emission spectra presented the correspondent bands to the transitions of the excited state of the ion for the fundamental (). The thickness films depend on deposition speed, we observed a large enhanced when the deposition speed increase of the 100–200 mm min−1 (0.1562–0.4552 nm) and less to 200–300 mm min−1 (0.4552–0.5364 nm). The refractive index for samples obtained in the deposition speed 200 and 300 mm min−1, are respectively 1.9798 and 1.9803. Both are different from the film deposited at 100 mm min−1 (2.3635).
Colloids and Surfaces A-physicochemical and Engineering Aspects, 2006
This work describes the synthesis of a first-generation iron porphyrin catalyst entrapped in a si... more This work describes the synthesis of a first-generation iron porphyrin catalyst entrapped in a silica matrix by the sol–gel route, leading to spherical particles. The catalyst was synthesized by the method of Stober, through hydrolysis and condensation of the alkoxysilane TEOS in a mixture of alcohol, water and ammonia, in the presence of the iron porphyrin Fe(TPP)Cl. The relation between particle morphology and catalytic activity of the different Fe(TPP)–SiO2, obtained using different H2O/silane molar ratios and ammonia concentrations in the xerogel syntheses, was studied.The obtained catalysts were characterized by UV–vis spectroscopy, NMR 29Si, thermogravimetric analysis and transmission electron microscopy. Their ability to catalyze (Z)-cyclooctene epoxidation and cyclohexane oxidation was tested using iodosylbenzene as oxygen donor; the oxidation products were analyzed by gas chromatography and the catalysts obtained in a form of particles spherical and monodispersed showed to be a promising catalytic system for selective oxidation.
Materials Research-ibero-american Journal of Materials, 2005
In this work titanium sol was prepared from tetraethylorthotitanate (TEOT) in ethanol, stabilized... more In this work titanium sol was prepared from tetraethylorthotitanate (TEOT) in ethanol, stabilized with beta-diketonate 2,4 pentanedione in molar ratio 1:1 homogenized by magnetic stirring, europium ion was add as structural probe. The xerogels were heat treated at 500, 750 and 1000 °C and the characterization was realized by x-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA/DSC) and photoluminescence (PL). The excitation spectra of Eu (III) ion present maximum in 394 nm correspondent to 5L6 level and emission spectra present bands characteristic transitions arising from the 5 D0 ® 7FJ (J = 0, 1, 2, 3, 4) manifolds to samples treat at 500 and 750 °C. The Eu (III) emission disappear, when heated at 1000 °C, probably due to phase transition anatase to rutile and migrations of ions to the external surface that was proved by x-ray diffraction, transmission electronic microscopy and the thermogravimetric analyses of xerogels.
This work describes optimized conditions for preparation of a cobalt complex entrapped in alumina... more This work describes optimized conditions for preparation of a cobalt complex entrapped in alumina amorphous materials in the form of powder. The hybrid materials, CoNHG, were obtained by a nonhydrolytic sol–gel route through condensation of aluminum chloride with diisopropylether in the presence of cobalt chloride. The materials were calcined at various temperatures. The presence of cobalt entrapped in the alumina matrix is confirmed by ultraviolet visible spectroscopy. The materials have been characterized by X-ray diffraction (XRD), surface area analysis, thermogravimetric analysis (TGA), differential thermal analyses (DTA) and transmission electron microscopy (TEM). The prepared alumina matrix materials are amorphous, even after heat treatment up to 750 °C. The XRD, TGA/DTA and TEM data support the increase of sample crystallization with increasing temperature. The specific surface area, pore size and pore diameter changed as a function of the heat treatment temperature employed. Different heat treatment temperatures result in materials with different compositions and structures, and influence their catalytic activity. The entrapped cobalt materials calcined at 750 °C efficiently catalyzed the epoxidation of (Z)-cyclooctene using iodozylbenzene as the oxygen donor.
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