The contribution of grain boundary sliding to total strain has been investigated in a 21 vol% zirconia–spinel composite crept under stresses of 12 and 90 MPa. To this goal, the surface topography and ...its changes with strain were investigated on a face parallel to the compression axis by atomic force microscopy in contact mode. Due to the low zirconia content, only sliding on spinel–spinel (S–S) and spinel–zirconia (S–Z) boundaries really contributes to strain and was consequently analysed. Insensitive to stress value, boundary sliding can account for 70–80% of the total strain. However, if the two investigated interfaces behave similarly at 90 MPa, at 12 MPa sliding on S–Z boundaries is larger than on S–S ones. That difference is to relate to a stress–strain rate sensitivity dependent on stress, 1.8 and 4.2 at 90 and 12 MPa, respectively, an increase in the stress exponent able to be induced by the existence of a threshold stress that would concern spinel–spinel boundaries.
An uncracked thin film made of stable large columnar tetragonal zirconia crystals (t-ZrO2, 100–400nm wide and ∼3μm long) has been synthesized at room temperature. The thin film obtained is not ...nanostructured and stabilization of the tetragonal phase do not necessitate the incorporation of stabilizing dopant elements. In view of the microstructure characterizations performed, we propose that defects in the crystalline structure (dislocations and amorphous domains) are responsible for the stability of the unexpected tetragonal zirconia phase at room temperature.
This paper presents a systematic study of alumina supported silver catalysts, a novel catalytic system proposed for the liquid phase aerobic partial oxidation of glycerol to glycolic acid, the ...smallest α-hydroxyacid with numerous industrial applications (raw material in the chemical industry, ingredient in textiles, food, cosmetics, plastics, adhesives, pharmaceuticals,
etc.
). We evaluated the effect of the preparation method, the silver loading and the type of alumina support on the properties and the activity of the solids. We showed that numerous parameters can affect the catalytic performances, the most important of which were the following: the type of solvent used during preparation, the basicity and phase composition of the support, as well as the amount of base used during glycerol oxidation. The most active catalysts were at the same time the most selective ones to glycolic acid, which clearly differentiates the silver catalysts from other noble metals conventionally used in glycerol oxidation, such as Au, Pd and Pt, characterized by a high selectivity to glyceric acid. The best results in terms of conversion and selectivity to glycolic acid were obtained over the catalyst prepared by the chemical reduction method in a basic methanol solution, using formaldehyde as a reductant. After 3 h of reaction at 60 °C under 5 bar of oxygen pressure over such a catalyst loaded with 3.6 wt% Ag, an 85% glycerol conversion together with a 57.1% selectivity to glycolic acid were achieved. Moreover, the catalysts showed good stability in the continuous mode and very good resistance to the impurities present in a crude glycerol fraction.
A series of silver supported catalysts have been developed and proposed for mild oxidation of glycerol in the liquid phase. High selectivity to glycolic acid, stability in both continuous-flow and periodic mode of reaction, and good resistance to crude glycerol impurities have been achieved.
This paper presents a systematic study of alumina supported silver catalysts, a novel catalytic system proposed for the liquid phase aerobic partial oxidation of glycerol to glycolic acid, the ...smallest alpha -hydroxyacid with numerous industrial applications (raw material in the chemical industry, ingredient in textiles, food, cosmetics, plastics, adhesives, pharmaceuticals, etc.). We evaluated the effect of the preparation method, the silver loading and the type of alumina support on the properties and the activity of the solids. We showed that numerous parameters can affect the catalytic performances, the most important of which were the following: the type of solvent used during preparation, the basicity and phase composition of the support, as well as the amount of base used during glycerol oxidation. The most active catalysts were at the same time the most selective ones to glycolic acid, which clearly differentiates the silver catalysts from other noble metals conventionally used in glycerol oxidation, such as Au, Pd and Pt, characterized by a high selectivity to glyceric acid. The best results in terms of conversion and selectivity to glycolic acid were obtained over the catalyst prepared by the chemical reduction method in a basic methanol solution, using formaldehyde as a reductant. After 3 h of reaction at 60 degree C under 5 bar of oxygen pressure over such a catalyst loaded with 3.6 wt% Ag, an 85% glycerol conversion together with a 57.1% selectivity to glycolic acid were achieved. Moreover, the catalysts showed good stability in the continuous mode and very good resistance to the impurities present in a crude glycerol fraction.
The confinement of catalytically active metallic nanoparticles within discrete and robust microenvironments was successfully achieved by using a water-compatible three-dimensional ...β-cyclodextrin-based polymer. The strategy was examined using ruthenium through an aqueous colloidal approach involving the chemical reduction of ruthenium nitrosyl nitrate by sodium borohydride in the presence of a water-soluble β-CD polymer crosslinked with citric acid (poly(CTR-β-CD)). The advantage of this polymer for nanoparticle synthesis is that (i) additional stabilizing effects are exerted through steric interactions (crosslinked chains and β-cyclodextrin entities) and electrostatic interactions (ionisable-COOH groups) and (ii) accessible nanopockets are provided between the stable junctions of the polymer skeleton. The poly(CTR-β-CD) Ru(0) system was characterized at different stages of the synthesis by combining proton nuclear magnetic resonance spectroscopy, dynamic light scattering and transmission electron microscopy measurements. The results highlighted that, in contrast with a series of control colloidal ruthenium catalysts, the specific use of poly(CTR-β-CD) allowed not only the stabilization of smaller size-controlled ruthenium nanoparticles (approximately 1.8 nm) but also their confinement in individual superstructures having sizes mostly in the range of 50 to 100 nm. These polymer-encapsulated ruthenium nanoparticles were applied as catalysts for the aqueous phase hydrogenation of biomass-derived 2-furaldehyde and 3-(2-furyl)acrolein under mild reaction conditions,
i.e.
303 K and 1 MPa. The high reactivity was related to the presence of individual globular objects acting as catalytic "microreactors", in which the consecutive hydrogenation reactions and product/substrate diffusional exchanges can occur efficiently in the confined spaces. The robustness of the system was demonstrated through recycling experiments and TEM characterizations after catalytic tests.
Robust and highly efficient ruthenium nanoparticles confined within individual microenvironments formed by a three-dimensional β-cyclodextrin polymer were easily prepared for the hydrogenation of biomass-derived furan compounds in water.
Tin dioxide is a wide-band gap (3.6 eV) semiconductor with numerous potential applications in batteries, gas sensors, and dye-sensitized solar cells. In this study nanocrystalline tin oxide nanowires ...have been synthesized by electrochemical deposition and oxidation in anodic aluminum oxide template. Electrochemical synthesis has been controlled by chronoamperometry and oxidation by X-ray diffraction. Polycrystalline nanowires with 140 nm in diameter and 3 mu m in length have been obtained. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies have highlighted a uniform nanowire structure. High resolution transmission electron microscope (TEM FEI Tecnai G2-20 twin) was employed to characterize the crystalline structure of 5 nm diameter tin oxide grains. Tetragonal tin oxide phase has been characterized by X-ray powder diffraction and the interplanar distance of 0.32 nm corresponding to the SnO sub(2) crystal obtained by HRTEM has confirmed the structure.
This paper presents a systematic study of alumina supported silver catalysts, a novel catalytic system proposed for the liquid phase aerobic partial oxidation of glycerol to glycolic acid, the ...smallest α-hydroxyacid with numerous industrial applications (raw material in the chemical industry, ingredient in textiles, food, cosmetics, plastics, adhesives, pharmaceuticals, etc. ). We evaluated the effect of the preparation method, the silver loading and the type of alumina support on the properties and the activity of the solids. We showed that numerous parameters can affect the catalytic performances, the most important of which were the following: the type of solvent used during preparation, the basicity and phase composition of the support, as well as the amount of base used during glycerol oxidation. The most active catalysts were at the same time the most selective ones to glycolic acid, which clearly differentiates the silver catalysts from other noble metals conventionally used in glycerol oxidation, such as Au, Pd and Pt, characterized by a high selectivity to glyceric acid. The best results in terms of conversion and selectivity to glycolic acid were obtained over the catalyst prepared by the chemical reduction method in a basic methanol solution, using formaldehyde as a reductant. After 3 h of reaction at 60 °C under 5 bar of oxygen pressure over such a catalyst loaded with 3.6 wt% Ag, an 85% glycerol conversion together with a 57.1% selectivity to glycolic acid were achieved. Moreover, the catalysts showed good stability in the continuous mode and very good resistance to the impurities present in a crude glycerol fraction.
In this study, a fully dense and crack-free alpha titanium alloy was fabricated using selective laser melting (SLM) of commercially pure titanium (CP Ti) blended with 1 vol.% micrometre-sized Mo2C ...powder. The microstructure and mechanical properties of the fabricated Ti alloy were systematically investigated. It was found that the fabricated Ti alloy consisted of both alpha (α) and beta (β) phases and exhibited a nest-like inhomogeneous microstructure with graded local phase formation, composition and crystallographic texture. This novel microstructure was formed through melting and rapid solidification of CP Ti and Mo2C during SLM, assisted by the high laser absorptivity and resultant high temperature rise of the Mo2C powder. The fabricated Ti alloy exhibited higher tensile strength (∼1250 ± 50 MPa) and improved ductility (elongation ∼17 ± 1%) when compared to CP Ti fabricated using the same SLM process. The underlying reasons were mainly attributed to (i) the nest-like inhomogeneous microstructure consisting of fine grained α-Ti and β-Ti, (ii) the overall solid solution strengthening of the Ti matrix by interstitial C, and (iii) the high dislocation density in the Ti matrix arising from the mismatch between α-Ti and β-Ti phases. This study not only provides a fundamental knowledge about the modification of CP Ti with minor addition of secondary particles through SLM but also provides insight into the fabrication of inhomogeneous Ti alloys with graded microstructure and local composition through SLM for enhanced mechanical properties.
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In this paper, we report on the preparation of decyl-modified silicon nanoparticles (decyl-SiNPs) and their encapsulation into silica nanoparticles (NPs). The decyl-SiNPs were obtained by the ...photoinduced hydrosilylation of hydride-terminated SiNPs (H-SiNPs), liberated from porous silicon (pSi), followed by encapsulation into silica NPs (SiNPs@SiO2) via the Stöber process. Two different sized SiNPs@SiO2 were synthesized, similar15 and 25 nm in diameter. Their composition, size, shape, luminescence properties, colloidal and spectral stability in different environments and under ultraviolet (UV) light irradiation were studied by various techniques, including Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), UV-vis absorption, dynamic light scattering (DLS) and photoluminescence (PL) spectroscopy. The results indicate that the SiO2 coating renders the hydrophobic alkylated SiNPs dispersible in water, but leads to some loss of their PL intensity. The SiNPs@SiO2 NPs exhibit a wide pH stability, but show a pronounced PL degradation due to a blinking behavior. The photobleaching process could be partially suppressed by increasing the SiO2 outer shell thickness. Some investigations were made on the luminescence quenching, spectral shift and photobleaching. For potential bioapplications, the SiNPs@SiO2 NPs were modified with aminopropyl groups under acidic conditions without obvious luminescence loss and further conjugated with folic acid (FA). Considering the features of red-emission, versatile SiO2 surface chemistry and controlled size, the present SiNPs@SiO2 nanocomposites may find wide applications in cellular fluorescence labeling and the preparation of light-emitting devices.
ZnO nanoparticles were synthesized using sol--gel method. The structural and optical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron ...microscopy (TEM), high resolution TEM (HRTEM), Raman spectroscopy, and photoluminescence (PL). XRD analysis demonstrates that the nanoparticles have the hexagonal wurtzite structure and the particle size is increased with annealing temperature. The average size of the nanoparticles was determined by SEM as well as XRD data and found to be ${\sim}50$ nm after annealing at 800 °C. A sharp, strong and dominant UV emission with a suppressed green emission has been observed at 300 and 10 K, indicating the good optical properties of ZnO nanoparticles. The 10 K UV band is dominated by a neutral-donor bound exciton, and the surface-related SX emission at 3.31 eV is evidenced.
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