Efficiency evaluation of Neem (Azadirachta indica) oil and copper-ethanolamine in the protection of wood against a subterranean termite attack

The demand for environmentally safe preservatives for wood is increasing all around the world. This study is focused on the evaluation of the ability of Neem (Azadirachta indica) seed oil and copper-ethanolamine to protect Sydney blue gum (Eucalyptus saligna) and Ayous (Triplochiton scleroxylon) against termites. Wood blocks were impregnated with solutions of Neem oil in acetone and/or an aqueous solution of copper-ethanolamine. Impregnated woods with a retention rate of up to 108.3 kg/m3 were obtained. A leaching experiment was used to determine the fixation of preservatives in wood. The termicidial effect of the preservatives was studied through exposure in a termitarium. Neem oil was less efficient for Sydney blue gum but showed significant protection for Ayous at a higher retention rate. At the concentration investigated, the treatment of both wood species with copper-ethanolamine solution was not suitable. However, a combination of copper-ethanolamine and Neem oil showed an improvement in the protection of Sydney blue gum wood. Nevertheless, the impregnated woods still suffered an increased termite attack after leaching

Elaboration et caractérisation de thermistances céramiques CTN (Coefficient de Température Négatif) à structure pérovskite Y(Cr,Mn)O3

Les matériaux de formulation Y(Cr,Mn)O3, étudiés dans ce manuscrit, sont issus du diagramme ternaire Y2O3-Mn2O3-Cr2O3. Ce sont des thermistances à Coefficient de Température Négatif (CTN) de structure pérovskite pour applications haute température. Les mesures zêtamétriques et rhéologiques ont permis de définir les conditions optimales de dispersion et de stabilité des mélanges. Pour le taux de charge de 40 %, le pH a été fixé à 11. L influence des temps de broyage a permis de mettre en évidence la différence de frittabilité : le taux de densification varie entre 83 et 95 % en fonction de ces temps. L étude de l influence de la nature de l atmosphère (oxydante, réductrice et neutre) de frittage a révélé que les caractéristiques structurales, microstructurales et les propriétés CTN y sont fortement dépendants. Les valeurs de B peuvent aller de 3400 à 3880 K et de 7500 à 10600 K en fonction de la nature de l atmosphère et de la gamme de température. Sous atmosphères neutre et réductrice la résistivité à 25 C est de l ordre de 105 W.cm alors qu elle est de 104 W.cm sous condition oxydante. La réoxydation des matériaux frittés préalablement sous atmosphère réductrice permet de se rapprocher des propriétés de ceux frittés sous flux d oxygène. Les tests de vieillissement ont révélé que les matériaux frittés sous atmosphères réductrice et neutre présentent des dérives moins importantes que ceux frittés sous flux d oxygène. La technique de frittage SPS a permis de densifier le matériau avec un gain de température d environ 300 à 400 C. L étude de la formulation YCr1-xMnxO3 a montré que le taux de manganèse permet de moduler les propriétés des matériaux.Y(Cr,Mn)O3 materials, synthesized from the ternary diagram, were studied. They are thermistors with Negative Temperature Coefficient (NTC) used for high temperature applications. Optimization conditions of the dispersion and the stability of the mixture were defined from the zeta potential and rheological measurements. Thus, for 40 % of solid fraction, pH 11 is convenient. The influence of grinding time was carried out. The percentage of densification varies from 83 to 95 % depending on grinding time. Structure, microstructure and NTC properties are considerably influenced by the nature of sintering atmosphere (oxidizing, reducing, neutral). B values stay between 3400 and 3880 K at low temperature, whereas they are ranging from 7500 to 10600 K at high temperature. Those B values also depend on the nature of the sintering atmosphere. Under neutral and reducing atmospheres, the order of magnitude of the resistivity at 25 C is the same (105 W.cm) but it is 10 times smaller under oxidizing conditions. Reoxidation of the samples previously sintered under reducing atmosphere have shown that the properties are close to those sintered under oxidizing conditions. Ageing tests have revealed that, sintered materials under reducing and neutral conditions are more stable than those sintered under oxygen. In terms of temperature, the gain is roughly 300 to 400 C for the SPS sintering method compared to conventional sintering. The study of the compositions of YCr1-xMnxO3 has shown that, the properties of sintered materials depend on the manganese fraction.CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Synthesis and NTC properties of YCr1−xMnxO3 ceramics sintered under nitrogen atmosphere

International audienceYCr1−xMnxO3 (0 ≤ x ≤ 0.8) negative temperature coefficient (NTC) compositions were synthesized by classical solid state reaction at 1200 °C, and sintered under nitrogen atmosphere at 1500 °C and 1600 °C. XRD patterns analysis has revealed that for x ≤ 0.6, the structure consists of a solid solution of an orthorhombic perovskite YCrO3 phase with Mn substitute for Cr. For x ≥ 0.8, a second phase with a structure similar to the hexagonal YMnO3 phase appears. SEM images and calculated open porosity have shown that the substitution of Mn for Cr results in a decrease in porosity. Whatever the sintering temperature, the electrical characterizations (between 25 and 900 °C) have shown that the increase in the manganese content involves the decrease in both resistivity and material constant B (parameter which characterizes the thermal sensitivity of material) when x ≤ 0.6. The magnitude order of the resistivity at 25 °C is of 104–108 Ω cm and activation energies vary from 0.28 to 0.99 eV at low and high temperatures, respectively

Texturation of lead-free BaTiO3-based piezoelectric ceramics

International audienceNowadays, piezoelectric ceramics are integrated in a wide range of devices, in particular in ultrasonic applications (underwater sonar systems, medical imaging, non-destructive testing…). Most of them use Pb(Zr,Ti)O3 (PZT). However, due to health care and environmental problems, lead content must be reduced in such applications [1]. Recent reviews demonstrated that few lead-free materials families can be considered: the alkaline-niobates (K0.5Na0.5NbO3), the alkaline-bismuth-titanates (Na0.5Bi0.5TiO3) and barium titanate based materials (BaTiO3) [2, 3]. One of the limitations of ceramic materials is their isotropic nature. This is the reason why texturation process has been developed in order to improve their properties in particular electromechanical parameters. The aim of the present study is thus to obtain textured BaTiO3 based materials by using the templated grain growth process (TGG) and to measure their piezoelectric properties. Nanosized BaTiO3 powders were prepared by classical solid state route at relatively low temperature. BaTiO3 templates of different morphologies were elaborated by a molten salts process. Dispersing agent, binder and plasticizer, the mixture of the templates and matrix particles was then dispersed in the appropriated solvent using non-aqueous formulation. The slurry was then tape-casted on plastic film. After drying, the green sheet was cut, stacked, thermo compressed and then sintered at the appropriated temperature. This process allowed obtaining highly-oriented materials with a texturation degree around 95% (fig. 1), presenting Kt values around 35-40%, higher than for non-textured BaTiO3 ceramics. Fig. 1: X-ray diffraction diagram of (tetragonal) textured sample BaTiO3 and (tetragonal) non-textured BaTiO3 ceramic as reference

{111}-textured BaTiO 3 ceramics elaborated by Templated Grain Growth using NaNbO 3 templates

International audienceHighly textured {111} BaTiO 3 ceramics were obtained by templated grain growth using NaNbO 3 templates, with Lotgering factor F 111 , around 95 %, one of the best values reported in the literature. Solid solution formation with NaNbO 3 templates changes the tetragonal structure into cubic, with paraelectric behaviour. The relative permittivity is lower than "pure" tetragonal BaTiO 3 , but dielectric losses are improved with better thermal stability

Preparation, surface characterization, and water resistance of silicate and sol-silicate inorganic–organic hybrid dispersion coatings for wood

The purpose of this study was to comparatively investigate the behavior of silicate and sol-silicate coatings non-modified or modified with an organosilane on wood and on wood precoated with silica-mineralized primers. Adhesion strength, morphology, and water permeability and related damages were studied to evaluate the possibility of utilizing such inorganic-based coating systems for durable protection of wood without or with relatively cheap and water-borne primers. Potassium silicate and potassium methylsiliconate aqueous solutions and a colloidal silica were used for the preparation of the coatings. The white coating paints were brushed on beech wood substrates at a rate of 220 g·m$^{−2}$. The coatings exhibited good coverage ability. The pull-off adhesion strength values appeared to be related to pH following a polynomial law. The adhesion strength for the silicate coatings were adequate (above 3 MPa and up to 5 MPa) for wood, whereas the values for the sol-silicates were too low for practical applications. The adhesion values were in general higher for the samples cured in a climate room (23 ± 3 °C and 75 ± 2% relative humidity) than the samples cured in the ambient atmosphere of the laboratory (23 ± 3 °C and 25 ± 5% relative humidity). The presence of microdefects (cracks, holes) was revealed in the coating layers by optical and scanning electron microscopy. The surface roughness parameters assessed by confocal scanning laser microscopy were dependent on the magnification applied for their measurement. The arithmetic average roughness S$_a$ was between 5 µm and 10 µm at magnification 5× and between 2.5 µm and 10 µm at magnification 20×. The maximum peak-to-valley height S$_z$ confirmed the presence of open pores emerging through the coatings. The open pores constitute free pathways for water ingress through the coatings, and could explain the high water absorption of the coatings including the methysiliconate-containing silicate coating and despite the relatively high water contact angle and low wettability exhibited by this sample. The post-application of a hydrophobizing solution containing hexadecyltrimethoxysilane and dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride considerably reduced the water permeability, while application of nanosilica-containing organic primers increased the adhesion for the coatings. Silicate coatings with adhesion great enough and resistance against water damages can be generated on wood even without a primer using low silica-to-alkali ratio binders and an organosilane additive. The sol-silicate coatings appear to be applicable only with a primer. The improvement of the paint formulations to control the formation of microcracks and open pores could be useful to reduce the liquid water permeability and increase durability. Otherwise, the application of a hydrophobizing treatment can be used for this purpose

Ultrafine Grinding of Oxide Powders with a Controlled Viscosity of Slurries

International audienceThis study shows the importance of controlling the rheological behavior of slurries during attrition milling in aqueous media. Indeed, during grinding, the creation of new surfaces that react with the aqueous dispersing medium leads to modification of the slurry's properties, in particular pH and rheological behavior. The slurry can then flocculate and its viscosity increases. Thus, grinding efficiency can very quickly become null and a “setting” of the slurry in the grinder is sometimes noted. Our approach of the problem is in two steps. First, we determine the optimum dispersion conditions to obtain deflocculated slurries. This is possible by control of the solid load or pH, or by the addition of dispersant in order to enhance electrostatic and/or steric repulsion between particles. The characterization of the dispersion state is also possible with tools such as zetametry and rheology. The second step is to preserve this deflocculated state of dispersion throughout the milling process. This is possible, for example, by maintaining relatively constant the optimal pH value for the slurry. We apply this concept for the grinding of classically used powder oxides TiO2 and Al2O3. To this end, we implement a horizontal attrition mill (dyno‐mill), using different kind of balls: zircon or stabilized yttrium–zirconia with diameters ranging from 0.4 to 1.6 mm. We have observed the grinding efficiency by powder BET specific area measurements, and by DRX and TEM observations. So the grinding is very efficient, starting powders areas of about 10 m2 · g−1 have reached 40 m2 · g−1 after grinding, that is to say, average grains diameter lower than 50 nm

Synthèse de TiO2 dopé au LiF par réaction de Flash Combustion en utilisant deux combustibles différents pour des applications de photocatalyse

International audienceThe flash combustion method was used to prepare LiF-doped TiO2 photocatalysts materials using glycine or urea as a fuel with different weight percentage of LiF. The synthesized powders have been characterized by thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) with energy dispersive spectrometer (EDX) analyzer, the specific surface area measurement was performed by BET. The crystallization and the phase transformation anatase-rutile for the powders have been verified by XRD. SEM micrographs for these powders shows the presence of nanoparticles. To investigate the optical band gap of the synthesized samples, UV-Vis spectroscopy was conducted using the diffuse reflectance mode (DRS). The O2-/F- substitution and the presence of Ti3+ centers was confirmed by electron paramagnetic resonance (EPR) analysis. The photocatalytic activity of the TiO2-xLiF powders were evaluated through the photocatalytic degradation of Methylene blue (MB) in water under UV-visible light exposure. The results indicated that during the flash combustion synthesis, the nature of the fuel and the percentage of the doping element led to the presence of different polymorphs of TiO2 which influences the photocatalytic efficiency attributed to the synergistic effect between the two phases (anatase and rutile). The LiF-doped TiO2 powders synthesized by flash combustion in both cases (by using glycine or urea) showed high performance in MB degradation compared to commercial TiO2 and undoped synthesized TiO2 powders, with an optimal degradation of 99 % achieved with 2 wt. % LiF-doped TiO2 using glycine as a fuel and after 6 hours of UV-Vis irradiation