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A microstructural approach to the prediction of heat flux transport in porous geopolymers is used experimentally to understand the effects of the pore size distribution and pores connectivity to the transfer of the thermal flux across the porous network of geopolymers. Controlling the mix design and the concentration of porogen agent, capillary pores can be introduced into the system for a final homogeneous microstructure. The roundness of pores, their geometrical distribution, and their connectivity allow the possibility to extend the length of the pathway of the tortuous route for potential heat flux. The nonlinear relationship between tortuosity–porosity and tortuosity–thermal conductivity confirms that the volume of pores is not the only parameter affecting the heat flux transport. The results achieved in terms of homogeneous microstructure with geometric description of pore, their level of isolation, and the spatial distribution allow the prediction of the heat flux transport in environmentally friendly and sustainable porous geopolymer materials. [ABSTRACT FROM AUTHOR]

An optimized sol–gel protocol was carried out to produce an yttrium aluminum garnet (YAG) xerogel from aluminum alkoxide and an yttrium salt on a semi-pilot scale. This xerogel was successfully used without prior pyrolysis as a solid load with the aid of additives in the preparation of pastes. Thermal treatment of the green bodies, obtained by robocasting of the paste, led to cohesive single-phase YAG ceramics. Manufacturing ceramic pieces by additive methods will allow shaping complex forms, while the single step conversion/consolidation would simplify the technological process, reducing global energy costs. Since YAG possesses high strength and good creep behavior at high temperatures, these refractory pieces could replace the metal alloys used in turbine blades for deep space exploration. Structural, thermal and chemical characterizations were performed on xerogel powders, pastes, and YAG ceramics. [ABSTRACT FROM AUTHOR]

The influence of drying on the microstructure, physical and chemical properties of some tropical wood species has been investigated using thermogravimetric analysis, differential scanning calorimetric (DSC), FTIR-ATR spectroscopy, mercury intrusion porosimetry (MIP) and environmental scanning electron microscopy (ESEM) analysis. Eleven tropical species were used in this study. Results showed that the common Cameroonian wood species can be grouped into three classes: Ga (lightwood) with cross-linking fibers having high volume of macropores, density in the range 0.2–0.4 g cm−3 and high lignin content; Gb (medium dense) with unidirectional fibers packing, density around 0.6 g cm−3 and Gc group showing high densification of unidirectional fibers and low porosity justifying the density > 0.8 g cm−3. Both the Gb an Gc groups have less significant lignin content. A relatively high rate of drying for Ga with respect to low drying rate for Gc was observed in direct relation with their porosity of ~ 72 Vol% and ~ 36 Vol%, respectively. LTF and WG showed similar cumulative pore volume (0.44 mL g−1) with different pore size distribution: 28% and 22% of macropores, 39% and 60% of mesopores and 33% and 18% micropores, respectively. Thermal analysis revealed that lightwoods have the highest amounts of residues and lower thermal stability of chemical components than dense woods. It has been found that the degradation process of hemicellulose, cellulose and lignin occurs mainly at about 200–300 °C, 300–350 °C and 350–500 °C, respectively. The group Ga with low drying rate, a low cycle of reproduction, a high volume of porosity together with large pore sizes appeared promising candidates for the design of ecological, environmental and sustainable management policy of wood transformation in developing countries and even worldwide. [ABSTRACT FROM AUTHOR]

Thermophysical and microstructural behavior of eleven tropical woods widely available and commonly used was investigated. Experimental measurements of thermal conductivity and thermal diffusivity of wood were performed using the heat flow meter and transient plane source technique. The results show values in the range of 0.2–0.37 mm2/s for thermal diffusivity and 0.12–0.34 W m−1 K−1 for thermal conductivity. The correlation between the thermal conductivity and parameters as porosity, pore size distribution, intensity ratio of lignin and microstructure was drawn. The thermal conductivity of wood decreases with the increase in pores volume (vp). For vp > 70%, the values are between 0.1 and 0.15 W m−1 K−1 and reach 0.23 W m−1 K−1 for vp between 40 and 60%. For dense woods with the vp less than 40%, the values are between 0.24 and 0.35 W m−1 K−1. The results show experimental values of the effective thermal conductivity of wood species closer to the values of parallel model. The presence of ray and parenchyma which appear perpendicular to the axis of the fibers in the structure of the wood species makes it difficult to have straight correlation. This suggests that heat flux which travels through the matrix of wood follows a very complex road linked to the microstructural features of each class of wood. These results appear as significant contribution for the future development of sustainable energy technologies in relation to the prediction of energy saving and building energy metering. [ABSTRACT FROM AUTHOR]

The aims of this study correspond to (i) determine the feasibility of synthesize geomaterial from two main Pb-contaminated mining sediments (Sed1 and Sed2) without prior activation in substitution to metakaolin (MK), (ii) understand the mechanisms involved toward two types of silicate solution (Na and K one), and (iii) to evaluate the change in the Pb metallic element speciation and leaching after alkali treatment. The raw material as well as consolidated material were characterized by X-ray diffraction, infrared spectroscopy, and electron microscopy. The mechanical properties were evaluated, and the leaching behavior realized according to EN12457-2. The results evidence the limit of mining sediment incorporation by substitution near 50% whatever the sediments and the alkaline solution used. There is no difference in the mechanical properties up to 10% substitution then decrease with the increase of sediment content. The Pb-bearing phases are dissolved during alkaline treatment and redistributed in the geomaterial matrix. Finally, the leaching experiments clearly evidenced the possibility to stabilize Pb into MK-based geomaterial matrix up to 25–30% weight of mine waste. [ABSTRACT FROM AUTHOR]

Abstract: The sol-gel synthesis of yttrium aluminum garnet (YAG) was performed using different metal precursors (salts and alkoxides of aluminum and yttrium) and metal concentrations (up to a concentration factor of 7.4). The cross-reactivity of the aluminum and yttrium precursors is not clear, and generally, the sol-gel process leads to polyphasic samples consisting of hexagonal YAlO3 and a monoclinic yttrium-aluminum oxide. Nevertheless, the high reactivity of the yttrium precursor can be offset by the use of an aluminum alkoxide and yttrium salt as the precursors, which results in the synthesis of pure-phase YAG at 1000 °C. The effects of the metal concentration in the sol-gel synthesis on the crystallite size of the resulting YAG are reported for the first time and are found to be significant with the crystallite size varying from 55 to 123 nm. Repeated experiments demonstrate that the proposed synthesis protocol is relatively robust.Effect of precursors on crystallization of YAG gel was studied and a pure YAG powder has been synthesized by a simple sol-gel process from yttrium chloride and aluminum butoxide. Influence of precursor concentration on crystallite size and SSA of YAG powder is reported for the first time. Poly-cationic syntheses lead generally to polyphazed samples in Al2O3-Y2O3 diagram.Cross-reactivity of Al- and Y-precursors can be adjusted with an Al-alkoxide and an yttrium salt.YAG can successfully be synthetized by sol gel method from aluminum alkoxide and yttrium salt.Crystallite size increases significantly with precursor concentration. [ABSTRACT FROM AUTHOR]

Lanthanum zirconate with a pyrochlore structure exhibits interesting thermal and structural properties for thermal barrier coating applications operating at high temperature. This study focused on the synthesis of La2Zr2O7 powders by soft chemistry (citrate, coprecipitation, and sol-gel methods), and the effects of the solvent and the nature of the precursors used on the powder properties were investigated. The nature of the counter-cation influenced the structural phase of the compound. A low polarizable counter-cation (chloride) permitted the elaboration of a pyrochlore structure within a larger range of parameters compared with highly polarizable counter-cations (nitrate and acetate). Moreover, the nature of the solvent, and specifically the strength of the interactions within it, had an impact on the particle size. Specifically, the use of water, which is a solvent with strong interactions, led to a smaller particle size than the use of ethanol, which has weaker interactions. Based on these results, the crystalline phase of the powders can be predicted as a function of the precursor and the solvent used for the different synthesis routes, and the particle size can be used to evaluate the reactivity of the powders. [ABSTRACT FROM AUTHOR]

Solution precursor plasma spraying (SPPS) is an innovative process for obtaining finely structured coatings from metallic salt solutions. Lanthanum and zirconium precursors were studied to understand their influence on lanthanum zirconate (LaZrO) synthesis by SPPS. Thermal analysis revealed that the nature of the precursor and the solvent affected mixture decomposition by changing the decomposition temperature. The surface tensions of precursor solutions in various media were investigated and revealed the influence of the nature of the counter-cation. Different solutions of precursor mixtures were used to obtain LaZrO splats on metallic substrates. A decrease in solution surface tension led to an increase in splat size. Coating mechanisms by SPPS are governed by the nature of the precursors and solvents. [ABSTRACT FROM AUTHOR]

Nephroblastoma (Wilms' tumor; WT) is the most common renal tumor of childhood. To date, several genetic abnormalities predisposing to WT have been identified in rare overgrowth syndromes. Among them, abnormal methylation of the 11p15 region, GPC3 and DIS3L2 mutations, which are responsible for Beckwith-Wiedemann, Simpson-Golabi-Behmel and Perlman syndromes, respectively. However, the underlying cause of WT remains unknown in the majority of cases. We report three unrelated patients who presented with WT in addition to a constitutional 9q22.3 microdeletion and dysmorphic/overgrowth syndrome. The size of the deletions was variable (ie, from 1.7 to 8.9 Mb) but invariably encompassed the PTCH1 gene. Subsequently, we identified a somatic PTCH1 nonsense mutation in the renal tumor of one patient. In addition, by array comparative genomic hybridization method, we analyzed the DNA extracted from the blood samples of nine patients with overgrowth syndrome and WT, but did not identify any deleterious chromosomal imbalances in these patients. These findings strongly suggest that patients with constitutional 9q22.3 microdeletion have an increased risk of WT, and that PTCH1 have a role in the pathogenesis of nephroblastomas. [ABSTRACT FROM AUTHOR]

Porous potassium based geopolymers with a mutli-scale porosity were synthesized. Silica fume is introduced as an additive to the geopolymer formulation. The free silicon contained inside this silica fume is oxidized in alkaline solution, releasing molecular hydrogen which generates the porosity. Previous work has shown how the porosity can be controlled with temperature, repeated temperature cycles and the mass introduced. Using this protocol, homogeneous foams were made and then studied with scanning electron microscopy. In particular the foam expansion has been followed with time in relation to the microstructure. The thermal conductivity values of the foams were evaluated using a fluxmeter method. The effective thermal conductivities are comprised between 0.12 and 0.35 W m K for apparent densities ranging from 0.40 to 0.85 g cm. The corresponding calculated pore volume fractions are in the range of 65-85%. The interest of this material is that it combines the advantages of low bulk density and insulating properties with the characteristics of a geopolymer skeleton. Literature reports a very good fire and acid/base resistance, a low cost of production and the possibility of recycling industrial waste in the form of silica fume. [ABSTRACT FROM AUTHOR]

The behavior of sodium silicate solutions in an alkaline medium has been studied in the 11.56-9 pH range by adding different amount of hydrochloric acid into a concentrated commercial solution ([Si] = 7 mol/L, Si/Na = 1.71, pH = 11.56). The formed products and their evolution during long ripening (up to 150 days) have been characterized by cryo-SEM, elementary analysis (ICP-AES), X-ray diffraction and surface area and relative density measurements. In the studied narrow ranges of pH (11.56-9) and silicon concentration (7-0.2 mol/L) four different situations have been observed: (i) a stable and clear solution, (ii) a reversible and transparent physical gel; (iii) a soluble white gel characterized by a significant contraction during ripening and (iv) an irreversible gel which presents a slow syneresis leading to a consolidate solid. The characterizations of the different solids, liquids and gels have shown that the observed behaviors were the results of the formation of nanometric soluble NaSiO particles and/or insoluble silica-like (NaSiO) grains and of the contribution of a dissolution/precipitation mechanism. [ABSTRACT FROM AUTHOR]

In this work, we present the opportunity to prepare perovskite materials in powder and in balls by sol–gel process. BaTiO3 as spheres of 1–2 mm in diameter, presenting the same physico-chemical properties than powders, have been prepared by an oil-drop process. The shape forming of a dielectric material permits its use in a plasma reactor and promotes the efficiency of the system. [ABSTRACT FROM AUTHOR]

Silver-Russell syndrome (SRS, OMIM 180860) is a congenital disorder characterized by severe intrauterine and postnatal growth retardation, dysmorphic facial features and body asymmetry. SRS is genetically heterogenous with maternal uniparental disomy with respect to chromosome 7 occurring in ∼10% of affected individuals. Given the crucial role of the 11p15 imprinted region in the control of fetal growth, we hypothesized that dysregulation of genes at 11p15 might be involved in syndromic intrauterine growth retardation. We identified an epimutation (demethylation) in the telomeric imprinting center region ICR1 of the 11p15 region in several individuals with clinically typical SRS. This epigenetic defect is associated with, and probably responsible for, relaxation of imprinting and biallelic expression of H19 and downregulation of IGF2. These findings provide new insight into the pathogenesis of SRS and strongly suggest that the 11p15 imprinted region, in addition to those of 7p11.2-p13 and 7q31-qter, is involved in SRS. [ABSTRACT FROM AUTHOR]