Influence of pressure and dwell time on pressure-assisted sintering of calcium cobaltite

Calcium cobaltite Ca₃Co₄O₉, abbreviated Co349, is a promising thermoelectric material for high-temperature applications in air. Its anisotropic properties can be assigned to polycrystalline parts by texturing. Tape casting and pressure-assisted sintering (PAS) are a possible future way for a cost-effective mass-production of thermoelectric generators. This study examines the influence of pressure and dwell time during PAS at 900°C of tape-cast Co349 on texture and thermoelectric properties. Tape casting aligns lentoid Co349. PAS results in a textured Co349 microstructure with the thermoelectrically favorable ab-direction perpendicular to the pressing direction. By pressure variation during sintering, the microstructure of Co349 can be tailored either toward a maximum figure of merit as required for energy harvesting or toward a maximum power factor as required for energy harvesting. Moderate pressure of 2.5 MPa results in 25% porosity and a textured microstructure with a figure of merit of 0.13 at 700°C, two times higher than the dry-pressed, pressureless-sintered reference. A pressure of 7.5 MPa leads to 94% density and a high power factor of 326 µW/mK² at 800°C, which is 11 times higher than the dry-pressed reference (30 MPa) from the same powder.     

Global modeling of hydrogen using GFDL-AM4.1: Sensitivity of soil removal and radiative forcing

Hydrogen (H₂) has been proposed as an alternative energy carrier to reduce the carbon footprint and associated radiative forcing of the current energy system. Here, we describe the representation of H₂ in the GFDL-AM4.1 model including updated emission inventories and improved representation of H₂ soil removal, the dominant sink of H₂. The model best captures the overall distribution of surface H₂, including regional contrasts between climate zones, when v_d(H₂) is modulated by soil moisture, temperature, and soil carbon content. We estimate that the soil removal of H₂ increases with warming (2–4% per K), with large uncertainties stemming from different regional response of soil moisture and soil carbon. We estimate that H₂ causes an indirect radiative forcing of 0.84 mW m^?2/(Tg(H₂)yr^?1) or 0.13 mW m^?2 ppbv^?1, primarily due to increasing CH₄ lifetime and stratospheric water vapor production.     

Geopolymer assembly by emulsion templating: Emulsion stability and hardening mechanisms

This work investigates emulsion templating to synthesize hexadecane oil/geopolymer composites. In a system with hexadecane as the internal (dispersed) phase and an alkali activated continuous phase without added surfactant, adding aluminosilicate clay particles does not increase resistance against creaming or coalescence, while adding a surfactant (L35 or CTAB) stabilizes the solid-liquid interface. Infrared studies and rheological studies of the associated geopolymerization determined that the presence of the organic phase or surfactant has no significant effect on the geopolymerization kinetics, as determined by the change in time of the Si-O-T IR stretching frequency and the rheological moduli involved during the process. The stabilization of the organic template is reminiscent of Pickering emulsion even though we employ a much greater amount of inorganic material for geopolymer formation. Although the addition of surfactant has a significant effect on the behavior of the paste, the percolation of the network remains unmodified, highlighting the fact that the phenomenon is not dependent on viscosity. Finally, rheological measurements were used to obtain the mass fractal dimension of the as-made gel network, which is able to differentiate the interfacial effect between surfactant molecules with a slightly denser interphase when a cationic surfactant is used.     

Innovative method to produce large-area freestanding functional ceramic foils

Using thick and thin films instead of bulk functional materials presents tremendous advantages in the field of flexible electronics and component miniaturization. Here, a low-cost method to grow and release large-area, microscale thickness, freestanding, functional, ceramic foils is reported. It uses evaporation of sodium chloride to silicon wafer substrates as sacrificial layers, upon which functional lead titanate zirconate ceramic films are grown at 710?°C maximum temperature to validate the method. The freestanding, functional foils are then released by dissolution of the sacrificial sodium chloride in water and have the potential to be integrated into low-thermal stability printed circuits and flexible substrates. The optimization of the sodium chloride layer surface quality and bonding strength with the underlying wafer is achieved thanks to pre-annealing treatment.     

Spirobifluorene Dimers: Understanding How The Molecular Assemblies Drive The Electronic Properties

Spirobifluorene (SBF) is one of the most important scaffolds used in the design of organic semi-conductors (OSCs) for electronics. In recent years, among all the structures developed for these applications, SBF dimers have been highlighted due to their great potential in thermally activated delayed fluorescence and in phosphorescent organic light-emitting diodes. Attaching two SBF units generate 10 dimers, each possessing its own structural specificity, which in turn drives its electronic properties. These ten SBF dimers are gathered herein. Understanding how the molecular assembly determines the electronic properties has been one of the pillars of organic electronics. This is the goal of this article. As positional isomerism is a key tool to design OSCs, defining the design guidelines for the SBF scaffold appears of interest for the future of this building block. Herein, the importance of the two main parameters involved in the electrochemical and photophysical properties, namely the nature of the phenyl linkages and the steric congestion between the two SBF units is discussed. The combination of these two parameters drives the electronic properties but their respective weight is different as a function of the regioisomer involved or of the property considered (frontier orbitals energy level, absorption, fluorescence, phosphorescence).     

Mastering the structure of PLA foams made with extrusion assisted by supercritical CO2

In this study, the outcome of operating conditions of extrusion assisted by supercritical CO₂ for the manufacture of poly(lactic acid) foams was investigated. It was found that the temperature before and inside the die was the most prominent parameter to tune the foam properties. Foam porosity as high as 96% could be obtained (for die temperature between 109 and 112 °C), representing a total expansion exceeding 30. In this temperature range, low crystallinity (≈6%) was induced giving foams with high radial expansion i.e., large diameters and open porosity. At 112 °C, the CO₂ was able to greatly expand the foams, providing 73% of its potential blowing effect. On the other hand, a low die temperature (below a die temperature of 107 °C) induces a significantly higher level of crystallinity resulting in foams with closed‐porosity and a large longitudinal expansion due to higher strength of the polymer melt. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45067.     

Role of ABCA7 in Human Health and in Alzheimer’s Disease

Several studies, including genome wide association studies (GWAS), have strongly suggested a central role for the ATP-binding cassette transporter subfamily A member 7 (ABCA7) in Alzheimer’s disease (AD). This ABC transporter is now considered as an important genetic determinant for late onset Alzheimer disease (LOAD) by regulating several molecular processes such as cholesterol metabolism and amyloid processing and clearance. In this review we shed light on these new functions and their cross-talk, explaining its implication in brain functioning, and therefore in AD onset and development.     

Direct Radiation Effects on the Structure and Stability of Collagen and Other Proteins

In this review, recent progress in understanding the direct effects of radiation on the structure and stability of collagen, the most abundant protein in the human body, and other proteins is surveyed. Special emphasis is placed on the triple-helical structure of collagen, as studied by means of collagen mimetic peptides. The emerging patterns are the dose dependence of radiation processes and their abundance, the crucial role of radicals in covalent-bond formation (crosslinking) or cleavage, and the influence of the radiation energy and nature. Future research should allow fundamental questions, such as charge transfer and fragmentation dynamics triggered by ionization, to be answered, as well as developing applications such as protein-based biomaterials, notably with properties controlled by irradiation.     

Design of Watertight Barriers for Retention Ponds of Cyanide Using Sludge from Water Purification Station （Ziga）

In a context of sustainable development and use of eco- materials, it was examined the possibility of using sewage sludge from the water treatment plant of Ziga as an inorganic support to achieve sealing barriers that can withstand high stresses to overcome any weaknesses of the geological barrier （called passive barrier）. The station Ziga that potabilises the water from the river Nakamb6 is located 45 km north east of Ouagadougou. Some experiments on the rheology of sludge from Ziga as well as the filtration of the mixture Ziga＇s sludge and clays from Nouna, Zorgho and Ticare, three regions of Burkina Faso, were conducted. These studies demonstrated the complex hydro-mechanical behavior of Ziga＇s slurries： Newtonian fluid thixotropic threshold for solids contents less than 16.5 wt% and non-Newtonian for higher values. Sludge from the water treatment station Ziga have a hydraulic conductivity of 10^-8 m/s. The results are below regulatory requirements. However, the permeability can be reduced to achieve the value of 10^-9 m/s in particular by adding the clay from Zorgho or Nouna to mixtures of Ziga＇s sludge and neutral leachate, typically mineral water. Beside neutral leachate, two types of leachate were used. One type is composed of acid leachate and the other type is basic. It was shown that the limewater solutions cause deterioration of the seal probably due to the presence of hydroxide ions.