Revealing the impact of organic spacers and cavity cations on quasi-2D perovskites via computational simulations

Two-dimensional hybrid lead iodide perovskites based on methylammonium (MA) cation and butylammonium (BA) organic spacer—such as BA2MAn−1PbnI3n+1—are one of the most explored 2D hybrid perovskites in recent years. Correlating the atomistic profile of these systems with their optoelectronic properties is a challenge for theoretical approaches. Here, we employed first-principles calculations via density functional theory to show how the cation partially canceled dipole moments through the NH3+ terminal impact the structural/electronic properties of the PbnI3n+1 sublattices. Even though it is known that at high temperatures, the organic cation assumes a spherical-like configuration due to the rotation of the cations inside the cage, our results discuss the correct relative orientation according to the dipole moments for ab initio simulations at 0 K, correlating well structural and electronic properties with experiments. Based on the combination of relativistic quasiparticle correction and spin-orbit coupling, we found that the MA horizontal-like configuration concerning the inorganic sublattice surface leads to the best relationship between calculated and experimental gap energy throughout n = 1, 2, 3, 4, and 5 number of layers. Conversely, the dipole moments cancellation (as in BA-MA aligned-like configuration) promotes the closing of the gap energies through an electron depletion mechanism. We found that the anisotropy → isotropy optical absorption conversion (as a bulk convergence) is achieved only for the MA horizontal-like configuration, which suggests that this configuration contribution is the majority in a scenario under temperature effects

Effects of the addition of glass fibers, mica and vermiculite on the mechanical properties of a gypsum-based composite at room temperature and during a fire test

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Impact of perlite, vermiculite and cement on the Young modulus of a plaster composite material: Experimental, analytical and numerical approaches

International audienceThe mechanical behavior of a new composite material used in building construction is studied in this work. The composite panel results of combination of a calcium sulfate hydrates matrix mainly water and inorganic mineral additives. The effective young modulus of the composite is measured by three bending test. Analytical and numerical models are used to determine the composite young modulus which can be expected vs the type and rate of additives. The experimental values are compared with analytical and numerical results. The results from models are near or lightly lower than the experimental values and allow an estimation of the effective properties which can be expected for the new composite developed. (C) 2016 Elsevier Ltd. All rights reserved

Study of the KNO3–LiNO3 and KNO3–NaNO3–LiNO3 eutectics as phase change materials for thermal storage in a low-temperature solar power plant

International audienceFor heat storage applications, the solid–liquid phase changes of the LiNO3–KNO3 and LiNO3–KNO3–NaNO3 mixtures of eutectic compositions have been investigated by Differential Scanning Calorimetry (DSC) and with a home built calorimeter working on large samples – typically 500 g. The design of the new calorimeter matches at best the geometry and the thermal transfers in the industrial application. The kinetics of crystallization has been particularly studied. Density measurements of the salts in the liquid state allowed to calculate the volumetric storage capacit

Impact of perlite, vermiculite and cement on the thermal conductivity of a plaster composite material: Experimental and numerical approaches

International audienceThis work is dealing with the thermo mechanical behaviour of a new composite material used as thermal insulator and for fire passive protection in building construction. The composite panel results of combination of a calcium sulphate hydrates matrix mainly water and inorganic mineral additives. The effective thermal conductivity of the composite is measured by the hot-disc method. Analytical and numerical models are used to determine the composite thermal conductivity which can be expected vs the rate of additives. The experimental values are compared with analytical and numerical models. In particular, effective medium percolation theory (EMPT) for a two-phase system gives analytical values which are close to the experimental results. Moreover, the numerical model based on a simple description can allow the description of the thermal conductivity evolution with the rate of additives. An unexpected phenomenon which can be attributed to the confined water in additives can explain the gap between the numerical models and the experimental results

A new composite based on gypsum matrix and mineral additives: Hydration process of the matrix and thermal properties at room temperature

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Heated blends of phosphate waste: Microstructure characterization, effects of processing factors and use as a phosphorus source for alfalfa growth

International audienceMicrostructure of expandable lightweight aggregates (LWAs), which was composed of phosphate waste (PW), cement kiln dust (CKD) and raw clay (RC) was investigated, and the effects of processing factors (temperature, waste content, soaking time) on their physical properties were quantified by using response surface methodology (RSM). The potential use of LWAs as a phosphorus source was assessed through the use of seeds of alfalfa. It was found that the main minerals of the waste, namely carbonates and fluorapatite, were involved in the formation of labradorite/anorthite and melt respectively. Stability of mullite- the main constituent of CKD- was sensitive to the melt content. The assemblage of the identified phases was discussed based on the CaO-SiO2-Al2O3 phase diagram. The results of RSM showed that the change of compressive strength, firing shrinkage and water absorption of LWAs versus processing factors was well described with a polynomial model and the weights of the effects of the factors increased in the following order: sintering temperature > waste content (in the case of PW-RC) > soaking time. On the other hand, it was found that due to the release of phosphorus by soil-embedded pellets, the growth of alfalfa plants improved, and the rate enhanced in this order: PW-RC > PW-CKD > PW-CKD-RC. The absorbed quantity of phosphorus (0.12%) was still lower than the common uptake amount. (C) 2016 Elsevier Ltd. All rights reserved

Heated blends of clay and phosphate sludge: Microstructure and physical properties

International audienceBlends of a naturally occurring clay (0-30 wt.%) and phosphate sludge were heated at different temperatures and times and their microstructures were investigated using impedance spectroscopy, dilatometry, X-ray diffraction and scanning electron microscope. The weights of the effects of the change of temperature, soaking time and clay addition on some physical ceramic properties (shrinkage, water absorption and compressive strength) were assessed. For the latter purpose, the response surface methodology was used. The results showed that the sintering process was effective between 750 and 1000 degrees C and occurred by melt flow. It was accompanied with low activation energy for ionic conduction (0.20-0.35 eV). Due to the quantitative formation of gehlenite (the unique neoformed phase), the ionic conduction regressed and the melt formation was limited. Also, it was shown that the effects of the experimental factors on physical properties of the blends were well described with the adopted polynomial models, and the weights of the effects of the factors followed the order: temperature > clay content > soaking time. The effects of the interactions between the factors on the properties studied were evaluated and discussed in relation to the microstructure change. (C) 2015 The Ceramic Society of Japan and the Korean Ceramic Society. Production and hosting by Elsevier B.V. All rights reserved

Analyse calorimétrique de matériau de stockage thermique pour valorisation de chaleur fatale industrielle,

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