Nouveaux modèles thermodynamiques pour solutions liquides

Revue de la littérature sur les modèles thermodynamiques pour solutions liquides -- Modèle des solutions idéales -- Modèles des solutions régulières -- Expansions polynomiales de l'énergie en excès -- Solutions diluées -- Solutions aqueuses -- Modèle des complexes anioniques particuliers -- Modèles quasichimiques -- Modèle d'association -- Modèle cellulaire (Kapoor et Frohberg, 1971) -- Modèle des solutions réciproques conformes -- Modèle des solutions réciproques ioniques (Hillert, Jansson, Sundman et Agren, 1985) -- Modèle des solutions réciproques quasichimiques (Dessureault et Pelton, 1991) -- Procédure d'optimisation des paramètres des modèles thermodynamiques -- Contributions aux modèles thermodynamiques pour solutions liquides -- Critique et amélioration des méthodes d'estimation de l'énergie de Gibbs en excès des systèmes multicomposants à partir des paramètres binaires des modèles -- Modifications du modèle quasichimique pour solutions liquides

Tension au travail et consommation de médicaments psychotropes

Les objectifs de cette étude étaient de mesurer l'association entre la tension au travail et l'utilisation de médicaments psychotropes ainsi que l'association entre le ratio efforts extrinsèques/reconnaissance et l'utilisation de médicaments psychotropes chez un groupe de cols blancs de la région de Québec. Les données furent recueillies par questionnaires auto-administrés. L'utilisation de médicaments psychotropes fut mesurée sur une période de 48 heures. La prévalence d'utilisation a été de 6,2%. Aucune association entre la tension au travail et la consommation de médicaments psychotropes ne fut observée. L'inadéquation entre les efforts extrinsèques et la reconnaissance a été associée à l'utilisation de médicaments psychotropes (RC ajusté 1,7; IC 95% 1,4-2,2). Les résultats de cette étude suggèrent que l'inadéquation entre les efforts extrinsèques et la reconnaissance est un déterminant de l'utilisation de médicaments psychotropes. Les efforts intrinsèques, le soutien social ainsi que le sexe ne modifient pas ces associations

Temperature and oxygen adsorption coupling effects upon the surface tension of liquid metals

An accurate knowledge of the surface tension of liquid metals is critical for many theoretical and practical applications, especially in the current context of emerging growth of nanotechnology. The surface tension and its temperature dependence are drastically influenced by the level of impurities in the metal such as oxygen, sulphur or carbon. For this reason, experimental surface tension data of metals reported in literature are scattered. Strictly speaking, when referring to the surface tension of liquid metals, both variables temperature and oxygen content must be specified. There exists no clear formalism describing the coupling effect temperature and the oxygen content upon the surface tension of liquid metals. The aim of this work is to fill this gap. A thermodynamically self-consistent formulation for the surface tension of liquid metals and semiconductors as a function of temperature and oxygen content is established. According to the proposed formalism, a reliable expression for the surface tension of pure and oxygen saturated metals is then derived. The proposed model is found to be in good agreement with available experimental data, showing a good predictive capability. Aluminium is chosen and thoroughly evaluated as a case study, due to its very high sensitivity to oxygen level. Its surface tension is explicitly formulated as a function of temperature and oxygen content

Modeling the Coal Tar Pitch Primary Carbonization Process

ABSTRACT: The properties of the carbon materials obtained as the final product of coal tar pitch carbonization process are a consequence of the type of chemical and physical phenomena occurring through the process. A new simplified approach for modeling of the primary carbonization is presented to provide the semi-quantitative knowledge about the process useful for improving the efficiency of the industries that deal with this process. The proposed approach is based on defining thermodynamic and kinetic equations simply representing numerous phenomena happening during primary carbonization. Partial pressures of emitted volatiles in a simple pitch system are studied. The model enables estimating the mass and enthalpy changes of pitch through thermal treatment consistent with experimental data for mass losses of pitch heat treated up to 550 ◦C. Application of the model to describe molecular weight distribution changes of pitch during primary carbonization is demonstrated, showing a good agreement between the presented results and the investigations reported by Greinke. For the first time, the effect of important parameters in pitch carbonization, such as the heating rate of the pitch and the carrier gas flow rate, on the emission rate of volatiles is successfully modeled. The present model is well able to estimate the energy requirement for thermal treatment of pitch up to 350 ◦C

Why some carbons may or may not graphitize? The point of view of thermodynamics

RÉSUMÉ: Not all carbons graphitize in equal measure. Some will develop a structure which approaches the one of perfect graphite (graphitizable carbons) upon heat treatment, while others will not (non-graphitizable carbons). The present work develops a phenomenological model for the conceptual understanding of graphitizability (capacity to graphitize). To support this model, a mathematical formalism, inspired from thermodynamics, is proposed to calculate the Ultimate Graphitizability (eta(g)) of some graphitizable and non-graphitizable carbon materials. eta(g) is the average interlayer spacing (d(002)) of a graphenic carbon following graphitization at similar to 3400 K. eta(g) can be estimated assuming a topological graphitization mechanism operating between 1700 K and 3400 K. Two independent variables define eta(g): d(002) (T alpha) and d(002) (T beta). T alpha and T beta are arbitrarily selected temperatures between 1700 K and 2550 K (the graphitization threshold). In order to better understand the parameters affecting d(002) (T-alpha) and d(002) (T-beta), new carbonization/ graphitization experimental results are presented. These suggest that d(002)(T-alpha) and d(002) (T-beta) are correlated to the oxygen/hydrogen composition ratio and the relative mesoscale crystallite orientation of some graphitizable carbons following the end of primary carbonization. (C) 2019 The Authors. Published by Elsevier Ltd

Important variation in vibrational properties of LiFePO4 and FePO4 induced by magnetism

A new thermodynamically self-consistent (TSC) method, based on the quasi-harmonic approximation (QHA), is used to obtain the Debye temperatures of LiFePO4 (LFP) and FePO4 (FP) from available experimental specific heat capacities for a wide temperature range. The calculated Debye temperatures show an interesting critical and peculiar behavior so that a steep increase in the Debye temperatures is observed by increasing the temperature. This critical behavior is fitted by the critical function and the adjusted critical temperatures are very close to the magnetic phase transition temperatures in LFP and FP. Hence, the critical behavior of the Debye temperatures is correlated with the magnetic phase transitions in these compounds. Our first-principle calculations support our conjecture that the change in electronic structures, i.e. electron density of state and electron localization function, and consequently the change in thermophysical properties due to the magnetic transition may be the reason for the observation of this peculiar behavior of the Debye temperatures

Experimental determination of the thermal diffusivity of α-Cryolite up to 810 K and comparison with first principles predictions

In aluminum electrolysis cells, a ledge of frozen electrolyte is formed on the sides. Controlling the side ledge thickness (a few centimeters) is essential to maintain a reasonable life span of the electrolysis cell, as the ledge acts as a protective layer against chemical attacks from the electrolyte bath used to dissolve alumina. The numerical modeling of the side ledge thickness, by using, for example, finite element analysis, requires some input data on the thermal transport properties of the side ledge. Unfortunately, there is a severe lack of experimental data, in particular, for the main constituent of the side ledge, the cryolite (Na3AlF6). The aim of this study is twofold. First, the thermal transport properties of cryolite, not available in the literature, were measured experimentally. Second, the experimental data were compared with previous theoretical predictions based on first principle calculations. This was carried out to evaluate the capability of first principle methods in predicting the thermal transport properties of complex insulating materials. The thermal diffusivity of a porous synthetic cryolite sample containing 0.9 wt % of alumina was measured over a wide range of temperature (473–810 K), using the monotone heating method. Because of limited computational resources, the first principle method can be used only to determine the thermal properties of single crystals. The dependence of thermal diffusivity of the Na3AlF6 + 0.9 wt % Al2O3 mixture on the microstructural parameters is discussed. A simple analytical function describing both thermal diffusivity and thermal conductivity of cryolite as a function of temperature is proposed

Experimental study of the Al-Mg-Sr phase diagram at 400°C

TheAl-Mg-Sr systemis experimentally studied at 400∘C using EPMA and XRD techniques. It was determined that the intermetallic phases in the Al-Mg-Sr system have a tendency to form extended substitutional solid solutions. Two ternary phases were found in this system. Solubility limits of binary and ternary phases were determined and the phase equilibria among phases were established. The isothermal section of the Al-Mg-Sr system at 400∘C has been constructed using results of the phase analysis and experimental literature data