Oxidation kinetics of a Ni-Cu based cermet at high temperature

The oxidation kinetics of a cermet composed of Ni–Cu alloy and nickel ferrite was studied by thermogravimetry at 960 °C under oxygen in the range 0.5–77 kPa. After an initial mass increase up to 15 g/m2 due to oxidation of surface metallic particles, the mass change was attributed to both outwards NiO growth and internal oxidation. Above 40 g/m2, the NiO scale thickness remained constant and the oxidation kinetics followed a complete parabolic law. The variations of the kinetic rate with oxygen partial pressure allowed to propose mechanisms, rate-controlling steps and kinetic laws in both transient and long term oxidation periods

Regressive approach for predicting bearing capacity of bored piles from cone penetration test data

© 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. In this study, the least square support vector machine (LSSVM) algorithm was applied to predicting the bearing capacity of bored piles embedded in sand and mixed soils. Pile geometry and cone penetration test (CPT) results were used as input variables for prediction of pile bearing capacity. The data used were collected from the existing literature and consisted of 50 case records. The application of LSSVM was carried out by dividing the data into three sets: a training set for learning the problem and obtaining a relationship between input variables and pile bearing capacity, and testing and validation sets for evaluation of the predictive and generalization ability of the obtained relationship. The predictions of pile bearing capacity by LSSVM were evaluated by comparing with experimental data and with those by traditional CPT-based methods and the gene expression programming (GEP) model. It was found that the LSSVM performs well with coefficient of determination, mean, and standard deviation equivalent to 0.99, 1.03, and 0.08, respectively, for the testing set, and 1, 1.04, and 0.11, respectively, for the validation set. The low values of the calculated mean squared error and mean absolute error indicated that the LSSVM was accurate in predicting the pile bearing capacity. The results of comparison also showed that the proposed algorithm predicted the pile bearing capacity more accurately than the traditional methods including the GEP model

Études thermodynamiques sur les Semi-Clathrate Hydrates de TBAB + gaz contenant du Dioxyde de Carbone

CO2 capture has become an important area of research mainly due to its drastic green-house effects. Gas hydrate formation as a separation technique shows tremendous potential, both from a physical feasibility as well as an envisaged lower energy utilization criterion. Briefly, gas (clathrate) hydrates are non-stoichiometric, ice-like crystalline compounds formed through a combination of water and suitably sized guest molecule(s) under low-temperatures and elevated pressures. As the pressure required for gas hydrate formation is generally high, therefore, aqueous solution of tetra-n-butyl ammonium bromide (TBAB) is added to the system as a gas hydrate promoter. TBAB generally reduces the required hydrate formation pressure and/or increases the formation temperature as well as modifies the selectivity of hydrate cages to capture CO2 molecules. TBAB also takes part in the hydrogen-bonded cages. Such hydrates are called "semi-clathrate" hydrates. Evidently, reliable and accurate phase equilibrium data, acceptable thermodynamic models, and other thermodynamic studies should be provided to design efficient separation processes using the aforementioned technology. For this purpose, phase equilibria of clathrate/semi-clathrate hydrates of various gas mixtures containing CO2 (CO2 + CH4/N2/H2) in the presence of pure water and aqueous solutions of TBAB have been measured in this thesis. In the theoretical section of the thesis, a thermodynamic model on the basis of the van der Waals and Platteeuw (vdW-P) solid solution theory along with the modified equations for determination of the Langmuir constants of the hydrate formers has been successfully developed to represent/predict equilibrium conditions of semi-clathrate hydrates of CO2, CH4, and N2. Later, several thermodynamic consistency tests on the basis of Gibbs-Duhem equation as well as a statistical approach have been applied on the phase equilibrium data of the systems of mixed/simple clathrate hydrates to conclude about their quality.Capturer le CO2 est devenu un domaine de recherche important en raison principalement des forts effets de serre dont il est jugé responsable. La formation d'hydrate de gaz comme technique de séparation montre un potentiel considérable, d'une part pour sa faisabilité physique et d'autre part pour une consommation énergétique réduite. En bref, les hydrates de gaz (clathrates) sont des composés ″cages″ non-stoechiométriques, cristallins comme la glace et formés par une combinaison de molécules d'eau et de molécules hôtes convenables, à basses températures et pressions élevées. Puisque la pression exigée pour la formation d'hydrate de gaz est généralement forte, il est judicieux d'ajouter du bromure tétra-n-butylique d'ammonium (TBAB) comme promoteur de formation d'hydrate de gaz. En effet, le TBAB permet généralement de réduire la pression exigée et/ou d'augmenter la température de formation aussi que de modifier la sélectivité des cages d'hydrates au profit des molécules de CO2. TBAB participe à la formation des cages par liaisons ″hydrogène″. De tels hydrates sont nommés "semi-clathrate hydrates". Évidemment, des données d'équilibres de phase fiables et précises, des modèles thermodynamiques acceptables, et d'autres études thermodynamiques sont requises pour concevoir des procédés de séparation efficaces utilisant la technologie mentionnée ci-dessus. Dans ce but, des équilibres de phase de clathrate/semi-clathrate hydrates de de divers mélanges avec des gaz contenant CO2 (CO2 + CH4/N2/H2) ont été mesurés, ici, en présence d'eau pure et de solutions aqueuses de TBAB. La partie théorique de la thèse présente un modèle thermodynamique développé avec succès sur la base de la théorie des solutions solides de van der Waals et Platteeuw (vdW-P) associée aux équations modifiées de la détermination des constantes de Langmuir des promoteurs d'hydrates pour la représentation/prédiction des équilibres en présence de ″semi-clathrate hydrates″ de CO2, CH4, et N2. Plusieurs tests de cohérence thermodynamique basés soit sur l'équation de Gibbs-Duhem, soit sur une approche statistique ont été appliqués aux données d'équilibre de phase des systèmes de ″clathrate hydrates″ simples/mélanges afin de statuer sur leur qualité

Thermodynamic studies on Semi-Clathrate Hydrates of TBAB + gases containing Carbon Dioxide

Capturer le CO2 est devenu un domaine de recherche important en raison principalement des forts effets de serre dont il est jugé responsable. La formation d'hydrate de gaz comme technique de séparation montre un potentiel considérable, d'une part pour sa faisabilité physique et d'autre part pour une consommation énergétique réduite. En bref, les hydrates de gaz (clathrates) sont des composés ″cages″ non-stoechiométriques, cristallins comme la glace et formés par une combinaison de molécules d'eau et de molécules hôtes convenables, à basses températures et pressions élevées. Puisque la pression exigée pour la formation d'hydrate de gaz est généralement forte, il est judicieux d'ajouter du bromure tétra-n-butylique d'ammonium (TBAB) comme promoteur de formation d'hydrate de gaz. En effet, le TBAB permet généralement de réduire la pression exigée et/ou d'augmenter la température de formation aussi que de modifier la sélectivité des cages d'hydrates au profit des molécules de CO2. TBAB participe à la formation des cages par liaisons ″hydrogène″. De tels hydrates sont nommés "semi-clathrate hydrates". Évidemment, des données d'équilibres de phase fiables et précises, des modèles thermodynamiques acceptables, et d'autres études thermodynamiques sont requises pour concevoir des procédés de séparation efficaces utilisant la technologie mentionnée ci-dessus. Dans ce but, des équilibres de phase de clathrate/semi-clathrate hydrates de de divers mélanges avec des gaz contenant CO2 (CO2 + CH4/N2/H2) ont été mesurés, ici, en présence d'eau pure et de solutions aqueuses de TBAB. La partie théorique de la thèse présente un modèle thermodynamique développé avec succès sur la base de la théorie des solutions solides de van der Waals et Platteeuw (vdW-P) associée aux équations modifiées de la détermination des constantes de Langmuir des promoteurs d'hydrates pour la représentation/prédiction des équilibres en présence de ″semi-clathrate hydrates″ de CO2, CH4, et N2. Plusieurs tests de cohérence thermodynamique basés soit sur l'équation de Gibbs-Duhem, soit sur une approche statistique ont été appliqués aux données d'équilibre de phase des systèmes de ″clathrate hydrates″ simples/mélanges afin de statuer sur leur qualité.CO2 capture has become an important area of research mainly due to its drastic green-house effects. Gas hydrate formation as a separation technique shows tremendous potential, both from a physical feasibility as well as an envisaged lower energy utilization criterion. Briefly, gas (clathrate) hydrates are non-stoichiometric, ice-like crystalline compounds formed through a combination of water and suitably sized guest molecule(s) under low-temperatures and elevated pressures. As the pressure required for gas hydrate formation is generally high, therefore, aqueous solution of tetra-n-butyl ammonium bromide (TBAB) is added to the system as a gas hydrate promoter. TBAB generally reduces the required hydrate formation pressure and/or increases the formation temperature as well as modifies the selectivity of hydrate cages to capture CO2 molecules. TBAB also takes part in the hydrogen-bonded cages. Such hydrates are called "semi-clathrate" hydrates. Evidently, reliable and accurate phase equilibrium data, acceptable thermodynamic models, and other thermodynamic studies should be provided to design efficient separation processes using the aforementioned technology. For this purpose, phase equilibria of clathrate/semi-clathrate hydrates of various gas mixtures containing CO2 (CO2 + CH4/N2/H2) in the presence of pure water and aqueous solutions of TBAB have been measured in this thesis. In the theoretical section of the thesis, a thermodynamic model on the basis of the van der Waals and Platteeuw (vdW-P) solid solution theory along with the modified equations for determination of the Langmuir constants of the hydrate formers has been successfully developed to represent/predict equilibrium conditions of semi-clathrate hydrates of CO2, CH4, and N2. Later, several thermodynamic consistency tests on the basis of Gibbs-Duhem equation as well as a statistical approach have been applied on the phase equilibrium data of the systems of mixed/simple clathrate hydrates to conclude about their quality

Evaluation of experimental data for wax and diamondoids solubility in gaseous systems

International audienceThe Leverage statistical approach is herein applied for evaluation of experimental data of the paraffin waxes/diamondoids solubility in gaseous systems. The calculation steps of this algorithm consist of determination of the statistical Hat matrix, sketching the Williams Plot, and calculation of the residuals of two selected correlations results. In addition, the applicability domains of the investigated correlations and quality of the existing experimental data are examined accompanied by outlier diagnostics. Two previously applied Chrastil-type correlations including the original Chrastil and Mèndez-Santiago and Teja correlations are used to calculate/estimate the solubility of paraffin waxes (including n-C 24H 50 to n-C 33H 68) and diamondoids (adamantane and diamantane) in carbon dioxide/ethane gases, respectively. It can be interpreted from the obtained results that the applied equations for calculation of the corresponding solubilities are statistically valid and correct, and none of the experimental data can be designated as outliers

A statistical method for evaluation of the experimental phase equilibrium data of simple clathrate hydrates

International audienceWe, herein, present a statistical method for diagnostics of the outliers in phase equilibrium data (dissociation data) of simple clathrate hydrates. The applied algorithm is performed on the basis of the Leverage mathematical approach, in which the statistical Hat matrix, Williams Plot, and the residuals of a selected correlation results lead to define the probable outliers. This method not only contributes to outliers diagnostics but also identifies the range of applicability of the applied model and quality of the existing experimental data. The available correlation in the literature in exponential form is used to represent/predict the hydrate dissociation pressures for three-phase equilibrium conditions (liquid water/ice-vapor-hydrate). The investigated hydrate formers are methane, ethane, propane, carbon dioxide, nitrogen, and hydrogen sulfide. It is interpreted from the obtained results that the applied correlation for calculation/estimation of the phase behavior of simple clathrate hydrate systems is statistically valid and correct, 5 hydrate dissociation data are found to be probable doubtful ones and 10 data points are out of applicability domain of the applied correlation

Semi-clathrate hydrate phase equilibrium measurements for the CO2+H2/CH4+tetra-n-butylammonium bromide aqueous solution system

International audienceIn this communication, clathrate/semi-clathrate hydrate dissociation conditions for the systems containing mixtures of CO2 (0.1481/0.3952/0.7501 mol fraction)+H2 (0.8519/0.6048/0.2499 mol fraction) in the presence of water or 0.05 and 0.30 mass fractions tetra-n-butylammonium bromide (TBAB) aqueous solutions and CO2 (0.4029 mol fraction)+CH4 (0.5971 mol fraction) in the presence of water, 0.05 and 0.3 mass fractions TBAB have been measured and are reported. An apparatus comprising a high pressure equilibrium cell as the main part has been employed for the measurements following the isochoric pressure-search method. The range of conditions for the measurements are 275.5-292.8 K up to 15.91 MPa. Significant decrease in operating pressure of gas hydrate formation for separation of CO2 from the corresponding gas mixtures is observed due to the promotion effects of TBAB

Monodisperse thermodynamic model based on chemical + flory-Hüggins polymer solution theories for predicting asphaltene precipitation

International audienceAsphaltene precipitation is traditionally modeled using the Flory-Hüggins polymer solution theory. The existing thermodynamic models, generally, do not take into account the aggregation/association phenomena in the system. This work aims at providing a monodisperse thermodynamic model for estimating asphaltene precipitation by taking into account the aforementioned phenomena. The chemical theory of associated solutions with physical interactions along with the Flory-Hüggins polymer solution theory is applied to develop this model. The results of this method are compared with some selected experimental data from the literature. It is shown that taking into account the aggregation/association phenomena in the system can lead to better predictions of the model. Moreover, it is shown that this method simplifies to the existing activity coefficient based models when ignoring the association