43 research outputs found
Study of titanium(IV) speciation in sulphuric acid solutions by FT-Raman spectrometry
Issu de : ICSC30 2007 - 30th International Conference on Solution Chemistry, Perth, AUSTRALIA, 16-20 July 2007International audienceThe effects of the addition of titanium(IV) to aqueous solutions of sulphuric acid were studied by FT-Raman spectroscopy. Solutions containing 0 M to 4.01 M of titanium(IV) and 1.98 M to 6.17 M of sulphuric acid were analysed. A new peak, characteristic of titano-sulphate complexes, has been observed, in addition to the peaks characterising ions SO42â and HSO4â. Free HSO4â and SO42â concentrations have been determined from the Raman peak areas. From mass balance it was deduced that two complexes are present in the solution: [Ti(OH)2SO4] (aq) and [Ti(OH)2(SO4)2]2â (aq). Their apparent constants of formation have been estimated
Optimal control of crystallization of alpha-lactose monohydrate
16 pagesInternational audienceWe present a mathematical model for solvated crystallization of alpha -lactose monohydrate in semi-batch mode. The process dynamics are governed by conservation laws including population, molar and energy balance equations. We present and discuss the model and then control the process with the goal to privilege the production of small particles in specific the range. We compare several specific and unspecific cost functions leading to optimal strategies with significantly different effects on product quality. Control inputs are temperature, feed rate, and the choice of an appropriate crystal seed
Amorphous magnesium silicate ultrasound-assisted precipitation in a mixing system: Population balance modelling and crystallization rates identification
International audienceNatural talc is a very interesting filler for plastic and rubber materials and paints because it enables polymer matrix properties to be improved. Nano-sized particles are required to get a good dispersion of the solid in the polymer matrix. However, at the moment the main drawback in the use of natural talc is that, with a conventional milling process, nanometric particle sizes are difficult and expensive to obtain. A process of magnesium silicate synthesis made by ultrasound-assisted precipitation has been developed in two steps. The first step consists of the synthesis of amorphous magnesium silicate by precipitation from sodium metasilicate and acid magnesium chloride. In the second step, the amorphous solid is transformed in a crystalline solid under pressure. In this study an ultrasound-assisted synthesis of amorphous magnesium silicate is proposed. Some process parameters (ultrasound power, initial reactants molalities and reactants flow rate) have effects on the particle-size distribution. The population balance is modelled and solved by moments method in the steady state to identify nucleation and growth rates and agglomeration kernel as a function of operating conditions and to understand how these conditions affect the particle-size distribution
Stabilisation of heavy metal from automobile shredder residues : beneficial reuse of the residues
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ContrÎle de la cristallisation du alpha-lactose monohydraté
National audienceLa cristallisation est une opĂ©ration utilisĂ©e dans diffĂ©rents domaines industriels comme la pharmacie, l'agro-alimentaire ou la chimie fine. Ce processus consiste Ă isoler un produit en solution pour le rĂ©cupĂ©rer sous forme solide dans l'objectif de confĂ©rer au solide synthĂ©tisĂ© des spĂ©cifications voulues en vue de contrĂŽler ses propriĂ©tĂ©s d'usage. Un grand intĂ©rĂȘt est portĂ© Ă l'Ă©tude du processus de cristallisation afin de le maĂźtriser, et donc d'amĂ©liorer les propriĂ©tĂ©s du produit final. Un modĂšle dynamique fiable dĂ©crivant les phĂ©nomĂšnes mis en jeu est nĂ©cessaire pour l'Ă©tudier, et appliquer des stratĂ©gies de contrĂŽle afin de produire des solides conformes aux cahiers des charges et aux exigences industrielles. Dans ce travail, nous nous intĂ©ressons Ă la cristallisation du α-lactose monohydratĂ© en mode semi-continu avec ensemencement. Le lactose est un sucre rĂ©ducteur prĂ©sent dans le lait, qui existe sous deux formes anomĂ©riques α et ÎČ en solution (mutarotation). La modĂ©lisation mathĂ©matique de la cristallisation du α-lactose monohydratĂ© comprend le bilan de population sur les cristaux de α-lactose monohydratĂ©, les bilans de matiĂšres sur le α-lactose, le ÎČ-lactose et l'eau, avec prise en compte de la mutarotation et le bilan d'Ă©nergie. Cette Ă©tude prĂ©sente le contrĂŽle du processus de cristallisation selon deux objectifs d'optimisation : minimisation du taux de nuclĂ©ation et minimisation du coefficient de variation de la distribution de taille en volume
De l'industrialisation à l'innovation pédagogique avec une chaßne éditoriale
International audienceThe « Groupe des Ecoles des Mines » (GEM) has experimented and established a publishing chain for the production of educational resources. After an exploratory phase and feedbacks with the first uses of existing tools, the ICTE GEM teams have developed various document models to meet the expectations of teachers and to allow the achievement of media for targeted educational practices. Now, teachers have access to innovative tools enabling the creation of complex resources (supports for smartphones or tools allowing non-linear path).Le Groupe des Ecoles des Mines (GEM) a expérimenté et mis en place une chaine éditoriale pour la production de ressources pédagogiques. AprÚs une phase exploratoire et des retours sur les premiers usages avec les outils existants, les équipes TICE des écoles ont conçu divers modÚles documentaires pour répondre aux attentes des enseignants et permettre la réalisation de supports pour des usages pédagogiques ciblés. Ces derniers ont ainsi aujourd'hui à leur disposition des outils innovants autorisant la création de ressources complexes (supports pour smartphones ou outils autorisant des parcours non-linéaires)
L'apprentissage en autonomie. Exemple de formation en ligne sur les fondamentaux de la cristallisation
National audienceUn cours en ligne sur les fondamentaux de la cristallisation et la précipitation a été conçu par une communauté de chercheurs et d'enseignants-chercheurs en cristallisation/précipitation. Ce cours vise plusieurs publics : élÚves ingénieurs, étudiants de master, doctorants, enseignants, industriels. Aussi correspond-il en pratique à plusieurs types de prestations et d'outils pédagogiques, qui vont au-delà d'un simple document consultable à distance. Le cours propose déjà des outils pédagogiques originaux : - auto-apprentissage avec multiples animations illustratives et entrées possibles, - auto-évaluation à distance, sur la base d'exercices applicatifs interactifs. Pour aller plus loin dans la compréhension de ce qui se passe lors d'une cristallisation, l'intégration de programmes de simulation interactifs dans le support pédagogique a été réalisée. Ces simulateurs pédagogiques permettent de mettre en évidence la sensibilité d'une opération de cristallisation aux valeurs de ses paramÚtres opératoires
Détection de la nucléation de cristaux de glace au voisinage d'une bulle de cavitation
International audienceThe application of power ultrasound in liquids produces thousands of bubbles. This phenomenon is called acoustic cavitation. The bubbles formed do not have the same size, their oscillations are not in phase, and their spatial density in the fluid is very not homogeneous: this phenomenon is thus very complex and involves multiple variables which are very difficult to isolate. Even if the phenomenon is chaotic, its macroscopic effects on the nucleation and growth of of ice crystals in undercooled solutions are noticeable. These effects have a crucial importance for industrial applications such as freezing and lyophilisation (also called freeze drying) of pharmaceutics products. Although the effects of ultrasound on crystallization are well-known, their physical origin remains unclear. Multi-bubble experiments do not give any hint in the microscopic mechanisms involved. Therefore, in order to isolate the main actor of these effects, this study aims at creating and observing a single cavitation bubble. To do so, a cubic levitation cell with optical glass walls was build. In this cell, in order to maintain a single bubble levitating, a pressure wave is imposed by a piezoelectric ceramic glued to the base of the cell. A piezoelectric microphone is also glued on the lateral wall in order to record the bubble response, which is strongly linked to the bubble dynamics. The presence or appearance of any foreign body near the levitating bubble may perturb the latter and alter the periodicity of its oscillation. We wish to exploit this loss of periodicity for early detection of crystals nucleation near the bubble. As a preliminary step, to simulate the later, a micro-fiber of diameter smaller than 50 ÎŒm is approached to the bubble. By performing an autocorrelation study of the microphone signal, we can detect the perturbation of the periodicity of the bubble dynamics. In a second step, crystallization experiments will be conducted, and the detection principle will be used to trigger the recording of images in the early phase of the crystals formation.L'application des ultrasons de puissance dans un liquide produit des milliards de bulles. Ce phĂ©nomĂšne est appelĂ© cavitation acoustique. Les bulles formĂ©es ne font pas toutes la mĂȘme taille, leurs oscillations ne sont pas en phase, et leur densitĂ© spatiale dans le fluide est trĂšs inhomogĂšne: ce phĂ©nomĂšne trĂšs complexe implique donc de nombreuses variables difficiles Ă isoler. MĂȘme si le phĂ©nomĂšne est chaotique, ses effets macroscopiques sur la nuclĂ©ation et la croissance des cristaux de glace dans une solution sous-refroidie sont notables. Ces effets sont d'une importance capitale pour des applications industrielles comme la congĂ©lation ou la lyophilisation. Bien que les effets des ultrasons sur la cristallisation soient rĂ©putĂ©s, leur origine reste mal connue. Les expĂ©riences impliquant des milliards de bulles ne fournissent aucune piste sur les mĂ©canismes microscopiques mis en jeu. Afin d'isoler l'acteur essentiel de ces effets, l'Ă©tude menĂ©e vise Ă crĂ©er et observer une bulle unique de cavitation. Pour cela, une cellule de lĂ©vitation carrĂ©e en verre a Ă©tĂ© conçue. Dans cette cellule, pour maintenir une bulle unique en lĂ©vitation, une onde de pression est imposĂ©e par un piĂ©zoĂ©lectrique positionnĂ© Ă la base de la cellule. Un microphone est collĂ© sur une face latĂ©rale afin d'enregistrer sa rĂ©ponse qui est fortement liĂ©e Ă la dynamique de la bulle. Lorsque un corps Ă©tranger apparaĂźt ou s'approche de la bulle, il la perturbe et affecte sa pĂ©riodicitĂ©. Nous souhaitons exploiter cette perturbation pour dĂ©tecter la formation des premiers cristaux au voisinage de la bulle. Dans un premier temps, afin de simuler cette perturbation, une micro-fibre de diamĂštre infĂ©rieur Ă 50 ”m est approchĂ©e de la bulle. L'Ă©tude de l'auto-corrĂ©lation du signal du microphone nous permet de dĂ©tecter la perturbation engendrĂ©e sur la pĂ©riodicitĂ© de la dynamique de bulle. Dans un second temps, des expĂ©riences de cristallisation seront menĂ©es, et le principe de dĂ©tection sera alors mis Ă profit pour dĂ©clencher l'enregistrement d'images dans la phase initiale de formation des cristaux
Perturbation of a radially oscillating single-bubble by a micron-sized object
A single bubble oscillating in a levitation cell is acoustically monitored by a piezo-ceramics microphone glued on the cell external wall. The correlation of the filtered signal recorded over distant cycles on one hand, and its harmonic content on the other hand, are shown to carry rich information on the bubble stability and existence. For example, the harmonic content of the signal is shown to increase drastically once air is fully dissociated in the bubble, and the resulting pure argon bubble enters into the upper branch of the sonoluminescence regime. As a consequence, the bubble disappearance can be unambiguously detected by a net drop in the harmonic content. On the other hand, we perturb a stable sonoluminescing bubble by approaching a micron-sized fiber. The bubble remains unperturbed until the fiber tip is approached within a critical distance, below which the bubble becomes unstable and disappears. This distance can be easily measured by image treatment, and is shown to scale roughly with 3â4 times the bubble maximal radius. The bubble disappearance is well detected by the drop of the microphone harmonic content, but several thousands of periods after the bubble actually disappeared. The delay is attributed to the slow extinction of higher modes of the levitation cell, excited by the bubble oscillation. The acoustic detection method should however allow the early detection and imaging of non-predictable perturbations of the bubble by foreign micron-sized objects, such as crystals or droplets