Michel Cournil

Study of ammonium chloride crystallization in a mixed vessel

Abstract This work is devoted to the study of ammonium chloride (NH 4 Cl) crystallization from an aqueous solution in a stirred vessel. Initial supersaturation is created by the addition of potassium chloride (KCl) crystals into a nearly saturated NH 4 Cl solution. From continuous recording of both electrical conductivity and turbidity of the medium information can be derived about the crystallization rate and the granular state of the so formed NH 4 Cl crystals. These are ramified agglomerates of 5xa0μm primary crystals. Their size is clearly correlated with the Kolmogorov microscale. Respective roles of primary and secondary nucleation, growth, agglomeration and fragmentation are discussed in the framework of a model.

The influence of aluminium ions on the kinetics of nucleation-growth of potassium dihydrogen phosphate from aqueous solutions

Precipitation of potassium dihydrogen phosphate from aqueous solutions is studied in presence of aluminium ions. Conductivity experiments, chemical analyses and microscopic observations are performed. They allow to determine the kinetics of precipitation, and to know the effect of the additive on the separate steps of the crystallization : primary nucleation, growth, and secondary nucleation. Morphological aspects are particularly studied. Some qualitative and quantitative interpretations of the effects of aluminium ions are proposed.

Interactive Education in Control and Management for General Scope Engineering Students

Abstract The challenges and constraints of a Control Engineering course in a general scope engineering school are outlined. The main characteristic points of the schools strategy for control engineering courses are outlined: flexibility, simulation, interactivity, autonomy. Dedicated, interactive Computer Aided Instruction (CAI) tools are presented, which have been developed with Matlab™, Siman™ or G2™ in the fields of process control, simulation of manufacturing systems and real-time process supervision.

Etude experimentale du vieillissement de la composition pyrotechnique: Zirconium-chromate de plomb

The aging of pyrotechnic mixtures Zr-PbCrO4 was proved experimentally through its action on the burning rate and on some physical properties of the reactive medium. Complementary experiments were performed on freshly prepared mixtures in order to determine the nature of the process. It was concluded that aging is due to the formation of an oxygen-rich layer on the surface of the zirconium grains; the presence of this layer brings about decreases in the solid-solid contact and in the thermal conductivity of the medium.ZusammenfassungDie Wirkung von pyrotechnischen Zr-PbCrO4-Gemischen auf die Brenngeschwindigkeit und auf einige physikalische Eigenschaften des reaktiven Mediums wurde experimentell untersucht. Zur Bestimmung der Art des Prozesses wurden zuzügliche Experimente an frisch dargestellten Gemischen durchgeführt. Die Wirkung scheint auf der Bildung einer sauerstoffreichen Schicht an der Oberfläche der Zirkoniumpartikel zu beruhen; die Existenz dieser Schicht verursacht eine Herabsetzung des Fest-Festkörperkontaktes und somit der Wärmeleitfähigkeit des Mediums.РезюмеСтарение пиротехнич еских смесей Zr-PbCrO4 было экспериментально по дтверждено посредством влияния ее на скорость воспла менения и на некоторые другие физ ические свойства этой реакционной сре ды. Для выяснения прир оды этого процесса, были провед ены дополнитель-ные исследования со свеж е полученными смесям и. Сделано заключение, ч то старение обусловлено образов анием обогащенного к ислородом слоя на поверхности ц иркониевых зерен. Наличие такого слоя в ызывает уменьшение к онтакта твердое тело-твердое тело и термической проводимости среды.

Thermodynamic model of supersaturated liquid solutions: Application to the homogeneous nucleation of potassium sulfate

Abstract It is now well known that a supersaturated phase contains clusters, aggregates, or embryos of atoms, molecules, or ions. The many kinetic models of homogeneous nucleation generally refer to the equilibrium states of these supersaturated systems. In this paper, a thermodynamic model inspired by Prigogine and Defays “associated solutions model” allows one to work out the Gibbs free energy of a supersaturated liquid solution and to make more precise essential notions such as critical nucleus and stability. At the same time, a new step-by-step description of the nucleation process is proposed. Lastly, a few experimental results concerning the precipitation of potassium sulfate from its supersaturated aqueous solutions are presented and the influence on the kinetics of precipitation of thermal treatments of the liquid phase is interpreted.

Multiplicity and stability analysis in a free boundary problem arising from a dissolution-growth process

Abstract We study a phenomenon of growth and dissolution occurring in processes of mineralization (metasomatism) in geology. The heterogeneous system considered is a grain exchanging mass with a liquid solution impregnating a porous medium which gives rise to a source term. The system is bounded, of spherical symmetry, and the concentration is fixed on the external boundary. The evolution of the concentration of the liquid solution is described by a moving boundary problem. The associated stationary problem is a free boundary problem which may exhibit zero, one, two, or three solutions. A study of the stability by means of the associated evolution problem is set up, mainly by numerical techniques. In the cases studied, uniqueness in the stationary problem implies instability. When three solutions occur, we observe two unstable solutions, and only one stable solution.

Modelling and Supervision of Intra-Peritoneal Chemohyperthermia (IPCH)

Abstract Intraperitoneal chemohyperthermia is more and more considered as an interesting therapeutic option in cases of some abdominal cancers, particularly of digestive origin. However, many technical aspects of this treatment remain far from being mastered, particularly the homogeneous dispatch of temperatures and drugs within the abdomen cavity. The project described in this paper consists, first of all: in an experimental study, which has been carried out on a physical, in vitro «prototype» of the abdomen, on which different hot fluid flows and injection conditions (configurations) are investigated. The results of this experimental study have enabled to obtain a model of the « system » behaviour. The modelling results have helped to optimize the injection circuit and its running parameters while applied to the in vivo treatment of patients. A real-time software has been written to perform in vivo data acquisition and to provide an “on-line” help to the surgeon as well as to the radiesthesist, who are monitoring the operation. It has been validated during several in vivo IPCHs. Data has thus been acquired and first comparison conclusions could be drawn concerning the models as well as the supervision assistance.

Following photochemical reactions by thermogravimetry

A new thermal analysis system has been designed to follow the influence of light on solid reactants. This method is based upon the association of a thermogravimetric system for the kinetic measuring method, and a U. V. irradiation system for the activation method. This instrument allows comparative studies of a thermal reaction and the corresponding photochemical one under exactly the same experimental conditions. The experiments, carried out in silver carbonate, have provided new information on photochemical kinetics, but also on solid-state reactivity and even on thermal processes. More generally, this device, designed for studies on reactivity, can be applied to any other system needing the action of light. With the device, the influence of the light intensity, the wavelength and the lifetime of light effects on many reactions can be studied.ZusammenfassungEin neues thermisches Analysensystem zur Untersuchung der Einwirkung von Licht auf feste Reaktanden wird beschrieben. Die Methode beruht auf einer Kombination eines thermogravimetrischen Systems für kinetische Meßmethoden mit einem UV-Bestrahlungssystem für die Aktivierungsmethode. Das Gerät ermöglicht vergleichende Untersuchungen einer thermischen und der entsprechenden photochemischen Reaktion unter gleichen Versuchsbedingungen. An Silbercarbonat ausgeführte Untersuchungen haben neue Informationen über die photochemische Kinetik, aber auch über die Festkörperreaktivität und sogar über thermische Prozesse ergeben. Allgemeiner gesagt, das für Reaktivitätsstudien konstruierte Gerät kann auch zur Untersuchung anderer die Einwirkung von Licht erfordernden Systeme benutzt werden. Mit dem Gerät können der Einfluß der Lichtintensität, der Wellenlänge und der Wirkungsdauer der Lichteffekte auf viele Reaktionen untersucht werden.РезюмеРазработаны новые те рмоаналитические системы, позволяющие исследовать влияние света на твер дые реагирующие веще ства. Основой является сое динение термогравим етрической системы в методе изме рения кинетики с УФ облучательной си стемой в методе активации. Ус тановка позволяет пр оводить сравнительные иссле дования термической реакции и соответств ующей фотохимическо й реакции при точно оди наковых эксперимент альных условиях. Эксперимен ты, проведенные с карбонатом серебра, п озволили получить новую инфор мацию не только о кине тике фотохимических реак ций, но также о реакционной способ ности вещества в твер дом состоянии и о различн ых термических процессах. Более того, эта установка может б ыть присоедина к другой к акой-либо системе для изучения действи я света и с помощью кот орой может быть изучено влияние интенсивности света, длины волны и пр одолжительность дей ствия света на многие реакц ии.

Caractérisation d'un mélange de solides pulvérulents. Cas des alumines industrielles

Les proprietes physico-chimiques des melanges pulverulents, telles quelles apparaissent au travers de resultats danalyse ou bien detudes cinetiques sont globales. Les auteurs proposent ici une demarche fondee sur un modele simple qui permet de preciser les caracteristiques respectives de chaque constituant dun melange binaire. Une application au cas des alumines industrielles rend compte des differences de comportement observees lors de leur dissolution dans les bains delectrolyse