13 research outputs found
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
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers âŒ99% of the euchromatic genome and is accurate to an error rate of âŒ1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead
Etude de la précipitation de silicate de magnésium amorphe en présence d'ultrasons
National audienceĂtude de la prĂ©cipitation de silicate de magnĂ©sium amorphe en prĂ©sence d'ultrasons Campus Jarlard, 81013 ALBI cedex 9 (b) Imerys Talc, 2 place E. BouillĂšres 31036 TOULOUSE RĂ©sumĂ© Le silicate de magnĂ©sium est formĂ© par prĂ©cipitation Ă partir de mĂ©tasilicate de sodium et de chlorure de magnĂ©sium. Le rapport molaire initial Mg/Si est constant et Ă©gal Ă 0,75. La prĂ©cipitation est rĂ©alisĂ©e dans une cuve agitĂ©e, Ă©quipĂ©e de quatre chicanes. Cette Ă©tude prĂ©sente l'addition parallĂšle des rĂ©actifs par l'intermĂ©diaire d'un mĂ©langeur muni d'une sonde ultrasonore. Dans ce travail, ne sont prĂ©sentĂ©s que les rĂ©sultats en sortie de prĂ©mĂ©langeur afin d'Ă©tudier l'influence des ultrasons. La connaissance de la constante d'Ă©quilibre du silicate de magnĂ©sium amorphe dĂ©terminĂ©e Ă l'aide du logiciel PHREEQC a permis de calculer les rapports de sursaturation du silicate de magnĂ©sium amorphe et de la silice amorphe en sortie du mĂ©langeur pour les diffĂ©rents essais. Ainsi, il semblerait que seul le silicate de magnĂ©sium prĂ©cipite dans le mĂ©langeur quels que soient les paramĂštres de l'opĂ©ration de prĂ©cipitation. Les vitesses de nuclĂ©ation et de croissance, et le noyau d'agglomĂ©ration, ont pu ĂȘtre calculĂ©s dans le mĂ©langeur, en fonction des paramĂštres opĂ©ratoires. Pour cela, le mĂ©langeur, qui fonctionne en continu, a Ă©tĂ© supposĂ© parfaitement agitĂ©. Des mesures de distribution de temps de sĂ©jour ont Ă©tĂ© rĂ©alisĂ©es et ont montrĂ© qu'Ă dĂ©bit moyen sans ultrasons et Ă tous dĂ©bits Ă©tudiĂ©s avec ultrasons, le prĂ©-mĂ©langeur peut ĂȘtre considĂ©rĂ© comme parfaitement agitĂ© (rĂ©sultats non prĂ©sentĂ©s dans ce travail). La diminution de la taille des particules et agglomĂ©rats sous l'effet des ultrasons serait due Ă une augmentation de la vitesse de nuclĂ©ation, ainsi qu'Ă une diminution de la vitesse de croissance et du noyau d'agglomĂ©ration. L'augmentation de la puissance ultrasonore dissipĂ©e dans la suspension permettrait d'accroĂźtre ces effets. Cependant, l'augmentation de la vitesse de nuclĂ©ation serait limitĂ©e : Ă partir d'une certaine puissance ultrasonore, cette vitesse n'augmente plus. De plus, le rapport de sursaturation est modifiĂ© par l'utilisation des ultrasons, mais pas par l'augmentation de la puissance ultrasonore. La taille des particules et agglomĂ©rats a Ă©galement tendance Ă diminuer Ă faibles molalitĂ©s initiales des rĂ©actifs. On a pu observer deux effets inverses des molalitĂ©s initiales des rĂ©actifs sur le rapport de sursaturation du silicate de magnĂ©sium amorphe, selon que la prĂ©cipitation est assistĂ©e ou non par ultrasons. Dans le cas du recours aux ultrasons, la puissance ultrasonore serait inhibĂ©e lorsque la concentration en solide augmente. Ă faible molalitĂ© initiale des rĂ©actifs, l'utilisation d'ultrasons provoque une augmentation de la vitesse de nuclĂ©ation et une diminution de la vitesse de croissance et du noyau d'agglomĂ©ration qui seraient Ă l'origine de la diminution de la taille des particules et agglomĂ©rats. Mots-clĂ©s : ultrasons, silicate de magnĂ©sium, prĂ©cipitatio
Compatibilization of polypropylene/polyamide 6 blends using new synthetic nanosized talc fillers: Morphology, thermal, and mechanical properties
New synthetic nanotalc and a commercially available natural fine talc (Luzenac© A3) were chosen in order to establish a comparative study in terms of their contributions on the improvement of the morphology as well as the final properties of PP/PA6 blends prepared by melt processing. At first, the TEM and SEM micrographs showed that both talc particles have a preferential affinity for the more hydrophilic polyamide 6 phase compared with the continuous PP matrix. Moreover, in both cases, the addition of talc fillers induces a significant decrease of the size of the PA6 domains but the better compatibilization efficiency was obtained in the presence of synthetic nanotalc particles. In this work, the positive change induced by the talc nanofillers on the crystallization kinetics and final morphology was highlighted. In addition, compared with natural talc, a highly level of dispersion of talc layers has been obtained with the synthetic nanotalc which is more hydrophilic. Thus, this better dispersion greatly improves the thermal stability of PP/PA6 blends and leads to better mechanical properties (+ 40% in Young's modulus).Fil: Mohamed, Yousfi. UniversitĂ© de Lyon. Lyon; Francia. INSA Lyon. Villeurbanne; Francia. Centre National de la Recherche Scientifique; FranciaFil: Sebastien, Livi. Centre National de la Recherche Scientifique; Francia. UniversitĂ© de Lyon. Lyon; Francia. INSA Lyon. Villeurbanne; FranciaFil: Dumas, Angela. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. UniversitĂ© de Toulouse. Toulouse; Francia. Centre National de la Recherche Scientifique; FranciaFil: CrĂ©pin Leblond, JĂ©rome. Imerys Talc. Toulouse; FranciaFil: Greenhill Hooper, Mike. Imerys Talc. Toulouse; FranciaFil: Duchet Rumeau, Jannick. UniversitĂ© de Lyon. Lyon; Francia. INSA Lyon. Villeurbanne; Francia. Centre National de la Recherche Scientifique; Franci
Ionic compatibilization of polypropylene/polyamide 6 blends using an ionic liquids/nanotalc filler combination: morphology, thermal and mechanical properties
International audienceIn this study, room temperature ionic liquids (RTILs) based on phosphonium cations have been used as effective compatibilizers of polyolefin/polyamide 6/synthetic talc blends using a melt extrusion process. Thus, different ionic liquids functionalized by various counteranions (phosphinate versus bistriflimide) were introduced at various concentrations (1, 5 and 10 wt%) in the polymer mixtures. Then, the crystallization behaviour, the thermal and mechanical properties of blends as well as the morphologies were investigated. The transmission electronic microscopy (TEM) micrographs demonstrated that the use of a very low amount of ILs (1 wt%) led to a significant reduction of the size of the dispersed PA 6 phase. Moreover, the thermal properties of PP/PA6/talc were dramatically enhanced (+80 degrees C) and the mechanical performance was improved without reducing the strain at break suggesting a synergistic effect between nanotalc and ionic liquids
Use of new synthetic talc as reinforcing nanofillers for polypropylene and polyamide 6 systems: thermal and mechanical properties.
International audienceNew layered synthetic nanotalc prepared at a lab-scale by a conventional hydrothermal process and commercial natural fine talc were used in order to establish a comparative study in terms of their contributions on the improvement of the final properties of two different polymers: a nonpolar polyolefin matrix and a polyamide. All samples were prepared by melt extrusion in a co-rotating micro compounder. The surface properties of talc -surface energy and isoelectric point- were probed. The particles crystalline structure and the distribution/dispersion within the polymer matrix were performed using transmission electron microscopy and X-ray diffraction. The effect of talc particles on the cristallinity, the thermal and mechanical properties was highlighted as a function of the surface properties of talc. In the case of talc filled PP systems, it seems that the incorporation of both natural and synthetic talc greatly improves the thermal stability of polypropylene matrix. The highest elastic modulus was obtained in presence of highly nucleating natural talc. Oppositely the best ductility was observed for the synthetic talc filled PP systems. For PA6/talc nanocomposites, a remarkable improvement in the dispersion of talc layers was shown and a significant increase in Young's modulus was determined due to the closer affinity between the hydrophilic nanotalc lamellae and the polar PA6 matrix
CARACTERISATION PAR CHROMATOGRAPHIE GAZEUSE INVERSE DE DIFFERENTS SILICATES DE MAGNESIUM SYNTHETIQUES.
International audiencePour permettre une meilleure dispersion des particules de talc dans des matrices polymÚres, celles-ci doivent présenter une taille nanométrique non accessible par broyage. Apparaßt alors comme une alternative au broyage la synthÚse de silicate de magnésium comprenant deux étapes : une précipitation à pression atmosphérique conduisant à un produit amorphe, suivie d'une étape sous pression permettant de transformer le produit amorphe en produit cristallin. Les propriétés de surface des différents produits synthétisés lors de la premiÚre étape, essentielles lors des interactions silicate de magnésium-matrice polymÚre, ont été caractérisées par chromatographie gazeuse inverse. La composante dispersive de l'énergie de surface γ s d a été déterminée pour des silicates de magnésium synthétisés, comparée avec celle du talc naturel et corrélée avec d'autres caractéristiques comme le volume des micro et méso-pores et la dispersibilité des solides dans l'eau
Myartspace: Design and evaluation of support for learning with multimedia phones between classrooms and museums
This paper presents a description and evaluation of Myartspace, a service on mobile phones for inquiry-led learning that allows students to gather information during a school field trip which is automatically sent to a website where they can view, share and present it, back in the classroom or at home.
The evaluation focused on three levels: a micro level, concerned with issues of usability; a meso level, which examined educational effectiveness in terms of learning breakthroughs and breakdowns; and a macro level, which looked at the impact of the new technology on school museum visits practice. Issues of implementing mobile learning across school and museum settings are identified and cross-level influences are discussed.
The study showed that the service was effective in enabling students to gather information in a museum and this provided resources for effective construction and reflection in the classroom. Minor usability problems did not detract from the learning, however there are significant issues concerning how to structure the visit and on the viability of Myartspace as a regular service