La nano-intégration : un besoin d'adaptation des procédés de fabrication actuels

L'arrivée des nanomatériaux parmi les objets du quotidien semble porteuse de fonctions d'usage innovantes, mais pose de nombreux problèmes de mise en œuvre lors de l'intégration de particules nanométriques dans des procédés de fabrication standardisés. Il semble donc impératif d'adapter les procédés de transformation habituels

Micro-Nano : des comportements différents, des procédés à adapter

6 pagesL'arrivée de nanomatériaux parmi les différents matériaux utilisés en pyrotechnie pose de nombreux problèmes de mise en œuvre. En effet, leurs propriétés texturales particulières ne permettent pas de les utiliser comme des matériaux classiques. Il est impératif d'adapter les procédés de mise en œuvre habituels. Pour obtenir l'adéquation de ces nouveaux matériaux et de nos procédés, des études spécifiques du comportement des nanomatériaux au cours des procédés de mise en œuvre par coulée ont été réalisés. L'observation des écarts de comportement des nanomatériaux par rapport aux "micro-matériaux" pour une même nature chimique et des conditions identiques de mise en œuvre permet d'établir des lois de comportement spécifiques, fonction de la taille des particules manipulées. Les mentalités, comme les procédés, doivent évoluer et prendre en compte l'élévation de surface spécifique qu'offre le passage à l'échelle nanométrique. Ainsi un chargement moindre en nanomatériaux ne sera pas forcement synonyme de lacunes sur les caractéristiques du produit fini (propriétés mécaniques ou pyrotechniques). Deux questions peuvent alors se poser : faut-il adapter les formulations aux procédés, en prenant en compte les caractéristiques des matières premières ou bien adapter des procédés devant supporter des taux de chargement élevés en nanomatériaux ? Le manque de connaissance et le recul sur le comportement des nanomatériaux sont un frein à leur intégration dans des composés pyrotechniques mais les propriétés exhibées laissent présagées d'un grand intérêt en vue de l'optimisation des propriétés des composés fabriqués

A Flow Time Model for Melt-Cast Insensitive Explosive Process

International audienceDiphasic flows of concentrated suspensions of melt-cast insensitive explosives exhibit specific rheological properties. In order to limit the handling of pyrotechnical products presenting a risk with respect to the mechanical and thermal shocks, a lot of work has been undertaken for many years in the civil engineering sector. The objective of this study is to propose a predictive model of the flow time of a concentrated suspension through a nozzle located at the bottom of a tank. Similar to our industrial process, the suspension is made out of insensitive energetic materials and flows under gravity. Experimental results are compared to three models (Quemada, Krieger-Dougherty, and Mooney) predicting the viscosity μ of a suspension as a function of the solid volume fraction ϕ, the maximum packing density ϕm and the viscosity μ0 of the interstitial liquid. De Larrard's model is used to calculate ϕm. The value of viscosity measured for the pure liquid is close to the one predicted by the Bernoulli theorem, where liquids are considered as incompressible and inviscid. Finally, it was found that the Quemada's model gives a fair agreement between predictions and experiments

Application d'un modèle de viscosité à la coulée d'explosifs : Modélisation du temps de coulée.

14 pagesLa rhéologie des coulées d'explosifs est décrite par la dynamique des écoulements diphasiques de suspensions concentrées. Afin d'améliorer la manipulation de produits présentant par nature un risque vis-à-vis des agressions mécaniques et thermiques, des avancées issues des travaux de recherche menés depuis de nombreuses années dans le secteur du génie civil permettent de développer de nouveaux procédés pyrotechniques. L'objectif de ces travaux est de proposer un modèle prédictif des temps d'écoulement des suspensions concentrées en matériaux énergétiques dans une configuration similaire au procédé de mise en oeuvre développé en production. Les résultats expérimentaux sont comparés à trois modèles (Quémada, Krieger-Dougherty, Mooney) représentant la viscosité dynamique comme étant fonction de la fraction volumique solide , de l'empilement compact maximal et de la viscosité du fluide interstitiel . Le modèle de De Larrard est utilisé pour le calcul de . Les hypothèses d'un fluide parfait et incompressible, pour le calcul du temps de coulée du fluide interstitiel , aboutissent à la relation de Bernoulli et satisfont à l'expérience. Nous montrons que le modèle de Quémada conduit à des valeurs théoriques du temps de coulée de la suspension en bon accord avec les valeurs expérimentales

Development of a new mixing rheometer for studying rheological behaviour of concentrated energetic suspensions

International audienceThe overall objective is to present a procedure based on a Couette analogy to quantitatively analyse torque/rotor speed data and extract viscosity/shear-rate curves using a non-conventional geometry. Diphasic flows of energetic concentrated suspensions of melt-cast insensitive explosives exhibit particular rheological properties. The characterization of these complex fluids may be a challenging task when conventional rheometers are used. Placing these tense suspensions in a classic cylindrical geometry may lead to a partial destruction of the internal fluid structure. To prevent that, a "RheoXF" a mixer-type rheometer has been developed : it consists of a mixing device with quite a complex geometry rotating in a cylindrical tank

Emptying time of a tank filled up with explosive paste. Comparison between experimental measurements and predictions based on rheological characterization of the paste

International audienceOne industrial process used by Nexter Munitions to manufacture pyrotechnical materials consists in preparing an emulsion of wax in TNT (2,4,6-trinitrotoluene) and adding Aluminium and ONTA (3-nitro-1,2,4-triazole-5-one) particles. When the suspension is homogeneous, it is allowed to flow by gravity through a pipe located at the bottom of the tank and to fill up a shell body. The suspension is characterized by a solid volume fraction of 53.4%, which leads to high viscosities. In some circumstances, the emptying time is prohibitively long and the economic profitability is reduced. This study has been performed to make the emptying time lower with the constraint of unchanged volume fractions and grains mean diameter. So, we investigated the influence of the grain size distribution on the suspension viscosity. Different samples of Aluminium and ONTA have been used, with rather small differences in grain size distributions. The suspensions have been prepared in the industrial tank and the flow cast times measured. It has been observed that they differ by one order of magnitude. To avoid situations with too high emptying times, a procedure has been implemented to make prior characterization of the suspension rheology. Because of particles sedimentation and emulsion destabilisation, the classical Couette rheometer is not adapted. So, we designed and built a small size tank (113 cm3), where the suspension is continuously stirred and kept homogeneous. The measurement of the torque and rotational speed together with the use of the Couette analogy allowed us to observe an Ostwald fluid behaviour (flow consistency index k, flow behaviour index n). To gain in prediction, we established a correlation between the measured (k, n) values and the grain size distributions. We characterized each suspension by the ratio of to , where is the solid volume fraction (imposed by the commercial specifications) and is the maximum packing fraction. Because of the strong analogy between concrete and energetic paste, we chose the widely used De Larrard model to compute . A linear dependance between the ratio and the indices k and n was observed. The second step was to provide an analytical expression for the flow cast time of a power-law suspension from a tank with a given geometry. Considering the large difference between the industrial inner tank diameter and the evacuation pipe diameter, we assumed that all the pressure drop was located in the evacuation pipe. Then, extending the Hagen-Poiseuille equation to Ostwald fluid, we were able to predict the emptying time with the knowledge of k and n. Experimental and predicted emptying time are in very good agreement. This work helped the industrial manufacturer to divide the emptying time by a factor 12

Control by arbuscular endomycorrhizae of Pratylenchus brachyurus in pineapple microplants

Pratylenchus brachyurus (Godfrey) Filip & Schurr-Steekh. has been reported in association with pineapple roots and is considered as an important pathogen on pineapple. Microplants of Queen Tahiti, Smooth Cayenne and Spanish varieties were inoculated with Glomus sp. (LPA21) and/or P. brachyurus at transplanting from axenic conditions or one month later. The presence of the nematode did not affect shoot growth of endomycorrhizal plants. Late P. brachyurus inoculation did not influence growth of nonmycorrhizal plants while early pathogen application caused reductions in nonmycorrhizal plant growth. Nematode number per g of root was significantly decreased for endomycorrhizal plants when pathogen was introduced at outplanting or one month later. Nematode inoculation affected endomycorrhizal colonization estimated by non vital staining for the Queen Tahiti and Spanish varieties but did not alter development of metabolically active arbuscules in roots of the three varieties. P concentration of endomycorrhizal shoots was higher for all treatments and P. brachyurus tended to decrease mineral concentration of nonmycorrhizal plants with early nematode application

Biomarkers of oxidative stress and its association with the urinary reducing capacity in bus maintenance workers

<p>Abstract</p> <p>Background</p> <p>Exposure to particles (PM) induces adverse health effects (cancer, cardiovascular and pulmonary diseases). A key-role in these adverse effects seems to be played by oxidative stress, which is an excess of reactive oxygen species relative to the amount of reducing species (including antioxidants), the first line of defense against reactive oxygen species. The aim of this study was to document the oxidative stress caused by exposure to respirable particles <it>in vivo</it>, and to test whether exposed workers presented changes in their urinary levels for reducing species.</p> <p>Methods</p> <p>Bus depot workers (n = 32) exposed to particles and pollutants (respirable PM₄, organic and elemental carbon, particulate metal content, polycyclic aromatic hydrocarbons, NO_x, O₃) were surveyed over two consecutive days. We collected urine samples before and after each shift, and quantified an oxidative stress biomarker (8-hydroxy-2'-deoxyguanosine), the reducing capacity and a biomarker of PAH exposure (1-hydroxypyrene). We used a linear mixed model to test for associations between the oxidative stress status of the workers and their particle exposure as well as with their urinary level of reducing species.</p> <p>Results</p> <p>Workers were exposed to low levels of respirable PM₄(range 25-71 μg/m³). However, urinary levels of 8-hydroxy-2'-deoxyguanosine increased significantly within each shift and between both days for non-smokers. The between-day increase was significantly correlated (p < 0.001) with the concentrations of organic carbon, NO_x, and the particulate copper content. The within-shift increase in 8OHdG was highly correlated to an increase of the urinary reducing capacity (Spearman ρ = 0.59, p < 0.0001).</p> <p>Conclusions</p> <p>These findings confirm that exposure to components associated to respirable particulate matter causes a systemic oxidative stress, as measured with the urinary 8OHdG. The strong association observed between urinary 8OHdG with the reducing capacity is suggestive of protective or other mechanisms, including circadian effects. Additional investigations should be performed to understand these observations.</p

Personal non-commercial use only

ABSTRACT. Objective. To report the 5-year outcome of a large prospective cohort of patients with very early rheumatoid arthritis (RA), and to identify factors predictive of outcome. Methods. Patients were recruited if they had early arthritis of &lt; 6 months&apos; duration, had a high probability of developing RA, and had never been prescribed disease-modifying antirheumatic drugs (DMARD) or steroids. Logistic regression analysis was used to determine factors that predict outcome. Results. We included 813 patients from December 2002 to April 2005. Age was 48.1 ± 12.6 years, delay before referral 103.1 ± 52.4 days, 28-joint Disease Activity Score (DAS28) 5.1 ± 1.3, Health Assessment Questionnaire (HAQ) 1.0 ± 0.7; 45.8% and 38.7% had rheumatoid factor or antibodies to cyclic citrullinated peptide (anti-CCP), respectively; 22% had hand or foot erosions; 78.5% fulfilled the American College of Rheumatology/European League Against Rheumatism criteria for RA at baseline and 93.8% during followup. At 5 years, 573 patients were evaluated. The outcome was mild for most patients: disease activity (median DAS28 = 2.5) and HAQ disability (median 0.3) were well controlled over time; 50.6% achieved DAS28 remission and 64.7% low disease activity. Radiographic progression was low (2.9 Sharp unit/year) and only a few patients required joint surgery. Nevertheless, some patients developed new comorbidities. During the 5 years, 82.7% of patients had received at least 1 DMARD (methotrexate, 65.9%), 18.3% a biological DMARD, and about 60% prednisone at least once. Anti-CCP was the best predictor of remaining in the cohort for 5 years, of prescription of synthetic or biologic DMARD, and of radiographic progression. Conclusion. The 5-year outcome of an early RA cohort in the 2000s was described. Anti-CCP was a robust predictor of outcome. The generally good 5-year outcome could be related to early referral and early effective treatment, key processes in the management of early RA in daily practice

5-year RA outcomes Personal non-commercial use only

ABSTRACT. Objective. To report the 5-year outcome of a large prospective cohort of patients with very early rheumatoid arthritis (RA), and to identify factors predictive of outcome. Methods. Patients were recruited if they had early arthritis of &lt; 6 months&apos; duration, had a high probability of developing RA, and had never been prescribed disease-modifying antirheumatic drugs (DMARD) or steroids. Logistic regression analysis was used to determine factors that predict outcome. Results. We included 813 patients from December 2002 to April 2005. Age was 48.1 ± 12.6 years, delay before referral 103.1 ± 52.4 days, 28-joint Disease Activity Score (DAS28) 5.1 ± 1.3, Health Assessment Questionnaire (HAQ) 1.0 ± 0.7; 45.8% and 38.7% had rheumatoid factor or antibodies to cyclic citrullinated peptide (anti-CCP), respectively; 22% had hand or foot erosions; 78.5% fulfilled the American College of Rheumatology/European League Against Rheumatism criteria for RA at baseline and 93.8% during followup. At 5 years, 573 patients were evaluated. The outcome was mild for most patients: disease activity (median DAS28 = 2.5) and HAQ disability (median 0.3) were well controlled over time; 50.6% achieved DAS28 remission and 64.7% low disease activity. Radiographic progression was low (2.9 Sharp unit/year) and only a few patients required joint surgery. Nevertheless, some patients developed new comorbidities. During the 5 years, 82.7% of patients had received at least 1 DMARD (methotrexate, 65.9%), 18.3% a biological DMARD, and about 60% prednisone at least once. Anti-CCP was the best predictor of remaining in the cohort for 5 years, of prescription of synthetic or biologic DMARD, and of radiographic progression. Conclusion. The 5-year outcome of an early RA cohort in the 2000s was described. Anti-CCP was a robust predictor of outcome. The generally good 5-year outcome could be related to early referral and early effective treatment, key processes in the management of early RA in daily practice