Powder processing methodology for fabrication of Copper/Graphite composite materials with enhanced thermal properties

International audienceThis study focuses on the powder processing methodology (PPM) for the fabrication of metal matrix composite using Graphite flakes (Grf) reinforced Copper (Cu). The manufacturing route involved (1) a reductive treatment of Grf powder to purify and increase its quality, (2) the mixing of the Cu and the Grf (0–40 vol%) powders with a fast and efficient Resonant Acoustic (RA) mixer, and finally (3) the cold and hot-pressing of composite powders. Comparison of PPM is made with literature and a usual method used in our laboratory. The quality of Grf after different steps was analyzed by Raman spectroscopy and XRD. Microstructure of the composite materials were analyzed by SEM. It was shown that this new PPM demonstrated better composite structural and thermal properties even at low volume fraction of Grf with a maximum of 630 W·m−1·K−1 obtained with 40 vol% of Grf at 70 °C

Association of kidney function with effectiveness of procalcitonin-guided antibiotic treatment:A patient-level meta-analysis from randomized controlled trials

Patients with impaired kidney function have a significantly slower decrease of procalcitonin (PCT) levels during infection. Our aim was to study PCT-guided antibiotic stewardship and clinical outcomes in patients with impairments of kidney function as assessed by creatinine levels measured upon hospital admission. We pooled and analyzed individual data from 15 randomized controlled trials who were randomly assigned to receive antibiotic therapy based on a PCT-algorithms or based on standard of care. We stratified patients on the initial glomerular filtration rate (GFR, ml/min/1.73 m2) in three groups (GFR >90 [chronic kidney disease; CKD 1], GFR 15-89 [CKD 2-4] and GFR0.05). This individual patient data meta-analysis confirms that the use of PCT in patients with impaired kidney function, as assessed by admission creatinine levels, is associated with shorter antibiotic courses and lower mortality rates

Synergetic Effect of Discontinuous Carbon Fibers and Graphite Flakes on Thermo-Mechanical Properties of Aluminum Matrix Composites Fabricated by Solid–Liquid Phase Sintering

Aluminum (Al) matrix composite materials reinforced with graphite flakes (GF) and pitch-based carbon fibers (CF) were fabricated by solid–liquid phase sintering with a small amount of Aluminum–Silicon eutectic alloy (Al-12 wt%Si). The amount of Al–Si is optimized for a carbon content of 50 vol% in order to achieve, in the plane of GF reinforcement, a higher thermal conductivity (TC) and a lower coefficient of thermal expansion (CTE) compared to identical composite material fabricated by conventional powder metallurgy route. Al/(GF + CF) composite materials were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray microscopy and X-ray tomography in order to highlight the distribution of the Al–Si liquid phase and the formation of a carbon network in the aluminum matrix. A small amount of CF allows to control the through-plane CTE without affecting significantly the in-plane TC of the Al-C composites. The (GF + CF) mixture and the solid–liquid phase sintering allow to achieve a TC of 410 W/m K (in-plane direction) and a CTE of 2.4 × 10−6/K (trough-plane direction), which is, for example, applicable for lightweight heat sink material

Fabrication and characterization of copper and copper alloys reinforced with graphene

The consistent rise in current density within electrical wires leads to progressively more substantial heat losses attributed to the Joule effect. Consequently, mitigating the electrical resistivity of copper wires becomes imperative. To attain this objective, the development of a composite material that incorporates a more conductive reinforcement, like graphene, holds great promise. The conception of a copper/graphene composite using a powder metallurgy-based approach is presented. An optimum graphene quantity of 0.06 vol.% was obtained by calculation in order to limit the phenomenon of overlapping layers. This synthesis technique enables the dispersion of graphene and the meticulous control of the interface through the growth of CuO(Cu) nanoparticles that are tightly bonded to the reinforcement. The increase in the hardness of the various materials with separation of the graphene sheets by ultrasonic treatment (55.3 to 67.6 HV) was obtained. It is an indicator of the correct distribution of the reinforcement. The influence on the electrical properties of dendritic copper (ρe = 2.30 µV.cm) remains limited, resulting in a modest reduction in electrical resistance of around 1.4%. Nevertheless, for flake copper (2.71 µV.cm) and brass (7.66 µV.cm), we achieved a more substantial reduction of 2.7% and 10%, respectively. With the improvement of graphene quality, there exists a greater potential for further enhancing the electrical properties

Nitrogen Radiofrequency Plasma Treatment of Graphene

The incorporation of nitrogen (N) atoms into a graphitic network such as graphene (Gr) remains a major challenge. However, even if the insertion mechanisms are not yet fully understood, it is certain that the modification of the electrical properties of Gr is possible according to the configuration adopted. Several simulations work, notably using DFT, have shown that the incorporation of N in Gr can induce an increase in the electrical conductivity and N acts as an electron donor; this increase is linked to the amount of N, the sp2/sp3 carbon configuration, and the nature of C-N bonding. Nitrogen radiofrequency (RF) plasma has been used to incorporate N into Gr materials. The RF plasma method shows the possibility to incorporate N-graphitic nitrogen into Gr after a pre-treatment with nitric acid. X-ray photoelectron spectroscopy and Raman spectrometry were used to quantify the functionalized groups. The modifications of the graphene surface chemistry along the amount of N inside the Gr change the chemical environment of N. This method, enabling the incorporation of N inside Gr matrix, opens up a route to a broad range of applications

Nitrogen radiofrequency plasma treatment of graphene

The incorporation of nitrogen (N) atoms into a graphitic network such as graphene (Gr) remains a major challenge. However, even if the insertion mechanisms are not yet fully understood, it is certain that the modification of the electrical properties of Gr is possible according to the configuration adopted. Several simulations work, notably using DFT, have shown that the incorporation of N in Gr can induce an increase in the electrical conductivity and N acts as an electron donor; this increase is linked to the amount of N, the sp 2 /sp 3 carbon configuration, and the nature of CÀ N bonding. Nitrogen radio-frequency (RF) plasma has been used to incorporate N into Gr materials. The RF plasma method shows the possibility to incorporate N-graphitic nitrogen into Gr after a pre-treatment with nitric acid. X-ray photoelectron spectroscopy and Raman spectrometry were used to quantify the functionalized groups. The modifications of the graphene surface chemistry along the amount of N inside the Gr change the chemical environment of N. This method, enabling the incorporation of N inside Gr matrix, opens up a route to a broad range of applications

Effect of procalcitonin-guided antibiotic treatment on clinical outcomes in intensive care unit patients with infection and sepsis patients : a patient-level meta-analysis of randomized trials

BACKGROUND: The clinical utility of serum procalcitonin levels in guiding antibiotic treatment decisions in patients with sepsis remains unclear. This patient-level meta-analysis based on 11 randomized trials investigates the impact of procalcitonin-guided antibiotic therapy on mortality in intensive care unit (ICU) patients with infection, both overall and stratified according to sepsis definition, severity, and type of infection. METHODS: For this meta-analysis focusing on procalcitonin-guided antibiotic management in critically ill patients with sepsis of any type, in February 2018 we updated the database of a previous individual patient data meta-analysis which was limited to patients with respiratory infections only. We used individual patient data from 11 trials that randomly assigned patients to receive antibiotics based on procalcitonin levels (the "procalcitonin-guided" group) or the current standard of care (the "controls"). The primary endpoint was mortality within 30 days. Secondary endpoints were duration of antibiotic treatment and length of stay. RESULTS: Mortality in the 2252 procalcitonin-guided patients was significantly lower compared with the 2230 control group patients (21.1% vs 23.7%; adjusted odds ratio 0.89, 95% confidence interval (CI) 0.8 to 0.99; p = 0.03). These effects on mortality persisted in a subgroup of patients meeting the sepsis 3 definition and based on the severity of sepsis (assessed on the basis of the Sequential Organ Failure Assessment (SOFA) score, occurrence of septic shock or renal failure, and need for vasopressor or ventilatory support) and on the type of infection (respiratory, urinary tract, abdominal, skin, or central nervous system), with interaction for each analysis being > 0.05. Procalcitonin guidance also facilitated earlier discontinuation of antibiotics, with a reduction in treatment duration (9.3 vs 10.4 days; adjusted coefficient -1.19 days, 95% CI -1.73 to -0.66; p <  0.001). CONCLUSION: Procalcitonin-guided antibiotic treatment in ICU patients with infection and sepsis patients results in improved survival and lower antibiotic treatment duration

ÉCRITURES EN LIGNE: PRATIQUES ET COMMUNAUTÉS. Sous la dir de Brigitte Chapelain. (485 p.)

"La communication écrite est encore jeune" écrivait R.Escarpit1 en 1973 ajoutant que celle-ci vieillissait moins vite que d'autres moyens de communication. Nous ne pouvons aujourd'hui que constater la pertinence de cette réflexion . En effet les formes de communication médiatisée par les technologies du numérique et des réseaux proposent une palette d'outils complémentaires d'écriture et de lecture, d'annotation, et d'édition personnelles et collectives qui ont développé le traitement de texte, l'écriture hypertextuelle, les mails , les chats , et des sites web comme les wikis. Ces dernières années Internet et son double pouvoir "numérique et connectique"2s'est révélé, comme ce fut le cas du livre, être un dispositif scripturaire, "qui condense et organise, qui schématise et appauvrit parfois"3, revalorisant le rôle informationnel et cognitif de l'écriture dont le développement relève de nombreux domaines culturels, éducatifs et professionnels. Le phénomène blog est sans doute l'exemple4 le plus récent de ces outils d'écriture. Les blogs sont notamment utilisés dans des applications littéraires, pédagogiques et entrepreneuriales donnant à l'écriture en ligne des nouveaux outils moins contraignants et plus maniables. Un colloque organisé à l'université de Rennes 2, en Septembre 2002, a engagé une réflexion pluridisciplinaire sur les dispositifs d'écriture en ligne et les pratiques communautaires émergentes. La littérature, l'éducation et l'organisation qui ne sont que rarement réunies ont retenu particulièrement notre attention. Le carrefour disciplinaire que constituent les sciences de l'information et de la communication permet de mettre à l'épreuve cette problématique commune que représente l'écriture en ligne en s'appuyant sur ces trois champs. Nous avons choisi d'en traiter deux dimensions essentielles :la dimension processuelle et la dimension organisationnelle. C'est ainsi qu'ont émergé les deux thèmes retenus du colloque: les pratiques et les communautés de l'écriture en ligne. La dimension processuelle porte sur les processus de production de ces écritures: les textes produits, les modes éditoriaux qui leur sont associés, les rôles de l'auteur et du lecteur, les genres d'écrits. La dimension organisationnelle s'inscrit dans les structures de travail et de création, la gestion des personnes et des savoirs,et les modes de développement et de circulation des productions d'écriture. Les travaux du colloque ont tenté de répondre à deux grandes interrogations portant sur ces dimensions. En quoi les pratiques d'écriture en ligne proposent-elles des procédures de travail et de création et des modèles de communication qui témoignent d'une réelle spécificité processuelle? Quelles formes organisationnelles et managériales caractérisent ces pratiques d'écriture? Comment les définir? Peut-on parler de communautés

Effect of flake powder metallurgy on thermal conductivity of graphite flakes reinforced aluminum matrix composites

The optimization of metal–matrix composite material is linked firstly with the intrinsic properties of the matrix and the reinforcement used and secondly with the reinforcement–matrix interfacial zone and the distribution/orientation of the reinforcement inside the metal–matrix. Flake powder metallurgy was used to fabricate graphite flake reinforced aluminum matrix (Al/GF) composites fabricated by vacuum hot pressing. Two types of aluminum powders morphology were used: spherical (AlS) and flake (AlF) powders. A higher thermal conductivity in the in-plane direction of the graphite flakes was obtained for Al/GF composite materials fabricated with aluminum flake powder. In addition to a better orientation of the GF in the flake aluminum matrix, a 3D puckered surface and plane surface are formed at the Al/GF interface in, respectively, AlS/GF and AlF/GF composite materials. Due to the morphology incompatibility between the graphite flakes and the spherical powder, the damaged inner structure of GF contributes to a limited enhancement of thermal conductivity in AlS/GF composite materials