Fabrication by powder metallurgy of Copper/Graphene composite with improved physical properties

Les problématiques énergétiques sont dans toutes les conversations depuis de nombreuses années tant du point de vue de la consommation, en croissance permanente, que de son coût de plus en plus excessif, particulièrement en ce moment. Au regard des informations recueillies auprès de l’IEA, la consommation électrique mondiale est en forte croissance avec une augmentation de 88% sur les vingt dernières années qui ne fera que s’accentuer. Avec l’objectif d’atteindre la neutralité carbone d’ici 2050, la consommation électrique mondiale ne fera que croître. En effet, le CME estime que la consommation d’énergie augmentera entre 27 et 61% suivant les deux scénarios envisagés, l’un favorisant la croissance économique et l’autre notre planète. Cependant, même si l’augmentation de notre production d’électricité est primordiale, elle ne constitue pas la seule option pour satisfaire nos besoins actuels et futurs. En effet, selon le gestionnaire RTE et la société ERDF, on estime que les pertes totales représentent pas moins de 10% de l’électricité produite. Dans ces pertes, on retrouve majoritairement les déperditions énergétiques thermiques aussi appelées : effet Joule. Ce problème, la société Schneider Electric spécialiste mondial de la gestion de l’énergie et des automatismes, la bien compris. En effet, certains organes de raccordement électrique 2D, notamment de type glissant, sont utilisés pour permettre une mise en sécurité rapide des installations, si nécessaire. Toutefois, ce type de raccordement est cinq fois plus résistif qu’un raccordement boulonné classique, ce qui a pour effet d’engendrer de forte élévation de température. Afin de diminuer cet échauffement (et les pertes), des simulations de profil thermique ont montré qu’une diminution de la résistivité électrique du matériau engendrerait une importante réduction de la température du connecteur. Ceci permettait une meilleure mise en sécurité des installations (prévention des risques d’incendies) et une réduction des pertes énergétiques. C’est dans ce but que ce travail de thèse propose l’élaboration de composite à matrice cuivre (plaquette ou dendritique) à renfort graphène. En effet, le graphène est un matériau 2D nanométrique connu pour ses propriétés singulières dans le domaine mécanique, thermique et aussi électrique. Toutefois l’élaboration de ce type de composite n’est pas triviale. La taille nanométrique du renfort ne permet pas l’utilisation de méthode de caractérisation conventionnelle et surtout ne permet pas une caractérisation directe de ses propriétés intrinsèques. Pour cela, plusieurs problématiques sont à résoudre. Tout d’abord, le carbone et le cuivre sont des matériaux non chimiquement réactifs. Par conséquent, la formation d’une interface pour l’obtention d’une liaison chimique forte, entre la matrice de Cu et le renfort graphite, est nécessaire. La croissance de nanoparticule de cuivre en surface du graphène sera la voie choisie. Le graphène étant un matériau anisotrope et nanométrique, un contrôle parfait de son orientation et de sa distribution dans la matrice est primordial. Enfin, une étude sur l’élaboration de graphène dopé azote utilisant les états supercritique et plasmatique de la matière seront utilisés afin d’accroitre ses propriétés.Energy issues are in every conversation for many years, as much for its consumption, which is constantly growing, that for its increasingly excessive cost, especially currently. Based on the information from the IEA, global electricity consumption is growing strongly, with an increase of 88% over the last 20 years. With the goal of achieving carbon neutrality in 2050, global electricity consumption can only grow. Indeed, the CME estimates that energy consumption will increase between27 and 61% according to the scenarios foreseen by this organization, one promoting growth and the other our planet. However, while increasing our electricity production is critical, it is not the only option to meet our current and future needs. Indeed, according to the RTE manager and the company ERDF, the total losses are estimated to represent no less than 10% of the electricity produced. In these losses, we mainly find thermal energy loss also called the Joule effect. This problem is well understood by Schneider Electric a global specialist in energy management and automation. Indeed, some 2D electrical connection devices, like sliding type, are used to allow a quick safety of the installation, if necessary. However, this type of connection is five times more resistive than a conventional bolted connection, this resulting in a high temperature rise. To reduce this heating (and energy loss), thermal profile simulations have shown that a decrease in the electrical resistivity of the material leads to a significant reduction of the temperature connector. Indeed, a 25% decrease of the electrical resistivity resulting in a decrease of 12°C. The reduction of electrical resistivity allows better safety of the installations (prevention of fire risks) and a reduction of energy loss. It is with this purpose that this PhD thesis proposes the elaboration of composite copper matrix (flake or dendritic) with graphene reinforcement. Indeed, graphene is a nanometric 2D carbon material known for its singular properties in the mechanical, thermal, and also electrical fields. However, the development of this type of composite is currently a real challenge. In fact, the nanometric size of the reinforcement does not allow the use of conventional characterization method, and above all does not allow a direct characterization of the intrinsic properties of the reinforcement. So, the elaboration of the material is always needed to study the impact of reinforcement. To this end, few problems need to be solved. At first, carbon and copper are non-reactive material, so the formation of a strong chemical link is necessary. For that, copper nanoparticle growth on top of graphene is the chosen way. Then, graphene is a nanometric anisotropic material, so a perfect control of the orientation and of the distribution of the reinforcement is primordial. Finally, a study of the elaboration of nitrogen doping graphene using supercritical and plasma state of matter will be achieved to enhance the properties of this carbon reinforcement

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