Dissertations / Theses on the topic 'Aluminium Graphite/Graphene Composite'

In this study, the composite of aluminum metal-organic framework MIL-68(Al) and reduced graphene oxide (MA/RG) was synthesized via a one-step solvothermal method, and their performances for pnitrophenol (PNP) adsorption from aqueous solution were systematically investigated. The introduction of reduced graphene oxide (RG) into MIL-68(Al) (MA) significantly changes the morphologies of the MA and increases the surface area. The MA/RG-15% prepared at RG-to-MA mass ratio of 15% shows a PNP uptake rate 64% and 123% higher than MIL-68(Al) and reduced graphene oxide (RG), respectively. The hydrogen bond and pi-pi dispersion were considered to be the major driving force for the spontaneous and endothermic adsorption process for PNP removal. The adsorption kinetics, which was controlled by film-diffusion and intra-particle diffusion, was greatly influenced by solution pH, ionic strength, temperature and initial PNP concentration. The adsorption kinetics and isotherms can be well delineated using pseudo-second-order and Langmuir equations, respectively. The presence of phenol or isomeric nitrophenols in the solution had minimal influence on PNP adsorption by reusable MA/RG composite.

O aumento das preocupações com o meio ambiente tem trazido à indústria de tratamento de superfícies novos desafios quanto ao desenvolvimento de revestimentos com maior desempenho quanto à resistência à corrosão e ao desgaste, observando a redução do impacto ambiental. Neste contexto, o objetivo do presente trabalho é obter um filme compósito à base de silano com incorporação de partículas de óxido de grafeno visando o aumento da resistência à corrosão e ao desgaste da liga de alumínio AA 2024-T3. A liga de alumínio AA 2024-T3 é um material bastante usado na indústria aeronáutica devido às propriedades mecânicas e à baixa densidade. Contudo, essa liga não oferece a resistência à corrosão e ao desgaste exigidos para aplicação na indústria aeronáutica, sendo necessário o emprego de revestimentos protetores. Dentre os revestimentos propostos para essa aplicação os revestimentos híbridos têm sido estudados, e mais recentemente a incorporação de partículas à essa matriz tem sido proposta visando melhorar as propriedades desses filmes. Nesse trabalho os revestimentos compósitos de matriz híbrida com incorporação de óxido de grafeno foram obtidos pelo processo de sol-gel a partir de um sol contendo os precursores alcoóxidos tetraetoxisilano (TEOS) e 3-trimetoxisilil-propil-metacrilato (MAP) com dispersão de partículas de óxido de grafeno em diferentes concentrações (1 g.L-1, 0,5 g.L-1, 0,25 g.L-1 e 0 g.L-1). Os filmes foram obtidos empregando-se o método de dip-coating à temperatura ambiente, com velocidade de retirada de 10 cm.min-1. O óxido de grafeno utilizado foi caracterizado quanto à estrutura utilizando as análises de FTIR, Raman, TGA e microscopia eletrônica de varredura de alta resolução. Para avaliar a estrutura do filme compósito obtido foram utilizadas as análises de FTIR, Raman e TGA. Microscopia eletrônica de varredura de alta resolução foi usada a fim de verificar a uniformidade do filme e avaliar a dispersão das partículas no filme. Os ensaios de polarização potenciodinâmica e impedância eletroquímica foram utilizados para analisar o comportamento referente à corrosão. Avaliou-se também a molhabilidade dos filmes, pelo método da gota séssil. As propriedades mecânicas do filme foram avaliadas empregando-se o ensaio de desgaste pela técnica de esfera sobre plano e teste de adesão. Nas condições estudas, a adição das partículas de óxido de grafeno não alterou a resistência à corrosão, contudo evidenciou-se uma contribuição positiva quanto ao aumento da resistência ao desgaste do filme.
The growing concern with the environment has created new challenges to the surface treatment industry, encouraging the development of coatings with a better performance in regards to the mechanical resistance and corrosion properties, observing the reduction of the environmental impact. In this context, this work aims to make a composite coating with graphene oxide charge to improve the corrosion and wear resistance in aluminum alloy AA 2024-T3. The aluminum alloy AA 2024-T3 is a material used in the aeronautics industry due to its low density and good mechanical proprieties. However, this alloy does not have the corrosion and wear resistance required by the aeronautics industry, requiring the use of protective coatings. Among the protective coatings proposed for this application, the hybrid films have been studied and more recently the incorporation of particles has been proposed to improve the proprieties of this film. In this work the hybrid matrix composite coating with incorporation of graphene oxide was obtained by sol-gel process from a sol containing alkoxide precursors Tetraetoxisilano (TEOS) and 3-(trimetoxisililpropil) metacrylate (MAP) with graphene oxide dispersion in different concentrations (1 g.L-1, 0,5 g.L-1, 0,25 g.L-1 e 0 g.L-1). The films were obtained using the dip-coating method in room temperature with 10 cm.min-1 of removal rate. For the characterization of the graphene oxide structure FTIR, Raman, TGA and scanning electron microscope were used. To measure the structure of composite films proprieties FTIR, Raman and TGA were used. In addition, the scanning electron microscope was used on composite film on aluminum alloy in order to verify the uniformity of film and to assess the behavior of the particles on film. The potentiodynamic polarization and the electrochemical impedance were used to analyze the behavior against corrosion. To measure the wettability contact angles measured by the sessile drop method were used. The film was examined for mechanical proprieties with the ball-on-plate and with the adhesion test. In the studied conditions, the adding of the particles of graphene oxide did not change the corrosion resistance, but it showed a positive contribution to the wear resistance.

The thermo-mechanical response of unidirectional P100 graphite fiber/6061 aluminum matrix composites (v_f = 0.47) was investigated at four temperatures: -150°F, +75°F, +250°F and +500°F, using test methods developed at Virginia Tech. Two types of tests, off-axis tension and Iosipescu shear, were used to obtain the desired properties. Good experimental-theoretical correlation was obtained for E_xx, v_xy and G₁₂. It is shown that E₁₁ is temperature independent, but E₂₂, v₁₂ and G₁₂ generally decrease with increasing temperature. Compared with rather high longitudinal strength, very low transverse strength was obtained for the graphite/aluminum. The poor transverse strength is believed to be due to the low interfacial bond strength in this material. The strength decreases significantly with increasing temperature. The tensile response at various temperatures is greatly affected by the residual stresses caused by the mismatch in the coefficients of thermal expansion of fibers and matrix. The degradation of the aluminum matrix properties at higher temperatures has a deleterious effect on composite properties. The composite has a very low coefficient of thermal expansion in the fiber direction.
M.S.

A test fixture for combined tension-compression cyclic testing of unidirectional composites was designed and characterized using 606l-O aluminum specimens. The elastoplastic response of graphite/aluminum l5° off-axis and 90° specimens under tension-compression cyclic loading was subsequently investigated at three temperatures, -l50°F, room temperature and 250°F. The test results showed that the tensile response was predominantly elastoplastic, whereas the compressive response could not be characterized exclusively on the basis of the classical plasticity theory. Secondary dissipative mechanisms caused by inherent voids in the materialâ s microstmcture had an apparent influence on the elastoplastic behavior in compression. At different test temperatures, the initial yield stress in tension and compression were translated in the tension direction with increasing temperature. This is believed to be caused by residual stresses induced inieach phase of the composite. The micromechanics model proposed by Aboudi was subsequently employed to correlate the experimental and analytical results at room temperature. A semi-inverse methodology was incorporated to determine the in-situ properties of the constituents. Comparison between the analytical and experimental results showed good agreement for monotonic tensile response. For tension-compression cyclic loading, fairly good correlation was obtained for l5° specimens, but poor for 90° specimens. The major cause of the discrepancy is suggested to be caused by the secondary dissipative mechanisms.

Master of Science

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1992.
Vita.
Includes bibliographical references (leaves 176-185).
by Mark Anthony Buonanno.
Ph.D.

Magister Scientiae - MSc (Chemistry)
Electrochemical platforms were developed based on pencil graphite electrodes (PGEs) modified electrochemically with reduced graphene oxide metal nanoparticles (ERGO–metalNPs) composite and used for the high-sensitivity determination of Bisphenol A (BPA) in water samples. Synergistic effects of both reduced Graphene Oxide sheets and metal nanoparticles on the performance of the pencil graphite electrode (PGE) were demonstrated in the oxidation of BPA by differential pulse voltammetry (DPV). A solution of graphene oxide (GO) 1 mg mL-1 and 15 ppm of metal stock solutions (1,000 mg L-1, atomic absorption standard solution) (Antimony or Gold) was prepared and after sonication deposited onto pencil graphite electrodes by cyclic voltammetry reduction. Different characterization techniques such as FT-IR, HR-SEM, XRD and Raman spectroscopy were used to characterize the GO and ERGO–metalNPs. Parameters that influence the electroanalytical response of the ERGO–SbNPs and ERGO–AuNPs such as, pH, deposition time, deposition potential, purging time were investigated and optimized. Well-defined, reproducible peaks with detection limits of 0.0125 μM and 0.062 μM were obtained for BPA using ERGO–SbNPs and ERGO–AuNPs respectively. The rGO-metalNPs–PGE was used for the quantification of BPA in tap water sample and proved to be suitable for the detection of BPA below USEPA prescribed drinking water standards of 0.087 μM.

The report on research activity of this doctoral thesis is divided into two sections. In the first section the study, production and functionalization of some newly discovered carbon structures called carbon nanoscrolls (CNS) are reported. These rolled structures arises from the curling of graphene sheets to produce tubular cylinders similar to the already known carbon nanotubes. Currently, these objects are studied mainly from a theoretical point of view but are considered good candidates for hydrogen storage, nanodevice production and reinforcement in composite materials. The production of CNS is carried out through an initial stage of reaction with metallic potassium, to give a graphite intercalation compound of minimum formula KC8, characterized by alternating graphene plans and potassium atoms, pale bronze in colour and highly reactive. A direct reaction with ethanol, under inert atmosphere, produces hydrogen and heat that producethe expansion of graphene sheets. The rolling of grapheme sheets is mediated by high power ultrasounds. The application of ultrasounds overcomes the energy barrier required for the bending of the sheets so that the edges can overlap and adhere by Van der Waals forces giving CNS. It has been devised a general procedure for CNS synthesis starting from a natural Madagascar-type graphite, purified by heat treatment and commercially available in flakes. The many experiments that we carried out (intercalation, exfoliation, ultrasonication) gave some rolled sheets in the samples but in a unexpectedly low yield. We then tried to optimize the CNS synthesis by implementing a preliminary expansion of graphite. Using a mixture of concentrated H2SO4/HNO3 as intercalating agents, followed by an expansion stadium by a thermal or treatment with microwaves. In both cases, the expansion of the graphemes was very good. We also applied a mechanical demolition procedure using a high-power ball-miller. This study was implemented on the basis of SEM observations, that showed how the large slats of graphite hampered wrapping. Actually the effect was beyond expectations, excessive crushing of graphite produced too small leaflets and even the formation of amorphous carbon, thereby invalidate this step. A new and efficient CNS synthetic procedure was pursued, using ozone and fuming HNO3 as intercalating agents, followed by exfoliation with ethanol and ultrasonication. This treatment produces a considerable improvement in the production of CNS. Some funzionalization reactions were also carried out on prepared CNS through the 1,3-dipolar cycloaddition reaction of azomethine ylides and the sidewall diazotation in a similar way used for carbon nanotubes. The second part of the project has involved the production of composite materials based on graphite oxide and polithiophenes to produce a material that synergistically combine the mechanical properties of graphite with an organic semiconducting polymer, with a possible use as component in electronic devices. The graphite oxide has been obtained with permanganate oxidation in strong mineral acids; it is easily dispersable in water and can restore the starting graphite in form of carbon nanoplatelets after reduction with hydrazine. The polymer has been produced in aqueous environment using thienyl monomers such as the 3.4-etilenedioxythiophene (EDOT) and the 3-hexylthiophene (3HT), pure or blended, in the presence of graphite oxide, ammonium persulphate (APS) as polymerizing agent and a surfactant to prevent precipitaion. After evaporation of the solvent, a composite material was obtained, in the form of thin and shiny black films, with little roughness, and relatively transparent to light in water. The conductiong, composite material was used for some tests, in a transistor (FET) configuration, at the Zernike Institute for Advanced Materials of the Universityt of Groningen. It has been shown that the composite is a good candidate to prepare organic-based diodes.

Dans l'industrie microélectronique, l'augmentation constante de la densité de puissance due à la miniaturisation des composants électroniques nécessite un matériau de dissipation thermique ayant une conductivité thermique élevée (CT), un faible coefficient de dilatation thermique (CTE) et des propriétés mécaniques (PM) appropriées pour une dissipation efficace de la chaleur. Des métaux purs, tels que Al et Cu, ont déjà été utilisés. Cependant, ils ont des CT limitées (ex. 240 W/m.K pour Al) et leurs CTE sont trop élevés (ex. 23 10-6/K pour Al), ce qui est incompatible avec ceux des composants électroniques (ex. 4 10-6/K pour Si), conduisant à une défaillance en service due à la fatigue thermique. À cet égard, les composites à matrice métallique se sont révélés être un matériau prometteur. Les matériaux en carbone, comme le graphite, le diamant et la fibre de carbone, ayant été introduits comme renforts en raison de leurs excellentes propriétés thermiques (c'est-à-dire un CT très élevé et un faible CTE) dans une matrice Al. Dans ces travaux de thèse, des matériaux composites à matrice en Al renforcé par des plaquettes de graphite peu coûteuses et facilement usinables (ci-après appelé composite Al/Gf) ont été développés dans le but de maximiser le CT, d'adapter le CTE proche de 6 10-6/K, ainsi que d'améliorer les PM.La CT intrinsèque du Gf est hautement anisotrope, c'est-à-dire 1000 W/m.K dans le plan et 5-10 W/m.K hors du plan. Il est donc clair que la bonne orientation de Gf dans la matrice d'Al assure un CT élevée, dans la direction du plan du graphite, ainsi qu’à l’échelle du matériau produit dans cette même direction. Dans cette étude, un procédé de remplissage des poudres étape par étape, a été appliquée avec succès afin d’obtenir cet arrangement 1D conventionnel. Ainsi, les valeurs de CT théoriques prévues les plus élevées peuvent être atteintes expérimentalement. En outre, les matériaux composites 2D et 3D de Gf ont été élaborés à l'aide de pistons spécialement conçus afin d'adapter le CTE anisotrope des Gf (c'est-à-dire -1 10-6/K dans le plan et 28 10-6/K hors plan). La structure 2D permet de réduire la CTE, qui est alors compatible avec celui du matériau du substrat (voisin de 8 10-6/K), tout en maintenant une CT élevée. Enfin, les efforts ont été consacrés à renforcer la matrice Al en intégrant des nanoparticules dispersées (ex-situ) de SiC et (in-situ) de TiB2 pour améliorer les PM globales du composite Al/Gf
In the microelectronic industry, the ever increase in power density due to miniaturization of electronic components requires heat sink materials with a high thermal conductivity (TC), a low coefficient of thermal expansion (CTE), and specific mechanical properties (MP). Pure metals, such as Al and Cu, have been previously used. However, they have limited TCs (e.g. 240 W/m.K for Al) and their CTEs are too high (e.g. 23 × 10-6/K for Al), being incompatible with those of electronic components (e.g. 4 × 10-6/K for Si), leading to failures in service due to thermal fatigue. Regarding this, metal matrix composites have been proven to be promising material where carbon materials, such as graphite, diamond, and carbon fibres, have been introduced as reinforcements because of their excellent thermal properties (i.e. very high TC and low CTE). In this Ph.D. project, Al matrix composites reinforced with low-cost and easily machinable graphite flakes (hereafter called Al/Gf composite) were developed with the aim to maximize TCs, tailor CTEs close to 6×10-6/K, as well as improve MPs.The intrinsic TCs of Gf are highly anisotropic, i.e. in-plane TC of 1000 W/m.K and out-of-plane TC of 5-10 W/m.K, respectively. It is thus clear that the strong orientation of Gf in the Al matrix ensures the high TCs, along the direction of graphite plane, in the as-produced composite. In this study, a new approach to combining flake powder metallurgy with a step-by-step powder filling process was successfully applied to achieve this conventional 1D arrangement. As such, the highest TC values theoretically predicted can be achieved experimentally. Further, the 2D and 3D arrangements of Gf were made using specifically designed punches in order to tailor the anisotropic CTEs of Gf (i.e. in-plane CTE of -1 × 10−6/K and out-of-plane CTE of 28 × 10−6/K), being unavailable in the 1D arrangement. The 2D arrangement allows to achieve the reduced CTEs being compatible with those of the substrate materials while maintaining a high TCs, demonstrating the strong potential for applications. Finally, the efforts were devoted to strengthen the Al matrix by integrating dispersed (ex-situ) SiC and (in-situ) TiB2 nanoparticles to improve the overall MPs of the Al/Gf composites

L'objectif de la thèse est d'expérimenter et de valider de nouvelles voies d'exfoliation des feuillets de graphène dans des élastomères de type silicone (PDMS) et des thermoplastiques de type polyéthylène (PE). Ce projet s'appuie sur des étapes de modifications chimiques des feuillets de graphite oxydé (GO) dont la polarité initiale n'offre pas une compatibilité satisfaisante avec les matrices étudiées. Différentes approches ont été explorées : la synthèse du GO greffé PDMS a été réalisée avec succès par greffage directe d'un PDMS fonctionnalisé triéthoxysilane et par une réaction d'hydrosilylation catalytique de GO modifiés vinyltriméthoxysilane en présence de polyméthylhydrogénosiloxane. Une étude des propriétés viscoélastiques de suspensions de GO et GO modifié/PDMS a montré l'importance de l'interaction charge-charge sur la formation d'un réseau percolant. Le seuil de percolation rhéologique du GO a été obtenu à 1,75 %wt avec Af~60. En se basant sur le greffage radicalaire du pentadécane par abstraction d'atomes d'H par un peroxyde à haute température, il a été possible d'extrapoler cette réaction pour procéder au greffage d'un PE de faible masse molaire (Mn~2000). De plus, des PE fonctionnalisés thiol et azoture de Mn similaire ont aussi été greffés sur des dérivés du graphite par addition radicalaire et de Michael. Après sélection d'une charge présentant une conductivité en poudre proche du graphite et une bonne affinité pour les milieux alcanes, un nano-composite à base de PEBD présentant des propriétés électriques convenables pour une application de blindage électromagnétique (4.105 Ω.cm à 25%wt) a été réalisé et ceci sans utiliser d'agents réducteurs toxiques
The aim of this thesis was to experiment and validate new means of graphene exfoliation in an elastomer matrix such as silicone (PDMS) and a thermoplastic matrix such as polyethylene (PE). Because of the low affinity of graphene oxide for these matrices due to its high polarity, its chemical modification was carried out. Different approaches were explored: the grafting of PDMS onto GO was carried out with success by a direct functionalization with a PDMS terminated triethoxysilane and by a catalytic hydrosilation reaction of a PDMS terminated Si-H onto vinyltrimethoxysilane modified GO. The viscoelastic behavior of GO and modified GO/PDMS suspensions showed the importance of the filler-filler interaction on the formation of a percolating network. The rheological percolation threshold of the GO/PDMS suspension was obtained at ~1.75 wt% with an aspect ratio (Af) of ~60. In addition, the grafting of PE onto GO was studied with the high temperature radical grafting of pentadecane formed by a hydrogen atom abstraction with a peroxide, which was then extrapolated to a low molecular PE (Mn~2000). Moreover, thio and azide functionnalized PE with a similar Mn were also grafted onto graphite derivatives by a radical and a Michael addition. After choosing the filler which presented the closest electrical conductivity to the one of graphite powder and a good affinity for a heptane media, a LDPE based nano-composite that presented suitable electrical properties for an electromagnetic shielding application (4 105 Ω.cm at 25 wt%) was obtained and this without any use of toxic reducing agents

Composite materials are multifunctional materials having unique mechanical and physical properties that can be tailored to meet the requirements of a particular application. Aluminium based Metal Matrix Composites (MMC) always draw the attention of researchers due to its unique characteristics such as better strength to weight ratio, low wear rate and lower thermal expansion coefficient. There are various methods for manufacturing of MMC that can be grouped into two major categories: (a) Solid sate method such as powder metallurgy, co-extrusion and (b) Liquid state method such as stir casting. All of these methods for production of composites have their own advantages and disadvantages. Porosity, and poor wettabilty of dispersoids with matrix are few common problems in solid state route. Formations of undesirable phases, and segregation of dispersoids are common problems in liquid state processing route. Friction Stir Processing (FSP) technique, a derivative technique of Friction Stir Welding (FSW) has emerged as a major solid state technique to produce composites. However, there are several challenges associated with it. Most of the past work has been on limited volume of material. Researchers have tried to combine FSP technique with powder metallurgy technique to overcome aforementioned challenges associated with these techniques. Where on one hand, powder metallurgy ensures the uniform dispersion of dispersoids in the matrix, on the other hand FSP on sintered billet removes the pores and other defects. The combination of these two techniques leads to a more controlled and uniform properties. However, at the same time, it can be noted that the combination of these processes is tedious and time consuming. In this study, an attempt is made to achieve bulk dispersion of a second phase into an aluminium matrix using FSP technique. A 5 mm thickness composite is attempted in this work. To achieve this objective proper and uniform mixing of the particles is required. To achieve this, new tools and processing steps are to be designed and analyzed for a better understanding of material flow around the tool pin and the effect of different tool pin geometries on the material flow. Keeping this objective, a detailed study is carried out on material flow during FSW process using aluminium as base metal. A marker material technique is employed to understand the material flow. A strip of copper is selected as the marker material. Material flow can be qualitatively predicted during the process by observing the distribution of marker material in the weld nugget. Three different kinds of tools, each with an additional feature are designed for this purpose (a) Plain frustum shape pin (b) threaded frustum shape pin and, (c) Triflute pin . The material flow due to the plain pin tool can be considered as primary flow during the FSP. Three different kinds of flow zones are observed in the weld nugget in the case of plain tool. It is found that higher numbers of geometrical features (threads and flutes) not only enhance the material flow but also lead to the additional flow currents and more thorough and uniform mixing. A closer study of the weld nugget revealed that the copper marker particles and the matrix were diffusion bonded. Based on the reaction time available and temperature in the weld nugget a diffusion layer thickness of 4 nm is expected between copper and aluminium. However, the diffusion layer thickness was found to be 3.5 μm, which is nearly three orders of magnitude higher. This can be attributed to the enhancement of diffusion due to simultaneous application of strain and temperature. As copper is soluble in the aluminium, an insoluble marker material tin was used for study of flow in the weld nugget. However, the effect of insolubility and lower melting point had some unexpected effect on the processing loads. The normal load during steady state tool traverse in conventional butt-welding is found to be around 2.7 KN while it attains an average value of 14.7 KN when a thin strip of tin is sandwiched between these plates. However, a drop in the torque of around 13.12 NM is observed when tin was sandwiched between the plates as compared to the case when no insert was present. On closer examination of the flow behavior, it is seen that the tin melted, squeezed out and formed a lubricious layer between the tool and the work piece. This reduced the torque significantly and a concomitant drop in temperature was observed. The interaction between the tool and the colder aluminium work piece would thus result in much larger normal and transverse load Based on the expected and unexpected results of flow pattern in the weld nugget, a new FSP tool and processing steps were developed to manufacture MMC. Tungsten, which is the highest melting point metal is chosen as the dispersing phase. Further, as tungsten has high melting point, the kinetics of intermetallics formation would be low for the given FSP processing time at the processing temperature. This would lead to tungsten acting as a more ductile strengthening particle, which is expected to should give some unique characteristics to the MMC. Tungsten powder with an average diameter of 414 nm was dispersed in aluminum matrix with three different proportions after optimizing all the process parameters. It is noted that the mechanical properties are significantly influenced as the tungsten content in the matrix increases. In practice, MMC shows relatively low ductility compared to the parent metal. However in this case the composite exhibited even better ductility than the as received aluminium plates (rolled sheets). The composite showed around 129 MPa of yield strength along with 21% ductility when tungsten content is 3.8 at.%. It is also found that the reaction between aluminum and tungsten occurs during the processing and form the Al12W intermetallic phase. Though the formation of this intermetallic phase was unlikely due to the low temperature and short time available during the process, the reaction kinetics between aluminium and tungsten would have been enhanced due to the simultaneous application of strain and temperature. Given that the metal-metal, tungsten-aluminium composite produced by FSP had unique properties and also formed intermetallics, a study on incorporation of a highly insoluble material, graphite was carried out. Further graphite with its own unique properties and very low wettability with aluminium could possibly impart completely different properties to the system. Past work on graphite aluminium composites produced by other methods did not show promise. As FSP imposes high strains at relatively high flow stresses on the processed material, it was seen that the graphite got sheared to form multi-layer graphene composites with the aluminium. The graphene sheets are formed by mechanical exfoliation of graphite particles during its incorporation in the matrix. The formation of graphene was confirmed after separating the graphite from the processed zone and TEM studies of the composite. It is seen that most of the graphite got converted into multilayer graphene. This aluminium-graphene composite exhibited enhanced ductility and UTS. As received aluminium plates exhibited only 11% ductility and around 100 MPa of UTS while this composite exhibited around 26 % ductility and 147 MPa of UTS. However, there is only a slight improvement in yield strength of this composite.

Composite materials are multifunctional materials having unique mechanical and physical properties that can be tailored to meet the requirements of a particular application. Aluminium based Metal Matrix Composites (MMC) always draw the attention of researchers due to its unique characteristics such as better strength to weight ratio, low wear rate and lower thermal expansion coefficient. There are various methods for manufacturing of MMC that can be grouped into two major categories: (a) Solid sate method such as powder metallurgy, co-extrusion and (b) Liquid state method such as stir casting. All of these methods for production of composites have their own advantages and disadvantages. Porosity, and poor wettabilty of dispersoids with matrix are few common problems in solid state route. Formations of undesirable phases, and segregation of dispersoids are common problems in liquid state processing route. Friction Stir Processing (FSP) technique, a derivative technique of Friction Stir Welding (FSW) has emerged as a major solid state technique to produce composites. However, there are several challenges associated with it. Most of the past work has been on limited volume of material. Researchers have tried to combine FSP technique with powder metallurgy technique to overcome aforementioned challenges associated with these techniques. Where on one hand, powder metallurgy ensures the uniform dispersion of dispersoids in the matrix, on the other hand FSP on sintered billet removes the pores and other defects. The combination of these two techniques leads to a more controlled and uniform properties. However, at the same time, it can be noted that the combination of these processes is tedious and time consuming. In this study, an attempt is made to achieve bulk dispersion of a second phase into an aluminium matrix using FSP technique. A 5 mm thickness composite is attempted in this work. To achieve this objective proper and uniform mixing of the particles is required. To achieve this, new tools and processing steps are to be designed and analyzed for a better understanding of material flow around the tool pin and the effect of different tool pin geometries on the material flow. Keeping this objective, a detailed study is carried out on material flow during FSW process using aluminium as base metal. A marker material technique is employed to understand the material flow. A strip of copper is selected as the marker material. Material flow can be qualitatively predicted during the process by observing the distribution of marker material in the weld nugget. Three different kinds of tools, each with an additional feature are designed for this purpose (a) Plain frustum shape pin (b) threaded frustum shape pin and, (c) Triflute pin . The material flow due to the plain pin tool can be considered as primary flow during the FSP. Three different kinds of flow zones are observed in the weld nugget in the case of plain tool. It is found that higher numbers of geometrical features (threads and flutes) not only enhance the material flow but also lead to the additional flow currents and more thorough and uniform mixing. A closer study of the weld nugget revealed that the copper marker particles and the matrix were diffusion bonded. Based on the reaction time available and temperature in the weld nugget a diffusion layer thickness of 4 nm is expected between copper and aluminium. However, the diffusion layer thickness was found to be 3.5 μm, which is nearly three orders of magnitude higher. This can be attributed to the enhancement of diffusion due to simultaneous application of strain and temperature. As copper is soluble in the aluminium, an insoluble marker material tin was used for study of flow in the weld nugget. However, the effect of insolubility and lower melting point had some unexpected effect on the processing loads. The normal load during steady state tool traverse in conventional butt-welding is found to be around 2.7 KN while it attains an average value of 14.7 KN when a thin strip of tin is sandwiched between these plates. However, a drop in the torque of around 13.12 NM is observed when tin was sandwiched between the plates as compared to the case when no insert was present. On closer examination of the flow behavior, it is seen that the tin melted, squeezed out and formed a lubricious layer between the tool and the work piece. This reduced the torque significantly and a concomitant drop in temperature was observed. The interaction between the tool and the colder aluminium work piece would thus result in much larger normal and transverse load Based on the expected and unexpected results of flow pattern in the weld nugget, a new FSP tool and processing steps were developed to manufacture MMC. Tungsten, which is the highest melting point metal is chosen as the dispersing phase. Further, as tungsten has high melting point, the kinetics of intermetallics formation would be low for the given FSP processing time at the processing temperature. This would lead to tungsten acting as a more ductile strengthening particle, which is expected to should give some unique characteristics to the MMC. Tungsten powder with an average diameter of 414 nm was dispersed in aluminum matrix with three different proportions after optimizing all the process parameters. It is noted that the mechanical properties are significantly influenced as the tungsten content in the matrix increases. In practice, MMC shows relatively low ductility compared to the parent metal. However in this case the composite exhibited even better ductility than the as received aluminium plates (rolled sheets). The composite showed around 129 MPa of yield strength along with 21% ductility when tungsten content is 3.8 at.%. It is also found that the reaction between aluminum and tungsten occurs during the processing and form the Al12W intermetallic phase. Though the formation of this intermetallic phase was unlikely due to the low temperature and short time available during the process, the reaction kinetics between aluminium and tungsten would have been enhanced due to the simultaneous application of strain and temperature. Given that the metal-metal, tungsten-aluminium composite produced by FSP had unique properties and also formed intermetallics, a study on incorporation of a highly insoluble material, graphite was carried out. Further graphite with its own unique properties and very low wettability with aluminium could possibly impart completely different properties to the system. Past work on graphite aluminium composites produced by other methods did not show promise. As FSP imposes high strains at relatively high flow stresses on the processed material, it was seen that the graphite got sheared to form multi-layer graphene composites with the aluminium. The graphene sheets are formed by mechanical exfoliation of graphite particles during its incorporation in the matrix. The formation of graphene was confirmed after separating the graphite from the processed zone and TEM studies of the composite. It is seen that most of the graphite got converted into multilayer graphene. This aluminium-graphene composite exhibited enhanced ductility and UTS. As received aluminium plates exhibited only 11% ductility and around 100 MPa of UTS while this composite exhibited around 26 % ductility and 147 MPa of UTS. However, there is only a slight improvement in yield strength of this composite.

碩士
義守大學
材料科學與工程學系
104
In This study, two parts of experimental contents were to investigate. In part I, different milling mixing, forming and sintering methods were used to make different Al/CNT specimens. The objective of part I was to investigate the relevance between mixing method of Al/CNT powder and the specimen''s formability. In part Ⅱ, it was focused on the effect of process paramaters on the mechanical, electrical, and tribological properties of different specimens. In part I, the results show that the specimens prepared through wet-mixing, dry-milling, and 200℃ forming method exhibit well formability. Therefore, Al/CNT specimens further prepared through the hot press sintering show increasing hardness, density, and decreasing apparent porosity. In Part Ⅱ, to compare with the pure Al specimen, experimental results show that the hardness of those specimens adding with SiC increased, but the conductivity decreased. Adding graphite, CNT and graphene will reduce the specimen''s hardness and flexural strength, but improve the conductivity.

Accumulative Roll Bonding (ARB) was used to fabricate Graphene Oxide-reinforced Al-matrix composites, benefiting from a grain refinement effect of the metal-lic matrix. Graphene Oxide reinforcement was suspended in a stabilized aqueous solution and applied, prior to each ARB cycle, through airgun spraying, in order to obtain a ho-mogeneous distribution. Concentrations of 0.5, 2.5 and 10 mg/ml (graphene ox-ide/millipore water) were used. For each concentration, samples produced have under-gone up to 5 rolling cycles. Optical and electron scanning microscopies were used for microstructural char-acterization of the rolled composites which revealed a non-homogenous deformation of the layers across the composite’s thickness. Although not desired but expected, Alumin-ium oxide formation occurred where the reinforcement was applied. Although the presence of graphene-oxide promoted an increase in the micro-hardness, higher values were obtained with its lowest concentration for the same num-ber of ARB cycles. The number of ARB cycles and the direction of the tested sections also influenced the microhardness results since the 5-cycle samples and the rolling di-rection sections for all the samples achieved higher hardness results. Graphene Oxide revealed to be a major contributor to the increase of stiffness during bending of the test-ed samples. The ARB processed samples revealed a decrease on the electrical conductivity when compared with the annealed Aluminium, since the Graphene Oxide and Alumini-um oxide have insulator properties. The contribution of the reinforcement to this de-crease was only noticeable when using higher concentrations, since the sample with less concentration of the applied Graphene Oxide revealed slightly better results than the sample without any reinforcement.

Advanced aluminum graphite composites have unique thermal properties due to opposing coefficients of thermal expansion of aluminum and graphite. The thermal and mechanical properties of such composites are anisotropic due to directional properties of graphite fibers and their designed orientation. A joint with different fiber orientations would theoretically produce an isotropic material for thermal management. This paper presents results for welding and brazing of the composite using different joining techniques. Laser welding of Al-Gr composite showed that a power density above 30kW/mm2 gives a weld with microstructure defects. Also the laser beam melts the matrix and delaminates the graphite fibers. The molten aluminum reacts with graphite to form aluminum carbide (Al4C3). The joint strength is compromised when laser welding at optimal conditions to minimize the carbide formation. Also porosity and redistribution of graphite fibers is seen during laser welding. These defects prompt us to consider a low temperature joining. Brazing is considered since the low melting temperature of a filler material suppresses the formation of Al4C3 while minimizing pores and microstructural defects in the joint. Microstructural study and shear test are performed to analyze the joints. Shear strengths of brazed joints are determined to be 20-21MPa which is comparable to the composite shear strength (46.5MPa in x-y plane and 19MPa in z plane). The fracture surface is found to be mostly on the composite rather than in brazed material or along the interface. Also, the microstructural study showed no Al4C3 formation and minimal porosity in the brazed region. These results show a successful joining of the composite using laser brazing and resistance brazing methods.

碩士
國立臺北科技大學
材料科學與工程研究所
99
In this study, we combine natural flake graphite (NFG) with aluminum to form graphite/aluminum composites used for thermal management materials. Because NFG has characteristics of small density and poor wettability with aluminum, these can cause difficulty in manufacturing. Therefore, vacuum hot press in semi-solid liquid state is employed to make graphite/aluminum matrix composites. The result shows that the relative density achieves about 98% for composites containing 10~70vol.% graphite. With the increase of flake graphite from 10 to 90vol.% in the composites heat capacity increases from 0.992 to 1.043J/g•K; thermal diffusivity values increase from 136 to 340mm^2/s; thermal conductivity increase from 338.20 to 757W/m•K; the coefficients of thermal expansion (CTE) in direction parallel to basal planes of NFG decrease from 16.89 to -2.51ppm/K, while the CTE perpendicular to basal planes decreases from 15.19 to 10.06ppm/K; and lastly, electrical conductivity decreases from 19.76×106 to 0.34×106/m•Ω. Thermal conductivity values of composites are shown to agree well with parallel model estimation. The CTEs of composites in a-axis agree with rule of mixture and Kerner model estimation, while the CTEs of composites along c-axis are consistent with Turner model estimation. These properties of composites are adequate for thermal dissipation applications in electronic packaging. Furthermore, to improve the flexural strength of composites, carbon fiber is added. In composites with 10~40vol.% graphite addition, the composites demonstrate ductile behavior. The flexural strengths of composites containing 50~90vol.% graphite addition decreases gradually from 47.9 to 12.3MPa. The addition of 10vol.% carbon fiber effectively improves the strength by 13.48% to 53.3MPa. When carbon fiber addition increases to 20vol.% or higher, the flexural strengths of composites greatly decrease due to poor wettability between aluminum and carbon fibers.

碩士
國立中正大學
機械工程系研究所
104
Metal Matrix Composites (MMCs) containing ceramic particles for particulate reinforcement have been developed for the applications demanding high specific stiffness, high strength and wear resistance. For the joining of particulate reinforced MMC, the FSW process provides a promising solution since the ceramic particles would remain uniformly distributed in the weld zone, while the effect of particulate reinforcement would be lost in the fusion zone if the AMCs were welded using conventional fusion welding processes. In this study, we not only improve the coherence of ceramic particles but also enhance mechanical properties by stirring the graphene nano-flake into stir zone to become MMC. Numerous literature indicates that Al3Ni intermetallic particles has a positive effect on the mechanical properties, so we used electroless plating to coat a nickel thin film on SiC particles. Then, we use chemical vapor deposition (CVD) to grown graphene layer on nickel coated SiC particles. Finally, by stirring nickel coated SiC particles and the graphene-SiC-based multi-scale particulate reinforcement into a 6061 Aluminum alloy substrate by friction stir processing (FSP). A local particulate strengthened zone is formed. The in situ formation of Al3Ni particles during FSP was confirmed by EDS and XRD analysis. Both Hardness and tensile test showed that the mechanical property of stire zone with SiC or Nickel coated SiC particles is similar. The SEM, BSE observation on longitudinal tensile fracture surface were conducted. A large number of nickel coated SiC particles remained in the dimple structure after two pass FSP. The presence of SiC & nickel coated SiC particles played a major role in improving the wear resistance of 6061 stir zone.

碩士
清雲科技大學
機械工程系所
97
This thesis uses anodization process on AA5083 Aluminum Alloy surface, use electroless containing Graphite powder(diameter 3μm)、Al2O3 powder(diameter 3μm)、Nano Al2O3 powder (diameter 20-30nm) additive with different concentration for plating on AA5083 Aluminum Alloy surface. Measure analysis surface morphologies, element compositions and surface roughness of the composite coatings before and after all tests are analyzed by scanning electron microscopy (SEM), X-ray energy dispersive analyzer (EDS) and surface roughness measurement. Experimental results indicated that electroless Cu/Nano Al2O3/Graphite composite coating exhibited the smoothes more dense and fine surface structure, consequently, giving the corrosion and highest hardness, wear-corrosion resistance in the 3.5%NaCl solution, and the anodizing treatment of AA5083 showed a beneficial effect to enhance these properties.

碩士
國立雲林科技大學
化學工程與材料工程系
106
In this experiment, a copper catalyst was deposited on a copper foil substrate by liquid phase deposition on a copper foil by chemical vapor deposition (CVD). In this study, two methods were employed to form N-doped CNTs/ graphene. (1) N-doped CNTs/ graphene bundle arrays were synthesized in a CVD system with a mixture of C2H2 and ammonia (NH3). (2) After the synthesis of CNTs/ graphene bundle arrays by CVD, the samples were transferred to another chamber for nitrogen plasma treatment to form nitrogen-doped vertically aligned CNTs/ graphene bundle arrays. Better preparation of CNTs / graphene composite material conditions for Ammonia flow rate 60 sccm, growth time 10 minute. and then aluminum oxide thin film is formed by chemical liquid phase deposition,coated solid electrolyte PEDOT,.finally, assembling a capacitor CR2032. As a result of CNTs/graphene composite electrode material, the capacitance is 2394.5μF/cm2 and the rate of decline is 18.1%；Better preparation of the Al2O3 / CNTs / graphene composites were by chemical liquid phase deposition (LPD) to grow the SrTiO3 thin film. Better preparation of the titanium dioxide film were 4.5 hours, the heat treatment temperature was 600℃, Coated with solid electrolyte PEDOT, and then assembled into a capacitor CR2032. As a result of the SrTiO3 / Al2O3 / CNTs / graphene c composite electrode material, the capacitance is 13425.7μF/cm2 and the rate of decline is14.13 %. Keywords：Chemical vapor deposition、Liquid-Phase Deposition、Carbon nanotubes、Graphene、Nitrogen doped、Al–Ti composite oxide films、Solid capacitor

碩士
健行科技大學
機械工程系碩士班
104
This study using electroless-plating techniques to deposit the Ni-P-Cu/Graphene composite coatings on AA6061 aluminum alloy substrate after pre-treatment including thermal oxidation or anodizing evaluates the structure, mechanical properties of the composite coatings as well as their corrosion and wear resistance in 0.5M H2SO4 solution. The corrosion resistance behavior of the composite coatings was performed by using electrochemical polarization measurements. The surface morphology and elemental analysis and surface hardness of the composite coatings before and after all tests are analyzed by scanning electron microscopy (SEM) and X-ray energy dispersive analyzer (EDS). The surface hardness of the specimens was measured by a Vickers′ micro-hardness tester. It is hoped that the effect of the thermal oxidation or anodizing pre-treatment on the surface structure, corrosion and wear resistance of the composite coatings could be evaluated. The results indicated that AA6061 aluminum alloy after anodizing oxidation increases its surface hardness as well as the electroless Ni-P-Cu/Graphene composite coatings. Moreover, these composite coatings could present the well corrosion and wear protection ability to the aluminum alloy substrate. Because the graphene has a good lubrication ability such that the Ni-P-Cu/Graphene composite coating has the best corrosive wear resistance property especially as the alloy substrate after anodizing pre-treatment.

Lithium-ion battery is attractive for various applications because of its high energy density. The performance of Li-ion battery is influenced by several properties of the electrode materials such as particle size, surface area, ionic and electronic conductivity, etc. Porosity is another important property of the electrode material, which influences the performance. Pores can allow the electrolyte to creep inside the particles and also facilitate volume expansion/contraction arising from intercalation/deintercalation of Li+ ions. Additionally, the rate capability and cycle-life can be enhanced. The following porous electrode materials are investigated. Poorly crystalline porous -MnO2 is synthesized by hydrothermal route from a neutral aqueous solution of KMnO4 at 180 oC and the reaction time of 24 h. On heating, there is a decrease in BET surface area and also a change in morphology from nanopetals to clusters of nanorods. As prepared MnO2 delivers a high discharge specific capacity of 275 mAh g-1 at a specific current of 40 mA g-1 (C/5 rate). Lithium rich manganese oxide (Li2MnO3) is prepared by reverse microemulsion method employing Pluronic acid (P123) as a soft template. It has a well crystalline structure with a broadly distributed mesoporosity but low surface area. However, the sample gains surface area with narrowly distributed mesoporosity and also electrochemical activity after treating in 4 M H2SO4. A discharge capacity of about 160 mAh g-1 is obtained at a discharge current of 30 mA g-1. When the acid-treated sample is heated at 300 °C, the resulting porous sample with a large surface area and dual porosity provides a discharge capacity of 240 mAh g-1 at a discharge current density of 30 mA g-1. Solid solutions of Li2MnO3 and LiMO2 (M=Mn, Ni, Co, Fe and their composites) are more attractive positive electrode materials because of its high capacity >200 mAh g-1.The solid solutions are prepared by microemulsion and polymer template route, which results in porous products. All the solid solution samples exhibit high discharge capacities with high rate capability. Porous flower-like α-Fe2O3 nanostructures is synthesized by ethylene glycol mediated iron alkoxide as an intermediate and heated at different temperatures from 300 to 700 oC. The α-Fe2O3 samples possess porosity with high surface area and deliver discharge capacity values of 1063, 1168, 1183, 1152 and 968 mAh g-1 at a specific current of 50 mA g-1 when prepared at 300, 400, 500, 600 and 700 oC, respectively. Partially exfoliated and reduced graphene oxide (PE-RGO) is prepared by thermal exfoliation of graphite oxide (GO) under normal air atmosphere at 200-500 oC. Discharge capacity values of 771, 832, 1074 and 823 mAh g -1 are obtained with current density of 30 mA g-1 at 1st cycle for PE-RGO samples prepared at 200, 300, 400 and 500 oC, respectively. The electrochemical performance improves on increasing of exfoliation temperature, which is attributed to an increase in surface area. The high rate capability is attributed to porous nature of the material. Results of these studies are presented and discussed in the thesis.

Lithium-ion battery is attractive for various applications because of its high energy density. The performance of Li-ion battery is influenced by several properties of the electrode materials such as particle size, surface area, ionic and electronic conductivity, etc. Porosity is another important property of the electrode material, which influences the performance. Pores can allow the electrolyte to creep inside the particles and also facilitate volume expansion/contraction arising from intercalation/deintercalation of Li+ ions. Additionally, the rate capability and cycle-life can be enhanced. The following porous electrode materials are investigated. Poorly crystalline porous -MnO2 is synthesized by hydrothermal route from a neutral aqueous solution of KMnO4 at 180 oC and the reaction time of 24 h. On heating, there is a decrease in BET surface area and also a change in morphology from nanopetals to clusters of nanorods. As prepared MnO2 delivers a high discharge specific capacity of 275 mAh g-1 at a specific current of 40 mA g-1 (C/5 rate). Lithium rich manganese oxide (Li2MnO3) is prepared by reverse microemulsion method employing Pluronic acid (P123) as a soft template. It has a well crystalline structure with a broadly distributed mesoporosity but low surface area. However, the sample gains surface area with narrowly distributed mesoporosity and also electrochemical activity after treating in 4 M H2SO4. A discharge capacity of about 160 mAh g-1 is obtained at a discharge current of 30 mA g-1. When the acid-treated sample is heated at 300 °C, the resulting porous sample with a large surface area and dual porosity provides a discharge capacity of 240 mAh g-1 at a discharge current density of 30 mA g-1. Solid solutions of Li2MnO3 and LiMO2 (M=Mn, Ni, Co, Fe and their composites) are more attractive positive electrode materials because of its high capacity >200 mAh g-1.The solid solutions are prepared by microemulsion and polymer template route, which results in porous products. All the solid solution samples exhibit high discharge capacities with high rate capability. Porous flower-like α-Fe2O3 nanostructures is synthesized by ethylene glycol mediated iron alkoxide as an intermediate and heated at different temperatures from 300 to 700 oC. The α-Fe2O3 samples possess porosity with high surface area and deliver discharge capacity values of 1063, 1168, 1183, 1152 and 968 mAh g-1 at a specific current of 50 mA g-1 when prepared at 300, 400, 500, 600 and 700 oC, respectively. Partially exfoliated and reduced graphene oxide (PE-RGO) is prepared by thermal exfoliation of graphite oxide (GO) under normal air atmosphere at 200-500 oC. Discharge capacity values of 771, 832, 1074 and 823 mAh g -1 are obtained with current density of 30 mA g-1 at 1st cycle for PE-RGO samples prepared at 200, 300, 400 and 500 oC, respectively. The electrochemical performance improves on increasing of exfoliation temperature, which is attributed to an increase in surface area. The high rate capability is attributed to porous nature of the material. Results of these studies are presented and discussed in the thesis.