Carbon composite pdf

In the literature, for reinforcement phase composition, ceramic phases, such as SiC [1,2], Al2O3 [3], graphite [4], glassy carbon [5], and TiB2 [6], can be primarily found; however, in terms of size and shape, they are microsized and nanosized particles [1—3,7], fibers and nanofibers [8—10]. For these components, consolidation and composite fabrication, powder metallurgy techniques and cast methods, as well as complex processes, such as differing combinations, are required.

In this study, we have demonstrated a new idea of a magnesium matrix composite fabricated by a pressure infiltration method. In the literature, there are examples of carbon reinforcement application using magnesium base composites; however, they focus on components that have a very different geometry.

Some studies have reported the use of magnesium matrix composites with continuous carbon fibers [11]. These composites were applied to increase the mechanical properties and to ensure low density characteristics for magnesium. Metals , 9, ; doi These materials were used to improve mechanical properties and to improve tribological properties due to the formation of a solid lubricant, which comprises of a shredded carbon component [12,14].

However, independently of carbon component forms and the consolidation technique of carbon reinforcement with magnesium matrix, a basic problem of composite processing is reinforcement segregation [16]. However, composite manufacturing is the primary technological issue to obtain a proper filling of foam cells by metal matrix and a continuous and strong bonding zone between the components.

Porous components that employ a metal matrix composite with Al2O3 foams and carbon foams are known as inter alia [17—21]. Because both magnesium and carbon can be used as biomaterials, the composite is composed of components that seem to be good candidates for implants, which was also the primary motivation for conducting this study. Because of the extremely different corrosion resistance of components, a selective biological corrosion of composites is expected. The growth of biological cells in carbon foam will be possible because of free space, which will be gradually induced in composites as a result of electrochemical corrosion.

However, we obtained successful results for consolidating foams with magnesium when magnesium powder was applied as a raw material [33]. This technological solution was accompanied by additional effects, i. To overcome disadvantages of powder metallurgy technology, in addition to other costs and limitations in the final product size and shape, the usability of pressure infiltration for Cof—Mg composite processing was tested.

For the obtained materials, the microstructure, hardness, compressive strength, flexural strength and tribological properties in dry friction conditions were characterized; moreover, the influence of matrix composition on microstructure and properties was analyzed. Materials and Methods 2. Components and Technology of Composite Fabrication For the experiment, we applied pure magnesium The microstructure is shown in Figure 1.

Table 1. Chemical composition of applied matrix alloys, wt. SEM micrograph of Duocell reticulated vitreous carbon foam Cof of ppi. For mechanical properties, characterization of compression tests according to ASTM E9 standard, 3 samples of size 5.

Macrostructure and Microstructure Composite discs obtained using pressure infiltration are shown in Figures 2a,3a and 4a. There are visible differences in their macrostructure. This observation agrees with that of light microscopy LM micrographs Figures 2b,3b and 4b because it indicates a strong influence of the chemical composition of the matrix for infiltration effects. For the Cof—RZ5 composites, there were visible macropores and micropores as well as carbon foam damage.

This reveals an inefficient infiltration of Cof by this magnesium alloy and destructive influence of the RE alloying elements on the carbon component.

For the other two investigated composites, Cof—Mg and Cof—AZ31, the bonding between components is continuous and infiltration effects were favorable; however, the differences in interface microstructure because of the presence of the matrix alloying elements are evident Figure 5 Figure 6 Figure 7. In the Cof—Mg composite interface, only oxygen enrichment is detected because of the oxide bonding formation effect, which is typically observed in the C—Mg system. For the Cof—AZ31 composite, a zone formed at the interface is thicker with the presence of irregular, primarily slim phases Figures 5b and 7.

Using EDS, we detected the enrichment of that zone with oxygen, aluminum and sometimes Mn. Furthermore, our examination using SEM and EDS methods of the Cof—AZ31 composite corrosion in distilled water presented in reference [37] confirmed the presence of hydrophilic phases at the interface, which also indicated the occurrence of reactions between components during the consolidation process. Figure 2. Metals , 9, 5 of 14 Figure 3.

Figure 4. Figure 5. Metals , 9, 6 of 14 Figure 6. Figure 7. Properties 3. Physical and Mechanical Properties Table 2 lists the results of density and porosity measurements.

Note that the measured values of open porosity were in good agreement with the results of macrostructure and microstructure observations. They indicated that the best infiltration effect was observed for pure magnesium porosity 1.

Metals , 9, 7 of 14 Table 2. Physical, mechanical and tribological properties of composites and component materials. One type arises because of the foam filling by the liquid metal, while the other type appears because of metal shrinkage. Moreover, the acceptable value of pressure in infiltration process of vitreous carbon skeleton Cof is limited because of the possibility of it being damaged. While analyzing the composites hardness measurements Table 2 , it is observed the value is different and increases in the following order: Cof—Mg, Cof—AZ31, and Cof—RZ5.

Furthermore, the direction of hardness value increases in the same manner as that for applied matrices. Note that the results for Cof—RZ5 composite clearly confirm the irrelevance of the RZ5 matrix; therefore, further examination of that system was not continued. Similarly like for hardness, the Rs value was higher when the AZ31 alloy matrix was applied. The analyses of compression test curves shape Figure 8 reveal an increase in composite stiffness; moreover, the effect is stronger when the pure magnesium matrix is used.

The differences in the angle of inclination at the compression curves, in a range of elastic deformation, were observed, and the value is evidently higher for composites than for matrix material. The reason for the difference in the composite material properties is because of the matrix and interface microstructure. The oxygen reduction reaction proceeds by two pathways as follows [29]: 3. Results and discussion 3. Electrocatalytic properties of the carbon-based metal-free catalysts used as a support for the carbon composite catalyst Carbon-based metal-free catalysts were synthesized by modify- ing the porous carbon black with the surface functional groups such 1 as oxygen and nitrogen.

Nitrogen groups were incorporated into the graphitic structure using polymerization of low-cost organic where subscripts a and b denote the species adsorbed on the elec- precursors e. In par- cesses. The transport of the adsorbed H2 O2 to the bulk solution reaction 4.

RRDE measurements were performed in 0. For comparison, the curve measured on the as- degrade over time due to attack by peroxide radicals [12,45]. The received Ketjen black is also shown in Fig. Here, the value of N was taken as Remarkable increase in the catalytic activity towards oxygen 0. The metal-free catalysts synthesized by novel methodolo- different metal-free catalysts. Polarization curves of PEM fuel cells prepared with the different cathode catalysts: the metal-free carbon support, the as-pyrolized carbon composite cat- alyst, and the as-leached carbon composite catalyst.

The cathode catalyst loadings were maintained at 6. The experiments were performed using 30 psi back pressure on both anode H2 and cathode O2 compartments. The increased activity is attributed to the oxygen and nitrogen functional groups introduced on the car- bon surface [42—44].

A further improvement in the activity was Fig. Polarization curves on the rotating disk electrodes for the as-received carbon, achieved with the pyrolysis in the presence of Co1 Fe1 Nx complex, the metal-free carbon support and the carbon composite catalyst as-leached.

The followed by the chemical leaching treatment. The carbon compos- measurements were performed in 0. The as-pyrolized carbon composite catalyst pro- for oxygen reduction duced a relatively large amount of H2 O2 , due probably to excess transition metals on the carbon support as discussed in the follow- The carbon composite catalyst was prepared as follows: i ing section. For comparison, the curve measured on the as-received support, ii the as-pyrolized carbon composite catalyst, and iii carbon is also presented in Fig.

The as-received carbon did not the as-leached carbon composite catalyst. The cathode catalyst show any catalytic activity toward oxygen reduction. The metal- loadings were maintained at 6. The experiments were free carbon support exhibited much higher activity when compared performed using 30 psi 2. Ohmic potential drop was not compen- sated for in the measurement. Particularly, it should be noted that the subsequent dissolution of Co and Fe metals from the as-pyrolized catalyst does not cause any activity loss, but rather increases the activity.

The PEM fuel cell with the as-leached carbon composite catalyst showed the current densities of 0. The carbon composite catalysts were synthesized by the deposi- tion of the metal-nitrogen complexes with different compositions i. The fuel cell test results are summarized in Fig. As shown in Fig. The fuel cell performances of the optimized carbon composite catalyst were presented in Fig.

Characterizations of metal—nitrogen complexes and metallic species in the carbon composite catalyst Fig. The catalyst was prepared by the CoNx deposition onto the metal-free carbon support, followed by the pyrolysis.

No chemical leaching was conducted on the pyrolized catalysts. For compari- son, a reference spectrum for a pure cobalt foil is given in Fig. As indicated in Fig. All the catalysts were subjected to the chemical leaching.

The experiments dination with nitrogen. Therefore, it is clear that the metal—nitrogen were performed using 30 psi back pressure on both anode H2 and cathode O2 compartments.

As a matter of fact, the dissolution of metal- lic species from the as-pyrolized catalyst increases the activity as and the carbon composite catalyst. The XRD pattern for the carbon presented in Fig. The carbon Cox Fey and to the cementite phase Fe3 C. H2 SO4 solution. ICP-MS analysis shows that the concentra- covered with graphitic layers of the carbon composite catalyst, and tions of Co and Fe decreased from XPS detected result of the pyrolysis in the presence of Co and Fe metals [40,47].

Since Fig. Therefore, the composition analysis by two techniques indicates that Co and Fe particles on the pyrolized catalyst sur- face were removed by the subsequent chemical treatment in H2 SO4 solution, whereas metal particles encased in the carbon structure survived the leaching treatment as indicated in Figs.

TEM images of a the metal-free carbon support and b the carbon compos- ite catalyst. The carbon composite catalyst was subjected to the chemical leaching.

The Co Fe results are summarized in Table 4 along with the nitrogen content and the fuel cell performance of each sample. The current den- before leaching Upon pyrolysis, the peak splits into three broad peaks at ca. Finally, the XPS spectrum obtained after the chemical leaching shows no dominant peak for pyrrolic nitrogen. Pyridinic nitrogen refers to the nitrogen atom bonded to two carbon atoms on the edge of graphite planes that is capable of adsorbing molecular oxygen and its intermediates in the oxygen reduction reaction.

Recently, Sidik et al. Using a semi-empirical quantum chemical simulation, Strelko et al. Also, two mechanisms of oxy- Fig. Powder XRD patterns of the metal-free carbon support and the carbon composite catalyst.

The carbon composite catalyst was subjected to the chemical gen chemisorptions on evacuated carbons were suggested: namely, leaching. The data indicate that oxygen. Galvanostatic potential transient measured on the carbon composite catalyst for stability test. The cathode catalyst loading was 2. XPS spectra of N 1s region obtained for the catalysts pyrolized in the absence 3.

Durability study of PEM fuel cell with the carbon composite and presence of transition metals Co and Fe. The carbon composite catalysts were cathode catalyst subjected to the chemical leaching. The results indicated a remark- fuel cell with the carbon composite cathode catalyst for stability able fold enhancement for hydroperoxide decomposition for test. The authors have concluded out applying the back pressure. The cathode catalyst loading was that pyridinic nitrogen doping into edge plane defects is an impor- 2.

Note that only ca. Two dominant peaks are observed at doped with pyridinic and graphitic nitrogens facilitates the reduc- This result con- oxygen functionalities, due to an increased electron-donor property of carbon.

The XPS data are presented in Fig. It was found data not shown that the catalyst prepared without metal—nitrogen com- plexes showed no improvement in the activity in comparison to the metal-free carbon support. Yeager [29] and Wiesener [30] have suggested that the transition metals do not act as an active reaction site for oxygen reduction, but rather serve primarily to facilitate the stable incorporation of nitro- gen into the graphitic carbon during high-temperature pyrolysis of metal—nitrogen complexes.

This means that high-temperature pyrolysis in the presence of transition metals yields a carbona- ceous layer with substantial nitrogen groups that are catalytically active for oxygen reduction.

Our electrochemical and XPS results also indicate that the high-temperature pyrolysis combined with the chemical leaching facilitates the joint incorporation of pyri- Fig. References [1] M. Rao, B. Damjanovic, J. Adzic, in: J. Lipkowski, P. Ross Eds. Markovic, P. Ross, Electrochim. Acta 45 Ross, Surf. Gasteiger, S. Kocha, B. Sompalli, F.

Wagner, Appl. B 56 9. Jasinski, Nature Widelov, R. Larsson, Electrochim. Acta 37 Lalander, R. Cote, D. Guay, J. Dodelet, L. Weng, P. Bertrand, Electrochim. Acta 42 Cote, G. Lalande, D. Dodelet, J. Gouerec, M. Savy, J. Download preview PDF. Skip to main content. This service is more advanced with JavaScript available. Advertisement Hide. Authors Authors and affiliations John D. This process is experimental and the keywords may be updated as the learning algorithm improves.

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