Carbon Nanofilaments Research Articles

Effect of carbon fiber structure of Marimo carbon on polymer electrolyte fuel cell performance

Fibrous carbon has attracted attention for use as a carbon support of polymer electrolyte fuel cells (PEFC). In this study, Marimo carbon (MC), a fibrous carbon, was used as the carbon support. The MC has a higher order structure in which many carbon nanofilaments (CNFs) are grown on the surface of diamond particles (dia.). The MC was synthesized by the contact reaction between a Ni supported oxidized diamond (Ni/O-dia.) and CH4 gas, the carbon source of the CNFs. The flow rate of the CH4 gas during the MC synthesis altered the structure of the CNFs. A thick CNFs was observed in the MC with a low CH4 gas flow rate, which was not observed in the MC with a high CH4 gas flow rate. The MC with the thicker CNFs had wider interspaces between the CNFs and higher Pt supporting amounts. Electrochemical measurements of the Pt support MC (Pt/MC) were evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and current–voltage (I–V) measurements. The lower CH4 gas flow rate of the MC indicated faster charge transfer. The MC structural and charge transfer changed with the flow rate of the CH4 gas altered the electrochemical active surface area (ECSA), the oxygen reduction reaction (ORR) catalytic activity and the I–V performance of the Pt/MC.

Effect of fine structure and pore volume in the Marimo-like carbon cathode material on the oxygen reduction reaction for the polymer electrolyte fuel cell

We measured the rotating ring-disk electrode (RRDE) voltammetry curves of a Pt catalyst supported on Marimo-like carbon (MC) to clarify the effect of carbon nanofilaments (CNFs) morphology and fine structures consisting of MC cathode material on the oxygen reduction reaction (ORR) activity for Polymer electrolyte fuel cells. The specific surface area and pore volume of MCs are influenced by their morphology and fine structures. MCs grown with Ni–Cu bimetal catalyst (represented as Ni80Cu20MC), having an octopus-like morphology, yielded four times larger total pore volume than that measured from the MC grown with Ni catalyst (Ni100MC). In the case of Ni80Cu20MC, coin-stacked graphenes perpendicular to the filament axis formed CNFs. Ni100MC consists of cup-stacked CNFs. The difference in the graphene stacked fine structure resulted in a different number of graphene edges covering the CNF surface; however, both supported Pt particle sizes and their distributions were similar. Linear sweep voltammetry with a RRDE revealed that the Pt/Ni80Cu20MC ORR onset potential was higher than that observed from the Pt/Ni100MC. This value is suggested to be correlates with the ORR activity. The origin of the ORR difference was discussed on the basis of the structural difference in the MCs.

Production of hydrogen and carbon nanofilaments using a novel reactor configuration: hydrodynamic study and experimental results

A novel reactor configuration combining two beds, a central fluidized bed and an annular mobile bed, was designed for the production of hydrogen and carbon nanofilaments via dry reforming of gases produced from the pyrolysis of plastic waste. This combination allows for easy recovery of these nanomaterials and, since the mixture of catalyst and carbon formed is continuously fluidized, it also prevents blockage. Understanding the hydrodynamics is crucial for choosing the optimal operating conditions. Thus, a cold mock-up unit of the same size has been built and used. Since the gases produced by plastic pyrolysis are mainly composed of unsaturated hydrocarbons, the prototype reactor setup has been operated using ethylene as a surrogate molecule. The preliminary experimental results of the reactor operation with ethylene obtained so far are very promising and confirm the operability of the process. Next step is to operate continuously for longer time and reach a production of 1kg/h of carbon nanofilaments.

Marimo nanocarbons composed of a cup-stacked carbon nanofilaments as anode catalyst support for enhanced power performance of direct methanol fuel cells

Marimo nanocarbon(MNC) derived from C2 H4 and C3H6 contain many carbon nanofilaments (CNFs) with small filament diameters, whereas C2H6 and C3H8 contain many CNFs with large filament diameters. MNC(C2H4) and MNC(C3H6) pore sizes were approximately 25 nm, and MNC(C2 H4) and MNC(C3H6) specific surface area tended to be larger (C3H6). As a result, mesoporous MNC with small pore sizes can be synthesized using highly reactive alkanes as raw materials. The higher the carbon number of the raw material, the more functional groups and MNC(C2H4) and MNC(C3H6) were observed, as well as the more side chains and amorphous components. The highest surface functional group ratio was found in MNC(C3H8), while the lowest was found in MNC(C3H6). The stacking angle of graphene in CNF is gentler in MNC(C2H6) and MNC(C3H8), according to XRD results, and crystallinity is also higher in MNC (C3H8). As a result, high crystallinity MNC can be synthesized using low reactivity alkanes as raw materials. Finally, when used as a catalyst support for DMFCs, MNCs with more functional groups can improve power generation performance.

Carbon nanomaterial production using waste plastic pyrolysis over a new catalyst made from mining residues: Effect of plastic type

Pyrolysis and in-line catalytic decomposition of plastic waste were performed for the production of carbon nanomaterials (CNMs) and hydrogen. A new catalyst, Ni-UGSO (Nickel-UpGraded Slug Oxide), was used in a continuous mode, and its activity was compared to that of a typical Fe/Al2O3 catalytic formulation. Moreover, the pyrolysis-catalysis of different plastics (virgin high-density polyethylene (HDPE), used HDPE, and mixed plastics) was studied to investigate the effect of the plastic type on the quantity and quality of the produced CNMs. Ni-UGSO exhibited the highest catalytic activity for the production of CNMs and H2 of the two formulations tested, with yields of 56.6 kg/100 kgplastic and 13.2 kmol/100 kgplastic, respectively. The high activity and performance of Ni-UGSO were attributed to the synergistic effect of the Ni and Fe in Ni-UGSO. Scanning transmission electron microscopy (STEM) results revealed that most of the produced carbon was in the form of carbon nanofilaments (CNFs) of different diameters, ranging from 8 to 90 nm. The use of mixed plastics as a feedstock decreased the yield of CNMs by 10 wt%, and a layer of amorphous carbon covered the CNFs. This layer is due to the presence of polystyrene (PS), polyethylene terephthalate (PET), and other contaminants in the feedstock. Raman spectroscopy showed that the CNFs produced from used HDPE had the highest intensity ratio G/D (1.13).

Catalytic Conversion of Hydrocarbons and Formation of Carbon Nanofilaments in Porous Pellets

Catalytic conversion of hydrocarbons occurring at metal nanoparticles in porous pellets is often accompanied by the formation of coke in the form of growing heterogeneous film-like aggregates or carbon nanofilaments. The latter processes result in deactivation of metal nanoparticles. The corresponding kinetic models imply the formation and growth of film-like coke aggregates. Herein, I present an alternative generic kinetic model focused on the formation and growth of carbon nanofilaments. These processes are considered to deactivate metal nanoparticles and reduce the rate of reactant diffusion in pores. In this framework, the kinetically limited reaction regime is described by simple analytical expressions. The diffusion-limited regime can be described as well but only numerically. The model presented can be used for interpretation of experimental results.Graphical

The effect of copper on the multiple carbon nanofilaments growths by the methane decomposition over the oxidized diamond-supported nickel\u2013copper bimetallic catalyst

To clarify the indispensable parameters for the multiple carbon nanofilaments (CNFs) growths, in other words, having a unique Octopus-like morphology consisting of the Marimo-like carbon (MC), we have systematically studied to synthesize the MC by the decomposition of methane using oxidized diamond-supported Ni–Cu bimetallic catalysts. We discovered that a Cu addition of 20 wt.% by weight and a growth temperature in the region of 550 °C to 600 °C resulted in many CNF forms from a single catalyst particle, specifically the "Octopus-like" morphology of CNFs. We also discovered that the several CNFs forms might occur from the carbon dissolved in the sintered catalyst particles. We described a model process of the unique structure formation. We expect that the Octopus-like CNFs growth gives enough space volume in the MC for a mass transfer, consequently, it should contribute to realizing a higher power generation performance of a polymer electrolyte fuel cell (PEFC) although under a higher-voltage generation region.

Unveiling the existence and role of a liquid phase in a high temperature (1400 °C) pyrolytic carbon deposition process

Based on experiments aiming at depositing pyrolytic carbon onto carbon nanotubes by means of a chemical vapor deposition (CVD) process at 1400 °C, the work we report here demonstrates that the deposition involves the transient formation of a liquid phase (here organic), and that wetting physics is still able to apply in spite of the high temperature and the nanoscale, i.e., far beyond the condition range usually investigated. This was unexpected, because the high temperature makes all the physical and chemical processes involved transitory, including the fact that the liquid turns itself into solid carbon because of the ongoing carbonization process. The observations provide an estimate of the time scales of the involved processes, as they have to be short enough to complete in spite of the high temperature conditions. From a practical point of view, as the resulting material is a solid, all-graphenic carbon, the work demonstrates that using wetting physics in high temperature CVD can be a way to dramatically modify the surface energetics and the nano/microscale morphology of carbon nanofilaments. The statement is assumed to also apply to other chemical systems.

An enzymatic glucose sensor based on glucose oxidase immobilized cup-stacked carbon nanofilaments

An enzymatic glucose sensor based on glucose oxidase immobilized cup-stacked carbon nanofilaments

An enzymatic glucose sensor based on glucose oxidase immobilized cup-stacked carbon nanofilaments

An enzymatic glucose sensor based on glucose oxidase immobilized cup-stacked carbon nanofilaments

Platinum nanocluster catalysts supported on Marimo carbon via scalable dry deposition synthesis.

The development of efficient fuel cells greatly promotes reducing the consumption of fossil energy, and it is crucial to enhance the platinum (Pt) catalytic activity by optimizing both the nanoparticle size and support effect. In this study, we generate a smaller and uniform size of naked Pt nanocluster (NC) catalysts via a dry process in the gas phase, and using the direct powder embedded trapping method, the Pt NCs are spatioselectively supported on Marimo carbon (MC) that comprises a high density of carbon nanofilaments. At a minimum Pt loading of 0.05 mgPt cm−2 for both the anode and cathode in a single cell configuration, a membrane-electrode assembly (MEA) formed by the dry-deposition Pt-NC(d)/MC exhibits superior power density (rated) of 0.105 gPt kW−1 at a current density of 1.2 A cm−2, which is better output power density than the conventional MEA formed by Pt catalysts via a wet process. The origin of the improved performance is investigated using transmission electron microscopy; dry-deposition Pt catalysts that are monodispersely loaded on the outer surface of MC can facilitate not only the gas reaction but also leaving the generated water. The present results demonstrate that the dry deposition of Pt NCs on MC can be used as a scalable catalyst synthesis method to reduce the Pt loading.

A BRIEF METHOD FOR THE SYNTHESIS AND CHARACTERIZATION OF A HYBRID MATERIAL BASED ON CARBON NANOTUBES AND ALUMINA

This research is presented in the area of composite materials; whose matrix is alumina with carbon nanotubes. The synthesis of CNT-based materials in alumina is driven by the exceptional chemical and mechanical properties of both materials. For this proposal, critical aspects such as the processing technique, the interfacial mechanisms between the Al2O3matrix and CNTs were revised, without losing the focus on the application of this composite in the structural area and determining the strengthening of the matrix due to the presence of reinforcements. This study deals with the synthesis and characterization of a hybrid material based on multi-walled carbon nanotubes (CNTs) and alumina. A simple and efficient methodology is proposed, in which the composite material CNTs/alumina is prepared from the combination of nanofilaments with an aluminum-rich material. Characterization by MET gave evidence of typical carbon nanotube structures supported on aluminous material. Furthermore, MEB-EDS analysis of hybrid composite material confirmed the presence of carbon nanofilaments embedded in the alumina matrix. This study as an initial phase of the research allowed to identify a simple and novel methodology that will be extended in characterization and determination of structural relationships with processing parameters, and it is considering to perform multiscale modeling to know the mechanisms inherent in the compatibility between the matrix and nanofilaments, and thus the phenomenon of reinforcement

Development of Negative Electrode for Calcium Ion Battery Using Marimo Nano Carbon

Lithium-ion batteries (LIBs) are used in various fields due to their high energy density and high cycle characteristics. In general, graphite materials are used for the negative electrode materials for lithium-ion batteries (LIBs). However, since the amount of Li ion that can be stored in the graphite material of the negative electrode is approaching the theoretical value for LIBs, a significant increase in capacity cannot be expected.Calcium ion batteries (CIBs) use Ca ion as charge carriers. Therefore, they can be expected to have twice the capacity of LIBs. In LIBs, charge and discharge mechanism occurs by intercalation and deintercalation of Li ion into graphite layers. However, Ca ion are poor in reactivity, intercalation and deintercalation of Ca ion do not occur in the graphite negative electrode, and charge and discharge capacity cannot be obtained. For this reason, we used Marimo Nano Carbon (MNC) as a new negative electrode material. MNC is an aggregate of carbon nano filaments (CNF). CNF has a layered structure similar to graphite and also has amazing electronic properties and many other unique properties. This CNF has coin-stacked structure in which graphene layers are stacked, and the edge surface is exposed. Hence, we expected that MNC negative electrode would react with less reactive Ca ions and indicated larger charge / discharge capacity than that of the graphite negative electrode. In this study, we evaluated MNC negative electrode performance.For MNC synthesis, nano metal particles carried on oxidized diamond were used. Oxidized diamond has oxygen-containing functional groups arranged regularly. Thus, nano metal particles are a highly dispersed on it. Pd metal was used for carried metal. Pd metal could synthesized CNF having coin-stacked structures. Pd metal was carried on oxidized diamond by metal nano-colloidal method. C2H4 as a feedstock for CNF was used, and MNC was synthesized by the chemical vapor deposition (CVD) method.When MNC was used as the negative electrode material, the charge and discharge capacity was larger than that of the graphite negative electrode. In addition, the intercalation of Ca ions between the graphene layers was confirmed.

Preparation of Catalyst for a Polymer Electrolyte Fuel Cell Using Different Loading Methods

1. IntroductionPlatinum (Pt) exhibits high catalytic activity in polymer electrolyte fuel cells (PEFCs). However, reducing the amount of Pt is necessary because it is rare and expensive. For a Pt catalyst support, we have applied Marimo-like carbon (MC) which is a novel spherical carbon material comprising entangled carbon nanofilaments (CNFs). Since the CNFs in MC have a cup-stack primary structure of the graphene sheets, the sheet edge can effectively function as a site for the Pt catalyst. Although the supported Pt catalysts have been typically prepared via a wet process, a better loading method is being explored. In this study, the catalyst is prepared via a dry process, where Pt nanoparticles (NPs) generated in a gas phase are directly deposited onto the support surface. The catalytic activity is improved due to increasing the specific surface area which facilitates highly dispersive Pt loading with a small particle size.2. ExperimentalThe catalyst supports used were carbon black and MC. MC was synthesized by chemical vapor deposition1,2), using an oxidized diamond-supported Ni catalyst as the catalyst core. Methane was used as the reaction gas. The Pt loading by the dry process was performed using magnetron sputtering system, nanojima®3); Pt atoms or ions generated by sputtering a Pt disk target were grown into Pt NPs in a gas phase by introducing a cooled buffer-gas. Alternatively, Pt NPs were loaded using a nano-colloidal solution method in the wet process; Pt precursor was added to the carbon suspension with a sodium hydroxide solution, where the reducing agent for the platinum precursor yielded metallic Pt NPs on the carbon surfaces. The obtained suspension was centrifuged, washed and dried to prepare the Pt/C catalyst. The amounts of Pt loading were 6-8 wt%. The characteristics of the catalyst was evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The catalyst performance was evaluated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) with a rotating ring disk electrode (RRDE).3. Results and discussionThe morphologies of the loaded Pt catalysts were observed using TEM. The Pt NPs supported on the MC prepared by the dry process were ultra-fine NPs with the average size of 2.25 nm in diameter. In the dry process, highly dispersed and small Pt NPs were prepared because the Pt NPs synthesized in the beam could be supported directly on the carbon surfaces. In the wet process, on the other hand, the average diameter of the Pt NPs on the MC was 2.68 nm. The larger size in the wet process is caused by grain growth in the reduction reaction, because reduced Pt on the carbon surfaces acts as a catalyst. These results suggest that the dry process was more viable than the wet process for the preparation of a supported Pt catalyst with a small size, increasing the specific effective Pt surface area.The electrochemical measurements were performed for the prepared catalysts. For each sample, the electrochemical surface area (ECSA) value was evaluated from the CV curve based on the hydrogen adsorption peak. When MC was used as the catalyst support, the ECSA value was higher than that with a catalyst support of carbon black. Since carbon black is porous, hindered diffusion of the substances (i.e. reaction gases and/or product water) results in much less catalytic activity of Pt supported in a nanopore. Therefore, carbon black causes a decrease in the ECSA. In contrast, MC is a fibrous carbon, and the Pt NPs supported on the CNFs surfaces can be effectively used. The results have revealed that the fibrous structures in the MC support exhibit a higher ECSA value than that for the porous support of carbon black.1) K. Nakagawa et al., J. Mater. Sci. 44, 221-226 (2009). 2) T. Ando et al., US Patent No. 7608331 (2004.5.24). 3) A. Nakajima et al., US Patent No. 10283333 (2019.5.7). Figure 1

Synthesis of Si/Marimo Carbon Composite and Its Charge-Discharge Performance for a Lithium Ion Battery

1. IntroductionThe theoretical capacity of graphite as a lithium ion battery (LIB) anode (372 mAh g-1) is not enough sufficient for electric vehicles (EVs). Si can include Li ions into its crystal lattice with a charge voltage as low as that of graphite. The use of Si for LIB applications has attracted considerable attention because of its high capacity (3579 mAh/g). However, insertion of Li ions into Si crystal lattice causes a large volume change (approximately about 300 %), which produces many cracks in the Si crystal during charge-discharge processes. Although carbon black is used to improve the conductivity of Si, a large volume change could break the electron conduction networks. This phenomenon makes Si anodes not viable for LIBs, particularly due to the shortening of battery lifetime. In this research, we applied a new carbon material, Marimo carbon (MC), as a conductivity enhancer. MC has a spherical structure comprising carbon nanofilaments (CNFs) growing radially from an oxidized diamond core. The CNFs are intertwined with each other in a complicated fashion. Moreover, there are vacant space volumes of a few hundred nanometers between the CNFs (1). We attempted to synthesize Si/MC composites in which Si particles existed in the space volumes between the CNFs. These space volumes can minimize the influence of volume changes of Si particles. Si/MC composites can maintain a uniform electron network during charge-discharge processes (2).2. ExperimentalOxidized diamond supported Ni catalyst (Ni-O-diamond, containing 5 wt% Ni metal) was prepared by impregnating an aqueous solution of Ni(NO3)2 · 6H2O into the suspended O-diamond, followed by evaporation, and calcination at 400 °C 3 h in air. Si powder and Ni-O-diamond were mixed to prepare Si+Ni-O-diamond by dry or wet processes. In the dry process, 500 mg of Si+Ni-O-diamond was prepared by mixing 450, 400, and 250 mg Ni-O-diamond and 50, 100, and 250 mg of Si powder, respectively, a rotary device for 1 h at room temperature. In the wet process, Si+Ni-O-diamond was prepared by dispersing Ni-O-diamond and Si powder in the same aforementioned proportions in 30 mL hexane, followed by drying at room temperature for a few days. Si/MC composites were synthesized in a chemical vapor deposition rotary fluidized bed flow-reactor. CNFs were grown by heating Si+Ni-O-diamond at 550 °C for 3h in methane gas. The charge-discharge tests of the composites were performed between 0.05 to 1.5 V using a three-electrode cell assembled in Ar-filled globe box. A lithium foil was used as counter electrode, and a solution of 1 M LiPF6 in a mixture of ethylene carbonate, ethyl methyl carbonate (v/v = 1 : 2) and 1 % vinylene carbonate was used as the electrolyte.3. Results and discussionWe succeeded in synthesizing Si/MC composites without the separation of Si and MC regardless of the process or the proportions of the samples. We conducted charge-discharge tests on three samples to determine which might have more CNFs based on the SEM images. These samples were synthesized using Si+Ni-O-diamond prepared in the following proportions and processes : (A) Si : Ni-O-diamond = 1 : 1 in the dry process, (B) Si : Ni-O-diamond = 4 : 1 in the wet process, (C) Si : Ni-O-diamond = 9 : 1 in the dry process. Figure 1 shows the results of the charge-discharge tests at 0.05 mA cm-2 between 0.05 and 1.5 V. We concluded that the Si/MC composites were viable anodes as all samples exhibited charge-discharge curves. Sample C gave the best specific discharge capacity (968 mAh g-1). We intend to improve the synthesis process to attain the target capacity for EVs (2830 mAh g-1). Sample C, which had the highest proportion of Si, exhibited charge-discharge plateaus at a voltage bellow 0.4 V. All samples showed gaps between the charge capacity and discharge capacity. This irreversible capacity loss is caused by the decomposition of the electrolyte on the surface of the electrode to form SEI. In future studies, we aim to reduce this gap for increasing the initial coulombic efficiency. Nonetheless, we expect Si/MC composites to increase the anode capacity based on our success in synthesizing a Si/MC composite which contained a high proportion of Si (79.1 %) using Si+Ni-O-diamond prepared in the proportion of 9 : 1 (Si : Ni-O-diamond) in a dry process.(1) K. Nakagawa et al., J.Mater Sci. 44, 221-226 (2009), (2) T. ANDO and Y. Kanda, JP Patent No.6106870 (2013) Figure 1

Failure analysis of secondary reformer burner nozzles made from Incoloy 825 in an ammonia production plant

The aims of this study were to perform failure analysis and to assess the microstructural changes of secondary reformer burner nozzles made from Incoloy 825 in an ammonia production plant. The nozzles were in service for about 3 years under the atmosphere of synthesis gas (syngas) and wet air. Various techniques including on-site visual inspection, scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), grazing incidence X-ray diffraction (GIXRD), and micro-hardness testing were employed to assess the root causes of failure. Results of visual inspection showed green rot, pitting, cracking, spallation, and coking in the secondary reformer burner nozzles. Microscopic data and Phase analysis of the external surface of the nozzle indicated the formation of a substantial amount of oxides and spinel from elements such as Fe, Cr, Mn, and coke in the form of carbon nano-filaments. Moreover, some voids, cracks, and intergranular and intragranular internal oxidation were observed in the cross-section of the outer wall of the nozzle. The formation of oxides and spinel, as the product of in-situ oxidation of carbides, is suggestive of the occurrence of type III metal dusting. Under these conditions, the alloy underwent considerable volume expansion that led to the nucleation and growth of voids and cracks, and ultimately, the failure of the nozzle. Some of the microstructural changes observed include the nucleation and growth of massive secondary carbides of Cr21Mo2C6 type and platelet carbides of (Ti,Mo)C type, and degeneration of primary precipitates of Ti(C,N) type formed in the nozzles.

Catalytic Dry Reforming and Cracking of Ethylene for Carbon Nanofilaments and Hydrogen Production Using a Catalyst Derived from a Mining Residue

In this study, iron-rich mining residue (UGSO) was used as a support to prepare a new Ni-based catalyst via a solid-state reaction protocol. Ni-UGSO with different Ni weight percentages wt.% (5, 10, and 13) were tested for C2H4 dry reforming (DR) and catalytic cracking (CC) after activation with H2. The reactions were conducted in a differential fixed-bed reactor at 550–750 °C and standard atmospheric pressure, using 0.5 g of catalyst. Pure gases were fed at a molar ratio of C2H4/CO2 = 3 for the DR reaction and C2H4/Ar = 3 for the CC reaction. The flow rate is defined by a GHSV = 4800 mLSTP/h.gcat. The catalyst performance is evaluated by calculating the C2H4 conversion as well as carbon and H2 yields. All fresh, activated, and spent catalysts, as well as deposited carbon, were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), temperature programmed reduction (TPR), and thermogravimetric analysis (TGA). The results so far show that the highest carbon and H2 yields are obtained with Ni-UGSO 13% at 750 °C for the CC reaction and at 650 °C for the DR reaction. The deposited carbon was found to be filamentous and of various sizes (i.e., diameters and lengths). The analyses of the results show that iron is responsible for the growth of carbon nanofilaments (CNF) and nickel is responsible for the split of C–C bonds. In terms of conversion and yield efficiencies, the performance of the catalytic formulations tested is proven at least equivalent to other Ni-based catalyst performances described by the literature.

Carbon Nanotube Effect on the Ductility, Flexural Strength, and Permeability of Concrete

Recently, remarkable types of carbon nanofilaments called carbon nanotubes (CNTs) have raised the interest of many concrete and cementitious composite researchers due to their significant mechanical, electrical, thermal, kinetic, and chemical properties. These nanofilaments are considered promising applicants to use in producing high-performance cement-based composite materials. In this research, the effect of CNT use on the flexural strength, strain capacity, permeability, and microstructure of concrete was investigated. Concrete batches of 0, 0.03, 0.08, 0.15, and 0.25 wt.% CNTs were prepared using a mixing method that consisted of a 30-minute solution sonication and a 60-minute batch mixing. On the 28th day, the mechanical properties were determined. The results indicated that concrete prepared using high CNT contents of 0.15 and 0.25 wt.% increased the flexural strength by more than 100% in comparison with 0% CNT concrete. Furthermore, the results showed that CNTs would increase the ductility of concrete beams by about 150%. The permeability test results showed the benefits of CNT inclusion in reducing the permeability of concrete. The permeability coefficient (kT) decreased by at least 45% when CNTs were added to concrete. A qualitative microstructural analysis illustrated the uniform dispersion of CNT filaments within the concrete hydration products in all batches.

Carbon Fiber Reinforced Thermoplastics Molding by Using Direct Resistance Heating to Carbon Nanofilaments Grafted Carbon Fiber

In the automobile industry, carbon fiber reinforced thermoplastics (CFRTP) have attracted attention as potential materials to reduce the weight of the automobile body. In order to apply CFRTP to mass-produced automobile parts, it is necessary to develop the reduction of molding time and the impregnation method into the carbon fiber (CF) for the thermoplastic resin, which has relatively high viscosity. Although the conventional hot press molding uses only the heat transfer from the mold to the molding materials, it is expected to develop a new molding method for CFRTP using heat generation of the materials themselves to overcome these issues. As a method of heating the carbon fiber, there is a direct resistance heating method, in which carbon fiber is directly energized and heated by Joule heat. We have developed resistance welding methods in which carbon nanotube (CNT) grafted carbon fiber (CNT-CF) is used for the heating elements, and revealed that the higher welded strength is obtained by using CNT-CF instead of CF. Therefore, the carbon nanofilaments (CNF) grafted carbon fiber (CNF-CF) including CNF-CF is expected not only to be used as a resistance heating medium at the time of joining but also as a reinforcing fiber and as a self-heating member at the time of molding. In this study, we develop the CFRTP molding method by using direct resistance heating to CNF-CF in the hot press molding. CFRTP ([0°]20) with the volume fractions (Vf) of 40% are molded by conventional hot press and hot press with direct resistance heating to reinforcing fiber. CF or CNF-CF is used for reinforcement. CFRTP molded by hot press with direct resistance heating to CNF-CF indicated lower void content than CFRTP molded by hot press with direct resistance heating to CF. Compared to CFRTP molding by only hot press, hot press molding with direct resistance heating to CNF-CF can mold CFRTP with low void content.

Effects of Carbon Nanofibers and Carboxyl Functionalized Multi-Walled Carbon Nanotubes on Mechanical Damping Behavior of Cement Paste.

Different ratios of carbon nanofibers (CNF) and carboxyl functionalized multi-walled carbon nanotubes (CMWCNT), dispersed by the polycarboxylate based superplasticizer, were added in this study to investigate mechanical damping behavior of cement paste. The additions of CNF and CMWCNT simultaneously improved loss tangent, storage modulus and loss modulus of cement paste to different extents at 0.2 Hz the frequency. The cement paste exhibited higher storage modulus and loss modulus with addition of CNF. The addition of CMWCNT provided higher loss tangent but lower modulus compared to the CNF modified cement paste. The damping mechanisms for cement incorporated with CNF and CMWCNT were explained by the effective "stick-slip" motion which was generated by the possible sliding among the nanofilaments at the interface between the fibers and cement particles. The enhanced stiffness was attributed to the optimized microstructure and bridge effect induced by the nanoscale nanofilaments. Both total porosity and mesoporosity decreased due to the nano-filler effect from the carbon nanofilaments. The SEM technique indicated that excessive addition of CNF/CMWCNT should be avoided to minimize possible fiber agglomeration in the cement matrix.