Carbon Filaments Research Articles

Gasification characteristics of carbon species derived from model reforming compound over Ni/Ce–Zr–O catalysts

This work addresses a thermogravimetric method for the steam gasification of carbon deposited over ceria–zirconia supported nickel (10% Ni/CZO) catalysts. The carbon deposits, which were obtained from the decomposition of isooctane over 10% Ni/CZO catalyst at 500, 650, and 725°C, respectively, were used as the model species. Gasification temperature and characteristics of different carbon species have been investigated, and the resulting gaseous products were measured by FT-IR spectroscopy and mass spectroscopy. The carbon species formed at different decomposition temperatures indicated distinctly different ability for gasification. Combined with features of TPO profiles and SEM images, our experiments suggest that the coating carbon, which covers the surface of Ni/CZO catalyst, can be removed by gasification at low temperatures around 600°C. However, the gasification degree of filamentous carbon species depends on its formation temperature. For filamentous carbon obtained from isooctane decomposition at 500°C the gasification starts at 690°C, while filamentous carbon species obtained from isooctane decomposition at temperatures ≥650°C undergo complete gasification at this temperature.

Study of tensile behavior for high-performance fiber materials under high-temperature loads

Textile high-performance filament yarn subjected to extremely high thermal loads can be found in various technical application fields. Besides the mechanical loads, textile fiber materials have to also satisfy high safety requirements in these applications with respect to thermal loads. Some of the main fields of application in the field of mechanical engineering are turbines, drive devices, rocket components and fire protection coatings. Textile grid-like structures are also being increasingly used in civil engineering as reinforcements (textile concretes). The design and development of textile structures for these applications demands studying and acquiring the material behavior under high thermal loads. Neither sufficient data nor standardized testing methods have been extensively achieved for evaluating the tensile characteristics of filament yarns under thermal influences. Hence, studying the thermal behavior of these yarns, which are used as input material for the reinforcing structures, is essential. The impact of the standard atmospheric condition on the oxidation behavior of the yarns, as in the case of carbon filament yarns and their influence on the physicochemical and tensile mechanical properties, have to be studied as well. This paper aims to address this issue and provides an insight into the current research about the development and realization of a novel test stand and the subsequent study of tensile mechanical behavior for textile high-performance fiber material under extreme thermal loads together with their physicochemical behavior.

TiO2-supported catalysts for the steam reforming of ethanol

TiO2 was used as support for Ni, Co and Cu to prepare catalysts for the steam reforming of ethanol, due to its known tendency to form strong metal–support interaction (SMSI) with some metals. The samples were prepared following different procedures, tuning the reducibility of the active phase and its interaction with the support. The latter parameter showed pivotal to impart suitable catalytic activity and most of all stability towards coking. Indeed, the insurgence of SMSI may allow to keep the active phase dispersed, improving activity and inhibiting the formation of carbon filaments over the active phase.The comparison between different active phases (Ni, Co, Cu, 10wt%) confirmed Ni as very active, although it has a higher tendency to form carbon filaments. This drawback may be at least partially controlled by favouring high Ni dispersion through the formation of a mixed oxide with the support. The calcination temperature, and in general the preparation procedure for the catalyst, showed of pivotal importance to establish SMSI. In particular, calcination at relatively low temperature (i.e. 500°C) induced initially a higher dispersion of the active phase (mean Ni crystal size 7nm), however not accompanied by sufficient stabilisation during activity testing (mean Ni crystal size increased to 44nm). By contrast, calcination at higher temperature (i.e. 800°C) favoured the instauration of a SMSI and the formation of a mixed oxide (NiTiO3), which, after activation, allowed the coexistence of smaller particles, more active and resistant to deactivation and sintering, together with the more sintered ones (mean Ni crystal size 27nm before and after activity testing). Different characterisation data (XRD, FT-IR, TPR, TEM) allowed to conclude the need of calcination at high temperature to achieve sufficient activity and resistance of the catalyst for this application.Co and Cu proved more promising as for C balance, although their activity at low temperature was unsatisfactory, mainly due to poor activity for CC bond cleavage.The characterisation of the spent catalysts by XRD, TEM and Raman allowed to evidence the different types of C deposed and to check for active phase stability against sintering.

Comparative Study of the Growth of CNTs on Stainless Steel with and without the External Catalyst

Multi-walled carbon nanotubes were synthesized on 316 stainless steel substrate by chemical vapor deposition through two different methods: 1- without use of any external catalyst and using ethylene as the carbon precursor and 2- using ferrocene as an external source of catalyst particles, dissolved in toluene, as the carbon precursor. Carbon nanotubes grown by the two methods were characterized by scanning and transmission electron microscopy and X-ray diffraction methods and were compared subsequently to determine certain characteristics of each method. Good coverage and homogeneity was observed in both cases. However, the carbon layer was thicker and denser in externally catalyzed samples. Two different mechanisms, namely, base and tip modes, were observed for the nanotubes growth, each with particular characteristics stemming from the synthesis methods. Surface nano-features and external catalyst behavior were found to have the dominant role in determining the morphology of carbon filaments in intrinsically and externally catalyzed samples, respectively.

Autothermal syngas production from model gasoline over Ni, Rh and Ni–Rh/Al2O3 monolithic catalysts

On-board reforming of liquid fuels is attractive for fuel cell-powered auxiliary power units in vehicles. In this work, monometallic Ni/Al2O3/cordierite, Rh/Al2O3/cordierite and bimetallic Ni–Rh/Al2O3/cordierite monolithic catalysts were prepared, characterized and tested in ATR of isooctane for syngas production. Compared to monometallic formulations, the bimetallic Ni–Rh/Al2O3 catalyst was active for ATR at lower temperature and H2 production already reached the equilibrium composition in 400–550 °C temperature range. The Ni–Rh/Al2O3 catalyst exhibited stable performances for 140 h in ATR of isooctane at 700 °C, and was unaffected by oxidizing conditions at 700 °C. Thermoneutral reactions conditions at H2O/C = 2 were obtained with O/C = 0.66. Carbon deposition was marginal during ATR of isooctane and no carbons whiskers were detected. Post-reaction characterizations showed that the Ni particles were small enough to prevent filamentous carbon formation, while Rh also prevented carbon film deposition by improving the gasification of adsorbed C with steam.

Hydrogen induced redox mechanism in amorphous carbon resistive random access memory

We investigated the bipolar resistive switching characteristics of the resistive random access memory (RRAM) device with amorphous carbon layer. Applying a forming voltage, the amorphous carbon layer was carbonized to form a conjugation double bond conductive filament. We proposed a hydrogen redox model to clarify the resistive switch mechanism of high/low resistance states (HRS/LRS) in carbon RRAM. The electrical conduction mechanism of LRS is attributed to conductive sp2 carbon filament with conjugation double bonds by dehydrogenation, while the electrical conduction of HRS resulted from the formation of insulating sp3-type carbon filament through hydrogenation process.

Hydrogen and multiwall carbon nanotubes production by catalytic decomposition of methane: Thermogravimetric analysis and scaling-up of Fe–Mo catalysts

Fe-based catalysts doped with Mo were prepared and tested in the catalytic decomposition of methane (CDM), which aims for the co-production of CO2-free hydrogen and carbon filaments (CFs). Catalysts performance were tested in a thermobalance operating either at isothermal or temperature programmed mode by monitoring the weight changes with time or temperature, respectively, as a result of CF growth on the metal particles. Maximum performance of Fe–Mo catalysts was found at the temperature range of 700–900 °C. The addition of Mo as dopant resulted in an increase in the rate and amount of deposited carbon, reaching an optimum in the range 1.7–5.1% (mol) of Mo for Fe–Mo/Al2O3 catalysts, whereas for Fe–Mo/MgO catalyst an optimum at 5.1% Mo loading was obtained. XRD study revealed the effect of the Mo addition on the Fe2O3/Fe crystal domain size in the fresh and reduced catalysts. Tubular carbon nanostructures with high structural order were obtained using Fe–Mo catalysts, mainly as multiwall carbon nanotubes (MWCNTs) and bamboo carbon nanotubes. Fe–Mo catalysts showing best results in thermobalance were tested in a rotary bed reactor leading to high conversions of methane (70%) and formation of MWCNTs (5.3 g/h).

Study of the properties of supported Pd catalysts for steam and autothermal reforming of methane

The effect of support kind on the structure, surface properties and catalytic behavior of Pd catalysts supported on alumina and mixed La2O3–Al2O3 oxides, prepared by impregnation and sol–gel method was studied. It was found that the catalytic performances of Pd catalysts in steam reforming (SR) and autothermal reforming (ATR) of methane were significantly affected by the kind of support. The highest specific reaction rate and TOFsCH4 of La-containing Pd catalysts in SRM were related to the electronic interaction between Pd and modified alumina support surface with La oxide species and formation of Pd0[Pdδ+OxLa] like species, promoting the CH4 activation and carbon oxidation. Despite the filamentous carbon formation these catalysts exhibited the highest activity and stability in ATR caused by the presence of small Pd particles with average particle size of about 14–17nm. It was shown that the wide particle size distribution up to 70nm and the formation of encapsulated carbon species are responsible for the fast deactivation of non-La promoted Pd/Al catalyst.

Highly Coke‐Resistant Ni Nanoparticle Catalysts with Minimal Sintering in Dry Reforming of Methane

Nickel catalysts are typically used for hydrogen production by reforming reactions. Reforming methane with carbon dioxide, called dry reforming of methane (DRM), is a good way to produce hydrogen or syngas (a mixture of hydrogen and carbon monoxide) from two notable greenhouse gases. However, Ni catalysts used for DRM suffer from severe coke deposition. It has been known that small Ni nanoparticles are advantageous to reduce coke formation, but the high reaction temperature of DRM (800 °C) inevitably induces aggregation of the nanoparticles, leading to severe coke formation and degraded activity. Here, we develop highly coke-resistant Ni catalysts by immobilizing premade Ni nanoparticles of 5.2 nm in size onto functionalized silica supports, and then coating the Ni/SiO2 catalyst with silica overlayers. The silica overlayers enable the transfer of reactants and products while preventing aggregation of the Ni nanoparticles. The silica-coated Ni catalysts operate stably for 170 h without any degradation in activity. No carbon deposition was observed by temperature programmed oxidation (TPO), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. The Ni catalysts without silica coating show severe sintering after DRM reaction, and the formation of filamentous carbon was observed. The coke-resistant Ni catalyst is potentially useful in various hydrocarbon transformations.

Effect of CO<sub>2</sub> Pretreatment Operation Conditions on the Catalytic Performance and Structure of Ni-Co Bimetallic Catalyst

The performance of the Ni-Co bimetallic catalyst was significantly improved by a novel H2 and CO2 (HCD) pretreatment in the dry reforming of methane compared with traditional H2 pretreatment. The effects of the HCD pretreatment operating conditions, such as pretreatment time, temperature, gas feeding ratio, and gas flow rate, on the catalytic performance of Ni-Co bimetallic catalyst were investigated. The optimal pretreatment time, temperature, gas feeding ratio (CH4/CO2), and gas flow rate were 0.5-1 h, 780800 °C, 0:10, and 175-200 mL∙min-1, respectively. Biogas was simulated with CH4 and CO2 in a volume ratio of 1 and without any other diluted gas. The catalyst was characterized by Xray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetry (TG) coupled to differential scanning calorimetry (DSC). In a 511 h stability test under the optimized operating conditions, the catalyst pretreated with both H2 and CO2 exhibited excellent stability. The average conversions of CH4 and CO2, selectivities for H2 and CO, and volume ratio of H2/CO were 96%, 97%, 98%, 99%, and 0.98, respectively. The average carbon deposition rate over the Ni-Co bimetallic catalyst was only about 0.2 mg∙g-1∙h-1. The characterization results revealed that the sintering speed of the metal greatly decreased with testing time, and the metal particle will not greatly sinter with further testing time. The amount of deposited carbon on the catalyst gradually decreased and growth of filamentous carbon over the surface of the catalyst could be inhibited. 1325 Acta Phys. -Chim. Sin. 2014 Vol.30

Intrinsic Safety Factors for Glass & Carbon Fibre Composite Filament Wound Structures

The determination of intrinsic safety factors for glass and carbon fibre unidirectional composites and filament wound internally pressurised structures, is described. In such structures the fibres are placed on geodesic paths and the pressure induces tensile forces in them. The fibres ensure the strength of the composite and must break for it to fail. Failure is seen in such structures, to depend mainly on the accumulation of fibre breaks. These are initially randomly distributed but become critical when clusters of breaks develop. Long term behaviour of carbon fibre composites is controlled by the viscoelastic relaxation of the matrix around breaks, which can lead to further delayed fibre breaks. Failure in glass fibre structures can additionally be induced by stress corrosion of the glass fibres. This process does not seem to occur with carbon fibres and as the latter are increasingly used in critical structures emphasis is given to them. Until the development of clusters of fibre breaks, in a filament wound structure, no macroscopic changes in the composite behaviour are evident so that failure occurs in a sudden death manner. Multi-scale simulation, taking into account the characteristics of the composite components and scaling up their behaviour under load, accurately describes the overall behaviour of the composite structure. This approach not only allows the behaviour to be described, as a function of time, but also calculates the scatter which will occur in the behaviour of the structure. This allows the intrinsic safety factors of the composite structure to be quantified.

Selective oxidation of methane and carbon deposition over Fe2O3/Ce1−x Zr x O2 oxides

A series of Fe2O3/Al2O3, Fe2O3/CeO2, Ce0.7Zr0.3O2, and Fe2O3/Ce1−x Zr x O2 (x = 0.1–0.4) oxides was prepared and their physicochemical features were investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), and H2-temperature-programmed reduction (H2-TPR) techniques. The gas–solid reactions between these oxides and methane for syngas generation as well as the catalytic performance for selective oxidation of carbon deposition in O2-enriched atmosphere were investigated in detail. The results show that the samples with the presence of Fe2O3 show much higher activity for methane oxidation compared with the Ce0.7Zr0.3O2 solid solution, while the CeO2-contained samples represent higher CO selectively in methane oxidation than the Fe2O3/Al2O3 sample. This suggests that the iron species should be the active sites for methane activation, and the cerium oxides provide the oxygen source for the selective oxidation of the activated methane to syngas during the reaction between methane and Fe2O3/Ce0.7Zr0.3O2. For the oxidation process of the carbon deposition, the CeO2-containing samples show much higher CO selectivity than the Fe2O3/Al2O3 sample, which indicates that the cerium species should play a very important role in catalyzing the carbon selective oxidation to CO. The presence of the Ce–Zr–O solid solution could induce the growth direction of the carbon filament, resulting in a loose contact between the carbon filament and the catalyst. This results in abundant exposed active sites for catalyzing carbon oxidation, strongly improving the oxidation rate of the carbon deposition over this sample. In addition, the Fe2O3/Ce0.7Zr0.3O2 also represents much higher selectivity (ca. 97 %) for the conversion of carbon to CO than the Fe2O3/CeO2 sample, which can be attributed to the higher concentration of reduced cerium sites on this sample. The increase of the Zr content in the Fe2O3/Ce1−x Zr x O2 samples could improve the reactivity of the materials for methane oxidation, but it also reduces the selectivity for CO formation.

Ethanol Reforming Reactions Over Co and Cu Based Catalysts Obtained from LaCoCuO3 Perovskite-Type Oxides

The performance of catalysts derived from LaCo1−xCuxO3 (x = 0.0 or 0.2) perovskite-type oxides for steam reforming (SR) and oxidative SR of ethanol at 773 K was evaluated. All catalysts deactivated during SR of ethanol. In the absence of Cu, the increase of calcination temperature from 873 to 1,073 K did not affect the stability of the samples. On the other hand, for the samples containing Cu, it was detected a higher rate of deactivation when the calcination temperature was increased. The loss of activity of LaCoO3 was attributed to the oxidation of Co metallic particles and amorphous carbon formation as revealed by in situ XAFS and thermogravimetric analyses. The addition of Cu favored the formation of carbon filaments. Moreover, the presence of oxygen in the feed decreased the carbon formation, improving the stability of the catalysts.

Nickel catalyst auto-reduction during steam reforming of bio-oil model compound acetic acid

Transition metal catalysts widely used in refineries are provided as oxides and require pre-reduction to become activated. The auto-reduction of a NiO/Al2O3 catalyst with acetic acid (HAc) followed by HAc steam reforming was investigated in a packed bed reactor. Effects of temperature and molar steam to carbon ratio (S/C) on reduction kinetics and catalyst performance were analysed. Results showed that a steady steam reforming regime along with complete NiO reduction could be obtained after a coexistence stage of reduction and reforming. A 2D nucleation and nuclei growth model fitted the NiO auto-reduction. The maximum reduction rate constant was attained at S/C = 2. Steam reforming activity of the auto-reduced catalyst was just below that of the H2-reduced catalyst, probably attributed to denser carbon filament formation and larger loss of active Ni. Despite this, a H2 yield of 76.4% of the equilibrium value and HAc conversion of 88.97% were achieved at 750 °C and S/C = 3.

Adsorption of sulfur and nitrogen compounds on hydrophobic bentonite

The successful synthesis of hydrophobic magnetic composites formed by carbon filaments on bentonite surface has been obtained via chemical vapor deposition of ethanol and studied by electron microscopy, XRD, Mössbauer spectroscopy, Raman, and thermal analysis measurements. Bentonite clay was impregnated with different concentrations of iron salt and subjected to a chemical vapor deposition using ethanol as carbon source. The results suggest the reaction of iron on the surface of bentonite with ethanol leading to the formation of reduced iron phases and carbon. The carbon deposited is present as graphite, amorphous and filaments and the resulting materials show hydrophobic behavior besides magnetic properties conferred by the iron phases. This magnetic property is very interesting and allows the materials to be easily removed from the system. The hydrophobic bentonite was used as adsorbent of sulfur and nitrogen compounds, important contaminants in fuels, showing adsorption capacity of 38.7mgg−1 and 54.5mgg−1 for nitrogen and sulfur compounds respectively, a very high adsorption capacity compared with other materials with carbon presented in the literature.

Study on the Properties of Coffee Carbon Filament Yarns

Coffee carbon fiber is a kind of functional polyester fiber. Waste coffee grounds is milled into nanometer powder and then added to the polyester spinning fluid. Coffee carbon filament yarns have the functions of antibacterial deodorant, sending anion, and thermal insulation. In this paper, the morphology and properties of coffee carbon filament yarns were tested, such as scanning electron microscopy, tensile, moisture regain and cohesion. Polyethylene terephthalate filament yarns were selected for comparison with coffee carbon yarns. The results show that coffee carbon powder is distributed both on the surface and inside of filament yarns; the moisture regain of coffee carbon filament yarns is higher than that of PET yarns; the strength and elongation of coffee carbon filament yarns and of PET filament yarns is close; the boiling water shrinkage of coffee carbon filament yarns is lower than that of PET filament yarns; the addition of carbon powder can not reduce the cohesion of coffee carbon filament yarns.

Steam-methane reforming at low temperature on nickel-based catalysts

In this work, we report the activity results obtained in steam-methane reforming (SMR) at 500 and 600°C using four nickel-based catalysts: (a) Ni/α-Al2O3 and Ni/SiO2, prepared by incipient wetness impregnation method and (b) Ni–Zn–Al and Ni–Mg–Al, prepared by coprecipitation method. In all of the samples, the nickel load ranged between 7% and 9%. The catalytic activity in SMR at steady state followed the pattern: Ni–Mg–Al≅Ni–Zn–Al>Ni/α-Al2O3>Ni/SiO2. According to characterization results, the interaction between Ni2+ species and support in precursor oxides was stronger in Ni–Mg–Al and Ni–Zn–Al than in Ni/α-Al2O3 and Ni/SiO2. After activation in H2 flow, large metal nickel particles with low or none interaction with the support were obtained in the case of Ni/α-Al2O3 and Ni/SiO2. On the contrary, small metal particles, between 3 and 6nm, in high interaction with support were obtained in Ni–Zn–Al and Ni–Mg–Al catalysts. The metal phase formed in Ni–Mg–Al and Ni–Zn–Al was the most active and resistant to sintering under reaction conditions at T⩽600°C. It was also found that carbon nanofibers were formed on Ni/α-Al2O3, Ni/SiO2 and Ni–Mg–Al catalysts during SMR at 600°C. The amount and diameter of nanofibers formed on Ni–Mg–Al were lower than on catalysts prepared by impregnation method, which is in agreement with the relative sizes of metal nickel particles in each case. Amazingly, no filamentary carbon was detected on the used Ni–Zn–Al sample: only amorphous coke in low amounts was formed. This was attributed to the proper interaction of small metal nickel particles with the non-stoichiometric zinc aluminate-like phase formed after thermal treatments of catalyst precursor.

Characteristics of carbon fiber based strain sensors for structural-health monitoring of textile-reinforced thermoplastic composites depending on the textile technological integration process

The paper presents an effective online measurement technology for non-destructive and continuous monitoring of endless glass fiber reinforced thermoplastic (FRTP) composite structures using the numerous possibilities of textile process technologies for the design and one-step integration of one- and two-dimensional sensor structures based on piezo-resistive exPAN carbon filament yarn (CFY) in textile reinforced structures.The focus of this paper is directed at the analysis of such textile technological integrated sensors as an integral part of the textile reinforcement and their usability for in situ monitoring of local and/or global mechanical loading conditions in difficult or inaccessible areas within short distance of the structural load-bearing layers of FRTP's. If the adhesion of the carbon filament yarn sensor (CFYS) to the surrounding FRTP is sufficient enough, a change in geometry and thereby in resistivity of the carbon filaments can be measured by any mechanical load of the sensor-carrying FRTP component.The advantages and disadvantages of the tailored fiber placement (TFP), flat knitting and weaving textile processes for creating sensor structures will be shown, wherein the mentioned variety of interlacing techniques are used.The effects of the used textile manufacturing processes on the sensory properties are being compared. Furthermore, the effects of the integrated CFY on the mechanical properties of the basic structure are quantified. Sensor structures with minimal influence on the composite structure can be derived from it as well as sensors that enable a selective reinforcement of the composite structure. The textile integration provides a routing of one CFY through several layers of reinforcement. Thus, a damage-free and reproducible production of more complex, 3-dimensional, textile-based sensor networks is feasible in one step.

Effects of carbon concentration and filament number on advanced internal Mg infiltration-processed MgB2 strands

In this paper we show that an advanced internal Mg infiltration method (AIMI) is effective in producing superconducting wires containing dense MgB2 layers with high critical current densities. The in-field critical current densities of a series of AIMI-fabricated MgB2 strands were investigated in terms of C doping levels, heat treatment (HT) time and filament numbers. The highest layer Jc for our monofilamentary AIMI strands was 1.5 × 105 A cm−2 at 10 T, 4.2 K, when the C concentration was 3 mol% and the strand was heat-treated at 675 ° C for 4 h. Transport critical currents were also measured at 4.2 K on short samples and 1 m segments of 18-filament C doped AIMI strands. The layer Jcs reached 4.3 × 105 A cm−2 at 5 T and 7.1 × 104 A cm−2 at 10 T, twice as high as those of the best powder-in-tube strands. The analysis of these results indicates that the AIMI strands, possessing both high layer Jcs and engineering Jes after further optimization, have strong potential for commercial applications.

In situ XAS and FTIR studies of a multi-component Ni/Fe/Cu catalyst for hydrogen production from ethanol

Multicomponent catalysts containing Ni, Fe, Cu active for ethanol reforming reactions, prepared by solution combustion synthesis are characterized by multiple techniques such as ex situ XRD, XPS, and in situ XAFS and FTIR. XRD results indicate copper to be present in the reduced state as CuNi bimetal while nickel and iron are observed to be partially in a spinel NiFe2O4 structure. In situ XANES and XAFS analysis show a change in Ni, Fe and Cu oxidation states during reaction. Cu, which was fully reduced before reaction, became partly oxidized upon exposure to ethanol and oxygen. Ni is mostly (75%) reduced and does not seem to change its oxidation state during the reaction. Fe is not present in metallic form after reduction and during the reaction, but some change in the oxidation state from Fe(II) to Fe(III) occurred during the reaction. XPS and SEM images indicate the formation of carbon filament on the spent catalyst. XPS results also indicate the enrichment of surface by Fe and Cu during the reduction of the catalyst. Based on the activity and characterization results obtained, and literature review, the role of predominant phases during ethanol decomposition reaction is proposed.