Wear studies of hydroxyapatite composite coating reinforced by carbon nanotubes

Multi-walled carbon nanotubes (CNTs) have been successfully introduced into hydroxyapatite (HA) coatings using laser surface alloying. It is evident from transmission electron microscopy (TEM) observations that the CNTs present in the matrix still keep their multi-walled cylinder graphic structure, although they undergo the laser irradiation. Scratching test results indicated that the as-alloyed HA composite coatings exhibit improved wear resistance and lower friction coefficient with increasing the amount of CNTs in the precursor material powders. These composites have potential applications in the field of coating materials for metal implants under high-load-bearing conditions.     

Influence of ionic substitution in improving the biological property of carbon nanotubes reinforced hydroxyapatite composite coating on titanium for orthopedic applications

The present work is aimed for the development of carbon nanotubes (CNTs) reinforced single mineral (Sr, Mg, Zn) as well as multi minerals (Sr+Mg+Zn) substituted hydroxyapatite composite (M-HAP) coatings on titanium (Ti). The effect of different mineral ions substitution and CNTs reinforcement in HAP composite coating is discussed in detail. Fourier Transform Infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis (EDX), and high resolution transmission electron microscopy (HRTEM) were used to characterize the structural and morphological behavior of the composite coatings. The corrosion resistance of the composite coatings in simulated body fluid (SBF) solution was evaluated by the potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) studies. In addition, the biocompatibility of the composite coatings was evaluated by in vitro culture of human osteoblast MG63 cells on the composite coated Ti. All these results essentially suggest that CNTs/M-HAP composite coated Ti can be a potential candidate for orthopedic applications.     

Pulsed electrodeposition of carbon nanotubes-hydroxyapatite nanocomposites for carbon/carbon composites

Carbon nanotubes-hydroxyapatite (CNTs-HA) composite coatings, which behaved like single composites, were synthesized by a combined method composed of electrophoretic deposition and pulsed electrodeposition. The phase compositions and the microstructure of the composite coatings were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectrometry (FTIR). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies showed that the CNTs-HA composite coatings protected the bare carbon/carbon composites from corrosion in simulated body fluid (SBF) solution. The adhesion strength of CNTs-HA composite coating prepared by the combined method is 14.57±1.06 MPa achieved at the CNTs EPD time of 10 min. Compared to the other CNTs-HA composite coatings with different content of CNTs, the CNT-HA composite coating with the electrophoretic deposition of 10 min showed the best corrosion resistance. The morphology of CNTs-HA composite coatings immersed in SBF solution rendered the formation of HA crystallites. In addition, in vitro cellular responses to the CNTs-HA composite coatings were assessed to investigate the proliferation and morphology of mouse cells 3T3 cell line.     

Vinyl–carbon nanotubes for composite polymer materials

We report herein a simple method for attaching vinyl groups onto the sidewalls of carbon nanotubes (CNTs) and the application of vinyl–carbon nanotubes (CNT–C?C) in fabricating polymer composites. The synthesis of CNT–C?C was monitored with IR spectroscopy, Raman spectroscopy, and thermogravimetric analysis. The obtained CNT–C?C showed good compatibility with the in situ polymerization of poly(methyl methacrylate) (PMMA) and exhibited no tendency for phase separation in the final composite. A transmission electron microscopy study revealed a uniform coating on the CNT–C?C tubes, indicating good grafting efficiency of PMMA. The uniform dielectric PMMA coating was responsible for the lower electrical conductivity of the CNT–C?C/PMMA composites versus that of the CNTs without vinyl modification. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Development of lightweight high‐performance polymeric composites with functionalized nanotubes

In this article, we highlight the various properties of an ultralightweight poly(ether ketone) (PEK) composite. In this study, special emphases were laid on the preparation of low‐density, high‐performance polymeric foams with foaming agents and activators. PEK, foamed PEK, and carbon nanotube (CNT)–reinforced foamed PEK composites were considered for this study. The density of the polymer decreased with the reinforcement of the foaming agent. We also noted that with the reinforcement of the modified CNT in the foamed PEK, there were marginal increases in the density and hardness of the composites. We also noted that the mechanical properties of the CNT‐reinforced foamed PEK was on par with those of basic PEK. Thermogravimetric analysis gave us a clear indication that the thermal stability of the composites was not affected by the reinforcing foaming agent and nanoparticles. Scanning electron microscopy and transmission electron microscopy clearly indicated the formation of foams and also the dispersion of nanoparticles in the composite structure. We also observed that because of the reinforcement of multiwalled CNTs in the composite, there was an improvement in the hardness of the composite. An increase in the specific strength was observed in the foamed PEK composites. The CNT‐reinforced foamed PEK showed a marginal decrease in the specific strength without a compromise in the impact strength. The impact strength of the CNT‐reinforced foamed PEK composite was found to be similar to that of the basic PEK. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43471.     

Effect of noncovalent chemical modification on the electrical conductivity and tensile properties of poly(methyl methacrylate)/carbon nanotube composites

Noncovalent chemical modification by initiated chemical vapor deposition technique is applied to carbon nanotubes (CNTs) to reduce average agglomerate size of the nanoparticles in the polymer matrix and to improve surface interaction between the composite constituents. CNT surfaces are coated conformally with thin poly(glycidyl methacrylate) (PGMA) polymer film and coated nanoparticles are incorporated in poly(methyl methacrylate) (PMMA) polymer matrix using solvent casting technique. Conformal PGMA coatings around individual nanotubes were identified by scanning electron microscopy analysis. Transmission electron microscopy and optical microscopy analyses show homogeneous composite morphology for composites prepared by using PGMA coated nanotubes. Fourier Transform Infrared and X‐ray photoelectron spectroscopy analyses show the successful deposition of polymer with high retention of epoxide functionality. PGMA coating of CNTs exhibits improvement in electrical conductivity and tensile properties of PGMA‐CNT/PMMA systems when compared with uncoated nanoparticles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Electrophoretic Codeposition of La0.6Sr0.4Co0.8Fe0.2O3−δ and Carbon Nanotubes for Developing Composite Cathodes for Intermediate Temperature Solid Oxide Fuel Cells

Carbon nanotubes (CNTs)/La_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (LSCF) composite films have been fabricated by electrophoretic codeposition on Ce_0.9Gd_0.1O_1.95 (CGO) substrates. CNTs are used as a sacrificial phase to produce ordered porous LSCF cathodes for intermediate temperature solid oxide fuel cells. The synthesis of LSCF powder by a modified sol–gel route is presented. The possible mechanism of formation of CNT/LSCF composite nanoparticles in suspension is discussed. Moreover the optimal suspension composition and the conditions for achieving successful electrophoretic deposition (EPD) of CNTs/LSCF composite nanoparticles were evaluated. Experimental results showed that the CNTs were homogeneously distributed and mixed with LSCF nanoparticles forming a mesh-like structure, which resulted in a highly porous LSCF film when the CNTs were burned out during heat treatment in air at 800°C for 2 h. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques were employed to characterize the microstructure of the precursors and of the composite films.     

Polypyrrole/carbon nanotube composites: Molecular modeling and experimental investigation as anti-corrosive coating

In this work we present a computational method based on molecular mechanics (MM) and dynamics (MD), to predict mechanical properties of polypyrrole (PPy)/polyaminobenzene sulfonic acid-functionalized single-walled carbon nanotubes (CNT-PABS) and PPy/carboxylic acid-functionalized single-walled carbon nanotubes (CNT-CA) composites. Furthermore, experiments were carried out to assess the anticorrosive features of the PPy film and CNT-PABS and CNT-CA PPy reinforced composite coatings. Computational bulk models of PPy/CNT-PABS and PPy/CNT-CA were implemented at atomistic scale and composite coatings were grown in situ onto carbon steel (OL 48-50) electrodes. PPy, PPy/CNT-PABS and PPy/CNT-CA computational models and films were investigated concerning mechanical properties by using computational tools. The obtained films were assessed experimentally as anticorrosive materials using potentiodynamic measurements, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results clearly confirmed that the CNT-PABS and CNT-CA are properly dispersed in the composite coatings and have beneficial effect on mechanical integrity. Moreover, the anticorrosion protecting ability of the composite coatings is significantly higher than the one characteristic to pure PPy. The Young's moduli generally increased with increasing of CNT content and values ranged from 2.67 GPa in the case of pure PPy to 4.15–4.61 GPa in the case of PPy/CNT-PABS composite system.In agreement with earlier results from the literature for conducting polymer organic coatings, the higher conductivity of material leads to a more efficient anticorrosion protection capability, our results exhibited an enhance of conducting features even for very low mass of CNT-PABS or CNT-CA loaded in composites coatings therefore, an improvement of anticorrosion protecting ability.     

Development of HA-CNTs composite coating on AZ31 Magnesium alloy by cathodic electrodeposition. Part 2: Electrochemical and in-vitro behavior

The carbon nano-tubes (CNTs) reinforced hydroxyapatite (HA), with various functionalized CNTs concentration ranging from 0 to 1.5?wt%, were deposited on AZ31 magnesium alloy by direct and pulse cathodic electrodeposition methods. The corrosion resistance of the coatings was tested in simulated body fluid (SBF) using different electrochemical methods such as open circuit potential, polarization and electrochemical impedance spectroscopy. The in-vitro behavior, changes in solution pH as well as the amount of evolved hydrogen of these coatings were also evaluated during five days immersion in SBF. The results indicated that the pulse deposited HA having 1% CNTs coating was the optimum condition which decreased the corrosion current density of AZ31 magnesium alloy from 44.25?µA/cm² to 0.72?µA/cm². Moreover, it stabilized the alkalization behavior of AZ31 alloy and caused a tenfold decrease in the amount of hydrogen generation in SBF. Additionally, the formation of new hydroxyapatite layer on the surface of the pre-exist coatings after five days immersion in SBF was confirmed by SEM characterization.     

Tribological behavior of plasma sprayed carbon nanotubes reinforced TiO2 coatings

Intrinsic structural limitations of plasma-spray TiO₂ coating deteriorate its wear resistance. Herein, CNTs are incorporated in the coating to assess their effects on the microstructure and tribological properties. Structurally, degradation degree of CNTs in TiO₂ matrix during plasma spraying was revealed by Raman spectroscopy. And high resolution transmission electron microscopy manifested that TiO₂/CNT interface was well bonded along with presence of notable interfacial carbothermic product Ti_nO_2n-1 at atomic scale. The phenomenon indicates a beneficial effect for transferring stress from matrix to CNTs effectively. Then, the influence of CNTs on coating’s friction behavior was investigated by zirconia ball-on-disk tribometer under dry-sliding condition. As compared to TiO₂ coating, the nanocomposite coating exhibited a moderate decrease in friction coefficient and an enormous reduction (～93.6%) in wear volume. The remarkable advance in tribological properties of the reinforced coating can be attributed to four kinds of frictional effects of CNTs: tribo-reorientation, tribo-protruding, tribo-film and tribo-degradation.     

The effect of carbon nanotube aspect ratio and loading on the elastic modulus of electrospun poly(vinyl alcohol)-carbon nanotube hybrid fibers

The reinforcement effect of carbon nanotubes (CNTs) has been examined as a function of their loading and aspect ratio in poly(vinyl alcohol) (PVA) based hybird fibers. Lignosulfonic acid sodium salt (LSA) was used to disperse CNTs to produce consistently high CNT loaded PVA-LSA-CNT hybrid fibers using an electrospinning process. The elastic modulus of individual fibers was measured using atomic force microscopy. The presence of CNTs significantly increased the average elastic modulus of PVA-LSA-CNT fibers compared to PVA-LSA fibers. The elastic modulus, however, exhibited no fiber diameter dependency. Transmission electron microscopy (TEM) was used to determine the loading and the aspect ratio of CNTs in each hybrid fiber. The CNT loading in PVA-LSA-CNT fibers varied widely due to non-uniform CNT dispersion and displayed no relationship with the elastic modulus. Our results also demonstrated that the average value of CNT aspect ratio significantly affected the elastic modulus of the hybrid fibers. Such a result was in agreement with theoretical prediction in which the stress transfer efficiency in a composite matrix is strongly dependent on the CNT aspect ratio.     

Carbon nanotube deposits and CNT/SiO2 composite coatings by electrophoretic deposition

Abstract

Multiwalled carbon nanotube (CNT) films have been successfully fabricated by electrophoretic deposition (EPD) on stainless steel substrates. Electrophoretic deposition was performed using optimised aqueous suspensions under constant voltage conditions. Triton X-100 was used as a surfactant to disperse CNT bundles, and iodine was added as a particle charger. CNT/SiO₂ composite coatings were prepared by electrophoretic co-deposition. Experimental results show that the CNTs were efficiently mixed with SiO₂ nanoparticles to form a network structure. Layered CNT/SiO₂ porous composites were obtained by sequential EPD experiments alternating the deposition of CNT and SiO₂ nanoparticles. The structure of all films deposited was studied in detail by scanning electron microscopy. Possible applications of CNT and CNT/SiO₂ films are as porous coatings in the biomedical field, thermal management devices, biomedical sensors and other functional applications where the properties of CNTs are required.     

Polypyrrole/carbon nanotube composites: Molecular modeling and experimental investigation as anti-corrosive coating

In this work we present a computational method based on molecular mechanics (MM) and dynamics (MD), to predict mechanical properties of polypyrrole (PPy)/polyaminobenzene sulfonic acid-functionalized single-walled carbon nanotubes (CNT-PABS) and PPy/carboxylic acid-functionalized single-walled carbon nanotubes (CNT-CA) composites. Furthermore, experiments were carried out to assess the anticorrosive features of the PPy film and CNT-PABS and CNT-CA PPy reinforced composite coatings. Computational bulk models of PPy/CNT-PABS and PPy/CNT-CA were implemented at atomistic scale and composite coatings were grown in situ onto carbon steel (OL 48-50) electrodes. PPy, PPy/CNT-PABS and PPy/CNT-CA computational models and films were investigated concerning mechanical properties by using computational tools. The obtained films were assessed experimentally as anticorrosive materials using potentiodynamic measurements, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results clearly confirmed that the CNT-PABS and CNT-CA are properly dispersed in the composite coatings and have beneficial effect on mechanical integrity. Moreover, the anticorrosion protecting ability of the composite coatings is significantly higher than the one characteristic to pure PPy. The Young's moduli generally increased with increasing of CNT content and values ranged from 2.67 GPa in the case of pure PPy to 4.15–4.61 GPa in the case of PPy/CNT-PABS composite system.In agreement with earlier results from the literature for conducting polymer organic coatings, the higher conductivity of material leads to a more efficient anticorrosion protection capability, our results exhibited an enhance of conducting features even for very low mass of CNT-PABS or CNT-CA loaded in composites coatings therefore, an improvement of anticorrosion protecting ability.     

Tribological application of carbon nanotubes in a metal-based composite coating and composites

Ni-P-carbon nanotube (CNT) composite coating and carbon nanotube/copper matrix composites were prepared by electroless plating and powder metallurgy techniques, respectively. The effects of CNTs on the tribological properties of these composites were evaluated. The results demonstrated that the Ni-P-CNT electroless composite coating exhibited higher wear resistance and lower friction coefficient than Ni-P-SiC and Ni-P-graphite composite coatings. After annealing at 673 K for 2 h, the wear resistance of the Ni-P-CNT composite coating was improved. Carbon nanotube/copper matrix composites revealed a lower wear rate and friction coefficient compared with pure copper, and their wear rates and friction coefficients showed a decreasing trend with increasing volume fraction of CNTs within the range from 0 to 12 vol.% due to the effects of the reinforcement and reduced friction of CNTs. The favorable effects of CNTs on the tribological properties are attributed to improved mechanical properties and unique topological structure of the hollow nanotubes.     

Synthesis and properties of HA/ZnO/CNT nanocomposite

The goal of this study was to examine the tribomechanical properties of hydroxyapatite (HA)/ZnO and HA/ZnO/CNT composite ceramics (carbon nanotubes; with different ratios 0.5?wt%, 1.0?wt%, and 1.5?wt%). The composites were synthesized using the hydrothermal method in an autoclave. The structure and morphology of the composites were analyzed using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX) and transmission electron microscope (TEM). The consolidation process was performed by sintering the compounds at 1150?°C under an argon gas atmosphere. The effects of ZnO and CNT on the mechanical properties and wear resistance of the HA-nanoparticle-based ceramic composites were investigated using a Vickers hardness tester, nanoindentation, and reciprocating wear tester equipment. The nanohardness and elastic modulus of the sintered samples increased and the friction coefficient of the sintered samples decreased as the fraction of CNTs increased compared to the pure HA and HA/ZnO compounds. Furthermore, the wear loss of HA/ZnO/CNT composites decreased with the increase in the CNT content compared to the HA and HA/ZnO samples.     

Plasma sprayed graphene/carbon nanotube reinforced lanthanum-cerate hybrid composite coating

Lanthanum cerate (LC: La₂Ce₂O₇) is a potential material for thermal barrier coating, whose improved toughness is a crucial necessity for the pathway of its industrialization. Herein, we demonstrated a promising approach to develop graphene/carbon nanotube hybrid composite coating using a large throughput and atmospheric plasma spraying method. Graphene nanoplatelets (GNP: 1 wt %) and carbon nanotube (CNT: 0.5 wt %) reinforced lanthanum cerate (LCGC) hybrid composite coatings were deposited on the Inconel substrate. Addition of 1 wt % GNP and 0.5 wt % CNT in LC matrix has significantly increased its relative density, hardness, and elastic modulus up to 97.2%, 2–3 folds, 3–4 folds, respectively. An impressive improvement of indentation toughness (8.04 ± 0.2 MPa m^0.5) was observed on LCGC coating, which is ～8 times higher comparing the LC coating. The toughening was attributed to the factors: such as the distribution of GNPs and CNTs in the LC matrix, synergistic toughening offered by the GNPs and CNTs; (i) GNP/CNT pull-out, (ii) crack bridging and arresting, (iii) splat sandwiching, mechanical interlocking, etc. Finally, this improved toughness offered an exceptional thermal shock performance up to 1721 cycles at 1800 °C, without any major failure on the coating. Therefore, the GNP and CNT-reinforced LC hybrid composite coating can be recommended to open a path for turbine industries.     

Effect of carbon nanotubes and aluminum oxide on the properties of a plasma sprayed thermal barrier coating

To protect the structural components of a power generating unit from the corrosive environment, thermal spray coatings are applied to the components. In the present work, four different types of thermal barrier coating (TBC) viz. partially stabilised zirconia (8YSZ), zirconia-20% alumina (ZA) composite coating without carbon nanotube (CNT) reinforcement, and ZA with 1% and 3% CNT reinforcement. The coating was deposited on NiCrAlY coated P91 steel using a plasma spraying process. The coating microstructure and phases were characterised using field emission scanning electron microscope (FE-SEM) with energy dispersive spectroscopy (EDS). The phases of the coating were analyzed using X-ray diffraction technique. The effect of CNT reinforcement on the thermal conductivity, porosity, and hardness of the composite coatings was investigated. The protective behavior of the coatings was characterised by potentiodynamic polarization testing and electrochemical impedance measurements. The thermal conductivity of the composite coating was found to be increased with increasing CNT content. Hardness was found to be highest for 3% CNT reinforcement and the thermal conductivity was found to increase with decreasing porosity. The electrochemical measurements indicate that reinforcement of CNT in zirconia alumina composite coating improved its corrosion resistance.     

Size and synergy effects of nanofiller hybrids including graphene nanoplatelets and carbon nanotubes in mechanical properties of epoxy composites

We study mechanical reinforcement in a widely used epoxy matrix with the addition of graphene nanoplatelets (GnPs) and various mixture ratios of carbon nanotubes (CNTs) with GnPs. Two different dimensions of GnPs were used with flake sizes of 5 μm and 25 μm to investigate the influence of nanofiller size on composite properties. In GnP reinforced composites, bigger flakes showed greater reinforcement at all GnP concentrations as they actively control the failure mechanisms in the composite. In the mixture samples, highest CNT content (9:1) showed marked improvement in fracture toughness of 76%. The CNT:GnP ratio is an interesting factor significantly influencing the properties of the epoxy based nanocomposites. The combination of high aspect ratio of CNTs and larger surface area of GnPs contribute to the synergistic effect of the hybrid samples. Thermal conductivity consistently increases with incorporation of GnPs in the matrix. Transmission electron microscopy (TEM) images confirm the uniform nanofiller dispersion achieved in the composites. For the hybrid samples CNTs are seen to align themselves on the GnP flakes creating an inter-connected strong nanofiller network in the matrix. The homogeneous nanofiller dispersions have been achieved by high shear calendaring which is a method capable of being industrially scaled up.     

Growth and electrical characterization of high-aspect-ratio carbon nanotube arrays

The remarkable properties of carbon nanotubes (CNTs) make them attractive for microelectronic applications, especially for interconnects and nanoscale devices. In this paper, we describe a microelectronics compatible process for growing high-aspect-ratio CNT arrays with application to vertical electrical interconnects. A lift-off process was used to pattern catalyst (Al₂O₃/Fe) islands to diameters of 13 or 20 μm. After patterning, chemical vapor deposition (CVD) was involved to deposit highly aligned CNT arrays using ethylene as the carbon source, and argon and hydrogen as carrier gases. The as-grow CNTs were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the CNTs have high purity, and form densely-aligned arrays with controllable array size and height. Two-probe electrical measurements of the CNT arrays indicate a resistivity of ∼0.01 Ω cm, suggesting possible use of these CNTs as interconnect materials.     

Characterization and compression properties of injection molded carbon nanotube composites

Since the development of carbon nanotubes (CNTs) in 1991, they have received much attention with improved mechanical, thermal, and electrical properties of their composites compared to common polymer composites. The CNTs are currently used to increase the modulus of common thermoplastics and thermosets, including urethanes and epoxies. The CNTs are difficult to disperse within any media because of limited chemical reactivity and potential agglomeration in their “as grown” state. This study evaluated the effect of incorporating bundled and unbundled CNTs at different concentrations into Polyurethane/CNT/woven fiber reinforced composites. Optical microscopy and atomic force microscopy (AFM) characterized the dispersion of CNTs within the polymer matrix in injection molded CNT/polyurethane composites. Polyurethane/CNT/woven fiber reinforced composite plaques were prepared and then characterized by mechanical compression testing. Optical microscopy and AFM qualitatively determined a decreased agglomerate size resulting in improved mechanical properties. Results of this study show significant differences in yield stress, stress at failure, and modulus of elasticity within the various treatments. No significant differences were found for yield strain, strain at failure, and toughness. However, the conservativeness of the statistical model warrants further investigation for strain at failure and toughness with possible interaction effects of CNT concentration for each composite. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008