Microstructural and Mechanical Characterization of Magnesium-AZ31 Alloy Reinforced with Carbon Nanotubes and Nano-Hydroxyapatite

Carbon Nanotubes (CNT) offer exceptional thermal, electrical and mechanical properties. While an increase in thermal and electrical conductivity can be readily achieved by addition of CNT to a polymer base, the subsequent effect on mechanical properties must be investigated. In this study, nanocomposite samples were manufactured using injection molding process. Multiwall Carbon Nanotube (MWCNT) masterbatch with 15 wt.% MWCNT concentrations were diluted with PA 6/6 pellets to create five different CNT concentration ranging from 3 wt.% in 3 wt.% increments. The neat polymer sample was also manufactured as a control specimen. Mechanical properties such as Young’s modulus, Tensile strength and elongations were determined to see the effect of CNT content on overall properties. Scanning Electron Microscopy (SEM) images were used to evaluate the uniform distribution of CNT in the polymer phase. The results showed that the stiffness increased as the CNT content increased, however, the increase in strength reached a threshold value around 6 wt.% beyond which the strength decreased. It was observed that the elongation decreased significantly by addition of CNT into the polymer. The elongation dropped from an average of 190% for the neat sample to 5% for 15 wt.% CNT content sample. Such decrease in elongation might render the polymer unsuitable for the application it has been designed for. The findings of this study show that improving thermal and electrical properties of polymers does not come without a sacrifice on mechanical properties.

This study focuses on the development of CuO nanoneedle and multi wall carbon nanotube (CNT) reinforced poly (vinyl chloride) (PVC) nanocomposites for medium voltage cable applications. CuO nanoneedles were synthesized using a pulsed wire evaporation technique and integrated with CNTs to create CuO/CNT nanocomposites. The nanocomposites were then used to reinforce PVC films through a solution casting method. Microstructural characterization confirmed the uniform dispersion of CuO nanoneedles and CNTs concentrations (0–0.4 wt%) within the PVC matrix. Microstructural characterization by XRD, SEM, and TEM confirmed the formation of CuO nanoneedles (diameter ∼4 nm, length 200–250 nm) and their uniform dispersion within the PVC matrix along with CNTs. Optical studies revealed reduced optical bandgap and Urbach tail width in PVC/CuO/CNT nanocomposites compared to neat PVC/CuO. Electrical characterization showed significantly improved AC conductivity (up to eight orders of magnitude) with increasing CNT loading, attributed to the formation of efficient charge transport networks. Dielectric studies revealed concurrent improvements in dielectric permittivity and losses with CNT addition. Simulations demonstrated a more uniform electric field distribution in PVC/CuO/CNT nanocomposites, mitigating hotspots. The synergetic effects of CuO nanoneedles and CNTs led to excellent improvements in the electric properties of PVC, underscoring their potential in medium voltage cable applications.

The main challenge in the production of metal matrix composites reinforced by carbon nanotubes (CNTs) is the development of a manufacturing process ensuring the dispersion of nanoparticles without damaging them, and the formation of a strong bond with the metallic matrix to achieve an effective load transfer, so that the maximum reinforcement effect of CNTs will be accomplished. This research focuses on the production by powder metallurgy of aluminum and nickel matrix composites reinforced by CNTs, using ultrasonication as the dispersion and mixture process. Microstructural characterization of nanocomposites was performed by optical microscopy (OM), scanning and transmission electron microscopy (SEM and TEM), electron backscattered diffraction (EBSD) and high-resolution transmission electron microscopy (HRTEM). Microstructural characterization revealed that the use of ultrasonication as the dispersion and mixture process in the production of Al/CNT and Ni/CNT nanocomposites promoted the dispersion and embedding of individual CNT in the metallic matrices. CNT clusters at grain boundary junctions were also observed. The strengthening effect of the CNTs is shown by the increase in hardness for all nanocomposites. The highest hardness values were observed for Al/CNT and Ni/CNT nanocomposites, with a 1.00 vol % CNTs.

A novel class of hybrid composites was prepared containing carbon fibers along with carbon nanotubes and silicon carbide particles in phenolic resin for improved mechanical performance. The loading of carbon fibers was ~60 wt% while carbon nanotubes and silicon carbide particles were reinforced in the fractions of 0.1 wt% and 5 wt%, respectively. Individually reinforced composites containing 0.1 wt% carbon nanotubes and 5 wt% silicon carbide particles were also manufactured for comparison with hybrid composites. Microstructural and mechanical property characterization was performed using electron microscopy and mechanical testing, respectively. Uniform dispersion of nanometer-scale carbon nanotubes and micrometer-scale silicon carbide particles was observed under microscopy. The pooled effect of carbon nanotubes and silicon carbide particles significantly increased the tensile, compressive, and flexural performance of composites while carbon nanotubes offered greater weight fraction value improvement than silicon carbide particles.

Mechanical properties and microstructure characterization of well-dispersed carbon nanotubes reinforced copper matrix composites

The advanced solar cells used in space vehicles today are rapidly moving towards thin-film-based inverted metamorphic multijunction (IMM) solar cells mounted on flexible substrates. However, the IMM cells are more prone to cracking than state-of-the-art triple junction cells. The cell cracking can lead to metal contact failure on IMM cells, compromising the power generation. To mitigate the power loss and increase the lifetime of IMM cells, silver metal films imbedded with carbon nanotubes (CNTs), otherwise known as metal matrix composites, have been developed and investigated for the reinforced mechanical strength against stress-induced cracking. We have primarily focused on (1) surface functionalization of CNTs to make their surface more hydrophilic and wetting to metals, (2) optimization of a cyanide-free electrochemical deposition of silver, (3) electrochemical deposition, drop casting and nanospreader technique to control the composite microstructure, and (4) mechanical and electrical characterization of the composite films. We observe that carboxylation of CNTs produces a stable, homogeneous suspension of negatively charged CNTs at pH > 6. Lustrous-mirror-finish silver films are also successfully deposited, using a commercial cyanide-free silver-plating solution with precise control of current density. Currently, one of the microstructures being explored is a silver-carbon-nanotube layer-by-layer structure, where the surface coverage of CNTs is an important parameter that directly affects the CNT packing fraction and metal intercalation through the CNT network. We quantify the CNT surface coverage as a function of different deposition variables by digitally analyzing scanning electron microscopy images. In this presentation, we will further discuss how this surface coverage correlates to the mechanical and electrical properties of the MMC films. We characterize the mechanical properties, using nanoindentation and strain failure tests. The initial nanoindentation analysis reveals that the composite film has a lower elastic modulus (10 GPa) than pure silver (73 GPa), which is contrary to our initial prediction given the high elastic modulus of CNTs (1000 GPa). The lower elastic modulus is attributed to the electroplating process of silver, in which hydrogen is incorporated and trapped within the composite. Our finite element analysis also corroborates this speculation, where the elastic modulus near 10 GPa is predicted with approximately 4% void fraction. While the composite elastic modulus is lower than that of pure silver, the strain failure tests show that carbon nanotubes can bridge 20 to 50-μm-wide microcracks, maintaining electrical conductivity of the composite

Over the last decade, rapid progress in the field of nanoscience has been increasingly driving the attention of the scientific community as well as society at large on the corresponding technological applications, which are the object of so-called nanotechnology. A strong interest in assessing the current state of the art of this fast growing field, as well as stimulating research networking, prompted the organization of the International School and Workshop 'Nanoscience & Nanotechnology (n&n2007)', under the patronage of the Italian Institute for Nuclear Physics (INFN), the University of Rome Tor Vergata, the Tor Vergata Polyclinic, and the Catholic University of Rome, with generous sponsorship from 3M, 2M Strumenti, MTS, Ape Research, Crisel Instruments, Veeco and Amira. The aims of this event were as follows:

With properties including high stiffness, high strength, low density, and high aspect ratio, carbon nanotubes (CNTs) are ideal reinforcements for ceramic matrix composites (CMCs) for enhanced strength and toughness. However, prior studies on CNT- reinforced CMCs generally showed limited mechanical and multifunctional property enhancements due to damage, random orientation, low volume fraction, and agglomeration of the introduced CNTs. In this study, we developed a bulk nanocomposite laminating process for ceramic matrix composites (BNL4CMC) to overcome such limitations and to enable the fabrication of ceramic nanocomposite laminates reinforced with highly aligned, uniformly distributed CNTs of ultrahigh packing densities (>40 vol%). Instead of direct mixing, the polymer precursors for the ceramic can be infused into horizontally aligned CNT (HA-CNT) arrays followed by curing and pyrolysis to convert the polymer matrix to ceramic while preserving the CNTs’ high degree of alignment and packing density. Silicon oxycarbide (SiOC), which possesses high modulus, high hardness, creep resistance, and good thermal/chemical stability, is selected as the matrix for this study. Using the BNL4CM approach, we successfully fabricated 4-ply HA-CNT/SiOC laminates with ultrahigh CNT packing density (> 40 vol%), uniform distribution, and nanofiber alignment. Microstructure and morphology characterizations including X-ray micro-computed tomography (X-ray μCT) and scanning electron microscopy (SEM) are used to study the evolution of HA- CNT/SiOC laminates’ microstructure during the fabrication process. Nano-indentation was performed to obtain the elastic modulus and hardness of the fabricated HA- CNT/SiOC laminates. The process-structure-property relation obtained will inform the design and manufacturing of other HA-CNT reinforced ceramic systems for enhanced mechanical and multifunctional properties.

The field emission properties of carbon nanotubes (CNTs) from various sources are investigated for the application of field emission displays. Comparisons are made between graphite with Ni metal as catalyst and polycyclic aromatic hydrocarbon as precursor by the arc discharge method. Cathode deposits are examined using scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) to determine microstructure. Carbon structure is studied using Raman spectroscopy. Electron field emission characteristics are measured with the diode method at 10-6 torr pressure. In this study, SEM micrographs of cathode deposits show dense random fiber-like carbon nanotubes. The HRTEM images clearly exhibit characteristic features of multiwalled carbon nanotubes. Microstructural investigation provides evidence that both the metal catalyst and the precursor can be used to synthesize carbon nanotubes. The Raman spectrum shows a stronger peak at about 1580 cm-1 indicating formation of a well-graphitized carbon nanotube. The degree of carbon nanotube graphitization is high and is in good agreement with the HRTEM result. From field emission measurements, the lowest onset field is about 1.0 V/μm and can be attributed to highly sharp tips and the high density of carbon nanotubes. Based on microstructure characterization and field emission measurements, the influence on field emission properties including turn on voltage and threshold voltage of carbon nanotubes synthesized from different sources is discussed.

Development of HA-CNTs composite coating on AZ31 magnesium alloy by cathodic electrodeposition. Part 1: Microstructural and mechanical characterization

Improved dispersion of carbon nanotubes in aluminum nanocomposites

This study is undertaken to explore, first, the dispersibility of dual-modified carbon nanotubes (CNTs) by way of non-covalent modification. Various non-ionic and ionic surfactants were employed and mutually combined with varying relative proportions. Then, the best few combinations from the dispersion test were used further for producing mortar mixtures reinforced with CNTs. These samples were later assessed for their mechanical strength and chloride resistance. A suite of morphological, thermal and microstructural characterisations was carried out to understand the underlying mechanisms. The results show that, compared with the single modification, the dispersibility of CNT could be improved more significantly by way of the dual modification. In particular, 70–90% of non-ionic surfactant, in proportion to the total surfactant addition, imparted the best dispersibility to CNTs in an aqueous solution. In addition, X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry and scanning electron microscopy outputs reveal that the enhanced dispersion of CNTs by dual modification promoted the hydration process and the ensuing microstructure evolution of mortar specimens. Together, these offset the strength reduction imparted by entrained pores when introducing chemical surfactants and, more importantly, empowered the chloride resistance of CNT-reinforced mortars.

Carbon nanotubes (CNTs) was introduced into Ni60/Al2O3coating by flame spraying. The effect of adding CNTs on the tribological properties of the coating was studied by varying the CNTs content as 0.0, 1.5, 3.0 and 4.5 wt% in the Ni60/Al2O3powders. The microhardness tester was used to measure the microhardness of the coating. Wear tests were performed on a pin-on-disk tribometer, to evaluate the tribological properties of the Ni60/Al2O3/CNTs coatings. Microstructural characterization was performed using scanning and transmission electron microscopy. Ni60/Al2O3/CNTs coatings revealed a lower wear rate and friction coefficient compared with the original coating, and their wear rates and friction coefficients showed a decreasing trend with increasing mass fraction of CNTs within the range from 0 to 3.0 wt% due to the effects of the reinforcement and reduced friction of CNTs. The results showed that the CNTs played dual roles in improving the tribological performance of the coating, indirectly by influencing the microstructure and mechanical properties of the coating and directly by acting as a lubricating medium.

Mechanical properties, permeability and microstructural characterisation of rice husk ash sustainable concrete with the addition of carbon nanotubes

CNTs-improved electromagnetic wave absorption performance of Sr-doped Fe3O4/CNTs nanocomposites and physical mechanism