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Quasicrystalline alloys and their composites have been extensively studied due to their complex atomic structures, mechanical properties, and their unique tribological and thermal behaviors. However, technological applications of these materials have not yet come of age and still require additional developments. In this review, we discuss the recent advances that have been made in the last years toward optimizing fabrication processes and properties of Al-matrix composites reinforced with quasicrystals. We discuss in detail the high-strength rapid-solidified nanoquasicrystalline composites, the challenges involved in their manufacturing processes and their properties. We also bring the latest findings on the fabrication of Al-matrix composites reinforced with quasicrystals by powder metallurgy and by conventional metallurgical processes. We show that substantial developments were made over the last decade and discuss possible future studies that may result from these recent findings.
The mitigation of CMAS (calcium–magnesium–aluminum–silicon oxide) infiltration is a major requirement for the stability of thermal barrier coatings. In this study, yttria-stabilized zirconia (YSZ)–Al2O3–SiC, YSZ–Al2O3–Ta2O5, and YSZ–Al2O3–Nb2O5 self-healing composites produced by uniaxially pressing powders were investigated as an alternative to YSZ. CMAS infiltration in these materials was tested at 1250 °C for 10 h. Comparing the depth of CMAS infiltration using scanning electron microscope (SEM) in tandem with electron-dispersive X-ray spectroscopy (EDS), all self-healing materials were found to perform better than the reference materials. While standard YSZ shows massive CMAS infiltration, SEM micrographs and EDS maps revealed a 33-fold improvement in CMAS resistance for the YSZ–Al2O3–Nb2O5 system, which exhibited the best performance among the selected self-repairing materials. X-ray diffraction and high-resolution SEM micrographs taken 10 μm below the surface revealed that CMAS only infiltrated pores in the topmost region of the samples. Both YSZ–Al2O3–Ta2O5 and YSZ–Al2O3–Nb2O5 systems showed no signs of chemical reaction with CMAS.
Thermal conductivity behaviors are one of the most important evaluations of carbon fiber-reinforced carbon matrix (C/C) composites in the field of thermal protective structures. In order to deepen the understanding of the thermal conductivity behaviors of C/C composites, the out-of-plane thermal conductivity of C/C composites is studied by considering voids and the fiber volume fractions. The representative volume element (RVE) models of microscale and mesoscale are proposed. The parameters of the RVE models are captured by X-ray micro-computed tomography. The carbon matrix equivalent models and fiber volume fraction models along the z-direction were established. The effects of the porosity and fiber volume fraction along the z-direction on the thermal conductivity were analyzed. The proposed model was validated by experimental results at room temperature. Further, the numerical methods developed in this study can provide guidance for predicting the thermal conductivity of C/C composites with complex structures.
The aim of this research was to develop the UV-cured epoxy/carbon composites. The rheological properties of the uncured neat epoxy and epoxy composite with graphite, graphene, and multi-walled carbon nanotube (MWCNT) were evaluated to observe the macroscopic flow behavior and the microstructure by shear force. The results showed that epoxy/carbon composites at high filler content exhibited shear-thinning behavior with a high yield stress value and epoxy/MWCNT at 30 phr showed this characteristic obviously. The fractured surface and particle dispersion in the epoxy matrix were evaluated by scanning electron microscopy and transmission electron microscopy, respectively. Epoxy/carbon composites at high filler content displayed rough fracture surface with particle agglomeration, thus the electrical conductivity increased. The result showed that the epoxy/MWCNT composites had high potential to use as a conductive adhesive with a 3D printing process due to high electrical conductivity with high viscosity that could be formed easily during processing.
Hydrothermal carbon microsphere (HTC) is a carbon-based fluorescent material, which can be synthesized by hydrothermal carbonization of glucose. In this article, a series of 4ZnO·B2O3·H2O:Ln3+/HTC (where Ln = Eu or Tb) composites were prepared under hydrothermal conditions. The effects of the glucose concentration on the morphology, photoluminescence (PL) intensity and emission color of Zn3.64:Eu0.24[B2O7]·H2O/HTCx and Zn3.55:Tb0.3[B2O7]·H2O/HTCy were investigated. The relationship between morphology and PL intensity of composites was discussed. The results revealed that the presence of HTC did not change the original emission color of 4ZnO·B2O3·H2O:Ln3+ (where Ln = Eu or Tb) materials, but greatly increased their PL intensity, the sphere-like morphology composites have the strongest PL intensity. The Zn3.64:Eu0.24[B2O7]·H2O/HTCx and Zn3.55:Tb0.3[B2O7]·H2O/HTCy emit bright red light and green light, respectively, under respective excitation wavelengths. The present research suggests that the 4ZnO·B2O3·H2O:Ln3+/HTC (where Ln = Eu or Tb) composites may be candidates of red and green phosphors for display and lighting applications.
Vast improvements have been made to the capabilities of advanced manufacturing (AM), yet there are still limitations on which materials can effectively be used in the technology. To this end, parts created using AM would benefit from the ability to be developed from feedstock materials incorporating additional functionality. A common three-dimensional (3D) printing polymer, acrylonitrile butadiene styrene, was combined with bismuth and polyvinylidene fluoride via a solvent treatment to fabricate multifunctional composite materials for AM. Composites of varying weight percent loadings were extruded into filaments, which were subsequently 3D printed into blocks via fused filament fabrication. Investigating the material properties demonstrated that in addition to the printed blocks successfully performing as radiation shields, the chemical, thermal, and mechanical properties are suitable for AM. Thus, this work demonstrates that it is possible to enhance AM components with augmented capabilities while not significantly altering the material properties which make AM possible.
The addition amount and dispersion of inorganic particles into poly(lactic acid) (PLA) still remain a great difficulty, and in the present study, epoxidized soybean oil was used to improve the compatibility between hydroxyapatite (HA) and PLA via the melt blending method. Scanning electron microscopy shows that HA particles can be well dispersed in the PLA matrix when the addition amount is less than 20% in mass, whereas the agglomeration of HA particles and a discrete phase of PLA could be observed when the amount increases to 30%. Therefore, the maximum amount of HA particles can be achieved for the composite with 20% HA which can be also maintaining the bending strength of 71.6 MPa. The osteoblast cells were used to characterize the biocompatibility of the HA/PLA composite, and the results indicate that the number of cells in per unit volume cultured on the HA/PLA composite is 10% higher than that of the PLA. Based on the improved cell biocompatibility and mechanical strength compared to PLA, the composite of HA/PLA prepared in the present study can be served as a potential candidate for the bone fracture repair.
Environmental issues such as climate change are leading to sustainability challenges for the aerospace industry. New materials such as composites allow significant weight reduction, which leads to a lower fuel consumption. However, composites involve complex processes and there is a lack of knowledge on their social and environmental consequences. Through two cases based on real aero-engines components, this paper shows that the weight savings provided by composites reduce significantly the CO2 emissions during flight which compensates the environmental drawbacks from production and recycling.
Biomagnetic field sensors based on AlN/FeCoSiB magnetoelectric (ME) composites desire a resonant frequency that can be precisely tuned to match the biomagnetic signal of interest. A tunable mechanical resonant frequency is achieved when ME composites are integrated onto shape memory alloy (SMA) thin films. Here, high-quality c-axis growth of AlN is obtained on (111) Pt seed layers on both amorphous and crystallized TiNiCu SMA thin films on Si substrates. These composites show large piezoelectric coefficients as high as d33,f= 6.4 pm/V ± 0.2 pm/V. Annealing the AlN/Pt/Ta/amorphous TiNiCu/Si composites to 700 °C to crystallize TiNiCu promoted interdiffusion of Ti into the Ta/Pt layers, leading to an enhanced conductivity in AlN. Depositing AlN onto already crystalline TiNiCu films with low surface roughness resulted in the best piezoelectric films and hence is found to be a more desirable processing route for ME composite applications.
The nitrogen-decorated CeO2/reduced graphene oxide nanocomposite (CeO2/N-rGO) was one-step synthesized by a facile hydrothermal technique and applied as counter electrode materials for dye-sensitized solar cells (DSSCs). For comparison, CeO2/rGO and rGO were also synthesized by adjusting corresponding reactants. It was found that the as-synthesized CeO2/N-rGO shows better electrocatalytic activity for triiodide/iodide reduction than that of pure rGO and CeO2/rGO, and a synergistic effect of nitrogen and CeO2 on the rGO sheets was observed. The photoelectric conversion efficiency of DSSCs based on CeO2/N-rGO counter electrode was 3.20%, which is higher than that of CeO2/rGO (2.45%) and rGO counter electrode (1.37%). Furthermore, the synergistic effect of nitrogen and CeO2 on the rGO sheets was also discussed in detail with different CeO2 amount levels. It is believed that this one-step synthetic method is a potential way to synthesize low-cost and efficient rGO-based multiple composited counter electrode materials to replace more expensive Pt.
We here design and fabricate a new kind of copper matrix composites, where titanium carbide nanoparticles are in situ incorporated into and embedded within the copper matrix, by virtue of laser powder-bed-fusion (L-PBF) process. We made a multiscale examination on the microstructures of the additively manufactured samples, unraveling that there are many unusual microstructural features, including grain refinement, the existence of high-density dislocations, and supersaturation of titanium solute atoms in the as-printed metal matrix composites. These unique microstructural features are mainly interpreted by the intense thermal history and the rapid solidification nature of the L-PBF process. The resultant composites then integrate the most important four strengthening mechanisms in metals: grain boundary strengthening, dislocation strengthening, solid solution strengthening, and second-phase strengthening, rendering this new kind of copper matrix composites a remarkably high yield strength (~490 MPa) and large uniform elongation (~12%), surpassing many high-performance copper matrix composites and copper alloys.
Al-based composites with micrometer and submicro-TiB2 reinforcements (1 wt%) have been produced by selective laser melting (SLM) from mixed powder under different processing conditions. The results show that the densification level of SLM-processed composite with submicro-TiB2 particles (>99.0%) was 0.3–2.4% larger than that of micrometer TiB2-reinforced composite under the same processing conditions. The distribution of Si precipitates in the matrix experienced a transform from continuous cellular to directional line-like morphology with reinforcement size decreasing from micron to submicron. The reinforcement size added in the matrix also exhibited a critical influence on preferred orientation and grain size of matrix. The SLM-processed composites exhibited improved tensile strength and ductility with a decrease of reinforcement size. High tensile strength of ∼400 MPa and elongation of ∼3.6% were obtained for the fine TiB2-reinforced samples, increasing by 6 and 13% compared with that of micro-TiB2–added samples, respectively.
Titanium and its alloys are probably the most suitable materials for selective laser melting (SLM) additive manufacturing to process. However, the high cost of raw powder materials limits the industrial application of as-printed Ti products. In this study, we have formulated a cost-affordable Ti–TiB composite powder for SLM, to simultaneously achieve excellent mechanical performance and cost effectiveness. The optimization of the processing parameters will be shown to lead to high relative density (99.3%) for the as-printed Ti–TiB composites containing (0.5, 1, and 2 wt%) TiB2. Furthermore, by incorporating TiB2, the as-printed composites exhibit much improved fracture strength (up to 1813 MPa) and microhardness (up to 412 HV), among which the Ti–0.5 wt% TiB2 has demonstrated a great combination of strength (1007 and 1646 MPa as yield and fracture strengths, respectively) and tensile ductility (~8%). The solidification pathway for the Ti–TiB composite during SLM has been investigated, and the underlying mechanism for achieving high yield strength is discussed based on existing models for shear-lag strengthening, grain refinement, and dispersion strengthening.
Polymer nanocomposites possess unique sets of properties that make them suitable for different applications, including structural and flame-retardant material, electromagnetic wave reflector, sensors, thin film transistor, flexible display, and many more. The properties of these nanocomposite are dependent on nanofiller dispersion and bonding with polymer matrix (i.e. particle-matrix interaction). Thermography is a non-destructive method that may be used to gain insight into dispersion and particle-matrix interaction. Infrared (IR) radiation emitted from these nanomaterial polymer composite depends on the emissivity of the individual components. In addition, during flash heating and cooling, different thermal conductivity of components in the nanocomposite can influence pixel intensity differently in the IR image or video being captured. We have used an economical mid wavelength IR camera Fluke RSE600 equipped with a close-up macro lens and algorithm based on MATLAB image processing toolbox to analyse dispersion, voids and thermal diffusivity of patented graphene polymer nanocomposite materials (G-PMC) in micro-scale. These G-PMCs can act as a standard material to determine the potential of our IR thermography technique due to their homogeneity and lack of impurity due to unique fabrication process. Thermal diffusivity and dispersion of nanoparticles in our G-PMCs was estimated after irradiation with a xenon flash lamp by spatially mapping transient IR radiations from different G-PMCs using the Fluke RSE600 thermal imager. Results from thermography experiments were compared with scanning electron microscope (SEM) and Raman spectroscopy results. Micro-scale thermography was able to detect millimetre scale thermal diffusivity variation in the injection molded G-PMC samples and relate it to change in dispersion of nanofillers, unlike SEM and Raman, where micro-scale measurements could not determine the reason behind millimetre scale property variation. We believe this low cost, fast, micro-scale, non-destructive technique will provide valuable insight into functional polymer nanocomposite fabrication and corresponding electrical and thermal properties.
The prepared silver/chitosan nanocomposite and chitosan nanoparticles in this study may demonstrate the potential in optimizing the minimum amount required to achieve complete inactivation of various Coliform bacteria in Nile water. Chitosan nanoparticles were prepared based on the ionic gelation of the prepared chitosan and silver nanoparticles were reduced by Solenostemma Argel extract. Finally, chitosan silver-loaded nanoparticles were prepared by dispersing silver nanoparticles onto the chitosan nanoparticles. The SEM images exhibited a diameter range of 10 nm–30 nm for both of the fabricated silver nanoparticles and chitosan nanoparticles. The UV-Vis analysis confirmed the formation of Ag nanoparticles by the appearance of the characteristic peak at 410 nm. The antibacterial activity of chitosan nanoparticles and silver-loaded nanoparticles was evaluated against the Coliform bacteria. Results show an improvement in the inhibition of the growth of various bacteria tested when silver nanoparticles were introduced which was (0.03g/100ml). Consequently, chitosan silver-loaded nanoparticles could be recommended as an efficient antibacterial material for water disinfection.
Fused deposition modelling (FDM) type of 3D printing is widely used for manufacturing complex shaped polymer products. Recently, the metal/polymer composite products can be made by 3D printer using metal/polymer composite filament. Now, we are planning to develop a new manufacturing process of the thermoelectric (TE) elements or modules by combining the FDM-type 3D printing and the degreasing-sintering process. In this work, we focused on the degreasing-sintering process of the mixture of Mg2Si and polylactic acid (PLA) powders. Mg2Si compound powder was synthesized by a liquid-solid phase reaction (LSPR) method. The powder mixtures of Mg2Si, Al and PLA were pressed and heated in a pulse discharge sintering (PDS) chamber under a vacuum in various degreasing conditions. Following the degreasing, the sintering of Mg2Si was carried out in the same PDS chamber at various starting sintering temperatures. Sintered density, Seebeck coefficient and electrical resistivity of the consolidated Mg2Si were measured and the power factor as a TE performance was estimated from the TE properties. The optimum conditions of degreasing-sintering process maximizing the sintered density and the TE performance of Al-doped Mg2Si were investigated. Furthermore, the influences of the additive amount of Al on the sintered density and the TE performance of Mg2Si fabricated via the optimized degreasing-sintering process were investigated.
This paper presents a recent study on recycling poly-ethylene-tetraphylate (PET), known as plastic waste material in Ghana, to wealth. Composites were produced by heating aggregates together with shredded PET plastic waste material, while bitumen was added to the plastic-coated aggregates. The composites produced were reinforced with 4.5 wt%, 9.0 wt%, 13.6 wt%, and 18.0 wt% PET. Mechanical properties of the fabricated composite samples were studied with a Universal testing machine for optimization. The work demonstrated that shredded PET plastic waste material acts as a strong binding agent for bitumen that can improve on the shelf life of the asphalt. From the results, 13.6 wt% concentration of PET was shown to experience the maximum compressive strength and flexural strength. Besides, water resistance was shown to increase with PET concentrations/weight fraction. From the data characterized 13.6 wt% of PET plastic gives the optimum plastic concentration that enhances the rheological properties of bitumen. The implications of the result are therefore discussed for the use of 13.6 wt% PET in road construction.
To improve the corrosion resistance and to increase the hardness of copper substrate in marine environment, the Cu-Ni/Ni-P composite coatings were prepared on the copper substrate using the galvanostatic electrolytic deposition method. The deposition current densities were explored to find the optimized deposition conditions for forming the composite coatings. Corrosion resistance properties were analyzed using the polarization curves and electrochemical impedance spectroscopy (EIS). Considering the corrosion resistance and hardness, the −20 mA/cm2 was selected to deposit Cu-Ni coatings on copper substrate and the −30 mA/cm2 was selected to deposit Ni-P coating on the Cu-Ni layer. The Cu-Ni/Ni-P composite coatings not only exhibited superior corrosion resistance compared to single Cu-Ni coating in 3.5 wt.% NaCl solution, but also showed much better mechanical properties than single Cu-Ni coating.
Role of MOFs in CO2 chemical conversion; Photocatalytic and electrocatalytic CO2 reduction; Role of linkers and metals in CO2 chemical conversion; and MOF composites and films in CO2 conversion.
In this review, we analyze the emerging field of metal–organic frameworks (MOFs) as catalysts for chemical conversion of CO2, with examples ranging from heterogeneous CO2 organic transformation to heterogeneous CO2 hydrogenation, from photocatalytic to electrocatalytic CO2 reduction. We also discuss the role of MOF composites and films in CO2 transformation. Our goal is to have an instrument useful to identify the best MOFs for CO2 conversion.
We examined a working hypothesis of sticky thermoelectric (TE) materials, which is inversely designed to mass-produce flexible TE sheets with lamination or roll-to-roll processes without electric conductive adhesives. Herein, we prepared p-type and n-type sticky TE materials via mixing antimony and bismuth powders with low-volatilizable organic solvents to achieve a low thermal conductivity. Since the sticky TE materials are additionally injected into punched polymer sheets to contact with the upper and bottom electrodes in the fabrication process, the sticky TE modules of ca. 2.4 mm in thickness maintained temperature differences of ca. 10°C and 40°C on a hot plate of 40 °C and 120°C under a natural-air cooling condition with a fin. In the single-cell resistance analysis, we found that 75∼150-µm bismuth powder shows lower resistance than the smaller-sized one due to the fewer number of particle-particle interfaces in the electric pass between the upper and bottom electrodes. After adjusting the printed wiring pattern for the upper and bottom electrodes, we achieved 42 mV on a hot plate (120°C) with the 6 x 6 module having 212 Ω in the total resistance. In addition to the possibility of mass production at a reasonable cost, the sticky TE materials provide a low thermal conductivity for flexible TE modules to capture low-temperature waste heat under natural-air cooling conditions with fins for the purpose of energy harvesting.