Bulk Nanocomposites Research Articles

Effect of Increasing the Strength of Aluminum Matrix Nanocomposites Reinforced with Microadditions of Multiwalled Carbon Nanotubes Coated with TiC Nanoparticles.

Aluminum matrix composites reinforced with multiwalled carbon nanotubes (MWCNTs) are promising materials for applications in various high-tech industries. Control over the processes of interfacial interaction in Al/MWCNT composites is important to achieve a high level of mechanical properties. The present study describes the effects of coating MWCNTs with titanium carbide nanoparticles on the formation of mechanical properties and the evolution of the reinforcement structure in bulk aluminum matrix nanocomposites with low concentrations of MWCNTs under conditions of solid-phase consolidation of ball-milled powder mixtures. Using high-energy ball milling and uniaxial hot pressing, two types of bulk nanocomposites based on aluminum alloy AA5049 that were reinforced with microadditions of MWCNTs and MWCNTs coated with TiC nanoparticles were successfully produced. The microstructural and mechanical properties of the Al/MWCNT composites were investigated. The results showed that, on the one hand, the TiC nanoparticles on the surface of the MWCNT hybrid reinforcement reduced the damage of reinforcement under the intense exposure of milling bodies, and on the other hand, they reduced the contact area of the MWCNTs with the matrix material (acting as a barrier interface), which also locally inhibited the reaction between the matrix and the MWCNTs.

High thermoelectric performance in high crystallinity epitaxial Si films containing silicide nanodots with low thermal conductivity

High crystallinity Si films containing silicide nanodots (NDs) were epitaxially grown on Si substrates at high temperature (∼750 °C), where the silicide phase of NDs (metallic α-FeSi2 or semiconductor β-FeSi2) was selectable by tuning the Fe deposition amount. The high crystallinity high-temperature-grown Si films with NDs exhibited lower thermal conductivity (5.4 W m−1 K−1) due to the phonon scattering at the ultrasmall ND interfaces than bulk Si-silicide nanocomposites that have ever been reported. In this ND system with extremely low thermal conductivity, due to the less point defects and high quality ND interface, the thermoelectric power factor (∼28 μW cm−1 K−2) was observed to be the same as the high value of Si films without NDs at room temperature, which is the highest value among Si-silicide bulk nanocomposites ever reported. The simultaneous achievement of a high power factor and low thermal conductivity in the high quality ND system will provide the key for design of high thermoelectric performance of Si-based nanostructured films.

A review on the mechanical and thermal properties of graphene and graphene-based polymer nanocomposites: understanding of modelling and MD simulation

ABSTRACTSimulation of molecular dynamics (MD) allows mimicking the systematic variation of mechanical properties beyond the capacity of experimental methods. In this review, the status of the molecular modelling, simulation and mechanical and thermal characterisation of graphene and the properties of bulk nanocomposites using MD are extensively examined. The molecular models of graphene (pristine and functionalised), and the most common epoxy matrix with preeminent MD energy minimisation tools are thoroughly examined. The presence of MD’s simulation setup and the computational procedure for different styles of mixing the polymer matrix with graphene as nanofiller are exhaustively reviewed. In particular, in the analysis of several papers on graphene and their composites, it has been noticed that mechanical, thermal and interfacial properties are ubiquitous to most of the engineering applications. In this review, advances in the molecular modelling and simulation of graphene and their composites has been discussed in detail keeping graphene structures, aspect ratio, weight fraction and density effect as major factors. Finally, the research gaps and future scope are discussed, which indeed helps the researchers in scaling up their researches in graphene and their composites, which may further lead to their experimental findings.

Investigation of microstructure and temperature and frequency dependent dielectric relaxation of Molybdenum-zinc-selenite glass nanocomposite systems

Transition metal oxide doped glass nanocomposite bulk samples of the composition xMoO3–(1-x) (0.5ZnO–0.5SeO2), for x = 0.05, 0.1, 0.2 and 0.3 weight percent, have been developed via the process of slow cooling of the melt. The dependency of dielectric properties on temperature and frequency has been studied. Using transmission electron microscopy (TEM) micrographs, the growth of nanocrystallites and their lattice fringes have been noticed and selected area electron diffraction images have as well been observed. The results of the differential scanning calorimetric (DSC) process describe the thermal property of these compositions. The dielectric constant (ε/) and dielectric loss (ε//) value increases with the increment in temperature and reduces as frequency increases considerably. The dynamic conductivity relaxation process is non-Debye type as Kohlrausch stretching exponent (β) value is not equal to unity and obtained relaxation time shows Arrhenius behavior. The scaled electric okmodulus (complex) spectra discloses that the dynamic conductivity relaxation process depends on the composition but does not depend on temperature.

Synergetic effect of reactive ball milling and cold pressing on enhancing the hydrogen storage behavior of nanocomposite MgH2/10 wt% TiMn2 binary system

Intermetallic TiMn2 compound was employed for improving the de/rehydrogenation kinetics behaviors of MgH2 powders. The metal hydride powders, obtained after 200 h of reactive ball milling was doped with 10 wt% TiMn2 powders and high-energy ball milled under pressurized hydrogen of 70 bar for 50 h. The cold-pressing technique was used to consolidate them into 36-green buttons with 12 mm in diameter. During consolidation, the hard TiMn2 spherical powders deeply embedded into MgH2 matrix to form homogeneous nanocomposite bulk material. The apparent activation energies of hydrogenation and dehydrogenation for the fabricated buttons were 19.3 kJ/mol and 82.9 kJ/mol, respectively. The present MgH2/10 wt% TiMn2 nanocomposite binary system possessed superior hydrogenation/dehydrogenation kinetics at 225 °C to absorb/desorb 5.1 wt% hydrogen at 10 bar/200 mbar H2 within 100 s and 400 s, respectively. This new system revealed good cyclability of achieving 414 cycles within 600 h continuously without degradations. For the present study, the consolidated buttons were used as solid-state hydrogen storage for feeding proton-exchange membrane fuel cell through a house made Ti-reactor at 250 °C. This nanocomposite system possessed good capability for providing the fuel cell with hydrogen flow at an average rate of 150 ml/min. The average current and voltage outputs were 3 A and 5.5 V, respectively.

Spark Plasma Sintered Bulk Nanocomposites of Bi2Te2.7Se0.3 Nanoplates Incorporated Ni Nanoparticles with Enhanced Thermoelectric Performance.

Bi2Te3-based compounds are important near room temperature thermoelectric materials with commercial applications in thermoelectric modules. However, new routes leading to improved thermoelectric performance are highly desirable. Incorporation of superparamagnetic nanoparticles was recently proposed as a means to promote the thermoelectric properties of materials, but its feasibility has rarely been examined in mainstream thermoelectric materials. In this study, high quality single-crystalline Bi2Te2.7Se0.3 nanoplates and Ni nanoparticles were successfully synthesized by solvothermal and thermal decomposition methods, respectively. Bulk nanocomposites consisting of Bi2Te2.7Se0.3 nanoplates and superparamagnetic Ni nanoparticles were prepared by spark plasma sintering. It was found that incorporation of Ni nanoparticles simultaneously increased the carrier concentration and provided additional scattering centers, which resulted in enlarged electric conductivities and Seebeck coefficients. The greatly improved ZT was achieved due to the increase in power factor. Spark plasma sintered bulk nanocomposites of Bi2Te2.7Se0.3 nanoplates incorporated by 0.4 mol %Ni nanoparticles (in molar ratio) showed a figure-of-merit ZT of 0.66 at 425 K, equivalent to 43% increase when compared to pure Bi2Te2.7Se0.3 nanoplates. The results revealed that incorporation of magnetic nanoparticles could be an effective approach for promoting the thermoelectric performance of conventional semiconductors.

Superior Biomimetic Nacreous Bulk Nanocomposites by a Multiscale Soft-Rigid Dual-Network Interfacial Design Strategy

Summary Biomimetic bulk structural materials have been paid increasing attention for their huge application prospects. Integrating close-to-ideal, ultrathin, and flexible nanostructured units into high-performance nacreous bulk nanocomposites is worth considering yet remains challenging due to the elusive micro- and nano-interface connections. Here, by introducing a multiscale soft-rigid polymer dual-network interfacial design strategy that enables us to appropriately reinforce the nanoscale building blocks or their bridging, we can construct a type of nacreous bulk nanocomposites with tunable mechanical properties in the mild, eco-friendly, and highly efficient bottom-up assembly process. The resultant nanocomposites can achieve continuously reinforced mechanical transformation without experiencing environmentally threatening interfacial manipulation processes. This interfacial design strategy, supported by sufficient experiments and simulations, endows the assembled nacreous nanocomposite with superior mechanical enhancement and improved stability under high humidity and temperature conditions. Combined with the scalable assembly technique, it will pave the way for the design of high-performance biomimetic bulk nanocomposites for structural applications.

Synthesis of β-type NbXTi (X= 50 at %) /carbon nanotubes by FCT-FAST-SPS: For metallic orthopedic components

The synthesize of β-type phase NbxTi (x=50 at%)/SWCNTs intermetallic matrix nanocomposite by mechanical alloying to ensure the effective distribution of single walled carbon nanotubes (SWCNTs) within the matrix. It has been stated by several researchers that during ball-milling of NbxTi (x=50 at%) powder mixtures, Nb-Ti intermetallic compound formation occurs either gradually along milling time, or suddenly through a mechanically self- propagating reaction (MSPR), which occurs after a ignition time of MA. For this purpose, 0.4 and 0.8 wt% of SWNTs were added to the powder mixture after the completion of reaction between Nb and Ti. The resultant powders Nb50Ti intermetallic compound and with addition of powder of SWCNTs and then also ball-milled.Bulk samples were compacted and then sintered by field actived sintering technic spark plasma sintering method (FAST- SPS) at lower temperature in the range (1273 to 1473 K) with short time that retained the integrity of SWNTs in the intermetallic matrix. Structural and characteristics evolutions of the nanocomposites were investigated by X-ray diffractometery (XRD). Field emission scanning electron microscopy (FESEM) micrographs showed that the offered MA approach caused the SWNTs to uniformly embed in the in situ synthesized NbTi intermetallic matrix. Meanwhile better distribution of SWCNTs resulted in higher density of FAST-SPS-FCT bulk nanocomposite as well as higher hardness up to 2.75 GPa compared to2.4 of Nb50Ti intermetallic alloy obtained from the after MA time. The total porosity, compressive strength, and compressive elastic modulus of the FAST-SPS-FCT manufactured material were determined as 7%, 600 MPa, and 120 MPa, respectively. The alloy’s and its intermetallic nanocomposite have Young’s elastic modulus is comparable to that of healthy cancellous bone which makes it applicable in the biomedical field. The in vitro biocomptability will be performed in the near future. The comparable results for the FAST-SPS-FCT nanocomposites were 3%, 650 MPa, and 130 MPa. The alloy’s elastic modulus is comparable to that of healthy cancellous bone. This difference in mechanical properties results from different porosity and phase composition of the bot β-phase NbxTi (x=50 at%) and NbxTi (x=50 at%)/SWCNTs intermetallic matrix nanocomposite. More other nanotechnologies applications of the nanocomposite will be focused in the study of the superconducting type I for the ITER Poloidal Field Coils by measuring of Jc (T, B) characteristics.

Photopolymerized hybrids containing TiO2 nanoparticles for gradient-index lens

An ultra violet (UV)-cured nanocomposite material, based on TiO2 nanoparticles was prepared by sol-gel process from 3-(methacryloxy)propyltrimethoxysilane (MPTS) and 1,12-dodecanediol dimethacrylate (DDDMA). The evolution of structural properties for the inorganic-organic hybrid network was studied by FT-IR and NMR during UV curing, while the photo-polymerization kinetics of hybrid organic-inorganic matrix was evaluated using Raman spectroscopy. It was found that the three-dimensional (3D) organic-inorganic network was formed mainly by polymerization of C=C bonds in methacrylate units and Si–O–Ti bonds were formed when the hybrid matrix solution was cured by UV light. The influence of TiO2 dosage on the particle size and morphology was investigated by DLS and TEM respectively. We observed that introducing TiO2 nanoparticles into the polymeric matrix allows to fabricate a bulk nanocomposite with good optical quality and with positively charged particles that enables us to tailor the refractive index of the material; a property that can be potentially used in the production of GRIN lenses.

Thermoelectric Properties of Reduced Graphene Oxide/Bi2Te3 Nanocomposites

Reduced graphene oxide (rGO)/Bi2Te3 nanocomposite powders with different contents of rGO have been synthesized by a one-step in-situ reductive method. Then, rGO/Bi2Te3 nanocomposite bulk materials were fabricated by a hot-pressing process. The effect of rGO contents on the composition, microstructure, TE properties, and carrier transportation of the nanocomposite bulk materials has been investigated. All the composite bulk materials show negative Seebeck coefficient, indicating n-type conduction. The electrical conductivity for all the rGO/Bi2Te3 nanocomposite bulk materials decreased with increasing measurement temperature from 25 °C to 300 °C, while the absolute value of Seebeck coefficient first increased and then decreased. As a result, the power factor of the bulk materials first increased and then decreased, and a power factor of 1340 μWm−1K−2 was achieved for the nanocomposite bulk materials with 0.25 wt% rGO at 150 °C.

Influence of B4C nanoparticles on mechanical behaviour of Silicon brass nanocomposite through mechanical alloying and hot pressing

Abstract This research article has concentrated to develop a novel silicon brass of [82Cu4Si14Zn]100-x – x wt.% B4C (x = 0, 3, 6, 9, and 12) nanocomposites which were synthesized by mechanical alloying followed by vacuum hot pressing for consolidation of powders into bulk samples. Single vial planetary ball mill was used to synthesize the nanocomposite powders in which the ball-to-powder ratio of 10:1 with the milling time of 20 h was used. The milled powders were compacted and sintered simultaneously using vacuum hot pressing equipment for 1 h at 900 °C. The structural, mechanical and tribological properties were characterized and investigated by x-ray line profile analysis (XRD), scanning electron microscopy (SEM), electron backscattered diffraction images (EBSD), energy dispersive x-ray spectroscopy (EDS), Vickers microhardness, compression test, and dry sliding wear behaviour analysis. It has been found that B4C nanoparticles had homogeneously distributed and embedded in the nanocrystallite matrix. As a result, the fabricated nanocomposites were exhibited superior properties than the conventional alloy. Here, 12 wt% B4C reinforced silicon brass of bulk nanocomposite was produced higher hardness and compressive strength than the unreinforcement matrix. Further, the worn morphologies were evidenced the mild wear occurred at higher reinforced nanocomposites owing to decohesion and lower wear rate with considerable wear resistance.

Enhancement of the active/passive anti-corrosion properties of epoxy coating via inclusion of histamine/zinc modified/reduced graphene oxide nanosheets

Abstract This research introduces a green/novel route for preparation of an epoxy system with bi-functional active/passive anti-corrosion properties via inclusion of modified/reduced graphene nanoparticles. For the first time, the reduced nanosheet (RGO) with the barrier-inhibitive activities was prepared using bioactive reductant based on histamine. Also, zinc cations were loaded onto RGO sheets by two sequence based (RGO-Hist-Zn-I nanosheet) and in-situ based (RGO-Hist-Zn-II nanosheet) approaches. Characterization of the synthesized RGOs using X-ray photoelectron spectroscopy, field emission-scanning electron microscopy, transmittance electron microscopy, ultraviolet-visible and inductively coupled plasma techniques approved the precision of graphene oxide reduction via histamine and zinc cation's chemical adsorption. The performance of the RGO nanosheets was investigated by electrochemical impedance spectroscopy, potentiodynamic polarization, salt spray, pull off adhesion, cathodic disbondment (CD) and energy dispersive X-ray spectroscopy analyses. The results clarified that the epoxy coating reinforced with RGO-Hist-Zn-I provided the best anti-corrosion performance (log |Z|10 mHz = 9.73 Ω cm2 after 60 days immersion in NaCl solution), self-healing property (liberation of histamine and zinc cations from the nanocomposite bulk to the scratch region after 8 h immersion), adhesion to steel surface (lowest adhesion loss, i.e. 14.2% after 38 days of immersion and CD resistance (ca. 4.7 mm).

Synthesis and Characterization of Fe-Based Nanocomposites

This study reports on the elaboration and characterization of bulk nanocomposites samples obtained by dispersion of metallic powders at the nanoscale as reinforcements in a polymer matrix. Elemental Fe powders were successfully nanostructured via high-energy ball milling. Structural characterization of the produced powders was conducted using X-Ray Diffraction (XRD) analysis and Scanning Electron Microscopy (SEM). The Halder-Wagner approach was adopted to determine the powder’s average grain size, internal strain, lattice parameters and the mixing factors. Structural parameters evolution and morphological changes according to milling progression are discussed. Bulk nanocomposites samples were shaped in a home moulder by dispersion of coarse Fe and nanostructured Fe powders in a continuous matrix of commercial epoxy resin. The obtained bulk samples match the metallic X-band wave-guide WR-90 dimensions used for electromagnetic characterization. The two-port Sij scattering parameters were measured via an Agilent 8791 ES network analyzer. The measured scattering parameters served to calculate the loss factor of samples and to extract the dielectric permittivity via the Nicholson-Ross-Weir conversion. Spectra evolution of the scattering parameters, the loss factor and the dielectric constant for epoxy resin with coarse Fe and nanostructured Fe reinforcements are commented.

Design Strategy for High-Performance Thermoelectric Materials: The Prediction of Electron-Doped KZrCuSe3

Thermoelectric materials enable direct conversion of heat into electrical energy, providing a promising route for power generation and waste heat recovery. A very active research effort is ongoing to search for high-performance thermoelectric systems including bulk materials and nanocomposites. In this paper, we propose an efficient strategy for identifying thermoelectric materials with high figures of merit among the tens of thousands of known compounds from the inorganic crystal structure database. The search strategy integrates several steps to find materials with a very low lattice thermal conductivity and a high power factor by the virtue of the coexistence of rattling atomic vibrations with favorable electronic band structures. Using our approach, we predict a very high figure of merit (ZT) in electron-doped KZrCuSe3 crystals along the crystallographic a-axis, with an estimated average over temperature ZTave of about 1.9 from 300 to 1000 K. The overall ZTave performance of electron-doped KZrCuSe3 is...

Discovery of a FeCoNiPdCu High‐Entropy Alloy with Excellent Magnetic Softness

The authors report on the discovery of a magnetically soft high‐entropy alloy of composition FeCoNiPdCu, which performs comparably to the best commercial soft magnets for static and low‐frequency applications. Properly heat‐treated FeCoNiPdCu develops nanostructure that can be viewed as a two‐phase bulk nanocomposite of randomly intermixed FeCoNi magnetic domains and PdCu nonmagnetic “spacers”, both of 2–5 nm cross dimensions. Due to the nanometric size, the FeCoNi domains are magnetically single‐domain particles, and since the particles are exchange‐coupled across the boundaries, exchange averaging of magnetic anisotropy takes place, resulting in an almost vanishing coercive field and excellent magnetic softness. The formation of a two‐phase nanostructure favorable for the exchange averaging of magnetic anisotropy is a consequence of specific values of the binary mixing enthalpies for the chosen elements. Though high‐entropy alloys are generally considered to be random solid solutions of multiple elements on a topologically ordered crystal lattice, clustering of the atoms into preferential chemical environments on a nanoscale essentially determines their magnetic properties. Experimentally, the magnetic properties of the FeCoNiPdCu high‐entropy alloy are compared to the commercial, magnetically soft non‐oriented silicon electrical steel.

Exchange Bias in Bulk Nanocomposites for Permanent Magnet Applications.

Here we report on the microstructural factors influencing the formation of the interfacial exchange bias effect in three-dimensional transition-metal-based nanocomposite systems, with relevance to permanent magnet applications. Bulk phase-separated nanocomposites consisting of the ferromagnetic -Fe and metastable antiferromagnetic phases exhibit a notable low-temperature exchange bias and substantial coercivity ( , ) as well as a near room-temperature blocking temperature. Structural investigation by synchrotron X-ray diffraction, neutron scattering, and transmission electron microscopy confirm that the ferromagnetic -Fe phase nucleates as small precipitates ( ) at the grain boundaries of the antiferromagnetic grains ( ) and grows anisotropically upon heat treatment, resulting in an elliptical geometry. These results indicate that optimization of the exchange bias effect in bulk nanocomposite systems may be achieved through maximizing the surface-to-volume ratio of ferromagnetic precipitates in an antiferromagnetic matrix, enhancing the magnetocrystalline anisotropy of the antiferromagnetic phase to facilitate interfacial pinning and ensuring a balanced distribution of the ferromagnetic and antiferromagnetic phases. This work further clarifies critical factors influencing the formation of an exchange bias in an inexpensive transition-metal-based bulk nanocomposite system with potential for scalable production.

Nanoscale integration of oxides and metals in bulk 3D composites: leveraging SrFe12O19/Co interfaces for magnetic exchange coupling

The integration of different material classes (e.g, oxides and metals) with nanoscale dimensions in large 3D materials remains a fundamental challenge in nanocomposite fabrication. The incentive is that some of the most interesting properties occur at nanoscale interfaces, while the challenge arises from the difficulty in densifying the materials without deleterious reaction at the interface. Here, we introduce a method based on the synthesis of core–shell powders followed by efficient, relatively low-temperature densification with current-activated pressure-assisted densification. The composition of the bulk nanocomposites can be controlled by varying the core–shell weight ratio, leading to controllable thicknesses of the hard/soft magnetic phases. We demonstrate intimate mixtures of nanoscale strontium ferrite (hard magnetic phase) and Co–Fe (soft magnetic phase) with minimal reaction. The high volume content of high-quality oxide/metal interfaces leads to magnetic exchange coupling in the composites.

Core-shell nanospheres to achieve ultralow friction polymer nanocomposites with superior mechanical properties.

Core-shell nanospheres have been widely used in catalysis, batteries, medicine, etc. owing to their unique structural characteristics, which exhibit optimal performance and integrated functions of both the core and shell materials. To simultaneously achieve outstanding mechanical properties and remarkable lubrication properties in desirable polymer composites, core-shell nanospheres with polytetrafluoroethylene (PTFE) as the core and poly methyl methacrylate (PMMA) as the shell have been adopted as structural units to form bulk nanocomposites. We demonstrated that the mechanical and lubrication properties of the nanocomposites prepared using core-shell nanospheres as the continuous matrix were dramatically improved. Specifically, when compared with that of pure PTFE, the compressive strength of the PTFE@PMMA nanocomposite obviously increased up to one order of magnitude (from ∼9 to ∼90 MPa), the friction coefficient reduced to 25% (the lowest value was 0.03), and the wear rate decreased up to two orders of magnitude. Moreover, the mechanical and lubrication properties of the nanocomposites could be adjusted by changing the core-shell ratio, and an appropriate core-shell ratio was beneficial for achieving the desired comprehensive properties. It has been proposed that the properties, such as the confinement effect, improved dispersion capacity, etc., imparted by the core-shell structure effectively lead to high dispersion of the reinforcement phase, improvement of the binding force of the transfer film to the friction surface, and interruption of the wear process of the polymer composite.

Performance Analysis of Silver-Based Graphene Nanocomposite Bulk Materials Obtained by Spark Plasma Sintering

Silver-based bulk materials containing Ag/reduced graphene oxide (Ag/rGO) nanocomposite were prepared via a two-step procedure. First, a one-pot procedure was used to form Ag/rGO nanocomposites from AgNO3 and GO using hydrazine as a reductant. Then, Ag/rGO nanocomposites with various graphene contents were mixed with silver nanopowder and consolidated using spark plasma sintering. The hardness of the bulk material increased to 70 HV when the graphene content was increased to 2.5 wt.%. The bulk densification varied from 87.2% to 96% and was highest at graphene content of 2.5 wt.%. The conductivity (43.00–53.73 MS/m) was highest at 0.7 wt.% graphene content. The variation of the intensity and conductivity is mainly related to the formation of Ag-C bonds, while the variation of the density is mainly related to the sintering process.

High-performance copper reinforced with dispersed nanoparticles

Copper (Cu) has high electrical conductivity and is widely used for many industrial applications. However, pure Cu is very soft and improving the mechanical properties of Cu comes at the great expense of electrical and thermal conductivity. In this work, high-performance Cu with superior mechanical properties and reasonable electrical/thermal conductivity was fabricated using a scalable two-step method. First, Cu micro-powders with uniformly dispersed tungsten carbide (WC) nanoparticles were created by a molten salt-assisted self-incorporation process. A bulk nanocomposite was then obtained by melting the powders under pressure. The as-solidified Cu with 40 vol% uniformly dispersed WC nanoparticles exhibits high hardness, a yield strength over 1000 MPa, a Young’s modulus of over 250 GPa, and reasonable electrical and thermal conductivity.