Nano-sized Fillers Research Articles

On electric field distortion for breakdown mechanism of nanofilled transformer oil

In this paper, a proposed breakdown mechanism of nanofilled transformer oil is presented. The proposed mechanism is based on electric filed distortion results from charge accumulation over the surfaces of nanoparticles when exposed to external electric field. Different factors affecting breakdown strength of nanofilled transformer oil are considered. These factors are oil temperature, type, concentration levels and size of nanofiller. Therefore, breakdown strength of nanofilled transformer oil is experimentally evaluated at 35, 70, 100 and 130 °C to simulate the real operating conditions from no load to heavy load. Accordingly, preparation of nanofilled transformer oil samples is carried out considering different nanofiller material types and concentration levels. The adopted nanofiller material types are SiO2, TiO2, and ZrO2 considering the same particle size of 25 nm. The selected material types have different relative permittivities of 4.3, 70 and 100 for SiO2, ZrO2, and TiO2, respectively. The studied nanofiller concentration levels are 0.05, 0.1, 0.2, and 0.4 g/L. Also, the effect of particle size on breakdown strength is studied considering TiO2 nanoparticles of 25 nm and 100 nm particle sizes at the adopted concentration levels. The breakdown strength test is carried out on all prepared samples according to ASTM D1816 standard for all prepared samples. The evaluation of breakdown strength is based on average breakdown voltage. Electric field distortion in the nanofilled transformer oil is validated using finite element analysis. The obtained results show that concentration levels, type, and size of nanofiller as well as oil temperature have a significant effect on breakdown voltage of nanofilled transformer oil.

Evaluation of the Degree of Dispersion of Polymer Nanocomposites (PNCs) Using Nonlinear Rheological Properties by FT-Rheology

Characterizing dispersion quality of polymer nanocomposite (PNC) is as important as dispersing nanosized fillers in the polymer matrix. In this study, to quantify the dispersion quality of PNCs, we...

Preparation of boron nitride nanosheets using a chemical exfoliation method as a thermal conductive filler for the development of silicone thermal composites Part I: effect of single- and hybrid-filler additions on the silicone composite performance

This study developed a nano-size filler as a thermally conductive filler for a silicone thermal pad (STP) by exfoliating hexagonal-boron nitride ( h-BN) with the chemical exfoliation-free radical polymerization method to produce boron nitride nanosheets (BNNSs). We used N,N-dimethylacrylamide as the intercalation agent. After polymerization, it became poly( N,N-dimethylacrylamide) to exfoliate the h-BN layer. BNNSs were taken as a single-filler and hybrid-fillers with Al2O3 and then compared with h-BN to investigate their effect on the silicone composite properties. As the free radical polymerization reaction time increased, the interlayer distance of BNNSs lengthened to 0.35 nm, while the thickness of h-BN sheets decreased. The X-ray diffractometer results showed how the h-BN (002) crystal plane was enhanced and displaced. The Fourier transform infrared spectra showed that the characteristic peaks of 1372 and 812 cm−1 were enhanced, and the Raman results showed that the E2 g displacement and full width at half maximum increased, thus validating the successful preparation of BNNSs. Based on the scanning electron microscope-transmission electron microscope results, BNNSs with 24-hour reaction time offered the best results with a thickness of 5 nm. The highest thermal conductivity reached 3.66 W m−1 K−1 with the addition of 50 wt% BNNSs, and tensile strength of up to 11.30 kg/cm2. Hybrid-fillers showed enhancement of thermal conductivity to 5.28 W m−1 K−1 and tensile strength to 7.32 kg cm−2. Finally, the STP showed that the volume resistance (>1010 Ω cm), withstand voltage (>10 kV mm−1), and flame resistance (V-0) of the STP prepared by this study comply with the industrial application specifications.

Terahertz absorption spectra of several polymer nanocomposites indicating polymer-filler interactions

Optical absorption spectra in a frequency range from 0.5 to 5.0 THz were measured in several epoxy resin nanocomposites with and without co-addition of micro-sized fillers, aiming at obtaining important information on intermolecular interactions between filler and polymer. As a result, significantly large absorption appears when both micro-sized MgO and nano-sized SiO2 fillers were added in epoxy resin. Similar but smaller absorption is also found in an epoxy resin composite with nano-sized TiO2 fillers.

Improvements on Mechanical Property and Microstructure of Cementitious Composite Incorporated with Silica Fume and Carbon Nanotube

Nano-size fillers (ultrafine silica fume (USF) or/and multi-walled carbon nanotube (MWCT)) were incorporated into cement matrix to fabricate nano-fillers reinforced cementitious materials (NFRCs) with surfactant ultrasonic dispersion and subsequently mix cast process. The flexural and compressive strengths of four groups NFRCs with varied nano-filler loading were comprehensively investigated. Results show, there are positive effects on the flexural and compressive strength of NFRCs with nano-fillers loading, especially when USF and MWCT are incorporated simultaneously, and the correspondent maximal flexural and compressive strength can increase by above 17%, 28% with respect to the baseline, respectively. The pozzolan infilling effect of USF and the crack-bridging effect of dispersed MWCT result in the dense and integrated network microstructures of cured NFRC.

Synthesis and Investigation into Apatite-forming Ability of Hydroxyapatite/Chitosan-based Scaffold

Synthesis and Investigation into Apatite-forming Ability of Hydroxyapatite/Chitosan-based Scaffold

Synergistic effect of nano-SiO2 and graphene oxide: hybrid filled thermosetting polyimide nanocomposites with ultralow wear

In this work, nano-SiO2, GO and nano-SiO2/GO hybrid reinforced thermosetting polyimide (TPI) composites are synthesized by in situ polymerization method, respectively, and their mechanical performances are simulated using the finite element software to guide the design and manufacture of these tribological coatings. The tribological results show that the nano-SiO2/GO/TPI hybrid composites demonstrate better wear resistant ability, particularly under high load, than TPI composites that are added anyone of the SiO2 or GO nanoparticles alone, and the lowest wear rate of this hybrid composite 4.25 × 10−8 mm3N−1m−1 is obtained at high load, which is more than 1 order of magnitude lower than pure TPI’s 11.48 × 10−7 mm3N−1m−1. Tribological mechanism analysis shows that the improvement of tribological properties is mainly attributed to the synergistic effect of nano-SiO2 and GO in the tribological process. This hybrid nanocomposites can be promising material used as tribo-material in dry sliding condition under high load, and this study demonstrates a way to design and prepare polymer composite coatings with good tribological properties by considering the synergistic effect of nanosize fillers.

Experimental and numerical study of the effect of silica filler on the tensile strength of a 3D-printed particulate nanocomposite

Polymers are commonly found to have low mechanical properties, e.g., low stiffness and low strength. To improve the mechanical properties of polymers, various types of fillers have been added. These fillers can be either micro- or nano-sized; however; nano-sized fillers are found to be more efficient in improving the mechanical properties than micro-sized fillers. In this research, we have analysed the mechanical behaviour of silica reinforced nanocomposites printed by using a new 5-axis photopolymer extrusion 3D printing technique. The printer has 3 translational axes and 2 rotational axes, which enables it to print free-standing objects. Since this is a new technique and in order to characterise the mechanical properties of the nanocomposites manufactured using this new technique, we carried out experimental and numerical analyses. We added a nano-sized silica filler to enhance the properties of a 3D printed photopolymer. Different concentrations of the filler were added and their effects on mechanical properties were studied by conducting uniaxial tensile tests. We observed an improvement in mechanical properties following the addition of the nano-sized filler. In order to observe the tensile strength, dog-bone samples using a new photopolymer extrusion printing technique were prepared. A viscoelastic model was developed and stress relaxation tests were conducted on the photopolymer in order to calibrate the viscoelastic parameters. The developed computational model of nano reinforced polymer composite takes into account the nanostructure and the dispersion of the nanoparticles. Hyper and viscoelastic phenomena was considered to validate and analyse the stress–strain relationship in the cases of filler concentrations of 8%, 9%, and 10%. In order to represent the nanostructure, a 3D representative volume element (RVE) was utilized and subsequent simulations were run in the commercial finite element package ABAQUS. The results acquired in this study could lead to a better understanding of the mechanical characteristics of the nanoparticle reinforced composite, manufactured using a new photopolymer extrusion 5-axis 3D printing technique.

Thermal Properties of Composite Materials Based on the Powder Systems “Copper–CNTs”

The influence of the metal matrix filling with carbon nanotubes on the thermal properties of copper-based powder composite materials has been studied. It has been revealed that the powder systems ″copper–CNTs″ obtained according to the powder-metallurgy technology by electric-contact sintering possess anisotropic thermal conductivity under certain conditions. It has been found that during uniaxial molding, in the process of electric-contact sintering, CNTs are oriented in one direction, which leads to a rise in the values of the thermal-conductivity coefficient in this direction. It has been established that at a CNT concentration below the percolation threshold, experimental values of the thermal-conductivity coefficient of the composite materials are in good correlation with the values obtained with the Maxwell–Garnett theoretical model. It was noted for the first time that the Maxwell–Garnett theoretical model can be used to assess the distribution of a nanosize filler in a metal matrix.

Effect of SiC nano-size fillers on the aging resistance of XLPE insulation: A first-principles study

Effective strategies to prevent the electrical tree growth and extend the lifetime of cross-linked polyethylene (XLPE) insulation are of crucial importance for the development of power cable industry. The first-principles study with DFT method was performed to understand the mechanism of aging resistance for SiC/XLPE nanocomposite. The Bader charge redistribution calculations between different types of silicon carbide and XLPE suggest that SiC fillers have the ability of capturing hot electrons to suppress the accumulation of space charges because of their unsaturated electronic structures and magnetism on the Si- or C-terminated surfaces. The interfacial behavior between SiC and XLPE was investigated based on the physical interaction and chemical reactivity. The 3C, 4H and 6H-type SiC with flat Si-terminated surfaces are proposed to be favorable additives by showing relatively strong physical interaction with XLPE to limit its movement, and high activation energy for the hydrogen migration reaction to protect the XLPE.

Effects of nanoparticles size and interactions on dielectric properties of polymer matrix flexible dielectric nanocomposites

Effects of particle size on the dielectric properties of polymer matrix flexible nanocomposites were studied. Synthesized barium titanate (BaTiO3; BT) nanoparticles (NPs) with different sizes were effectively dispersed in the matrix polymer using a simple phase separation method. The dielectric responses of free-standing thin composite films were studied by impedance spectroscopy. The interactions between nanoparticles were also studied by finite element analysis and compared with experimental data using a time harmonic-electric current solver in the AC/DC module of COMSOL Multiphysics® 5.2. The dielectric permittivity of polymer matrix nanocomposites was remarkably affected by the BT particle size, while the dielectric loss did not show any noticeable changes. The real permittivity exhibited the highest value when the BT particle size was near 100 nm. The calculated energy density based on measured real permittivity and breakdown strength was as high as 17.24 J/cm3. The dielectric properties of polymer matrix nanocomposites can be improved by controlling the particle size of nanofillers in conjunction with surface treatment of fillers.

How are the thermal properties of polypropylene/graphene nanoplatelet composites affected by polymer chain configuration and size of nanofiller?

The leading purpose of this work was to broaden the current knowledge about the impacts of various chain configurations of polypropylene (PP), i.e., linear and branched form, on the thermal properties (thermal stability, thermal conductivity, crystallinity, thermal mechanical properties) of PP nanocomposites reinforced by graphene nanoplatelet (GnP) particles. The utilization of GnP with different particle size gave us good information about the impacts of filler's dimension on the thermal properties as well. Regardless of the PP type, EC1500-filled (small size GnP) composites showed higher storage modulus in the dynamic mechanical analysis. With respect to DSC results, incorporation of GnP, particularly GnP with smaller particles, led to a striking increment in crystallization temperature and crystallinity, and nucleating efficiency of GnP in linear PP-based composites was higher. The employment of GnP brought about an improvement in degradation temperature and thermal stability of nanocomposites, and smaller GnP was more effective in this context. However, due to its higher aspect ratio, EC100 GnP (large size GnP) could enhance thermal conductivity more satisfactory, specifically in linear PP-based samples.

Buckling behavior of various metallic glass nanocomposites reinforced by carbon nanotube and Cu nanowire: A molecular dynamics simulation study

The reinforcement of various materials by nanofillers as nanocomposites has recently received the attention of many researchers. In the present research, molecular dynamics simulations are used to investigate the influence of nanowire (NW)/carbon nanotube (CNT) reinforcement on the buckling behavior of metallic glass matrix nanocomposites (MGMNCs). The buckling characteristics of nanocomposites made by adding Cu NWs, CNTs and Cu NW-encapsulated CNTs to metallic glass matrices are studied. The results demonstrate that MG alloys comprising just two elements (Cu and Zr) with higher Cu percentage have higher mechanical stability. Also, it is observed that adding NW leads to a negative effect on the buckling behavior, while adding CNT and NW-encapsulated CNT considerably increases the buckling force and strain of the metallic glass models. Moreover, it is found that the filled CNT is the most effective nanofiller for amending the buckling behavior of metallic glasses. Furthermore, as the size of nanofillers gets larger, the critical force increases and the critical strain decreases.

Effect of Nano Filler Reinforcement on Mechanical Properties of Epoxy Composites

Nano-sized functional fillers, such as Nano-clay (N-C) and Nano-calcium carbonate (N-CC), have attracted a great deal of awareness due to their unexpected intrinsic properties. Extensive research has been done on clay material for epoxy nanocomposites but only a few have ventured into a comparison with other Nanofillers. In this paper, a study has been made of the mechanical properties of epoxy containing N-C and N-CC fillers. These composites were studied for their mechanical properties such as hardness, tensile, flexural and impact strength as per ASTM standards. Fraction of void cohort in the samples was quantified following the rule of mixture. Experimental results demonstrated that incorporation of N-C fillers expanded the hardness, impact strength and module of epoxy nanocomposites. However, the tensile and flexural properties have shown declining trend for N-C/N-CC nanocomposites. The morphological and fractographic features were examined utilizing scanning electron microscopy.

Strengthening of the composite materials based on metal matrix and carbon nanotubes

Carbon nanotube (CNT)-reinforced powder nanocomposites based on copper matrix were successfully fabricated using a spark plasma sintering method. In this work, the mechanisms of hardening the metal matrix with nanosized filler particles were shown. A comparative analysis of the calculated and experimental values of the ultimate compressive strength for samples based on the copper matrix and carbon nanotubes was performed. Linear and root-mean-square models of hardening of composite materials with nano-sized filler were presented. The root-mean-square model allowed us to calculate reliably the values of the ultimate compressive strength at a concentration of CNT in the material up to 0.07 wt.%. The ultimate compressive strength decreases sharply when the content of CNTs in the material is more than 0.07 wt.%. The Orovan mechanism is the predominant mechanism of strengthening of composite materials: copper – CNT. The predominance of Orovan mechanism over other strengthening mechanisms is explained by the relatively low transfer efficiency of the load between the initial components of the material due to the weak interfacial connection between the matrix and the filler, the insufficiently uniform distribution of CNTs in the metal matrix, the agglomeration of nanosized filler, the location of a certain number of CNTs in the pore space of the metal matrix, the presence of pores of irregular shape. The results of the work were used in the development of new antifriction composite materials with improved strength properties for friction units of machines and mechanisms for various purposes.

Characterizations of PMMA-based polymer electrolyte membranes with Al2O3

Abstract Poly(methyl methacrylate) (PMMA)-based polymer electrolyte membranes are prepared through the solution cast method, with PMMA:ethylene carbonate (EC):LiCF3SO3:Al2O3 weight ratio of 55.13:18.34:24.5:2. The effect of Al2O3 filler grain sizes of 50 nm and 10 μm on the polymer electrolytes was studied in this work. From the Cole-Cole plot obtained through electrochemical impedance spectroscopy, the highest ionic conductivity for 50-nm Al2O3 in the PMMA-LiCF3SO3-EC-Al2O3 sample was measured as 1.52 × 10−4 S/cm at room temperature. The bonding formation among the host polymer and other additives in the polymer electrolytes has been studied using Fourier transform infrared spectroscopy. A strong occurrence of CH3 stretching mode has proven that nano size Al2O3 results in a much stronger bonding effect with the host polymer. The particle sizes were calculated by applying the Debye-Scherrer equation from the X-ray diffraction results. This work considers the effect of instrument broadening to further improve the accuracy of particle broadening for particle size calculation. The average particle size of nano size Al2O3 in the PMMA sample is calculated as 2.9693 nm. Moreover, a higher amorphousity level obtained from nano size filler polymer electrolyte of 98.5% computed from differential scanning calorimetry thermograms had also explained the achievement of high ionic conductivity in this work.

Effect of Filler Concentration on Tracking Resistance of ATH-Filled Silicone Rubber Nanocomposites

It is necessary for polymeric materials to have superior tracking resistance against various stress conditions for outdoor applications. In this study, the effect of nano-sized alumina tri-hydrate (ATH) particles on the tracking resistance of silicone rubber (SiR) is studied. Specimens with filler loadings of 1, 3, 5, 10, and 20 wt % are used for performance characterization. From the inclined plane test (IPT) results, apparent improvement in tracking resistance was achieved by mixing 3 wt % of nano-sized fillers, compared to unfilled specimens. ATH/SiR nanocomposites with 5 wt % loading showed comparable tracking performance to SiO2/SiR microcomposites with 20 wt % loading. For detailed analysis, measurements of surface contact angle (SCA) and surface leakage current, and thermo-gravimetric analysis (TGA) were performed. As the nano-ATH filler concentration increased, both thermal stability and leakage current characteristics were improved. Such results agreed with the tracking resistance performance by showing that thermal decomposition and surface charge transport is inhibited in ATH/SiR nanocomposites. Furthermore, performance improvement in nanocomposites was achieved, even at low filler loadings, compared to microcomposites. Meanwhile, the change in SCA was found to be rather limited, regardless of filler loading and filler size.

Wear performance of UHMWPE based composites including nano-sized fumed silica

Fumed silica has been utilized in various applications due to its advanced mechanical properties. In addition to this advantage, the branch-like structure of fumed silica leads to a very high specific surface area in comparison to spherical nano-sized particles. Since the major contribution of the nano-sized fillers is growing the filler/matrix interaction surface, we used the fumed silica particles in the UHMWPE matrix to enhance the wear performance of the base material. The composites were produced by using the compression molding method and in order to determine the molding parameters such as molding pressure and molding temperature, a set of experiments was carried out by using the neat UHMWPE prior to the composite fabrications. After completing the molding stage, the specimens were subjected to the wear tests in a ball-on-disk configuration against a tungsten carbide (WC) counterpart. In addition, the composites were exposed to a nitric acid attack to investigate the effect of the fumed silica on the oxidation behavior. According to this work, fumed silica provides beneficial results for the wear performance of UHMWPE based composites. However, excessive loadings of the fumed silica lead to the formation of particle clusters in the microstructure and thereby reducing the wear resistance of the composites. The anti-oxidation performance of the composites was also enhanced with the addition of the fumed silica in the UHMWPE matrix.

Nanoporous polymer-based composites for enhanced hydrogen storage

The exploration and evaluation of new composites possessing both processability and enhanced hydrogen storage capacity are of significant interest for onboard hydrogen storage systems and fuel cell based electric vehicle development. Here we demonstrate the fabrication of composite membranes with sufficient mechanical properties for enhanced hydrogen storage that are based on a polymer of intrinsic microporosity (PIM-1) matrix containing nano-sized fillers: activated carbon (AX21) or metal–organic framework (MIL-101). This is one of the first comparative studies of different composite systems for hydrogen storage and, in addition, the first detailed evaluation of the diffusion kinetics of hydrogen in polymer-based nanoporous composites. The composite films were characterised by surface area and porosity analysis, hydrogen adsorption measurements, mechanical testing and gas adsorption modelling. The PIM-1/AX21 composite with 60 wt% AX21 provides enhanced hydrogen adsorption kinetics and a total hydrogen storage capacity of up to 9.35 wt% at 77 K; this is superior to the US Department of Energy hydrogen storage target. Tensile testing indicates that the ultimate stress and strain of PIM-1/AX21 are higher than those of the MIL-101 or PAF-1 containing composites, and are sufficient for use in hydrogen storage tanks. The data presented provides new insights into both the design and characterisation methods of polymer-based composite membranes. Our nanoporous polymer-based composites offer advantages over powders in terms of safety, handling and practical manufacturing, with potential for hydrogen storage applications either as means of increasing storage or decreasing operating pressures in high-pressure hydrogen storage tanks.

Effect of graphene oxide as a filler material on the mechanical properties of LLDPE nanocomposites

Graphene oxide (GO) has high aspect ratios than many nanosize fillers such as carbon nanotubes and clay, besides its better mechanical properties than many polymers; so they are preferred as a filler material in polymer matrix composites. In this study, the effect of GO on the mechanical properties of linear low-density polyethylene (LLDPE) were experimentally investigated. LLDPE-GO nanocomposites were prepared by melt compounding method, and the extruded nanocomposite was shaped by injection molding machine for the mechanical tests. The mechanical properties investigated included tensile properties, fatigue properties, as well as hardness properties. Differential scanning calorimeter (DSC) was employed to study the thermal characterization of the composites. The results revealed that the addition of GO nanosheets indeed had a positive effect on the tensile, fatigue, and hardness properties. The tensile strength, Young's modulus, and Shore D hardness value were increased by 27.4%, 31.3%, and 9%, respectively, with a GO loading ranging from 0 wt.% to 2 wt.%. The addition of GO had a significant effect on the fatigue properties of the composites such as nearly exponential increment in the cyclic numbers. The samples with 2 wt.% of GO could endure up to 106 cycles during the tests, which is 100 times that of pure LLDPE. The morphological analysis via X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that GO nanosheets were well exfoliated in the LLDPE matrix. However, there is no significant effect on the melting temperature, crystallization temperature and crystallinity of LLDPE based on DSC result.