Distribution Of Al2O3 Nanoparticles Research Articles

A novel way to prepare PbZrO3 nanocomposite films for increasing electrical properties and energy storage performance

The energy storage performance of dielectric materials depends largely on their polarization properties and electric breakdown strength. Nanocomposites have emerged as an effective method for improving these properties. In this study, we propose a novel method to prepare PbZrO3-Al2O3 nanocomposite films by combining chemical solution deposition with thermal evaporation of a metal Al layer. The resulting composite films exhibit a layered distribution of Al2O3 nanoparticles (NPs) on the PbZrO3 matrix, which can be used to control the shape and characteristics of the polarization-electric field (P-E) hysteresis loop by varying the thickness of the Al layer. We thoroughly investigated the effects of Al2O3 NPs on the microstructure, polarization, leakage current, and energy storage properties of the composite films. Our results show that as the content of Al2O3 NPs increases, the property of the composite films gradually evolves from antiferroelectric characteristics to ferroelectric characteristics. Specifically, the maximum polarization, remanent polarization, and electrical breakdown strength increase, while the leakage current decreases. Compared to PbZrO3 thin films, the electrical breakdown strength (1850 kV/cm) and energy storage density (25.0 J/cm3) of the nanocomposite thin films increased by 189% and 93%, respectively. Our study presents a new method to prepare dielectric nanocomposite films and opens up a new avenue for designing energy storage capacitor materials using nanocomposites.

Effect of milling time on microstructural and mechanical properties of nano-Al2O3P/6061Al composites prepared by transient liquid-phase sintering

In this study, 5 vol% Al2O3 nanoparticles reinforced 6061 Al matrix nanocomposite was prepared by mechanical alloying the corresponding powders followed by hot-pressing. The effect of the milling time on the morphology of powder as well as the microstructure and mechanical properties of resulting nanocomposites was studied. The result shows that the effect of the milling time on the mechanical properties of nanocomposites comes from its effect on the distribution of Al2O3 nanoparticles in Al matrix. The long milling time is required to uniformly disperse Al2O3 nanoparticles within Al grains, in order to obtain good mechanical properties. The nanocomposite made from the powder milled for 50 h exhibits a tensile strength of 602 MPa and an elongation to failure of 8.8%, which are higher than those ever reported for the similar materials. The higher mechanical properties are mainly attributed to Orowan strengthening, grain boundary strengthening, and high dislocation density.

Al2O3 nanoparticle reinforced heterogeneous CrCoNi-matrix composites with improved strength-ductility synergy

Novel Al2O3 nanoparticle-reinforced heterogeneous CrCoNi-matrix composites (CrCoNi–Al2O3P) with 10–30 wt% of coarse grain (CG) matrix were prepared by multi-step mechanical milling plus hot pressing sintering. The relationships between microstructure and mechanical properties of the composites were studied in detail. The results reveal that the heterogeneous structure in CrCoNi–Al2O3P composites is composed of CG region and ultrafine grain (UFG) region with uniform distribution of Al2O3 nanoparticles. With increasing content of CG matrix in the nanocomposite, the hardness first decreases but then increases, and the increase of hardness may be due to the formation of carbides. Compared with homogeneous CrCoNi–Al2O3P composite, the compressive fracture strain of heterogenous composite increases by 53.2% at most, while sacrificing a small amount of strength, among which the 20 wt% CG heterogeneous composite exhibits an excellent strength-ductility synergy. For the mechanisms of strengthening and toughening, hetero-deformation induced (HDI) hardening makes the heterogeneous composites almost as strong as the homogeneous composite. Meanwhile, the CrCoNi matrix with low stacking fault energy can be deformed by dislocation slipping and twinning at room temperature, which improves the plasticity of the composite. Furthermore, the heterogeneous structure with soft and hard domains increases the work hardening ability of the composite.

Achieving a better combination of strength and electrical conductivity of Cu-Al2O3 nanocomposites by accumulative roll-bonding to ultrahigh cycles

Copper matrix nanocomposites reinforced by Al2O3 nanoparticles were fabricated by accumulative roll-bonding (ARB) processed to ultrahigh rolling cycles. The effects of ARB cycles on the distribution of Al2O3 nanoparticles and properties of the nanocomposites were investigated. It was found that a higher ARB cycle was needed to obtain a uniform distribution of Al2O3 nanoparticles with a larger volume fraction. Significant strengthening, as well as a good combination of tensile strength and electrical conductivity of the Cu-Al2O3 nanocomposites can be obtained, through optimizing the uniform dispersion of Al2O3 nanoparticles by applying ultrahigh ARB cycles. The enhanced strength (maximum: 735 MPa) of the nanocomposites can be attributed to the maximized contribution of nanoparticles by various mechanisms through optimizing the uniform dispersion of them.

Synthesis and Characterizations of Fe3O4 Added with Al2O3 Nanoparticles via Sol-Gel Technique

A single step sol-gel has been established as a new route for synthesizing AkCb-added Fe3O4 nanoparticles. In this work, the effects of Al2O3 composition towards the micro structure and magnetic properties of AkCb-added Fe3O4 samples were investigated. A series of Fe and Al nitrate mixture solutions were prepared by varying the Al nitrate composition from 2.0 wt. % to 10.0 wt. %. A dropwise of propylene oxide has dimed out the clear red mixture solution with a significant release of heat before turned into a gel. The gel was dried at 90 °C for 48 h in a ventilated oven which then pulverized into a powder by using mortar grinder. The powder was calcinated at 900 °C for 1 h in a normal furnace atmosphere. The XRD results revealed that the existence of polycrystalline Fe3O4 were completed at calcination temperature 900 °C. The SEM images of the Fe3O4 with 10.0 wt.% of Al2O3 samples showed a distinct nanoparticles micro structure due to the increased of Fe3O4 nucleation initiated by Al2O3 nanoparticles. The Vickers microhardness of the Al2O3 added Fe3O4 samples were significantly increased as the Al2O3 content was increased up to 10.0 wt.% attributed from good distribution of Al2O3 nanoparticles in the sample. Subsequently, the magnetic properties of Fe3O4 investigated by alternating gradient magnetometer, AGM was insignificantly reduced by the addition of Al2O3 nanoparticles. This work indicated that the sol-gel reaction is an effective method to achieve uniform distribution and high purity of AkCb-added Fe3O4 nanoparticles with optimum microhardness and ferromagnetic performances.

Processing and characterizations of polycarbonate/alumina nanocomposites by additive powder fed friction stir processing

The powder fed friction stir process (FFSP) is a new and attractive solid-state manufacturing technique that enables the fabrication of polymer matrix nanocomposites (PNC). Herein, we present the fabrication of polycarbonate (PC)-based nanocomposites by in-situ injection of colloidal alumina nanoparticles (<100 nm) into the plasticized polymer under stir friction of a steel tool. Microstructural features and mechanical durability of the prepared nanocomposites were studied. The mechanical properties of the processed materials including hardness, tensile strength, flexural strength, and impact energy were elaborated. The tensile strength of PNC in the longitudinal direction was ~73 MPa, which was higher than the PC matrix by 109%. However, a lower bending strength (~48 MPa) compared with PC was measured. Fractographic studies determined the presence of mist patterns on flexural samples and crack growth from shrinkage holes and river patterns. The distribution of Al2O3 nanoparticles was found to improve the impact energy in both transverse and longitudinal directions by 111% (~28 kJ/m2) and 127% (32 kJ/m2), respectively. Crack deviation by the hard inclusions was found to be the mean mechanism of enhanced impact resistance.

Optimization of the microstructure and mechanical properties of heterogeneous Al-Al2O3 nanocomposites

High-energy ball milling and hot-press sintering were employed to synthesize heterogeneous aluminum (Al) matrix nanocomposites reinforced by 5 vol.% alumina (Al2O3) nanoparticles. The heterogeneous structure was formed by the nonuniform distribution of Al2O3 nanoparticles in Al matrix, and it composed of an isolated irregular soft phase (pure Al) and a continuous hard phase (Al reinforced by Al2O3 nanoparticles). It was found that the size of soft phase is optimized with increasing ball milling time, resulting in an increase in the yield strength and ultimate strength, as well as retained failure strain. It is worth noting that the ultimate strength of heterogeneous Al nanocomposite with milling time of 20 h (referred to as Heter-20) reached 610 MPa under compression testing. In particular, the introduced soft phase exhibited severe plastic deformation and interface microcracks under compression, which led to higher failure strain (∼30% for Heter-20) and toughness compared to traditional homogeneous Al matrix composites. Furthermore, coexistence of brittle and ductile fractures was observed in the heterogeneous Al nanocomposites under quasi-static compression.

Effects of Al2O3 nanoparticles volume fractions on microstructural and mechanical characteristics of friction stir welded nanocomposites

The objective of the present study is to investigate the effect of Al2O3 nanoparticles volume percentage on tribological, mechanical and microstructural characteristics of 6061-T6 aluminum alloy based particulate-nanocomposite (P-NCs) fabricated using friction stir welding (FSW) process. Optical microscopy (OM) and scanning electron microscopy (SEM) was employed to evaluate the (a) microstructures of the produced nanocomposites to ascertain the distribution of Al2O3 nanoparticles in the nugget zone; (b) nanocomposite depth formed on Al-alloy matrix, and (c) fractured and wear characteristics. Results reveal that the produced P-NCs had a depth of 3286 µm across the perpendicular x-section of the weld nugget zone of P-NCs. With the increase in a volume percentage of Al2O3 nanoparticles there was a tremendous increment in the microhardness up to 125 HV which is higher than as-received AA6061-T6. It was also noticed that the tensile strength and the wear resistance of produced P-NCs were significantly increased at 0.3 vol% of Al2O3 nanoparticles as compared to 0.2 and 0.4 vol%. The corresponding mechanical and wear properties results were correlated to microstructure and fractography results.

Production of AA6061-T6/Al2O3 reinforced nanocomposite using friction stir welding

Heat-treatable AA6061-T6 weldability leads to a decline in the physio-mechanical and tribological properties due to strengthening precipitates dissolution in the nugget zone of FS-welded joints. Improvement in these properties is governed by reinforcement particles addition in the weld joint line for non-heat treatable Al-alloys. Although, its application to AA6061-T6 is scant. In the present work, FS-welded joints were produced by reinforcing Al2O3 nanoparticles into the faying surface of the base matrix. The purpose of Al2O3 nanoparticles addition is to refine the microstructure of the nugget zone and to obstruct the granular growing in the heat-affected zone. FSW was conducted at constant rotating 2000 rpm, transverse 70 mm min−1 speed to illustrate the influence of Al2O3 addition on mechanical, microstructure, micro-hardness, and wear properties of welds compared to parent alloy and unreinforced joints. Findings revealed that Al2O3 nanoparticles addition along the joint line leads to noteworthy grains refinement structure of weld zone (6μm) compared with the base material (38μm) and unreinforced nugget (18μm) joints. In addition, reinforced FS-W nugget zone have banded structure of alternate regions namely, nanoparticles-rich and free those have a difference in grain size, such that, the nanoparticle-rich region has fine grain size (6μm) than nano particle-free (14μm) region. Due to Zener-influence occurred via Al2O3 nanoparticles helps to avoid the grain growth accompanied by dynamic recrystallization throughout FSW process which results in granular size reduction. Tensile strength (246 MPa/73%), microhardness (88HV/52%), and wear properties was notably increased for reinforced FSW joint compared to unreinforced joint (tensile strength (180MPa), micro-hardness (46 HV), and lower wear resistance, under similar parameters which attribute to nanoparticles presence in processed area. Moreover, single FSW pass leads to non-uniform distribution of Al2O3 nanoparticles and nucleation of voids at Al/Al2O3 boundary in the heat-affected zone which leads to early fracture of welded joint during tensile loading.

Comparison of Mechanical Properties and Corrosion Behavior of Al-NanoAl2O3 with Al-MicroAl2O3 Composites Made by SPS Process

In this research, spark plasma sintering (SPS) was used as a new method in the fabrication of Al–Al2O3 composites. The effect of Al2O3 particle size (both nano and micron) and its amount on the relative density, hardness, resistance, corrosion and compressive strength in Al–Al2O3 composite were investigated. Evaluation and size characterization of nano particle was carried out by transmission electron microscope. The distribution of particles throughout sample, as well as the detection of the elements in the structure were studied by scanning electron microscopy equipped by corresponding energy dispersive X-ray spectrometer analysis. According to the results, in the sample containing 3 wt% of nanoparticle of Al2O3, the mechanical properties of composite and corrosion resistance were improved due to uniform distribution of Al2O3 nanoparticles. However, by increasing weight percent or particle size of Al2O3 in composite, properties such as corrosion resistance and mechanical strength were considerably reduced. It can be attributed to the porosity and agglomeration of particle that were produced in composite.

Influence of tool rotational speed on the properties of friction stir spot welded AA7075-T6/Al2O3 composite joint

The growing importance of Aluminium alloys in automobiles and aerospace applications provides the implementation of composite materials and promising joining method like Friction Stir Spot Welding (FSSW). In this research, Al2O3 nanoparticles reinforced FSSW is carried out on 7075-T6 Aluminium alloy and the influence of tool rotational speed on mechanical properties is studied. The base metal of thickness of 2 mm is spot welded using a threaded cylindrical profile tool with four different tool rotational speeds varying between 900 rpm and 1700 rpm, where volume of Al2O3 is being unchanged. The results of mechanical tests show that the sample made with a tool rotational speed of 1300 rpm has a better weld of good strength. Moreover, the result from Field Emission Scanning Electron Microscopy also evidences the uniform distribution of Al2O3 nanoparticles in the weld region which causes the improved strength. Also observed that the lower and higher tool rotational speeds from the selected range do not result homogeneous distribution of nano fillers in the weld nugget.

Nanoindentation behavior of nanostructured bulk (Fe,Cr)Al and (Fe,Cr)Al-Al2O3 nanocomposites

The purpose of the present study was to design a new generation of FeAl-based intermetallic compounds with improved mechanical and oxidation properties. Synthesis of powders of FeAl, (Fe,Cr)Al and (Fe,Cr)Al in situ composites with 5 and 10% Al2O3 contents was reported elsewhere. In this paper the sintering behavior is reported. FeAl, (Fe,Cr)Al and (Fe,Cr)Al - Al2O3 powders were sintered by a hot-pressing method at 1600 °C and 5.5 GPa for 15 min to produce bulk specimens for mechanical and microstructural characterization. Microstructural characterization by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of theses nanocomposites disclosed uniform distribution of Al2O3 nano-particles. XRD analysis indicated the presence of FeAl, (Fe,Cr)Al and Al2O3 phases. The presence of nano-sized Al2O3 particles effectively retarded grain growth by pinning the grain boundary during hot pressing. Nanoindentation tests indicated that with increasing content of Cr and Al2O3 reinforcement, the hardness and Young's modulus increased, and the fracture toughness reaches a high value of 19.6 ± 0.4 MPa m1/2 for the (Fe,Cr)Al-10%Al2O3 composition, with a hardness value of 21.7 ± 1.8 GPa. Nanoindentation creep tests at room temperature showed that composites with Al2O3 nanoparticles had higher creep rate than FeAl and (Fe,Cr)Al. It was found that improvements in the mechanical properties of FeAl intermetallic compound can be achieved by adding Cr and uniform distribution of Al2O3 nanoparticles.

Mg improves the distribution of Al2O3 nanoparticles in an Al matrix via solidification

We report the effect of Mg addition on the distribution of a low content of Al2O3 nanoparticles in the Al matrix as well as the mechanical properties of the prepared nanocomposites. The results show that the average grain size was slightly smaller in nanocomposites with Mg than those without. The addition of Mg leads to complete dispersion and uniform distribution of Al2O3 nanoparticles in the Al matrix. The uniform distribution of Al2O3 nanoparticles is contrary to the view that most Al2O3 nanoparticles are pushed to the grain boundary with the low volume fraction of nanoparticles added into the metal melt. MgAl2O4 formed at the interfaces improved the interfacial wetting and bonding between nanoparticles and the Al matrix. The addition of magnesium leads to a significant increase in the elongation of nanocomposites. Orowan strengthening increased the yield strength and tensile strength of nanocomposites with Mg versus those without Mg. The tensile strength and yield strength of nanocomposites with Mg were 265 MPa and 206 MPa, respectively—an increase of approximately 29% and 51% versus Mg-free nanocomposites.

Wear Behavior of AZ31/Al2O3 Magnesium Matrix Surface Nanocomposite Fabricated via Friction Stir Processing

The aim of this study was to produce magnesium-based surface nanocomposites via friction stir processing and to investigate the effect of tool rotational speed on the microstructure, hardness and wear behavior. The surface of the nanocomposites was characterized using optical and scanning electron microscopes, as well as through microhardness and wear tests. The results indicated that with the increase in rotational speed, the grain size of the surface nanocomposites increased, but its hardness decreased despite the improved distribution of Al2O3 nanoparticles. It was also found that the wear resistance has a direct relation to the distribution of the Al2O3 nanoparticles. Furthermore, the addition of nano-Al2O3 changed the wear mechanism from the adhesive mode in the as-received AZ31 to the abrasive mode in the nanocomposite specimens. The rotational speed of 1400 rpm was an optimum parameter to achieve a suitable composite layer with the highest wear resistance.

Interaction of aluminum oxide nanoparticles with flow of polyvinyl alcohol solutions base nanofluids over a wedge

Polyvinyl alcohol (PVA) is an important industrial chemical, which is used in numerous chemical engineering applications. It is important to study and predict the flow behavior of PVA solutions and the role of nanoparticles in heat transfer applications to be used in chemical processes on industrial scale. Therefore, the present study deals with the PVA solution-based non-Newtonian Al2O3-nanofluid flow along with heat transfer over wedge. The power-law model is used for this non-Newtonian nanofluid which exhibited shear-thinning behavior. The influences of PVA and nanoparticles concentrations on the characteristics of velocity and temperature profiles are examined graphically. The impacts of these parameters on wall shear stress and convective heat transfer coefficient are also studied through tabular form. During the numerical computations, the impacts of these parameters on flow index and consistency index along with other physical properties of nanofluid are also considered. In this study, we found an improvement in heat transfer and temperature profile of fluid by distribution of Al2O3 nanoparticles. It is also noticed that resistance between adjacent layers of moving fluid is enhanced due to these nanoparticles which leads to decline in velocity profile and increases in shear stress at wall.

Optimizing and investigating influence of manufacturing techniques on the microstructure and mechanical properties of AZ80-0.5Ca-1.5Al2O3 nanocomposite

In the present study, it has been attempted to evaluate the effect of stir and rheo-casting techniques on microstructure and mechanical properties of AZ80-0.5wt%Ca/1.5 vol%Al2O3 nanocomposite. In the first step, preference selection index (PSI) criterion was successfully utilized to achieve the best stirring conditions in both casting processes. Then, the nanocomposite samples were fabricated by two different routes of stir and rheo-casting processes. Microstructural studies of the samples indicated that type and amount of the eutectic phase and particles distribution were influenced remarkably by casting techniques. The rheo-cast nanocomposite with fully divorced eutectic phase provided higher strength, better reinforcement distribution and less porosity in comparison with the stir-cast one. Then nanocomposites were subjected to extrusion at 450 °C with an extrusion ratio of 12:1. Hot-extrusion of the nanocomposites induced dynamic recrystallization by two different mechanisms, consisting of rotational dynamic recrystallization (RDR) and particle stimulation nucleation (PSN), which caused refining grain size. Tensile properties of the extruded rheo-cast nanocomposite were higher than values of the extruded stir-cast nanocomposite, which was mainly attributed to more uniform distribution of Al2O3 nanoparticles.

Preparation and Characterization of Polyimide/Alumina Composite Films as Improved Solid Dielectrics

Polyimide/alumina (PI/Al₂O₃) nanocomposite films were prepared by incorporating different nano-sized Al₂O₃ contents into PI which derived from pyromellitic dianhydride (PMDA) and a flexible diamine 4,4-bis(3-aminophenoxy) biphenyl (4,3-BAPOBP). The micromorphology, chemical structure, dielectric, mechanical properties and glass transition temperatures (T g ) of prepared films were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), LCR metry, electronic tensile testing and differential scanning calorimetry (DSC). SEM images show uniform distribution of Al₂O₃ nanoparticles in matrix. FTIR spectra indicate that Al₂O₃ nanoparticles are functionalized with γ-aminopropyl triethoxysilane (γ-APS) and the imidization was complete. XRD patterns reveal the peaks of PI/Al₂O₃ composite films were similar to those of Al₂O₃, indicating that the crystal structure of Al₂O₃ remains unchanged and stable after being doped into PI matrix. Meanwhile, the effects of additives on the dielectric and mechanical properties of composite films were also studied. The results show the dielectric constant and dielectric loss of hybrid materials increase with the addition of Al₂O₃ nanoparticles. The electrical breakdown strength and tensile strength of PI/Al₂O₃ can be markedly improved by the addition of appropriate amounts of Al₂O₃ to the PI matrix.

Investigating the effects of traveling speeds and post-weld heat treatment on mechanical properties of nano-Al2O3-fortified AA6061-T6 friction stir welds

In this study, 6 mm thick AA6061-T6 plates were friction stir welded (FSWed) at different traveling speeds while Al2O3 nano-particles were incorporated between adjoining plates. The solution heat treatment was applied on samples for one hour at 540 ℃ and subsequently aged for 18 h at 180 ℃ to investigate the effect of post-weld heat treatment on mechanical properties of specimens. All joints were investigated macro- and micro-structurally. The microstructural characterization of the FSWed samples was carried out using scanning electron microscopy (SEM) and light microscopy techniques. Distribution of Al2O3 nano-particles in the stir zone was studied by SEM. The specimen FSWed at 40 mm/min exhibited the most homogeneous particles distribution. Tensile properties including ultimate tensile strength, elongation, and fracture surfaces were studied. Microhardness of specimens was also investigated. Surprisingly, all specimens exhibited inferior hardness compared to the as-received AA6061-T6 alloy. This phenomenon was attributed to the dissolution of precipitates during FSW process.

The influence of heat treatment on microstructure and wear properties of friction stir welded AA6061-T6/Al2O3 nanocomposite joint at four different traveling speed

In the present study, 6mm thick AA6061-T6 alloy was friction stir welded (FSWed) at different traveling speeds while Al2O3 nano-particles were incorporated between adjoining plates. To investigate the influence of post weld heat treatment (PWHT) on microstructure and wear properties, solution treatment cycle was applied to FSWed specimens for 1h at 540°C then aged for 18h at 180°C. Distribution of Al2O3 nano-particles in the stir zone (SZ) was observed via scanning electron microscopes (SEM). After heat treatment, grain size changed imperceptibly. Surprisingly, all specimens exhibited inferior hardness to the as-received AA6061-T6 alloy which was attributed to precipitates solution during FSW. After heat treatment, hardness value of the specimen FSWed at 40mm/min improved. In the meantime, the uniform dispersion of Al2O3 particles in this specimen resulted in refinement and homogenous distribution of strengthening precipitates. Thanks to Al2O3 nano-particles, wear loss reduced remarkably (62%). Additionally, after heat treatment, the specimen FSWed at 40mm/min showed improved wear behavior.

Ion conduction and relaxation in PEO-LiTFSI-Al2O3 polymer nanocomposite electrolytes

Ion conduction and relaxation in PEO-LiTFSI-Al2O3 polymer nanocomposite electrolytes have been studied for different concentrations of Al2O3 nanoparticles. X-ray diffraction and differential scanning calorimetric studies show that the maximum amorphous phase of PEO is observed for PEO-LiTFSI embedded with 5 wt. % Al2O3. The maximum ionic conductivity ∼3.3 × 10−4 S cm−1 has been obtained for this composition. The transmission electron microscopic image shows a distribution of Al2O3 nanoparticles in all compositions with size of &amp;lt;50 nm. The temperature dependence of the ionic conductivity follows Vogel-Tamman-Fulcher nature, indicating a strong coupling between ionic and polymer chain segmental motions. The scaling of the ac conductivity implies that relaxation dynamics follows a common mechanism for different temperatures and Al2O3 concentrations. The imaginary modulus spectra are asymmetric and skewed toward the high frequency sides of the maxima and analyzed using Havriliak-Negami formalism. The temperature dependence of the relaxation time obtained from modulus spectra also exhibits Vogel-Tamman-Fulcher nature. The values of the stretched exponent obtained from Kohlrausch-Williams-Watts fit to the modulus data are fairly low, suggesting highly non-exponential relaxation for all concentrations of Al2O3 in these electrolytes.