Addition Of Nano-sized Particles Research Articles

Morphological control of grafted polymer films via attraction to small nanoparticle inclusions

Control of the morphologies of polymer films and layers by addition of nanosize particles is a novel technique for design of nanomaterials and is also at the core of some important biological processes. In order to facilitate the analysis of experimental data and enable predictive engineering of such systems, solid theoretical understanding is necessary. We study theoretically and computationally the behavior of plane-grafted polymer layers (brushes) in athermal solvent, decorated with small nanoparticle inclusions, using mean field theory and coarse-grained simulations. We show that the morphology of such layers is very sensitive to the interaction between the polymers and the nanoparticles and to the nanoparticle density. In particular, the mean field model shows that for a certain range of parameters, the nanoparticles induce a sharp transition in the layer height, accompanied by a sharp increase in the number of adsorbed nanoparticles. At other parameter values, the layer height depends smoothly on the nanoparticle concentration. Predictions of the theoretical model are verified by Langevin dynamics simulations. The results of the paper are in qualitative agreement with experiments on in vitro models of biological transport and suggest strategies for morphological control of nanocomposite materials.

Influence of C doping on the fracture mode and abrasive wear of Al2O3

Abstract Previous studies have shown that the addition of SiC nanoparticles to Al 2 O 3 changes the fracture mode from intergranular to transgranular and in doing so improves the wear resistance. The reason for this is not clear but a change to the grain boundary chemistry caused by impurities such as C added with the SiC may be involved. The aim of the current study was to investigate the influence of small amounts of C doping on the fracture mode and wear properties of Al 2 O 3 . The microstructure and properties of Al 2 O 3 doped with 0 and 0.012 wt% C were studied. Al 2 O 3 showed mainly intergranular fracture. The addition of 0.012 wt% C to Al 2 O 3 changed the fracture mode to mainly transgranular. The wear resistance improved and the percentage of surface grains pulled out was lower compared to pure Al 2 O 3 .

Friction and wear behaviors of Sialon–Si3N4 graded nano-composite ceramic materials in sliding wear tests and in cutting processes

Sialon–Si3N4 graded nano-composite ceramic materials were fabricated by hot-pressing. Sliding wear tests against Inconel 718 were conducted on these graded ceramic composites using the pin-on-disk method. The friction coefficient and the wear rate were measured. The tribological and wear behaviors were discussed in relation to its mechanical properties and microstructure. The results showed that the graded material exhibits good mechanical properties which were attributed to its synergistic strengthening and toughening mechanisms induced by the graded compositional structure and the addition of nano-sized particles. The friction coefficient and the wear rate of the reference material were higher than those of the graded material. Both the friction coefficient and the wear rate of the composites decreased with the increase of the sliding speed. The wear mechanisms of the composites were adhesion, chipping and abrasion in sliding wear tests. The cutting performance and wear mechanisms of the graded tools were also investigated via turning of Inconel 718. The graded tools showed better cutting performance compared to the homogeneous ones, as a result of their enhanced mechanical properties, higher abrasion and fracture resistance. The main wear mechanisms in the machining tests were adhesion, abrasion and flaking.

Mechanical Spectroscopy of Nanostructured Composite Materials

The thermo-mechanical behavior of different nano-structured composite materials, which were processed within the SAPHIR European Integrated Project, has been characterized by mechanical spectroscopy. The obtained results show clearly that creep resistance of fine grain ceramics such as zirconia can be improved by carbon nano-tube (CNT) reinforcements. On the other hand the elastic modulus and the damping capacity of aluminum matrix composites were increased by SiC nano-particle additions. It has also been observed that CNT additions are responsible for a better thermal stability of polymer such as ABS (Acrylonitrile-Butadiene-Styrene) used in automotive industry.

Processing, microstructure and mechanical properties of magnesium matrix nanocomposites fabricated by semisolid stirring assisted ultrasonic vibration

Particulate reinforced magnesium matrix nanocomposites were fabricated by semisolid stirring assisted ultrasonic vibration. Compared with the as-cast AZ91 alloy, the grain size of matrix alloy in the SiCp/AZ91 nanocomposite stirring for 5 min was significantly decreased due to the addition of SiC nanoparticles. SiC nanoparticles within the grains exhibited homogeneous distribution although some SiC clusters still existed along the grain boundaries in the SiCp/AZ91 nanocomposite stirring for 5 min. With increasing the stirring time, agglomerates of SiC nanoparticles located along the grain boundaries increased. The ultimate tensile strength, yield strength and elongation to fracture of the SiCp/AZ91 nanocomposite stirring for 5 min were simultaneously improved compared with the as-cast AZ91 alloy. However, the ultimate tensile strength and elongation to fracture of the SiCp/AZ91 nanocomposite decreased with increasing the stirring time.

Cutting performance and wear mechanisms of Sialon–Si3N4 graded nano-composite ceramic cutting tools

Sialon–Si3N4 graded nano-composite ceramic tool materials were fabricated by using hot-pressing technique. The residual stresses in the surface layer of the graded ceramic tool materials were calculated by the indentation method. The cutting performance and wear mechanisms of the graded tools were investigated via turning of Inconel 718 alloy in comparison with common reference tools. The surface roughness of the finish hard turning of Inconel 718 and the microstructures of the chips were also examined. Worn and fractured surfaces of the cutting tools were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that graded structure in Sialon–Si3N4 graded ceramic tool materials can induce residual compressive stresses in the surface layer during fabrication process. Tool lifetime of graded ceramic tool was higher than that of the common reference tool. The longer tool life of the graded nano-composite ceramic tool was attributed to its synergistic strengthening and toughening mechanisms induced by the optimum graded compositional structure of the tool and the addition of nano-sized particles. Wear mechanisms identified in the machining tests involved adhesive wear and abrasive wear. The mechanisms responsible for the higher tool life were determined to be the formation of compressive residual stress in the surface layer of the graded tools, which led to an increase in the resistance to fracture.

Effect of Nano Size TiO<sub>2</sub> Particles on Mechanical Properties of AWS E 11018M Type Electrode

Addition of nano size particles of TiO2 in the coating of shielded metal arc welding electrode (E 11018M) partially substituting the conventional micro size TiO2 was studied for possible enhanced electrode characteristics. The results show that the nano size particle of TiO2 improved recovery of elements such as Mn, Ni, Mo, Ti etc. as well as increased all-weld-metal tensile and charpy impact properties at –51℃. Furthermore, the charpy impact properties were found to be very sensitive to variations in Ti content of the weld deposit.

Investigation of a strategy for well controlled inducement of microcellular and nanocellular morphologies in polymers

AbstractThis study is an effort to modify conventional batch processes to be able to produce polymeric foams with high cell density and small cell size, which cannot be reached by conventional batch foaming processes. This has been attained by controlling the foaming temperature and controlled stabilization of the cellular structure. The method was tested for both with and without addition of nanosized particles in polymeric matrix. The desired morphologies were obtained using a novel apparatus with the capability of instantaneous pressure drop and controlling stabilization of the foam structure. The design of the said apparatus was based on the idea that in a foaming process, nucleation is the predominant mechanism that determines the final foam structure. The produced foam products have uniform structures without any unfoamed skin. Results show that the control of the foaming temperature and the cell stabilization are the predominant factors in adjustment of the final foam morphology. A wide range of microcellular structures with cell densities between 107 and 1012 bubbles/cm3 and average cell sizes of 500 nm–20 μm were produced. Foaming of polystyrene‐nano‐silica nano‐composites with the same method showed that nanoparticles act as nucleating agent and increase the cell density in the final foam products compared with that of neat polystyrene. POLYM. ENG. SCI., 50:1558–1570, 2010. © 2010 Society of Plastics Engineers

The effect of SiC nanoparticle addition on the flux pinning properties of MgB 2

The nanoparticle–MgB 2 composite superconducting sample, (SiC) 4wt.%(MgB 2) 96wt.% ((SiC) 4–MgB 2), was prepared, and the effect of nanoparticle additions on the magnetic flux pinning was investigated. The measurement and comparison of isothermal magnetization M( H), for pure-MgB 2 powder and sintered pellets of (SiC) 4–MgB 2 and pure-MgB 2 were carried out at temperatures between 5 and 50 K in fields up to 8.5 T. The magnetic irreversibility Δ M( H) curves of the (SiC) 4–MgB 2 follow almost identical lines of both pure-MgB 2 powder and sintered bulk MgB 2 in the region above a specific magnetic field (called a merged field), which gradually decreases as the temperature increases. The (SiC) 4–MgB 2 composite superconductor has exhibited the flux pinning effect which comes from both the grain boundaries and the point defect weak pinning centers in the region below the merged field line. This is different from the case of pure-MgB 2 powder and sintered bulk MgB 2 which showed mostly the grain boundaries pinning.

Reasearch on Heat-Shocking Resistance of SiC<sub>(w)</sub>/ZrO<sub>2</sub>-MoSi<sub>2</sub> Ceramic Composites

The heat-shocking resistance of SiC(w)/ZrO2-MoSi2 ceramic composites prepared by hot-pressing sintering was studied by indentation-quench method together with the calculation of the crack propagation rate of ceramic nanocomposites. The results showed that the crack propagation rate of MoSi2 matrix ceramics samples decreased remarkably with the addition of ZrO2 and SiC nanoparticles. The crack propagation rate of SiC(w)/ZrO2-MoSi2 ceramic composites was obviously lower than that of ZrO2-MoSi2 ceramic composites, which revealed that the synergism between SiC(w) and ZrO2 was more advantageous to enhance the heat-shocking resistance of MoSi2 ceramic. Moreover, the ability of ZrO2 particles to hinder the heat-shocking crack propagation was better than that of SiC whiskers. The synergism between SiC(w) and ZrO2 changed the crack propagation path and shape in MoSi2 ceramics. The mechanisms of ZrO2 to improve the heat-shocking resistance of the MoSi2 ceramic were mainly phase transfer toughening, while that of SiC whiskers to improve the heat-shocking resistance of the MoSi2 ceramic were mainly crack deflection and bridge union.

Influence of SiC nanoparticles and saccharin on the structure and properties of electrodeposited Ni–Fe/SiC nanocomposite coatings

In this study, Ni–Fe/SiC nanocomposite coatings with smooth and crack-free surface were successfully prepared by means of the conventional electrodeposition in the presence of saccharin in electrolyte. The goal of this work was to investigate the effect of SiC nanoparticles and saccharin on the structure and properties of permalloy nanocomposite coatings. The nanocomposite coatings were characterized using optical and scanning electron microscopy, energy dispersive X-ray (EDX) analysis and X-ray diffraction (XRD) technique. The significant variation in the crystallographic texture of the coatings was observed due to the addition of SiC nanoparticles and saccharin in the electrodeposition bath. Increasing the amount of saccharin in the electrolyte led to a change in the texture from a (2 0 0) fiber texture to mixed (3 1 1) and (2 0 0) textures. Our results indicated that inclusion of SiC nanoparticles suppressed the preferred growth direction of the Ni–Fe matrix, resulting in a decrease in the sharpness of the (2 0 0) fiber texture and formation of a more random texture. The presence of SiC nanoparticles in the metallic matrix also led to the production of composite films with better corrosion resistance and higher microhardness than the Ni–Fe coating.

Study on Mechanical, Thermal and Electrical Characterizations of Nano-SiC/Epoxy Composites

This report covers the results of a study on evaluating the effect of nano-SiC particles on mechanical, thermal and electrical properties of epoxy by lap shear, TGA, DSC and electrical tests. Epoxy composites filled with micro-SiC particles were also studied for comparison. The mechanisms of performance improvement were discussed in detail. The results showed that with identical loading, silane treated nano-SiC filled nanocomposites have the best properties. The volume resistivity decrease, dielectric constant e increase and loss tangent tan(δ) increase by addition of silane treated nano-SiC particles are smaller than those by the other fillers. Silane treatment of nanoparticles improves each performance, including increases shear strength, thermal stability, volume resistivity and decreases e and (δ). The addition of nano-SiC particles remarkably improves shear strength, e and tan(δ), while slightly enhances thermal stability of epoxy. 8 vol. % silane treated nano-SiC/epoxy composite has the highest shear strength 10.6 MPa with the maximum enhancement, 80%, over the neat resin. It also has good temperature independence of dielectric properties and enough volume resistivity, which meet the demand of some microelectronics materials.

Alumina Nanoparticles Enhance the Flow Boiling Critical Heat Flux of Water at Low Pressure

Many studies have shown that addition of nanosized particles to water enhances the critical heat flux (CHF) in pool boiling. The resulting colloidal dispersions are known in the literature as nanofluids. However, for most potential applications of nanofluids the situation of interest is flow boiling. This technical note presents first-of-a-kind data for flow boiling CHF in nanofluids. It is shown that a significant CHF enhancement (up to ∼30%) can be achieved with as little as 0.01% by volume concentration of alumina nanoparticles in flow experiments at atmospheric pressure, low subcooling (<20°C), and relatively high mass flux (⩾1000kg∕m2s).

Effect of SiC Nanoparticle Additions on Microstructure and Microhardness of Sn-Ag-Cu Solder Alloy

In this work, lead-free composite solders were produced by mechanically mixing nominal 20 nm moissanite SiC particles with Sn-3.8Ag-0.7Cu solder paste. The effects of the amount of SiC addition on the melting behavior, microstructure, and microhardness of as-solidified composite solders were systematically investigated. In comparison with solder without the addition of SiC nanoparticles, the subgrain of β-Sn, the intermetallic compounds (IMCs) average grain size and distance decreased significantly in the composite solder matrix. This was possibly ascribed to the strong adsorption effect and high surface free energy of the SiC nanoparticles. Our results showed that 0.05 wt.% addition of SiC nanoparticles could improve the microhardness by 44% compared with the noncomposite and that the average grain size and distance changed from 0.5 μm to 0.2 μm and from 0.6 μm to 0.32 μm, respectively. The refined IMCs, acting as a strengthening phase in the solder matrix, enhanced the microhardness of the composite solders, in good agreement with the prediction of the classic theory of dispersion strengthening.

Silicon carbide foams produced by siliciding carbon foams derived from mixtures of mesophase pitch and nano-SiC particles

Silicon carbide foam with high bending strength and well oxidation resistance was prepared by infiltrating liquid silicon into carbon foam derived from mesophase pitch added with nano-SiC particles. Microstructure observation and phase identification of resultant foams were performed by scanning electron microscope and X-ray diffraction, respectively. Bending strength and bulk density of final SiC foams were also measured and calculated. Oxidation resistance of foams was appraised by the analysis of thermogravimetric curves of specimen in flowing air from room temperature to 1473 K. Results showed that addition of nano-SiC particles could significantly reduce the crystal size and compact struts during the infiltration of liquid silicon into carbon foams, which results in the increase of bending strength of silicon carbide foams. As the addition amount of nano-SiC was 15 wt%, silicon carbide foams with low bulk density of 0.54 g/cm 3 were obtained, which possessed high bending strength of 11.96 MPa and excellent oxidation resistance.

Effects of Nanoparticle Doping on Electrical Properties of ${\rm MgB}_{2}$ Bulks and Wires Obtained by Reactive Mg Liquid Infiltration Technique

The effect of SiC nanoparticle and colloidal C additions on the electric transport properties of MgB2 samples, bulks and wires, was investigated at different applied magnetic fields. The samples were obtained by the Reactive Mg Liquid Infiltration (RLI) in boron powder preforms, technique with the advantages of good mechanical characteristics of the products with an easy manufacturing. It was found that SiC nanoparticle additions produce an improvement of both the irreversibility field and the upper critical field as well as the enhancement of the n-exponent in the power law voltage-current curves and of the pinning energy. In particular the analysis of the pinning energy dependence on the current density turned out that the SiC doping-induced pinning centers are of similar nature than the pristine ones. Moreover only a slight decrease of the critical temperature was measured as a consequence of the SiC doping. Higher pinning-capability enhancement was found for the C doped wires which exhibit a sharper irreversibility field enhancement at the external field increase. This issue together with a stronger critical temperature decrease (0.7 K) points towards a higher amount of C substitution for B in the MgB2 lattice than in the SiC-doped bulk samples.

Tribological Behaviours of Epoxy Composites Filled with Silicon Carbide Nanoparticles

Epoxy composites filled with silicon carbide nanoparticles were fabricated in this work. Sliding wear tests in association with morphological observation indicated that the wear mode of the nanocomposites was rather mild, forming a striking contrast to the severe wear of unfilled epoxy characterized by substantial material loss under the same measurement conditions. Both specific wear rate and friction coefficient of the nanocomposites were significantly lower than those of the unfilled epoxy. On the basis of mechanical testing and tribochemical analysis, it was found that the addition of nano-SiC particles into epoxy increased the mechanical properties of the matrix and facilitated some favourable tribochemical reactions during rubbing, which accounted for the great improvement in the tribological performance.

SiC Nanoparticles Reinforced Magnesium Alloys by Semisolid Process

In this paper, SiC nanoparticles reinforced AM60 alloys were fabricated by semisolid process with pretreatment of SiC nanoparticles. The microstructure, hardness and mechanical properties of the alloys have been investigated. The X-ray photoelectron spectroscopy (XPS) was also used for analyzing elements chemical status of the nanoparticles and the alloys. The microstructure, hardness and mechanical properties of SiC nanoparticles reinforced magnesium alloys are better than those of AM60 alloys without SiC nanoparticles addition. The results show that semisolid process was suitable for fabricating SiC nanoparticles reinforced magnesium alloys.

Microstructure and room-temperature mechanical properties of β sialon/SiC nanocomposites

Microstructure and room-temperature mechanical properties of two β sialon/SiC nanocomposites, one comprised 20 wt.% β SiC nanoparticle and the other comprised 40 wt.% β SiC nanoparticle (denoted as Sm20 and Sm40, respectively), were studied and compared with those of the monolithic (denoted as Sm0) in this article. The three-point flexural strength values were measured to be 747, 712 and 755 MPa for Sm0, Sm20 and Sm40, respectively, while the Vickers hardness values were 18.4, 16.3 and 17.1 GPa and the indentation fracture toughness values were 8.70, 6.83 and 8.71 MPa m 1/2 for Sm0, Sm20 and Sm40, respectively. Weibull modulus values on Vickers hardness were determined to be 39, 33 and 43, while those on fracture toughness were 19, 22 and 19 for Sm0, Sm20 and Sm40, respectively. The addition of SiC nanoparticles to the matrix Sm0 has little positive effect on RT mechanical properties. This scenario is ascribed to the impurity SiO 2 on the surface of SiC nanoparticles, which accelerates the α → β transformation and results in the weak bond between sialon grains and the increase of uncertainty of mechanical properties.

Effect of SiC nanoparticle addition on the critical current density ofMgB2 tapesfabricated from MgH2, B and MgB2 powder mixtures

The effects of the addition of SiC nanoparticles were compared forMgB2 tapesprepared from two different starting powders with respect to the improvement in the critical current, Jc, at 4.2 K and 10 T. The starting powder was prepared by blending premixedMgH2 andB(MgH2+2B) andpremixed (MgH2+2B) and MgB2 (30% MgB2) in a ratio of 7:3. All tapes were fabricated by the in situ powder-in-tube method. The use of30% MgB2 as standard powderyields higher Jc valuesthan MgH2+2B in the caseof the pure MgB2 tape;however, the highest Jc (1.8 × 104 A cm−2) was obtainedfor the tape from MgH2+2B with 10 mol% SiC additive. The tape from30% MgB2 contained regionswith Si-free MgB2 grains, while Si compounds were distributed homogeneously across the tape prepared fromMgH2+2B. Furthermore,the use of 30% MgB2 instead of MgH2+2B was found to reduce the effect of carbon substitution of the SiCadditive. These data indicate that the technique, which enhancesJc–B characteristicsof the pure MgB2 tape, does not promise further improvement through the addition of nanosized impurityparticles. It is concluded that we should improve the fabrication technique of theMgB2 tape by keeping (or improving) the overall reactivity between the standard powder andnanosized impurity particles.