Preparation and properties of cast aluminium alloy–sillimanite particle composite

An attempt has been made to explore the possibility of using natural mineral namely sillimanite for synthesizing aluminium alloy composite through a solidification technique. The sillimanite particles were characterized in terms of X-ray, differential thermal analysis in order to examine their suitability for preparing the composite. An aluminium alloy (BS:LM6) was used as the matrix alloy. The sillimanite particles of mean size 140 μm (major axis) were used as reinforcement. The sillimanite particles were added into the matrix melt by creating a vortex with the help of a mechanical stirrer and the melt temperature was maintained between 750 and 800°C. The cast composite was characterized in terms of microstructural, mechanical and abrasive wear properties. It was noted that the sillimanite particles were reasonably uniformly distributed within the matrix and exhibited good mechanical bonding with the matrix. The strength of the composite was noted to be marginally lower than that of the base alloy but the hardness and the wear resistance of the composite were found to be significantly higher than those of the base alloy.     

Effect of particle size on in vitro cytotoxicity of titania and alumina nanoparticles

Aluminium oxide (Al₂O₃) and titanium dioxide (TiO₂) nanoparticles (NPs) have been widely used in nanotechnology-based products. Recently, researchers and the public have raised concerns about the adverse effects of these NPs in biological systems, particularly in humans. The aim of this study was to investigate the possible adverse effects of these two common metal oxide NPs on human lung epithelium cells (A549) and to investigate NP size-dependent effects on these cells, considering both the primary and hydrodynamic particle size. NPs were found to inhibit cell viability and proliferation at the highest concentration level (10?mg/mL) included in this study, as measured by a clonogenic assay. Moreover, cell viability, proliferation and metabolism were impaired to a greater extent by the smaller NPs (5?nm TiO₂ and 10?nm Al₂O₃) relative to the larger particles (200?nm TiO₂ and 50?nm Al₂O₃) included in this study, as measured by cell proliferation and metabolism. Notably, the observed cytotoxic effects correlated to the primary size, rather than the hydrodynamic size. Similarly, NP cytotoxicity was found to be correlated with the NP surface area. These findings highlight the importance of including primary size and surface area information in NP characterisation in cytotoxicity studies.     

Main and interaction effects of matrix particle size,reinforcement particle size and volume fraction on wear characteristics of Al–SiCp composites using central composite design

The aim of this study was to investigate the effects of matrix particle size, reinforcement particle size, volume fraction, and their interactions on the wear characteristics of Al–SiC_p composites. Central composite design method was used to perform a series of experiments. The statistical analysis of experimental results showed that both main effect and interaction effect of factors investigated were effective on the wear behavior of Al–SiC_p composites. Wear loss decreased as volume fraction increased; however, beyond volume fraction of 17.5%, it increased due to reinforcement particle clustering depending on volume fraction and matrix particle size to reinforcement particle size ratio. With decreasing of matrix particle size and increasing of reinforcement particle size, wear loss also decreased. However, after a certain volume fraction, large sized reinforcement particles had a negative effect on the wear resistance.     

Influence of heat treatment and particle shape on mechanical properties of infiltrated Al2O3 particle reinforced Al–2 wt-% Cu

Abstract

Carbon dioxide (CO₂) generation by ultraviolet irradiation of poly(ethyleneterephthalate) (PET) films in oxygen was monitored by in situ Fourier transform infrared spectroscopy. Typically, the CO₂ absorbance increased by ～100 × 10^?4 in 180 min, with no evidence of hindrance by restricted diffusion of O₂ into, or CO₂ out of, the films. It was concluded that Fourier transform infrared spectrometry monitoring of CO₂ conveniently, reliably and rapidly measures PET films photostability.

Quantitative analysis of the CO₂ evolved from progressively thinner films from successive stages of the biaxial film drawing process indicated that CO₂ was generated within a few microns of the film surface and that the same amounts were generated from the irradiated surface of 540 μm cast, 150 μm uniaxially drawn and 85 μm biaxially drawn films. Although drawing increased film crystallinity, photoreactivity appeared to be unchanged. However, total CO₂ formation followed the pattern PET cast相似文献   

Reactive sintering and particle morphology control of β″-alumina-based water purification filters

This paper reports on the preparation of porous membranes consisting of plate-like β″-alumina grains and the evaluation for microfiltration properties. Porous β″-alumina-based ceramics were prepared by the solid-state reactive sintering of Na₂CO₃ and α-Al₂O₃ at 1100–1300 °C. To study the effect of impurities in the starting powder mixtures, LiF-doped membranes were also prepared. As for the water filtration test, the turbidity before and after the vacuum filtration was measured using sintered porous membranes. To simulate bacteria-contaminated water, a suspension of a commercial boehmite powder (D ₅₀ = 0.7 μm) in distilled water was used. The non-doped samples sintered at 1200 °C were composed of β″-alumina (84 wt%) and β-alumina (16 wt%) grains and showed a good microfiltration performance; the turbidities before and after filtration were 894.4 NTU and 1.46 NTU, respectively.     

Microstructure and mechanical behavior of Mg-5Zn matrix influenced by particle deformation zone

The effect of particle deformation zone(PDZ) on the microstructure and mechanical properties of SiC_p/Mg-5Zn composites was studied.Meanwhile,the work hardening and so ftening behavior of SiC_p/Mg-5Zn composites influenced by PDZ size were analyzed and discussed using neutron diffraction under in-situ tensile deformation.The evolution of FWHM(full width at half maximum) extracted from the diffraction pattern of SiC_p/Mg-5Zn composites was used to interpret the modification of dislocation density during in-situ tension,which discovered the effect of dislocation on the work hardening behavior of SiC_p/Mg-5Zn composites.In addition,the tensile stress reduction(△P_i) values during in-situ tension test were calculated to analyze the effect of PDZ size on the softening behavior of SiC_p/Mg-5Zn composites.The results show that the work hardening rate of SiC_p/Mg-5Zn composites increased with the enlargement of PDZ size,which was attributed to the grain size of SiC_p/Mg-5Zn composites increased with the enlargement of PDZ size.Moreover,the stress reduction(△P_i) values increased continuously during in-situ tensile for SiC_p/Mg-5Zn composites due to the increased stored energy produced during plastic deformation,which provided a driving force for the softening effect.However,the effect of grain size on the softening behavior is greater than that of the stored energy,which led to the tensile stress reduction(△P_i) values of P30(d_PDZ=30 μm)-SiC_p/Mg-5Zn composite were higher than that of P60(d_PDZ=60 μm)-SiC_p/Mg-5Zn composite when the ε_ri were 0.25,0.5,0.75 and 1,respectively.     

Experimental and numerical investigation of effects of particle shape and size distribution on particles’ dispersion in a coaxial jet flow

In this study, an experimental and a numerical investigations are performed to investigate the effect of particle’s shape and size distribution on its dispersion behavior. Firstly, particle dispersion of pulverized coal and spherical polymer particles is observed by Particle Image Velocimetry (PIV) technique in the experiment. Secondly, a simulation is performed to analyze the particle dispersion in detail. Spherical and spheroidal motion models are applied to particle’s movement to investigate the shape effect. Furthermore, monodisperse and polydisperse for particles are applied to investigate the size distribution effect on the dispersion. Experimental results show that in the jet turbulence flow, pulverized coal particles, which have complex shapes and various sizes, have quite different dispersion behavior compared to spherical particles. In terms of the results of the simulation, this difference is mainly caused by the size distribution effect. Although particle’s shape affects the dispersity, it is weakened by the size distribution effect.     

Effect of WC particle size and Ag volume fraction on electrical contact resistance and thermal conductivity of Ag–WC contact materials

In this work, theoretically dense (> 99%) composites of Ag and WC have been prepared by press–sintering–infiltration for making electrical contacts used as an arc-resistant material in a model switching device. Composites with varying silver content and WC particle size were investigated to get an insight on their electrical contact resistance (R_c) and their ability to withstand enormous thermal stresses during switching. A break-only model switching sequence was used, where the evolution of R_c was measured over 50 cycles and the post-switching microstructures were investigated for thermal stress induced crack formation. A well-established 2D computational microstructure based model, object-oriented finite element analysis version 2 (OOF2), was used to determine the composite thermal conductivity (k) for various grades as a function of temperature. R_c was observed to be consistently low for the coarser WC containing composite and higher silver content composites. This response was attributed to the ductility of the surface layers formed during switching. Crack formation after switching was found to be a direct consequence of large thermal gradients during 50 cycles, which was minimal for coarser WC grained and higher silver content composites which have a higher thermal shock resistance.     

Mesoscale analysis of rubber particle effect on young’s modulus and creep behaviour of crumb rubber concrete

International Journal of Mechanics and Materials in Design - This paper presents a mesoscale model to investigate the rubber particle effect on the mechanical properties of crumb rubber concrete...     

Effect of alumina particle size and thermal condition of casting on microstructure and mechanical properties of stir cast Al–Al2O3 composites

Abstract

Metal matrix composites are considered as a distinct category of the advanced materials, which have low weight, high strength, high modulus of elasticity, low thermal expansion coefficient and high wear resistance. Among them, Al–Al₂O₃ composites have achieved significant attention due to their desired properties. In the present research, Al–Al₂O₃ composites with 5 vol.-% alumina were produced by stir casting at a temperature of 800°C. Two different particle sizes of alumina were used as 53–63 and 90–105 μm. The microstructure of the samples was evaluated by SEM. In addition, the mechanical properties of the samples were measured, and hence, the optimum temperature and particle size of alumina to be added to the Al matrix were determined. The results demonstrated the positive effect of alumina on improving the properties of Al–Al₂O₃ composites.     

Effect of filler level and particle size on dental caries-inhibiting Ca–PO4 composite

Secondary caries and restoration fracture are common problems in restorative dentistry. The aim of this study was to develop Ca–PO₄ nanocomposite having improved stress-bearing properties and Ca and PO₄ ion release to inhibit caries, and to determine the effects of filler level. Nanoparticles of dicalcium phosphate anhydrous (DCPA), two larger DCPA powders, and reinforcing whiskers were incorporated into a resin. A 6 × 3 design was tested with six filler mass fractions (0, 30, 50, 65, 70, and 75%) and three DCPA particle sizes (112 nm, 0.88 μm, 12.0 μm). The DCPA nanocomposite at 75% fillers had a flexural strength (mean ± SD; n = 6) of 114 ± 23 MPa, matching the 112 ± 22 MPa of a commercial non-releasing, hybrid composite (P > 0.1). This was 2-fold of the 60 ± 6 MPa of a commercial releasing control. Decreasing the particle size increased the ion release. Increasing the filler level increased the ion release at a rate faster than being linear. The amount of ion release from the nanocomposite matched or exceeded those of previous composites that released supersaturating levels of Ca and PO₄ and remineralized tooth lesions. This suggests that the much stronger nanocomposite may also be effective in remineralizing tooth lesion and inhibiting caries. In summary, combining calcium phosphate nanoparticles with reinforcing co-fillers in the composite provided a way to achieving both caries-inhibiting and stress-bearing capabilities. Filler level and particle size can be tailored to achieve optimal composite properties. Disclaimer: Certain commercial materials and equipment are identified to specify the experimental procedure. This does not imply recommendation or endorsement by NIST or ADAF.     

Surface properties of aged coal and their effects on bubble–particle attachment during flotation

Aged coal after mining often shows poor flotation performance due to the formation of hydrophilic oxygenated functional groups. In this study, different meta-bituminous aged coal was characterized by XPS and SEM analysis, and contact angle, zeta potential and bubble–particle attachment measurements. Following aging process, the changes in flotation behavior of the coal samples were quantified at different diesel dosages. It was found that the percentage of hydrophobic functional groups of the fresh coal was about 1.31 times higher than that in the case of the aged coal. The contact angle of the fresh coal was 78.9° while that for the aged coal was 36.7°. It means that the hydrophilicity of the aged coal samples was significantly higher than that of the fresh coal. The results of zeta potential, FTIR, XPS and SEM measurements agreed well with the contact angle results. The combustible flotation recovery of the fresh coal in the presence of collector was 98% while that of the aged coal was about 20%. Despite the significant differences in the surface properties of the fresh and aged coal, the induction time slightly changed i.e. the induction time for the most hydrophobic coal (i.e the fresh coal in the presence of collector) was 10 ms while that for the least hydrophobic coal (i.e. the aged coal in the absence of collector) was 11.6 ms. The attachment efficiency and flotation rate shows an exponential decay relationship with induction time.     

γ′ particle coarsening and yield in Alloy 800

The age strengthening of Alloy 800 by ordered particles of-Ni₃(Al, Ti) phase has been studied by using both transmission electron microscopy and room-temperature tensile tests on aged specimens. The samples have been aged in the temperature range 525 to 650° C up to a maximum time of 10⁴ h. Two groups of samples with different Ti/Al ratios have been investigated in order to obtain more reliable information on the role played by these alloying elements on the age-hardening behaviour. The linear dimension increases with time,t, ast ^1/3 and an activation energy of 70.0 kcal mol^–1 was derived from the temperature dependence of the coarsening rate. The particle volume-fraction, as measured by electron microscopy, has been found to remain constant on ageing in the temperature range 525 to 600° C. The increase in the critical shear stress due to the particles is found to agree quantitatively with the equations of Brown and Ham which describe hardening by ordered particles. Antiphase boundary energies of 227 and 279 mJ m^–2 have been measured, respectively, for the two groups of samples investigated.     

A note on the application of BaF2 scintillators to γ-ray and charged particle detection

Two practical aspects of the application of BaF₂ crystals as detectors for nuclear radiation are considered: (1) wavelength shifting of the fast UV light component by a thin p-terphenyl layer, and (2) identification of light charged particles by measuring the intensity ratio between the fast and slow light components. Experimental tests have yielded satisfactory results in both directions.     

The effect of internal particle heat conduction on heat transfer analysis of turbulent gas–particle flow in a dilute state

In many cases the conduction mechanism inside a particle can not be ignored (large particles, low thermal conductivity and high porosity) during turbulent gas–particle flows. However, the accurate solution might be difficult to apply. Therefore, we first develop here the ability to conduct accurate solution and then we define the criterion for which the internal conductivity might be ignored. A combination between commercial C.F.D. code and user defined programs was developed to predict numerically the gas–particle velocity and temperature profiles. The selected criterion (defined at the outlet of the pipe’s cross-section), referred to the relation between the computational desirable average temperature difference without ignoring internal heat conductivity and the average particles temperature by ignoring internal heat conductivity, determines whether to consider the heat conduction mechanism in numerical simulations or to ignore it. It was found that the average particles temperature for T _p =  f(r) is lower than the case when T _p =  constant. Also, it was found that the non-dimensional temperature difference criterion is a continuous function of [Bi ×  (d _p/D)] for a specific geometry, various pipe and particle diameters, various particles’ thermal conductivities, constant heat flux and Re number. The numerical code enables to extend the classical criterion for Bi number of solids to various gas–particle systems and different operational conditions.     

Effects of particle–particle collisions on sudden expansion gas-particle flows via a two-phase kinetic energy-particle temperature model

In the framework of the gas–particle two-fluid mode, an improved gas–particle two-phase kinetic energy incorporating into a particles collision model (k–k_p–θ) is proposed to study the sudden expansion gas–particle turbulent flows in a cylindrical pipe section. Anisotropy of gas–solid two-phase stress and the interaction between two-phase stresses are considered by means of a transport equation of two-phase fluctuation velocity correlation. Xu and Zhou [10] experimental data is used to quantitatively validate k–k_p–θ and k–k_p model for analysis the effects of particle–particle collision. Numerical predicted results show that time-averaged velocity, fluctuation velocity of gas and particle and correlation of two-phase fluctuation velocity considering particles collision are better than those of the without particle temperature model and they are in good agreement with experimental data. Larger particle concentration and particle temperature located at shear layer adjacent to wall surface and re-circulation region. Energy dissipation due to smaller scale particles collision contributes to homogeneous distribution of Reynolds stress and affects the particle transportation behavior together with particle inertia.     

Three-dimensional simulation of the particle distribution in a downer using CFD–DEM and comparison with the results of ECT experiments

A three-dimensional numerical model of the down-flow fluidized bed (Downer) with a newly designed distributor was applied to investigate the particle distribution profiles using combined computational fluid dynamics (CFD) and the discrete element method (DEM). A realistic model of DEM, which calculates the contact force acting on the individual particles, is used to monitor the movement of individual particles in the bed. The contact force is calculated using the concepts of the spring, dash-pot, and friction slider. The flow field of gas is predicted by the Navier–Stokes equation. This CFD–DEM model provides information regarding the particle movement and distribution, the particle velocity, and the gas velocity in the bed under different air-particle mixture conditions. The results demonstrate that the air supply conditions directly influence the particle distribution uniformity. Furthermore, the numerical predictions for the axial and radial profiles of the particle distribution were found to agree well with the experimental results obtained by electrical capacitance tomography (ECT).