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.     

Evaluating the effect of feed particles size and their hardness on the particle size distribution of semi-autogenous (SAG) mill’s product

The main target of this research was to provide the optimal size of mills’ feed with acceptable accuracy, in order to find the size range of particles to achieve the maximum grinding product. Nowadays, experimental semi-autogenous (SAG) mill and drop-weight test are used for evaluation of grinding circuit regarding changes in feed particle size distribution, size of the ball, speed of mill, prediction of energy required, and product size distribution for complete grinding in AG and SAG mills. In this study, the effect of initial size ranges of feed (+13.2–315?mm) on the amount of grinding product and its size distribution has been evaluated, in order to find the size range of particles to achieve the maximum grinding product. The results showed that the feed size range of 19–22.4?mm had the highest amount of grinding product and breakage index number in different energy levels and the validity of results was evaluated with ball drop-weight test, as well.     

Effect of grain size and indium addition on tensile characteristics of Al–1Si alloy

Abstract

The effect of grain size and indium addition on the workhardening characteristics of Al–1Si (wt-%) alloy has been investigated at room temperature (RT). The samples were preaged at different temperatures in the range 523–623 K. The yield stress, the fracture stress, the fracture time and the linear workhardening coefficient generally decreased with increasing temperature and/or grain size, while the fracture strain and dislocation slip distance increased. The yield and fracture stresses for different grain sizes at different temperatures were found to be linearly related to grain diameters. Indium addition caused general increase for all the measured strength parameters. As concluded from transmission electron microscope (TEM) investigations, In addition to Al–Si alloy may retard the coarsening of Si particles. The energies activating the operating fracture mechanisms were found to be 79·6±0·4 and 32·4±0·4 kJ mol^?1 for alloys Al–1Si and Al–1Si–0·2In respectively. This suggests a value of 47·2 kJ mol^?1 as a binding energy between Si and In atoms in Al matrix.     

Effects of environment and temperature on ceramic tensile strength–grain size relations

Overall strength ()–grain size (G), i.e. –G-1/2, relations retain the same basic two-branched character to at least 1200–1300°C. However, some polycrystalline as well as single crystal strength shifts or deviations are seen relative to each other, and especially relative to Young's moduli versus temperature for poly- and single crystals. The variety and complexity of these deviations are illustrated mainly by Al2O3, BeO, MgO and ZrO2 for which there is considerable data. At 22°C, Al2O3 polycrystals show substantial strength decrease due to H2O while MgO, ZrO2 and BeO polycrystals have limited, variable decreases. Al2O3 single crystals (sapphire) also show substantial strength decreases, but ZrO2 and MgO single crystals show little or none. Sapphire's strength markedly decreases from at least –196°C to a minimum in the 400–600°C range, then rises to a maximum at1000°C, followed by an accelerating decrease with further temperature increase. Polycrystalline Al2O3 shows similar (but less pronounced) strength minima and maxima, or alternatively an approximate strength plateau from 22 to 1000°C interrupting the normally expected strength decreases with increasing temperature at suitably large grain size and absence of defects (e.g. pores) dominating failure. BeO crystals show a linear strength decrease with increasing temperature (T) similar to that of Young's modulus. BeO polycrystals often show a significant strength (apparently grain size and impurity dependent) maximum (at 500–800°C) or plateau (from 22 to 1000°C) interrupting an otherwise continuous decrease. MgO shows similar temperature behaviour to BeO, but more pronounced crystal strength decrease and less pronounced polycrystalline strength maxima. Polycrystalline ZrO2 shows more rapid Young's modulus (E), and especially strength, decreases at 200–500°C than single crystals. More limited data for other materials also shows greater, variable –T versus E–T trends, e.g. MgAl2O4 has a similar, but less pronounced decrease than ZrO2. Collectively these deviations suggest variable impacts on primarily flaw controlled –G-1/2 behaviour due to factors such as microplasticity, machining stresses, and thermal expansion and elastic anisotropies requiring more comprehensive testing and evaluation to better sort out these effects.     

Effects of Si and Cu contents on grain size of Al–Si–Cu alloys

The influence of the silicon and copper contents on the grain size of high-purity Al–Si, Al–Cu, and Al–Si–Cu alloys was investigated. In the Al–Si alloys, a poisoning effect was observed and a poor correlation between the grain size and growth restriction factor was obtained. A possible cause of the poisoning effect in these alloys is the formation of a TiSi₂ monolayer on the particles acting as nucleation sites or another poisoning mechanism not associated with TiSi₂ phase formation. In the Al–Cu alloys, a good correlation between the grain size and growth restriction factor was found, whereas in the Al–Si–Cu alloys, the correlation between these two parameters was inferior.     

Effect of the length and the aggregate size of MWNTs on the improvement efficiency of the mechanical and electrical properties of nanocomposites—experimental investigation

An experimental investigation of the effect of nanotube length and aggregate size on the mechanical and electrical properties of the composites was reported. Three treatments, that affect mainly the length and aggregate size, were applied on the CVD MWNTs before they were added into a resin matrix. They had a very clear impact on the dielectric properties of the composites and on the improvement efficiency. There was an insulator-to-conductor transition with the as-prepared MWNTs at 0.5 wt%. Regarding the mechanical properties, the addition of MWNTs increased the Young's modulus and reduced the fracture strain. In that case, the pre-treatment on MWNTs, however, had a much more moderate effect on the improvement efficiency.     

X-ray determination of crystallite size and effect of lattice strain on Debye–Waller factors of platinum nano powders

In the present study, nano platinum particles were produced by ball milling process. The lattice strains in platinum (Pt) powders produced by milling have been analysed by X-ray powder diffraction. The lattice strain ( ${\varepsilon}$ ) and Debye-Waller factor (B) are determined from the half-widths and integrated intensities of the Bragg reflections. In Pt, the Debye–Waller factor is found to increase with lattice strain. From the correlation between the strain and effective Debye–Waller factor, the Debye–Waller factors for zero strain have been estimated for Pt. The variation of energy of vacancy formation as a function of lattice strain has been studied.     

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.     

Application of a max–min ant system to joint layout and size optimization of pipe networks

The application of a max–min ant algorithm to the layout and size optimization of pipe networks is described in this paper. The formulation conventionally used for the pipe size optimization of networks with fixed layout is extended to account for the layout determination of the networks. This is achieved by including new constraints regarding the reliability of the network and modifying some of the constraints of the optimization problem. A deterministic concept of reliability is used in which the number of independent paths from source nodes to each of the demand nodes is considered as a measure of reliability. The method starts with a predefined layout which includes all possible links. The method is capable of designing the layout and pipe sizes of water distribution networks of predefined reliability including tree-like and looped networks. It is also shown that a layout optimization of a network followed by size optimization does not lead to an optimal or a near-optimal solution. This emphasizes the need for simultaneous layout and size optimization of networks if an optimal or near-optimal solution is desired. The performance of the method for layout and pipe size optimization of pipe networks is tested against two benchmark examples in the literature and the results are presented. The first example is considered to show the necessity of joint layout and size optimization even for the simple tree networks while the second example is considered to illustrate the efficiency of the proposed method for layout and size optimization of real-world networks with different levels of reliability.     

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.     

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.     

Wet centrifugal classification of calcite fines — effect of feed size

The wet classification of various fine calcite materials (<8, <12 and <45 μm) by a diskstack nozzle centrifuge is presented and the results are discussed with respect to feed size. It has been found that the influences of disk-geometry, G-force and feed rate on the classification performance are not related to feed size. However, the selection of a split suitable for an efficient separation depends on the particle size distribution of the feed material. Feed size has an impact on the residence time of particle separation. The results showed that an optimum efficiency can be achieved when a calcite material with a particle size below 12 μm is treated. An excessive amount of fine or coarse calcite particles in the feed affects the efficiency of the classification in the centrifuge. It is also indicated that an effective classification of calcite fines requires a moderate G-force and high flow rates through a disk section bound by stud spacers in the centrifuge.     

Effect of temper embrittlement and specimen size on Charpy impact testing of a Cr–Mo–V rotor steel

Abstract

Full and sub­size Charpy V notch specimens from several locations of a high pressure–intermediate pressure Cr–Mo–V turbine rotor were tested. A comparison between full and sub­size impact energy data showed that the smaller specimens exhibited qualitatively similar behaviour, with a systematic reduction in fracture appearance transition temperatures (FATTs). The full and sub­size impact energy data were normalised against the specimen area and volume. The latter normalisation produced the closest match and the offset between the two data sets was described by a simple linear equation. The sensitivity of impact energy and FATT to specimen size was examined in samples possessing different degrees of temper embrittlement. It was found that the difference in FATT between full and sub­size specimens for embrittled samples was at least double that of de­embrittled samples. It is proposed that the observed specimen size/impact energy/FATT variations with degree of embrittlement arise from sensitivity of intergranular fracture to lineal specimen thickness, since fracture occurs predominantly through a two­dimensional network of grain boundaries.     

A new route to size and population control of silver clusters on colloidal TiO₂ nanocrystals

Formation of hybrid Ag-TiO(2) nanocrystals (NCs) in which Ag clusters are uniformly deposited on individual TiO(2) NC surface has been achieved by using hydrophobic surfactant-capped TiO(2) NCs in combination with a photodeposition technique. The population of Ag clusters on the individual TiO(2) NC surface can be controlled by the degree of hydrophobicity (e.g., the number of vacant sites) on the TiO(2) NC surface while their size may be altered simply by varying irradiation time. A reversible change in color of the resulting hybrid Ag-TiO(2) NCs is induced by alternating UV light and visible-light illumination; however, the size and population of Ag clusters on TiO(2) NCs are almost unchanged. Furthermore, these materials also exhibit much higher photocatalytic performance as compared to that of Ag supported on commercial TiO(2)-P25.     

An analysis of the role of grain size on superplasticity of γ titanium aluminides

The superplastic data for several microcrystalline and submicrocrystalline TiAl alloys has been analyzed to establish the rate controlling mechanism. The results show that the lattice diffusion controlled slip-accommodated grain boundary sliding mechanism is operative for the entire grain size range, 150 nm–20 m. The detail of the nature of ₂ phase, i.e. ordered or disordered, does not influence the kinetics of superplastic flow. The optimum superplastic temperature decreases with the decrease in grain size. The optimum superplastic flow stress shows an intrinsic inverse dependence on the grain size. This grain size dependence of the optimum superplastic flow stress can be explained as the stress required to nucleate dislocations from grain boundary edge during slip accommodation of grain boundary sliding. Superplasticity in nanocrystalline TiAl remains an intriguing possibility because it has the potential for increasing the optimal superplastic strain rate or alternatively, decreasing the superplastic forming temperatures.     

Architecturally modified Al–DRA composites: the effect of size and shape of the DRA rods on fracture behavior

Architectural modification of aluminum matrix composites is considered as an efficient method to improve fracture toughness. Al–DRA (Al–Al/SiC/20_p) composites were fabricated via “powder extrusion–casting–ingot extrusion” route with structures similar to that of reinforced concrete, so that DRA rods were surrounded by unreinforced aluminum. The effects of variation in shape, size, and number of DRA rods on fracture behavior of Al–DRA composites were investigated. Composites containing DRA rods with hexagonal cross-section exhibited higher resistance to crack initiation and growth, in comparison to those containing circular rods. In the case of hexagonal rods, increasing the number of rods (reducing the rods’ cross-section surface) led to further enhancement of fracture toughness. Fracture surface observations of all samples revealed the existence of desirable cohesion between rods and the surrounding matrix. The remained sharp and unblunted corners of hexagonal DRA rods caused stress concentration and microcrack formation upon loading. Hence, plastic deformation constraint of aluminum ligament between rods was alleviated, which, in turn, led to further energy consumption during the fracture process.     

Biodegradation mechanisms of selective laser-melted Mg–xAl–Zn alloy: grain size and intermetallic phase

Grain size and intermetallic phase were two key factors affecting the biodegradation behaviour of Mg alloys. In the paper, different grain size and intermetallic phase volume fraction were obtained by introducing Al into Mg–Zn alloy via selective laser melting. Results showed that the grain size refined while the intermetallic phase volume fraction increased with Al increasing. As Al was less than 3?wt.%, the grain refinement was the major factor affecting the degradation behaviour. The finer grain would create many grain boundaries, making the alloy passivate readily and resulted in a reduced degradation rate. However, with Al further increasing, the intermetallic phase became the main factor influencing the degradation behaviour though grain size was further refined. The large intermetallic phase volume fraction caused severe galvanic corrosion, accelerating the degradation. This work may provide guidance for balancing grain size and intermetallic phase on degradation behaviour of Mg alloys.     

Influence of grain size on the small fatigue crack initiation and propagation behaviors of a nickel-based superalloy at 650 °C

GH4169 at 650 °C in atmosphere was investigated by using single edge notch tensile specimens. The number of main cracks and crack initiation mechanisms at the notch surface strongly depended on the grain size. The crack initiation life accounted for more percentages of the total fatigue life for the alloy with smaller grain size. The fatigue life generally increased with increasing crack initiation life. The small crack transited to long crack when its length reached ˜10 times the grain size.