Effect of particle size on the photocatalytic activity of nanoparticulate zinc oxide

In this study, a three-stage process consisting of mechanical milling, heat treatment, and washing has been used to manufacture nanoparticulate ZnO powders with a controlled particle size and minimal agglomeration. By varying the temperature of the post-milling heat treatment, it was possible to control the average particle size over the range of 28–57 nm. The photocatalytic activity of these powders was characterized by measuring the hydroxyl radical concentration as a function of irradiation time using the spin-trapping technique with electron paramagnetic resonance spectroscopy. It was found that there exists an optimum particle size of approximately 33 nm for which the photocatalytic activity is maximized. The existence of this optimal particle size is attributable to an increase in the charge carrier recombination rate, which counteracts the increased activity arising from the higher specific surface area for a sufficiently small particle size.

The importance of particle size in porous titanium and nonporous counterparts for surface energy and its impact on apatite formation

The importance of particle size in titanium (Ti) fabricated by powder metallurgy for the surface energy and its impact on the apatite formation was investigated. Four sorts of Ti powders of different mean particle size were realized through 20 min, 2 h, 5 h and 8 h of ball milling, respectively. Each sort of Ti powder was used to fabricate porous Ti and its nonporous counterparts sharing similar surface morphology, grain size and chemical composition, and then alkali-heat treatment was conducted on them. Surface energy was measured on the surfaces of the nonporous Ti counterparts due to the difficulty in measuring the porous surfaces directly. The surface energy increase on the alkali-heat-treated porous and nonporous Ti was observed due to the decrease in the particle size of the Ti powders and the presence of Ti–OH groups brought by the alkali-heat treatment. The apatite-inducing ability of the alkali-heat-treated porous and nonporous Ti with different surface energy values was evaluated in modified simulated body fluid and results indicated that there was a strong correlation between the apatite-inducing ability and the surface energy. The alkali-heat-treated porous and nonporous Ti discs prepared from the powders with an average particle size of 5.89 ± 0.76 μm possessed the highest surface energy and the best apatite-inducing ability when compared to the samples produced from the powders with the average particle size varying from 19.79 ± 0.31 to 10.25 ± 0.39 μm.

Influence of particle size and size distribution in deep bed filtration and dynamic microfiltration

Particle size and size distribution is an important parameter in solid liquid separation process especially in granular bed filtration and in dynamic microfiltration. This paper discusses their effects on the above processes from extensive experimental data obtained. In granular bed filtration, the experimental results showed that the initial efficiency follows the pattern reported by previous experimental and theoretical studies, i.e., lower efficiency for particles which fall in the range of critical size of 1 m. However, the particle removal during the transient stage increased with an increase in particle size for the range of sizes studied. An attempt was made to quantify these effects in granular bed filtration using semi-empirical approach. In dynamic membrane filtration also, the particle size plays a major role in the retention. However, despite the relative thickness of the membrane (compared to particle size) dynamic microfiltration appears more as a sieving process; the retention is mainly related to the largest pore size.

Wire EDM mechanism of MMCs with the variation of reinforced particle size

The size of reinforced particles notably affects the electro-discharge machining (EDM) of metal matrix composites (MMCs). This paper explores the mechanism of wire EDM of MMCs with different sizes of reinforced particles as well as the corresponding unreinforced matrix material. The mechanisms of material removal, surface generation, and taper kerf formation were investigated. This study shows that the particles’ ability to protect matrix materials from the intense heat of electric arc controls the material removal rate, surface generation, and taper of kerf. The low melting point matrix material is removed very easily, but the heat resistance reinforced particles delay the removal of material and facilitate the transfer of the workpiece material to wire electrode and vice versa. Thus, the material stays longer in touch with intense heat and affects the surface generation, wire electrode wear, and width of the kerf.

Ti-SrO metal matrix composites for bone implant materials

Titanium-strontia (Ti-SrO) metal matrix composites (MMCs) with 0, 1, 3 and 5% (weight ratio) of SrO have been fabricated through the powder metallurgy method. Increasing the weight ratio of SrO from 0 to 5%, the compressive strength of Ti-SrO MMCs increased from 982 MPa to 1753 MPa, while the ultimate strain decreased from 0.28 to 0.05. The elastic moduli of Ti-3SrO and Ti-5SrO MMCs were higher than those of Ti and Ti-1SrO MMC samples. Additionally, the micro hardness of Ti-SrO MMCs was enhanced from 59% to 190% with the addition of SrO. The enhanced compression strength and micro hardness of Ti-SrO MMCs were attributed to the Hall-Petch effect and the SrO dispersion strengthening in the Ti matrix. MTS assay results demonstrated that Ti-SrO MMCs with 3% SrO exhibited enhanced proliferation of osteoblast-like cells. Alkaline phosphatase activity of cells was not influenced significantly on the surface of Ti-SrO MMCs compared with pure Ti in a term longer than 10 days. The cell morphology on the Ti-SrO MMCs was observed using confocal microscopy and scanning electron microscopy, which confirmed that the Ti-3%SrO MMCs showed optimal in vitro biocompatibility. This journal is © the Partner Organisations 2014.

Correlation between optical and SEM measurements of wool cortical cell size

Wool fibres consist of micro to nano scale protein constituents that could be used for innovative applications. While techniques for extracting these constituents or making wool fibres into organic powders have been developed, effectively dispersing the particles and accurately determining their size has been difficult in practice. In this study, an ultrasonic method was employed to disperse cortical cells extracted from wool fibres into an
immersion oil or ethanol. Specimens of the cortical cells were then observed under optical microscopy and scanning electron microscopy, respectively. Cell length and maximum cell diameter were measured to quantify the cell size. The results suggest significant discrepancies exist in the cortical cell size obtained from the two different measurement techniques. The maximum diameter of wool cortical cells obtained from the optical microscope was much larger than that from the scanning electron microscope, while the length was much shorter. A correction factor is given so that cortical cell size obtained from the two measurement techniques can be compared.

Multiscale particle-in-cell modelling for advanced high strength steels

Advanced High Strength Steels (AHSS) offer outstanding characteristics for efficient and economic use of steel. The unique features of AHSS are direct result of careful heat treatment that creates martensite in the steel microstructure. Martensite and carbon content in the microstructure greatly affects the mechanical properties of AHSS, underlining more importance on microstructural discontinuities and their multiphase characteristics. In this paper, we present the Multiscale Particle-In-Cell (MPIC) method for microstructural modelling of AHSS. A specific particle method [1] usually used in fluid mechanics is adapted and implemented in a parallel multiscale framework. This multiscale method is based on homogenisation theories; with Particle-In-Cell (PIC) method in both micro and macroscale, and offers several advantages in comparison to finite element (FE) based formulation. Application of this method to a benchmark uniaxial tension test is presented and compared with conventional FE solutions.

Effect of particle characteristics on the two-body abrasive wear behaviour of a pearlitic steel

The specific wear rate and friction coefficient of a pearlitic microstructure subjected to different abrasive environments (i.e. SiC and alumina) were examined. A CSM high temperature pin-on-disc tribometer was used to simulate the two-body abrasive condition (i.e. the metallic surface abrading against the abrasive particles). The characteristics of the abrasive particles (i.e. particle size and density) revealed a significant impact on the amount of material loss. The specific wear rate of the pearlitic microstructure decreased with a reduction in the abrasive particle size, irrespective of the particle type. In addition, distinct particle deterioration mechanisms were observed during the abrasion process, which was largely determined by the abrasive particle size. Attrition, shelling and fracture were some of the dominant particle deterioration mechanisms occurring in both of the abrasive environments. SEM and EDX analysis on the wear debris displayed a unique metallic chip formation with respect to the particle type. Furthermore, the abrading efficiency (i.e. threshold level) of the abrasive particles was identified by means of interrupted abrasive wear tests. The dense packing nature of the alumina abrasive particles resulted in a significantly higher material removal rate than the SiC abrasive environment.

Anaerobic degradation of organic materials - significance of the substrate surface area

In anaerobic degradation of substrates containing mainly particulate organic matter, solids hydrolysis is rate-limiting. In these investigations, the particle size of various substrates was reduced by comminution to support hydrolysis. Two positive effects of comminution were observed. For substrates with high fibre content, which are particularly resistant to biodegradation, a significant improvement of the degradation degree was observed as a result of comminution. Secondly, for all substrates tested, and particularly for those rich in fibres, the degradation rate of comminuted samples was significantly higher. The first reason for both effects is an increase of the sample surface area. Several methods for measuring the specific surface area of organic materials, including particle size analysis, Nitrogen-adsorption and enzyme adsorption, were used and compared for the purpose of this study, where the surface area accessible to microbial enzymes is critical. The significance of the surface area in anaerobic degradation of particulate substrates was investigated through a kinetic model where the hydrolysis rate was based on the sample surface area. Good agreements were obtained between model and experiments carried out with samples of various specific surface areas. These results reinforced the significance of the sample surface area in anaerobic degradation processes. However, other effects of comminution responsible for the increased degradation degree and degradation rate were identified and discussed. These include: the increase of dissolved compounds due to cell rupture, exposition of surface areas previously inaccessible for microbial degradation, and alteration of the sample structure such as the lignin-cellulose arrangements.

Equal channel angular pressing of metal matrix composites: effect on particle distribution and fracture toughness

An Al6061-20%Al₂O₃ powder metallurgy (PM) metal matrix composite (MMC) with a strongly clustered particle distribution is subjected to equal channel angular pressing (ECAP) at a temperature of 370 °C. The evolution of the homogeneity of the particle distribution in the material during ECAP is investigated by the quadrat method. The model proposed by Tan and Zhang [Mater Sci Eng 1998;244:80] for estimating the critical particle size which is required for a homogeneous particle distribution in PM MMCs is extended to the case of a combination of extrusion and ECAP. The applicability of the model to predict a homogeneity of the particle distribution after extrusion and ECAP is discussed. It is shown that ECAP leads to an increase of the  uniformity of the particle distribution and the fracture toughness.

Plane wave scattering by a spherical di-electric particle in motion : a relativistic extension of the Mie theory

Light scattering from small spherical particles has applications in a vast number of disciplines including astrophysics, meteorology optics and particle sizing. Mie theory provides an exact analytical characterization of plane wave scattering from spherical dielectric objects. There exist many variants of the Mie theory where fundamental assumptions of the theory has been relaxed to make generalizations. Notable such extensions are generalized Mie theory where plane waves are replaced by optical beams, scattering from lossy particles, scattering from layered particles or shells and scattering of partially coherent (non-classical) light. However, no work has yet been reported in the literature on modifications required to account for scattering when the particle or the source is in motion relative to each other. This is an important problem where many applications can be found in disciplines involving moving particle size characterization. In this paper we propose a novel approach, using special relativity, to address this problem by extending the standard Mie theory for scattering by a particle in motion with a constant speed, which may be very low, moderate or comparable to the speed of light. The proposed technique involves transforming the scattering problem to a reference frame co-moving with the particle, then applying the Mie theory in that frame and transforming the scattered field back to the reference frame of the observer.

Silk powder for regenerative medicine

Two approaches are used for silk particle production: bottom up and top down. In the bottom up approach, different liquid-solid phase transfer techniques are adapted to fabricate particles from silk solution. In the top down approach, silk fibres are milled by various means to prepare ultrafine silk particles. Many important properties of particles such as size, geometry, porosity, stability and biodegradability are dependent on the specific methods of particle production. These properties influence drug loading and release, delivery modes, biocompatibility and their clearance from the body. Particle properties also determine biomechanical properties of particle reinforced composite scaffolds. Thus correlation between preparation, characterisation and application of silk particles for a specific biomedical application is critical. Progress made in this direction and challenges ahead are discussed in this chapter. © 2014 Woodhead Publishing Limited. All rights reserved.

Functionalized mesoporous silica nanoparticles with redox-responsive short-chain gatekeepers for agrochemical delivery.

The controlled release of salicylic acid (SA), a key phytohormone, was mediated by using a novel decanethiol gatekeeper system grafted onto mesoporous silica nanoparticles (MSNs). The decanethiol was conjugated only to the external surfaces of the MSNs through glutathione (GSH)-cleavable disulfide linkages and the introduction of a process to assemble gatekeepers only on the outer surface so that the mesopore area can be maintained for high cargo loading. Raman and nitrogen sorption isotherm analyses confirmed the successful linkage of decanethiol to the surface of MSNs. The in vitro release of SA from decanethiol gated MSNs indicated that the release rate of SA in an environment with a certain amount of GSH was significantly higher than that without GSH. More importantly, in planta experiments showed the release of SA from decanethiol gated MSNs by GSH induced sustained expression of the plant defense gene PR-1 up to 7 days after introduction, while free SA caused an early peak in PR-1 expression which steadily decreased after 3 days. This study demonstrates the redox-responsive release of a phytohormone in vitro and also indicates the potential use of MSNs in planta as a controlled agrochemical delivery system.