Particle Edge Research Articles

Adhesion of Particles with Sharp Edges to Air–Liquid Interfaces

In order to study the effect of sharp edges on solid particle adhesion to air-liquid interfaces, spherical colloidal probes were modified with a circumferential cut by focused ion beam milling. The interaction of the modified particles with water drops and bubbles was studied using the colloidal probe technique. When the modified particles were brought into contact with air-liquid interfaces, the contact line was pinned at the edge of the cut. Contact hysteresis between the approach and retraction components of the measured force curves was eliminated. The contact angle at the edge takes a range of values within the limits defined by the Gibbs inequality. These limits determine the adhesion force. As such, the adhesion force is a function of the particle wettability and edge geometry.

Simulations of density profiles, pellet fuelling and density control in ITER

The paper presents the results of 1.5-dimensional simulations of density profiles and pellet fuelling for the ITER baseline scenario performed with the ASTRA and JETTO transport codes by the ITER Scenario Modelling working group within the European Task Force on Integrated Tokamak Modelling. The first part of the paper describes the physics of the problem and how it is implemented in the different codes available to the working group. The second part presents the results of the simulations. Results obtained with the GLF23 physics based transport model and a simplified description of the pellet particle source are described alongside results obtained with the simpler Bohm/gyro-Bohm semi-empirical transport model and a more sophisticated pellet ablation/deposition code providing a completely self-consistent description of the pellet source. A parametric study has been performed to assess the effect of varying parameters independently, the values of which in ITER are either uncertain or not easily controllable (such as particle diffusivity, edge stability, wall recycling and boundary conditions), on the target plasma density, temperature, Q and pellet frequency required to achieve a certain degree of density control. To this end the edge particle diffusivity was increased by a factor of three, the pedestal normalized critical pressure gradient for ballooning stability was decreased by 20%, the boundary conditions on density and temperature were modified by 30–40% and the wall recycling particle source was increased from zero to 20% of the particle outflux. The results show that variations in the order of 15% for density and temperature, 40% for Q and 100% for the pellet frequency can be expected. Open problems and modelling needs are also discussed in the paper.

Sorption behavior of heavy metals on birnessite: Relationship with its Mn average oxidation state and implications for types of sorption sites

Abstract Sorption mechanisms of heavy metals at the mineral/water interface are largely controlled by the type and number of sorption sites on the mineral surfaces. However, in the case of layered manganese oxides, with a highly reactive interlayer (internal) region, the effects of variable substructures on their sorption sites, sorption capacities and characteristics are still obscure. Sorption experiments at pH 4.5 combined with powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were performed to investigate the sorption characteristics and mechanisms of Pb 2 + , Cu 2 + , Zn 2 + and Cd 2 + onto hexagonal birnessites with various Mn average oxidation states (AOS), together with detailed physicochemical characterizations of the birnessites. The results show that a decrease in Mn AOS of birnessites decreased considerably the sorption capacity for heavy metals, despite the fact that the specific surface area increased almost linearly. The sorption capacity for any given birnessite followed the order Pb 2 + ≫ Cu 2 + > Zn 2 + > Cd 2 + ; for Pb 2 + ranging from 1.6 to 3.9 times greater than those of the other metals, while Cu 2 + , Zn 2 + , and Cd 2 + sorbed with similar maxima among them. The large differences between maximum Pb 2 + sorption and that of the other metals were approximately of the same absolute magnitude regardless of the specific birnessites compared, as opposed to decreasing in equal relative proportions as would be expected in a homogeneous-site model. This evidence agrees well with previous work on hexagonal birnessites that proposes a general two-site structural model for metal-binding to birnessite, and the sorption maxima differences obtained in this work were used to estimate the concentration of low-energy and high-energy binding sites in the different birnessites. Relating these to previous structural information allowed us to assign these site types roughly to particle edge sites and vacancy sites at interlayers, respectively. In this manner, we found that for the birnessite containing exclusively Mn(IV), the contributions of edge sites and interlayer sites to total Pb 2 + sorption were approximately equivalent; but as Mn AOS decreased, the contribution of vacant sites at interlayers sensibly decreased, probably through the increasing presence of layer Mn(III) at the expense of vacant sites. The results presented here of highly distinctive affinity site types are valuable for a fundamental understanding of the behavior of birnessites towards heavy metal sorption, which in turn contributes both to predictions of the geochemical behavior of birnessites and to applications for remediation schemes of metal-contaminated aqueous environments.

Patterned Self-Assembly of Fine Particles as a Proposal of Precisely Allocated Cutting-Edge Tool

This paper discusses fine-particle self-assembly and its potential applications to abrasive tools. Dispensing suspensions containing particles on substrates, packed structures are self-assembled as solvent evaporates. Applying relative motion between the dispenser and substrate produces patterned assembly without the need for a mask. Silica particles 1 µm in size were typically assembled along lines 20 µm-100 µmwide. Diamond particles were also assembled because these also act as the cutting edge of abrasive tools. Assembled particles were transferred to another substrate using ultraviolet curing resin. The particle edge height was aligned at the same level independent of the assemblylayer number - the key to this process.

In Situ Observation of Water Dissociation with Lattice Incorporation at FeO Particle Edges Using Scanning Tunneling Microscopy and X-ray Photoelectron Spectroscopy

The dissociation of H2O and formation of adsorbed hydroxyl groups on FeO particles grown on Au(111) were identified with in situ X-ray photoelectron spectroscopy (XPS) at water pressures ranging from 3 × 10(-8) to 0.1 Torr. The facile dissociation of H2O takes place at FeO particle edges, and it was successfully observed in situ with atomically resolved scanning tunneling microscopy (STM). The in situ STM studies show that adsorbed hydroxyl groups were formed exclusively along the edges of the FeO particles with the O atom becoming directly incorporated into the oxide crystalline lattice. The STM results are consistent with coordinatively unsaturated ferrous (CUF) sites along the FeO particle edge causing the observed reactivity with H2O. Our results also directly illustrate how structural defects and under-coordinated sites participate in chemical reactions.

Multilayered Nano-Architecture of Variable Sized Graphene Nanosheets for Enhanced Supercapacitor Electrode Performance

The diverse physical and chemical aspects of graphene nanosheets such as particle size surface area and edge chemistry were combined to fabricate a new supercapacitor electrode architecture consisting of a highly aligned network of large-sized nanosheets as a series of current collectors within a multilayer configuration of bulk electrode. Capillary driven self-assembly of monolayers of graphene nanosheets was employed to create a flexible, multilayer, free-standing film of highly hydrophobic nanosheets over large macroscopic areas. This nanoarchitecture exhibits a high-frequency capacitative response and a nearly rectangular cyclic voltammogram at 1000 mV/s scanning rate and possesses a rapid current response, small equivalent series resistance (ESR), and fast ionic diffusion for high-power electrical double-layer capacitor (EDLC) application.

Methane Activation by Platinum: Critical Role of Edge and Corner Sites of Metal Nanoparticles

Complete dehydrogenation of methane is studied on model Pt catalysts by means of state-of-the-art DFT methods and by a combination of supersonic molecular beams with high-resolution photoelectron spectroscopy. The DFT results predict that intermediate species like CH(3) and CH(2) are specially stabilized at sites located at particles edges and corners by an amount of 50-80 kJ mol(-1). This stabilization is caused by an enhanced activity of low-coordinated sites accompanied by their special flexibility to accommodate adsorbates. The kinetics of the complete dehydrogenation of methane is substantially modified according to the reaction energy profiles when switching from Pt(111) extended surfaces to Pt nanoparticles. The CH(3) and CH(2) formation steps are endothermic on Pt(111) but markedly exothermic on Pt(79). An important decrease of the reaction barriers is observed in the latter case with values of approximately 60 kJ mol(-1) for first C-H bond scission and 40 kJ mol(-1) for methyl decomposition. DFT predictions are experimentally confirmed by methane decomposition on Pt nanoparticles supported on an ordered CeO(2) film on Cu(111). It is shown that CH(3) generated on the Pt nanoparticles undergoes spontaneous dehydrogenation at 100 K. This is in sharp contrast to previous results on Pt single-crystal surfaces in which CH(3) was stable up to much higher temperatures. This result underlines the critical role of particle edge sites in methane activation and dehydrogenation.

Influence of morphology in the catalytic activity of bioconjugated platinum nanostructures

Platinum nanoparticles stabilized by a protein, bovine serum albumin, have been synthesized successfully with two different morphologies such as cuboctahedra and nanorods. They have been characterized by the use of different techniques such as XPS, PCS, TEM, and STEM-HAADF. These nanoparticles have been applied as catalysts for the hydrogenation of allyl alcohol in an aqueous solution. A key finding of this article is the superior catalytic activity of the nanorods compared to the cuboctahedral particles. This difference in the catalytic activity was justified because of the variation in the amount of protein to stabilize the nanorods. A model for the nanorods and equations that describe the proportion of atoms in the different sites of the particle (face, vertex, edge, or interior) is used to calculate the percentage of atoms that are located on the nanorod surface. The stability of these particles as catalysts was also studied. The results showed that Pt nanorods and Pt cuboctahedra particles were degraded after 24 h of reaction.

Investigating the Outskirts of Fe and Co Catalyst Particles in Alumina-Supported Catalytic CVD Carbon Nanotube Growth

Using thermal CVD, the synthesis of multi-walled carbon nanotubes exhibiting roots anchored directly onto alpha-alumina supports, rather than the catalyst particle, is reported. At such roots, the alignment of the graphitic planes with the support lattice fringes depends on the support crystal structure and orientation. Surface defects may alter the reactivity of the surface or control the anchoring of supported atoms or nanoparticles. We argue this surface defect is provided by the catalyst particle's edge interaction with the support, in other words its circumference. The development of oxide-based catalysts is attractive in that they potentially provide an appropriate solution to directly integrate the synthesis of carbon nanotubes and graphene into silicon-based technology.

A nanoscale friction investigation during the manipulation of nanoparticles in controlledenvironments

Future micro/nanodevices will contain very small features such that liquidlubrication is not practical and inherent lubricity is needed. In this study, ananoscale friction investigation was carried out during the manipulation of Au andSiO2 nanoparticles on silicon using atomic force microscopy (AFM). Nanoparticle sliding wascharacterized by quantifying the lateral force associated with the AFM tip twisting as ithits the particle edge. The friction force varies with particle area and humidity,illustrating how meniscus forces on nanoparticles affect friction. A large tip slid on thenanoparticle-coated surface exhibited friction reduction due to nanoparticle sliding andcontact area reduction.

Pedestal Studies in DIII-D

Studies of the H-mode pedestal in the DIII-D tokamak are presented. The global energy confinement increases as the plasma pressure on top of the pedestal increases. The best empirical description for a pedestal width parameter is Δpe ∝ (βpolPED)0.4, where Δpe is the width of the electron pressure pedestal and βpolPED is the poloidal beta at the top of the pedestal. The edge profiles of electron density ne, electron temperature Te, and ion temperature Ti can all have different shapes. Thus, a simple width scaling for the edge might not exist, and studies of the physics of individual profiles have been initiated. A model for the ne profile, based on self-consistent treatment of edge particle sources and edge particle transport, agrees with several experimental observations. The steep gradient region for the Te profile often extends farther into the plasma than the ne pedestal step. Magnetohydrodynamic stability provides the ultimate limits to the evolution of the pedestal and usually leads to edge instabilities called edge-localized modes (ELMs). However, the absence of ELMs in a regime called the Quiescent H-mode shows that large pedestals can be produced without ELMs.

Particle confinement and density profile behaviour on HL-1M

In this paper the density profile behaviour and the particle confinement operation regime on HL-1M have been studied under the pellet injection (PI), supersonic molecular beam injection (SMBI), gas puffing (GP) and lower hybrid current drive experimental situations. The relationships between density profile, particle confinement time and edge safe factor have been explored. The density profile, which is measured by six-channel far-infrared ray laser interferometer has been analysed by using the peaking coefficient calculation code. Changes of the outward and inward diffusion velocities before and after the peaking of the central density profile have been calculated using the global particle balance equations. The particle confinement operation regimes have been discussed. The peaking density profile can be easily obtained under the condition of efficient fuelling. In ohmic discharges, confinement time increases as the peaking density profile factor rises and is saturated at a critical value related to the fuelling efficiency. The particle confinement time of SMBI lies between the values of GP and PI and its value is about 3–5 times of the energy confinement time.

On the Role of Different Adsorption and Reaction Sites on Supported Nanoparticles during a Catalytic Reaction: NO Decomposition on a Pd/Alumina Model Catalyst

We have studied the catalytic decomposition of NO on a structurally well-defined Pd model catalyst, employing a combination of molecular beam techniques and time-resolved IR reflection absorption spectroscopy (TR-IRAS). In a first step, different active sites such as facets and edges/defects on the catalyst nanoparticles are identified spectroscopically. Subsequently, these spectroscopic signatures are utilized to monitor the site occupation by reactant species (NO) and products (atomic oxygen and nitrogen) under reaction conditions. Simultaneously, the kinetics of NO dissociation is investigated. It is found that atomic nitrogen and oxygen species are initially formed in the vicinity of edge or defect sites. At temperatures up to 300 K, the mobility of these atomic species is suppressed, whereas at higher temperature, diffusion onto the (111) facets of the particles can occur. It is shown both by IR spectroscopy of adsorbed NO under reaction conditions and by control experiments using CO as a probe molecule that nitrogen and oxygen species preferentially occupy particle edge and defect sites. By means of molecular beam CO titration experiments and TR-IRAS, it is demonstrated that the presence of these atomic species critically controls the NO dissociation activity. Specifically, the presence of strongly bound nitrogen in the vicinity of edge and defect sites gives rise to an enhanced dissociation probability under conditions of high adsorbate coverage.

Nanocoating individual cohesive boron nitride particles in a fluidized bed by ALD

Experiments are conducted with alumina (Al 2 O 3 ) deposition on a wide size range of hexagonal boron nitride (BN) platelet-like particles. Successful deposition of alumina films on these particles, with film thickness controllable at the Angstrom level, is observed based upon TEM imaging, ICP-AES, particle size distributions, and surface area analysis. While fluidizing, fine BN particles aggregate in the bed. The aggregates are the entities fluidizing, not the primary particles. However, individual particles are coated using Atomic Layer Deposition (ALD), not aggregates. Since ALD is a surface chemistry phenomenon, the films grow uniformly on every primary particle. BN particles are small platelets with different functional groups on the basal planes and edge planes. A small exposure to reagents [2.5×10 6 Langmuir (L) per reagent per cycle], will only coat the edge planes of uncoated BN particles. A larger dose of 1×10 8 L will coat the entire uncoated BN particle (edge and basal planes). After 10 ALD cycles of the 1×10 8 L dose, the exposures can be reduced to 1×10 6 L as the film is then growing on alumina and not BN. Peel strength data indicate that adhesion between the coated particles and a cured epoxy in a filled composite is ∼25% stronger than that of uncoated particles and the epoxy. The overall thermal conductivity drops ∼17% for an identical filler loading as expected due to the additional thermal resistance added by the film. However, the viscosity of an epoxy resin loaded with coated BN is as much as five times lower than that of the resin loaded with the same amount of uncoated BN. These results indicate that the loading of Al 2 O 3 nanocoated BN particles in an epoxy matrix can be substantially increased relative to that of uncoated particles. The thermal conductivity of the more highly filled composite will be increased without adversely impacting filled resin viscosity or the peel strength of the cured material. This is the first reported study indicating that cohesive primary particles that fluidize as aggregates in a fluidized bed can be individually coated with a nano-thick ceramic film using ALD.

Nanocoating individual cohesive boron nitride particles in a fluidized bed by ALD

Experiments are conducted with alumina (Al 2O 3) deposition on a wide size range of hexagonal boron nitride (BN) platelet-like particles. Successful deposition of alumina films on these particles, with film thickness controllable at the Angstrom level, is observed based upon TEM imaging, ICP-AES, particle size distributions, and surface area analysis. While fluidizing, fine BN particles aggregate in the bed. The aggregates are the entities fluidizing, not the primary particles. However, individual particles are coated using Atomic Layer Deposition (ALD), not aggregates. Since ALD is a surface chemistry phenomenon, the films grow uniformly on every primary particle. BN particles are small platelets with different functional groups on the basal planes and edge planes. A small exposure to reagents [2.5×10 6 Langmuir (L) per reagent per cycle], will only coat the edge planes of uncoated BN particles. A larger dose of 1×10 8 L will coat the entire uncoated BN particle (edge and basal planes). After 10 ALD cycles of the 1×10 8 L dose, the exposures can be reduced to 1×10 6 L as the film is then growing on alumina and not BN. Peel strength data indicate that adhesion between the coated particles and a cured epoxy in a filled composite is ∼25% stronger than that of uncoated particles and the epoxy. The overall thermal conductivity drops ∼17% for an identical filler loading as expected due to the additional thermal resistance added by the film. However, the viscosity of an epoxy resin loaded with coated BN is as much as five times lower than that of the resin loaded with the same amount of uncoated BN. These results indicate that the loading of Al 2O 3 nanocoated BN particles in an epoxy matrix can be substantially increased relative to that of uncoated particles. The thermal conductivity of the more highly filled composite will be increased without adversely impacting filled resin viscosity or the peel strength of the cured material. This is the first reported study indicating that cohesive primary particles that fluidize as aggregates in a fluidized bed can be individually coated with a nano-thick ceramic film using ALD.

Edge Turbulence During Limiter Biasing Experiments in the TJ-II Stellarator

The influence of limiter biasing on plasma confinement, turbulence and plasma flows has been investigated in the TJ-II stellarator. Experimental results show that it is possible to modify global particle confinement and edge plasma parameters with both positive and negative biasing. Significant and minor modifications in the structure of plasma fluctuations have been observed during the transition to improved confinement regimes induced by limiter biasing. These results show evidence of electric field induced improved confinement via multiple mechanisms. The investigation of the relaxation of plasma potential and electric fields shows evidence of two different characteristic decay times.

Recognition of texture types of wear particles

Microscopic wear particles are produced in all machines containing moving parts in contact. The particles, transported by a lubricant from wear sites; carry important information relating to the condition of the machinery. This information is classified by compositional and six morphological attributes of particle size, shape, edge details, color, thickness ratio, and surface texture. This article describes an automated system for surface texture identification of wear particles by using artificial neural networks. The aim is to classify these particles according to their morphological attributes and by using the information obtained, to predict wear failure modes in engines and other machinery. This approach will enable the manufacturing industry to improve quality, productivity and economy. The procedure reported in this article is based on gray level co-occurrence matrices which are used to train a feed-forward neural network classifier in order to distinguish among seven different patterns which can aid in the identification of wear particles. The investigated patterns are: smooth, rough, striations, holes, pitted, cracked, and serrated. An accuracy classification rate of 94.64% has been achieved and is shown by a confusion matrix.

Lattice measurement and alloy compositions in metal and bimetallic nanoparticles

A new reliable method for determining the lattice spacings of metallic and bimetallic nanoparticles in phase contrast high resolution electron microscopy (HREM) images was developed. In this study, we discuss problems in applying HREM techniques to single metal (Pt and Au) and bimetallic (AuPd) nanoparticles of unknown shapes and random orientations. Errors arising from particle tilt and edge effects are discussed and analysis criteria are presented to reduce these errors in measuring the lattice parameters of nanoparticles. The accuracy of an individual particle lattice measurement is limited by an effective standard deviation which depends on the size of the individual nanoparticle. For example, the standard deviation for 20–30 Å Pt or Au nanoparticles is about 1.5%. To increase the accuracy in determining the lattice spacings of nanoparticles, statistical methods have to be used to obtain the average lattice spacing of an ensemble of nanoparticles. We measured approximately 100 nanoparticles with sizes in the range of 20–30 Å and found that the mean lattice spacing can be determined to within 0.2%. By applying Vegard's law to the AuPd bimetallic systems we successfully detected the presence of alloying. For 30 Å nanoparticles, the estimated ultimate error in determining the composition of the AuPd alloy is about 3% provided that at least 100 particles are measured. Finally, the challenges in determining the presence of more than one alloy phases in bimetallic nanoparticle systems were also discussed.

Theory of pseudogaps in charge density waves in application to photo electron spectroscopy

For a one-dimensional electron-phonon system we consider the photon absorption involving electronic excitations within the pseudogap energy range. Within the adiabatic approximation for the electron - phonon interactions these processes are described by ronlinear configurations of an instanton type. We calculate the subgap absorption as it can be observed by means of photo electron or tunneling spectroscopies. In details we consider systems with gapless modes: 1D semiconductors with acoustic phonons and incommensurate charge density waves. We found that below the free particle edge the pseudogap starts with the exponential decrease of transition rates changing to a power law deeply within the pseudogap, near the absolute edge.

Computer vision techniques for wear debris analysis (CVTWDA)

Computer vision is a process to locate and recognise objects in digital images. The terms or debris come from the field of tribology. Tribology is the study of wear, friction and lubrication. Wear particles are produced in all machines containing moving parts in contact. This paper addresses the analysis of microscopic wear particles generated by wear mechanisms by using computer vision and image processing techniques. The aim is to develop an automated system to classify and identify wear particles in terms of their morphological and textural features and by using the information obtained to predict wear failure modes in engines and other machinery. An interactive control system, CAVE, is devised to process and store the quantitative information of particle size, shape and edge details. The identification and analysis of wear particles are effectively demonstrated by the devised system with the ability to make human-like, even better and objective diagnosis. This obviates the need for specialists and reliance on human visual inspection techniques.