Particles In Close Contact Research Articles

The immersed boundary method for confined flows: Numerical diffusion and simulation accuracy of a boundary retraction scheme

Diffuse-interface immersed boundary methods (IBM) have been successfully applied to numerous complex fluid–structure interaction problems because of their simple and efficient implementation. Despite their ability to suppress numerical oscillations significantly compared to sharp-interface methods, the diffuse interface is likely to reduce simulation accuracy of the flow field around the solid boundary. The present work investigates the diffusive effects of IBM and the mitigation method for surface-confined particulate flows by comparing results to sharp-interface methods. It is found that increasingly-confined geometries accentuate interface diffusion effects and decrease simulation accuracy. To minimise the diffusive effects of IBM, a boundary retraction scheme is used and its effectiveness is examined, in particular for particles in close contact where the diffuse interfaces overlap. It is shown that this simple implementation is capable of alleviating interface diffusion errors, thus increasing accuracy while limiting computational costs. With an optimal boundary retraction scheme, IBM can successfully capture fluid–structure interactions at different degrees of confinement, comparable to sharp-interface methods.

Flash Colloidal Gold Nanoparticle Assembly in a Milli Flow System: Implications for Thermoplasmonic and for the Amplification of Optical Signals

The assembly and stabilization of a finite number of nanocrystals in contact in water could maximize the optical absorption per unit of material. Some local plasmonic properties exploited in applications, such as photothermia and optical signal amplification, would also be maximized which is important in the perspective of mass producing nanostructures at a lower cost. The main lock is that bringing charged particles in close contact requires the charges to be screened/suppressed, which leads to the rapid formation of micrometric aggregates. In this article, we show that aggregates containing less than 60 particles in contact can be obtained with a milli-flow system composed of turbulent mixers and flow reactors. This process allows to stop a fast non-equilibrium colloidal aggregation process at millisecond times after the initiation of the aggregation process which allows to control the aggregation number. As a case study, we considered the rapid mixing of citrate coated gold nanoparticles (NP) and AlCl3 in water to initiate a fast aggregation controlled by diffusion. Injecting a solution of polycation using a second mixer allowed us to arrest the aggregation process after a reaction time by formation of overcharged cationic aggregates. We obtained within seconds stable dispersions of a few milliliters composed of particle aggregates. Our main result is to show that it is possible to master the average aggregation number between 2 and 60 NP per aggregate by varying the a reaction time between 10 ms and 1 s.

Feasibility of lime‐modified carbonate soil for highway subgrade filling

AbstractFor the lime modified carbonate rock soil road subgrade of port highway, after the lime modified carbonate rock filler is used to treat it, the particle discrete unit has the characteristics of sparsity, and the particle gradation is caused by the seepage of soil mass, and with the increase in load, overload load occurs. It is therefore necessary to establish relevant mathematical models to analyze the load variation of lime‐modified carbonate roadbed under boundary conditions. The probability mathematical model of the load overload of lime‐modified carbonate fill was studied, and a feasibility analysis model of lime‐modified carbonate soil used in port city highway subgrade filling was put forward based on the discrete hysteretic characteristic curve method. The load characteristics of lime‐modified carbonate soil were analyzed within the limited area distribution range of adjacent two holes. The load energy transfer model of lime‐modified carbonate packing in foundation soil was analyzed in PFC3D software. The foundation stress reinforcement method was used to improve the carbonate soil foundation construction and, combined with the seepage model of the radial consolidation of the foundation, a filling feasibility analysis of the urban highway subgrade of lime‐modified carbonate soil port was carried out. The simulation results show that this method can effectively realize the load overload analysis of lime‐modified carbonate packing, improve the load capacity of subgrade filler for port city highway, and improve the load property of highway subgrade of port city. Keep the soil particles in close contact. This study provides a feasible basis for future highway construction and the application of lime‐modified carbonate.

Hydrogen purification for fuel cells through CO preferential oxidation using PtCu/Al2O3 structured catalysts

Cordierite monoliths and alumina foams substrates were washcoated with PtCu/Al2O3 powder with a low loading of Pt (0.2 and 0.5 wt. %) and 4 and 8 wt. % of Cu in order to be used for the CO Preferential Oxidation (COPrOx) reaction. These catalysts exhibited a high performance in CO oxidation at temperatures between 110–130 °C. The presence of platinum caused a synergistic effect on the Cu/Al2O3 catalyst, which greatly enhanced the CO conversion. The most active catalyst reached 100% CO conversion at 110 °C, and proved high tolerance to CO2 and H2O in the feed. A good adherence between the catalytic film and the ceramic monolithic walls was reached after preparation by the washcoating method and calcination at 300 °C. The macropores of the monolithic wall were covered by aggregates of 2–5 μm of PtCu/Al2O3 that filled the substrate cavities. The higher CO conversions obtained at low temperatures were probably due to the simultaneous formation of small Pt particles in close contact with copper species. In addition, XPS data showed metallic Pt0 and Cu0 particles on the catalytic surface of the foam and monoliths. The bimetallic monoliths with low Pt loading, very active for the COPrOx at low temperature in the presence of CO2 and H2O, are promising catalysts for practical applications.

Scale Formation on Na4Mn9O18 Insertion Electrodes in Electrochemical Deionization

Several sodium insertion materials have been used as cathode materials in electrochemical deionization. [1][2][3][4]In this work, we evaluate the performance of sodium manganese oxide (Na4Mn9O18/ NMO), a layered insertion compound in separating sodium ions from a mixed cation (Na+/Ca2+) system (figure1). We observe that the specific capacity of a composite Na4Mn9O18/C electrode in 1M NaCl solution is 54 mAh/g, and is reduced to 23 mAh/g in 0.2 M CaCl2+ 1 M NaCl. We also observe that the capacity is not fully recovered when the electrode cycled in mixed ion solution is electrochemically cycled again in 1M NaCl. The X-ray diffractograms of the electrodes cycled in the mixed ion solutions reveals that in addition to the Na4Mn9O18 phase there is a second phase comprising primarily of calcite CaCO3. The presence of calcite on the NMO electrode is confirmed using SEM/EDX and XPS. It is expected that calcite is formed during the oxidation of carbon particles in close contact with NMO particles in the composite electrodes, and the capacity loss occurs due to the calcite layers that hinder ion transport to the NMO particles. [5] Reference [1] M.E. Suss, V. Presser, Water Desalination with Energy Storage Electrode Materials, Joule. 2 (2018) 25–35. doi:10.1016/j.joule.2017.12.010. [2] S. Shanbhag, Y. Bootwala, J.F. Whitacre, M.S. Mauter, Ion Transport and Competition Effects on NaTi2(PO4)3and Na4Mn9O18Selective Insertion Electrode Performance, Langmuir. 33 (2017) 12580–12591. doi:10.1021/acs.langmuir.7b02861. [3] J.F. Whitacre, A. Tevar, S. Sharma, Na4Mn9O18as a positive electrode material for an aqueous electrolyte sodium-ion energy storage device, Electrochem. Commun. 12 (2010) 463–466. doi:10.1016/j.elecom.2010.01.020. [4] F. Sauvage, L. Laffont, J.M. Tarascon, E. Baudrin, Study of the insertion/deinsertion mechanism of sodium into Na 0.44MnO2, Inorg. Chem. 46 (2007) 3289–3294. doi:10.1021/ic0700250. [5] C. Zhang, D. He, J. Ma, W. Tang, T.D. Waite, Faradaic reactions in capacitive deionization (CDI) - problems and possibilities: A review, Water Res. 128 (2018) 314–330. doi:10.1016/j.watres.2017.10.024. Figure 1

London-van der Waals Force Field of a Chemically Patterned Surface To Enable Selective Adhesion.

The London-van der Waals (L-vdW) force between a particle and a surface strongly depends on the topography and the chemical properties of the interacting surfaces. Although a great deal of work has been done to understand the effect of topographical heterogeneity on the L-vdW adhesion, the role of chemical heterogeneity has been discussed only rarely. This study makes an attempt to quantify the magnitude and range of the L-vdW force acting on a spherical particle in the vicinity of a chemically patterned surface. Specifically, an ideal system of a smooth spherical particle approaching a surface composed of parallel stripes of chemically distinct materials with different Hamaker constants is considered. The L-vdW forces for such systems are determined by solving the London dispersion potential for the entire volumes of the adhering bodies from first principles, using Hamaker's microscopic approach. The computational results elucidate that a chemical interface can apply a tangential L-vdW force, in addition to the normal L-vdW force, on nearby particles. This can cause lateral motion of particles neighboring a chemically inhomogeneous surface. The magnitude of the tangential L-vdW force is found to be maximum when the particle is centered at the interface and shows a gradual drop as it moves away from this location. The magnitude and range of the tangential L-vdW force can be large for large colloidal particles in close contact with a chemically patterned surface whose materials have distinct Hamaker constants. This study suggests that the tangential L-vdW force field generated by a chemical interface can be utilized as a tool to manipulate the path of an approaching particle to facilitate selective adhesion.

Preparation of AlB<sub>12</sub>-Type Al-B Alloys

AlB12-type Al-B alloys were prepared by high temperature treatment of AlB2-type Al-B alloy melts with different distribution morphologies of borides. The results show that when using the “immersion” method, the produced AlB2-type Al-B alloy melt (“alloy melt 1”) contain a small amount of AlB12 phase and many boride agglomerations. The AlB2-type Al-B alloy melt produced by using the “vortex” method (“alloy melt 2”) contains no AlB12 phase and exhibits a well dispersion of AlB2 particles. During the high temperature treatment, the AlB2 particles in close contact with each other in the alloy melts are prone to coalescence, causing the formation of relative large AlB12 particles. The high-speed stirring adopted during the high temperature treatment has an effect of prohibiting the coalescence of AlB2 particles in boride agglomerations.

EACMFS Prizes and Awards

We evaluated histologically and tomographically the effects of fresh frozen bone allograft (FFB) or bovine bone mineral (BBM) in maxillary sinus floor augmentations. In total, 30 maxillary sinuses from 30 patients (mean age = 51.17 ± 10.86 years) underwent sinus augmentation. Patients were divided in two test groups (15 sinuses each). The first group was grafted with allograft bone, and the second group received bovine bone mineral. After 6 months, bone samples from each group were collected for histological examination. Implant survival rates were 97.78% (FFB group) and 100% (BBM group) 6 months after functional loading. Median volumetric reductions of 31.2% (11.33–40.56) and 12.22% (9.91–20.59) were observed in the FFB and BBM groups, respectively. Comparisons between the groups for differences in initial and final volumes of bone (p = 0.015) and the rate of resorption (p = 0.009) showed statistically significant differences. The FFB group showed osteoblastic cells in close contact with osteoid matrix, connected through bridges between allograft bone particles and new bone formation. The BBM group showed BBM particles in close contact with new bone, with visible osteoid matrix bridges and osteoblastic cells surrounding it. None showed signs of acute or chronic inflammatory infiltrate. Despite better results with BBM, both FFB and BBM in maxillary sinus augmentation resulted in high percentages of new bone formation, and allowed implant placement with a low rate of failure of osseointegration at a 6-month follow-up.

Use of micro-reactors to obtain new insights into the factors influencing tricalcium silicate dissolution

A micro-reactor approach, developed previously, is used to study the early dissolution of tricalcium silicate. This approach uses micron-sized gaps mimicking particles in close contact to \\understand dissolution, nucleation, and growth processes. The main factors influencing the dissolution kinetics of tricalcium silicate are presented. We show that the presence of defects caused by polishing does not affect the extent of dissolution. A strong effect of aluminum in solution reducing the extent of dissolution is however identified. This effect is highly dependent on the pH, and is much lower above pH 13. We show also that superplasticizers reduce the extent of dissolution; however, the exact reason for this effect is not clear.

Micro‐reactors to Study Alite Hydration

A new approach to study the early hydration reaction of alite is presented. It relies on milling micron‐sized gaps into alite grains using a Focused Ion Beam. This provides for a “micro‐reactor” in which hydration in confined conditions can be followed after introducing aqueous solutions of any desired composition. Hydration is followed by stopping the reaction at desired ages using solvent exchange and imaging the gaps using a Scanning Electron Microscope. These micro‐reactors offer several advantages over conventional methods to monitor alite hydration. In particular, we can study the time evolution of dissolution in a reproducible manner using a setup that mimics particles in close contact. This paper presents this new methodology and applies it to studying the effects of solution composition and selected chemical admixtures on the dissolution of alite. New insights into the role of these factors are obtained and discussed.

Microstructure and oxygen evolution of Fe–Ce mixed oxides by redox treatment

The relationship between structure and reduction/redox properties of Fe–Ce mixed oxides with a Fe content of 5, 10, 20 or 30mol%, prepared by a coprecipitation method, were investigated by XRD, Raman, TEM, TPR and TPO techniques. It is found that all the iron ions can be incorporated into the ceria lattice to form a solid solution for the FeCe 5 (Fe 5%) sample, but amorphous or crystal Fe2O3 particles were found to be present on the Fe–Ce oxide samples with higher the iron content. The reducibility of single solid solution was much better than the pure CeO2, and the appearance of dispersed Fe2O3 particles improved the surface reducibility of materials. The iron ions incorporated into the CeO2 lattice accelerated the oxygen release from bulk to surface, and surface Fe2O3 particles in close contact to CeO2 acted as a catalyst for the reaction between solid solution and hydrogen. The microstructure of exposed Fe2O3 with Ce–Fe–O solid solution allows the Fe–Ce mixed oxides to own good reducibility and high OSC, which also counteracts the deactivation of the reducibility resulting from the sintering of materials in the redox cycling.

Oxygen release–absorption properties and structural stability of Ce0.8Fe0.2O2−x

Oxygen release–absorption properties and structural stability of Ce–Fe mixed oxides (Ce0.8Fe0.2O2−x) with different calcination temperatures (600–1000 °C) were investigated and correlated to their oxygen storage capacity. Iron ions could be incorporated into the CeO2 lattice to form a solid solution after calcination at low temperatures, but such solid solution was unstable under high-temperature thermal treatments. High-temperature (≥800 °C) calcination resulted in the appearance of exposed Fe2O3 phases on the surface of the solid solution, and this structural evolution finally affected the reduction behavior. The Fe3+ reduction from the Ce–Fe oxide solid solution was easier than the bulk Fe2O3 particles, while the small Fe2O3 particles in close contact with CeO2 could enhance the reducibility of cerium oxides. The strong interaction between the exposed small Fe2O3 particles and the solid solution made the Ce–Fe mixed oxides possess good reduction stability and high oxygen storage capacity (OSC) even after repeated redox treatments. Such interactions were absent toward the physically mixed sample. An unusual enhancement on the reducibility of Ce–Fe mixed oxides was observed after a successive redox treatment. Large oxygen evolution appeared at around 600 °C for the recycled samples, and the OSC rose to 1.31 mmol-O2/g after six redox cycles. The XRD, Raman, and TEM analyses revealed that the material structure of the mixed oxides was stabilized to have an inter-region between the Fe2O3 particles and the solid solution after the redox treatment. It was concluded that such microstructural evolutions of composite particle from solid solution under redox conditions brought beneficial property to the OSC of the Ce–Fe mixed oxides.

3D Localization of weak scatterers in digital holographic microscopy using Rayleigh-Sommerfeld back-propagation

The Rayleigh-Sommerfeld back-propagation method is a fast and highly flexible volume reconstruction scheme for digital holographic microscopy. We present a new method for 3D localization of weakly scattering objects using this technique. A well-known aspect of classical optics (the Gouy phase shift) can be used to discriminate between objects lying on either side of the holographic image plane. This results in an unambiguous, model-free measurement of the axial coordinate of microscopic samples, and is demonstrated both on an individual colloidal sphere, and on a more complex object — a layer of such particles in close contact.

Catalytic reduction of nitrates in water on Pt promoted Cu hydrotalcite-derived catalysts: Effect of the Pt–Cu alloy formation

In this work, the role of the Pt–Cu interaction and the influence of the Pt metal loading in the catalytic reduction of nitrates in water have been studied, using Pt supported on CuMgAl mixed oxides catalysts in a continuous reactor. Following three Pt impregnation protocols different surface chemistries were obtained, as confirmed by BET, TPR, HRTEM, XRD and FTIR spectroscopy. In the first protocol, the presence of Cu and Pt–Cu alloy formation has been promoted, whereas the second protocol leads to separated Pt and Cu particles in close contact. The third protocol leads to the presence of Cu, Pt and Pt–Cu alloy particles. The different catalytic behaviors were related to the differences in the surface metal chemistry of the samples. Low ammonium formation was detected in all cases but nitrite concentrations need to be improved to fulfill the maximum admissible concentration of the EU legislation. It is concluded that: (i) the presence of Pt–Cu alloy particles leads to an increase in nitrogen selectivity, enhancing the nitrite reduction but showing lower nitrate conversion, and (ii) to maximize the nitrate conversion it is necessary to obtain mainly Pt particles interacting with Cu and Pt–Cu alloy particles.

A Histologic and Histomorphometric Evaluation of Anorganic Bovine Bone Retrieved 9 Years After a Sinus Augmentation Procedure

Anorganic bovine bone (ABB) has been shown to have osteoconductive properties and no inflammatory or adverse responses as grafting materials used in sinus augmentation procedures. Despite these successful results, histologic data in humans over the long-term period are scarce. The purpose of this study was to analyze the histomorphometric data 9 years after surgery in a case of maxillary sinus augmentation using ABB. The histologic evaluation was performed in five different thin sections of the specimen, comparing histomorphometric measures for newly formed bone, marrow spaces, biomaterial particles remnants, and number of osteocytes embedded in both trabecular bone and bone tissue near the ABB. The investigation was carried out by means of scanning electron microscopy and brightfield and circularly polarized light microscopy. We observed a mean amount of newly formed bone of 46.0% +/- 4.67%, ABB remnants of 16.0% +/- 5.89%, and marrow spaces of 38.0% +/- 8.93%. The osteocyte index was 4.43 for bone around ABB and 3.27 in the trabecular bone at a distance from the particles. After 9 years, the tissue pattern appeared composed by residual ABB particles in close contact to the newly formed bone. The bone mineralized matrix around the ABB had collagen fibers randomly oriented and more osteocytes embedded. The results demonstrate both a high level of osteoconductivity and a "biomimetic" behavior over the long term.

31P Solid-State Nuclear Magnetic Resonance Study of the Sorption of Phosphate onto Gibbsite and Kaolinite

Sorption of phosphate onto gibbsite (gamma-Al(OH)3) and kaolinite has been studied by both macroscopic and 31P solid-state NMR measurements. Together these measurements indicate that phosphate is sorbed by a combination of surface complexation and surface precipitation with the relative amounts of these phases depending on pH and phosphate concentration. At low pH and high phosphate concentrations sorption is dominated by the presence of both amorphous and crystalline precipitate phases. The similarity between the single-pulse and CP/MAS NMR spectra suggests that the precipitate phases form a thin layer on the surface of the particles in close contact with protons from surface hydroxyl groups or coordinated water molecules. While the crystalline phase is only evident on samples below pH 7, amorphous AlPO4 was found at all pH and phosphate concentrations studied. As pH was increased the fraction of phosphate sorbed as an inner-sphere complex increased, becoming the dominant surface species by pH 8. Comparison of sorption and NMR results suggests that the inner-sphere complexes form by monodentate coordination to singly coordinated Al-OH sites on the edges of the gibbsite and kaolinite crystals. Outer-sphere phosphate complexes, which are readily desorbed, are also present at high pH.

Highly active gold-ceria catalyst for the room temperature oxidation of carbon monoxide

Ceria supported gold catalysts containing 0.1–5 wt.% gold are prepared by deposition–precipitation technique in which the precipitate is subjected to ultrasound treatment and aging in the parent solution at 65 °C for 2 h prior to filtration and drying. The catalysts are found to be very active for the room temperature oxidation of CO. Au/CeO 2 catalyst containing as low as 1 wt.% Au is found to be a highly active catalyst for the room temperature oxidation of CO to CO 2 with complete conversion of CO and specific activity up to 490 × 10 −4 mol CO s −1 g Au −1. The catalyst shows good stability and sustains its high activity for a prolonged period. Aging of the catalyst in the parent solution is found to be important in obtaining a highly active catalyst. The catalysts are characterized by XRD, SEM, TEM, XPS and TPR/TPD. TPR, TPD and XPS studies suggest that the active site for CO oxidation may be a combination of Au + OH − and metallic gold in interface with reduced Ce 3+ sites. In other words, the presence of highly dispersed gold particles in close contact with the ceria surface defects is vital for the superior performance of the catalyst.

A metal–polymer composite with unusual properties

Electrically conductive composites that contain conductive filler dispersed in an insulating polymer matrix are usually prepared by the vigorous mixing of the components. This affects the structure of the filler particles and thereby the properties of the composite. It is shown that by careful mixing nano-scale features on the surface of the filler particles can be retained. The fillers used possess sharp surface protrusions similar to the tips used in scanning tunnelling microscopy. The electric field strength at these tips is very large and results in field assisted (Fowler–Nordheim) tunnelling. In addition the polymer matrix intimately coats the filler particles and the particles do not come into direct physical contact. This prevents the formation of chains of filler particles in close contact as the filler content increases. In consequence the composite has an extremely high resistance even at filler loadings above the expected percolation threshold. The retention of filler particle morphology and the presence of an insulating polymer layer between them endow the composite with a number of unusual properties. These are presented here together with appropriate physical models.

FTIR study of low-temperature water-gas shift reaction on gold/ceria catalyst

Chemisorption and reactivity of the molecules involved in the water-gas shift (WGS) reaction on gold/ceria catalyst have been studied at 90 and 300 K by FTIR spectroscopy. Forward and reverse WGS reaction at 300 K and up to 573 K have been investigated, too. The FTIR results show that gold causes a strong modification of the surface properties of the support. The nanosized metallic gold particles in close contact with defective ceria play an essential role for the genesis of high catalytic activity in WGS reaction at low temperature and appear to be of crucial importance in explaining the remarkably high stability of this catalytic system. An electronic interaction between small gold metallic nanoparticles and ceria has been evidenced.

Characterization of Pd/MgO Catalysts: Role of Organometallic Precursor–Surface Interactions

Pd(acac)2 was supported on a highly dehydroxylated and decarbonated magnesium oxide surface (MgO500), on an untreated MgO surface (MgOAIR), and on a silica (SiO2450). EXAFS and DRIFT data indicate that the organopalladium complex is adsorbed intact on all the surfaces, but its dispersion is dependent on the nature of the surface. On MgO500, dispersion at the molecular level occurs, in contrast to the formation of islands of multilayers on MgOAIR and SiO2450. The final properties of the metal phase, formed by H2 treatment at 500°C, are dependent on precursor–surface interactions. HRTEM analysis shows a narrow distribution of the metal particles centered at 0.6 nm on MgO500, and a wide diameter distribution around 6.1 and 9.9 nm on MgOAIR and SiO2450, respectively. In the n-heptane dehydrocyclization at 500°C, the highest selectivity is shown by Pd/MgO500 catalysts and it is consistent with a predominant fraction of very small particles in close contact with surface basic sites.