Packing Volume Research Articles

Effect of long-range repulsive Coulomb interactions on packing structure of adhesive particles.

The packing of charged micron-sized particles is investigated using discrete element simulations based on adhesive contact dynamic model. The formation process and the final obtained structures of ballistic packings are studied to show the effect of interparticle Coulomb force. It is found that increasing the charge on particles causes a remarkable decrease of the packing volume fraction ϕ and the average coordination number 〈Z〉, indicating a looser and chainlike structure. Force-scaling analysis shows that the long-range Coulomb interaction changes packing structures through its influence on particle inertia before they are bonded into the force networks. Once contact networks are formed, the expansion effect caused by repulsive Coulomb forces are dominated by short-range adhesion. Based on abundant results from simulations, a dimensionless adhesion parameter Ad*, which combines the effects of the particle inertia, the short-range adhesion and the long-range Coulomb interaction, is proposed and successfully scales the packing results for micron-sized particles within the latest derived adhesive loose packing (ALP) regime. The structural properties of our packings follow well the recent theoretical prediction which is described by an ensemble approach based on a coarse-grained volume function, indicating some kind of universality in the low packing density regime of the phase diagram regardless of adhesion or particle charge. Based on the comprehensive consideration of the complicated inter-particle interactions, our findings provide insight into the roles of short-range adhesion and repulsive Coulomb force during packing formation and should be useful for further design of packings.

Thermal, optical and spectroscopic studies of boro-tellurite glass system containing ZnO

A series of stable and transparent glasses with the composition (72–0.5x)TeO2–(27.5–0.5x)B2O3–xZnO–0.5V2O5 (x=0, 6, 12, 18, 24 and 30mol%) were prepared by melt quenching technique. These glasses were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman, differential scanning calorimetry (DSC), EPR and optical absorption. XRD and DSC analysis confirmed the glassy nature of the prepared samples. The physical properties such as density (ρ), molar volume (Vm) and oxygen packing density (OPD) were calculated. FTIR and Raman studies showed that the glass network consists of TeO3, TeO3+1, TeO4, BO3 and BO4 units. These studies also revealed that TeO4 units transform into TeO3 units and BO4 into BO3 units with the addition of ZnO content at the expense of both B2O3 and TeO2 glass forming oxides. From DSC, it was found that the glass transition temperature (Tg) increases with the increase of ZnO content. The thermal stability (ΔT=To−Tg) of the sample with ZnO of 30mol% was found to be maximum (166°C).The optical band gap energy (Eopt) and Urbach energy (∆E) values of the glass system were calculated using the optical absorption data. Using electron paramagnetic resonance (EPR) spectra of the present glasses the spin Hamiltonian parameters of VO2+ ions were calculated.

Physical and absorption properties of titanium nanoparticles incorporated into zinc magnesium phosphate glass

We report the influences of Titania (TiO2) nanoparticles (NPs) on the physical and optical properties of melt quench synthesized zinc magnesium phosphate glasses. Five glass samples with composition (42−x)P2O5–50ZnO–8MgO–xTiO2, where x=0, 1, 2, 3, 4mol% are prepared and characterized. XRD pattern verified the amorphous nature of all samples. TEM images manifested the growth of Ti NPs of average size≈5.78nm. TiO2 NP concentration dependent variation in the physical properties including glass density, molar volume, molar refractivity, electronic polarizability and ionic packing density are determined. The values of glass refractive indices, density and ionic packing density are increased with the increase of TiO2 NP contents. Conversely, the Urbach energy, direct and indirect optical band gap are found to decrease with the increase of TiO2 NP concentration. These glass compositions may be potential for various solid state devices including laser.

Gold Nanoparticle Quantitation by Whole Cell Tomography.

Many proposed biomedical applications for engineered gold nanoparticles require their incorporation by mammalian cells in specific numbers and locations. Here, the number of gold nanoparticles inside of individual mammalian stem cells was characterized using fast focused ion beam-scanning electron microscopy based tomography. Enhanced optical microscopy was used to provide a multiscale map of the in vitro sample, which allows cells of interest to be identified within their local environment. Cells were then serially sectioned using a gallium ion beam and imaged using a scanning electron beam. To confirm the accuracy of single cross sections, nanoparticles in similar cross sections were imaged using transmission electron microscopy and scanning helium ion microscopy. Complete tomographic series were then used to count the nanoparticles inside of each cell and measure their spatial distribution. We investigated the influence of slice thickness on counting single particles and clusters as well as nanoparticle packing within clusters. For 60 nm citrate stabilized particles, the nanoparticle cluster packing volume is 2.15 ± 0.20 times the volume of the bare gold nanoparticles.

Physical, mechanical and structural properties of BaO–CaF2–P2O5 glasses

Mechanical properties and structure of melt-quenched ternary barium phosphate glasses belonging to the composition (50−X)BaO–XCaF2–50P2O5 (X=0 to 10mol%) were studied using Vickers indentation and vibrational spectroscopy. Elastic moduli of prepared samples were calculated using the Makishima and Mackenzie (M–M) model. Density of glasses was measured using the Archimedes method, while molar volume and atomic packing density were calculated from measured density to study structural changes in the glass matrix. Vickers hardness and brittleness increased and fracture toughness decreased with increase in CaF2 content. This can be attributed to increase in the compactness of phosphate bonds and reduction in the molar volume of glasses with partial substitution of Ba2+ with Ca2+. Infrared and Raman spectroscopies revealed that the glass network mainly consisted of metaphosphate units arranged in chain and ring structures together with small amounts of ultraphosphate and pyrophosphate units.

Synchrotron radiation phase-contrast computed tomography study on self-assembly of polystyrene colloidal crystals via solvent evaporation

The colloidal crystals of polystyrene (PS) spheres were assembled from the emulsion of PS by an in situ solvent evaporation method. The local internal 3D structure of the fabricated colloidal crystals was noninvasively characterized with synchrotron radiation phase-contrast computed tomography. The satisfactory contrast difference was obtained and the shapes of the spheres were clearly reconstructed. Based on the slice images, the two-stage mechanism of crystallization process for in situ evaporation was suggested. In the initial stage, stable nucleation and growth result in formation of an ordered face-centered cubic structure with the sphere volume fraction 70.2%, which is very close to the maximum sphere packing volume fraction 74%. In the second stage, the sphere concentration in suspension decreased too much to support an adequate sphere transfer through the solvent flux to the growth front. The transformation from square to hexagonal lattice did not therefore complete under the same evaporation rate. This incompleteness results in formation of local ordered structure with randomly arranged hexagonal and square packing with a slightly low volume fraction of 68.41%.

Thermal characterization of novel magnesium oxyhalide bismo-borate glass doped with VO2+ ions

In the present report, physical and thermal characterizations of magnesium oxyhalide bismuth borate glasses in the composition range of $$ x{\text{Mg}}X_{2} \left( {X = {\text{F}},\,{\text{Br}}} \right) \, \cdot \, \left( {30 - x} \right){\text{MgO }}\cdot \, 50{\text{B}}_{2} {\text{O}}_{3} \cdot \, 20{\text{Bi}}_{2} {\text{O}}_{3} $$ (x = 0, 2, 5, 7 and 10) containing 2 mol% of V2O5 prepared by standard melt-quench technique have been discussed. The non-crystalline nature of prepared glasses has been identified through peak free X-ray diffraction profiles. Density (D), molar volume (V m) and oxygen packing density have been measured/calculated, and varying trends are discussed by relating with physical changes governed in prepared glass structures on increasing/changing the halogen (fluoride/bromide) ions. The differential thermal analysis (DTA) and thermogravimetry have been carried out in the temperature range of 200–900 °C. Glass transition temperature (T g) and melting temperature (T m) are determined from the DTA thermographs. The glass stability parameter, T g/T m is calculated from the obtained values of characteristic temperatures and a sudden decrease in stability at x = 5.0 is observed in both series which reflects that halide ions (F−/Br−) modify the glass structure at low concentrations (up to 5.0 mol%) and contribute to glass network formation at high concentrations (>5.0 mol%). Infrared absorption spectra have been recorded in the mid-IR range and evaluated to report the possible cause of band vibrations present in the spectra.

Thermodynamic Properties and Free Volume Analyses of Polycarbonates by a Combined Experimental and Molecular Simulation Method

A combined experimental and computational approach is applied to amorphous polycarbonates (PCs) to link the macroscopic behavior and molecular features. The Simha–Somcynsky equation of phase (EOS) provides a more accurate description than the Tait EOS for describing the pressure–volume–temperature (PVT) relationship and thermal expansivity. The relationship between the specific volume and the hole free volume was investigated using PVT measurements, positron annihilation lifetime spectra, and molecular dynamics (MD) techniques, to examine the correlations between changes in the behavior of specific volume and molecular packing. We found that the specific volume and hole free volume have linear relationships with temperature. However, the occupied volume displayed remarkable compressibility. The analyses revealed that the PC with side methyl groups and long C–Si bonds contributed to the formation of large free volume. The MD results validate the effectiveness of molecular simulation techniques in designing materials at the molecular level.

Gauze packing for massive hemorrhage in pelvic fracture

Objective To investigate the clinical value of gauze packing for haemodynamically unstable pelvic fracture. Methods Between January 2006 and January 2014, gauze packing was used to treat haemodynamically unstable pelvic fracture in 42 patients consisting of 23 males and the 19 females aged 34.2 years (range, 18 to 54 years). AO classification of the fracture was type B1 in 9, B2 in 5, B3 in 3, C1 in 13, C2 in 4, and C3 in 8 patients. All the patients were diagnosed with hypovolemic shock upon admission with the systolic pressure of (75.4±4.3)mmHg and heart rate of (126.5±12.4)beats/min. Injury severity score (ISS) was (38.7±6.2)points. Anti-shock treatment, internal or external fixation of pelvic ring, and gauze packing were performed immediately to control the hemorrhage following pelvic fracture. Results Systolic pressure was (95.2±4.6)mmHg and mean heart rate was declined to (85.4±13.2)beats/min after pelvis volume control and gauze packing, with significant differences compared to these preoperatively (P<0.05). Red blood cell transfusion before internal or external fixation and gauze packing was (15.0±2.4)units versus (8.3±1.5)units within the first postoperative 24 hours (P<0.05). Twenty-four out of the 42 patients underwent temporary abdominal aorta occlusion. Six patients died postoperatively with the death rate of 14%. Mean time of removing the packing gauze was (51.4±10.3)hours (range, 24-168 hours). Conclusion Anti-shock treatment with concurrent gauze packing and pelvis volume control is effective to arrest the massive hemorrhage in hemodynamically unstable pelvic fracture. Key words: Pelvis, fractures; Hemorrhage; Surgical sponges; Damage control

Kinetic performance of CO2 absorption into a potassium carbonate solution promoted with the enzyme carbonic anhydrase: Comparison with a monoethanolamine solution

Development of enzyme-mediated solvents are regarded as a potential option to overcome the energy use disadvantages associated with the benchmark monoethanolamine (MEA) solvent for post-combustion CO2 capture. In this work, the kinetics of CO2 absorption into a 20wt% potassium carbonate (PC) solution promoted with the enzyme carbonic anhydrase (CA) was investigated using a stirred tank reactor. Experimental results showed no noticeable change in the intrinsic activity of the CA enzyme with increasing CO2 loading in PC solution. A rate-based mass transfer analysis was conducted using the enzymatic kinetics measured, and results revealed that in a packed-bed column, the CO2 absorption rates into a lean and rich PC solution with 3gL−1 CA were 50% lower and 2.2 times higher, respectively, than those into their 5M MEA counterparts. The liquid-phase mass transfer resistance was dominant for both PC- and MEA-based systems. Modeling results revealed the effective packing volume of the absorber with PC in the presence of 10gL−1 CA was only slightly larger than that with MEA for post-combustion CO2 capture.

Very high methane uptake on activated carbons prepared from mesophase pitch: A compromise between microporosity and bulk density

Two petroleum residues were pyrolyzed under two different conditions to obtain pitches with low or high mesophase content. The effect of the KOH: precursor ratio and the activation temperature on the packing density and porous texture of the carbons have been studied and optimized. Activated carbons combining high micropore volume (>1cm3/g) and high packing density (0.7g/cm3) have been successfully prepared. Regarding excess methane adsorption capacities, the best results (160cm3 (STP)/cm3 at 25°C and 3.5MPa) were obtained using the pitch with the higher content of the more organized mesophase, activated at relatively low temperature (700°C), with a medium KOH: precursor ratio (3:1). Some of the activated carbons exhibit enhanced adsorption capacity at high pressure, giving values as high as 175cm3 (STP)/cm3 at 25°C and 5MPa and 200cm3 (STP)/cm3 at 25°C and 10MPa (the same amount as in an empty cylinder but at half of the pressure), indicating a contribution of large micropores and narrow mesopores to adsorption at high pressure. The density of methane in pores between 1 and 2.5nm at pressure up to 10MPa was estimated to understand their contribution to the total adsorption capacity.

Bulk and interfacial stresses in suspensions of soft and hard colloids

We explore the influence of particle softness and internal structure on both the bulk and interfacial rheological properties of colloidal suspensions. We probe bulk stresses by conventional rheology, by measuring the flow curves, shear stress versus strain rate, for suspensions of soft, deformable microgel particles and suspensions of near hard-sphere-like silica particles. A similar behaviour is seen for both kinds of particles in suspensions at concentrations up to the random close packing volume fraction, in agreement with recent theoretical predictions for sub-micron colloids. Transient interfacial stresses are measured by analyzing the patterns formed by the interface between the suspensions and their solvent, due to a generalized Saffman–Taylor hydrodynamic instability. At odds with the bulk behaviour, we find that microgels and hard particle suspensions exhibit vastly different interfacial stress properties. We propose that this surprising behaviour results mainly from the difference in particle internal structure (polymeric network for microgels versus compact solid for the silica particles), rather than softness alone.

Molecular and biochemical characterizations of a new low-temperature active mannanase.

A mannanase-coding gene was cloned from Sphingobacterium sp. GN25 isolated from the feces of Grus nigricollis. The gene encodes a 371-residue polypeptide (ManAGN25) showing less than 74% identity with a number of hypothetical proteins and putative glucanases and mannanases. Before experiment's performance, ManAGN25 was predicted to be a low-temperature active mannanase based on the molecular characterization, including (1) ManAGN25 shared the highest identity of 41.1% with the experimentally verified low-temperature active mannanase (ManAJB13) from Sphingomonas sp. JB13; (2) compared with their mesophilic and thermophilic counterparts, ManAGN25 and ManAJB13 had increased number of amino acid residues around their catalytic sites; (3) these increased number of amino acid residues built longer loops, more α-helices, and larger total accessible surface area and packing volume. Then the experiments of biochemical characterization verified that the purified recombinant ManAGN25 is a low-temperature active mannanase: the enzyme showed apparently optimal activity at 35-40°C and retained 78.2, 44.8, and 15.0% of its maximum activity when assayed at 30, 20, and 10°C, respectively; the half-life of the enzyme was approximately 60min at 37°C; the enzyme presented a K m of 4.2mg/ml and a k cat of 0.4/s in McIlvaine buffer (pH7.0) at 35°C using locust bean gum as the substrate; and the activation energy for hydrolysis of locust bean gum by the enzyme was 36.0kJ/mol. This study is the first to report the molecular and biochemical characterizations of a mannanase from a strain.

Effects of fluid–pebble interactions on mechanics in large-scale pebble-bed reactor cores

In Pebble-Bed Modular Reactor (PBMR) systems, typical representatives of large-scale fluid–particle energy systems, the gaseous coolant has strong interactions with the fuel pebbles that slowly move downward. To accurately predict the coolant dynamics and fuel bed mechanical properties, the fluid–pebble interactions should be taken into consideration in the mechanical modeling of the core. However, previous research usually neglected these interactions in the pebble flow analysis, assuming a fixed bed that is not affected by the coolant. The effects of these interactions on the core behavior remain unknown and have never been fully addressed. To investigate the interaction effect on the pebble flow mechanics, a coupled multi-physics model is employed which accounts for the fluid–pebble interactions in the dynamics simulations of a large annular nuclear reactor system. Discrete Element Method is used to simulate the pebble motion and predict important granular properties such as pebble packing density, coordination number and contact stress distributions. Computational Fluid Dynamics is employed to predict the locally averaged coolant properties. The simulations of pebble flow and coolant flow are coupled through the calculation and exchange of fluid–pebble interaction forces between two simulation solvers at a fixed time interval. To observe the interaction effect, decoupled simulations are also performed as references for comparison, i.e. a single pebble flow simulation without interactions with coolant, followed by a single coolant flow simulation in a static fixed packed bed. The comparison indicates that the interactions have significant effects on the local mean pebble contact force and observable effects on the axial and radial distributions of pebble volume packing fraction, as well as the pebble flow velocity/pressure profiles. The interaction effects are especially noticeable in the regions near the wall and close to the core inlet. The change in the pebble packing distribution will consequently bring in discrepancies in the distributions of axial and radial fluid velocity and pressure. Therefore, the interactions between coolant and pebble cannot be negligible in the study of the thermal–hydraulic properties of large-scale fluid–particle energy systems, although some macroscopic properties of the pebble flow (such as the coordination number distribution) are barely changed by the fluid–pebble interactions.

Engineering and sustainability performance of self-compacting palm oil mill incinerated waste concrete

Abstract The different stages in the processing of palm oil generate various types of waste by-products, which have to be disposed of appropriately for a cleaner environment and to reduce pollution. In this study, palm oil clinker (POC), one of the by-products of the palm oil mill, was utilized in the production of self-compacting concrete (SCC). SCC has diverse types of structural application due to its own enhanced self-consolidating behaviour. The proportioning of the mixes was based on particle packing, which integrates both aggregate packing and void volume for a mix of aggregates. Combinations of POC and natural aggregate were studied at various substitution levels ranging from 0% to 100% for both fresh and hardened properties. In addition, a few of the results were integrated into sustainability components to evaluate the effectiveness of the concrete both economically and environmentally. It was found that POC aggregate require three times lower energy consumption for preparation compared to conventional aggregate. Overall, POC incorporation showed enhanced structural efficiency with a significant reduction in cost and energy usage. Furthermore, the sustainability of the construction industry can be conserved with the introduction of POC as an alternative source for concreting work.

Discrete element modelling of flexible fibre packing

This paper presents Discrete Element Model simulations of packing of non-cohesive flexible fibres in a cylindrical vessel. No interstitial fluid effects are modelled. Each fibre-particle is modelled as a series of connected sphero-cylinders. In an initial study each particle is modelled a single rigid sphero-cylinder; the method has been used before but this study considers higher aspect ratios up to 30. This posed some modelling challenges in terms of stability which were overcome by imposing limits on the particle angular velocity. The results show very good agreement with experimental data in the literature and more detailed in-house experiments for packing volume fraction. Model results on particle orientation are also shown. The model is developed to include flexibility by connecting sphero-cylinders as sub-elements to describe a particle. Some basic tests are shown for the joint model that connects the sub-elements. The simulation results show similar trends to the rigid particle results with increased packing fraction. The effects of number of sub-elements, joint properties and contact friction are examined. The model has the potential for predicting packing of fibrous particles and fibre bundles relevant to the preparation of preforms for the production of discontinuously-reinforced polymer, ceramic and metallic matrix composites.

Sm3+:Ag NPs assisted modification in absorption features of magnesium tellurite glass

Metallic nanoparticles (NPs) assisted enhancements in absorption and emission cross-section of tellurite glass is the present challenge. The influences of samarium (Sm3+) ions and silver (Ag) NPs ratio on physical and optical absorption properties of melt quench synthesized magnesium tellurite glasses are reported. XRD patterns verify the amorphous nature of glasses. Glass density, molar volume and ionic packing fraction are discerned to be in the range of 4.92–5.0gcm−3, 29.82–30.26cm3mol−1 and 0.452–0.446, respectively. Moderate reduction potential of tellurite glass converted Ag1+ to Ag0 via single step process and NPs are formed. TEM image manifest the existence of NPs of average diameter ∼16.94nm having Gaussian size distribution. The significant changes in structural properties in the presence of Ag NPs are discussed in terms of TeO4 tetrahedra distortion and network depolymerization process. The Sm3+:Ag NPs dependent variation in physical properties are ascribed to the alteration in the number of bridging oxygen to non bridging (NB) one. Enhancement in absorption intensity due to the local field effects of Ag NPs is attributed to the changes in Sm–O bond strength. Optical energy band gap (2.81–3.18eV) and Urbach energy (0.18–0.24eV) are found increase and decrease, respectively with the increase of Sm3+:Ag NPs up to 1.33 then quenches and enhances, respectively thereafter which are related to the changes in cross-link and NBO numbers. The FTIR spectra reveal modification in network structures evidenced from vibrational wave-number shifts of TeO4 and TeO3 structural units. The observed notable increase in HOH vibration mode suggests its helpfulness in promoting the absorption of water and light. It is asserted that the physical, optical and structural properties of magnesium tellurite glass can be tuned by controlling Sm3+:Ag NPs.

Effect of silver nanoparticles incorporated with samarium-doped magnesium tellurite glasses

Silver nanoparticles (Ag NPs) are incorporated in samarium doped tellurite glass of a composition (89−x)TeO2–10MgO–1Sm2O3–xAgCl, where 0.0≤x≤0.6mol%, by a melt quenching technique. It is found that all the glasses are amorphous in nature, and the existence of Ag NPs with an average size of 16.94nm is confirmed by Transmission Electron Microscopy. Meanwhile, their physical properties such as glass density, molar volume and ionic packing density are computed utilizing the normal method. The density and ionic packing density are observed to decrease with increasing Ag NPs, but increase when the Ag NPs are beyond 0.2mol%. On the other hand, the molar volume behaves exactly opposite to the increase in Ag NPs content. It decreases when the Ag NPs content value is more than 0.2mol%. The optical energy band gap and Urbach energy are evaluated from the absorption spectra in the range of 200–900nm at room temperature. It is also observed that the direct and indirect optical energy band gaps reduce with Ag NPs content, but enhance when the Ag NPs are beyond 0.2mol%. Meanwhile, the Urbach energy is found to increase as the Ag NPs content is increased but decreases when Ag NPs is 0.2mol%. The refractive index is deduced from indirect optical energy band gap. Meanwhile, molar refraction and electronic polarizability have been calculated from the Lorentz–Lorentz relation. Refractive index and electronic polarizability are also observed to raise with Ag NPs content, but drop off when Ag NPs content is more than 0.2mol%. In this paper, all properties are discussed with respect to the Ag NPs concentration.

Structure–property relationships of Fe2O3 doped novel oxyfluorophosphate glasses

The relationship between the network structure and properties of iron containing novel oxyfluorophosphate glasses with the composition 20ZnO–20CaF2–(60−x)P2O5:xFe2O3 with 0≤x≤5mol% has been studied. The density, molar volume, oxygen molar volume and oxygen packing density studies helped to understand the structural changes occurring in these glasses. The dissolution rate and pH of the immersion liquid are measured to explain the chemical durability of the glasses. Differential thermal analysis studies are carried out to analyze the thermal stability of the studied glasses. Deconvoluted infrared and Raman spectra of the glasses are analyzed to determine the relative areas of the vibrational bands corresponding to different structural units. Analysis of the vibrational spectra in conjunction with the other properties reveals that Fe2O3 enters the glass matrix in the form of Fe2+ and Fe3+ ions through the formation of more stable POFe2+ and POFe3+ bonds at the expense of easily hydrated POP bonds.

Macroscopic model with anisotropy based on micro–macro information

Physical experiments can characterize the elastic response of granular materials in terms of macroscopic state variables, namely volume (packing) fraction and stress, while the microstructure is not accessible and thus neglected. Here, by means of numerical simulations, we analyze dense, frictionless granular assemblies with the final goal to relate the elastic moduli to the fabric state, i.e., to microstructural averaged contact network features as contact number density and anisotropy. The particle samples are first isotropically compressed and then quasi-statically sheared under constant volume (undrained conditions). From various static, relaxed configurations at different shear strains, infinitesimal strain steps are applied to “measure” the effective elastic response; we quantify the strain needed so that no contact and structure rearrangements, i.e. plasticity, happen. Because of the anisotropy induced by shear, volumetric and deviatoric stresses and strains are cross-coupled via a single anisotropy modulus, which is proportional to the product of deviatoric fabric and bulk modulus (i.e., the isotropic fabric). Interestingly, the shear modulus of the material depends also on the actual deviatoric stress state, along with the contact configuration anisotropy. Finally, a constitutive model based on incremental evolution equations for stress and fabric is introduced. By using the previously measured dependence of the stiffness tensor (elastic moduli) on the microstructure, the theory is able to predict with good agreement the evolution of pressure, shear stress and deviatoric fabric (anisotropy) for an independent undrained cyclic shear test, including the response to reversal of strain.