Surface Energy Of Particles Research Articles

Quantitative measurements of changes in agglomerate size with oscillatory shear strain in polymer nanocomposites using online dielectric analysis

Shear strains during processing affect the agglomerate size of nanoparticles in nanocomposites and their final behavior in various applications. In this study, dielectric characterization technique as a novel and well-effective method is applied for quantitative measurement of average agglomerate size in polymer nanocomposites under shear strain sweep, combining with an existing analytical model. Examining how changes in filler content, surface energy and polarity of particles and the matrix control the strain-dependency of agglomerates size, two different nanoparticles, namely, titanium dioxide (TiO2) and carbon black (CB), with same average diameters and volumes were added to polystyrene (PS). It was found that larger agglomerates were present in the PS/CB nanocomposite prior to shearing and the CB agglomerates were less prone to deagglomeration under shear strain. This behavior was attributed to higher polarity of CB nanoparticles, leading to higher tendency for agglomeration and higher resistance to shear, in respect to TiO2 nanoparticles.

Microstructural transformations of swelling clay minerals

An original model of microstructural transformations during clay swelling is considered, a thermodynamic and physical-mechanical description of the properties of clays during the process of swelling in vapors and aqueous solutions is given. The model proposed to explain these properties is based on the concept of mutual displacement of clay particles in clay rock aggregates during swelling with the formation of new pores between clay particles forming crystallites and aggregates. The model is based on the mechanism of utilization of the excess surface energy of clay particles during hydration, taking into account the influence of certain environmental parameters, for example, the concentration of the solution, through a change in the mutual orientation of clay particles, mainly due to rotations or shifts relative to each other, with the formation of an area available for further wetting free surface. In the thermodynamic description, such a process will manifest itself in a change in the surface interaction energy on the wetted areas of the particles when moving during mutual shifts and rotations. At the same time, one of the most important parameters of clay rock, microporosity, also changes. In this work, this phenomenon was experimentally studied using the methods of static moisture capacity and Mössbauer (NGR) spectroscopy. The proposed model makes it possible to explain the features of the clay hydration process and to compare the observed experimental data with the theoretical description of the clay swelling process.

Energy multi-scale method to analyze the scale effect of soil particles

As a common geological material, soil is a key aspect of construction engineering. Soil has typical multi-scale characteristics, but current multi-scale methods analyze these characteristics only in regard to geometric space. More exploration of the coupling influence mechanism of the basic properties of particles on the microstructure and macroscopic properties of soil is needed. This study analyzed the influence of geometric scale and mineral composition on the surface energy of particles at the microscopic level for development of the energy multi-scale method. Experiments were performed to determine the influence of mineral composition and particle size on the plasticity index (Ip) of the soil, and experimental results are discussed and interpreted quantitatively using the energy multi-scale method. The conclusions derived from this work are as follows: 1) the mineral composition and particle size of the soil can cause interface and surface effects; 2) the comprehensive ratio of micro-force to weight (CRFW) of the particles can be determined using the energy multi-scale method and quantitatively reflects the influence of particle size and mineral composition on the microscopic properties of the soil; and 3) the energy multi-scale method explains the mechanism of the plasticity index of soil and has allowed identification of a new division of soil plasticity. When the CRFW was used as the control index, the plasticity index of the three materials was practically the same, even if the mineral composition and particle sizes of the three materials were different.

Novel magnetic catalysts for organic pollutant degradation via contact electro-catalysis

Contact-electro-catalysis (CEC) has been proposed as an efficient mechanism for organic pollutant degradation. However, the effects of chemical and physical properties of catalysts on the CEC efficiency have not been reported so far. Importantly, solving the secondary pollution caused by micro-nano catalysts due to the difficulty of recycling and inability to degrade is another bottleneck for achieving the commercial application of CEC. In this work, we synthesized a micro-nano catalyst with tunable chemical groups on the surface based on magnetic nanoparticles for the degradation of methyl orange (MO) via CEC. With the increase of the electronegativity of the chemical groups (R-F>R-CH3 >R-NH2), the degradation efficiency of MO also be improved obviously. The low surface energy of hydrophobic particles leads to the existence of a threshold (e.g., 20 mg R-F per 50 ml MO solution) for the exposed total surface area of the catalyst in aqueous solution, which is the main reason for the nonlinear increase of catalyst mass and CEC efficiency. Previously reported toxic non-degradable fluoride catalysts (e.g., FEP, PTFE) can be effectively replaced by catalysts R-CH3. Using the R-CH3 in CEC, the degradation efficiency of MO reaches 99% within 2 h. The micro-nano R-CH3 catalyst can be recycled by nearly 100% through the magnetic separator, and the catalytic efficiency can reach more than 97% after ten cycles of CEC. We expect this attractive catalyst to be a promising candidate for applications in large-scale organic pollutant degradation systems although more work on system parameter optimization needs to be further addressed.

A bubble coalescence kernel combining the characteristics of the film drainage, energy, and critical velocity models

A novel coalescence kernel with high predictive properties is constructed to be used within the population balance framework. The kernel includes the product of a collision frequency term and a novel binary coalescence probability expression. The probability expression employs critical velocity estimations from film drainage simulations that also considers particle surface and kinetic energies. Thus, the proposed expression possesses characteristics of all three commonly used approaches: film drainage, energy, and critical velocity models. The probability of a collision having a certain velocity and angle is considered through probability density functions while adapting to the Eulerian frame. A maximum collision angle that allows coalescence is defined. The kernel is free of artificially introduced tuning parameters and predicts the size distributions in bubbly pipe flow experiments exceptionally well, including complex behaviors such as emergence of secondary peaks in the distribution. The theory presented is equally valid for bubbles and droplets.

A Study on the Physical Properties of Banana Straw Based on the Discrete Element Method

To improve the application of discrete element models (DEM) to the design of agricultural crushers, in this study a new highly accurate model is elaborated. The model takes into account the fiber structure, porous nature of the material and the leaf sheath coating structure. Dedicated experimental tests are conducted to determine the required “intrinsic” and basic contact parameters of the considered banana straw materials. A large number of bonding parameters are examined in relation to the particle aggregation model in order to characterize different actual banana straws. Using the particle surface energy contact model, the viscosity characteristics of the crushed material are determined together with the related stacking angle (considered as the main response factor). Through single factor experiment analysis, it is found that when the surface energy is 0.9 J·m-2, the relative error between simulations and physical experiments is 5.288%.

True Molecular Composites: Unusual Structure and Properties of PDMS-MQ Resin Blends

Poly(dimethyl siloxane)-MQ rubber molecular composites are easy to prepare, as it does not require a heterophase mixing of ingredients. They are characterized by perfect homogeneity, so they are very promising as rubber materials with controllable functional characteristics. The manuscript reveals that MQ resin particles can significantly, more than by two orders of magnitude, enhance the mechanical properties of poly(dimethyl siloxane), and, as fillers, they are not inferior to aerosils. In the produced materials, MQ particles play a role of the molecular entanglements, so rubber molecular weight and MQ filler concentration are the parameters determining the structure and properties of such composites. Moreover, a need for a saturation of the reactive groups and minimization of the surface energy of MQ particles also determine the size and distribution of the filler at different filler rates. An unusual correlation of the concentration of MQ component and the interparticle spacing was revealed. Based on the extraordinary mechanical properties and structure features, a model of the structure poly(dimethyl siloxane)-rubber molecular composites and of its evolution in the process of stretching, was proposed.

Air-thermal oxidation of diamond nanopowders obtained by the methods of mechanical grinding and detonation synthesis

In this work, using the methods of X-ray phase analysis, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy, the features of the impact of annealing in air within the temperature range of t = 200÷÷550 °C on the morphology, elemental and phase composition, chemical state and structure of primary particles of nanopowders obtained by grinding natural diamond and the method of detonation synthesis are studied. It is shown that heat treatment in air at given values of temperature and heating time does not affect the elemental composition and atomic structure of primary particles of nanopowders obtained both by the methods of detonation synthesis (DND) and natural diamond grinding (PND). Using XPS, Raman spectroscopy, and transmission electron microscopy, it has been found that annealing in air within the temperature range of 400–550 °C results in the effective removal of amorphous and graphite-like carbon atoms in the sp2- and sp3-states from diamond nanopowders by oxidation with atmospheric oxygen. In the original DND nanopowder, containing about 33.2 % of non-diamond carbon atoms of the total number of carbon atoms, after annealing for 5 h at a temperature of 550 °C, the relative number of nondiamond carbon atoms in the sp2-state decreased to ~21.4 %. In this case, the increase in the relative number of carbon atoms in the sp3-state (in the lattice of the diamond core) and in the composition of oxygen-containing functional groups ranged from ~39.8 % to ~46.5 % and from ~27 % to ~32.1 %, respectively. In the PND nanopowder, which prior to annealing contains about 10.6 % of non-diamond carbon atoms in the sp2-state of the total number of carbon atoms, after annealing under the same conditions as the DND nanopowder, their relative number decreased to 7.1 %. The relative number of carbon atoms in the sp3-state increased from 72.9 % to 82.1 %, and the proportion of carbon atoms in the composition of oxygen-containing functional groups also slightly increased from 10.2 % to 10.8 %. It is demonstrated that the annealing of PND and DND nanopowders in air leads to a change in their color, they become lighter as a result of oxidation of non-diamond carbon by atmospheric oxygen. The maximum effect is observed at a temperature of 550 °C and an annealing time of 5 h. In this case, the weight loss of PND and DND nanopowders after annealing was 5.37 % and 21.09 %, respectively. The significant weight loss of DND nanopowder compared to PND is primarily caused by the high content of non-diamond carbon in the initial state and the high surface energy of primary particles due to their small size.

Revised Bell Particle‐Particle Drag Model of Bicomponent Cohesive Particles in a Fluidized Bed

AbstractIn the framework of the two‐fluid model, the kinetic theory of cohesive particle flow is applied to bicomponent cohesive particle flow. Based on the Bell particle‐particle drag model, the revised Bell particle‐particle drag model is presented for the bicomponent cohesive particle flow, considering the impact of the particle surface energy on the collision process. The flow characteristics of a mixture of Geldart group A particles and ultrafine particles were studied. The results show that the simulated elutriation rate is in good agreement with the experimental data, which verifies the effectiveness of the cohesive particles drag model.

Investigation on the Atomic Mechanism for Grain Refinement of Magnesium Alloys by Mg-Zr Master Alloy.

The valence electron structure, bond energy, and cohesive energy of Mg, Zr, and α-Mg containing Zr, and α-Zr containing Mg crystals were calculated using the empirical electron theory of solids and molecules (EET). The calculation results show that the bond and cohesive energies of Zr were much greater than those of Mg, so Zr particles could precipitate ahead of α-Mg in general magnesium alloy melts or insoluble Zr particles exist when the magnesium melt temperature is relatively low. The bond energy of α-Zr decreases with the increase in Mg content; therefore, at the end of the growth of Zr particles, the remaining Zr atoms in the melt exist in the form of Mg-Zr clusters. In order to reduce the surface energy of Zr particles, the outer surface of Zr particles tends to terminate with a Zr-Mg atomic layer, that is, a stable two-dimensional Zr-Mg atomic layer is formed first on the (0001) crystal surface of the outermost surface of Zr particles. Furthermore, on the basis of the calculated results, a complementary criterion to the edge-to-edge model of heterogeneous nucleation is also proposed. {ure and single Zr particles cannot become the heterogeneous nucleus of α-Mg, but when there is an atomic layer of two-dimensional Zr-Mg on its surface, the nucleation of particles can be activated. Mg atoms in the liquid phase preferentially attach to the Zr-Mg/Mg-Zr atomic layer on the surface of Zr particles to grow and form a stable ordered structure, which lastly transforms Zr particles into efficient heterogeneous cores.

Orientation Selection of Supported Au Nanoparticles on (111)- and (001)-Terminated SrTiO3 Substrates

Orientation-dependent performance has been demonstrated in different materials consisting of nanoparticles on substrates. The fabrication of desirably oriented nanoparticles requires knowledge of orientation selection rules. Based on the Wulff–Kaishew theory, our analysis shows that the energy-favorable orientation(s), is influenced by the surface energy of particles, in addition to the dominant factor, i.e., the energy difference between particle/substrate interfacial energy and surface energy of the substrate. To verify this, a model system of dewetted Au nanoparticles on SrTiO3 is studied. The {111}-terminated SrTiO3 supports only {111}-orientated Au particles, with the lowest interfacial energy. On the other hand, {100}-terminated SrTiO3 supports multiple Au particles, with {111}-, {100}-, {110}- orientations, as a possible result of close surface energy contributions. The above orientations can be additionally manipulated by changing the heat treatment temperature. Our results provide fundamental insights into fabricating supported nanoparticles for practical applications.

Developing Preparation Craft Platform for Solid Electrolytes Containing Volatile Components: Experimental Study of Competition between Lithium Loss and Densification in Li7La3Zr2O12.

Li7La3Zr2O12 (LLZO) is one of the most promising candidate solid electrolytes for high-safety solid-state batteries. However, similar to other solid electrolytes containing volatile components during high-temperature sintering, the preparation of densified LLZO with high conductivity is challenging involving the complicated gas-liquid-solid sintering mechanism. Further attention on establishing low-cost laborastory-scale preparation craft platform of LLZO ceramic is also required. This work demonstrates a "pellet on gravel" sintering strategy, which is performed in a MgO crucible and box furnace under ambient air without any special equipment or expensive consumables. In addition, the competition between lithium loss from the sintering system and internal grain densification is critically studied, whereas the influences of particle surface energy, Li-loss amount, and initial excess Li2O amount are uncovered. Based on the sintering behavior and mechanism, optimized craft platform for preparing dense LLZO solid electrolytes including mixing, calcination, particle tailoring and sintering is provided. Finally, exemplary Ta-doped LLZO pellets with 2 wt % La2Zr2O7 additives sintered at 1260-1320 °C for 20 min deliver Li+ conductivities of ∼9 × 10-4 S cm-1 at 25 °C, relative densities of >96%, and a dense cross-sectional microstructure. As a practical demonstration, LLZO solid electrolyte with optimized performance is applied in both Li-Li symmetric cells and Li-S batteries. This work sheds light on the practical production of high-quality LLZO ceramics and provides inspiration for sintering ceramics containing volatile compounds.

Copper recovery from copper slags through flotation enhanced by sodium carbonate synergistic mechanical activation

Flotation is one of the most important methods for recovering copper from copper slag, However, traditional grinding may be over grinding sometimes, resulting in smaller interface difference, which leads to a decrease in the selectivity of flotation. In this study, a sodium carbonate combined with mechanical activation enhanced flotation for recovering copper from copper slag was developed. Based on the phase analysis, the flotation experiment was conducted. It showed that adding sodium carbonate before wet grinding can change the surface energy of copper slag particles and increase the possibility of cracks between chalcocite particles and gangue particles, while sodium carbonate can also increase the Eh of the copper slag flotation system and improve the flotation effect. Under the optimal flotation conditions of 600 g/t sodium carbonate and 300 g/t xanthate, the recovery efficiency of copper can reach 98.07% with a concentration of 36.13%. Moreover, the flotation kinetic model of copper slag was established and the results showed that the movement of copper slag in the flotation process conforms to the first-order kinetics. The addition of sodium carbonate increased the stability of the pulp and improved the flotation kinetics greatly, resulting in a better flotation performance.

A “Sequential Design of Simulations” approach for exploiting and calibrating discrete element simulations of cohesive powders

The flow behaviours of cohesive particles in the ring shear test were simulated and examined using discrete element method guided by a design of experiments methodology. A full factorial design was used as a screening design to reveal the effects of material properties of partcles. An augmented design extending the screening design to a response surface design was constructed to establish the relations between macroscopic shear stresses and particle properties. It is found that the powder flow in the shear cell can be classified into four regimes. Shear stress is found to be sensitive to particle friction coefficient, surface energy and Young’s modulus. A considerable fluctuation of shear stress is observed in high friction and low cohesion regime. In high cohesion regime, Young’s modulus appears to have a more significant effect on the shear stress at the point of incipient flow than the shear stress during the pre-shear process. The predictions from response surface designs were validated and compared with shear stresses measured from the Schulze ring shear test. It is found that simulations and experiments showed excellent agreement under a variety of consolidation conditions, which verifies the advantages and feasibility of using the proposed “Sequential Design of Simulations” approach.

Discrete element method simulation of binary blend mixing of cohesive particles in a high‐intensity vibration system

AbstractThe effects of processing intensity, time, and particle surface energy on mixing of binary cohesive powder blends in high‐intensity vibration system were investigated via discrete element method simulations. The mixedness was quantified by the coefficient of variation, Cv; lower being better. The mixing rate, which is the speed at which homogeneity was achieved, was inversely proportional to the mixing Bond number, defined as the ratio of particle cohesion to the shear force resulting from the mixing intensity. Results show that both increasing processing intensity and reducing surface energy led to a faster mixing rate. However, the mixedness improved initially as mixing action (the product of mixing rate and mixing time) increased, but later deteriorated upon its further increase. Thus, both mixing rate and mixing intensity need to be tuned for optimum mixing performance depending on the cohesion level of particles; too high or too low mixing action should be avoided.

Cerium oxide catalysts for oxidative coupling of methane reaction: Effect of lithium, samarium and lanthanum dopants

The work presented herein reports on the oxidative coupling of methane (OCM) performance of a series of Li-free and Li-doped CeO2 and CeO2 modified with Sm3+ and La3+ catalysts. The supporting materials (Ce, Sm-Ce and La-Sm-Ce metal oxides) were synthesized using the microwave assisted sol-gel method in order to achieve nanophase complex materials with increased particle surface energy and reactivity. Lithium ions were added, using the wet impregnation technique, in order to further improve the physicochemical characteristics and reinforce the activity and selectivity, in terms of C2H6 and C2H4 production. All materials were characterized using N2 adsorption-desorption, XRD, Raman spectroscopy, CO2-TPD, H2-TPR, SEM and XPS. We showed that the addition of lithium species changed the reaction pathway and drastically enhanced the production of ethylene and ethane, mainly for the promoted catalysts (Li/Sm-Ce and Li/La-Sm-Ce). In particular, the presence and the synergy between the electrophilic oxygen species (peroxide and superoxide), population of oxygen vacancy sites and the surface moderate basic sites determined the reaction pathway and the desirable product distribution.

Assessment of hydration behaviour of Portland Cement-Based materials containing brick powders as partial replacement for fine aggregates

Researchers have used different micro fillers as a substitute for sand to understand their effects on the hydration behaviour of Portland cement-based materials (CBMs). Micro fillers can exhibit two effects, namely, physical effects attributed to particle fineness, surface energy, etc., and chemical effects if they are reactive, although the the effects of the latter have not been reported in most studies. Brick is one such material that contains significant silica and alumina contents and can be used in powder form to exhibit properties that a reactive micro fillers possess. Very few studies are currently available to understand the feasibility of using brick powders (BPs) as a sand substitute material, and hence, the main objective is to understand their effect on the hydration behaviour of CBMs. In this investigation, conventionally available burnt-clay bricks were crushed to sizes below 150 μm and used at 5% dosage in mixtures so that their water absorption effects after sand replacement were minimal. The hydration behaviour was assessed using Thermogravimetric Analysis (TGA), Electrical Impedance Spectroscopy (EIS) technique and compressive strength test at appropriate ages. Results indicated that the BP addition reduces the normalized Ca(OH)2 of pastes only after 7 days due to possible pozzolanic reaction. The high-frequency resistance (R1) and bulk resistivity (Rb) values obtained from EIS increased with BP addition at later ages, indicating the formation of more hydration products, refinement of pore structure, etc. The compressive strength trends also supported such behaviours for both mortar and concrete mixtures. At early ages, no significant improvement in properties was observed with BP addition, although improvements were substantial only at later ages. Overall, the positive effects of BP addition are evident although the study is limited only to the hydration and strength aspects. Since mixtures containing BP provided improved bulk resistivity, one can expect such mixtures to provide better durability also.

A predictive study on effective thermal conductivity of sintered nickel powder under different thermal processing conditions

Effective Thermal Conductivity (ETC) plays a key role in the thermal performance evaluation of samples with porous structure, which can be characterized by multiple physical properties such as particle sizes, porosity, and surface energy. The thermal conductivity of un-sintered porous material has been highlighted in most previous studies, while the evaluation of sintered thermal conductance is scarcely mentioned before. This study aims to develop an analytical model for the ETC prediction of sintered nickel powders based on the circuit equivalent model and sintering neck formation theory. Here, sixteen groups of sintering samples in three particle sizes are fabricated according to orthogonal design with four levels and four key factors, including sintering temperature (650∼800 °C), compressional stress (10∼25 MPa), heating rate (7∼20 °C/min), and holding time (1∼3 h). A dimensionless factor, formulated by the ratio of shrinkage rate to sintering contact area fraction, is proposed to reflect the effect of pore combination and grain growth at the late stage of sintering. The presented model is experimentally validated with an average deviation of three particle sizes equal to 7.11%, 6.38%, and 3.48%, respectively. Besides, simulated ETC agrees well with measured data for samples with medium-high porosity (0.44∼0.71) compared to those prepared with pore-forming agents.

Variations in aluminum particle surface energy and reactivity induced by annealing and quenching

Surface interface properties of fuel particles play an important role in their reactivity. Since diffusion-controlled reactions occur at the interface between a solid fuel and oxidizer, variations in surface energy alter diffusion rates in ways that can be measured macroscopically. In this study, surface energy was purposefully altered by annealing and quenching aluminum (Al) (3–4.5 µm particle diameter) powder. Bulk aluminum exhibits reduced surface energy resulting from annealing and quenching. In the current work, annealing and quenching was extended to powder media to assess the magnitude of reduced surface energy. An inverse gas chromatography (iGC) technique was used to energetically characterize the particle surface for both dispersive and polar properties. Results show up to a 40% decrease in surface energy with annealing and quenching. Both untreated and thermally processed powder were reacted by launching projectiles into a chamber where the ensuing powder explosions were examined. Experiments were performed in ambient air and repeated in argon environments at projectile velocities of 1200 m/s. Overall, higher surface energy resulted in a more pronounced system performance, i.e., in stronger reactions with higher probability of ignition and combustion. A theory explaining the differences in reactivity links surface energy with a mechanism for particle reaction.

Argon low-pressure plasma treatment to stainless steel particles to augment the wear resistance of Cu-free brake-pads

Nowadays, the usage of Copper in brake friction materials (FMs)/pads is a major concern in the brake industry. Despite some of the earlier attempts for the Cu substitution, an issue with high wear of FMs due to their low adhesion of metal particles with the matrix (i.e., phenolic resin) is still largely unresolved. In the current study, the surface energy (SE) of stainless steels (SS316, SS410) and Cu particles was augmented using the right kind of plasma in optimized dose to improve the wettability/adhesion of metal particles with the matrix. The SE of treated particles increased significantly due to the reduction of oxides from the surfaces. A series of seven types of brake-pads was developed containing 3 vol% of SS and Cu (untreated and treated) particles as the theme ingredients keeping parent composition fixed. A reference pad without metal particles was also developed for benchmarking. The developed pads were characterized for physical properties and then evaluated for the tribological and noise-vibration (NV) performance on a brake-dynamometer following global test standards. The results revealed that the pads with treated SS and Cu particles showed a higher fade resistance (~ 2–3%) and reduced wear by ~ 10% compared to the pads with untreated particles. Overall, based on optimized technique, treated SS316 particles proved the best. The underlying mechanisms were studied through worn surface analysis using a field emission scanning electron microscope attached (FESEM) with an energy dispersive X-ray spectroscopy (EDAX).