Bimodal Particle Size Distribution Research Articles

Separating provenance and palaeoclimatic signals from particle size and geochemistry of loess-palaeosol sequences using log-ratio transformation: Central European loess belt, Czech Republic

Loess-palaeosol sequences represent the most complete terrestrial archives of Quaternary climatic cyclicality. Particle size and geochemistry are widely used proxy data in palaeoclimatologic analysis of loess-palaeosol sequences. The palaeoclimatologic signals hidden in the texture and chemical composition of the Czech loess-palaeosol sequences, which are part of the European loess belt, are modulated by temporal changes in the interplay of oceanic and continental macroclimates and by the diverse bedrock geology of the Bohemian Massif.Innovative tools of compositional data analysis, including log-ratio transformation and scalar-on-function regression, can substantially enhance the information value of large granulometric and geochemical datasets, when compared to classical statistics of raw data. Particle size distribution and bulk-rock geochemistry of 389 and 542 samples, respectively, from four Czech loess-palaeosol sequence sections representing the last glacial-interglacial cycle were analysed in this study. Centered log-ratio transformation was applied to the key elemental proxies and their spatial (between sections) and stratigraphic (within section) distribution. Centered log-ratio transformed densities of key elements were then plotted against particle size distribution to assess the particle size control on element concentrations.Nearly all loess-palaeosol sequence samples exhibit a bimodal particle size distribution with medium/coarse silt and coarse clay fraction representing the main modes. The dominant silt fraction is completely allogenic. The clay component is partly allogenic, transported by high altitudes air stream, and partly authigenic (neoformed in situ by pedogenic processes). However there is only a minor variation in particle size between the sections, the centered log-ratio transformed density functions reveal that the particle size control on the distribution of major and trace elements is highly site-specific. The provenance signal is recorded especially in coarser-grained fractions transported for a short distance from the source area by near-surface wind. The proportion of the authigenic clay fraction, the alteration of feldspars, micas and low alkali contents indicated by high Rb/K ratio and high values of Rb/Sr and Sr/Ca ratios, which indicate the intensity of carbonate leaching, reflect the intensity of chemical weathering, which is highest in the podzols. Precipitation rates were likely the main microclimatic factor that controlled the compositional differences. The loess-palaeosol sequences in areas with higher present-day annual precipitation show higher contents of clay minerals, higher degree of loessification (cementation) and subsequent pedogenic changes.

A High-Strain-Rate Superplasticity of the Al-Mg-Si-Zr-Sc Alloy with Ni Addition.

The current study analyzed the effect of Ni content on the microstructure and superplastic deformation behavior of the Al-Mg-Si-Cu-based alloy doped with small additions of Sc and Zr. The superplasticity was observed in the studied alloys due to a bimodal particle size distribution. The coarse particles of eutectic origin Al3Ni and Mg2Si phases with a total volume fraction of 4.0–8.0% and a mean size of 1.4–1.6 µm provided the particles with a stimulated nucleation effect. The L12– structured nanoscale dispersoids of Sc- and Zr-bearing phase inhibited recrystallization and grain growth due to a strong Zener pinning effect. The positive effect of Ni on the superplasticity was revealed and confirmed by a high-temperature tensile test in a wide strain rate and temperature limits. In the alloy with 4 wt.% Ni, the elongation-to-failure of 350–520% was observed at 460 °C, in a strain rate range of 2 × 10−3–5 × 10−2 s−1.

Modeling energy requirements in planetary ball milling of rice grain

Modified rice flours were obtained by high-impact milling. A factorial design was performed in a planetary ball mill varying rotational speed (450–650 rpm) and milling time (10–40 min) while milling energy (0.3–4.3 kJ/g), particle size distribution (PSD) of rice flour, and changes in starch structure were recorded. The effect of rotational speed and time on milling energy was satisfactorily modeled by the Response Surface Methodology. Modified flours presented bimodal PSD unlike that of the control flour, which was monomodal with a lower size dispersion. A significant reduction of D[4,3] (mean diameter) was observed as the milling energy increased. However, the effect of milling energy on PSD was dependent on milling speed. Classical milling equations provided a satisfactory fit of energy-size records at low speed (450 rpm), but at higher speed, a poor adjustment was obtained due to the increasing relevance of heat dissipation. The empirical milling equation based on linear or exponential relationships between milling energy and size reduction ratio provided a good fit for experimental data. Significant correlations between milling energy and damaged starch, crystallinity, and gelatinization degree were found. The proposed mathematical models are a contribution to the milling process design for specific modifications of rice flour.

Effect of particle size distribution on functional properties of Ce0.9Y0.1O2-d ceramics

This paper has investigated the dependence of the mechanical and electrical properties of ceramics Ce0.9Y0.1O2-d (CeY) on changes in the proportion of submicron size particles in a powder with bimodal particle size distribution. The powder was prepared by mixing the products of sol-gel (submicron size fraction with average size of 0.2 μm and specific surface area of 39.52 m2/g) and solid-state synthesis (micron size fraction with average size of 5.68 μm and specific surface area of 4.81 m2/g) in a certain ratio to get different proportion of the fractions. All ceramics samples were formed by isostatic pressing with further annealing under identical conditions. The microstructure of ceramic samples was studied using scanning electron microscopy and static volumetric analysis. The impedance spectroscopy method has determined the temperature dependencies of the grain boundary resistance fraction, which are strongly related to the particle size distribution. The microhardness of samples was determined by the Vickers method. A nonlinear change of mechanical and electrical properties was found for the samples having approximately 20% content of submicron size particles. The dependence of the total electrical conductivity and the dependence of the microhardness on the particle size distribution possess the maxima and minima points for these compositions, respectively. The particle size distribution of powders has a strong impact on the ceramics formation process and allows to control the microstructure and physical properties of materials. We have proposed the ceramics model of “arched structure”, formed by bimodal compositions sintering, which allows to predict the properties of ceramics with other compositions.

Green Electrospinning of Polymer Latexes: A Systematic Study of the Effect of Latex Properties on Fiber Morphology.

Green electrospinning is a relatively new promising technology in which a polymer (latex) can be spun from an aqueous dispersion with the help of a template polymer. This method is a green, clean and safe technology that is able to spin hydrophobic polymers using water as an electrospinning medium. In this article, a systematic study that investigates the influence of the template polymer molar mass, the total solids content of the initial dispersion and the particle/template ratio is presented. Furthermore, the influence of the surfactant used to stabilize the polymer particles, the surface functionality of the polymer particles and the use of a bimodal particle size distribution on the final fiber morphology is studied for the first time. In green electrospinning, the viscosity of the initial complex blend depends on the amount and molar mass of the template polymer but also on the total solids content of the dispersion to be spun. Thus, both parameters must be carefully taken into account in order to fine-tune the final fiber morphology. Additionally, the particle packing and the surface chemistry of the polymer particles also play an important role in the obtained nanofibers quality.

Properties of graphite blocks consisting of ordered graphite flakes with bimodal particle size distribution

AbstractPetroleum pitch‐based graphite blocks (GBs) attract considerable attention owing to their low cost, high yield, and possible application as heat sink components. However, no studies have systematically investigated the particle size distribution of GBs, their structures, and the relationship between the structures and thermal properties resulting from graphitization. Hence, herein, we present a novel method for fabricating petroleum pitch‐based GBs using natural graphite flakes (GFs) of sizes ranging between 50 and 500 μm and a bimodal particle size distribution. Furthermore, the effects of the mean GF particle size, pitch binder content, and microstructure of the GBs with low GF contents on compression molding with elevated hot‐pressing temperatures after graphitization are investigated. To investigate the effect of packing density with a GF size of 500 μm, we mix a small‐sized GF (50 μm) and low pitch binder content by kneading. In particular, specimens in the in‐plane direction with a bimodal particle size distribution of GFs and 10 wt% pitch binder yield optimum density and thermal conductivity values of 1.74 g m−3 and 384 Wm−1 K−1, respectively, after high‐temperature graphitization at 2600°C. These findings provide insights for developing high‐performance GBs for use in heat sink components with high thermal conductivity.

Impact of Bimodal Particle Size Distribution Ratio of Functional Calcium Carbonate Filler on Thermal and Flowability Properties of Polyamide 12

In previous investigations, it was shown that the melting, as well as crystallization behavior of polyamide 12, could be manipulated by adjusting the particle size distribution of calcium carbonate as a functional filler. It was demonstrated that the melt properties of this compound show a significant dependency on the filler volume-based particle size. As finer and narrower the calcium carbonate particles in the polymer matrix become, the less influence the filler has on the melting properties, influencing the melt flow less significantly than the same surface amount of broad size distribution coarse calcium carbonate filler particles. However, due to increased nucleation, the crystallization behavior on cooling showed a markedly more rapid onset in the case of fine sub-micrometer filler particle size. To control further and optimize the thermal response properties of a filling compound for improved properties in additive manufacturing processing through selective laser sintering, the possibility to combine precisely defined particle size distributions has been studied, thereby combining the benefits of each particle size range within the chosen material size distribution contributes to the matrix. The melt flow at 190 °C, the melting speed, melting and crystallization point as well as crystallization time at 170 °C were analyzed. The thermal and flow properties of a polyamide 12 matrix can potentially be optimized with a combination of a precise amount of coarse and fine calcium carbonate filler. The improvements were exemplified using a twin-screw extruder for compounding, indicating the potential for optimizing functionally filled polymer in additive manufacturing.

Features of Hydrodynamics of a Bedisperse Boiling Layer

An experimental study of fluidization of two types of bidispersed layer with a pronounced bimodal particle size distribution has been carried out. The possibility of using the equivalent diameter of the mixture particles, calculated from the weight average diameter of the particles constituting the mixture, is shown.

The preparation of super lightweight magnetic Fe3O4/graphene/carbon aerogels and their use in electromagnetic interference shielding

Magnetic Fe3O4/graphene/carbon aerogels were prepared by the sol-gel method, followed by supercritical drying and pyrolysis. The microstructures, electrical properties and electromagnetic interference shielding performance of the aerogels were investigated. The aerogels were crushed into a fine powder with a bimodal particle size distribution (~0.1 and 10μm) and released into a chamber to a particle concentration of 1 gm-3 atroom temperature under atmosphere pressure using a dispensing device, where electromagnetic interference shieldingwas tested. Results indicate that the composite aerogels have high conductivity and a hierarchical pore structure with a density as low as 0.015 g cm-3. The concentration of the fine powder in the chamber decreased with time and levelled off above 20 min. The shielding is dominated by the particles that are difficult to settle due to their perturbation by air. The shielding for the visible wave band of the composite aerogels in powder form initially and after the release for 30 min are above 99.90% and 98.77%, respectively. Those for 3-5 μm and 8-12 μm infrared light are respectively 99.55% and 99.35% initially, and 99.05% and 96.79% after the release for 30 min. For the millimeter wave band, the shielding ratios initially and after the release for 30 min are above 83.68% and 82.54%, respectively.

Pt particles sintering on Pt/SiO2 during water denitrification

Platinum particle growth in aqueous phase has been investigated at 20 °C in the course of nitrite (NO2−) reduction by H2 reaction. A shift from a monomodal to a bimodal particle size distribution on used catalysts is accompanied with the disappearance of the smallest Pt particles in agreement with an Ostwald ripening mechanism. A two-step process involving consecutive dissolution and re- aggregation to form larger particles has been suggested according to a redox mechanism. Accordingly, the growth of large Pt particles at the expense of small ones induces a strengthening of the metallic character and a loss of Pt dispersion.

Optimized Birch Bark Extract-Loaded Colloidal Dispersion Using Hydrogenated Phospholipids as Stabilizer.

This study investigated the formulation and processing of aqueous colloidal dispersions containing a birch bark dry extract (TE) as the active substance and hydrogenated phospholipids (Phospholipon 90H) as stabilizer, which can be used in the preparation of electrospun wound dressings. Colloidal dispersions manufactured using a two-stage homogenization process had a bimodal particle size distribution, which was most significantly (p < 0.0001) affected by the phospholipid content. The size of the single particles decreased from an average particle size of about 4 µm to a particle size of approximately 400 nm. Dynamic interfacial tension studies performed using a profile analysis tensiometer (PAT) showed that the phospholipids strongly declined the interfacial tension, whereas a further decrease was observed when phospholipids were combined with birch bark extract. Interfacial viscoelasticity properties analyzed using the oscillating drop technique resulted in an increase of both interfacial elasticity and viscosity values. These results indicated that the phospholipids are preferentially located at the lipophilic/water interface and a stable film is formed. Furthermore, the results point to a synergistic interaction between phospholipids and TE. Confocal Raman microscopy (CRM) suggested that the TE is predominantly located in the oil phase and the phospholipids at the interface.

Graphite block derived from natural graphite with bimodal particle size distribution

This paper presents a novel method for the bimodal design of graphite blocks by optimizing the weight ratio of small-sized natural graphite (NG) particles (mean size of 5 μm) and large-sized NG particles (mean size of 500 μm). Graphite blocks were fabricated by subjecting a mixture containing large NG particles and a well-dispersed pitch/small-sized NG mixture (PSM) to pressure-mold heat treatment. The effect of the PSM contents on the structural, thermal, and mechanical properties of the graphite blocks was investigated. A correlation was found between the amount of small-sized NG particles, the micro-pore structure, and the distribution of large-sized NG particles. In particular, the graphite block, with small-sized NG particle content and pitch binder content of 21 wt% and 9 wt%, respectively, achieved maximum thermal conductivity and flexural strength values of 460 W m K−1 and 14 MPa, respectively, after pressure-mold heat treatment (graphitization) at 2600 °C. Our research advances the development of an eco-friendly solvent-free graphite block fabrication method that produces high-performance graphite blocks of varying size faster and more cost-effectively.

Particle Size Distribution of Bimodal Silica Nanoparticles: A Comparison of Different Measurement Techniques.

Silica nanoparticles (SNPs) belong to the most widely produced nanomaterials nowadays. Particle size distribution (PSD) is a key property of SNPs that needs to be accurately determined for a successful application. Many single particle and ensemble characterization methods are available for the determination of the PSD of SNPs, each having different advantages and limitations. Since most preparation protocols for SNPs can yield bimodal or heterogeneous PSDs, the capability of a given method to resolve bimodal PSD is of great importance. In this work, four different methods, namely transmission electron microscopy (TEM), dynamic light scattering (DLS), microfluidic resistive pulse sensing (MRPS) and small-angle X-ray scattering (SAXS) were used to characterize three different, inherently bimodal SNP samples. We found that DLS is unsuitable to resolve bimodal PSDs, while MRPS has proven to be an accurate single-particle size and concentration characterization method, although it is limited to sizes above 50 nm. SAXS was found to be the only method which provided statistically significant description of the bimodal PSDs. However, the analysis of SAXS curves becomes an ill-posed inverse mathematical problem for broad size distributions, therefore the use of orthogonal techniques is required for the reliable description of the PSD of SNPs.

Formulation of Bicelles Based on Lecithin-Nonionic Surfactant Mixtures.

Bicelles have been intensively studied for use as drug delivery carriers and in biological studies, but their preparation with low-cost materials and via a simple process would allow their use for other purposes as well. Herein, bicelles were prepared through a semi-spontaneous method using a mixture of hydrogenated soybean lecithin (SL) and a nonionic surfactant, polyoxyethylene cholesteryl ether (ChEO10), and then we investigated the effect of composition and temperature on the structure of bicelles, which is important to design tailored systems. As the fraction of ChEO10 (XC) was increased, a bimodal particle size distribution with a small particle size of several tens of nanometers and a large particle size of several hundred nanometers was obtained, and only small particles were observed when XC ≥ 0.6, suggesting the formation of significant structure transition (liposomes to bicelles). The small-angle neutron scattering (SANS) spectrum for these particles fitted a core-shell bicelle model, providing further evidence of bicelle formation. A transition from a monomodal to a bimodal size distribution occurred as the temperature was increased, with this transition taking place at lower temperatures when higher SL-ChEO10 concentrations were used. SANS showed that this temperature-dependent size change was reversible, suggesting the SL-ChEO10 bicelles were stable against temperature, hence making them suitable for several applications.

Polymer-inorganic hybrid colloids for ultraviolet-assisted direct ink write of polymer nanocomposites

Inorganic-polymer hybrid colloids present a modular and tunable route to fabricate polymer nanocomposites from low viscosity precursors; however, their use in additive manufacturing remains limited. This manuscript describes photocurable “hybrid colloids” to enable layered fabrication of elastomeric nanocomposites, i.e., combination of continuous-phase photocrosslinking chemistry with hybrid colloids of water-dispersible silica nanoparticles and styrene-butadiene rubber (SBR) latex particles. Varying the relative concentrations of polymeric and inorganic particles afforded precise tuning of filler loading in the final nanocomposite and introduced a bimodal particle size distribution with desirable rheological behavior for extrusion-based additive manufacturing. Specifically, ultraviolet-assisted direct ink write (UV-DIW) processing of the photocurable hybrid colloid pastes generated free-standing green bodies, which contained a combination of SBR and silica nanoparticles. Subsequent drying of the green bodies allowed SBR particle coalescence and penetration through the scaffold and surrounding the silica nanoparticles, which yielded a semi-interpenetrating network (sIPN) nanocomposite. Facile tuning of silica concentrations in the hybrid colloid enabled tuning of both the colloidal ink rheology and mechanical properties of the final sIPN nanocomposites to achieve additive manufacturing of silica-SBR nanocomposites with ultimate tensile strains exceeding 300 % and ultimate tensile strengths above 10 MPa.

Bimodal Size Distribution of VO2Nanoparticles in Hydrophilic Polymer Films for Temperature-Triggered Infrared Transmission Control

This work reports on a synthetic approach for enhanced thermochromic polymer films delivering vanadium oxide nanoparticles (VO2 NPs) in a bimodal particle size distribution: ∼50 and ∼300 nm. Monoclinic VO2 particles are the active ingredients in polymer coatings for temperature-triggered infrared (IR) transmission control. The bimodality promoted the dispersion of VO2 nanoparticles in the hydrophilic polymer coatings poly­(4-vinylpyridine) (P4VP) and polyvinyl­pyrrolidone (PVP). The superior dispersion enhanced the coating’s IR switching efficiency (ΔTIR) (i.e., transmission change due to the temperature-triggered phase transition). The effects of VO2 NP concentration in the polymers as well as coating thickness on the optical properties of the coatings were systematically evaluated. The resulting VO2(M)/P4VP films exhibited good infrared (IR) transmission switching, ΔTIR@2500nm, of 47% with an adequate visible transmittance, Tvis@680nm, of 41%. Hydrophobic VO2/poly­(methyl methacrylate) (PMMA) films gave a ΔTIR@2500nm of 30% and a Tvis@680nm of 29%. The superb performance of the VO2(M)/P4VP coating is ascribed to the uniform dispersion of VO2(M) nanoparticles within the matrix.

Vortex in liquid films from concentrated surfactant solutions containing micelles and colloidal particles

HypothesisNew dynamic phenomena can be observed in evaporating free liquid films from colloidal solutions with bimodal particle size distribution. Such distributions are formed in a natural way in mixed (slightly turbid) solutions of cationic and anionic surfactants, where nanosized micelles coexist with micronsized precipitated particles. ExperimentWithout evaporation of water, the films thin down to thickness < 100 nm. Upon water evaporation from the film, one observes spontaneous film thickening (above 300 nm) and appearance of a dynamic vortex with a spot of thinner film in the center. The vortex wall has a stepwise profile with step-height equal to the effective micelle diameter (ca. 8 nm) and up to 20–30 stratification steps. ResultsFor thicknesses greater than 100 nm, stratification in foam films from micellar solutions has never been observed so far. It evidences for the formation of a thick colloidal crystal of micelles in the evaporating film. The role of the bigger, micronsized particles is to form a filtration cake in the Plateau border, which supports the thick film. The developed quantitative mechanical model shows that the stepwise vortex profile is stabilized by the balance of hydrodynamic and surface tension forces. Vortex is observed not only in films from catanionic surfactant solutions, but also in films from silica and latex particle suspensions, which contain smaller surfactant micelles.

Fabrication strategy of complicated Al2O3-Si3N4 functionally graded materials by stereolithography 3D printing

For multi-ceramic materials based on the stereolithography (SL) principle, a 3D printing strategy was developed, and then an Al2O3-Si3N4 functionally graded material (FGM) ceramic part was fabricated using this strategy. Six groups of mixtures, with a Si3N4 content gradient of 20 vol% and a certain bimodal particle size distribution, were prepared using UV-curable pastes. A modified formula was proposed to evaluate the relationship between the actual minimum voidage of mixtures and the viscosities of their corresponding pastes. The viscosity of each paste was controlled using the prediction formula and optimization of dispersants. To design theprinting layer thickness, a mathematical relationship was established between Si3N4 content and curing depth of paste. The Al2O3-Si3N4 green body without deformation was printed using optimized parameters such as a layer thickness of 40 μm and a paste viscosity of ∼13,000 mPa·s. Finally, using debinding and sintering, denseparts having a complicated shape were obtained.

Eco-efficient blended cements with high volume supplementary cementitious materials

The ways of reducing CO2 emissions in the cement industry were analysed for the purposes of implementation of the low carbon development strategy. The optimal solution to this problem is the technologically optimised blended cements with high volume of supplementary cementitious materials of various genesis and fineness. The design of eco-friendly blended cements was achieved by a synergistic combination of the main constituents such as granulated blast furnace slag, superfine zeolite, fly ash and limestone, as well as by optimisation of the their granulometric composition, taking into account their bimodal particle size distribution by volume and surface area. Moreover, the article presents the technical, environmental and economic benefits of using eco-efficient blended cements.

Evaluation of models for fitting soil particle-size distribution using UNSODA and a Brazilian dataset

The mineral soil Particle Size Distribution (PSD) is a fundamental and very useful soil characteristic widely used to support soil classification, soil management and soil processes modeling. An important limitation of PSD is the lack of standardization for granulometric fractions obtained from different soil classification systems, making difficult to compare and combine data. To overcome this drawback several attempts have been made to mathematically fit PSD data in order to allow soil texture data conversion among soil databases. Parametric equations have been proposed and/or evaluated for particular systems, but none of them has been studied, compared and proved being effective for soils of different types, regions and textural classes. Thus, the purpose of this work was evaluating and comparing performances of several PSD equations on a more comprehensive soil database as well as providing a method capable of fitting a general model for any soil texture. Cumulative PSD data of 221 soil samples, carefully selected from UNSODA and Brazilian/Embrapa datasets to include 12 soil textural classes mapped in the texture triangle, were used in this study to evaluate the fitting performance of commonly applied PSD equations with three and four parameters for unimodal data (SKAG-3p, ANDE-4p, BEST-3p, FRED-4p) and a seven-parameters equation (FRED-7p) used for gap-graded bimodal shaped data. The FRED-7p equation showed outstanding fittings accuracies with average RMSE (100*g g−1) of 0.53 for all soils, about twice as low as the second best fitted equation (ANDE-4p). FRED-7p fitting accuracy was slightly influenced by soil texture, showing a small increase as sand content increases and a decrease as silt content increases. The FRED-7p equation, originally proposed to fit cumulative gap-graded bimodal PSD, performed properly and accurately for all textural classes, including both unimodal and bimodal shaped PSDs. As a result of that, it is strongly recommended as a general model for any kind of soil PSD.