Bimodal Mixture Research Articles

Exploring co-processing strategies for multi-material spark plasma sintering of pure Cu with AlSi10Mg by master sintering curves

Manufacturing complex multi-material metallic components without assembly operations is currently being explored using novel additive manufacturing techniques. For materials combinations that are difficult to process via melting-based processes, multi-material spark plasma sintering (SPS) appears as a promising alternative. However, due to different sintering kinetics, materials with very different melting points might have to be co-sintered at non-optimal conditions. In this work, the potential to improve the co-sinterability of dissimilar materials, namely pure copper and AlSi10Mg, is evaluated by altering the sintering kinetics of copper using different particle size distributions (PSD). Using the master sintering curve (MSC) approach, the densification behaviour of spherical pure copper powder during SPS is evaluated systematically to study the influence of PSD, uniaxial applied pressure, and isothermal holding temperature. An intermediate-sized monomodal and close-to-optimal bimodal PSD are compared for processing at lower sintering temperatures. It was observed that, compared to an intermediate monomodal PSD, a near-optimal bimodal powder mixture yields fully dense Cu–AlSi10Mg components at lower temperature and shorter process times. Therefore, the use of a bimodal mixture enables multi-material sintering, offers energy and cost savings to produce multi-material components, and improves compatibility between materials with very different melting points.

Fabrication of Titanium Alloy-Based Composite Materials from Bimodal Powder Mixtures Ti–6Al–4V–(Cu–Al) by Direct Selective Laser Melting

Fabrication of Titanium Alloy-Based Composite Materials from Bimodal Powder Mixtures Ti–6Al–4V–(Cu–Al) by Direct Selective Laser Melting

Critical parameters to standardize the size and concentration determination of nanomaterials by nanoparticle tracking analysis

The size and concentration are critical for the diagnostic and therapeutic applications of nanomaterials but the accurate measurement remains challenging. Nanoparticle tracking analysis (NTA) is widely used for size and concentration determination. However, highly repeatable standard operating procedures (SOPs) are absent. We adopted the “search-evaluate-test” strategy to standardize the measurement by searching the critical parameters. The particles per frame are linearly proportional to the sample concentration and the measured results are more accurate and repeatable when the concentration is 108-109 particles/ml. The optimal detection threshold is around 5. The optimal camera level is such that it allows clear observation of particles without diffractive rings and overexposure. The optimal speed is ≤ 50 in AU and ∼ 10 μl/min in flow rate. We then evaluated the protocol using polydisperse polystyrene particles and we found that NTA could discriminate particles in bimodal mixtures with high size resolution but the performance on multimodal mixtures is not as good as that of resistive pulse sensing (RPS). We further analyzed the polystyrene particles, SiO2 particles, and biological samples by NTA following the SOPs. The size and concentration measured by NTA differentially varies to those determined by RPS and transmission electron microscopy.

Phase Behavior and Rheological Properties of Size-Fractionated MXene (Ti3C2Tx) Dispersions.

Understanding the dispersion behavior of MXenes is interesting from a fundamental colloid science perspective and critical to enabling the fluid-phase manufacturing of MXene devices with controlled microstructures and properties. However, the polydispersity, irregular shape, and charged surfaces of MXenes result in a complex phase behavior that is difficult to predict through theoretical calculations. As two-dimensional (2D) nanomaterials, MXenes can form lyotropic liquid crystal phases, gels, and aggregates. This work aims to elucidate the effects of MXene (Ti3C2Tx) sheet size on their phase behavior and associated rheological properties. Aqueous dispersions of large sheets with an average lateral dimension of 3.0 μm, small sheets with an average lateral dimension of 0.3 μm, and a bimodal mixture of the two sizes were investigated by using cross-polarized optical microscopy and rheology. At low concentrations, the large MXene dispersions exhibited lyotropic liquid crystal behavior and extended aligned textures, but increasing concentration resulted in the formation of dense flocs. Dispersions of small sheets formed small birefringent domains with increasing concentration but lacked long-range ordering. A bimodal mixture of these sizes enabled the formation of liquid crystalline phases with extended aligned textures with less floc formation. These results provide insights into using polydispersity to tune dispersion microstructure and rheological properties that can be applied to designing dispersions for fluid-phase manufacturing methods, such as direct ink writing.

Optimal dichotomization of bimodal Gaussian mixtures

Despite criticism for loss of information and power, dichotomization of variables is still frequently used in social, behavioral, and medical sciences, mainly because it yields more interpretable conclusions for research outcomes and is useful for decision making. However, the artificial choice of cut-points can be controversial and needs proper justification. In this work, we investigate the properties of point-biserial correlation after dichotomization with underlying bimodal Gaussian mixture distributions. We propose a dichotomous grouping procedure that considers the largest standardized difference in group mean while minimizing information loss.

Experimental Characterization of Bimodal Granular Flow

Solid–liquid flows are encountered in various industrial and natural environments. The internal structure of such flows is highly sensitive to the grading of the solid particles present. In this experimental study, an extended stereometric method is employed to assess the distributions of velocity of particles of different fractions, distinguished by different colors, in vertical and nearly horizontal granular flows. In the vertical flow experiments, mixtures comprising three fractions of lightweight particles, characterized by a very similar density, size, and shape, were tested. The results affirmed the method’s ability to discern particle velocity differences on the order of millimeters per second, establishing its suitability for characterizing nearly horizontal open-channel flows with bimodal mixtures that are stratified and exhibit more complex velocity distributions. Tilting flume experiments, incorporating additional measurements of water velocity distribution, allowed for the evaluation of local slip between water and particles, as well as between particles of the two fractions in the flow. The results indicated that, although the local slip velocity was relatively small, the average slip velocity between the carrying water and transported particles was significantly larger. This factor must be taken into consideration when evaluating bed friction or bed erosion for granular flow in a channel with an erodible bed.

Evolution characteristics of micromechanics provides insights into the microstructure of pharmaceutical tablets fabricated by bimodal mixtures

This research focuses on the evolution of mechanical behavior of bimodal mixtures undergoing compaction and diametrical compression. The clusters were built and discrete element method (DEM) was used to investigate the densification process and micromechanics of bimodal mixtures. Additionally, a more comprehensive investigate of the respective breakage of the bimodal mixtures has been carried out. On this basis, qualitative and quantitative analysis of the compressive force, force chain, contact bonds and density field evolution characteristics of the clusters are investigated during the compression process. The entire loading process of the clusters is divided into three stages: rearrangement, breakage and elastic–plastic deformation. Additionally, there are differences in the evolution of micromechanics behavior of different particles in the bimodal mixture, with pregelatinized starch breakage and deformation occurring before microcrystalline cellulose. With the tablet deformation, the fragmentation process of the tablet started at the point of contact and extended toward the center, and the curvature of the force chain increased. This approach may potentially hold a valuable new information relevant to important transformation forms batch manufacturing to advanced manufacturing for the oral solid dosage form.

Features of processes of high-speed milling with a complex profile tool in the processing of aluminum alloys and composite materials

Complex computational and experimental studies substantiate rational modes of milling of complex contour equiaxed surfaces with high accuracy of shape, dimensions and roughness parameters. Bars made of nanostructured carbide composite (produced by extrusion of WC-Co-Al2O3 bimodal powder mixtures) with increased strength, crack resistance and heat resistance were used as a workpiece material for the manufacture of new original tool designs. The combination of these properties is a necessary prerequisite for the effective operation of the developed designs of multi-blade cutters at high cutting speeds and under conditions of variable cyclic loads. A more complex kinematics of the joint rotational movement of the tool during milling dictates the need for new approaches when assigning rational cutting modes. To obtain reliable calculation formulas, numerical experiments were previously carried out, including simulation of the processing process using the VisualStudio integrated development environment, which supports WindowsForms technology. The ability to display graphical 3D objects was implemented using an additional software product in the form of the Open CASCADE geometric core. Numerical experiments using MathCAD software products and based on the analytical provisions proposed in the work made it possible to evaluate the influence of cutting conditions, geometric parameters of the cutting part of the tool (profile and number of teeth), kinematics of relative movement in the “tool – part” system on the shape of surfaces and contour parameters (roughness obtained during milling. A technique, algorithm and program for the automated calculation of cutting conditions has been developed, which has been verified during full-scale experiments and the manufacture of complex profile parts from aluminum alloys for drives of aerospace products (in the form of a RC profile and parts of a pinion transmission of guidance mechanisms). At the same time, on the basis of a 3D model of products, control programs for CNC machines were created using MasterCAM. The practical significance and technical and economic efficiency of the proposed design and technological solutions is to increase productivity and reduce the complexity of processing (in comparison with the basic options) through the use of new multi-edge carbide tools for high-speed milling (including when processing composite materials).

Effects of Flow Unsteadiness on the Transport of Bimodal Bed Material

The grain size distribution of the transported bed load was experimentally investigated under unsteady flow conditions with bimodal mixture of sand and gravel in a laboratory flume. Five various triangular hydrographs were generated. A clockwise behavior for the total bed load versus shear velocity was observed meaning that the bed load during rising limb was higher than that of falling limb. It was found that the percent finer at the plateau of bimodal sediment size distribution curve had higher values during the initial and final phases compared to those obtained during the peak time. At all plateaus, the percent finer values related to the hydrograph peak discharge were in the same order of magnitude with that of the bed material. The sand content of the transported bed material initially decreased, then maintained a constant value during a certain time interval and finally returned to its original value. The sand percent of the bed load decreased in the falling limb showing a counterclockwise loop and the duration of the hydrograph did not affect the results considerably. The greater the peak flow rate of the hydrograph, the greater was the hysteresis. The bimodality index was calculated for all transported sediment samples and it was revealed that its initial and final values were less than that of the bed material but it was approximately the same elsewhere. The 5% finer sediment amount was nearly equal during rising and falling limbs. It was revealed that D50 value of the bed load decreased in the rising limb showing a clockwise loop. The hysteresis was not considerably changed according to the hydrograph characteristics. The clockwise type hysteresis was also observed for the size group of D95. The lag increased as the peak flow rate increased. A strong relation was found between the dimensionless total bed load Wt* and the total work index Wk as well as Wk and the ratio WR/WF. The correlations between the dimensionless total bed load and the unsteadiness parameters P, and Pmod were very weak, whereas a high value of determination coefficient was obtained with the unsteadiness parameter Pgt, implying an appreciable interdependence.

Enhanced arc erosion resistance via constructing W particle network structure in cold sprayed CuCrZr–W coating: Implication for electromagnetic launching system

In electromagnetic launching systems, arc erosion of rail material, such as Al2O3 dispersion-strengthened copper (ODS-Cu), remains a critical unresolved issue. Here, we report a cold-sprayed CuCrZr–W coating on ODS-Cu exhibiting enhanced arc erosion resistance. The coating was fabricated using a bimodal powder mixture comprising coarse CuCrZr and fine W particles, resulting in a dense structure with an embedded networks of fine W particles along intersplat boundaries. Compared to the ODS-Cu substrate, the CuCrZr–W coating displays superior arc erosion resistance, as evidenced by the reduced arc erosion area and depth, shorter arc duration, lower wielding force, and limited molten Al adhesion during arcing tests. The enhanced performance is attributed to a high density of W/CuCrZr interfaces that effectively disperse arcs, the W particle network that alters the flow path of molten Cu, lowering splashing and evaporation. This work provides valuable insights into developing high-performance, arc erosion-resistant coatings for applications where safeguarding against arc erosion is paramount.

Camera-measured velocity distribution in laboratory open-channel flow with intense transport of bimodal combined-load

Abstract An extended stereoscopic method, which identifies, and tracks particles based on their colour in solid-liquid flow, is tested for its capability to separately measure velocity distributions of particles of two fractions transported as bimodal sediment mixture in water flow through a laboratory flume. The principle of the tested method extension is a use of colour-based processing of images collected by two high-speed cameras which enables to filter out particles of one fraction from the image and leave particles of the other fraction in the image based on a selected colour hue range. The modified images are then processed by the original stereoscopic method to produce velocity distribution of particles of the individual fraction in the flow. The method extension is first tested in simple vertical flow carrying neutrally buoyant spherical particles of two distinct colours in a recirculation cell. In the next step, lightweight plastic particles of two fractions of different properties (size, shape, density) and colours are introduced to flow through a laboratory flume and velocity distributions of the two fractions are measured separately at flow conditions which mimic intense transport of bimodal combined-load in an open channel. Results exhibit a very good agreement with previous measurements with unimodal sediment in hydraulically similar flow.

Effect of feedstock bimodal powder mixture and infiltration process on mechanical behaviour of binder jetting processed 316L stainless steel

ABSTRACT Binder jetting additive manufacturing (BJAM) is a widely studied technique fabricating metal parts. In this study, bimodal 316L stainless steel powder mixture of coarse (D50 – 34.1μm) and fine (D50 – 6.28μm) powders were designed for BJAM. Infiltration was used to improve the density of BJAMed parts. Bimodal powder mixture showed clear advantage over unimodal powder system on density and mechanical property of BJAMed parts. Upon solid-phase sintering, BJAMed 316 stainless steel of bimodal powder mixture (9:1 mass ratio of coarse to fine powder) showed relative density 97.19% and tensile strength 343.62 MPa, as compared with relative density 84.55% and tensile strength 291.59 MPa for pure coarse powder. For the same bimodal powder mixture, bronze infiltration, compared with solid-phase sintering, resulted in noticeably higher relative density 99.92% and tensile strength 621.63 MPa. Compared with solid-phase sintering, infiltration significantly reduced the volumetric shrinkage.

The sizes of life.

Recent research has revealed the diversity and biomass of life across ecosystems, but how that biomass is distributed across body sizes of all living things remains unclear. We compile the present-day global body size-biomass spectra for the terrestrial, marine, and subterranean realms. To achieve this compilation, we pair existing and updated biomass estimates with previously uncatalogued body size ranges across all free-living biological groups. These data show that many biological groups share similar ranges of body sizes, and no single group dominates size ranges where cumulative biomass is highest. We then propagate biomass and size uncertainties and provide statistical descriptions of body size-biomass spectra across and within major habitat realms. Power laws show exponentially decreasing abundance (exponent -0.9±0.02 S.D., R2 = 0.97) and nearly equal biomass (exponent 0.09±0.01, R2 = 0.56) across log size bins, which resemble previous aquatic size spectra results but with greater organismal inclusivity and global coverage. In contrast, a bimodal Gaussian mixture model describes the biomass pattern better (R2 = 0.86) and suggests small (~10-15 g) and large (~107 g) organisms outweigh other sizes by one order magnitude (15 and 65 Gt versus ~1 Gt per log size). The results suggest that the global body size-biomass relationships is bimodal, but substantial one-to-two orders-of-magnitude uncertainty mean that additional data will be needed to clarify whether global-scale universal constraints or local forces shape these patterns.

Stratified and gradient films by evaporation-induced stratification of bimodal latexes. Potential of confocal and scanning electron microscopy for compositional depth profiling

In the field of bimodal latex film's formation, finding methods to quantify particle concentration profiles within the film thickness is a challenge. Herein the advantages and limitations of confocal fluorescence microscopy (CFM) and scanning electron microscopy (SEM) are presented. Films are prepared from a bimodal fluorescent acrylic mixture of large non-deformable particles and small deformable particles having high Péclet numbers. A fixed volume fraction of large particles (ΦL) in the dispersion is used with increasing volume fractions of small particles latex (ΦS). At low ΦS, a surface stratification of large particles occurs with thicknesses up to several micrometers, allowing detection by both CFM and SEM. Small particles form a stratified surface layer above a threshold ΦS value. Its thickness of less than 500 nm is evidenced only by SEM due to the resolution limit of the confocal scan. SEM is also able to reveal concentration gradients of large particles below the “small-on-top” stratified layer.

Influence of monomodal K2CO3 and bimodal K2CO3 + NaCl as space holders on microstructure and mechanical properties of porous copper

Porous copper is potentially very attractive for numerous advanced applications like heat exchangers, heat pumps, rechargeable batteries, fuel cells, catalytic substrates for chemical reactions, EMI absorbers, purification of drinking water, etc. Monomodal K2CO3 has often been used as space holders for the fabrication of porous copper and their mechanical properties have been well studied. Within the scope of this work, porous copper samples have been fabricated for the first time using a bimodal mixture of K2CO3 + NaCl. The particle size of the NaCl powders used was considerably larger than the K2CO3 particles and correspondingly, the pore structure of the bimodal samples consisted of both large pores and fine network pores. A detailed comparison of the microstructure, elastic properties, compressive stress-strain behavior, and energy absorption characteristics between monomodal and bimodal porous copper samples has been performed. The results show that due to the presence of a larger amount of liquid phase in the bimodal samples during sintering from the melting of lower melting point NaCl particles, improved bonding between the Cu particles was achieved in these samples. Correspondingly, for similar content of space holder particles, the compressive strength and stiffness of the bimodal samples were better than the monomodal samples. While for bimodal samples the energy absorbed until densification increased monotonically with increasing porosity, for monomodal samples, the energy absorbed first increased up to a critical porosity and then decreased. The densification behavior during compression of the two types was also different – while for the bimodal samples the densification resulted in enhanced stiffening, in monomodal samples, even after densification the pores played a major role in reducing the stiffness.

Parametric testing for normality against bimodal and unimodal alternatives using higher moments

This study examines population and small sample properties of the standardized fifth and sixth moments – the “higher moments” – for assessing univariate normality against bimodal and selected unimodal alternatives. Population parameters and distributions for selected bimodal mixtures are calculated and contrasted with those for the normal distribution. Using Gram-Charlier series expansion methods, an omnibus goodness of fit test incorporating the higher moments is specified and Monte Carlo simulation used to compare test power with parametric tests based on the standardized third and fourth sample moments: the asymptotic and size corrected versions of the Jarque-Bera score test and the omnibus D’Agostino K2 test. The studentized range and directional tests using the third through sixth moments are also considered. The results demonstrate that incorporating the fifth and sixth moments can provide enhanced parametric normality test power for bimodal normal mixture alternatives but not for various unimodal alternatives.

A Gaussian-Mixture based stochastic framework for the interpretation of spatial heterogeneity in multimodal fields

We provide theoretical formulations enabling characterization of spatial distributions of variables (such as, e.g., conductivity/permeability, porosity, vadose zone hydraulic parameters, and reaction rates) that are typical of hydrogeological and/or geochemical scenarios associated with randomly heterogeneous geomaterials and are organized on various scales of heterogeneity. Our approach and ensuing formulations embed the joint assessment of the probability distribution of a target variable, Y, and its associated spatial increments, ΔY, taken between locations separated by any given distance (or lag). The spatial distribution of Y is interpreted through a bimodal Gaussian mixture model. The modes of the latter correspond to an indicator random field which is in turn related to the occurrence of different processes and/or geomaterials within the domain of observation. The distribution of each component of the mixture is governed by a given length scale driving the strength of its spatial correlation. Our model embeds within a unique theoretical framework the main traits arising in a stochastic analysis of these systems. These include (i) a slight to moderate asymmetry in the distribution of Y and (ii) the occurrence of a dominant peak and secondary peaks in the distribution of ΔY whose importance changes with lag together with the moments of the distribution. This causes the probability distribution of increments to scale with lag in way that is consistent with observed experimental patterns. We analyze the main features of the modeling and parameter estimation framework through a set of synthetic scenarios. We then consider two experimental datasets associated with different processes and observation scales. We start with an original dataset comprising microscale reaction rate maps taken at various observation times. These are evaluated from Atomic Force Microscopy (AFM) imaging of the surface of a calcite crystal in contact with a fluid and subject to dissolution. Such recent high resolution imaging techniques are key to enhance our knowledge of the processes driving the reaction. The second dataset is a well established collection of Darcy-scale air-permeability data acquired by Tidwell and Wilson (1999) on a block of volcanic tuff through minipermeameters associated with various measurement scales.

Influence of particle size distribution on carbon-based flowable electrode viscosity and desalination efficiency in flow electrode capacitive deionization

Flow-electrode capacitive deionization (FCDI) is a potential energy-efficient electrochemical water desalination technology that combines ion-exchange membranes and flowable electrodes (FE). The performance of activated carbon (AC)-based FEs in FCDI systems is influenced by various factors, including particle size. Here, particle size of commercial AC was reduced by dry ball milling to produce FEs for FCDI. Physical analysis by scanning electron microscopy and particle size analyzer confirmed the particle size reduction after dry ball milling. Then, the effect of particle size distribution on the rheological behavior and desalination performances of AC-based FEs was investigated by desalination performance indicators, such as desalination efficiency, average salt adsorption rate and charge efficiency. FE samples were prepared using different mixtures of fine-size range (0.65–0.92 µm; fine AC, FAC) and large-size range (1.5–2.3 µm; AC) particles. The AC to FAC particle ratio influenced the rheological properties of AC-based FEs in FCDI. Pure FAC and bimodal mixture of 0.75 :0.25 FAC: AC particles displayed the highest desalination efficiency compared with pure AC FEs (71% and 72% versus 34%, respectively). More interestingly, in our FCDI set-up, 0.75:0.25 FAC:AC bimodal mixtures showed better flowing properties and lower pressure drop than the pure FAC FEs characterized by high viscosity.

Utility of apparent diffusion coefficient histogram analysis in differentiating benign and malignant palate lesions

ObjectivesTo explore the ability of conventional MRI and histogram analysis of apparent diffusion coefficient (ADC) for differentiating between malignant and benign palatal lesions. Materials and MethodsA retrospective analysis was performed on MRI images of 86 patients with palatal lesions confirmed by histopathology between January 2015 and December 2018. Each lesion was evaluated based on the conventional MRI characteristics, including size, location, morphology, inner texture, enhancement, capsule, bone destruction, and nerve invasion. ADC histogram analysis was fitted to a bimodal Gaussian distribution mixture curve. Nine histogram analysis parameters were extracted from ADC maps and were compared between malignant and benign palatal lesions. Statistical analysis was performed to assess the differential performance of each parameter individually and combined. ResultsOn conventional MRI, the capsule structure and nerve invasion were useful characteristics for the differential diagnosis of palatal lesions. Histogram analysis showed significant differences between the groups in terms of mean ADC values of the lower curve and overall curve of the bimodal histogram, as well as ADC10 and ADC50. The optimal diagnostic threshold of ADC value was ADC50 = 1.17 × 10−3 mm2/s (area under curve [AUC] = 0.934, sensitivity = 93.0 %, specificity = 86.2 %). The combination of conventional MRI and ADC values yielded the best predictive performance, with an AUC of 0.949, and an increase in sensitivity from 80.7 % to 96.5 % and specificity from 58.6 % to 82.8 %, compared to conventional MRI. ConclusionsHistogram analysis of DWI combined with conventional MRI allows accurate differentiation between benign and malignant palatal lesions.

Increasing density and mechanical performance of binder jetting processing through bimodal particle size distribution

Binder jetting is an additive manufacturing (AM) technology that has gained popularity and attention in recent years for production applications in tooling, biomedical, energy, and defense sectors. When compared to other powder bed fusion-based AM methods, binder jetting processes powder feedstock without the need of an energy source during printing. This avoids defects associated with melting, residual stresses, and rapid solidification within the parts. However, one of the challenges of this process is the relatively lower densities which impacts part density, and subsequently, sintering and mechanical properties. In this study, we investigated the influence of bimodal powder size distributions (a mixture of coarse to fine particles) as a method for increasing part density and mechanical strength, and used stainless steel (SS) 316L bimodal mixtures in this case. Four unimodal and two bimodal groups were evaluated under similar AM processing conditions for sintered density measurements and flexural strengths. Our results demonstrated that bimodal size distributions showed a statistically significant increase in density by 20% and ultimate flexural strength by 170% when compared to the highest performing unimodal group. In addition to experimental findings, reactive molecular dynamics simulations showed that the presence of finer powders along with coarser particles in the bimodal particle mixture contribute to additional bonds that are stronger across the particle interfaces. Findings from this study can be used to design bimodal particle size distributions to achieve higher density and better mechanical properties in binder jetting AM process.