Powders

In this work, a simple, inexpensive, and eco-friendly synthesis method of Cu−Ag microflakes has been developed. Firstly, Cu nanoparticles were synthesized by the reduction of copper nitrate in ethylene glycol at 180 °C in the presence of NaOH. The as-synthesized Cu powder was then dispersed in a mixture of ethyl alcohol and a dispersant followed by the mechanochemical treatment of the dispersion in a ball mill resulting in the formation of Cu flakes of approximately 0.2 μm thick and 2.7 μm lateral size. Next, by adding AgNO₃ dissolved in H₂O into the Cu particle dispersion, the bimetallic Cu−Ag microflakes were prepared. The particles so prepared were investigated by X-ray phase analysis and electron microscopy. It was shown that the Cu−Ag bimetallic particles were also flake-like in shape and similar in size to the original Cu microflakes. The effect of synthesis conditions, including parameters of mechanochemical processing, on thickness, size, and uniformity of the bimetallic microflakes was studied. The results obtained in this study were compared with those obtained by wet chemical synthesis alone. The flake-like Cu–Ag particles are supposed to be used in the manufacture of conductive pastes, adhesives, and composites for printed electronics. Full article

Powder mixtures based on copper or iron are used as metal binder materials in the manufacturing of abrasive and cutting tools. This article discusses some aspects and possibilities of using a high-energy ball milling process to modify the structure and properties of Cu-Sn, Cu-Sn-Ti and Fe-Ti powders, their sintered materials and composites with diamond. The structures of powders and sintered materials, as well as the binder-to-diamond interfaces in metal matrix composites with diamond fillers, were studied by XRD analysis, scanning electron microscopy and X-ray spectroscopy. Tribological properties and thermal stability of materials in the temperature range of 250–800 °C were investigated. Various mechanisms of dispersion strengthening during the heating of sintered materials are described. It is shown that due to the grain boundary distribution of titanium, it is possible to obtain single-phase powders in the form of a supersaturated solid solution of CuSn20Ti5 and FeTi20, which ensure the formation of thermally hardened alloys with a microhardness of 357–408 HV and 561–622 HV, respectively, in the temperature range of 350–800 °C. The wear resistance of sintered powder alloys increases more than twice. Furthermore, the simultaneous enhancement in both the strength and ductility of metal–diamond titanium-containing composites is achieved through the nanostructural state and the formation of a thin layer (up to 2 μm) of titanium carbide at the interface between the metal matrix and diamond. The developed alloy shows great potential as a binder in diamond tools which are designed for machining abrasive materials. Full article

The grossular garnet from rodingite-type rock from the Suva Česma area in western Serbia is characterized with its weak anisotropic nature. Because its anisotropy could indicate a non-cubic lower symmetry, SEM-EDS and Rietveld powder refinement methods were used. The SEM-EDS results have shown that the garnet has a (Ca_3.00Mn_0.01)_3.01(Al_1.82Fe_0.15Ti_0.02)_1.99(Si_2.97Al_0.03)_3.00O₁₂ chemical composition (i.e., Grs₉₁Adr₀₈), which can be more specifically explained as ferric iron containing grossular. The next step further used Rietveld powder refinements of the various crystal structures in the Ia‾3d, R‾3c, R‾3, I4₁/a, Fddd, C2/c, and I‾1 space groups as well as a single mixture, which was followed by a comparative analysis of the R-values, site occupancy factors, and bond lengths and angles. The synthesis of these results showed both that the studied grossular garnet is not cubic and that it crystallized in the disordered Fddd space group with the final R_B = 5.29% and R_F = 1.75%. It was presumed that the grossular formed at temperatures between 150 and ~600 °C. Full article

In this study, hydroxyapatite with the substitution of calcium cations by iron and phosphate by silicate groups was synthesized via a mechanochemical method. The as-prepared compounds have the general formula Ca_10−xFe_x(PO₄)_6−x(SiO₄)_x(OH)_2−xO_x/2 with x = 0–1.5. The thermal stability of the as-prepared compounds was studied by ex situ annealing of powders in a furnace. It has been established that, at 800 °C for x ≤ 0.5, a partial decomposition of the substituted apatites occurs with the formation of the β–Ca₃(PO₄)₂ phase. At high “x” values, the formation of this phase starts at the lower temperature of 700 °C, followed by the formation of Fe₂O₃ at 900 °C. The introduction of iron and silicate ions into the hydroxyapatite lattice was shown to decrease its thermal stability. Full article

Practically all particle separation processes depend on more than one particulate property. In the case of the industrially important froth flotation separation, these properties concern wettability, composition, size and shape. Therefore, it is useful to analyze different particle descriptors when studying the influence of particle wettability and morphology on the separation behavior of particle systems. A common tool for classifying particle separation processes are Tromp functions. Recently, multivariate Tromp functions, computed by means of non-parametric kernel density estimation, have emerged which characterize the separation behavior with respect to multidimensional vectors of particle descriptors. In the present paper, an alternative parametric approach based on copulas is proposed in order to compute multivariate Tromp functions and, in this way, to characterize the separation behavior of particle systems. In particular, bivariate Tromp functions for the area-equivalent diameter and aspect ratio of glass particles with different morphologies and surface modification have been computed, based on image characterization by means of mineral liberation analysis (MLA). Comparing the obtained Tromp functions with one another reveals the combined influence of multiple factors, in this case particle wettability, morphology and size, on the separation behavior and introduces an innovative approach for evaluating multidimensional separation. In addition, we extend the parametric copula-based method for the computation of multivariate Tromp functions, in order to characterize separation processes, also in the case when image measurements are not available for all separated fractions. Full article

Crystalline hematite nanoparticles as adsorbents for anionic Congo red dye were prepared by a hydrothermal process using urea hydrolysis. To examine the effects of coexisting anions in a solution on the formation of hematite nanoparticles, different iron(III) salts, including iron chloride hexahydrate, iron nitrate nonahydrate, iron sulfate n-hydrate, ammonium iron sulfate dodecahydrate, and basic ferric acetate, were employed as iron-ion sources. After the hydrothermal treatment of the solution, consisting of an iron salt and urea at 423 K for 20 h, a single phase of hematite was formed from the iron-nitrate solution. The results suggested that the hydrothermal formation of hematite depended on the stability of iron complexes formed in the starting solution. The average crystallite size and median diameter of hematite nanoparticles also depended on the coexisting anions, suggesting that the appropriate selection of the coexisting anions in the starting solution can allow for control of the crystallite size and particle diameter of hematite nanoparticles. The Congo red adsorption kinetics and isotherms of the hematite nanoparticles were described by the Elovich model and Langmuir model, respectively. The adsorption thermodynamics parameters were estimated, which suggested an exothermic and spontaneous process. The results demonstrated good adsorption properties for Congo red adsorption. Full article

Flaxseed oil is rich in polyunsaturated fatty acids, and its incorporation into food formulations is limited due to its hydrophobic nature and susceptibility to oxidation. The aim of this work was to analyze the effect of wall material mixtures (modified starch Capsul^® and rice and pea protein concentrate) on the efficiency of flaxseed oil encapsulation by freeze-drying, physical characterization, and determining oxidative stability. For the preparation of powders, four emulsions with an oil–wall material ratio of 1:3 were produced and characterized. The mass ratio between rice and pea proteins was fixed at 50–50%. The mass ratio of the protein-Capsul^® mixtures was varied by 0–100%, 10–90%, 20–80%, and 30–70%. Based on the creaming index results, all emulsions showed good stability after 24 h of analysis. The powders showed low moisture content (<3.23%), bulk density (<0.2659 kg/kg), and packed bulk density (<0.4389 kg/kg). Encapsulation efficiency decreased with increasing protein content, ranging from 93.40% (protein-Capsul^® ratio of 0–100%) to 18.26% (protein-Capsul^® ratio of 30–70%). However, the best oxidative stability results (smaller increases in the peroxide index values at the end of the stability experiments) were obtained for the powders containing the highest levels of vegetable proteins (protein-Capsul^® ratio of 20–80% and 30–70%, respectively). Full article

The harsh and hostile internal environment of semi-autogenous (SAG) mills renders real-time monitoring of some critical variables practically unmeasured. Typically, feed size fractions are known to cause mill fluctuations and impede the consistent processing behaviour of ores. There is, therefore, the need for continuous monitoring of mill parameters for optimal operation. In this paper, an acoustic-based sensing method is employed to estimate, in real time, a snapshot of the different feed size fractions presented to a laboratory-scale SAG mill. Employing the MATLAB 2020b programme, the mill acoustic signal is processed using various transform techniques such as power spectral density estimate (PSDE) by Welch’s method, discrete wavelet transform (DWT), wavelet packet transform (WPT), empirical mode decomposition (EMD), and variational mode decomposition (VMD). Different fractional bandpowers are obtained from the PSDE spectrum, while the statistical root mean square values are further extracted from DWT, WPT, EMD, and VMD as feature vectors. The features are used as input features in different machine-learning classification algorithms for different mill feed size fractions predictions. The various transform techniques and feed size fraction predictions are evaluated using the various performance indicators obtained from the confusion matrix such as accuracy, precision, sensitivity and F1 score. The study showed that the acoustic signal feature extraction techniques used in conjunction with the Support Vector Machine (SVM), linear discriminant analysis (LDA), and ensemble with subclass discriminant machine learning algorithms demonstrated improved performance for predicting feed size variations. Full article

The growing increase in emissions of ultrafine particles or nanoparticles by industries and urban centers has become worrisome due to the potential adverse health effects when inhaled. Particles in this size range have greater ease of pulmonary penetration, being able to access the bloodstream and deposit in other regions of the body. Thus, the development and optimization of equipment and processes aimed at the removal of aerosols of nanoparticles have been gaining importance in this current scenario. Among the equipment commonly used, electrostatic precipitators and filters stand out as being versatile and consolidated processes in the literature. This review explores and analyzes the theoretical bases of these two processes in the collection of such small particles in addition to providing a general overview of the development of technologies and studies on these topics. Full article

In the last decade, twin-screw wet granulation became an essential technology for continuous pharmaceutical tablet production. Consequently, interest in (semi-)continuous fluidized bed drying systems as a subsequent processing unit has grown. In parallel, it has become pivotal to fully understand and control manufacturing processes in line with in the quality-by-design paradigm. Formulation-generic prediction models would enormously facilitate digitally enhanced process development and require dedicated experimental data collection and process knowledge. To obtain this knowledge, three experimental campaigns were performed in this work. Firstly, an investigation into the effect of dryer process settings on drying behavior is presented. Secondly, the effect of active pharmaceutical ingredient properties on drying was assessed by producing granules of similar particle size and porosity and evaluating their drying and breakage behavior. Finally, additional experiments with varying active pharmaceutical ingredients and drug load were conducted to increase the genericity of the data set. This knowledge can be used in mathematical process modelling. Full article

In modern cold rolling mills in the steel industry, iron oxide powder is produced as a by-product when used pickling agents are recycled. Further processing of these iron oxide powders could enable the production of iron powder for various applications in powder metallurgy. For this purpose, a new process route with an eco-friendly hydrogen reduction treatment was developed. The process is able to manufacture a variety of iron particles through minor process adaptations. It was possible to manufacture spherical iron particles with high flowability. The flowability was measured by a Revolution Powder Analyzer, and an avalanche angle of 47.7° of the iron particles was determined. In addition, the bulk density measurements of the processed iron particles collective achieved values of 3.58 g/cm³, and a spherical morphology could be observed by SEM analysis. The achieved properties of the iron particles show high potential for applications where high flowability is required, e.g., additive manufacturing, thermal spray and hot isostatic pressing. By adjusting the process conditions of the developed process, irregular iron particles could also be manufactured from the same iron oxide powder with a very high specific surface of 1640 cm²/g and a low bulk density of 1.23 g/cm³. Therefore, the property profile is suitable as a friction powder metallurgy material. In summary, the developed process in combination with the iron oxide powder from steel production offers a cost-efficient and sustainable alternative to conventional iron powders for additive manufacturing and friction applications. Full article

The difficulty of obtaining a densely packed granular material as an initial condition is a very common problem in numerical simulations of granular materials. In this article, an Imaginary Coating Algorithm (ICA) is introduced. To avoid unreasonable particle deformation when using a longer time step and a lower Young’s modulus, the radii used in calculating the action forces in a binary collision are slightly larger than the real values. In other words, an imaginary coat is added to each particle or element. To validate this algorithm, simulations were carried out by using ÅDEM, and a A Discrete Element Method (DEM) software program was developed. Compared with traditional Simulated Annealing Algorithms (SAA), this technique can approach the densely packed state with less CPU/GPU time and is easy to operate. Full article

This study investigates the relationship between metallic powders and their flowability behavior (captured in terms of Hall flow rates using Hall flowmeters). Due to the many trait dependencies of powder flowability, which have made the formulation of a physical and mechanistic generalizable model difficult to resolve, this study seeks to develop an alternative data-driven framework based on powder size and shape characteristics for Hall-flow-rate predictions. A multiple-instance regression framework was both developed for processing multiple-instance powder data and compared with standard machine learning models. Data augmentation was found to improve the overall performance of the framework, although the limited dataset was a constraint. Still, the study contributes to ongoing efforts to identify traditional, associative, and generalizable patterns between powder properties and resultant flowability behaviors. The findings show promise for real-world applications with a larger dataset, such that this initial application of multiple instance regression frameworks for metal powder Hall-flow-rate predictions as a function of powder particle size and shape data can be scrutinized in full. Full article

Spiral jet mills used for fine and colloid grinding have an enormously high energy consumption resulting in a great potential for optimization. In order to increase their efficiency, it is essential to precisely understand the flow conditions within the grinding chamber and the influencing parameters. In this work, the experimental method of particle image velocimetry is applied, which is optimized to the extent that the velocity fields of the grinding gas flow can be determined in the entire mill cross-section. Additionally, the influence of the product outlet diameter and the grinding gas flow rate on the flow profiles are investigated. With decreasing outlet diameter, significantly higher velocities are obtained in the inner mill region resulting in higher classifying efficiencies. At the same time, as the outlet diameter declines, an overpressure builds up in the mill, causing a deceleration of the entire flow in the outer region, preventing the complete formation of the nozzle jets and leading to worse comminution efficiencies. Therefore, there is an optimum between the competing comminution and classifying processes regarding the effect of the product outlet diameter. In contrast, increasing the gas flow rate can consistently achieve a gain in velocity, improving both comminution and classifying efficiency. Full article

Cold gas dynamic spray (CS) is a unique technique for depositing material using high-strain-rate solid-state deformation. A major challenge for this technique is its dependence on the powder’s properties, and another is the lack of standards for assessing them between lots and manufacturers. The motivation of this research was to understand the variability in powder atomization techniques for stainless steel powders and their subsequent properties for their corresponding impacts on CS. A drastic difference (~30%) was observed in the deposition efficiencies (DEs) of unaltered, spherical and similar sized stainless steel (316) powders produced using centrifugal (C.A) and traditional gas atomization (G.A) techniques. The study highlights more the differences on a precursor level. Using recent advancements in large scale statistical measurements, such as laser diffraction shape analysis and µCT scanning; and traditional methods, such as EBSD and nanoindentation, an attempt was made to understand the powder’s properties. Insights on powder size and shape were documented. Significant differences were observed between C.A and G.A powders in terms of grain size, fraction of high-angle grain boundaries (HAGBs) and nanohardness. The outcomes of this study should be helpful for understanding the commercialization of the cold-spray process for bulk manufacturing of powder precursors. Full article

Electric fields have been used in the manufacturing of powders in a number of ways, including to enhance drying rates and retain heat-sensitive materials. Electrohydrodynamic drying and electrostatic spray drying use electric fields to accelerate the evaporation of liquid from a surface, resulting in faster drying times and improved product quality. These technologies are used in the food and pharmaceutical industries to manufacture powders from liquid feed materials. In addition to enhancing drying rates, the use of electric fields in powder manufacturing can also help to retain the bioactivity of compounds in the final product. Many bioactive compounds are sensitive to heat and can be degraded or destroyed during conventional drying processes. By using electric fields to dry powders, it is possible to reduce the amount of heat applied and therefore preserve the bioactive compounds in the final product. This article reviews the different mechanisms of various electric field assisted technologies, i.e., electrohydrodynamic atomization, electrohydrodynamic drying, pulsed electric fields and a new approach of electrostatic spray drying, along with their potential food industry applications. Full article

Powder breakage during pneumatic conveying negatively affects the properties of dairy products and causes increased dusting, reduced wettability, and decreased product performance. In particular, particle breakage is a serious issue for fat-filled milk powder (FFMP) which, if it breaks, releases fat that causes odours and leads to sticky blocked pipes. In this work, a conveying rig (dilute phase, positive pressure) with 50 mm diameter food grade stainless steel pipes (1.5 m high and 5 m conveying distance with three 90° bends, two in the vertical plane and one in the horizontal plane) was built as the test system. The effects of operating conditions (conveying air velocity and solid loading rate) on the attrition of FFMP in a dilute phase conveying system were experimentally studied. Four quality characteristics were measured before and after conveying: bulk density, particle size distribution, wettability, and solubility, to access the influence of particle breakage. Conveying air speed shows a significant impact on powder breakage. As air speed increased, more breakage occurred, and the volume mean diameter D[4,3] decreased by around 50%, using the largest conveying air speed of 38 m/s. Bulk density increased accordingly whereas wettability decreased with an increase in air speed, resulting from the higher breakage rate. On other hand, improving the solid loading rate can further reduce the breakage level, but the positive effect is not as good as decreasing air speed. Full article

The internal microstructure of a tablet, such as pore geometry and pore volume, impacts the tablet’s disintegration kinetics. Ideally, one could design the microstructure to control dissolution onset and therapeutical performance of immediate-release formulas; however, manufacturing tablets with a desired microstructure can be challenging due to the interplay between formulation and process parameters. Direct quantification of tablet microstructure can provide a framework for optimizing composition and process parameters based on a Quality-by-Design approach. This article reviews the importance of tablet microstructure design and liquid transport kinetics to help optimize the release and dissolution profiles of immediate-release products. Additionally, the formulation and process parameters influencing the tablet microstructure and liquid transport kinetics are discussed. Full article