Powders

Controlling injection parameters is paramount when it comes to producing high-quality green parts using powder injection molding. This work combines experimental and numerical approaches to study the impact of injection parameters on mold in-cavity pressure and on the overall quality of green parts produced by low-pressure powder injection molding. The properties of two low-viscosity feedstocks (formulated from a water-atomized stainless-steel powder and wax-based binder system) were measured and implemented in an Autodesk Moldflow numerical model to quantify the molding pressures, which were finally validated using experimental real-scale injections. The results confirmed that an increase in mold temperature, an increase in feedstock temperature, and a decrease in solid loading decrease the mold in-cavity pressure, which was correlated with the feedstock viscosity. As a key result, real-scale injections confirmed that a minimum flow rate was required to avoid atypical high in-cavity pressure leading to several visual defects such as weld lines, flow marks, cracks, sinks, and incomplete filling. Due to differences in its thermal transfer properties, this flow rate threshold value decreases as the feedstock solid loading increases. For injection speeds higher than this value, the injection pressure measured experimentally was linearly correlated with the injection flow rate. Full article

The effect of induction heating on the surface properties of hot-pressed ceramics based on plasma chemical nanopowders Si₃N₄ and TiN (additives: Al₂O₃, AlN, and Y₂O₃) has been studied. The research demonstrates the formation of a modified layer on the surface of the hot-pressed material. The study examines the porosity, hardness, fracture toughness, brittleness, distribution of elements, and wear of hot-pressed ceramics on the surface before and after additional grinding. Removal of the surface porous layer results in increased density and hardness, leading to a higher number of acoustic emission signals during scratching with a Vickers indenter. A different response to scratching indicates a transgranular or intergranular fracture of the structure. The presence of porosity and carbon contamination on the surface layer of materials negatively impacts the properties of TiN-reinforced ceramics based on Si₃N₄-Al₂O₃-AlN (SIALON). However, the addition of Y₂O₃ effectively prevents carbon penetration and reduces the effect of grinding. Additionally, the dark-colored tone observed on the outer volume of the samples suggests a non-thermal microwave effect of the induction furnace. Full article

In this paper, we present results of a study on the possibilities of the mechanochemical synthesis of copper-substituted hydroxyapatite with the replacement of calcium cations by copper cations. During the synthesis, various reagents—sources of copper cations—were used. It was found that the nature of the carrier of the doping cation plays an important role in the formation of the structure of Cu-substituted apatite. It was established that a single-phase material forms most efficiently when copper (II) phosphate is employed; however, even this reagent did not allow the introduction of a large amount of copper into the hydroxyapatite crystal lattice. Out of 10 calcium cations in the unit cell of hydroxyapatite, no more than two could be replaced by copper cations. A further increase in the copper concentration led to the formation of an amorphous product. The degree of copper substitution in hydroxyapatite increases as the oxidation state of copper increases. The thermal stability of the hydroxyapatite with the highest degree of substitution was studied. It was shown that the presence of copper cations significantly decreases the stability of hydroxyapatite. In a temperature range of 550–750 °C, it is gradually decomposed to form a mixture of rhombohedral Ca_2.57Cu_0.43(PO₄)₂ and CuO. The FTIR spectrum of Ca_2.57Cu_0.43(PO₄)₂, which is a copper-substituted β-Ca₃(PO₄)₂, was first studied. Full article

Mechanochemical technology is developing rapidly, judging by the scientific information in both basic and applied studies. However, many issues and points of view remain to be discussed. This review presents some new key issues for the optimization of mechanochemical processes in terms of theoretical and practical aspects. Emphasis is placed on powder technology aspects, which are not always discussed compared to functional or microscopic viewpoints. The transfer of chemical species across the interparticle interface between dissimilar species during the mechanosynthesis of nanocomposites offers many new opportunities. Since almost all material transport is preceded by charge transfer, its driving force has been sought using terminology beyond the well-established electrochemical terms. In particular, the valence state of the cationic species involved is of importance. The role of organic compounds throughout the process is emphasized, regardless of their survival in the final product. The similarity with pharmaceutical phenomena is pointed out, although its mentality is very different from that of the synthesis of nanocomposites. The rational amorphization and stabilization of molecular dispersion states with the participation of excipients are discussed. The effects of liquids, either added or formed by mechanochemical auto-liquefaction, are presented with reference to the comparison between wet and dry grinding. The mechanisms of the apparent stabilization of the mechanically activated states of the products are elucidated to investigate the practical applicability of these mechanochemically synthesized products. Finally, the most important aspects for the optimization of the mechanochemical processes of functional nanocomposites are listed. Full article

The understanding of granule growth mechanisms and the effects of formulation and operating conditions over product quality and process performance in fluidized bed co-melt granulation is nowadays of great interest. In this sense, this work systematically studies the combined effects of binder content (W_PEG) and fluidization air flowrate (F_A) and temperature (T_A) on granules’ quality and process-related variables (product mass (M_P), elutriated fines (M_f), mass stuck on walls (M_W)) by using a Box–Behnken-type design of experiments (DoE), as it is a statistical tool suggested by the Quality by Design (QbD) initiative. It was found that the granules’ size and powder flowability are significantly affected by W_PEG (higher W_PEG, higher granule size and better flowability). Interestingly, T_A is the process variable that significantly affects M_P, enhancing process performance at high temperature values. Regarding F_A, it significantly affects d₁₀, promoting the formation of small particles due to breakage at high flowrates and the presence of non-elutriated powder at low flowrates. As a consequence, intermediate F_A is the optimum for obtaining higher M_P. Regarding regime map studies, most runs experienced a rapid growth regime, which is in accordance with the granules’ high pore saturation. This result agrees with the observed high increment in particle size and the morphology of the final granules, allowing researchers to validate and extend existing previous maps. Full article

The paper presents the results of experimental studies on the production of fine char powder from sunflower seed husks by a novel method of thermomechanical treatment with pulsed shock waves and supersonic jets of the mixture of ultra-superheated (above 2000 °C) steam and carbon dioxide, as well as the results of examination of the produced char powder in terms of its chemical, phase, and granulometric composition and structural, morphological, and texture characteristics. The objective of the research is to explore the possibility of using the resulting char powder as a sorption-active material for organic substances. It is shown that the obtained char particles and their agglomerates have an average size of 20–30 nm and 12–24 µm, respectively, have the shape of disks and ellipsoids, consist mainly of amorphous carbon (up to 56 wt%) and oxygen (up to 42 wt%), and have a specific surface area of 1.1–1.7 m²/g. It is concluded that such a char powder can be used as an absorbent for organic substances when dried and deagglomerated. Full article

The CFD simulation of cyclone separators has remarkably evolved over the past decades. Nowadays, computational models are essential for designing, analyzing, and optimizing these devices. Due to the intrinsic anisotropy of the flow inside these separators, the Reynolds stress model (RSM) has been mostly employed. However, RSM models fail to solve most time and space scales, including those relevant to particle behavior. Consequently, the prediction of the grade collection efficiency may be hindered, particularly for low-Stokes-number particles. For example, the precessing vortex core phenomenon (PVC), a well-known phenomenon that is relevant for particle motion, is not usually captured in Reynolds-averaged Navier–Stokes (RANS) simulations. Alternatively, the large-eddy simulation (LES) has been proven to be a superior approach since it captures many time and space scales that would have been otherwise dissipated, allowing for more accurate predictions of particle collection. However, this accuracy comes at a considerable computational cost. To combine the advantages of these two models, the main objective of this research was to evaluate a new hybrid RSM-LES model applied to the cyclone’s flow. The results were compared to experimental data and with RSM model results. It showed that, compared to a RANS model given by the RSM closure model, the grade collection efficiency curve obtained by the hybrid model is closer to the experimental one, even for the coarser mesh. Beyond that, the results showed that while the improvement in results was not proportional to mesh refinement for RANS modeling, the hybrid model showed significant improvement with mesh refinement. Full article

The current state of separation technology often neglects the multidimensional nature of real particle systems, which are distributed not only in terms of size, but also in terms of other properties, such as surface charge. Therefore, the aim of this study is to experimentally investigate the applicability of magnetic seeded filtration as a multidimensional separation process. Magnetic seed particles are added to a multisubstance suspension, and a selective heteroagglomeration with the nonmagnetic target particles is induced, allowing for an easy subsequent magnetic separation. The results show that high separation efficiencies can be achieved and that the parameters pH and ionic strength govern the agglomeration process. Selective separation based on surface charge was observed, but undesirable heteroagglomeration processes between the target particles lead to a loss of selectivity. Particle size was clearly identified as a second relevant separation feature, and its partially opposite influence on collision frequency and collision efficiency was discussed. Finally, experimental data of multidimensional separation are presented, in which a size-distributed two-substance suspension is separated into defined size and material fractions in a single process step. This study highlights the need for multidimensional evaluation in general and the potential of magnetic seeded filtration as a promising separation technique. Full article

Mechanochemically synthesized particles of two types of magnesium ferrites, one of which with structural distortions and an average size of 170 nm, and another that is highly crystalline with an average size of 900 nm, were introduced into a matrix of ultra-high-molecular-weight polyethylene via the milling processing. The final material has been formed by hot pressing mechanocomposites based on ultra-high-molecular-weight polyethylene and magnesium ferrite particles of various fineness and concentration. Structural characteristics were studied using scanning electron microscopy, differential scanning calorimetry and X-ray diffraction analysis. The dielectric properties of the obtained composites were analyzed by testing the frequency dependence of the permeability, dielectric losses, and conductivity. The effect of filler concentration and particle size, as well as the crystallinity of the polymer, on the dielectric properties of the composite material were studied. Full article

In the current work, nanocrystalline powders with different compositions, namely Li_0.98Pr_0.02NbO₃, Li_0.93Pr_0.02Mg_0.05NbO₃ and Li_0.98Pr_0.02TaO₃ were synthesized for the first time using the method of high-energy ball milling of the starting materials (Li₂CO₃, Nb₂O₅, Ta₂O₅, MgO, Pr₆O₁₁), followed by high-temperature annealing. XRD data analysis confirmed the absence of parasitic phases in the obtained nanocrystalline compounds. The estimated particle sizes ranged from 20 to 80 nm. From the obtained nanopowders, ceramic samples were prepared using specially developed equipment, which allowed for pressing at elevated temperatures with a simultaneous application of a constant electric field. The obtained photoluminescence spectra exhibit characteristic features of Pr³⁺ ions in the crystal structure of LiNbO₃ and LiTaO₃ and are most efficiently excited by UV light. Samples pressed with an electric field application show higher intensity of photoluminescence. Investigations of the temperature dependence of electrical conductivity of the Li_0.98Pr_0.02NbO₃ sample, pressed with the application of an electric field, indicate that the conductivity mechanism is similar to that of LiNbO₃ single crystals and, at high temperatures, is attributed to the lithium conduction mechanism. Full article

Nowadays, the search for the coupled polymer nanocomposite thermoelectrics that exhibit a high value of thermoelectric figure of merit (ZT) and similar behaviour of physical properties for the use as legs of thermoelectric cells is a current challenge. The direct current (DC) conductivity is one of the three important components of thermoelectric figure of merit. The aim of this study was to obtain PANI-based nanothermoelectrics with Te⁰ and Bi₂Te₃ nanoparticles and MWCNT by mechanochemical methodology and to investigate the dependency of their DC electrical conductivity on temperature in the 298–353 K range using the Arrhenius and Mott’s variable range hopping (VRH) models. Inorganic Te⁰ and Bi₂Te₃ nanoparticles were pre-synthesized by the available and environmentally friendly method using a commercial tellurium powder. The samples obtained were characterized by X-ray diffractometry (XRD), IR and UV-Vis spectroscopy. The XRD study of ES-PANI/Te⁰ (4.4 wt% Te⁰) and ES-PANI/Bi₂Te₃ (2.9 wt% Bi₂Te₃) nanocomposites found that the nanoparticle average size was 32 nm and 17 nm, respectively. The DC conductivity study of the samples with different nanophase content (2.1, 4.4, 10.2 wt% Te⁰, 1.5, 2.9, 7.3 wt% Bi₂Te₃, 1.5 wt% MWCNT) by the two points measurement method reveals the following: (a) the presence of inorganic nanophase reduces the conductivity compared to the matrix, (b) the addition of MWCNT in ES-PANI increases its electrical conductivity, (c) the conductivity of ES-PANI/Te⁰ as well as ES-PANI/Bi₂Te₃ nanocomposite rises with the increasing inorganic nanophase content, (d) the observed increase in the electrical conductivity of MWCNT-based nanocomposites with increasing inorganic nanophase content is interrupted by a characteristic area of decrease in its value at average values of inorganic nanoparticles content (at Te⁰ content of 4.4 wt%, at Bi₂Te₃ content of 2.9 wt%), (e) a similar DC conductivity behaviour in ES-PANI/Te⁰—ES-PANI/Bi₂Te₃ and ES-PANI/Te⁰-MWCNT—ES-PANI/Bi₂Te₃-MWCNT nanocomposite pairs is observed. Full article

Quasicrystalline Al₉₃Fe₃Cr₂Ti₂ (at.%) gas-atomized powders, which exhibit a metastable composite microstructure, were used to produce coatings by cold spray additive manufacturing processing (CSAM) using different processing parameters. The metastable composite microstructure provides the Al₉₃Fe₃Cr₂Ti₂ alloy with excellent mechanical properties. At the same time, the metastability of its microstructure, achieved by the high cooling rates of the gas atomization process, limits the processability of the Al₉₃Fe₃Cr₂Ti₂ powder. The purpose of this study was to investigate the effect of process parameters on the CSAM of quasicrystalline Al₉₃Fe₃Cr₂Ti₂ powder. The powder was sieved and classified to a size range of −75 µm. Using N₂ carrier gas combined with different temperatures, pressures, nozzle apertures, and deposition substrate conditions, cold-sprayed coatings were produced. The porosity and thickness of the coatings were evaluated by image analyses. By SEM, XRD, DSC, and TEM, the microstructure was identified, and by Vickers microhardness, the mechanical properties of the coatings were investigated. Dense (≤0.50% porosity) and thick (~185.0 µm) coatings were obtained when the highest pressure (4.8 MPa), highest temperature (475 °C), and lowest nozzle aperture (A) were used in combination with an unblasted substrate. The SEM, XRD, and DSC data showed that the composite powder’s microstructure was retained in all coatings with no decomposition of the metastable i-phase into equilibrium crystalline phases. Supporting these microstructural results, all coatings presented a high and similar hardness of about 267 ± 8 HV. This study suggests that the CSAM process could, therefore. produce metastable quasicrystalline Al₉₃Fe₃Cr₂Ti₂ coatings with a composite microstructure and high hardness. Full article

Cu–Al bronzes are interesting metallic materials, demonstrating higher hardness, higher wear resistance, higher corrosion resistance and a lower friction coefficient as compared with unalloyed copper. The powder metallurgy approach to the fabrication of these alloys presents opportunities to tailor their phase composition and grain size. In the present work, the structural characteristics, phase composition and properties of Cu-10 wt.% Al alloys obtained by spark plasma sintering (SPS) of powder blends and a powder obtained by mechanical alloying (based on Cu(Al) solid solution) are reported. Alloys with different interaction degrees between the metals were obtained by SPS. The blends demonstrated better sinterability than the mechanically alloyed powder: a nearly fully dense alloy was obtained by SPS of the blend at 480 °C, whereas a temperature of 800 °C was necessary to consolidate the mechanically alloyed powder. The hardness and electrical conductivity of the sintered alloys were comparatively analyzed. It was shown that the Cu-10 wt.% Al alloys obtained without the mechanical alloying stage possess hardness and electrical conductivity comparable to those of the alloys obtained from the mechanically milled powder. Full article

The paper demonstrates the potential of wet ball milling of metals for the synthesis of various carbides and carbohydrides. The work reports on multicomponent carbides formed in Ti-(Cu/Fe/Si)-C, W-Fe-C, and Nb-(Cu/Fe/Si/Al)-C systems, as well as metastable or high-temperature intermetallics formed in Ti-Si, Nb-Si, Nb-Al, and Nb-Cu-Fe systems, which are stabilized with interstitial carbon. The formation of phase composition of powders fabricated under mechanochemical synthesis and subsequent thermal treatment has been studied. The as-fabricated powders have been used to produce bulk compacts and to apply wear-resistant coatings on steel (iron). Full article

The FeAl intermetallic compound is of great interest for industry due to its low density, low cost and high mechanical and corrosion resistance, so it can replace stainless steels and nickel-based alloys for some applications. In previous publications, the concept (principle) test for a novel FeAl powder manufacturing process has been shown. It consists mainly of the following stages: (a) metallic strip manufacture through rapid solidification, (b) water vapor exposure of these metallic strips for their disintegration and powder generation and (c) powder drying. Experimental tests were performed for 2 g of the FeAl intermetallic compound. However, this process can be extended to manufacture any other intermetallic compound containing aluminum, such as TiAl, NiAl, CoAl or any other that can be obtained from every element that can combine with aluminum, if the aluminum content is between 55 and 60 at.%. Nowadays, this process is at technology readiness level (TRL) 3. Therefore, in this paper, a process equipment up-scaling configuration for producing up to 15 kg powder is proposed. This manufacturing process is an industrial alternative to those commonly used to produce powders of this type of intermetallic compounds, such as mechanical alloying (MA). Moreover, several alternatives for employing renewable energy sources are given, making it even more environmentally sustainable. Full article

A novel method of the hot consolidation metal powders with shear deformation is proposed. The powders were encapsulated into tight containers and compacted after short-term heating in a furnace preheated to 900 °C. The method prevents powder oxidation, peripheral spalling and ensures the removal of the oxide films from the powder surfaces. Commercial titanium powders of different dispersivities and impurity concentrations were hot-compacted. The microstructure, hardness and bending strength of the compacts were investigated. The compacts from fine PTOM-1 powder, containing 0.32% of hydrogen, reveal the greatest values of the hardness and bending strength. Additional annealing results in 60% increase in the bending strength. Full article

Mechanochemistry is one of the ten great discoveries of green chemistry methods for synthesizing new substances. A drug substance from the fluoroquinolone group was exposed to high-intensity mechanical impacts using a laboratory knife mill for 21 min and constantly monitored by analyzing samples extracted every 3 min with DLS, SLS, LALLS, 2D-LS, optical and digital microscopy, FTIR, and Spirotox methods. A dispersity phenomenon was detected in an area where catastrophic dislocations formed and multiplied via laser methods. The positive correlation between the temperature of deformation and stress was demonstrated, similar to a typical stress–strain curve of a Bochvar–Oding curve and Young’s modulus: the angular coefficient of the straight section to OX was tgα = 10 min⁻¹. Z-Average, ζ-potential, and polydispersity index dependences were represented as discontinuous periodic oscillations analogous to the defect and impurity transitions near the dislocation core. Deformation r from the high-intensity mechanical impact resulted in covalent bonds showing hyper- and hypochromic effects under FTIR spectra, a bathochromic shift of the maximum, and an oscillation emission at 3240 cm⁻¹. A 2D-LS fingerprint diagram obtained via the topological convolution of the light scattering matrix made it possible to distinguish the off-loading samples from the native substance. The investigation of the dissolution kinetics in water via laser diffraction led to conclusions about the limiting diffusion stage and the acceleration of the mechanoactivation of the solid body’s dissolution under both linear and plastic deformation. The acceleration of ^obsE_a of the cell death process in the temperature range from 296 to 302 K indicated a significant (2.5-fold) decrease in the toxicity of the aqueous 9 mM (1:3) sample solution at 21 min compared to that of the native levofloxacin. Adherence to the mechanochemistry laws provides an opportunity for drug repositioning to change their brand status by identifying new physicochemical and biological properties. Full article

In the present work, we studied the interaction of polyphenylsilsesquioxane with various β-diketonate complexes of titanium by mechanochemical activation. Polyphenylsilsesquioxane, bis-(2,4-pentanedionate) titanium dichloride, bis-(1-phenyl-1,3-butanedionate) titanium dichloride, and bis-(1,3-diphenyl-1,3-propanedionate) titanium dichloride were used as starting reagents. Various chemical and physicochemical methods of analysis were used to study the synthesis products. The composition of the obtained compounds has been determined. It is shown that under conditions of mechanochemical activation, high-molecular-weight products with a Si/Ti ratio different from the specified ones are formed. In addition, under the action of mechanical stresses, the initial titanium complexes (except for acetylacetonate complex) polymerize with the formation of coordination of high-molecular-weight compounds, which are destroyed by the addition of ethyl alcohol. It has been established that with an increase in the volume of the organic ligand, titanium atoms enter the polymer siloxane chain to a lesser extent. This work is aimed at finding efficient and environmentally friendly methods for the synthesis and modification of organometallic macromolecular compounds. Full article

Changes in the morphology of betulin crystals during heating at selected temperatures corresponding to polymorphic transformations were investigated. It was shown that the prismatic crystals of starting betulin form III were converted into needles at 120 °C after water removal, followed by the III→II polymorphic transformation. During further heating up to 180 °C, the whiskers of betulin form I were grown. Experiments on betulin heating in the presence of dicarboxylic acids, adipic or suberic showed that the morphological changes can serve as a test for the formation of cocrystals. According to morphological changes, the formation of cocrystals of betulin with adipic acid under heating was identified. The interaction of adipic acid vapor with the surface of betulin crystals was suggested. In contrast, morphological changes in the mixture of betulin and suberic acid under heating provided only the evidence of polymorphic transformations of the components. The results on cocrystal formation by heating were compared with the preparation of cocrystals by the liquid-assistance grinding method. Despite the fact that polymorphic forms with a high surface area were formed when betulin was heated, dissolution studies showed that the starting betulin polymorph III exhibited the highest dissolution rate in comparison with betulin polymorphs obtained under heating. Full article