Search Results (100)

Al–Cu–Mg composites reinforced with sub-micron tungsten carbide (WC) particles were synthesized by powder metallurgy and subjected to T6 heat treatment to clarify the interplay between dispersion strengthening and precipitation hardening. Composites with 1–3 wt.% WC (average size 0.8 μm) were solution-treated at 540 °C for 3 h, water-quenched, and aged at 195 °C for up to 100 h. Microstructural analyses confirmed a uniform distribution of WC and demonstrated that its presence did not modify the dissolution–precipitation sequence of the Al-Cu-Mg matrix. Transmission Electron Microscopy observations provided direct evidence of θ′ (Al₂Cu) precipitates. The 3 wt.% WC composite reached peak hardness after 5 h (78 HRF), a 15% increase over the T6-treated unreinforced alloy, and exhibited a 40% higher yield strength (330 MPa). These improvements were attributed to the combined effects of Orowan strengthening and age-hardening precipitates (θ′). The results demonstrate that integrating powder metallurgy, sub-micron WC reinforcement, and T6 treatment is an effective route to enhance strength in Al–Cu–Mg alloys without delaying aging kinetics. Full article

In the quest to produce high-purity alumina, bottom-up engineering via architecting the interior of ceramic with bimodal structures of alumina powders in the absence of any additives has gained considerable attention owing to the simplicity offered. The present work investigated the influence of bimodal structures containing micron (~35 μm) and submicron (~600 nm) Al₂O₃ powders on the formation of dense Al₂O₃ ceramic. To this end, ball-milling was conducted to prepare the desired sizes of powders, followed by two-step sintering in a vacuum at 1450 °C and 1650 °C with 6 h and 4 h holding times, consecutively. The bimodal structures induced the formation of Al₂O₃ ceramic with nearly full densification (>99%; ρ 3.95 g/cm³). Both the coarse and fine-grained moieties synergistically balanced the densification kinetics whilst suppressing abnormal grain growth. The uniform and homogeneous grain size minimized the plasma porosity down to <6.0%, limiting the penetration of plasma during the etching process. Full article

In this study, a correlative approach using Raman spectroscopy and scanning electron microscopy (SEM) is introduced to meet the challenges of identifying impurities, especially carbon-related compounds in metal injection-molded (MIM) Mg-0.6Ca specimens designed for biomedical applications. This study addresses, for the first time, the issue of carbon residuals in the binder-based powder metallurgy (PM) processing of Mg-0.6Ca materials. A deeper understanding of the material microstructure is important to assess the microstructure homogeneity at submicron levels as this later affects material degradation and biocompatibility behavior. Both spectroscopic and microscopic techniques used in this study respond to the concerns of secondary phase distributions and their possible stoichiometry. Our micro-Raman measurements performed over a large area reveal Raman modes at ~1370 cm⁻¹ and ~1560 cm⁻¹, which are ascribed to the elemental carbon, and at ~1865 cm⁻¹, related to C≡C stretching modes. Our study found that these carbonaceous residuals/contaminations in the material microstructure originated from the polymeric binder components used in the MIM fabrication route, which then react with the base material components, including impurities, at elevated thermal debinding and sintering temperatures. Additionally, using evidence from the literature on thermal carbon cracking, the presence of both free carbon and calcium carbide phases is inferred in the sintered Mg-0.6Ca material in addition to the Mg₂Ca, oxide, and silicate phases. This first-of-its-kind correlative characterization approach for PM-processed Mg biomaterials is fast, non-destructive, and provides deeper knowledge on the formed residual carbonaceous phases. This is crucial in Mg alloy development strategies to ensure reproducible in vitro degradation and cell adhesion characteristics for the next generation of biocompatible magnesium materials. Full article

Manmade detention ponds have historically been impacted by anthropogenic activities such as rainwater runoff, car emissions, and drainage from infrastructures, which can lead to complications for pond ecosystems. Sediment samples collected from the northern, southern, western, and eastern regions of a small pond on a suburban high school campus on Long Island, NY, were analyzed for potential chemical changes resulting from an inundation of water by a broken water main. Incorporating synchrotron X-ray techniques, sediment was analyzed using Submicron Resolution Spectroscopy, Tender Energy X-ray Spectroscopy, and X-ray Powder Diffraction to examine heavy metals, light elements, and minerals. Results include a Zn:Cu ratio increase from 4:1 to 10:1 in the eastern zone and a higher heavy metal presence in the western zone for all elements examined, with greater distribution throughout the pond post-inundation. Lighter elements appear to remain relatively unchanged. The appearance of diopside in the eastern zone post-inundation samples suggests contamination from the water main break, while the presence of carbonate minerals in the western zone is consistent with erosion of asphalt material from the adjacent parking lot. Full article

Submicron particles are widely used in industrial applications due to their unique physical and mechanical properties that enhance the performance of composite materials. In particular, boron carbide particles are valued for their exceptional hardness and high wear resistance and are especially valuable in protective coatings and aerospace applications. However, these particles can agglomerate, significantly impairing their effectiveness. When this occurs during the development of composite materials, physical and mechanical properties are negatively affected. In this paper, a chemical-free method using a non-destructive, open-system dry mechanical deagglomeration technique is developed, leaving the primary particles unaltered, while breaking up strong adhesions between primary particles resulting from the manufacturing process. This method was tested for the deagglomeration of as-received boron carbide submicron particles, with an average primary particle diameter of d₅₀ = 300 nm, and its effect on particle size distribution is presented. Furthermore, X-ray diffraction and true density measurements were carried out on the raw powder. Submicron particles in the dry and as-received state were poured into an experimental mold without a dispersing agent or a protective atmosphere. Static pressure was applied up to 141 MPa to produce tablets at room temperature, finding that 70 MPa yielded the best results in terms of homogeneity, dispersibility, and reproducibility. In order to break apart the densified pressed tablets, ultrasonication was applied before running particle size measurements in the wet dispersed state. Using a tri-laser diffraction light scattering technique, it was determined that particle size distribution followed a Gaussian curve, indicating that this method is suitable to regain the primary submicron particles with uniform properties. It is also shown that applying ultrasound on the as-received powder alone failed to cause the complete deagglomeration of strongly adhering primary particles. These findings suggest that there is no significant wear on the primary particles and no alteration of their surface chemistry, due to the lack of any chemically supported mechanisms such as the alteration of surface charge or the adsorption of surfactants. Furthermore, as the static pressure exerts an immediate impact on all particles in the mold, there is a clear economical advantage in terms of a shorter processing time over other deagglomeration methods such as high shear mixing. Full article

Aiming at the high-value application of rare earth elements lanthanum (La), an Al-50% La alloy was selected and prepared in a vacuum medium-frequency induction furnace. The geometric characteristics of the Al-50% La alloy powders were compared and studied, with the powders prepared by two different methods: mechanical pulverization and gas atomization. The results showed that an Al-49.09% La master alloy was obtained, and the only intermediate phase containing La in the experimental alloy was Al₁₁La₃. From the perspectives of chemical and phase composition, La has a high yield. Additionally, an Al-La alloy with controllable rare earth intermediate phases can be obtained. The Al-La alloy powders prepared by the mechanical pulverization method are irregular in shape, but the particle size is relatively small, ranging from 0.25 to 66.9 μm. Submicron powders were obtained, with 4.38% of the powders having an equivalent particle size of less than 1 μm. Considering the characteristic of the selective laser melting (SLM) process forming micro-melt pools, a small amount of submicron Al-La alloy powders prepared by the mechanical pulverization method can be used as a trace additive for SLM preparation of CP-Ti. The powders prepared by gas atomization have good sphericity, with a particle size range of 1.65 to 76.0 μm. Among them, the powders with a size of 2–10 μm account for 75.52%, and this part of the powders can be used for the powder metallurgy preparation of composite materials. Full article

Submicron-sized TiB₂ powders (300 nm–1 μm) were prepared by the reaction of TiC, B₄C, and Ca assisted by molten CaCl₂. The optimal reaction procedure (1200 °C and 25 wt.% CaCl₂ + 25 wt.% Ca) was obtained by exploring the effects of the boronization reaction temperature and the addition of an amount of CaCl₂. It was found that the introduction of CaCl₂ not only promoted the reaction but also effectively inhibited the volatilization of excess Ca. Furthermore, SEM images of the products showed that the morphology and particle size of TiB₂ were inherited from the carbothermal reduction product TiC, which was dominated by the “template/growth” mechanism. The process of the boronization reaction was that B atoms migrated from B₄C and replaced the C atoms in the lattice of TiC. Full article

The aerosol deposition (AD) method utilizes high kinetic-energy submicron powders to impact and form a film on a substrate. It is a highly efficient deposition method, capable of producing films or coatings with a strong interfacial bonding and a dense nano-grain structure without thermal assistance. In this work, PbZr_0.53Ti_0.47O₃ (PZT53/47) films (~1.2 μm thick) were deposited on Pt/Ti/Si(100) substrates via the AD method. After a conventional annealing process (700 °C for 1 h), these PZT53/47 films displayed a dense, crack-free, nano-grained morphology, corresponding to an optimal electrical performance. A large maximum polarization (P_max = 70 μC/cm²) and a small coercive field (E_c = 104 kV/cm) were achieved under the maximum applicable electric field of 1.6 MV/cm. The PZT53/47 films also exhibited a large small-field dielectric constant of ~984, a high tunability of 72%, and a low leakage current of ~3.1 × 10⁻⁵ A/cm² @ 40 V. Moreover, the transverse piezoelectric coefficient (e_31.f) of these AD-processed films was as high as −4.6 C/m², comparable to those of sputter-deposited PZT53/47 films. These high-quality PZT53/47 thick films have broad applications in piezoelectric micro-electromechanical systems. Full article

It is vital to measure combustion temperature to define combustion models accurately. For single fuel particles in powder-fueled ramjets, their size distribution ranges from submicron to submillimeter, and their burn time is short to millisecond order. Moreover, the radiation intensity of different types of fuel particles significantly oscillated with several orders of magnitude. Current temperature measurement technology is facing this challenge. This paper proposes a highly spatiotemporal resolved pyrometry to measure the combustion temperature of fuel particles by coupling single-point photomultiplier tube (PMT)-based and two-dimensional complementary metal oxide semiconductor (CMOS)-based photoelectric devices. Both the offline calibration by blackbody furnace and online calibration by standard lamp confirmed the measurement accuracy of the pyrometry. Then, the pyrometry was used to measure the combustion temperature of fuel particles including micro-Al, nano-Al, micro-Mg, nano-B, and micro-B₄C. The temperature evolution and distribution of burning fuel particles were complementarily obtained, especially the interfacial flame temperature near the particle surface. Based on the obtained combustion temperature, the combustion characteristics and the energy release efficiencies among these fuels were evaluated and compared in detail, which are helpful to recognize, in depth, the combustion behavior and reveal the combustion mechanism of fuel particles in powder-fueled ramjets. Full article

Nanosuspensions (NS), with their submicron particle sizes and unique physicochemical properties, provide a versatile solution for enhancing the administration of medications that are not highly soluble in water or lipids. This review highlights recent advancements, future prospects, and challenges in NS-based drug delivery, particularly for oral, ocular, transdermal, pulmonary, and parenteral routes. The conversion of oral NS into powders, pellets, granules, tablets, and capsules, and their incorporation into film dosage forms to address stability concerns is thoroughly reviewed. This article summarizes key stabilizers, polymers, surfactants, and excipients used in NS formulations, along with ongoing clinical trials and recent patents. Furthermore, a comprehensive analysis of various methods for NS preparation is provided. This article also explores various in vitro and in vivo characterization techniques, as well as scale-down technologies and bottom-up methods for NS preparation. Selected examples of commercial NS drug products are discussed. Rapid advances in the field of NS could resolve issues related to permeability-limited absorption and hepatic first-pass metabolism, offering promise for medications based on proteins and peptides. The evolution of novel stabilizers is essential to overcome the current limitations in NS formulations, enhancing their stability, bioavailability, targeting ability, and safety profile, which ultimately accelerates their clinical application and commercialization. Full article

This article researches the effect of ultrafine (submicron) tungsten carbide powder addition on the microstructure and mechanical properties of WC-10Co cemented carbide produced by the extrusion of a highly filled polymer. This addition aims to develop a material with a good combination of toughness, hardness, and yield strength. The results demonstrate that increasing the ratio between ultrafine and micron WC particles from 0/100 to 45/55 in the initial powder results in successive decreases in average grain size from 2.61 µm to 1.75 µm. When 45% of ultrafine powder is introduced into the mixture, a high number of fine tungsten carbide grains is produced. This promotes inter-grain contact and reduces the free path of the binder phase, which results in a more rigid structure and in the material becoming more brittle. The best mechanical characteristics are achieved in WC-10Co cemented carbide with 15% content of ultrafine powder in the total weight of WC. Here, a microstructure with a bimodal distribution of tungsten carbide grains in a virtually non-intermittent cobalt phase was formed. This allowed us to achieve a compressive strength of 2449 MPa at the deformation of 6.69%, while the modulus of elasticity was 38.8 GPa. The results indicate a good combination of strength and ductility properties in the developed cemented carbide. Full article

Pack boriding with CeO₂ was performed on the powder metallurgical (PM) near-α type titanium alloy at a temperature of 1273–1373 K for 5–15 h followed by air cooling. The microstructure analysis showed that the boride layer on the surface of the alloy was mainly composed of a monolithic TiB₂ outer layer, inner whisker TiB and sub-micron sized flake-like TiB layer. The growth kinetics of the TiB₂ and TiB layers obeyed the parabolic diffusion model. The diffusion coefficient of boron in the boride layers obtained in the present study was well within the ranges reported in the literature. The activation energies of boron in the TiB₂ and TiB layers during the pack boriding were estimated to be 166.4 kJ/mol and 122.8 kJ/mol, respectively. Friction tests showed that alloys borided at moderate temperatures and times had lower friction coefficients, which may have been due to the fine grain strengthening effect of TiB whiskers. The alloy borided at 1273 K for 10 h had a minimum friction coefficient of 0.73. Full article

Submicron and nanosized powders have gained significant attention in recent decades due to their broad applicability in various fields. This work focuses on ultrasonic spray pyrolysis, an efficient and flexible method that employs an aerosol process to synthesize titanium-based nanoparticles by transforming titanium oxy-sulfate. Various parameters are monitored to better optimize the process and obtain better results. Taking that into account, the influence of temperature on the transformation of titanium oxy-sulfate was monitored between 700 and 1000 °C. In addition to the temperature, the concentration of the starting solution was also changed, and the flow of hydrogen and argon was studied. The obtained titanium-based powders had spherical morphology with different particle sizes, from nanometer to submicron, depending on the influence of reaction parameters. The control of the oxygen content during synthesis is significant in determining the structure of the final powder. Full article

The process of obtaining powders from the 5–50 μm fraction of a W-Ni-Fe system consisting of particles with predominantly spherical shapes was investigated. Experimental studies on the plasma–chemical synthesis of a nanopowder composed of WNiFe-90 were carried out in a plasma reactor with a confined jet flow. A mixture of tungsten trioxide, nickel oxide, and iron oxide powders interacted with a flow of hydrogen-containing plasma generated in an electric-arc plasma torch. The parameters of the spray-drying process and the composition of a suspension consisting of WNiFe-90 nanoparticles were determined, which provided mechanically strong nanopowder microgranules with a rounded shape and a homogeneous internal structure that contained no cavities. The yield of the granule fraction under 50 μm was 60%. The influence of the process parameters of the plasma treatment of the nanopowder microgranules in the thermal plasma flow on the degree of spheroidization and the microstructure of the obtained particles, seen as their bulk density and fluidity, was established. It was shown that the plasma spheroidization of the microgranules of the W-Ni-Fe system promoted the formation of a submicron internal structure in the obtained spherical particles, which were characterized by an average tungsten grain size of 0.7 μm. Full article

Solid crystalline suspensions (SCSs) containing submicron particles were introduced as a competitive solution to increase dissolution rates and the bioavailability of poorly water-soluble drugs. In an SCS, poorly water-soluble drug crystals are finely dispersed in a hydrophilic matrix. Lately, melt milling as an adapted wet milling process at elevated temperatures has been introduced as a suitable batch manufacturing process for such a formulation. In this work, the transfer from batch operation to a two-step continuous process is demonstrated to highlight the potential of this technology as an alternative to other dissolution-enhancing methods. In the first step, a powder mixture of a model drug (griseofulvin) and a carrier (xylitol) is fed to an extruder, where a uniform suspension is obtained. In the second step, the suspension is transferred to a custom-built annular gap mill, where comminution down to the submicron region takes place. The prototype’s design was based on batch grinding results and a narrow residence time distribution, intended to deliver large quantities of submicron particles in the SCS. The throughput of the mill was found to be limited by grinding media compression. By inclining the mill at an angle, the grinding media position was manipulated, such that compression was avoided. Different states of the grinding media in the grinding chamber were identified under surrogate conditions. This strategy allows the maintenance of an energy-optimized comminution without adaption of the associated process parameters, even at high throughputs. Using this new process, the production of an SCS with 80–90 % submicron particles in a single passthrough was demonstrated. Full article