Micron Powders Research Articles

Sintering polycrystalline silicon carbide composite ceramics with ultra-high hardness under high pressure

Silicon carbide (SiC) is an important structural ceramic material, exhibiting exceptional comprehensive properties that are unmatched by metals and other structural materials. In this study, a combination of α-SiC micron powder and β-SiC nanopowder was utilized as precursor materials for high pressure and high temperature (HPHT) sintering. Under a pressure of 5.0 GPa, polycrystalline SiC samples with mixed grain size were sintered within a temperature range from 1000 to 1700 °C, and compared with SiC samples sintered from single micron powder under identical temperature and pressure conditions. The microstructures of the two sets of SiC samples were observed using scanning electron microscopy. Additionally, the stress states and strengthening mechanisms among SiC grains with mixed grain size under HPHT were further analyzed in conjunction with X-ray diffraction results. The polycrystalline SiC composite ceramics sintered at 1700 °C exhibited superior mechanical and thermal properties, achieving a Vickers hardness of 35.2 GPa that is 23.5 % higher than that obtained by conventional spark plasma sintering and even surpassing the hardness of single crystal SiC, demonstrating thermal stability up to 1405 °C in air environment. Transmission electron microscopy was employed to analyze defects and plastic deformation in these samples. The study suggests that the primary strengthening mechanisms of the sintered polycrystalline SiC composite ceramics under HPHT include the increase in micro defects induced by in-situ plastic deformation at elevated temperatures and the effects of high-temperature creep. This study provides new insights into the HPHT sintering of hard materials.

A Novel Approach for Preparing Sepiolite Micron Powder Based on Steam Pressure Changes.

As a common method for preparing micron powder in industrial operations, the mechanical extrusion method simply pursues the particle size without considering the microstructure characteristics of sepiolite, which leads to problems such as bundles of sepiolite not being effectively dispersed, and thus the disruption of fibers is inevitably caused. In this work, a new micronization method for disaggregating these bundles while preserving the original structural integrity of the fibers is proposed based on steam pressure changes. The effects of steam pressure changes on the particle size distribution, microstructure, and properties of treated sepiolite are studied using X-ray fluorescence spectrometer (XRF), X-ray diffractometer (XRD), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), and a specific surface area and aperture analyzer (BET). The experimental results show that the particle size of sepiolite powder depends greatly on steam pressure, and sepiolite powder with mass ratio of 91.6% and a particle size D97 of 21.27 μm is obtained at a steam pressure of 0.6 MPa. Compared to the sepiolite after mechanical extrusion, the sepiolite treated with steam pressure changes can maintain the integrity of its crystalline structure. The specific surface area of sepiolite enhanced from 80.15 m2 g-1 to 141.63 m2 g-1 as the steam pressure increased from 0.1 to 0.6 MPa, which is about 1.6 times that of the sample treated with mechanical extrusion.

TO HIGHLY PRODUCTIVE SYNTHESIS OF ALUMINUM NANOPARTICLES IN PLASMA FLOW AT ATMOSPHERIC PRESSURE

Purpose. To study the highly productive evaporation of aluminum micron powder in an atmospheric pressure plasma jet for the synthesis of nanoaluminum. Using special plasma technology, nanoparticles can be produced by rapid melting and evaporation of the initial micrometer particles and their subsequent re-nucleation. Research methods. Methods of mathematical and computer modeling of subsonic plasma turbulent jets at atmospheric pressure and experimental studies of two-phase processes during thermal plasma treatment using an arc plasma torch. Results. Based on computer modeling, a special reactor system was designed and developed, which includes a plasma-jet reactor with an electric arc plasma torch for the synthesis of aluminum nanoparticles. Numerical modeling makes it possible to determine the position of the melting point, evaporation and crushing of a molten particle, the evolution of the fractional composition of the dispersed phase, and find the speed and temperature of the particle in the area from its melting point to the crushing point. An experimental test of the operation of the reactor system was carried out using arc plasma torches with a power of 30 and 150 kW. It has been shown that intensifying the fragmentation of dispersed raw materials in a plasma jet can be useful in technologies for producing nanomaterials. The consequence of the fragmentation process is the redistribution of the fractional composition of the powder along the plasma jet and the accompanying changes in the dynamics of movement, heating and evaporation of particles. It has been determined that when the temperature of the largest aluminum particles reaches 2500 C, the total amount of evaporated mass is theoretically equal to 100%. The main parameters influencing the behavior of particles in a plasma jet are particle diameter, powder injection rate, flow rate, temperature and composition of the plasma gas. Taking these parameters into account will allow the process to operate at increased productivity. Scientific novelty. A mathematical description of the process of fragmentation a polydisperse powder, based on a continuum approach, has been obtained, which makes it possible to determine the position of the crushing point of a molten particle, the fractional composition of the dispersed phase, and find the speed and temperature of the particle in the area from its melting point to the point of crushing and evaporation. It was shown for the first time that it is possible to carry out a process in which complete evaporation of a molten drop is achieved due to the high enthalpy of the plasma before the end of mixing with steam. Practical value. A special reactor system has been designed and developed, which includes a plasma-jet reactor with an electric arc plasmatron for the synthesis of aluminum nanoparticles. The operating parameters of the reactor system have been determined, which will allow the synthesis of aluminum nanoparticles to be carried out with high productivity.

Effect of Ti microalloying and laser remelting on the microstructure and mechanical properties of laser powder bed fusion Al–12Si alloy

This study explores the impact of micron-Ti microalloying and laser remelting on the microstructure and mechanical properties of laser powder bed fusion (LPBF) Al–12Si alloy, analyzing the underlying reasons. The findings show that the tensile strength and elongation at 300 °C (184 ± 13 MPa and 7.4 ± 1.4 %) are on par with other LPBF heat-resistant Al alloys, such as near-eutectic Al–Ce and Al–Ni. Introducing micron Ti (1 wt%) to AlSi12 effectively eliminates the α-Al <100> texture and refines the grain structure, thanks to the strong nucleation effect from the formed D022-(Al, Si)3Ti, leading to enhanced tensile strength in both as-built and heat-treated (300 °C for 2 h) samples, while maintaining ductility within the typical range for LPBF near-eutectic Al–Si alloys. Laser remelting further decreases the presence of unmelted Ti powder in AlSi12Ti and encourages the formation of D022-(Al, Si)3Ti, offering insights into LPBF Al alloy composition design through promoting the melt of the modified powder and improving material homogeneity, especially for incorporating micron powders with high melting points. Additionally, the superior mid-high temperature properties (300 °C) of AlSi12+1 wt% micron-Ti contribute to expanding the database of LPBF Al alloys.

Facile one-step deposition of nanosized Ni(OH)2–MoS2 heterostructure electrodes for efficient oxygen evolution reaction

There is an increasing need for environmentally friendly and sustainable energy sources that rely on efficient and abundant electrocatalysts for the oxygen evolution reaction (OER). OER plays a key role in energy conversion and storage applications. Using a vacuum kinetic spray technique operating at room temperature, electrocatalysts based on nano-sized Ni(OH)2–MoS2 nanocomposites (NCs) on nickel foam are fabricated from the corresponding micron powders. The Ni(OH)2–MoS2 NC modified working electrodes were exploited to investigate the OER at different weight ratios of MoS2 (25, 50, and 75 wt%). To comprehensively investigate and elucidate the surface state and morphology of the electrode, x-ray diffraction, scanning electron microscopy (SEM), Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS) were assessed. SEM images showed that the micro-sized particles were fragmented into smaller nanoscale particles. XPS spectra revealed the synergy enhancement in the Ni(OH)2–MoS2 NCs that resulted in a strong improvement in the OER activity. Ni(OH)2–MoS2 hybrid NCs with 75 wt% MoS2 exhibited the lowest overpotential of 282 mV at 10 mA cm−2 and a small Tafel slope of 54 mV⋅dec−1. Alongside, the prolonged OER durability at 50 mA cm−2 is verified for up to 50 h.

Synthesis and magnetic properties of some monotectic composites containing ultra-dispersed particles of YGdTbDyHo high-entropy alloy

Recent discoveries of low-dimensional and ultra-dispersed magnetocaloric materials revealed interesting results that help to uncover some fundamental aspects related to the magnetocaloric effect. One of the promising way to obtain ultra-fine metallic nanocomposites resistant to environmental conditions is the use alloy systems showing a liquid miscibility gap. Within this study we fabricate some monotectic composites containing YGdTbDyHo high-entropy alloy and examine their structure, microstructure, thermal conductivity, magnetic and magnetocaloric properties, employing X-ray diffraction, electron microscopy, magnetometry and ab initio molecular dynamics simulations. The results reveal that the use of chromium, vanadium and their mutual alloys as a host monotectic matrix in combination with standard arc-melting enables the YGdTbDyHo high-entropy alloy to be evenly dispersed in the form of small irregularly-shaped particles (droplets or lamellae) of less than 1–2 μm in size, practically uncontaminated with the host metal in which these inclusions are distributed. The monotectic composites have increased Neel points, but reduced magnetocaloric response compared to non-dispersed as-cast YGdTbDyHo alloy. The observed tendencies in the behavior of magnetic properties of the developed monotectic alloys turned out to be similar to the micron powders and thin films based on rare-earth metals studied to date, i.e. the effects of micro- and nanostructuring in all systems are of the same nature and play a decisive role in their magnetism. The study results allow us to conclude that using immiscible metals in alloy fabrication process is effectient for dispersing rare-earth high entropy alloys and opens up new prospects in designing low-dimensional and nanoscale magnetic phases with adjustable magnetocaloric properties.

Strengthen high-loading operation of wastewater treatment plants by composite micron powder carrier: Microscale control of carbon, nitrogen, and sulfur metabolic pathways

The concentration of activated sludge is a crucial factor influencing the capacity and efficiency of sewage wastewater treatment plants (WWTPs). However, high sludge concentrations can lead to sludge loss in the secondary sedimentation tank, resulting in reduced processing capacity, particularly during low-temperature stages and sludge bulking. This study investigated the impact of adding composite micron powder carriers (CMPC) in high-concentration powder carrier biofluidized bed (HPB) technology to the biochemical units of WWTPs on sludge concentration and settling performance. For the traditional activated sludge method (ASM), its hydraulic retention time (HRT) was 8 h, with an average effluent total nitrogen (TN) of 15.14 mg/L. Sludge bulking was prone to occur in low-temperature environments, resulting in a high average sludge volume index (SVI) of 560 mL/g. Conversely, with a CMPC dosage of 4 g/L, the HRT of HPB technology was 4.8 h, and the average effluent TN was 11.40 mg/L, with a removal efficiency of 67.43 %. During operation of HPB technology under high sludge concentration conditions (8 g/L), the average SVI remained at 85 mL/g, indicating excellent settling characteristics. Moreover, in the sequencing batch reactor (SBR), the SVI value of bulking sludge decreased from the original 695 to 111 mL/g by the 9th day of operation with the CMPC dosage of 2 g/L. At the same time, the filamentous bacteria almost disappeared, suggesting that CMPC inhibit the growth of filamentous bacteria. Metagenomic analysis demonstrated that CPMC enhance the utilization of small molecular fatty acids in activated sludge and promote electron transfer between nitrate and nitrite, thereby improving wastewater treatment capacity. Additionally, CMPC enhanced the relative abundance of Saprospiraceae in sludge, which accelerate the degradation of polysaccharides in extracellular polymeric substances, weaken sludge's hydrophilic properties, and improve sludge's settling performance. Overall, these findings suggested that CMPC effectively strengthen the high-loading operation of WWTPs by improving sludge concentration and sedimentation performance.

Time-resolved X-ray study of assisted fluidization of cohesive micron powder: On the role of mechanical vibration

Mechanical vibration has been broadly used to assist fluidization of cohesive powders, because of its capability to disrupt gas channels and agglomerates. However, the improvement reported in literature is mostly deduced from bulk response and ex-situ measurements, whereas the induced fluidization behavior and underlying physics remain largely unexplored. In this work, the fluidization behavior of micron-sized cohesive silica (Sauter mean diameter D32 = 7.9 μm) has been investigated experimentally under vibration of varying conditions. X-ray imaging was carried out to directly capture the temporal evolution of system hydrodynamics, and identify in-situ powder stratification, bubbling and channel formation. The study demonstrates that vibration effectively collapses gas channels, yet facilitates powder stratification and compaction, therefore developing three distinctive flow regions inside the bed with different fluidization states. Consequently, common measurements, such as pressure drop and bed expansion, tend to overestimate the improvement. In addition, increasing frequency, from 10 Hz to 30 Hz, is observed to increase the number of bubbles by 60 %, whereas a large amplitude (e.g., 2 mm) leads to a 10 % compaction in the top flow region.

Microstructural evolutions and mechanical characteristics of roll-bonding Mg/Al clad plate regulated by cold spraying micron particle interlayer

A new process of “cold spraying interlayer + roll-bonding” (CSIR) was put forward for the preparation of Mg/Al clad plates. First, the micron Ni and Al powders (including some Zn particles) were cold sprayed to form an ultrathin coating on Al or Mg substrate slabs. Then roll-bonding was performed at 400 °C. The influence of cold sprayed coating on slab surfaces, interfacial microstructures, texture evolutions, mechanical properties and the related mechanism were systematically investigated. The results show that the average shear strength of the as-rolled Mg/Al clad plate assisted by cold spraying Al and Ni micron powders interlayer on the substrate slabs was nearly twice (35.58 MPa) than that of conventional rolling under the same conditions (single pass, reduction ratio was 35%). For as-rolled Mg/Al clad plates, almost no reaction diffusion layers are generated, and the mechanical interlocking between cold sprayed coatings and substrate slabs is the main mechanism for improving the shear strength. The interface between the Al coating and the Ni coating is weakest of the as-rolled Mg/Al clad plates. As the reduction rate increases from 27.5% to 47.5%, the function of the mechanical interlocking of cold sprayed coatings will first increase and then weaken. After annealing at 400 °C for 1 h, the interface between the Al coating and the Mg substrate slab will form thick mixed brittle intermetallic compounds, including Al3Mg2, Mg17Al12, MgZn2 and AlMg4Zn11, and cause local gaps, holes, and cracks around the Zn-rich Ni coating. The fracture path after annealing starts from the vicinity of the defective Ni particles, and eventually enlarges along the mixed intermetallic compounds layer between the Al coating and the Mg substrate slab. The research indicates that the CSIR process has great potential in cooperating the metallurgical bonding with the mechanical interlocking of clad plates.

Highly Efficient Piezocatalytic Activity of Poly(tetrafluoroethylene) for Large-Scale Organic Wastewater Purification

Piezocatalysis is an emerging and promising catalytic technique for degrading organic pollutants by harvesting mechanical energy. However, the catalytic efficiency and environment compatibility of present piezocatalysts are still unsatisfactory. Here, the superior piezocatalytic performance of eco-friendly poly(tetrafluoroethylene) (PTFE) micron powders was demonstrated by degrading several typical dyes. Methylene blue can be degraded by 99% within 20 min (k = 0.246 min–1) using fresh PTFE under ultrasonic vibration, and PTFE exhibits excellent stability and reusability. In addition, rhodamine B, acid orange 7, and methyl orange can also be degraded by 100, 98, and 99% within 60 min, respectively, demonstrating the wide adaptability of PTFE. Catalytic mechanism investigations demonstrate that •OH and •O2– play major roles in dye degradation. Furthermore, the influence of various water sources and different containers on the catalytic performances of PTFE was explored, indicating that PTFE has nice environmental suitability and that the glass container facilitates catalytic degradation. Therefore, a designed glass spiral tube was applied for large-volume wastewater purification, which can be further extended for potential applications. This work thus demonstrates that PTFE can be regarded as a promising catalyst for wastewater treatment by harvesting mechanical energy, and the proposed Z-shaped wastewater degradation device has potential applications in wastewater treatment.

The microwave absorption properties of soft magnetic materials in frequency up to 40 GHz

With the continuous development of communication technology, the microwave frequency used has been extended to 24∼30 GHz or even higher. Thus, for the research on microwave absorption materials, the commonly used 2∼18 GHz frequency range might no longer be enough. More studies of microwave absorption properties in a higher frequency band are necessary. In this work, we report the microwave absorption properties of several soft magnetic composites in frequency up to 40 GHz. Magnetic materials such as iron, Y2Fe16Si, Ce2Fe17N3−δ, and La2Fe4Co10B micron powders which display excellent microwave absorption properties in 2∼18 GHz, are investigated. Within 2∼40 GHz, the reflection loss (RL) of iron/paraffin, Y2Fe16Si/paraffin, Ce2Fe17N3−δ/paraffin and La2Fe4Co10B/paraffin composites could reach −46.2 dB, −71.4 dB, −49.1 dB, and −40.1 dB, respectively. Moreover, their effective absorption bandwidth (RL &amp;lt; −10 dB) could reach 16.9 GHz, 8.53 GHz, 10.08 GHz, and 8.03 GHz, respectively. Though the measurements are extended to 40 GHz, the absorption properties of these composites become weak when the frequency rises to around 40 GHz, which is restricted by the cutoff frequencies of the materials. The measured data shows that these soft magnetic composites are good candidates for high-frequency microwave absorption materials, while exploring magnetic materials with further higher cutoff frequencies may result in better performance.

Dense and strong calcite ceramics prepared by room‐temperature cold sintering based on high‐pressure‐enhanced solubility

AbstractDense and strong calcite (CaCO3) ceramics were prepared by room‐temperature cold sintering with the aid of water and high pressure of up to 900 MPa. Under atmospheric pressure, calcite is barely soluble in water. However, the microstructure evolution and stress‐strain analysis during cold sintering revealed that the dissolution‐precipitation, plastic deformation, and pressure‐solution‐creep mechanisms played a crucial role in the densification and mechanical robustness of calcite ceramics, which was attributed to the significantly enhanced solubility of calcite in water under high pressure. The calcite ceramic cold sintered under 900 MPa from micron powder exhibited the highest relative density of 92.1% and best mechanical properties with compressive strength, flexural strength, hardness, and Young's modulus of 276.5 MPa, 52.5 MPa, 1.64 GPa, and 53.7 GPa, respectively. The as‐prepared calcite ceramic was stronger and harder than most stones and cement, indicating its promising application as novel building and biomimetic materials. The present study also provides a new strategy for densifying ceramics with low solubility by cold sintering.

Properties of Compacts from Mixtures of Calcium Fluoride Micro- and Nanopowders

In this work, compacts from mechanical mixtures of CaF2 micron powder (MCP) with CaF2 nanopowder (NP) additives were produced, with mass ratios of the mixture components ranging from 10:0.125 to 10:1, respectively, using magnetic pulse (MP) and static pressing (SP) methods. The effects of pressure (Pp) and pressing temperature (Tp), concentration and phase composition of the additive on the density and color of compacts were studied, taking into account the properties of the initial components of the mixtures. The evolution of pulsed cathodoluminescence (PCL) spectra and photoluminescence (PL) of compacts from pure powders and their mixtures depending on Pp, Tp and characteristics of initial CaF2 NP was also studied. A new near-infrared (NIR) band associated with fluoride vacancies was discovered with a maximum at ~765 nm in PCL spectra of compacts produced by MP at a temperature of 425 °C. A blue band at 435 nm associated with impurity oxygen vacancies in the CaF2 lattice was found in PL spectra compacts of pure NP and powder mixtures. The density of compacts of pure NP and MCP reached 89% of the theoretical density, and the density of compacts of mixtures did not exceed 78%. The defective structure and phase composition of the CaF2 NP had a decisive effect on the luminescent properties of compacts from mixtures of micro- and nanopowders.

Novel Ni-V-Y Electrocatalysts for Hydrogen Evolution Reaction

Generation of renewable energy is improving globally, the ability to store generated energy remains an issue. A new class of water electrolysers that utilize anion exchange membranes (AEMs) are effective at converting water to hydrogen gas which can be used as fuel. Novel electrocatalysts are required for AEMs to be active, stable, and cost effective when used in AEM water electrolysers. Previously, S. Ghobrial investigated the Ni-Nb-Y alloy system as an electrocatalyst for the hydrogen evolution reaction, with Ni and Y components contributed to electrocatalytic activity [1]. Nb phase did not contribute to electrochemical activity and behaved only as a glass former. For the second-generation alloy, V replaced Nb to create a Ni-V-Y alloy. Thermodynamic modelling via FactSage was used to develop the amorphous alloy system. To create the amorphous alloys, a two-step ball milling process was used. Elemental powders were mechanically alloyed and amorphized under cryogenic conditions. The micron sized alloyed powder was size reduced to nanoparticles suitable for use as electrocatalysts via surfactant assisted high energy ball milling (SA-HEBM). Both micron powders and nanoparticles were structurally characterized using X-ray diffraction and SEM. The catalytic activity of the electrocatalysts were electrochemically characterized using steady state polarization to determine Tafel slopes and exchange current densities. A Ni-V-Y alloy was successfully produced via cryomilling and SA-HEBM. The combination of the NiVY amorphous phase + Ni3V + Ni5Y phases in the micron and nanopowders improved activity relative to the intermetallics alone via the spillover effect. The surfactant used in SA-HEBM is not completely removed by the current centrifugation process leading to lower-than-expected activity and marginal spillover enhancement in nanoparticles. With an improved cleaning process, it is predicted the nanoparticles will have higher activities than their micron powder counterparts.[1] - S. Ghobrial, Amorphous Ni-Nb-Y Alloys as Hydrogen Evolution Electrocatalysts, Toronto: University of Toronto, 2019.

Rapid fabrication of ultra-fine grain intermetallic compound powder in milliseconds under ultrasonic vibrations

As a key raw material for industrial production and scientific research, intermetallic compounds (IMCs) powder has broad application prospects, and it has a performance breakthrough in its nanocrystalline state. Crystallized metallic glasses (MGs) are a class of IMCs, its powder has great potentials for electromagnetic conversion, catalysis, exhaust treatment and biomedical application. Although many powder fabrication methods exist, a simple, fast method to prepare ultra-fine grain IMC powders is still being pursued. Here we report a facile method to fabricate ultra-fine grain (<5 nm) crystallized MGs powder by ultrasonic vibration treatment (UVT). At room temperature and well below the ultimate material strength, UVT can rapidly breaks bulk crystallized MGs down to micron and nanoscale powders. Compared to other methods, UVT has an outstanding time advantage in within 60 s (1000 times faster than the ball milling). The experimental show that UVT causes rapid grain refinement in crystallized MGs, inducing fatigue crack nucleation at the grain boundaries (GBs) and then smash in milliseconds. Our results provide a fast and cost-efficient method for the production of micro and nano scale ultra-fine grain IMC powders.

Agglomeration in Composite Propellants Containing Different Nano‐Aluminum Powders

AbstractIn order to improve nano‐aluminized solid propellant properties and performance, different materials are being investigated for coating nano‐aluminum particles. Two of the powders which are considered are V‐ALEX, a fluoropolymer (Viton) coated nano‐aluminum, and L‐ALEX, a stearic acid coated nano‐aluminum. It is believed that a thin layer of coating should protect the aluminum core from premature oxidation, as well as provide an exothermic source which may accelerate particle ignition, resulting in reduction of agglomeration.This paper investigates the effect on the agglomeration phenomenon of replacing 33 % of the micron aluminum powder with ALEX, V‐ALEX and L‐ALEX powders, in solid propellant samples containing 20 % HTPB, 65 % AP and 15 % aluminum. Propellant strands were burned inside a windowed pressure chamber, allowing measurements of the agglomerates size and number using a high‐speed camera.The experimental data showed that propellants in which 33 % of the micron aluminum was replaced with nano‐powders exhibited reduced agglomeration, in terms of number of agglomerates and their total volume. The reason is the lower ignition time and temperature of the nano‐powders that ignite before aggregating to agglomerates. The propellants containing ALEX nano‐powder exhibited a reduction of up to 36 % in agglomerates volume compared to the propellants containing only micron powder, while the propellants containing coated nano‐powders, L‐ALEX and V‐ALEX, showed a higher reduction of up to 60 % in agglomerates volume. V‐ALEX showed slightly better performance than L‐ALEX. It can be concluded that by replacing some of the micron‐aluminum with coated nano‐aluminum in solid propellants, it is possible to significantly reduce the propulsive losses due to agglomeration.

Research on process control of intermittent electrodeposition for preparation of core-shell powder

The uniformity of composite powder is crucial for preparing composite materials with excellent performance. Herein, an Intermittent electrodeposition technology has been proposed, which can deposit a coating on micron powder and achieve evenly mixing on the particle scale. In this study, Taking the W@Cu core-shell powder as an example, the effect of cathode density, deposition time and pulse width on composition and cladding rate of the core-shell powder and its properties were determined. Furthermore, the relationship between cladding layer thickness and load capacity, current intensity and electrodeposition time was proposed. The experimental results showed that the core-shell powder obtained at the optimal current density of 7 A/dm2 had an average thickness of 2.8 μm cladding rate of 92.7% after electrodeposition for 40 min. It indicated the theoretical model can effectively predict the core-shell powder thickness. Finally, the formation processes of the cladding layer of the core-shell powder were also clarified.

Effects of operational and geometrical parameters on velocity distribution and micron mineral powders classification in cyclone separators

The application of cyclone separators in the classification of micron powders can achieve satisfactory performance with low operation costs. The effects of operational and geometrical parameters including the inlet velocity, vortex finder length, and vortex finder diameter on the velocity distributions and classification performance of micron powders in cyclone separators were studied via CFD simulation and experiments. The results revealed that the inlet velocity and vortex finder diameter significantly affect velocity distribution and particles separation owing to changes in swirl intensity and axial backflow. The vortex finder length influences the positive effects of vortex finder, and a sufficient length should be chosen to weaken the disturbance of inlet airflow and enhance particles separation. The classification results of micron ground calcium carbonate powder indicated that these parameters all significantly affect the cut size and classification sharpness, and moderate values of these parameters should be selected to obtain a satisfactory classification performance.

Solid Energetic Material Based on Aluminum Micropowder Modified by Microwave Radiation

The paper discusses the application of pulsed microwave radiation for the modification of crystalline components of a high-energy material (HEsM). The model aluminized mixture with increased heat of combustion was studied. The mixture contained 15 wt.% aluminum micron powder, which was modified by microwave irradiation. It was found that the HEM thermogram has an exo-effect with the maximum at 364.3 °C. The use of a modified powder in the HEM composition increased the energy release during combustion by 11% from 5.6 kJ/g to 6.2 kJ/g. The reason for this effect is the increase in the reactivity of aluminum powder after microwave irradiation. In this research, we confirmed that the powders do not lose the stored energy, even as part of the HEM produced on their basis. A laser projection imaging system with brightness amplification was used to estimate the speed of combustion front propagation over the material surface. Measurement of the burning rate revealed a slight difference in the burning rates of HEMs based on irradiated and non-irradiated aluminum micropowders. This property can be demanded in practice, allowing a greater release of energy while maintaining the volume of energetic material.

The Study of Biological Glue Droplet Impact Behavior of Bioceramic Powders Applied in 3D Printing of Bone Scaffolds

This paper aims to develop a reliable and effective model to investigate the behavior of micron-sized biological glue droplets impacting micron-sized bioceramic powder beds applied to the 3D printing process. It also endeavours to explore the common rules of droplet impact affected by particle size and the wettability of powder, which are supposed to provide process parameters guidance for the application of new materials in 3D printing. Firstly, based on the low impulse impact model, the simplified model was proposed. Then, the observation and simulation experiments of millimeter-scale droplet impacting were carried out under the same conditions to prove the effectiveness of the model. Furthermore, the characterization of a parametric experiment of a 3D printing practice was used to verify the significance and effectiveness of the simulation study method. Lastly, the method was performed to investigate the effect of wettability and particle size of the micron powder on the micron droplet impact. The results showed that the binder powder’s wettability and particle size could directly influence the droplet spreading behavior. The characterization results of samples printed in the simulation-predicted parameter showed that the amount of binder used could be reduced by 38.8~50.1%, while the green strength only lost 17.9~20%. The significance of this simulation method for prediction of 3D printing process parameters was verified.