Surface Of Larger Particles Research Articles

Effect of large particle mixing on cloud ignition and explosion of fine rice husk

Large particles mixed with fine dust are commonly found in the processing and transportation of grain dust. The mixture of dust is exposed to the risk of dust explosions when suspended in the environment. Using a 20 L spherical explosion device and the dust cloud minimum ignition energy (MIE) experimental platform, this study examines the effects of crushed brown rice mixture on the ignition and explosion of fine rice husk dust. The discovery of large granules of crushed brown rice being lifted up to form flow "obstacles" in the mixed dust cloud has a similar inhibitory effect to inert materials, causing the MIE of the dust cloud to increase from 40 mJ to 150 mJ. However, 5 % of crushed brown rice will lower the 10 mJ dust cloud's ignition energy when the concentration of dust clouds is 500 g/m3. Through testing the dispersibility of mixed dust clouds, it was found that fine dust particles adsorbed on the surface of large particles will peel off after being lifted, improving the dispersibility of the mixed dust cloud and forming a system of mixed dust clouds with finer effective particle size, thereby promoting ignition. Furthermore, due to the improvement in the dispersibility of mixed dust clouds by large particles, at mixing ratios below 30 %, large particles will also significantly increase the maximum rate of pressure rise (dP/dt)max, increasing the likelihood of dust ignition and the consequences of an explosion. Therefore, these findings should be taken into consideration during the process of grain processing and transportation.

Probing Particle-Carbon/Binder Degradation Behavior in Fatigued Layered Cathode Materials through Machine Learning Aided Diffraction Tomography.

Understanding how reaction heterogeneity impacts cathode materials during Li-ion battery (LIB) electrochemical cycling is pivotal for unraveling their electrochemical performance. Yet, experimentally verifying these reactions has proven to be a challenge. To address this, we employed scanning μ-XRD computed tomography to scrutinize Ni-rich layered LiNi0.6Co0.2Mn0.2O2 (NCM622) and Li-rich layered Li[Li0.2Ni0.2Mn0.6]O2 (LLNMO). By harnessing machine learning (ML) techniques, we scrutinized an extensive dataset of μ-XRD patterns, about 100,000 patterns per slice, to unveil the spatial distribution of crystalline structure and microstrain. Our experimental findings unequivocally reveal the distinct behavior of these materials. NCM622 exhibits structural degradation and lattice strain intricately linked to the size of secondary particles. Smaller particles and the surface of larger particles in contact with the carbon/binder matrix experience intensified structural fatigue after long-term cycling. Conversely, both the surface and bulk of LLNMO particles endure severe strain-induced structural degradation during high-voltage cycling, resulting in significant voltage decay and capacity fade. This work holds the potential to fine-tune the microstructure of advanced layered materials and manipulate composite electrode construction in order to enhance the performance of LIBs and beyond.

Probing Particle‐Carbon/Binder Degradation Behavior in Fatigued Layered Cathode Materials through Machine Learning Aided Diffraction Tomography

AbstractUnderstanding how reaction heterogeneity impacts cathode materials during Li‐ion battery (LIB) electrochemical cycling is pivotal for unraveling their electrochemical performance. Yet, experimentally verifying these reactions has proven to be a challenge. To address this, we employed scanning μ‐XRD computed tomography to scrutinize Ni‐rich layered LiNi0.6Co0.2Mn0.2O2 (NCM622) and Li‐rich layered Li[Li0.2Ni0.2Mn0.6]O2 (LLNMO). By harnessing machine learning (ML) techniques, we scrutinized an extensive dataset of μ‐XRD patterns, about 100,000 patterns per slice, to unveil the spatial distribution of crystalline structure and microstrain. Our experimental findings unequivocally reveal the distinct behavior of these materials. NCM622 exhibits structural degradation and lattice strain intricately linked to the size of secondary particles. Smaller particles and the surface of larger particles in contact with the carbon/binder matrix experience intensified structural fatigue after long‐term cycling. Conversely, both the surface and bulk of LLNMO particles endure severe strain‐induced structural degradation during high‐voltage cycling, resulting in significant voltage decay and capacity fade. This work holds the potential to fine‐tune the microstructure of advanced layered materials and manipulate composite electrode construction in order to enhance the performance of LIBs and beyond.

Investigation of engineering characteristics of red sand in Luanda, Angola

Red sand is widely distributed on the west coast of Africa, south of the Sahara, and is an essential material for local engineering construction. Red sand possesses orthostasis and high sensitivity to water, exhibiting characteristics that are different from ordinary sandy soil. Laboratory and in-situ tests were conducted to assess its engineering characteristics, including collapsibility, shear characteristics, and bearing capacity. The water sensitivity of red sand was analyzed along with the images from a scanning electron microscope. The findings indicate that red sand can be classified as silty sand. It demonstrates strong collapsibility, with the collapsibility coefficient decreasing as water content increases. The critical water content for red sand to avoid collapsibility is 13%. The shear strength, internal friction angle, and cohesion of undisturbed and remolded red sand decrease with increasing water content. The critical water content for red sand to lose cohesion is 13%. The bearing capacity and deformation modulus of red sand decrease with increasing water content. Red sand exhibits a softening property, with a softening coefficient of 0.4. The water sensitivity of red sand can be attributed to the cementing effects of fine-grained clay minerals adhering to the surface of large particles or aggregating at particle contacts.

Characteristic analysis of high-speed steel powder prepared by gas atomisation

The performance of high-speed steel (HSS) powder is a prerequisite for the preparation of high-performance powder metallurgy HSS. The physical properties, microstructure, and solidification characteristics of HSS powder prepared by nitrogen gas atomisation were systematically studied and analysed in detail. For the atomised TPM558 HSS powder, the morphology is spherical and the particle size distribution is wide. The smooth small particles of satellite powder attach to the surface of large particles. Shrinkage pits caused by solidification shrinkage exist on the surface of large particles. The average cooling rate is between 104 and 106 K·s−1, with the increase of cooling rate, the powder surface tends to be smooth, and the grain structure is transformed in the order of cellular to dendritic to radial. The single powder particle surface shows fine-equiaxed grains, while the internal presents columnar grains. The crystalline phases of the powder are austenite, ferrite, martensite, and carbide, and the carbide includes MC carbide with face-centred structure and M2C carbide with hexagonal structure. The average nano-hardness of the powder is 9.93 GPa, resulting in poor formability, and it can be pressed and formed only after adding binder.

Non-destructive three-dimensional imaging of artificially degraded CdS paints by pump-probe microscopy

Cadmium sulfide (CdS) pigments have degraded in several well-known artworks, but the influence of pigment properties and environmental conditions on the degradation process have yet to be fully understood. Traditional non-destructive analysis techniques primarily focus on macroscopic degradation, whereas microscopic information is typically obtained with invasive techniques that require sample removal. Here, we demonstrate the use of pump-probe microscopy to nondestructively visualize the three-dimensional structure and degradation progress of CdS pigments in oil paints. CdS pigments, reproduced following historical synthesis methods, were reproduced as oil paints and artificially aged by exposure to high relative humidity and light. The degradation of CdS to CdSO4·xH2O was confirmed by both FTIR (Fourier-transform infrared) and XPS (x-ray photoelectron spectroscopy) experiments. During the degradation process, optical pump-probe microscopy was applied to track the degradation progress in single grains, and volumetric imaging revealed early CdS degradation of small particles and on the surface of large particles. This indicates that the particle dimension influences the extent and evolution of degradation of historical CdS. In addition, the pump-probe signal decrease in degraded CdS is observable before visible changes to the eye, demonstrating that pump-probe microscopy is a promising tool to detect early-stage degradation in artworks.

Ni-Based SBA-15 Catalysts Modified with CeMnOx for CO2 Valorization via Dry Reforming of Methane: Effect of Composition on Modulating Activity and H2/CO Ratio.

Dry reforming of methane with ratio CH4/CO2 = 1 is studied using supported Ni catalysts on SBA-15 modified by CeMnOx mixed oxides with different Ce/Mn ratios (0.25, 1 and 9). The obtained samples are characterized by wide-angle XRD, SAXS, N2 sorption, TPR-H2, TEM, UV-vis and Raman spectroscopies. The SBA-15 modification with CeMnOx decreases the sizes of NiO nanoparticles and enhances the NiO-support interaction. When Ce/Mn = 9, the NiO forms small particles on the surface of large CeO2 particles and/or interacts with CeO2, forming mixed phases. The best catalytic performance (at 650 °C, CH4 and CO2 conversions are 51 and 69%, respectively) is achieved over the Ni/CeMnOx/SBA-15 (9:1) catalyst. The peculiar CeMnOx composition (Ce/Mn = 9) also improves the catalyst stability: In a 24 h stability test, the CH4 conversion decreases by 18 rel.% as compared to a 30 rel.% decrease for unmodified catalyst. The enhanced catalytic stability of Ni/CeMnOx/SBA-15 (9:1) is attributed to the high concentration of reactive peroxo (O-) and superoxo (O2-) species that significantly lower the amount of coke in comparison with Ni-SBA-15 unmodified catalyst (weight loss of 2.7% vs. 42.2%). Ni-SBA-15 modified with equimolar Ce/Mn ratio or Mn excess is less performing. Ni/CeMnOx/SBA-15 (1:4) with the highest content of manganese shows the minimum conversions of reagents in the entire temperature range (X(CO2) = 4-36%, X(CH4) = 8-58%). This finding is possibly attributed to the presence of manganese oxide, which decorates the Ni particles due to its redistribution at the preparation stage.

Modified monoclinic metastable β-MoO3 submicrospheres: controllable preparation, phase identification, and their formation mechanisms

In this work, a modified monoclinic metastable β-MoO3 (identified as N-doped β-MoO3-θ) submicrospheres (SMSs) were prepared by the method of sublimation with using industrial MoO3 as the raw material in the range of 1173–1373 K. Various technologies such as XRD, SEM, FE-SEM, TEM, Raman, and XPS spectra were adopted to characterize the as-prepared product. The result showed that the phase composition of the as-prepared product had no obvious relationship with the reaction temperature and cooling condition, while the pumping speed of the system exerted important roles on it. When the pumping speeds were low (4 and 15 cm/s), uniform N-doped β-MoO3-θ SMSs were prepared; increasing the pumping speeds to 20 cm/s or higher, both N-doped β-MoO3-θ SMSs and α-MoO3 nanoplates (NPs) were appeared. Optimum conditions for the controllable preparation of N-doped β-MoO3-θ SMSs were recognized as 1273 K, water cooling, and with a pumping speed of 4–15 cm/s. The growth mechanism of large MoO3 spherical-shaped particles were due to the collision and gases deposition effects. This work also discovered that the cracking phenomena were often occurred on the surface of large MoO3 particles obtained under the air cooling and high pumping speed conditions, and the possible cracking mechanisms were illustrated.

РЕЖИМ ФЛОТАЦИИ ЗОЛОТОСОДЕРЖАЩИХ РУД С ОБОРОТОМ ЧЕРНОВОГО КОНЦЕНТРАТА

The study of the dynamic properties of a thin layer of water enclosed between solid surfaces made it possible to reveal the role of fluid adhesion and slip in their interaction. The resistance to approach of solids is presented in the form of corrections for sticking and sliding. The effect of sticking hydrophobic fine gold on thin plates and flakes of native gold was studied during the flotation of a charge composed of gravity tailings of gold ore (yield 98.187%, gold content 1.1 g/t) and heavy concentrate (yield 0.059%, gold content 49.88 g). /t), isolated by gravity from the waste ofplacer washing. It has been established that grains of finely dispersed gold are more strongly attracted to the surface of large gold particles (aggregation constant 43.7) than to each other (aggregation constant 0.070).

Study on Wear Mechanism of Helical Gear by Three-Body Abrasive Based on Impact Load.

This study aimed to explore the wear characteristics and evolution mechanisms of large-scale wind power gears under the impact load of particles of the three-body abrasive Al2O3 (0.2 mg/mL) from four aspects: oil analysis, vibration analysis, amount of gear wear, and tooth-surface-wear profile analysis. A magnetic powder brake was used to simulate the actual working conditions. Combined with the abrasive particle monitoring and the morphology analysis of the tooth-surface-wear scar, by setting quantitative hard particles in the lubricating oil, the gears are mainly operated in the abrasive wear state, and wear monitoring and wear degree analysis are carried out for the whole life cycle of the gears. Oil samples were observed and qualitatively analyzed using a particle counter, a single ferrograph, a metallographic microscope, and a scanning electron microscope. The experiments demonstrate that the initial hard particles have a greater impact in the early wear stage of the gears (<20 h), and abrasive particle concentration increases by 30%. This means that Al2O3 particles accelerate the gear wear during the running-in period. The loading method of the impact load on the oblique gear exacerbates the abrasion particle wear and expands the stress concentration, which reduces the surface of large milling particles on the surface, and reduces the width of the tooth (the part above the pitch line is severely worn), which causes the gear to break into failure. The research provides help for analyzing the mechanism of abrasive wear of gears and predicting wear life.

Anomalous Formation of Irradiation-Induced Nitrogen-Vacancy Centers in 5 nm-Sized Detonation Nanodiamonds

Nanodiamonds containing negatively charged nitrogen-vacancy (NV$^-$) centers are versatile room-temperature quantum sensors in a growing field of research. Yet, knowledge regarding the NV-formation mechanism in very small particles is still limited. This study focuses on the formation of the smallest NV$^-$-containing diamonds, 5 nm detonation nanodiamonds (DNDs). As a reliable method to quantify NV$^-$ centers in nanodiamonds, half-field signals in electron paramagnetic resonance (EPR) spectroscopy are recorded. By comparing the NV$^-$ concentration with a series of nanodiamonds from high-pressure high-temperature (HPHT) synthesis (10 - 100 nm), it is shown that the formation process in 5 nm DNDs is unique in several aspects. NV$^-$ centers in DNDs are already formed at the stage of electron irradiation, without the need for high-temperature annealing. The effect is explained in terms of "self-annealing", where size and type dependent effects enable vacancy migration close to room temperature. Although our experiments show that NV$^-$ concentration generally increases with particle size, remarkably, the NV$^-$ concentration in 5 nm DNDs surpasses that of 20 nm-sized nanodiamonds. Using Monte Carlo simulations, we show that the ten times higher substitutional nitrogen concentration in DNDs compensates the vacancy loss induced by the large relative particle surface. Upon electron irradiation at a fluence of $1.5 \times 10 ^{19}$ e$^-$/cm$^2$, DNDs show a 12.5-fold increment in the NV$^-$ concentration with no sign of saturation. These findings can be of interest for the creation of defects in other very small semiconductor nanoparticles beyond NV-nanodiamonds as quantum sensors.

Effects of Oil and Sediment Properties and Mixing States on the Formation and Settling of Oil‐Particle Aggregates

AbstractUnderstanding the interaction of oil droplets with suspended particulate matter is important not only for sunken oil modeling but also for emergency response. In this study, the effects of mixing time and energy, oil type, and sediment concentration and size on the oil content, morphology, and density of oil‐particle aggregates (OPAs) were investigated through a series of wave tank experiments and sedimentation tests. The results showed that loads of oil and particles in OPAs are high under high mixing energy. Under turbulent hydrodynamics, moderately viscous oils form OPAs more easily and sink rapidly to the seabed. Moreover, an increase in the density and oil capacity of OPAs is observed at a higher sediment concentration. More oil is captured by finer sediments. However, the corresponding oil‐sediment aggregates generally show lower density compared with those formed by larger sediments. The oil‐seawater interfacial tension (IFTow) diminishes with the addition of sediments, further promoting oil dispersion. The increasing duration and mixing energy produce more flake OPAs and multiple‐droplet OPAs. Oil droplets tend to be surrounded by several small particles but attach to the surface of large particles. Regardless of oil type and sediment concentration, the structure of OPAs does not change significantly.

Structural Analysis of an Antigen Chemically Coupled on Virus-Like Particles in Vaccine Formulation.

Structure determination of adjuvant-coupled antigens is essential for rational vaccine development but has so far been hampered by the relatively low antigen content in vaccine formulations and by their heterogeneous composition. Here we show that magic-angle spinning (MAS) solid-state NMR can be used to assess the structure of the influenza virus hemagglutinin stalk long alpha helix antigen, both in its free, unformulated form and once chemically coupled to the surface of large virus-like particles (VLPs). The sensitivity boost provided by high-field dynamic nuclear polarization (DNP) and proton detection at fast MAS rates allows to overcome the penalty associated with the antigen dilution. Comparison of the MAS NMR fingerprints between the free and VLP-coupled forms of the antigen provides structural evidence of the conservation of its native fold upon bioconjugation. This work demonstrates that high-sensitivity MAS NMR is ripe to play a major role in vaccine design, formulation studies, and manufacturing process development.

Multiple antibiotics distribution in drinking water and their co-adsorption behaviors by different size fractions of natural particles

In recent years, natural particles in drinking water have attracted attention due to their carry of toxic organic matter. However, the adsorption behavior of multiple antibiotics at very low concentrations on different sized particles has not been revealed. Here, the content of 17 antibiotics in water samples collected from four process stages of the water supply plant was detected. Results showed the concentration of antibiotics in water plant was in the range of 0–69.24 ng L−1. Characterization of natural particles obtained directly from raw water of waterworks showed that the surface of large particles (>1 μm) was rougher and the composition was more complex than that of small particles (0.05–1 μm). Besides, the adsorption experiments of four antibiotics (nalidixic acid (NAL), trimethoprim (TMP), roxithromycin (ROX), and penicillin G potassium salt (PG)) on small (0.05–1 μm) and large (>1 μm) natural particles were studied. The results indicated that in the binary antibiotic system, the competition and synergy between antibiotics made a greater proportion of antibiotics soluble in water comparing with single systems, and the particle-water partition coefficient (kp-w) of the total antibiotics ranged from 1.13–1.78 was reduced to 0.57–0.84. The competitive adsorption of antibiotics appeared in the binary system showed that ROX and PG had a higher adsorption capacity than NAL and TMP. Furthermore, in the binary antibiotic systems, small particles played an important role in adsorption, suggesting the urgency of their removing. This work could help predict the possible risks of drinking water and provide some insights into future drinking water treatment.

CFD-DEM simulation of powders clogging in a packed bed with lateral inlet

Abstract Clogging behavior of powder particles in packed bed is a longstanding engineering challenge in many industrial processes, of particular interests to ironmaking reactors. In this work, a CFD-DEM model was developed to investigate the powders clogging in a packed bed with lateral inlet. The flow and clogging of powders of varying gas velocities flowing through the packed bed were studied. The results showed that two kinds of clogging powders inside the porous can be observed. One is mainly due to mechanical interactions between powder particles, which can create arches on packed bed and stop the flow. When the powders form a bridge across the pore throat of the orifice, the bottleneck of void space becomes the starting point for blockage formation. The other represents a part of clogging powders which is due to drag force and friction between one small particle rolling very slowly on the surface of large particles whose spacing is close to the diameter of powders. The powders distribution, mechanical behavior and pressure drop were also discussed. The findings of this work provides a fundamental understanding on clogging behavior of powders in a packed bed with lateral inlet, and is useful for industry processes’ understanding and optimization.

Study on Volume Reduction of Cesium Contaminated Soil by High Gradient Magnetic Separation: Design of Magnetic Filters

The superconducting magnetic separation was examined to reduce the volume of cesium contaminated soil by the Fukushima Daiichi nuclear power plant accident. By using superconducting high gradient magnetic separation, silt and clay with high radioactive concentration due to the large particle surface area per unit mass can be further separated into high-dose 2:1 type and low-dose 1:1 type clay minerals selectively. Here, we examined filter conditions to improve the magnetic separation performance in farmland soil that is rich in organic matter. The results of magnetic separation of uncontaminated soil suggested that the separation selectivity of 1:1 and 2:1 type clay minerals was larger with the filters with smaller wire diameter. On the other hand, it was found that it was difficult to magnetically separate 0-20 μm particles even with the filters with small wire diameter and high selectivity. To solve this problem, magnetic separation was performed under the same conditions on actual contaminated soil that was highly classified into 0-20 μm and 20-75 μm particles. As the result, it was found that the radioactivity can be further reduced by removed high-dose 0-20 μm particles and targeting the 20-75 μm particles.

Water model study of the removal effect of soluble gas floatation technology (SGFT) on inclusions with different characteristics

In this study, the removal effects of soluble gas floatation technology (SGFT) on inclusions with different characteristics were studied by using a self-made water model experimental device and Coulter counter. The water/CO2 system was used to simulate the molten steel/(H2, N2) system, and PP, PE and ABS particles were used to simulate the inclusions in molten steel. The experimental results show that this technology has good removal effects on particles with different characteristics. A large amount of fine bubbles can be formed when adding particles via heterogeneous nucleation, while no bubbles were formed without adding particles due to lack of nucleation cores. The removal rate of the particles increases with the increase of particle number. The size of the particles has a significant impact on its removal effect that the removal rate increases with the increase of particle size. The Ostwald ripening may appear on the bubble nucleation process on the surface of large particles, which can promote floating behavior and removal effect of the particles. The particles with different contact angles can be removed effectively by soluble gas floatation technology (SGFT), while the removal effect of particles with large contact angles is better.

A perspective on sodium-induced agglomeration of Zhundong coal gasification: Experiments and calculations

In order to provide basic knowledge for the gasification utilization of low-rank Zhundong (ZD) coal in the process of circulating fluidized bed (CFB), this study focuses on gasification reactivity and ash related agglomeration of ZD coal mainly induced by sodium transformation. Typical ZD coal was pyrolyzed in a horizontal tube reactor by a rapid pyrolysis method at 900 °C. Isothermal and non-isothermal thermogravimetric analyses were used to study the gasification reactivity of ZD char under CO2 atmosphere. The effect of temperature, ranging from 850 °C to 1050 °C, on isothermal gasification was investigated, and the obtained gasification residues were analyzed to observe microscope morphology and evaluate agglomeration degree. The ternary system relationship of Na2O–SiO2–Al2O3 at each gasification temperature was calculated with FactSage to compare with the experimental results. The results show that: the gasification reactivity of ZD coal char is greatly affected by the gasification temperature. Higher temperature can increase the average specific gasification rate, thus shorten the reaction time that the carbon conversion reaches equilibrium. The gasification reactivity of coal char is proved to be better at higher temperature. The agglomeration characteristics were also affected by the gasification temperature. There is almost no melting and agglomeration phenomenon for 850 °C gasification residue, while a strong tendency to agglomeration is showed in other samples. However, when the mass fraction of local CaO on the surface of large particles is more than 40%, the melting phenomenon can be alleviated. According to the Na2O–SiO2–Al2O3 phase diagram, the positions of ZD coal and ZD char are located near the complete Slag-liq region, indicating that using ZD coal and ZD char at the operation temperature of CFB above 950 °C has strong risk of slagging, and a relatively lower gasification temperature, ∼900 °C, is suitable for ZD coal/char gasification.

Formation of droplet-mode secondary inorganic aerosol dominated the increased PM2.5 during both local and transport haze episodes in Zhengzhou, China

The size distribution and formation of secondary inorganic aerosol play a key role in the increasing PM2.5 concentration. Size-segregated data including mass, number, and chemical component concentrations were obtained during a haze episode from January 12 to 23 in Zhengzhou to gain insight into the dominant factors for the growth of PM2.5. PM2.5 levels during two local processes (LP1 and LP2) were mainly affected by the accumulation and secondary formation of local pollutants. The transport process (TP) was affected by the air mass transported from the northern area of Zhengzhou. Results show that the growth of particle mass concentration in LP1 mainly occurred in the size range of 400–640 nm and 640–1000 nm. With the aggravated particles increases (LP2), 640–1000 nm and 1–1.6 μm particles dominated the increasing PM2.5 concentration. The particles carried by northern air mass (TP) were concentrated in the size range of 1–1.6 μm. Variation trends of hourly PM2.5 chemical components and size distribution of water-soluble inorganic ions suggested that the formation and growth of droplet-mode nitrate, sulfate, and ammonium dominated the increase of PM2.5, and the particle sizes of these components increased with the increasing PM2.5. High concentrations of aerosol water content and large surface area in droplet-mode were beneficial for the heterogeneous reactions for droplet-mode nitrate formation. Moreover, large particle surface area in droplet-mode particles also provided adequate carriers for the adsorption and condensation of gaseous HNO3 onto these particles. Elevated aerosol water, surface area, and particle acidity enhanced the H2O2 and transition metal (TMI) oxidation for aqueous-phase droplet-mode sulfate formation. The contribution of TMI-catalyzed oxidation significantly increased in LP2 because of the high TMI concentration and particle acidity. Relatively low aqueous-phase sulfate production rates in TP suggest that the observed high concentration of droplet-mode sulfate was mainly originated from the completely transformed SO42− carried by air masses. Moreover, droplet-mode particles exhibited moderate acidity, which enhanced the gas-particle partitioning of NH3(g)/NH4+(a).

The possibility of obtaining spherical microgranules without satellites for surface-plastic deformation of responsible products

Problem. To strengthen the surface-plastic deformation (SPD) of components of a responsible purpose, for example, in the aviation industry, working bodies (microspheres) are used, which can be obtained by the technology of gas atomization. Powders used for SPD of machine parts must be spherical without satellites with maximum monodisperses. Goal. The aim of this paper is to develop a process for obtaining spherical microgranules without satellites in the process of gas atomization and to study the quality parameters of the surface layer of parts treated with the use of microgranules as SPD working bodies. Methodology. To obtain spherical microgranules it is proposed to use the method of gas sputtering of a metal melt with the use of a progressive rotating gas stream. In the proposed method, the destruction of the jet and the subsequent destruction of individual small particles occur in the vacuum, which is created by two opposite directed helical gas flows. This leads to the expansion of the crushing zone of the metal, reducing the direct impact of the gas on the liquid metal particles and, thus, allows the separation of the motion of small and large droplets in space, which significantly reduces the probability of the formation of small satellites on the surface of larger particles. Spraying of a metal melt of ShH15 steel, heated to a temperature of 1580 оС, was carried out at a gas pressure of 1,4… 1,7 MPa, a melt flow of 0,5 kg/s and a specific gas flow rate of 1,0 m3 /kg. Results. The efficiency of the application of the obtained working bodies is proved by the results of the study of the operational properties of the surface layer of the parts being processed: surface roughness corresponds RA = 0,9...0,8 μm; the degree of deformed state reaches 18...30% at a depth of up to 120 microns; the residual compression stresses are 300...700 MPa at a depth of up to 100 μm. Scientific originality. The factors that influence the number of satellites on the surface of spherical microgranules are analyzed in the paper. It is established that the organization of the rotation of the gas flow around the axis of the atomization in the radial direction facilitates the process of removal of fine particles beyond the sputtering torch, which, in turn, leads to a decrease in the number of satellites on spherical powder particles. Practical value. According to the tests, the use of microspheres of ShH15 steel for SPD of a wide range of parts, gives significant technical and economic advantages in comparison with other methods: elimination of costs for surface finishing after SPD; increased by 10...30 % endurance of processed materials; increased by 2...6 times the durability of parts; 3 times increased product life.