Ultrafine Powders Research Articles

Синтез сложно-оксидной керамики в пучке быстрых электронов

The synthesis of ceramic materials in a fast electrons beam for the production of complex oxide ceramics is considered. Powder reagents, in addition to irradiation, are exposed to air currents that prevent gases and particles from entering the accelerator. To keep powder mixtures of ultrafine powders in the irradiation zone, they were granulated. Two methods of granulation of an ultrafine powder of the composition (in mass %) 80 % Al2O3 + 20 % (ZrO2 – 3 Y2O3) were used. The first method involves moistening, drying and then sifting through a coarse sieve. In the second method, a binding additive was introduced into the powder mixture, which gave the sample a stable volumetric shape. For the granulation methods used, the features of short-term heating of oxide powders in air with a powerful beam of fast electrons with an energy of 2 MeV and the synthesis of zirconia corundum under these conditions were studied. Granulation of the ultrafine powder made it possible to minimize the loss of its mass during irradiation. During irradiation of the powder mass, its local melting took place, which was accompanied by intense gas release processes leading to the formation of hollow ceramic droplets. X-ray phase analysis has shown that mutual dissolution of oxides in their walls does not occur, and recrystallization processes are accompanied by the formation of cubic aluminum oxide microcrystallites and the transition of aluminum oxide in them from the monoclinic to the corundum phase. The presence of microcrystallites of evenly distributed small particles of zirconia dioxide in the interboundary space indicates the production of zirconia corundum under irradiation. At the same time, the phase composition of zirconium dioxide after irradiation does not change in comparison with the initial powder.

Технология изготовления и свойства высокотемпературных пьезокерамических материалов на основе фаз системы (1 – у)(Bi0,8Ba0,2)Fe0,8Ti0,2O3 – у(Ba0,85Ca0,15)Ti0,90Zr0,10O3

In technology, using as precursors Fe(III) and Bi(III) nitrates, peroxo-nitrate complexes Ti(IV) and Zr(IV), as well as barium and calcium hydroxides, ultrafine powders of the (1 – у)Bi0.8Ba0.2Fe0.8Ti0.2O3 – уBa0.85Ca0.15Ti0.9Zr0.1O3 (у = 0,05 – 0,30). To reduce the electrical conductivity of ceramic samples made from these powders, the basic phases were alloyed with manganese compounds. To increase the d33 values of the piezoelectric elements, as well as to increase their operating temperature, a special sintering regime involving air hardening of the ceramic samples was used. The best samples of piezoceramics produced by the proposed technology have a Curie temperature above 550 °C and longitudinal piezoelectric modulus (standard conditions) values d33 ≥ 125 pC/N and their operating temperature reaches 340 – 350 °C.

Classification of Ultrafine Particles Using a Novel 3D-Printed Hydrocyclone with an Arc Inlet: Experiment and CFD Modeling.

Ultrafine particle classification can be realized using hydrocyclones with novel structures to overcome the limitations of conventional hydrocyclones with tangential inlets or cone structures. Herein, the hydrocyclones with different inlet structures and cone angles were investigated for classifying ultrafine particles. Computational fluid dynamics (CFD) simulations were performed using the Eulerian-Eulerian method, and ultrafine MnO2 powder was used as a case study. The simulation results show a fine particle (≤5 μm) removal efficiency of 0.89 and coarse particle (>5 μm) recovery efficiency of 0.99 for a hydrocyclone design combining an arc inlet and a 30° cone angle under a solid concentration of 2.5 wt %. Dynamic analysis indicated that the novel arc inlet provided a preclassification effect to reduce the misplacement of fine/coarse particles, which cannot be provided by conventional tangential or involute inlets. Furthermore, the proposed design afforded comprehensive improvement in the flow field by regulating the residence time and radial acceleration. Subsequently, a novel hydrocyclone with an arc inlet and 30° cone angle was manufactured using the three-dimensional (3D) printing technology. Experiments were conducted for classifying ultrafine MnO2 particles using the novel 3D-printed hydrocyclone and conventional hydrocyclone. The results demonstrate that the classification performance of the 3D-printed hydrocyclone was superior to that of the conventional one, in particular, the removal efficiency of fine particles from 0.719 to 0.930 using a 10 wt % feed slurry.

Fabrication of BaTiO3 nanopowders with high tetragonality via two-step assisted rotary furnace calcination for MLCC applications

Ultrafine ceramic powders with high tetragonality are essential for next-generation multi-layer ceramic capacitors (MLCC). The solid-state reaction synthesis commonly used in industry is challenging to prepare ultra-fine BaTiO3 powders due to issues of the coarse crystallization at high temperature calcinations. In this study, a two-step calcination combining with the rotary furnace was innovatively used to synthesize ultra-fine BaTiO3 powders with uniform particle and high tetragonality. Through the reaction kinetics study, it was found that the rotary furnace increases the point contact area of Ba2+ and Ti4+ by improving the heat transfer efficiency of the solid-phase reaction and decreases the diffusion rate of both, so that the diffusion-nucleation-growth rate is greater than the decomposition rate of BaCO3 to improve the tetragonality of BaTiO3 powders. The optimal process parameters were determined and the reaction mechanism was studied. Particularly, the optimized two-step assisted rotary furnace calcination had succeeded in preparing finer powders with an average particle size of 250 nm and tetragonality (c/a) of 1.0096. The BaTiO3 ultrafine powders sintered at 1200 °C has a ceramic density of 96%, dielectric constant of 9173 at the Curie temperature point (131 °C) and a grain activation energy of 0.821 eV, representing excellent dielectric properties and reliability.

Мессбауерові та магнетні дослідження високодисперсних порошків системи FeNiCrCoCu, виготовлених електроіскровою методою у різних рідких середовищах

Мессбауерові та магнетні дослідження високодисперсних порошків системи FeNiCrCoCu, виготовлених електроіскровою методою у різних рідких середовищах

Вплив вмісту міді на фазовий склад і магнетні властивості високодисперсних порошків високоентропійних стопів AlCoCrCuxFeNi ($x$ = 0, 1, 2), одержаних методою ультразвукового оброблення у кульовому млині

Вплив вмісту міді на фазовий склад і магнетні властивості високодисперсних порошків високоентропійних стопів AlCoCrCuxFeNi ($x$ = 0, 1, 2), одержаних методою ультразвукового оброблення у кульовому млині

Ultrafine powder coating: Smooth surface, dense structure and enhanced corrosion resistance

In recent years, powder coatings are capturing more of the liquid coatings market due to their economical, ecological, environmental, and energy-saving benefits, yet their low surface qualities still hinder their wider application. In this study, ultrafine powder coatings (∼22 µm in size) were fabricated and compared with coarse powder coatings (∼35 µm in size) in terms of particles deposition during spray, leveling of coating powder during curing, and surface qualities, inner structures, and anti-corrosive properties of the obtained coating films. The results show that the ultrafine particles pack more loosely and uniformly during spraying with smaller average air pockets and level and degas faster during curing than their coarse counterparts. These characters lead the ultrafine powder to demonstrate lower surface roughness, higher gloss, fewer inner voids, and higher corrosion resistance. The significant increase in corrosion performance is exhibited through high barrier properties and narrow salt spray creepage. This study contributes not only to the in-depth understanding of how particle size affects coating film structure and properties, such as gloss, surface roughness and corrosion protection, but also to the promotion of powder coating technology in broader fields such as electronics and automotive industries.

Generation of Hydrogen through the Hydrolysis of Gas Atomized High Purity Mg Powder

Generating hydrogen through hydrolysis of metal magnesium with water is a very promising strategy for portable applications because it is clean, has high energy density and operability. In the present study, high purity ultrafine Mg powder was prepared using close-coupled gas atomization. Thereafter, the microstructure of the powder was investigated through X-ray diffraction and scanning electron microscopy. The results showed that increasing the speed of ball milling improved the reaction activity of Mg powder. Moreover, a higher water temperature was shown to be beneficial in improving hydrolysis. Moderate amounts of alcohol in water could also improve the yield of hydrogen.

High frequency application of ultrafine submicron FeBP amorphous soft magnetic composites

A novel amorphous soft magnetic composites (ASMCs) for hundreds MHz frequency applications have been prepared under the hot-pressing molding by ultrafine submicron FeBP amorphous powders. These ultrafine submicron FeBP amorphous particles were synthesized with the NaBH4 chemical reduction method and the particles size was regulated by the drop rate of the reducing agent. The morphology, microstructure, elemental composition and high-frequency magnetic properties of the amorphous soft magnetic composites was systematically investigated. The particle sizes of FeBP amorphous powders are distributed in 600–900 nm which gradually increase with the decrease of the drop rate of the NaBH4 aqueous solution. Meanwhile, the Fe element content and saturation magnetization strength of the amorphous powder increase and the coercivity gradually decreases. The corresponded ASMCs also appear a commensurate permeability in the range of 6–9 responding to the GHz high frequency range with the lowest loss tangent only 0.20 and 0.44 at 500 MHZ and 1 GHz, respectively. Such ultrafine amorphous soft magnetic composites have enormous potential for high frequency applications in wide band gap semiconductor switching power supplies, RF inductors and chips.

Effect of Ultrafine Calcium Silicate on the Mechanical Properties of Oil Well Cement-Based Composite at Low Temperature

A low-temperature environment will reduce the hydration rate of oil well cement-based composites, resulting in the slow development of mechanical strength, which cannot meet the requirements of cementing operations. In order to improve the early strength of cement paste under low temperature, the influence of ultrafine calcium silicate powder on the rheological properties, water loss, thickening time and permeability of oil well cement-based composites was evaluated. The compressive strength, flexural strength and impact strength of cement paste with different contents of ultrafine calcium silicate were studied. The hydration process and microstructure of cement paste were analyzed by hydration heat measurement system, X-ray diffraction (XRD) and scanning electron microscope (SEM). The experimental results show that the ultrafine calcium silicate has a certain impact on the rheology and thickening time of cement slurry, and dispersants and retarders are required to adjust these properties when it is used. The ultrafine calcium silicate can improve the stability of cement slurry and reduce water loss and permeability. In addition, under the condition of curing at 20 °C for 24 h, the compressive strength, flexural strength and impact strength of cement paste with 8% ultrafine calcium silicate content increased by 243.0%, 278.5% and 66.3%, respectively, compared with the pure cement paste. The hydration of cement slurry is accelerated by ultrafine calcium silicate, the hydration temperature is enhanced and the heat release of hydration is increased. The ultrafine calcium silicate improves the formation degree of hydration products and makes the structure of cement paste more compact. The research results help to design a low-temperature and early-strength cement slurry system.

Preparation of ferric oxide powders by ultrasonic‐assisted impinging stream reaction

AbstractIn this paper, Fe3O4 powder was prepared by the chemical precipitation method using impinging stream technology. The influences of feed flow rate, L/D, reactant concentration, ratio of iron ion concentration, reaction temperature, and impact time on the size and distribution of particles were investigated by the orthogonal experiment method. The microstructure and morphology of Fe3O4 powders were characterized by scanning electron microscopy, X‐ray diffractometer, and granulometer. The results showed that when ratio of iron ion concentration c(Fe2+):c(Fe3+) = 0.75, reactant concentration c(Fe3+) = 0.4 mol · L−1, feed flow rate Q = 800 L · h−1, L/D = 3, reaction temperature T = 20°C, impact time t = 50 min, the prepared Fe3O4 had an average particle size of 1.815 μm and the most uniform distribution. The influence of ultrasonic enhancement on the mixing process and powder preparation in an impinging stream reactor was investigated. The size and distribution of the powders were significantly affected by ultrasonic enhancement. With the increase in ultrasonic power, the particle size of the powders decreased and the distribution became narrower. The particle size was reduced by 68.78%, and the particle distribution range was narrowed by 84.34% under ultrasound enhancement. This study promised the effective utilization of ultrasonic cavitation in the optimization of experimental equipment and the preparation of ultrafine powder, which provides a basis for process optimization of powder preparation.

A Novel Method to Formulate Pigmented Powder Coatings by Ultrafine Powders

Powder coatings are a green alternative to conventional solvent-borne liquid coatings, but they have the intrinsic drawback of color-matching and adjustment in production with the conventional extrusion process. In this study, an industrially applicable approach to formulate color powder coatings utilizing ultrafine powders, i.e., a powdery blending and pressing method, was invented. This novel method was validated by comparing samples prepared by the Method 1 conventional extrusion method with an extra ultramarine pigment at 3%; Method 2 powdery blending and pressing of the original coatings and the same coating with 6% ultramarine pigment utilizing regular (coarse) powder coatings; and Method 3 utilizing ultrafine powder coatings for the two coatings with the same formulations as Method 2. The coating powders were prepared to have similar particle sizes and particle size distributions, with three commonly used coating binders, namely polyester-epoxy hybrid, polyester/TGIC (triglycidyl isocyanurate), and polyurethane (PU). The powders prepared by Methods 1 and 3 had similar flow abilities in terms of angle of repose (AOR) and avalanche angle (AVA). The performance of the new coatings by Method 3 was close to or better than the ones prepared by Method 1 in terms of the specular gloss, DOI (distinctness-of-image), reflection haze and color values, being superior to Method 2. The coatings via ultrafine powders also exhibited a comparable ultramarine particle distribution in the coating cross-sections as the conventional ones, whereas the ones via regular powders had an inferior pigment dispersion. The new method can greatly enhance the production efficiency and reduce the cost of powder coatings with compound colors, especially for small batch manufacturing.

Fire Extinguishing Performance of Chemically Bonded Struvite Ceramic Powder with High Heat-Absorbing and Flame Retardant Properties.

Struvite is a chemically bonded ceramic product in the pipeline of a sewage treatment plant. In order to explore the fire extinguishing potential of struvite, a new type of struvite ultrafine dry powder with excellent performance was prepared by a simple process, and its fire extinguishing performance and mechanism were analyzed in depth. Under the same process conditions, the refinement degree (D50 = 5.132 μm) and the specific surface area (BET = 25.72 m2/g) of ultrafine struvite were larger than those of NH4H2PO4 (D50 = 8.961 μm, BET = 13.64 m2/g), making struvite more suitable for fire extinguishing. Besides, the pyrolysis process of struvite was relatively concentrated and absorbed more heat in a short time. Its heat absorption (458.4 J/mg) was higher than that of NH4H2PO4 (156.4 J/mg). Water, ammonia, and PO· were released during the pyrolysis of struvite, which effectively reduced fire temperature, diluted oxygen concentrations and captured free radicals. At the same time, the final products were magnesium orthophosphate and magnesium pyrophosphate, which formed a dense flame-retardant ceramic layer with good thermal insulation and environmental protection functions. In these cases, the fire extinguishing mechanism of struvite was determined to have three stages: the cooling effect, the asphyxiation effect, and the chemical effect. Correspondingly, the fire extinguishing time of struvite was three seconds faster than that of ammonium phosphate under 0.2 MPa based on the local oil basin test.

Laboratory Preparation and Performance Characterization of Steel Slag Ultrafine Powder Used in Cement-Based Materials

Steel slag is generally regarded as a supplementary cementitious material in cement-based materials, which is conducive to the realization of the goal of carbon peak and carbon neutralization. However, the lower cementitious activity and poorer volume stability of steel slag limit its high dosage in cement-based materials. In this paper, steel slag ultrafine powder (SSUP) was prepared in the laboratory through mechanical activation combined with grinding aids. Furthermore, the grinding time was optimized. The particle size, specific surface area, and microstructure characterization were evaluated for the SSUP compared with steel slag powder (SSP). The hydration properties of SSUP were studied by means of cement paste hydration heat and mortar strength. Meanwhile, the soundness of SSUP and SSP was compared by the Le chatelier soundness test. The process of preparing SSUP in the laboratory is as follows: the steel slag is ground by a horizontal ball mill for 50 min and then ground with a planetary ball mill mixing with the grinding aids for 15 min. The experimental results show that the hydration degree and rate of SSUP are better than that of SSP, and the activity index of SSUP is 94.19%, which is much higher than that of SSP (69.62%). The X-ray diffractometry (XRD) result shows that the content of the hydration products for SSUP is higher than that of SSP. The soundness test shows that the stability of SSUP is superior to that of SSP when the dosage is the same. Therefore, ultra-fining can effectively improve the cementitious activity and soundness of steel slag.

Study on the preparation and properties of CaCO3 ultrafine powder derived from waste eggshell

In this study, eggshell-derived CaCO3 ultrafine powder was prepared from waste eggshell with the method of omnidirectional planetary ball mill. The particle size distribution was measured by laser particle size analyzer. Then, the parameters of grinding kinetic equation of eggshell powder were obtained by software fitting, and the grinding model and characteristic equation of particle-size distribution of the eggshell-derived CaCO3 powder were discussed. The results showed that the best grinding conditions were as follows: using 3 mm zirconia grinding ball, 400 rpm, 50% filling rate, 50% slurry concentration, and ball-milling time of 30 min. The grinding kinetic equation can well simulate the eggshell crushing process. The equation showed that with the prolongation of milling time, the large particle size of the eggshell powder gradually decreased, and the milling efficiency was 0 after 60 min. The Rosin–Rammler–Bennet distribution model could be used to describe the distribution characteristics of the cumulative particle size of the eggshell powder, and the fitting degree of particle size distribution at each milling time could reach R2 > 0.99. No chemical change occurred in the eggshell powder before and after grinding. However, the calcite crystal structure of eggshell-derived CaCO3 ultrafine powder becomes incomplete.

Innovative technologies for the processing of raw materials of plant origin to improve the quality of food supply of the troops

The object of research: morphological and cultural characteristics of micromycetes: yeast Saccharomyces cerevisiae and mycelial fungi Mucorracemosus grown on agar medium.The subject of research: flax seed suspension, ultrafine powder of double oxide of divalent and trivalent ferrum, micromycetes: yeast Saccharomyces cerevisiae and mycelial fungi MucorracemosusInvestigated problem: ensuring the bacteriostatic properties of raw materials and obtaining products with an extended dates of expiry.The subject in scientific results: the impact of nanoparticles (NP FeO×Fe2O3) on the bacteriostatic (protective) properties of flax seeds against fungal infections has been studied and the dependence of bacteriostatic properties on the amount of nanomagnetite has been determined. The ability of nanomagnetite to improve the bacteriostatic properties of flax seeds has been proven: addition of 0.1 %; 0.15 %; 0.2 % of nanomagnetite suppresses the development of microflora (micromycetes) in flax seed samples by 8–20 times. A reduction in the number of micromycetes (yeast Saccharomycescerevisiae and mycelial fungi Mucorracemosus) by 8–10 times and the size by 10–20 times was established compared to the control.
 The rational content of nanoparticles (NPs FeO×Fe2O3–nanomagnetite) has been determined as 0.15 % of the weight of the recipe mixture.
 The proposed mathematical model makes it possible to predict the effectiveness of using NP FeO×Fe2O3 – nanomagnetite to inhibit the growth of mycelial fungi to ensure the bacteriostatic properties of raw materials, in particular, flax seeds.
 The area of practical use of the research results: food industry enterprises specializing in the production of bakery and flour confectionery products using a mixture of wheat and rye flour with the addition of food additives. Innovative technological product: flour raw material with a mineral nano-additive suspension based on the double oxide of divalent and trivalent ferrum, which allows to ensure quality and extend dates of expiry of the product. Scope of the innovative technological product: to enhance the quality of food supply of the troops in extreme conditions

Improvement of suspension-assisted total reflection X-ray fluorescence analysis of ores using wet grinding and empirical calibrations

In this study, the suspension-assisted total-reflection X-ray fluorescence analysis of ores was improved using the wet grinding procedure to produce ultra-fine suspended powder mixed with internal standard solution in aqueous media. The advantages of the proposed technique were demonstrated by the example of the determination of S, Fe, Ni, and Cu in sulfide copper‑nickel ores containing various ratios of sulfide and silicate minerals. We showed that the powerful mixing of 100 mg of ore powder and 4 mL of ultra-pure water as a dispersing medium with 20 g of grinding balls of 1 mm in diameter leads to the preparation of homogeneous suspension with monomodal particle size distribution having 90% of the particle size <6 μm. The suspension after wet grinding was diluted up to 50 mL with ultra-pure water to obtain a final concentration of the suspended powder of 2 mg/mL. Relative precision of the described sample preparation technique calculated from duplicate pairs of suspensions was 16% for S, 9% for Fe, 15% for Ni and 10% for Cu. Three spectral data processing techniques were further compared with respect to the quantification accuracy of target elements: internal standard, univariate and multivariate regressions. It was shown that the two latter methods can be used to improve the trueness of the internal standard method, especially for Cu and Fe.

Size-controlled preparations of tungsten and molybdenum borides in calcium or aluminum melt

Tungsten and molybdenum borides are widely used in ultra-high temperature ceramics (UHTCs) and electrode material. In this research, ultra-fine and ultra-coarse binary borides (WB, W2B5, MoB, Mo2B5) and MoAlB powders were prepared with W/Mo and B4C as raw materials and Ca/Al as the decarbonization agent. The feasibility of using Ca and Al as decarburizing agents was assessed by thermodynamic calculations. Meanwhile, the effects of reaction temperature, decarbonization agent type and its additional amount on the phase, morphology and size distribution of the powder products were thoroughly investigated. The results revealed that single phase products with carbon content of less than 1 wt% could be prepared. Moreover, the morphology and particle size of products were significantly affected by the reaction temperature and type of decarburization agent. When using Ca as the decarburizing agent, ultra-fine WB and MoB powders were effectively prepared, probably owing to the fact that W/Mo are essentially insoluble in Ca melt. However, the great solubility of W/Mo in Al makes it easily to synthesize ultra-coarse borides at high temperatures via the dissolution-precipitation mechanism. Additionally, ultra-fine borides particle can also be prepared by lowering the temperature and amount of Al to weak the dissolution-precipitation mechanism.

Improvement on fluidization and reduction of ultrafine CuO powders with the assistance of iron microspheres

Fluidization and reduction behaviors of ultrafine CuO powders with the assistance of iron microspheres are investigated. The ultrafine CuO powders that belong to Group C particles are difficult to fluidize due to the strong interactions between particles. However, robust fluidization is achieved with the addition of iron microspheres and the Cu products after the reduction reaction can be completely separated by using a magnetic field. Furthermore, the difference of improvement on fluidization with the assistance of iron microspheres between cold state and reaction state at high temperatures is revealed in the view of interactions between particles. This approach to enhance fluidization during reaction and simplify separation after reaction could be applied to the reaction of other Group C powders.

Liquefaction of waste tire rubber chips used for the absorptive recycling of spilled oils

Over 180,000 TPY (tons per year) of waste tire rubbers (WTRs) are to be disposed of in Taiwan. The waste tire rubber chips (WTRCs) also contain special hydrophobic and oil-philic properties for absorptive recovery of spilled oils on contaminated ground or seashore. Experimentally, waste tires were cut as 10–20 mesh chips to sorb spilled oil (motor oil), and then liquefied into product oils at 643 K, 1 atm. Valuable oil gases and carbon black powder were also produced in the period of WTRCs liquefaction. The product oils could be directly used without further purification due to similar methyl content with that of fresh motor oils. Flammable oil gases mainly containing C3 (11.32%) and C4 (31.40%) hydrocarbons had potential to be fuel gases. Ultrafine carbon black powders (c.a. 100 nm) with mesopores produced from WTRCs liquefaction were observed and analyzed. Elements (Si: 90.56%, Zn: 3.65%, S: 4.89%, Ca: 0.58%, and Cu: 0.10%) on carbon black powder surface from bead ring of tire were detected. Bond lengths of S and Fe atoms were respectively Fe–S (2.17 Å) and Fe–(S)–Fe (3.05 Å) with coordination numbers of 5.6 and 3.9. The economic paybacks of 20- and 10-TPD of these processes were evaluated to be 2.5 and 3.2 years, respectively.