Powder Technology最新文献

Well-defined particle size distributions are required for good flowability and powder packing properties of additive manufacturing powders. Mounting powders within a polymer and using standard metallurgical preparation techniques to cross-section and prepare powder particles for optical analysis allows for simple characterisation processes. However, measured diameters of cross-sectioned particles are typically underestimates of actual particle diameters and hence require stereological correction. The effectiveness of three stereological corrections are investigated in this work, namely the Scheil-Schwartz-Saltykov method, the Goldsmith-Cruz-Orive method and a Finite Difference Method. These methods are investigated against plasma-atomised, gas-atomised and ultrasonically processed Ti-6Al-4V powders. The corrected outputs are compared to laser size diffraction, benchmark data for each powder. Although all three stereological corrections produce improved estimations of the particle size distributions, the Finite Difference Method is recommended producing cumulative mean absolute error values of 2.4%, 3.1% and 7.5% for the plasma-atomised, gas-atomised and ultrasonically processed powders respectively.

This paper presents the application of the Discrete Element Method (DEM) to describe the physical properties of plant-origin grains with a low elasticity modulus for the needs of numerical simulation of processing processes. The study proposes the modelling of maize grains based on 3D scanning of real grains and further use of the multi-sphere method to fill the numerical model with a conglomerate of elementary spheres. The main aim of the paper is to develop a calibration method based on exploring parameter spaces at points selected using Sobol's grids. As criteria and functional limitations for the calibration, the following were proposed: the slope angle of repose (AoR), the radius of the heaped cone's vertex (Rad), the number of grains, and the slope height. The study results show that for the calibration of the DEM model describing maize grains, test points with a set of the following nine parameters should be used: Poisson's Ratio for grain, Density of grain, Shear Modulus, Coefficient of Restitution for grain-grain, Coefficient of Restitution for grain-material, Coefficient of static friction for grain- grain, Coefficient of static friction for grain-material, Coefficient of rolling friction for grain-grain, and Coefficient of rolling friction for grain-material.

High-proportion pellet smelting is the current development direction of blast furnace burden structures in China. And that is an inevitable trend for the future steel industry to achieve pollution reduction and carbon reduction. This study focuses on the mixed burden of magnesia flux pellets with different SiO₂ contents, sinter, and lump ore. The influence of SiO₂ content on the softening-melting behavior of comprehensive burden and the high-temperature interaction between magnesia flux pellets and sinter were studied through droplet experiments and visual experiments. The results show that with increasing SiO₂ content, the T₁₀ of magnesia flux pellets gradually decreases, while the T₁₀ of the comprehensive burden shows no significant change. The T_S of both shows a gradually decreasing trend with increasing SiO₂ content. However, due to the good matching of the melting range between sinter and magnesia flux pellets in the comprehensive burden, the trend of T_S change in the comprehensive burden is relatively slow. The air permeability of the comprehensive burden has significantly improved compared with the single magnesia flux pellets; The interaction between magnesia flux pellets and sinter occurs through the liquid phase. The fayalite phase in the pellets reacts with the main high melting point substance Ca₂SiO₄ in the sinter to generate a new low melting point kirschsteinite. With the increase of SiO₂ content, the content of kirschsteinite in the comprehensive burden increases. That is also the reason for the decrease in T_S of the high silicon comprehensive burden; With the increase of SiO₂ content, the maximum pressure difference and characteristic values of magnesia flux pellets and comprehensive burden gradually increase. When the SiO₂ content exceeds 6%, the maximum pressure difference and characteristic value of a single pellet sharply increase, while the trend of the maximum pressure difference and characteristic value change of comprehensive burden is relatively gentle. Its characteristic values are below 980 kPa·°C. At this time, the air permeability of the comprehensive burden is significantly improved compared to the single magnesia flux pellets. In the case of SiO₂ content exceeding 6%, the addition of a sinter can effectively address the soft melting performance of high-silica magnesia flux pellets and enhance column air permeability. In addition, the high drop temperature of the high-silica comprehensive burden is due to the presence of a large amount of MgO in the magnesia wustite during the later stage of reduction, which increases the melting point. And the MgO content in the slag is relatively low. That causes a sharp increase in slag viscosity and makes it difficult to separate the slag from iron.

A gas-driven anaerobic fluidized bed microbial fuel cell (GAFB-MFC) was designed and built to investigate the electricity generation performance and the sewage treatment time under different gas velocities, particle sizes and initial bed heights. The closed circuit voltage of the GAFB-MFC reached the highest value of 644.3 mV and the shortest sewage treatment time of 96 h at the gas velocity of 2.00 L/min,the particle size of 1.4 mm and the initial bed height of 10 cm. The open circuit voltage of the GAFB-MFC reached 747.5 mV, the maximum power density was 493.95 mW/m² and the internal resistance was about 205 Ω. The comprehensive energy consumption of the gas-driven system was proved to be much lower than that of the liquid-driven system. This work is of good significance for promoting the industrialization of the microbial fuel cell technology.

The envelope density of the roll-compacted ribbon is a widely accepted physical property that serves as a criterion for the transferability of dry granulation processes. Existing methods of obtaining ribbon density data have drawbacks in their reliability and availability at production facilities. A novel method is proposed in this paper and the performance thereof is compared to other established techniques. A pilot study was conducted on several roller compactors to prepare various batches of ribbons under different process parameters using model and real formulations from the industry. The presented method measures the envelope volume of roll-compacted ribbons by solid volume displacement of glass microspheres. The solid displacement method for measuring envelope density is as precise as mercury porosimetry, provided that the ribbon quality is adequate, even in the presence of minor structural failures, it is nondestructive allowing sample reuse, and it is scalable to larger ribbon sizes.

In waste and biomass combustion plants, ash adheres to the inside of the combustors and surfaces of air heaters, etc., accumulating over time and causing operational problems due to the deposited ash layer. Here, we evaluated the adhesion properties of calcium-rich ash using synthetic ash. Specifically, we investigated the role of Ca-Al in ashes. The adhesion of Ca-Al synthetic ash and mixed ash of Ca-Al and SiO₂, which is included in ash and utilized as a bed material in fluidized-bed combustion systems, was investigated. Adhesion was found to increase when three conditions were met: Ca/Al molar ratio >1, SiO₂ coexistence, and 900 °C. The increase in tensile strength of the powder bed corresponded to shrinkages in volume, specific surface area, and total pore volume, suggesting solid phase sintering as the cause of increased adhesion. Adding alumina nanoparticles to the highly adherent sample successfully suppressed the adhesion increase.

The presence of powder agglomerates results in product with poor content uniformity and intermittent high potency in the processing of pharmaceutical powders.

We developed a novel and easy-to-implement methodology, applying image analysis, to quantify the size of powder agglomerates when a powder passes through a screw feeder. Subsequently, agglomeration tendencies of twenty-one pharmaceutical powders were examined and classified. Notably, both the size and endurance of agglomerates were quantified, and our study revealed that the agglomeration tendency of powders can be explained by particle size and compressibility: Powders with small particle size (D50 < 30 μm), and large compressibility (> 35% at 15 kPa normal stress) tend to form large and enduring agglomerates, which can be difficult to eliminate in downstream processes. The study also illustrates how two materials, one that produces enduring and the other unenduring agglomerates, display substantially different content uniformity in the final product after being processed semi-continuously.

The ironmaking blast furnace (BF) is a counter-current chemical reactor. The porosity distribution of burden layers in BF plays an important role for the gas distribution and gas–solid two-phase interaction. In this research paper, to analyze how porosity distributions affect gas velocity, gas temperatures and reduction, the different porosity distributions were investigated using three distinct processes by numerical models. The results showed that the change of porosity along the radius direction had a more obvious effect than along the height direction. When the porosity is exponentially distributed, the gas velocity was allowed a great development, promoting the gas temperature and reduction. Besides, in the lower part (height = 1/3H), with increasing porosity, the gas velocity increases by 30% and reduction by 25%. In the middle part (height = 2/3H), the gas velocity is increased by 30%, the gas temperature is increased by 200 °C, and the reduction is increased by 20%.