Papers by Keyword: Particle Shape

Abstract: The article analyzes and develops an algorithm for the operation of the powder backfill process using vibration oscillations. The results of the study make it possible to predict the main properties of particles of any shape. The developed computer simulation model also provides for the superposition of horizontal and vertical oscillations. It should be noted that the difference between them is that the main one for the implementation of horizontal oscillations is the X - coordinate, and for vertical ones – the Y - coordinate. It is also important that the model algorithm provides for simultaneous application of vibration oscillations, which makes it possible to study the influence of the history of the backfill process. It should also be noted that in this scientific study, a number of experiments were conducted, the change in porosity during the imposition of oscillations was studied, and graphs of the obtained experimental dependences were constructed. Porosity from the main parameters of the bunker, in particular: width and height, is also studied. The obtained results made it possible to record the optimal porosity of the backfill with a reliable deviation error (± 1%).

Abstract: The effect of particle size and shape on flowability of FGH96 superalloy powder was investigated by field emission scanning electron microscopy (FE-SEM), laser particle size analyzer (LPSA) and X-ray photoelectron spectroscopy (XPS). The results showed that the powder flowability basically presented a decreasing trend as the median diameter decreased. The Hall velocity of the five median diameter powders (𝑑₅₀=203.9 μm, 106.3 μm, 83.2 μm, 73.8 μm, 19.9 μm) was 27.18 s/50g, 23.25 s/50g, 23.86 s/50g, 23.42 s/50g and none, respectively. The surface oxides/ hydroxide/nitride of the five median diameter powders were mostly the same, mainly including Al₂O₃, Cr₂O₃, MoO₃, Nb₂O₅, Ni (OH)₂, TiO₂ and TiN. The median diameter 𝑑₅₀, shape factors (circularity, aspect ratio, roundness, solidity) and fractal dimension were selected to quantitatively characterize particle size and shape. For the same fluctuation value of powder flowability, the roundness and solidity showed lower sensitivity. Compared with the two shape factors, the sensitivity of circularity and aspect ratio was at an intermediate level, while the median diameter and fractal dimension displayed higher sensitivity. The median diameter and fractal dimension can be used to characterize the principal variation of flowability. The circularity and aspect ratio can be utilized to characterize the variation of flowability supplementally.

Abstract: The results of the study of the shape, morphology and elemental composition of aluminum powder particles obtained in distilled water with the following electrical parameters of the electroerosive dispersion unit are presented: the capacity of discharge capacitors is 65 μF, voltage 100 V, pulse frequency 50 Hz. It is established that the powder consists of particles of regular spherical shape (or elliptical), irregular shape (conglomerates) and fragmentation, and the main elements of the powder are aluminum and oxygen. The obtained powder materials can be used for the manufacture of powder electrodes used in welding and surfacing of a wide range of parts.

Abstract: Gas atomization is one of the most cost-effective methods for preparing spherical powders. The Cu-9.7Sn-0.2P alloy powder for 3D printing was prepared by a self-developed double nozzle gas atomization technique with different deliver tube diameters, and the particle size and shape of the powder were characterized. Results show that the powder particles are mostly nearly spherical, mixed with a few irregular powders. The average O. Bluntness of the powders are 60~70%, the average Outgrowths are lower than 18%. The deliver tube diameter affects the powder characteristics directly. The increase of the diameter increases the particle size of the powder and reduces the sphericity. At the same time, the adhesion of the satellite powder decreases, the flowability becomes better and the oxygen content drop. The surface and internal structure of the powder are mainly cellular and dendritic structures.

Abstract: Silicon nitride with 50 mass zirconia ceramic matrix composites were processed by mechanical milling (MM) followed by spark plasma sintering (SPS). Two different of Si₃N₄ particle shapes for create harmonic microstructure were investigated. The microstructure of Si₃N₄-ZrO₂ with initial Si₃N₄ shape is like coin/flakes after MM for 144 ks was failed to create the harmonic microstructure after SPS. With another sphere shape of Si₃N₄ after MM for 144 ks, the harmonic microstructure could be formed after SPS. Thus, the initial powders shape of Si₃N₄ have an effect in the formation of harmonic microstructure could be fully achieved. The highest mechanical properties of Si₃N₄-ZrO₂ are on the powders with mechanical milling time for 144 ks. The Si₃N₄ ceramic with homogeneous fine grains of ZrO₂ dispersed on its surface was obtained, and the mechanical properties were improved. The Vickers hardness obtained on 144 ks is 1031 MPa and the bending strength is 262 MPa. The main factors explaining the improvement in the mechanical properties of Si₃N₄-ZrO₂ are considered to be the porosity decrease caused by the particles shape and appropriate condition of powder processing i.e. MM and SPS.

Abstract: Drum granulators are widely used in powder granulation industry, and particles’ sphericity is one of the important indexes of drum granulation quality. To improve the particle sphericity, it is necessary to study the influence of particle size and shape on particles’ motion of both attitude and trajectory in the drum. This paper presents a mixed method of the discrete element simulation, orthogonal design experiment and mathematical statistics to investigate the influencing factors of particle orientation. The study found that there is a certain effect of particle shape, size and the speed of the drum on the particle orientation. According to the range analysis, it can be concluded that the effect of the three factors on the particle orientation is in the order of particle shape > particle size > the speed of the drum. Optimum combination was observed to be particle shape, size, and the speed of the drum are homogeneous ellipsoidal particles, 3 mm and 40 rpm, respectively. The study will facilitate to optimize the granulation process parameters.

Abstract: Definition and studies on the shape of various bodies are an interdisciplinary issue, raising wide interest among scientists. In geology and geotechnics the studies refer to features related to the shape of soil and rock particles, especially of those used for practical purposes. Due to the complex shape of particles, its three components have been distinguished: sphericity, angularity and surface microtexture. Sphericity usually determines the degree of similarity of a given particle to a sphere, whereas defined as a form refers to the general shape of the particle [3]. Particle shape and parameters that characterise it have not been unequivocally defined and normalised, resulting in a large number of definitions and ways of their determination. An extensive paper presenting the definitions used to describe shape parameters has been presented by Szerakowska [13]. This paper is focused on the comparison of analytical methods and an attempt to select the most optimal method for determining sphericity of particles in construction and road aggregates.

Abstract: Particle shape raises more interest among geologists than among engineering geotechnical staff. It is commonly accepted that particle shape is the result of geological processes, such as transportation and sedimentation, and depends on many factors, such as mineral composition or structure and texture of the host rock. The influence of particle shape on the geotechnical properties of soil has been widely discussed in literature from the early 1900-ties, e.g. by Wadell [3], Riley [16], Pentland [6] and other scientists, who proposed their own definitions and methods of determining particle roundness and angularity. Finally, it has been decided that particle shape should be defined by three independent parameters [2]: roundness, reflecting the general shape of the particle in comparison to a sphere; angularity, describing changes in roundness in the corners of the studied particle; and microtexture, reflecting the complexity of the particle surface in micro scale; this parameter is also referred to as micromorphology. These three parameters describe particle shape at various magnifications and allow obtaining all important data on this feature. This report is focused on a review and analysis of the analytical methods determining particle angularity, and is an attempt to establish an optimal definition of determining particle angularity in road aggregates. We present selected definitions used to determine angularity, worked out by different authors over the years as an attempt to find the best analytical method of describing angularity.

Abstract: A numerical simulation method is hereby adopted in this paper to calculate and analyze the thermal dispersion influence factors of three particle-shaped porous mediums of two-dimensional porous medium with different skeleton structures. Result shows that the thermal dispersion influence factors include fluid thermal properties, Darcy velocity, porosity and skeleton structure, etc. Under the same condition, the thermal dispersion coefficient of a circular particle model is maximum, and it increases with the rise of Pe_d number; with the increase of the porosity or the reduction of Darcy velocity, the thermal dispersion coefficient reduces increasingly. When considering the thermal dispersion effect, the axial temperature variation of fluid is more applicable for numerical simulation, which proves that it shall consider the thermal dispersion during researches on porous medium models.

Abstract: To find out the influence of particle shape on the force situation and sampling efficiency of the drilling tool, the discrete element method is employed to build the lunar regolith model and simulate the interaction between soil and drilling tool. A three-dimensional contact model is introduced to represent the impact between particles. To make sure the validity of the model, a triaxial-test is conducted to optimize the micro-parameters of the model. Then, the model is employed to the simulation of drilling process. From the computational simulation results, conclusions can be made: the particle shape will change the interlocking between particles, and the strip particles have the largest interlocking which makes the force situation largest and the sampling efficiency smallest.