Papers by Keyword: Particle Distribution

Abstract: This paper deals with the research of a new chemically resistant cement repair mortar modified with selected secondary raw materials. The aim of this work is to study the influence of particle distribution of fly ash on selected characteristics of the developed remediation material. This new mortar will be suitable for use in the extremely aggressive environment of sewers. The monitored parameters include key physical-mechanical characteristics and resistance to the attack of aggressive biogenic sulfuric acid. The chemical resistance was tested by simulating the exposure environment in laboratory conditions, according to the methodology of DIN 19573. The obtained results show that by optimizing the particle distribution of fly ash it is possible to maintain the values of physical-mechanical characteristics and improve the chemical resistance of test specimens of new repair mortar.

Abstract: Aluminium matrix composites (AMCs) offer improved mechanical and tribological properties compared to monolithic materials and therefore provide great potential for various applications. This particularly applies to particle-reinforced AMCs revealing comparatively high contents of reinforcement particles. However, these types of composites are difficult to manufacture due to their abrasive characteristics as well as their complex rheological material behaviour. An approach to produce such AMCs is semi-solid powder processing, combining powder pressing and sintering in one step in order to produce fully dense composites with currently only cylindrical shapes. Therefore, the tools as well as the powder mixture are first heated into the semi-solid temperature range of the aluminium powder and subsequently formed using low pressures under 200 MPa. Due to the shear thinning behaviour of the semi-solid aluminium matrix the porous structure of the pressed powder is filled during compaction, resulting in homogenous particle distributions in the component. However, this process results in high process times as well as energy costs, due to the heating inside of the die. In contrast to the semi-solid powder processing in one step, in this paper, a novel process route combining cold uniaxial compaction of particle reinforced aluminium powders having up to 50 vol.% SiC with subsequent semi-solid forming is presented. Here, a particle reinforced and cylindrically shaped green body is utilized as raw material, in order to produce complex components through semi-solid forming. The parts produced in this way are featuring varying wall thicknesses and are used in order to determine the process limits for manufacturing particle reinforced components having up to 50 vol.% SiC. Thereby, the influence of reinforcement particle size as well as particle loading on the homogeneity of the resulting particle distribution of an academic component is investigated. Future main objective of the process route is the manufacturing of complex parts with homogenously distributed particles.

Abstract: This article examines the main problems of modelling spherical (circular) particles. The main method of the initial process of filling lobules using the Cauchy and Reynolds problem is substantiated. An image of an object-oriented complex of free fall of a spherical particle and their many non-collision spheres is presented. Based on the obtained research results, the main parameters of the process of filling particles of heterogeneous materials. An example of visualization of the developed software product for filling material particles is given, taking into account a number of cross-sections of a cylindrical hopper in height. A histogram of the distribution of material particles from porosity over the volume of a cylindrical hopper is also constructed.

Abstract: NiO nanoparticle was synthesized by a sol-gel method with three different pH values namely pH=1, 7 and 11, and then calcined at temperature of 450 ᵒC. The influence of different pH values on the physical properties of NiO nanoparticles were investigated by a particle size analyzer (PSA), field emission scanning electron microscope (FESEM) and X-ray diffractometer (XRD). Structural analysis confirmed that a cubic structure of NiO nanoparticle was obtained without any secondary phase for NiO powders prepared with pH=1, while the peak of secondary phase (Ni) appeared for NiO powders prepared with pH= 7 and 11. Morphological observation showed that the NiO nanoparticles prepared with pH=7 and 11 tend to form more agglomerates compared to one prepared with pH=1. The average diameter of NiO nanoparticles with pH 1, 7 and 11 were approximately in the range of 19-26 nm, 21-28 nm, and 24-30 nm, respectively. NiO powder that was synthesized with pH=1 was further used to prepare composite anode of NiO Nps-BaCe_0.54Zr_0.36Y_0.1O_2.95 (BCZY) powder. Unfortunately a composite of NiO Nps-BaCeO₃-BaZrO₃ was obtained instead of BCZY and governed by agglomerates with size in the range of 70-300 nm.

Abstract: As one of processing methods of functionally graded materials (FGMs), centrifugal mixed-powder method has been proposed. The centrifugal mixed-powder method is the casting process combined of centrifugal casting and powder metallurgy. This processing method has advantage that fine ceramics-particles, whose wettability with matrix melt is low, can be compounded into metallic material. However, effects of particle size on microstructure and mechanical properties of the FGMs fabricated by the centrifugal mixed-powder method are unclear. In this study, two kinds of Al-TiO₂ FGMs rings are fabricated by the centrifugal mixed-powder method. One contains TiO₂ particles having similar diameter with Al matrix particles (hereafter, small different-size (SD) TiO₂ particles), and the other one compounds TiO₂ particles with much smaller diameter than Al matrix particles (hereafter, large different-size (LD) TiO₂ particles). In case of the Al-TiO₂ FGMs ring containing SD-TiO₂ particles, the TiO₂ particles are homogeneously dispersed in Al matrix on outer surface of the ring. On the other hand, the TiO₂ particles in the Al-TiO₂ FGMs ring with LD-TiO₂ particles are distributed along grain boundary of Al matrix. Moreover, Vickers-hardness and wear resistance around outer surface of the Al-TiO₂ FGMs ring containing the SD-TiO₂ particles is higher than that of the Al-TiO₂ FGMs ring with LD-TiO₂ particles. Since Al particles in the mixed-powder with LD-TiO₂ particles are surrounded by the TiO₂ particles, the Al particles can be hardly melted by heat of molten Al at casting process. As a result, the Al-TiO₂ FGMs ring with LD-TiO₂ particles has low hardness and wear resistance. Therefore, it is found that TiO₂ particles having similar diameter with Al matrix particles are more suitable for fabrication of the Al-TiO₂ FGMs rings.

Abstract: In this paper, the rapid prototyping of W-Cu composites by laser cladding was reported. The influence of the mass ratio of W and Cu on the structure and properties were investigated. Ni and Co were added to the W-Cu composites to promote the sintering densification. The effect of the elements on the structure, phase composition and properties of W-Cu composites was investigated by using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDX) and hardness test. The results showed that when Cu content increases to 60 wt.%, W particles were distributed around Cu agglomerates. When Ni content increases to 3.0 wt.%, γ-Ni phase could be observed. It was found that Co was concentrated at the interface between W and Cu phase and enhance the diffusion of W in Cu phase. Both Ni and Co could increase the density of the W-Cu composites greatly.

Abstract: In this paper, Friction Stir Processing (FSP) is used to produce a homogenous AZ31/SiC Metal Matrix Composite (MMC). The product could be used in industries such as aerospace, which needs materials with a high strength to weight ratio. AZ31B magnesium alloy plates and about 5 vol % SiC powder are selected as matrix and reinforcement particles, respectively. The effect of the number of FSP passes, the rotational and traverse speed on the particle distribution and the matrix microstructure of MMC are investigated. Optical microscopy is used to observe both particle distribution and matrix microstructure. The results show that a perfect particle distribution with no defect can be achieved at very low rotational and transverse speeds which are 300 rpm and 15mm/min. Moreover, the number of passes significantly improves the particle distribution. The mean grain size decreases from 9.5 μm to 1.95μm for a 4-pass MMC.

Abstract: Functionally Graded Materials (FGM) is a newly evolved concept to get desired properties in the material wherein the intermediate layer is transient since the particle size distribution gradually changes. Centrifugal casting [1] can produce only hollow shapes and Centrifuge casting can produce solid shape FGM very effectively. The study of particle distribution in a fluid using centrifuge casting process is carried out considering sand as particle and its distribution is studied under water, for different viscosity values and for viscosity varying with respect to temperature. Based on centrifugal force and density difference, an attempt has been made to mathematically model the centrifuge casting force to estimate the particle distribution over the length of the specimen and also to assess the influence of process parameters such as rotational speed (G-force) and density of the particles.

Abstract: Evaluation methods for the spatial distribution uniformity of a large number of particles have important applications in a range of scientific and industrial problems. We report a quantitative image-processing method to evaluate the spatial distribution uniformity of particles using the Voronoi tessellation and Delaunay triangulation. Given the geometric particle centroids, we constructed the Voronoi tessellation and Delaunay triangulation. For each of the Voronoi cell, the volume, facet area, and number of neighbors (facets) were calculated. For the Delaunay simplices, the volume and the distance between neighbors were calculated and the distributive characteristics were compared between different particle patterns. Simulation results demonstrated that distributions of the above metrics were numerically related to the uniformity of the particle spatial displacement. More studies are needed to further validate the results and refine the method.

Abstract: With the demand of improving the second interfacial bonding strength and environmental protection, MTC cementing technology has obvious technical and economic advantages. However, due to containing lots of low-density materials and slurry treating agents, which make low strength, the application of low-density slag MTC cementing slurry system is restricted in the cementing of deep wells and low-pressure leakiness formations. According to the theory of particle distribution and based on particle size analysis of floating bead, micro silicon and slag, solid-phase proportioning design of low-density (1.35~1.55 g/cm³) slag MTC was carried out in this paper. By adjusting the adding amount of micro silicon and activators, the slag MTC cementing fluid system with the 24-hour compressive strength greater than 21.6MPa which has the density range of 1.35 to 1.55g/cm³ was get. This system has small initial consistency, short thickening transition time, low water loss and good rheological property. And at last, the mechanism of improving the strength of low-density slag MTC cementing fluid system was analyzed.