Powder Technology最新文献

Desilication of graphite ores helps to ensure their high-value applications. Surface modification and triboelectric separation methods were used to improve the desilication of graphite ore. Effects of friction media and chemicals on the charge properties of graphite and quartz were investigated by charge-to-mass ratio tests and the adsorption mechanism was analyzed. Furthermore, effects of electrode voltage and rotational speed on the desilication of graphite ore were investigated. The results showed that polyvinyl chloride was the best friction medium for graphite and quartz, and the charging effect of kerosene-modified graphite and quartz was better than that of ethanol. Kerosene modification made graphite more positively charged and quartz more negatively charged, enlarging the charge-to-mass ratio gap. Desilication efficiencies of 0.25–0.5 mm, 0.125–0.25 mm, and 0.074–0.125 mm graphite ores after kerosene modification were 42.27% (20.20% increase), 48.92% (17.18% increase), and 57.26% (19.92% increase), respectively. Our study provides guidance for the purification of graphite.

Coral reef limestone is a highly fossiliferous and porous sedimentary rock, ubiquitous in continental shelves and deep oceanic zones. To understand the slurry infiltration process from a microscopic perspective, we use X-ray computed tomography (CT) to reconstruct the complex three-dimensional pore structures of a coral reef limestone sample and further perform CFD-DEM simulations to capture the transport behavior of slurry particles passing through the reef limestone skeleton. The simulation results show that the kinetic energy of slurry particles in general follows a linear relationship with the applied pressure differential, which is influenced by the physical characteristics of pore channels. The particle infiltration time is inversely correlated to the pressure differential obeying a power-law function. In addition, statistical analysis of the length and spatial distribution of particle trajectories indicates the dominant role of high-coordination-number pore spaces in slurry suspension infiltration through the reef limestone. Our results have important implications for slurry shield tunneling through coral reef limestone strata.

In this article, meso-scale simulations and modeling on the multi-layer spreading and melting of tungsten through electron beam powder bed fusion (EB-PBF) were conducted by a three-dimensional discrete element method coupled computational fluid dynamics approach. The recurring pore defects at the edge were explored, and the cooperative effects of spreading/melting parameters on the edge pores were analyzed. On this basis, the mechanism of edge pore formation was revealed, and the occurrence frequency and edge pore size were quantified. Results show that in the multi-layer printing process, the presence of concavities will cause periodic edge pores at the end of the melted area. Increasing melting power and decreasing melting velocity will reduce the occurrence frequency and increase the average size of edge pores, while high spreading velocity and reverse direction can enlarge the total area and average size of the edge pores. The obtained highlighted results are not only of theoretical significance, but also of practical value for parametric setting and optimization in the actual EB-PBF of tungsten.

Sylvite (KCl) is a classical soluble mineral with high solubility, endowing the possibility to precisely adjust its surficial structure for flotation recovery. In this work, efforts have been originally made to study flotation behaviors of KCl with (200) and (222) exposing facets. KCl(200) crystals had a higher recovery than that of KCl(222) with octadecylamine hydrochloride (ODA). FTIR and XPS results indicated that interaction force between KCl and ODA was not chemical absorption. Zeta potential results further implied the mechanism that the ODA reacted with KCl by static force and KCl(200) possessed a lower potential than KCl(222) and thus facilitated the flotation process. 2D as well as 3D AFM results provided microscopic details of perfect cubic KCl(200) and octahedron KCl(222) samples where layered growing method of former samples exhibited more edges with hanging Cl bonds, leading to its more negative surficial potential and less hydrophilic property, enhancing flotation recovery. Moreover, adhesion & adsorption force further illustrated that KCl(200) obtained a stronger interaction with bubbles, in coincidence with its better flotation recovery. KCl crystals with (200) exposing faces promoted flotation in comparison with crystal with (222) faces, offering strategy to reserve (200) faces for designing KCl crystals with high recovery.

The conventional packing models generally rely on the dominant particle component assumption, where the structure of the particle mixture is dictated by the dominant particle skeleton. However, this assumption is not effective when applied to particle mixtures with multiple significant components, leading to a noticeable discrepancy between model predictions and experimental results. In this study, we draw from solution thermodynamics to introduce two new concepts, “ideal specific volume” and “excess specific volume,” for modeling packing density. Based on this new approach, we derived an equation which is capable of accurately describing the nonlinear packing behavior of these mixtures, named the Unified Non-Dominant Equation Model (UNDEM). This model does not depend on the dominant particle component assumption and employs a unified continuous function to represent changes in packing density. The UNDEM requires no additional parameters and exhibits broad applicability, particularly showing high accuracy in predicting the packing densities of multi-component particle mixtures. Its reliability has been validated against experimental data, showing that the UNDEM is generally more accurate than existing models and can accurately describe most experimental results.

Fluidized bed flotation (FBF) is demonstrating its effectiveness in the recovery of coarse minerals. This study compares the effect of various parameters on the separation efficiency of coarse molybdenite in an FBF cell. The distribution of the molybdenite-bearing particles including liberated and composite particles in the tailings is examined to investigate the difference in recovery between different molybdenite-bearing particles. The findings highlight that the maximum Mo recovery reached 90%–95%. Among the tested parameters, superficial gas velocity and kerosene dosage have a relatively notable influence on molybdenite recovery. During the FBF process, the liberated molybdenite particles exhibited exceptional recoverability, while that of the composite particles was relatively lower and affected by the surface exposure features of the molybdenite. In contrast, the recovery of composite particles required a higher collector dosage and air bubble concentration.

Metal powders for additive manufacturing (AM) are typically produced by atomizing metal melts. In this study, different spray configurations for producing particles for AM are analyzed. Two close-coupled gas-assisted atomizers (CCA) are compared for the atomization of hot working tool steel (AISI H13), namely discrete jets and annular slit nozzles. High-speed image analysis of the oscillations in the liquid spray indicated that the flapping behavior resulted in higher number of off-spec particles (flakes), which were related to the gas-to-melt ratio (GMR). This behavior was observed for both configurations, but flapping oscillations at lower GMR and a super pulsating mode at higher GMR, were identified for the annular slit nozzle. The use of hot atomizer gas resulted in an increase of the fine powder yield suitable for laser powder bed fusion (L-PBF), but at the expense of an increasing satellite particles, which may cause difficulties in powder flow during printing operations.

Binder-jetted parts require a subsequent sintering process to achieve the desired density and mechanical properties, resulting in anisotropic shrinkage and creep distortion. To compensate for this, accurate prediction of densification behavior is required. Although there has been research on optimizing the printing and sintering process to increase the reproducibility of Ti–6Al–4V parts, there is no accessible literature on modeling the densification behavior. In this study, the densification of binder-jetted Ti–6Al–4V samples is investigated experimentally through experiments with interrupted sintering cycles and dilatometry. Through these experiments, it is possible to determine the density changes throughout the entire sintering cycle as well as the anisotropic shrinkage of the printed samples. The results are used to calibrate phenomenological diffusion models for intermediate stage and final stage sintering capable of mapping the densification behavior throughout the entire sintering process. Due to experimental limitations, material parameters for grain growth are determined from experimental densification data.

This study aims to investigate the effect of Sn content on the structural, mechanical, wear, and electrochemical properties of Ti-6Al-xSn (x = 3.5–17.5, wt%) alloys fabricated by powder metallurgy method. The results showed that the microhardness generally decreased with increasing Sn content, although there was an unusual increase in microhardness in the alloy with 10.5 wt% Sn. Depending on the Sn content, various phases such as α-Ti, Ti₃Sn, and Ti₃Al indicated complex phase formations. The flexural and tensile strengths increased up to 10.5 wt% Sn content, but the strengths reduced above this level. The maximum values for flexural and tensile strengths were obtained as 270 MPa and 125.8 MPa, respectively. With increasing Sn content, the fracture surfaces shifted from cleavage mode to mixed brittle and ductile failure modes. The wear tests were conducted in two different environments: dry and wet conditions. Considering dry sliding conditions, the lowest specific wear rate was obtained as 0.85 × 10⁻⁶ mm³/N·m in the alloy coded 3.5Sn at a sliding distance of 1500 m. On the other hand, the highest wear was measured as 2.89 × 10⁻⁶ mm³/N·m in the 17.5Sn coded sample at a sliding distance of 6000 m in wet conditions. The wear results demonstrated a relationship between mechanical properties and wear resistance, which was influenced by the existence of porosity. The Ti-6Al-7Sn alloy exhibited the best corrosion resistance with a 2.22 × 10⁻⁷ i_corr value, while the one with Ti-6Al-17.5Sn alloy showed the worst performance with a 9.71 × 10⁻⁶ i_corr value.

The transient mixing dynamics of an initially segregated binary granular system in a half-filled rotating drum are experimentally investigated. The granular system consists of spherical beads having identical size. The density ratio between the two granular phases is 2.8. With its ability to scan three-dimensional opaque systems with a high frequency, the ultrafast X-ray computed tomography is used to capture the transient and steady-state segregation dynamics in the bulk. The segregation dynamics are also compared to those at the circular end-wall caps, which have been captured with a camera. The results show an axial migration of the denser particles towards the bulk and, more importantly, second-order overshooting dynamics in the radial mixing index, which tend to increase with the Froude number. The results will find application in industrial systems, where rapid mixing occurs. We also believe the presented data can serve as validation for future three-dimensional simulations focusing on the transient formation of segregation patterns in the bulk.