Powder Technology最新文献

This paper presents a novel photocatalysis-assisted mechanical polishing method for cobalt-based alloy cladding layers using TiO₂ nanoparticles. By leveraging the active oxygen species generated by the photocatalyst under illuminated conditions, surface oxidation reactions on cobalt-based alloys are initiated, thereby enhancing material removal efficiency. The underlying principles of photocatalytic oxidation are elucidated, particularly the promotion of oxidation by •OH when it interacts with the metal surface, leading to the formation of a CoO oxide film on the cladding layer surface and a subsequent reduction in surface hardness. An experimental platform was established, and research findings identified an etching time of 60 min and a TiO₂ concentration of 10 wt% as optimal process parameters. Comparative analysis with pure mechanical polishing and chemical mechanical polishing revealed that photocatalysis-assisted mechanical polishing yielded superior surface roughness of 60 nm and a material removal rate of 63.8 μm/min.

The Fe6.5Si soft magnetic alloy exhibits promising magnetic properties for energy applications, including near-zero magnetostriction, low magnetocrystalline anisotropy, and higher electrical resistivity than conventional electrical steels. However, its brittleness impedes industrial use. Recent advances in powder-based additive manufacturing show potential for processing high‑silicon electrical steels. This study focuses on the production cycle and properties of feedstock powder, which are crucial for such applications. Fe6.5Si alloy powders were produced via closed-coupled gas atomization. Comprehensive analysis covered mass balance, particle size distribution, powder flow, morphology, density, rheological properties, and thermal and magnetic behavior. Results suggest the feasibility of producing suitable Fe6.5Si alloy powder via gas atomization, enabling additive manufacturing of the next generation of medium/high-frequency electrical motors. The powder exhibited desirable characteristics within the size ranges applicable to laser powder bed fusion (20–75 μm) and direct energy deposition (75–106 μm), showing excellent flow behavior and morphological suitability for additive manufacturing.

Designing chemical reactor equipment requires a thorough understanding of powder flow. Solid rheology modelling offers various models for this purpose. A comparative study of two different CFD models, the Kinetic Theory of Granular Flow (KTGF) and the dense granular flow ($\mu \left(I\right)$ law), is proposed. Both models were confronted with experimental results obtained on a rotating drum for different rotation speeds and powder flowabilities. Image processing was used to compare the experimental gas/solid interfaces with those obtained from CFD. The KTGF model did not represent the powder rheology at low rotation speeds, regardless of the powder, whereas it was closer to experiments at higher speeds. The dense granular flow model was more appropriate for this system as it described the powder shape inside a rotating drum relatively well for each experiment. The latter model is recommended for modelling dense granular flows, while the KTGF is better suited to gas-solid flows.

The die-wall friction is one of the influential mechanical factors in the metal nano-powder compaction process that can noticeably impress the densification behavior of nanoparticles. In this study, the uniaxial cold compaction process of aluminum nano-powders, which are initially loaded into the nickel die-walls, is analyzed using the molecular dynamics (MD) method. The influence of die-wall friction is studied on the nano-powder compaction process. The results illustrate the effect of frictional die-walls on the characteristics of relative density–pressure and stress–strain curves, the pressure distribution of nano-powders, and the final green product. The evolution of the die-wall friction coefficient on the compaction velocity and temperature is determined during the compaction process. Applying the nonlinear regression method, an empirical relation is derived to estimate the frictional behavior of die-walls at different relative densities. It is demonstrated that the proposed computational model has acceptable accuracy to evaluate the die-wall friction during the nano-powder compaction process.

In the circulating fluidized bed (CFB), the non-uniform mesoscale structure formed by the particle clustering effect causes a substantial decrease in the gas-solid drag. Since the degree of particle clustering varies with operating conditions, an accurate drag model needs to be universal in different heterogeneous flow conditions. In this study, the relationships between the Ψ factor in clusters' solid holdup model that characterizes the flow non-uniformity and the operating parameters of CFB (including slip velocity Reynolds number, Re*, bed-averaged solid volume fraction, ε_s,bed, and solid mass circulation rate, G_s) are established. It improves the adaptability of the QC-EMMS drag model under different working conditions. In previous research, we established two types of models that related Ψ factor to Re* and ε_s,bed respectively. However, there exists a problem of high dispersion of points, indicating that the selected parameters cannot fully describe the flow non-uniformity. Therefore, G_s is reintroduced to modify the two types of models. The results show that the prediction accuracy of the modified models is improved and the relative error is <10%, indicating that the non-uniform factor Ψ has a strong correlation with G_s. In addition, the quantitative relation between Re*, ε_s,bed, and G_s is derived from modified models, and the trend of relation is highly consistent with the fluidization diagram proposed by Yerushalmi J., which verifies the accuracy of modified models. Finally, numerical simulation of typical CFB cases proves the adaptability of the modified models in wide operating conditions of fluidization.

This study investigates the impact of nanoparticle types on the thermal dynamics of film boiling in water-based nanofluids, specifically focusing on nanofluids containing Al${}_2$O${}_3$ and Cu nanoparticles along a vertical cylinder. The investigation employs the Continuous-Species-Transfer approach and also considers the effects of Brownian motion and thermophoresis. A 2D axisymmetric analysis is performed, evaluating the influence of nanoparticle type—Al${}_2$O${}_3$ and Cu—on the boiling heat transfer efficacy. Through the examination of volume fraction, temperature distributions, nanoparticle concentration, and thermophysical characteristics, the study also examines the Nusselt number. Results show the nanoparticle enrichment at the vapor–liquid interface and the degree of this nanoparticle enrichment influences nanoparticle concentration at the cylinder wall, with higher enrichment at the interface inversely related to wall concentration. While Al${}_2$O${}_3$ nanoparticles show higher concentration at the wall, Cu nanoparticles are more effective in enhancing Nusselt number, particularly in nanofluids with higher nanoparticle concentrations.

Increasing the overall performance of Si-based anodes is still challenging because of the influence of various parameters involved in the preparation processes. This study addresses this challenge by employing the design of experiment technique to assess the impact of ball milling parameters such as milling speed, time, ball to powder and medium to powder ratio on the properties of silicon/graphite (Si/Gr) powders, with a focus on their electrochemical performance. Si/Gr powders in 20:80 weight ratio and 4 factor - 2 level full factorial design were used to find the main effects and interactions. Crystallite sizes were calculated using the Scherrer equation, and span values were obtained from the particle size distribution (PSD) analysis. SEM analyses were carried out to check the microstructure of powders. Ultimately, regression equations were created with high adjusted R² values for crystallite size (93%), contamination (92%), and span (91%), respectively. Optimization experiments were carried out using the created regression equations, and the models were verified. It was found that crystallite size obtained by XRD data is more reliable to assess powder properties on the performance instead of PSD because of the agglomeration at the particle level throughout the milling. Further milling experiments were performed to elaborate the role of oxygen content and crystallite size. Results showed that while initial capacity is strongly related to total oxygen content, decay in the first cycles is correlated to the crystallite size of the silicon powder.

Accurate measurement of solids residence time distribution (RTD) is an important and challenging issue in developing fluidized bed reactors with continuous solids feeding and discharging. In this study, we proposed a new method for measuring solids residence time distribution, where coked bulk material was used for solids tracer and high-precision element analyzers were used to determine solids tracer fraction. A calibration procedure was established to achieve high-accuracy measurement of solids tracer fraction. The following validation tests had successfully proved the pseudo-CSTR solids flow pattern under different operating conditions and the staging effect of an inserted horizontal baffle in a small laboratory-scale fluidized bed cold model, which demonstrate the feasibility and advantages of this new solids RTD measurement method.

A CFD-PBM coupling model was developed to simulate and calculate multiphase flow parameters, flow morphology, and bubble diameter in the aerobic fluidized bed biofilm reactor (AFBBR) under different aeration rates. The simulated radial solid volume fraction values were generally in agreement (within ±15%) with the experimental values. The gas phase predominantly occupied the central area of the reactor, with three distinct velocity peaks observed in the liquid and solid phases. Higher aeration rates improve the mixing of multiple phases by augmenting fluidization velocity, gas-phase volume fraction, eddies size, and turbulence characteristics, thereby leading to a rise in the average size of bubbles from 1.54 mm to 2.03 mm. However, the proportion of small diameter bubbles (0.27–1.03 mm) decreased from 69.4% to 59.6%. These studies concluded that the multiphase flow parameters under an aeration rate of 5.77 m³/(h·m³) were more favorable for improving oxygen mass transfer efficiency and reducing energy consumption.