Powder Size Distribution Research Articles

Simulation of Binder Infiltration in Additive Manufacturing of Sand Molds

This article proposes a computational fluid dynamics approach to simulate binder infiltration in 3D printing of sand molds using OpenFOAM facilitating the identification of suitable levers for application‐specific material and process developments. A method for randomly generating powder bulks of designated powder size distributions (PSD) and procedures for automated analysis of the infiltration profile and volume are introduced. Simulation is utilized to investigate binder infiltration using different droplet spacings, representing different printheads’ resolutions. The apparent particle size at the exact location of the droplets’ impact, the droplets’ landing position in relation to the respective surface topography, and thus the statistical appearance of particle formations appear to be influencing the infiltration profile. High‐speed camera observations show the plausibility of the predicted infiltration kinetics. An exemplary use case compares the predicted infiltration profiles to the compressive strength of specimens printed from silica sand with low binder contents. Simulation predicts an average infiltration of 250 μm that presumably achieves reliable bonding for layer thicknesses up to 365 μm. A decrease in strength with increasing layer thickness at constant binder contents can be found in the experiment – at layer thicknesses above 350 μm, only minor strengths are achieved.

Effects of process parameters and scan strategy on the microstructure and density of stainless steel 316 L produced via laser powder bed fusion

The ability to produce reliable and reproducible components from 316 L using additive manufacturing is crucial to serve the need for customization, on-demand manufacturing and reduced lead times for various industries. Laser powder bed fusion is becoming widely accepted as a versatile additive manufacturing technique capable of producing near defect-free components with tailored microstructures and mechanical properties. However, despite the recent progress in process parameter selection and optimization, even a small change in any of the laser parameters, equipment and feedstock powder characteristics can influence the microstructure and subsequently the mechanical properties of the fabricated parts. The purpose of this work is to tackle the process optimization challenge through, a full factorial design of experiments approach, to systematically assess the widely adopted energy density factor to evaluate the density of the final component. A statistical approach was also followed to evaluate potential plastic anisotropy in different samples produced with various energy densities and scan strategies. Density measurements indicated that beyond laser power and scan speed, the interaction effects of the aforementioned parameters with the layer thickness and the powder size distribution have a significant effect on the sample. Microstructural features such as melt pools, grains and crystallographic texture were characterized against a range of volumetric energy densities and scan strategies represented by different angles of rotation between successive layers. Smaller angles of rotation per layer were found to decrease texture anisotropy and suppress the formation of keyhole porosity in finer and more homogenous microstructures. The assessment of plastic anisotropy in the produced samples was evaluated using microhardness measurements on all three orthogonal planes of the samples. The hierarchical microstructure of laser powder bed fusion materials induces several strengthening mechanisms, that can simultaneously be activated depending on the loading scenario, location and plane.

Study on the influence of oxygen content evolution on the mechanical properties of tantalum powder fabricated by laser powder bed fusion

In this work, the influence of reuse times on the properties of tantalum powder and its laser powder bed fusion (LPBF) product was investigated. For this purpose, a batch of tantalum powder was reused up to 16 times, and the particle size distribution, flowability, surface topography, and other characteristics of the powder were studied after different reuse times. The mechanical properties of the finished product samples were also tested. Results from the powder reuse showed that the particle size distribution of tantalum powder changed from 30.1 μm to 33.8 μm, and the oxygen content increased from 310 ppm to 450 ppm. The density and fracture strain of tensile specimens decreased from 16.57 g/cm3 to 16.48 g/cm3 and from 37.9% to 11.6%, respectively. The ultimate tensile strength and microhardness decreased after reaching a peak, ranging from 504 MPa to 614 MPa, and 227 HV to 245 HV, respectively. In addition, it was found that the oxides were mainly tantalum pentoxide, along with monovalent and bivalent oxides. The change in tensile properties was likely related to the interstitial solution of oxygen atoms. This study provides a reference for the reusability of LPBF tantalum powder.

The Influence of Powder Particle Size Distributions on Mechanical Properties of Alloy 718 by Laser Powder Bed Fusion

Currently, metallic powders for laser powder bed fusion (LPBF) primarily come in two commercially available powder size distributions (PSDs): 15+/45− for non-reactive powders and 15+/63− for reactive powders. These powders are generally produced via gas atomization processes that create highly spherical particles with a Gaussian PSD. Because of the standard deviation within a Gaussian distribution, only small portions of the total product are used for LPBF applications. This screening process makes the other particle sizes a waste product and, thus, increases processing costs. The non-reactive 718 powder was printed with both the typical PSD of 15+/45− and a wider bimodal experimental PSD. Compared to conventional 718, the 718 alloys with bimodal PSD shows less than a 0.2% difference in density, and insignificant change in mechanical behavior. Electron backscattered diffraction studies revealed that grain sizes and morphology were similar between the two sample sets, but bimodal 718 alloy has a slightly greater degree of large grains. The study suggests that particles with wide or bimodal size distributions show promise in producing equivalent high-quality products without sacrificing mechanical properties.

Conversion of Activated Calcium in Industrial Water to Micron CaCO3 Powder Based on CO2 Absorption and Mineralization

Carbon dioxide capture, utilization, and storage (CCUS) is one of the essential approaches to achieving permanent CO2 emission reduction. A new idea of absorbing and mineralizing CO2 with industrial wastewater and converting activated calcium into micron CaCO3 powder is proposed in this paper, which synchronizes water softening and CO2 fixation. Therefore, this paper investigated the characteristics of circulating water quality in the iron and steel industry and the transformation behaviors of CO2 capture by activated calcium to CaCO3 powder in the mild aqueous environment under different process parameters. The phase composition, morphology, and particle size distribution (PSD) of CaCO3 powder were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and (laser particle size analyzer) LPSA, respectively. In addition, a green integrated cycle system for industrial water capture of mineralized CO2 was preliminarily constructed, which provides a reference method for carbon reduction and economic utilization of carbon sources in an industrial system.

Local wear resistance of Inconel 625 coatings processed by different thermal techniques: A comparative study

Ni-base superalloys, like Inconel 625, are extensively used in several applications due to their good performance at high temperature and their corrosion resistance. The high costs of these alloys promote their usage as coatings deposited onto cheaper materials. This practice improves the component performance without an excessive increment in price. Cold Spray (CS) deposition is a relatively new technology that could be considered as a real solid-state coating processing method. Consequently, no oxides are formed during CS deposition and the coatings do not lose their potential oxidation resistance. However, mechanical and tribological behaviour of CS materials is highly dependent on the processing parameters and powder feedstock properties. For these reasons, the aim of this work is to evaluate the mechanical properties and the local wear behaviour of high-pressure CS Inconel 625 coatings deposited under different spraying conditions by using different particle size distributions of powders. Nanoindentation tests were carried out on the coatings with a diamond Berkovich tip which determined the elastic modulus and hardness. Additionally, microscratch tests were also conducted to compute the local wear rate through the estimation of the removed volume. The cross profile of the residual grooves was recorded using the same tip as the one used to make scratch tests. These measurements were checked by Atomic Force Microscopy (AFM) analysis. The values obtained by both techniques were similar in the validation tests. The local wear rates were correlated with the mechanical properties and the scratch micromechanisms which were analysed in the scanning electron microscope. Finally, the results obtained were compared with those corresponding to coatings processed by more traditional methods.

Liquid chromatography on a centrifugal platform for separation and collection of water-soluble dyes

A reversed-phase chromatographic process is developed on a centrifugal platform to separate and collect water-soluble dyes from a mixture. A separation column filled with C18-reversed phase silica gel was used to separate the components from a mixture and the eluate was collected by a series of collecting chambers. The purified components can then be identified and extracted from the collecting chambers. The effects of the silica gel's particle size (7–10, 20–45, and 46–63 µm) and the platform's rotational speed (1000, 1500, 2000 RPM) on the separation and collection efficiency were investigated. Experimental results showed that dye separation could be well performed in the column with smaller-sized silica gels (7–10 µm) under a low rotational speed (1000 RPM). However, for the eluate collection, the high eluent flowrate and long processing time resulted in a convective band-broadening problem in the collecting chambers, which affected the recovery ratio of the dyes. Experimental results showed that the convective band broadening effect can be reduced by reducing the flowrate, shortening the collecting time, and switching the eluent to a different composition. The best recovery ratio of the dyes in the current design can be achieved by using the column with a powder size distribution of 46–63 µm and operating at the rotational speed of 1500 RPM. This platform can process a sample volume of 1 μL and the processing time is about 30 min. Since the only instrument used is a motor, the complete chromatographic process, from separation to fraction collection, can be carried out on a centrifugal platform at a low cost.

Coupling of carbonization method with high-energy ball milling: Towards submicron-sized graphite powders transforming from waste COVID-19 masks

Disposable polypropylene medical masks are widely used to protect people from diseases caused by COVID-19 viruses worldwide. However, disposable medical masks are non-biodegradable materials, and the accumulation of waste masks can pollute the environment and waste resources without a reasonable recycling method. This study aims to recycle waste masks into submicron-sized graphite powders via coupling the carbonization method with high-energy ball milling. The waste masks were initially carbonized to get a carbon source after the carbon-bed heat treatment method. The resulting carbon source was a dense fiber structure with a diameter of about 10 μm and high quality for carbonized 10 h. Then, the carbon source turned into submicron-sized graphite powders after high-energy ball milling. The highest specific surface area, well-dispersed, smallest particle size, and narrowest particle size distribution of submicron-sized graphite powders were obtained after 12 h of ball milling. These findings suggest that waste face masks can be recycled to prepare high-added-value carbon materials and provide a green and low-cost method to reuse polypropylene waste materials.

Effect of the Particle Size Distribution of Irregular Al Powder on Properties of Parts for Electronics Fabricated by Binder Jetting

The present work analyzed the influence of the particle size of irregular aluminum powder on the properties of Binder-Jetting-printed parts, which can be used as electronic components. Powders of various particle sizes as well as blends in the ratio of 73–27 wt.% or 27–73 wt.% of coarse to fine powder particles were used. The parts were printed with constant parameters, such as a layer thickness of 120 µm, roller traverse speed of 10 mm/s, and binder saturation of 80%. For parts made of individual blends, analysis of the XRD, density, porosity, surface roughness, and dimensional changes in X, Y, and Z axes after the sintering process was conducted. The results confirmed the trend of smoothing the surface of 3D-printed parts with a reduction in the size of the powder particles used. The best results in terms of surface roughness were obtained for powder in which coarse particles (73%) had 50 µm and fine particles (27%) had 20 µm. However, the incorporation of coarser particles in an amount of 27 wt.% (AL160) to the fine-grained powder base (ALC100) allowed for the obtaining of details with higher density, lower total porosity, and relatively low surface roughness. The combination of these two powder particle sizes allowed the fine powder to fill the voids between the larger particles, resulting in properties that represent an excellent relationship between density, porosity, and surface quality. The research results indicate that the three-dimensional parts produced by Binder Jetting technology, through the phenomenal thermal conductivity of aluminum, can be successfully used as electronic components, such as heat sinks or transistor housings.

Optimizing the size distribution of zinc borosilicate glass powder by organic solvent and tetradecylphosphonic based wet milling

Zinc borosilicate glass are crucial adhesive medium in modern electronic industry. However, it is still hard to prepare the zinc borosilicate glass with uniform particle size distribution. Herein, narrow particle size distribution and reduced hemispherical point temperature of zinc borosilicate glass was obtained by choosing low polarity, viscosity and surface tension organic solvent as well as surface modifier in the wet ball milling method. It is found that xylene, ethanol and isopropyl alcohol are good liquid medium for wet ball milling. Moreover, tetradecylphosphonic acid (TDPA) as a surface modifier could effectively reduce the formation of surface hydroxyl group in glass powder by the nucleophilic substitution reaction of the phosphonic acid group, showing superb anti-aggregation properties. Therefore, this work provides a general method for controlling particle size distribution of glass powder.

Additive manufacturing of Inconel-625: from powder production to bulk samples printing

PurposeFor metal additive manufacturing, metallic powders are usually produced by vacuum induction gas atomization (VIGA) through the breakup of liquid metal into tiny droplets by gas jets. VIGA is considered a cost-effective technique to prepare feedstock. In VIGA, the quality and the morphology of the produced particles are mainly controlled by the gas pressure used during powder production, keeping the setup configuration constant.Design/methodology/approachIn VIGA process for metallic additive manufacturing feedstock preparation, the quality and morphology of the powder particles are mainly controlled by the gas pressure used during powder production.FindingsIn this study, Inconel-625 feedstock was produced using a supersonic nozzle in a close-coupled gas atomization apparatus. Powder size distribution (PSD) was studied by varying the gas pressure.Originality/valueThe nonmonotonic but deterministic relationships were observed between gas pressure and PSD. It was found that the maximum 15–45 µm percentage PSD, equivalent to 84%, was achieved at 29 bar Argon gas pressure, which is suitable for the LPBF process. Following on, the produced powder particles were used to print tensile test specimens via LPBF along XY- and ZX-orientations by using laser power = 475 W, laser scanning speed = 800 mm/s, powder layer thickness = 50 µm and hatch distance = 100 µm. The yield and tensile strengths were 9.45% and 13% higher than the ZX direction, while the samples printed in ZX direction resulted in 26.79% more elongation compared to XY-orientation.

Effects of carao (Cassia grandis L.) on physico-chemical, microbiological and rheological characteristics of yogurt

Yogurt fortification with functional ingredients can increase health benefits. Carao fruit has bioactive compounds which could exert antidiabetic potential. Objective was to study the influence of carao powder on physicochemical, microbiological, and rheological properties of yogurt. Carao powder was added at 0, 1.3, 2.65, and 5.3 g/L to milk to produce yogurt, which was stored for 42 days. The pH, titratable acidity (TA), syneresis, color, Streptococcus thermophilus (ST) and Lactobacillus delbrueckii spp. bulgaricus (LB) counts, viscosity, steady shear flow, thixotropic analysis, and frequency sweep measurements were evaluated over yogurt shelf life. The protease activity of yogurt starter culture bacteria and particle size of the carao were also measured. Particle size distribution of carao powder varied. Carao did not affect the syneresis and the growth of ST and LB. Carao yogurt decreased pH and L* values and increased a*, b*, n’, TA, and viscosity values. At 42 days, thixotropic behavior increased with the addition of carao. Carao also increased the protease activity of yogurt starter culture bacteria in skim milk. Carao could be added to yogurt without producing major changes to its characteristics.

Influences of double-sided molding method and initial particle size on fragmentation characteristics of reconstituted coal briquette

Using the reconstituted coal briquette to replace tectonic coal is a forced choice for many experimental studies on the mechanism of coal and gas outbursts. The molding method and initial particle size are two important factors affecting the properties of the soil-like coal briquette. In this study, tectonic coal particles with five different initial sizes were compressed into coal briquettes using three different molding methods. Each coal briquette was evenly divided into five parts along the vertical direction and each subunit was fragmented by a drop hammer to test the firmness. The results show that the briquette density first increases and then decreases with the rise of initial particle size. Briquettes obtained by the traditional one-sided molding method possess the lowest density. The fragment size distributions of the briquettes and the original tectonic coal have segmented and non-segmented fractal characteristics, respectively, which are mainly related to the initial particle size distribution of the coal powder used for making briquettes. Combining the vertical distribution laws of the surface work, Protodyakonov coefficients, and fractal dimension of the briquettes, it is determined that the coal briquettes obtained by the double-sided molding method are soft in the middle and possess a relatively symmetric structure. The surface work and Protodyakonov coefficients of the briquettes (9.03 ± 2.27 J/m2 and 0.10 ± 0.02, respectively) are comparable to those of the in-situ tectonic coal with the highest outburst risk.

Simulation Analysis of Spreading Process and Electron Beam Melting of Ti6Al4V Powder

Forming process control of powder bed fusion (PBF) additive manufacturing (AM) is the key to produce high-quality qualified parts. In this paper, spreading powder process and electron-beam melting (EBM) of Ti6Al4V powder were simulated based on simulation technology, and the state of powder bed powder and melting trajectory characteristics were characterized. Firstly, the particle size distribution of Ti6Al4V powder was tested, and the particle diameter of normal distribution for simulation was determined. Then, the simulation models of spreading powder and EBM model were established. Finally, based on the simulation results, the effect of processing parameters on the quality of powder laying is analyzed, and the morphology of EBM melting trajectory is characterized.

Effect of yttria addition on the microstructure and mechanical behavior of ODS ferritic alloys processed by High Energy Milling and Spark Plasma Sintering

Oxide dispersion strengthened (ODS) ferritic alloys are structural materials used in nuclear fusion reactors, which exhibit enhanced mechanical properties, as well as corrosion and irradiation resistance. In the present work, ODS ferritic alloys with composition Fe-14Cr-1.5W-0.4Ti-(0, 0.4, 0.8) Y2O3 (in wt.%) were prepared employing high energy milling (HEM) followed by Spark Plasma Sintering (SPS). The particle size distribution (PSD) of the milled powders was characterized by laser diffraction. These powders and the sintered materials produced were characterized using X-ray diffraction (XRD), and scanning electron microscopy (SEM). The sintered materials were also characterized by dilatometry, diametral compression, Vickers microhardness, and corrosion rate tests. The largest Young’s modulus, microhardness, and dimensional shrinkage/expansion were obtained for the 0.8 wt.% Y2O3 alloy. However, this alloy was the least ductile. Furthermore, the 0.8 wt.% Y2O3 alloy was the one with the least dimensional change. According to the potentiodynamic polarization studies, it was found that the protective layer of Cr2O3 formed on the surface of the three alloys studied was less effective for the yttria-free alloy, since in this case the rupture of such protective layer occurred earlier than for the case of the yttria-containing alloys. Based on these results, it is suggested that the 0.8 wt.% Y2O3 alloy having fine microstructure could constitute a potential alternative as a structural material for Gen IV-type reactors.

Ink Tuning for Direct Ink Writing of Planar Metallic Lattices

316L and Cu‐based inks are developed to 3D‐printed tetrachiral auxetic structures. The main objectives of the work are to study the effects of powders composition and powder:binder volume ratio on rheological properties and printability of the inks. Following these results, customized Gcode is developed using FullControl Gcode Designer open‐source software to 3D print intricate tetrachiral auxetic structures. The results reported in this work show how powder composition (316L versus Cu) has less effect on the inks’ rheological behavior than powder size distribution and powders:binder volume ratio. In terms of rheological parameters, the zero‐shear rate viscosity mainly affects the capability of the printed ink to retain its shape after printing, while the yield stress affects the printability. The printed and sintered auxetic structures achieve the intended lattice‐geometry design.

In situ self-assembly preparation and characterization of CaO–ZrO2 nanopowders under vacuum

CaO–ZrO2 nanocomposite powders were prepared by in situ self-assembly method under vacuum. The effects of calcium oxide content on the physical phase composition and microscopic morphology of the as-prepared nanopowders were investigated. The results showed that the content of the tetragonal phase in the powders gradually increased with increasing calcium oxide content. When the calcium oxide content reached 10 wt%, the prepared CaO–ZrO2 nanopowders were a pure tetragonal phase with good dispersion and average particle size about 57 nm. In comparison to the situation in air, the amorphous carbon particles formed by the pyrolysis of organic matter under vacuum were evenly distributed on the surface of the nanocomposite particles or between them. In this way, direct contact of the nanoparticles was avoided, thus inhibiting their rapid growth at high temperatures and facilitating the formation of fine grains with high surface energy. The preliminary results indicated that the smaller average particle size and narrower particle size distribution of the nanocomposite powders prepared in vacuum were significantly beneficial for improving the bending strength of the nanoceramic products compared to that in air. It is expected to provide valuable information for further optimization of the controllable preparation of high-quality nanoceramic powders.

The impact of coal gasification slag powder on fluidity, rheology and viscoelasticity properties of fresh cement paste

Coal gasification slag (GS) is a potential pozzolanic industrial waste discharged during coal gasification. The study aimed to investigate the effect of finely ground GS powder on the fluidity, rheology and viscoelasticity properties of cement paste, which is essential for utilizing GS as a supplementary cementitious material for building materials. The research revealed that the morphology, physical filling effect, and particle size distribution of GS powder played a vital role in the workability of cement. The particle size distribution of the GS-cement system followed the Rosin-Rammler distribution model, and the width of the particle size distribution negatively correlated with paste fluidity. The rheological characteristics of blended paste transitioned from Bingham to modified Bingham fluid with increased GS powder content, showing shear thinning. Plastic viscosity can predict the fluidity and thixotropy of the paste. GS powder at 10% content broadened the particle size distribution, improved fluidity and rheological properties, with minimal effect on viscoelastic characteristics. With increased GS powder content, plastic viscosity, yield stress, and thixotropy of blended paste increased continuously, resulting in a slow transition from viscosity to elastic solid. Extending mechanical grinding time improved the fineness and activity of GS powder, optimized the particle size distribution, and reduced water demand, minimizing negative effects.

Grain size and shape fractal characteristics of gangue in the process of 'jaw breaking-ball milling'.

This study investigates the fractal characteristics of the particle size and shape distribution of gangue powder in the "jaw crushing-ball milling" process using mudstone gangue. For this, fractal theory, laser particle size analyzer, scanning electron microscope and other mesoscopic research methods were introduced. This study has several main factors, including the discharge port width in the jaw crushing stage, the grinding particle size, ball-to-powder ratio in the ball milling stage, and the fractal dimension changes of the gangue in different crushing stages. The results indicate that in the process of "jaw crushing-ball milling", gangue's particle size and shape fractal dimension values changed periodically. During the jaw crushing stage, the particle size fractal dimension increases with the width of the discharge opening, ranging from 1.85 to 1.92. The value of the shape fractal dimension varies from 2.65 to 2.84. Ball milling causes the fractal dimension value of gangue particle size to increase with time before agglomeration and decrease after agglomeration. By comparing different in-grinding particle sizes and ball-to-powder ratio, it is found that the fractal dimension value of gangue particle size decreases with the increase of in-grinding particle size and increases with the increase of ball-to-powder ratio. The final gangue's particle size fractal dimension value is concentrated between 2.5 and 2.8. The fractal dimension of particle shape increases with the increase of the grinding particle size, and decreases with the increase of ball-to-powder ratio. A ball-to-powder ratio greater than 6 gradually reduces its influence on fractal dimensions, and the final shape dimension lies between 1.06 and 1.16. In addition, the increase/decrease range of particle size and shape fractal dimension decreases with the increase of ball milling time, which is also consistent with the grinding kinetics theory. As a result of the changes in particle size and shape fractal dimensions, parameters such as jaw crusher discharge port width, grinding particle size, and ball-to-powder ratio are calculated to provide a theoretical basis for the entire crushing process in the "jaw crusher-ball milling" crushing process.

Fumed Silica-Based Ultra-High-Purity Synthetic Quartz Powder via Sol-Gel Process for Advanced Semiconductor Process beyond Design Rule of 3 nm.

Fumed silica-based ultra-high-purity synthetic quartz powder was developed via the sol-gel process to apply to quartz wares and quartz crucibles for use in advanced semiconductor processes. The process conditions of preparing potassium silicate solution, gelation, and cleaning were optimized, i.e., the relative ratio of fumed silica (10 wt%) to KOH (4 wt%) for potassium silicate solution, gelation time 3 h, and cleaning for 1 h with 5 wt% HCl solution. It was observed that the gelation time strongly affected the size distribution of the quartz powder; i.e., a longer gelation time led to a larger size (d50) of the synthesized quartz powder: 157 μm for 2 h and 331 μm for 5 h. In particular, it was found that the morphology of the as-synthesized quartz powder greatly depended on the pulverizing process; i.e., the shape of quartz powder was shown to be rod-shaped for the without-gel-pulverizing process and granular-shaped with the process. We expect that the fumed silica-based ultra-high-purity quartz powder with an impurity level of 74.1 ppb synthesized via the sol-gel process is applicable as a raw material for quartz wares and crucibles for advanced semiconductor processes beyond the design rule of 3 nm.