Flowability Measurements Research Articles

Effect of waste travertine powder on properties of rhyolitic tuff-based geopolymer

This investigation explores the potential of geopolymer technology as an eco-friendly substitute for conventional construction materials by emphasizing the innovative use of naturally occurring green rhyolitic tuff and repurposed travertine powder in geopolymer paste formulations. Replacement levels of tuff with travertine at 40 %, 45 %, and 50 %, along with an alkaline solution with a NaOH molarity range of 8.2 M–22.1 M, have been analyzed for their impact on flowability, water absorption, porosity, compressive strength, and unit weight of the geopolymers over curing periods of 2, 28, and 90 days. The flowability measurements show that adding 40 %, 45 %, and 50 % travertine leads to approximately 7 %, 31 %, and 31 % reductions in the flowability of the geopolymer, respectively. It is demonstrated that adding 40 % travertine significantly improves the geopolymers’ compressive strength with an 11.5 M NaOH concentration, showing substantial increases of approximately 15.5, 9.0, and 2.4 times at the curing duration of 2, 28, and 90 days, respectively, relative to the geopolymer without travertine. As an optimum points, an 18.5 M NaOH and an 0.7 solution-to-powder ratio decrease the long-term apparent porosity and water absorption of the geopolymer without travertine by about 14 % and 19 % compared to those at the same solution-to-powder ratio with 11.5 M NaOH, respectively. Microscopic examinations were employed to validate the development of sodium aluminosilicate hydrate, calcium aluminosilicate hydrate, and calcium silicate hydrate gels, underscoring the advantageous contribution of the elevated CaO content in the travertine to the geopolymer matrix. This research not only highlights the environmental benefits of repurposing waste materials but also contributes to the development of more sustainable and durable geopolymer pastes, offering a promising approach to enhancing environmental stewardship in material science practices.

Real-Time Cone-Growth Model for Determination of Pharmaceutical Powder Flow Properties.

The flow properties of pellets or granules are crucial for further processing drug dosage forms. Optimal compression or filling of multiparticulate dosage forms into capsules is influenced by forces between discrete particles, which could be partially characterized by flow properties. Several techniques have been developed to examine flowability, including static and dynamic methods applying empirical studies and up-to-date chaos theory; however, the newest methods seem only to be powerful with the supplementation of empirical principles. Our experiments try to refine both the technique of analysis and the methods, by finding new, alternative ways. Our approach to the flowability measurements was to set up a dynamic time-dependent model that combined empirical observations and chaos theory on a geometrical basis, thus finding new characteristics regarding the flow properties of pellets and granules that could be relevant for drug developers. Our findings indicate that sphericity and particle size are the most significant factors influencing the flowability of pharmaceutical multiparticular preparations. Furthermore, this study confirms that integrating chaos theory and empirical observations in a time-dependent dynamic model provides a comprehensive understanding of particle flow behavior, pivotal for optimizing manufacturing processes.

Characterization and Microstructure of Recycled Eroded Particles from Die-Sink Electro Discharge Machining of H11 Alloy for Applicability in Additive Manufacturing

Different waste streams from electro discharge machining (EDM) were investigated for an upcycled usage in processes for additive manufacturing (AM). These erosion sludges accumulate in filter cartridges and at the bottom of machining basins. The enclosed particles were extracted, sieved and investigated via laser diffraction, dynamic image analysis, scanning electron microscopy, optical emission spectroscopy, elemental analysis and flowability measurements. Additionally, thermal, crystallographic and metallographic investigations as well as X-ray micro-computed tomography (µ-CT) were utilized for the characterization of particle and material properties. In general, eroded powders fulfill the requirements for AM regarding particle size and shape very well, which is confirmed in morphological investigations and powder flow characteristics showing similar properties as the H11 AM reference material. The chemical composition of the powders is equal to the machined H11 alloy, except for the high carbon content. Carbon is entrapped in the iron lattice originating from pyrolysis of the present dielectric fluid and the graphite electrode during rapid solidification, which leads to a transition from martensite to cementite structures. This change is observed in the microstructure of powders, in which acicular primary cementite and austenite are present. After remelting with slow heating and cooling rates the microstructure changed to ledeburite II with retained austenite and martensitic phases. The pore size and shape distributions obtained by µ-CT measurements showed a pore formation in the compact sample. These results provide a fundament of major properties as well as handling and recycling suggestions for eroded particles enclosed in waste sludges.Graphical

Underwater measurements of flowability by angle of repose, Hausner ratio and Jenike shear cell

Flowability is important for characterizing particulate materials. Some simple measurements, such as the Hausner ratio and angle of repose, are used to compare materials, and more sophisticated devices, such as the Jenike shear cell and ring shear tester, are used for design purposes. However, these devices are only used for measurements in air; thus, underwater operations lack such measurements and design models based on flowability measurements. This work shows that flowability can be measured underwater by simple modifications to the apparatuses. Although underwater flowability was found to be much smaller than that in air owing to negligible cohesive forces, such an approach enables the adoption of models developed for systems in air for underwater system design. In addition, more in-depth research on particulate material structure and flow by eliminating van der Waals forces can be conducted.

Developing a Virtual Flowability Sensor for Monitoring a Pharmaceutical Dry Granulation Line

Current technologies to measure granule flowability involve at-line methods that can take hours to perform. This is problematic for a continuous dry granulation tableting line, where the quality assurance and control of the final tablet products depend on real-time monitoring and control of powder flowability. Hence, a real-time alternative is needed for measuring the flowability of the granular products coming out of the roller compactor, which is the unit operation immediately preceding the tablet press. Since particle analyzers have the potential to take inline measurements of the size and shape of granules, they can potentially serve as real-time flowability sensors, given that the size and shape measurements can be used to reliably predict flowability measurements.This paper reports on the use of Partial Least Squares (PLS) regression to utilize distributions of size and shape measurements in predicting the output of three different types of flowability measurements: rotary drum flow, orifice flow, and tapped density analysis. The prediction performance of PLS had a coefficient of determination ranging from 0.80 to 0.97, which is the best reported performance in the literature. This is attributed to the ability of PLS to handle high collinearity in the datasets and the inclusion of multiple shape characteristics—eccentricity, form factor, and elliptical form factor—into the model. The latter calls for a change in industry perspective, which normally dismisses the importance of shape in favor of size; and the former suggests the use of PLS as a better way to reduce the dimensionality of distribution datasets, instead of the widely used practice of pre-selecting distribution percentiles.

A Comparative Study on Laser Powder Bed Fusion of Differently Atomized 316L Stainless Steel.

The significant growth of Additive Manufacturing (AM), visible over the last ten years, has driven an increase in demand for small gradation metallic powders of a size lower than 100 µm. Until now, most affordable powders for AM have been produced using gas atomization. Recently, a new, alternative method of powder production based on ultrasonic atomization with melting by electric arc has appeared. This paper summarizes the preliminary research results of AM samples made of two AISI 316L steel powder batches, one of which was obtained during Ultrasonic Atomization (UA) and the other during Plasma Arc Gas Atomization (PAGA). The comparison starts from powder particle statistical distribution, chemical composition analysis, density, and flowability measurements. After powder analysis, test samples were produced using AM to observe the differences in microstructure, porosity, and hardness. Finally, the test campaign covered an analysis of mechanical properties, including tensile testing with Digital Image Correlation (DIC) and Charpy’s impact tests. A comparative study of parts made of ultrasonic and gas atomization powders confirms the likelihood that both methods can deliver material of similar properties.

Charge reduction assisted production of diminutive fluid bed granules for high drug load minitablets

Micronized drug powders are generally unsuitable as tableting feed to produce minitablets due to their cohesivity and poor flow. The silicification of fine paracetamol powder (PCMF) with an optimal concentration range of fumed silica (fSi) [0.7–0.9%, w/w] reduced the net negative charge of PCMF and improved powder flow. The optimal fSi concentration range suitable was established through the measurement of charge and flowability of the silicified powders. Silicification of PCMF by physical mix did not satisfactorily overcome the cohesive forces between the PCMF crystals and improve powder flow sufficiently such that it will feed consistently into the smaller die orifices during tableting. Using a specialized fluid bed system with swirling air and side spray, controlled granulation of silicified PCMF packed and agglomerated the interlocking–prone needle shaped PCMF crystals into diminutive granules that are more spherical and free flowing. With optimized fSi concentration (≈ 0.8%, w/w) and granulation process parameters, high drug load diminutive granules (D50≃ 90 μm) were successfully prepared from PCMF as starter seeds (D50≃ 30 μm). Minitablets prepared from the diminutive granules had low weight variation, and were mechanically strong with disintegration time of <30 s. This study demonstrated the feasibility of producing high drug load minitablets from a cohesive, electrostatic–prone fine drug powder.

Synthesis of graphene oxide coated metal powders with improved flowability and reduced reflectance

In this study, a method has been developed to coat metal powder particles (Fe, 316L stainless steel and Cu) with graphene oxide (GO). The method is based on using a pH window where opposite zeta potentials cause the GO sheets to be attracted to the passive oxide layer of the metal powder surface and a rotary evaporator mixing to achieve good dispersion and control the concentration of GO. The pH-dependent interactions of GO and Cu and Fe metal powders in solution have been investigated by mixing the metal powder with GO dispersions between pH 4.2 and 11.3, and it could be observed that GO attached to the metal powder surfaces up to pH ~8 for both Cu and Fe. At lower pH the zeta potential of GO becomes less negative and oxidation of the metal becomes more prominent. Based on these observations, a pH window just below the IEP of the surface metal oxides was used to adhere GO on metal powders in a rotary evaporator with controlled GO concentrations and good distribution of the GO sheets which was verified with SEM and Raman spectroscopy mapping. X-ray diffraction and Raman spectroscopy has been used to evaluate the GO and the metal oxides. Some relevant powder properties were investigated before and after coating of GO. The reflectance of Cu powders in the near-infrared 1070 nm wavelength range was reduced by up to 66 %, depending on the amount of GO coating. Flowability measurements showed that the flowability of the coated 316L powder could be improved significantly while the flowability of pure Fe powder was relatively unaffected by the coating. The results show that GO coated metal powder can be useful in additive manufacturing processes using a laser powder fusion technique where low reflectance and high flowability are important.

Evaluation of a Uniaxial Powder Tester and Comparison with an Annular Shear Tester

Bulk flowability measurement of particulate systems for quality control and product development purposes requires a fast, repeatable, accurate and affordable characterization approach. In the present study, two versions of the recently developed Freeman Technology Uniaxial Powder Tester (UPT) are compared to the Schulze Ring Shear Tester and the Johanson Hang-Up Indicizer. The UPT instruments were found to have excellent repeatability in measurements of uniaxial unconfined yield stress and compressed bulk density across a broad range of materials. Amongst the testing devices investigated in this study, the computer-controlled Advanced UPT (AUPT) instrument showed higher repeatability than the Manual UPT (MUPT) and the Johanson Indicizer. The Schulze Ring Shear Tester (RST) had slightly better repeatability than the AUPT, but there were a few situations in which its automated software did not produce a value of unconfined yield stress, resulting in a need to manually process the data. For most of the test cases, the AUPT measured a higher value of uniaxial unconfined yield stress than the MUPT. This was attributed to the stress relaxation that the powder bed experiences in the MUPT, where the consolidation stress is not automatically maintained on the sample. The AUPT measured lower values of unconfined yield stress compared to the Schulze RST for all the cases in this study. This is a well-recognized occurrence as the Schulze RST and other biaxial testers, in contrast to the AUPT, brings the sample to the critical consolidation state before measuring the shear strength. The AUPT produced its flow function data in about half the time as the Schulze RST.

Self-adaptive anode design with graphene-coated SiOx/graphite for high-energy Li-ion batteries

Si-based materials are promising high-capacity anodes, which can improve the energy density of Li-ion batteries (LIBs) that are required for the advancement of electric vehicles. Nevertheless, the severe volume change of Si-based materials during repeated cycles limits their widespread applications in LIBs. Here, we report a durable and high-energy blended anode composed of artificial graphite (AG) and graphene (Gr)-coated SiOx (SiOx@Gr) particles. The Gr coating reduces the electrode swelling during repeated cycles and increases the initial Coulombic efficiency of SiOx. This further increases the areal capacity owing to the reduction of carbon black (CB) content to 3 wt%. The SiOx@Gr/AG blended anode exhibits excellent properties compared to the bare SiOx/AG anode. These results can be attributed to the self-adaptive behavior by Gr sheets coated on SiOx particles, which mitigates the mechanical damage on the AG particles and maintains the electron conduction pathways. Hence, the reversibility of the charge–discharge reactions improves, as revealed by Raman spectral mapping and powder flowability measurements. Furthermore, the full-cell with the SiOx@Gr/AG anode exhibits good cycling stability and high volumetric capacities over 300 cycles compared to the full-cell with the bare SiOx/AG anode and AG-only anode, demonstrating the applicability of the high-capacity Si-based anodes for LIBs.

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

Determination of fundamental mechanical properties of biomass using the cubical triaxial tester to model biomass flow

The flowability of biomass is an indicator of how amenable biomass is to handling. The flowability measurements are often determined with empirical or tertiary experiments. This status quo impedes employing engineering principles to advance the design and operation of biomass handling systems. It is imperative to establish an experimental protocol minimizing empirical aspects of flowability characterization to account for the variability of biomass. This study demonstrates the operational principles of the large chamber cubical triaxial tester and the procedure of triaxial tests to quantify bulk flow behaviors of two milled biomass feedstocks, namely corn stover 2 mm (CS) and Douglas fir 1 mm (DF). The Mohr-Coulomb (MC), Drucker-Prager (DP) and modified Cam-Clay (mCC) models are calibrated for both biomasses. Analysis indicates that CS will exhibit a cohesive flow with a larger cohesion coefficient of MC (3.8 ± 3.5 kPa) than DF (0.42 ± 0.9 kPa) and a larger d value of DP (6.9 kPa) than DF (0.0 kPa), respectively. CS exhibits a higher spring-back index of mCC (0.39 ± 0.05) than DF (0.27 ± 0.05) also suggesting handling issues, which agrees with the experiences in the industry. This study demonstrates the capability of a CTT in a quantitative investigation of biomass handling characteristics.

Development of a Virtual Sensor for Real-Time Prediction of Granule Flow Properties

We report progress of an ongoing work to develop a virtual sensor for flowability, which is a critical tool for enabling real time process monitoring in a granulation line. The sensor is based on camera imaging to measure the size and shape distribution of granules produced by wet granulation. Then, statistical methods were used to correlate them with flowability measurements such as ring shear tests, drained angle of repose, dynamic angle of repose, and tapped density. The virtual sensor addresses the issue with these flowability measurements, which are based on off-line characterization methods that can take hours to perform. With a virtual sensor based on real-time measurement methods, the prediction of granule flowability become faster, allowing for timely decisions regarding process control and the supply chain.

Reliability and properties enhancement of as-cast aluminum alloy through gating system design

In this work, the influence of temperature on fluidity and gating system design on the physical, and mechanical properties of as-cast AA6063-T6 aluminum alloy have been examined. The pouring temperature has been used as a controlling parameter for flowability measurement and a spiral ceramic placed in a sand mold for measuring the fluidity index of the molten alloy. A linear relationship between the casting temperature and the fluidity length was observed. These show that fluidity increases linearly with the pouring temperature. Also, an expanding systems and pressurized gating systems were experimented through sprue-runner to cross-sectional area variation. The ultimate tensile strength of the samples was not significantly affected by the in-gate system design. Meanwhile, the fracture elongation seemed to be more dependent on the melt quality than on the in-gate system design. The true stress-strain graph indicates that expanding systems are better than pressurized systems. The plot of residual against fit for regression analysis does not show random distribution about the reference point.

A Feasibility Study of Low Cement Content Foamed Concrete Using High Volume of Waste Lime Mud and Fly Ash for Road Embankment.

This paper aims to study the feasibility of low cement content foamed concrete using waste lime mud (LM) and fly ash (FA) as mineral additives. The LM/FA ratio was first optimized based on the compressive strength. Isothermal calorimetry test, ESEM, and XRD were used to investigate the role of LM during hydration. Afterward, the optimized LM/FA ratio (1/5) was used to design foamed concrete with various wet densities (600, 700, 800 and 900 kg/m3) and LM–FA dosages (0%, 50%, 60%, 70% and 80%). Flowability measurements and mechanical measurements including compressive strength, flexural strength, splitting strength, elastic modulus, and California bearing ratio were conducted. The results show that the foamed concretes have excellent workability and stability with flowability within 170 and 190 mm. The high alkalinity of LM accelerated the hydration of FA, thereby increasing the early strength. The significant power functions were fitted for the relationships between flexural/splitting and compressive strength with all correlation coefficients (R2) larger with 0.95. The mechanical properties of the foamed concrete increased with the density increasing or LM–FA dosage decreasing. The compressive strength, tensile strength, CBR of all prepared foamed concretes were higher than the minimum requirements of 0.8 and 0.15 MPa and 8%, respectively in the standard.

Powder properties and flowability measurements of tailored nanocomposites for powder bed fusion applications

The modification of metal alloy powders by coating with nanoparticles offers the possibility to improve additive manufacturing processes, in particular the powder bed fusion of metals with laser beams (PBF/LB-M), from the material side of view. Subsequently, component qualities including mechanical properties and microstructural characteristics could be improved. Furthermore, the modification enables improved energy utilization due to an increase in laser absorption. In this work three commercial additive manufacturing powders, namely stainless steel (1.4404), tool steel (1.2709), and aluminum alloy (3.2381) were coated with three different nanoparticles (Silicon carbide (SiC), few layer graphene (FLG), and iron oxide black (IOB) to increase the laser light absorption in the PBF/LB/M process, mechanical properties, and flowability of the powders. The coating was conducted within a fluidized bed system, resulting in homogeneous coatings. This study demonstrates, that well scalable processes i.e. stirred media milling and fluidized bed coating have the potential to improve the commercial AM powders regarding their bulk density, flowability, and energy absorption, which is a crucial step towards an improvement in the efficiency of the whole PBF process. Overall important information and relations were gathered to transfer them to the real powder deposition process in future work.

Powder characterization and part density for powder bed fusion of 17-4 PH stainless steel

PurposeCharacteristics of the metal powder are a key factor in the success of powder bed fusion (PBF) additive manufacturing. Powders for PBF from different manufacturers may have a different particle size and/or bulk packing and flow behavior. Powder properties change as the powder is reused for multiple builds. This study seeks to measure the variability of commercial 17-4 PH stainless steel powders to determine the effect of powder variability on part density and demonstrate characterization methods that ensure part quality.Design/methodology/approachCommercial atomized metal powders from four different vendors were produced with two different atomizing gases (N2 and argon). Powder was characterized in both new and extensively reused conditions. All powders were characterized for flow and packing behavior, particle size and internal porosity. Coupons were manufactured using the laser PBF process with optimized scan strategy and exposure parameters. The quality of fabricated parts was measured using bulk density measurement.FindingsDespite differences in powder flowability and particle size, fully dense parts (>99 per cent) were produced using all powders, except one. Residual porosity in these parts appeared to result from gas trapped in the powder particles. The powder with extensive reuse (400+ h in machine fabrication environment) exhibited reduced flowability and increased fraction of fine particles, but still produced full density parts.Originality/valueThis study demonstrates that full density parts can be fabricated using powders with a range of flowability and packing behavior. This suggests that a single flowability measurement may be sufficient for quality assurance in a production environment.

Effect of Adding Stone Sludge as Sand Replacement on Fresh Properties of Mortar

Shortage of river sand and disposal of stone sludge are the problem of the construction and stone product industries, respectively. Utilization of stone sludge in mortar is one of the feasible strategies to solve these two problems. To study the effects of addition of stone sludge on the performance of mortar, 20 mixes of stone sludge powder mortar with various water/cement ratios and various stone sludge powder contents were produced for flowability measurement. To further study the governing mechanism of flowability and the packing densities of the solid proportions of the 20 mortar mixes were measured. Based on the packing density results, the average film thickness (AFT) of the 20 mortar mixes were calculated for flowability indication. Results proved that addition of stone sludge powder as sand replacement would decrease the flowability. The flowability was mainly governed by the AFT.

Characteristics of Ti6Al4V Powders Recycled from Turnings via the HDH Technique

The objective of this research is for Ti6Al4V alloy turnings, generated during the machining of implants, to produce powders for the fabrication of Ti base coating via the cold spray method. In order to decrease the cost of powder production and increase the recycling rate of the turnings, the hydrogenation-dehydrogenation (HDH) process has been utilised. The HDH process consists of the following sequence: surface conditioning of the turnings, hydrogenation, ball milling (for powder production), and dehydrogenation. Afterwards, the properties of the recycled powder were analysed via phase, chemical, and morphological examinations, and size and flowability measurements. Usability of the powder in additive manufacturing applications has been evaluated via examining the characteristics of the deposit produced from this powder by the cold spray method. In short, promising results were obtained regarding the potential of the recycled powders in additive manufacturing after making minor adjustments in the HDH process.

Using a Freeman FT4 rheometer and Electrical Capacitance Tomography to assess powder blending

This study assesses the influence of mixing or segregation on flowability results from a Freeman FT4 powder rheometer as well as the use of Electrical Capacitance Tomography (ECT) to measure powder mixing and mixedness.The blending (or otherwise) of two powders of different physical properties (particle size, density, basic flowability) and contrasting electrical permittivity was studied in a Freeman FT4 rheometer. Two initial arrangements were used: one with the heavier, smaller powder on the top that would be expected to mix readily; and the other, the inverse, that would be expected to be resistant to the axial blending mechanism prevalent in the FT4. The torque and thus flow energy were tracked through 30 cycles of the FT4 impeller passing into and back out of the powder layer. In one case, the FT4 data were seen to evolve towards a steady state comparatively quickly, while, in the other, relatively little change in the basic flow energy was observed. The change in the first case is attributed to mixing of the powder, and the lack of change in the latter case to the absence of mixing.Simultaneous ECT measurements using a two plane sensing arrangement were taken. The reconstructed tomograms and the basic average permittivity data show clearly the mixing in the first case and the absence of blending for the latter. This confirms not only the sensitivity of powder flowability measurements to segregation of component powders, but also the potential of ECT as a measurement tool for powder mixing and segregation studies.