Powders

Research

Jump to: Review

16 pages, 6087 KiB

Open AccessArticle

Orthorhombic Crystal Structure of Grossular Garnet (Suva Česma, Western Serbia): Evidence from the Rietveld Refinement

by Pavle Tančić, Slađana Dušanić and Suzana Erić

Powders 2023, 2(2), 387-402; https://doi.org/10.3390/powders2020023 - 18 May 2023

Cited by 1 | Viewed by 1758

Abstract

The grossular garnet from rodingite-type rock from the Suva Česma area in western Serbia is characterized with its weak anisotropic nature. Because its anisotropy could indicate a non-cubic lower symmetry, SEM-EDS and Rietveld powder refinement methods were used. The SEM-EDS results have shown [...] Read more.

The grossular garnet from rodingite-type rock from the Suva Česma area in western Serbia is characterized with its weak anisotropic nature. Because its anisotropy could indicate a non-cubic lower symmetry, SEM-EDS and Rietveld powder refinement methods were used. The SEM-EDS results have shown that the garnet has a (Ca_3.00Mn_0.01)_3.01(Al_1.82Fe_0.15Ti_0.02)_1.99(Si_2.97Al_0.03)_3.00O₁₂ chemical composition (i.e., Grs₉₁Adr₀₈), which can be more specifically explained as ferric iron containing grossular. The next step further used Rietveld powder refinements of the various crystal structures in the Ia‾3d, R‾3c, R‾3, I4₁/a, Fddd, C2/c, and I‾1 space groups as well as a single mixture, which was followed by a comparative analysis of the R-values, site occupancy factors, and bond lengths and angles. The synthesis of these results showed both that the studied grossular garnet is not cubic and that it crystallized in the disordered Fddd space group with the final R_B = 5.29% and R_F = 1.75%. It was presumed that the grossular formed at temperatures between 150 and ~600 °C. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

15 pages, 5572 KiB

Open AccessArticle

Effects of Coexisting Anions on the Formation of Hematite Nanoparticles in a Hydrothermal Process with Urea Hydrolysis and the Congo Red Dye Adsorption Properties

by Takahiro Onizuka, Mikihisa Fukuda and Tomohiro Iwasaki

Powders 2023, 2(2), 338-352; https://doi.org/10.3390/powders2020020 - 8 May 2023

Cited by 1 | Viewed by 3305

Abstract

Crystalline hematite nanoparticles as adsorbents for anionic Congo red dye were prepared by a hydrothermal process using urea hydrolysis. To examine the effects of coexisting anions in a solution on the formation of hematite nanoparticles, different iron(III) salts, including iron chloride hexahydrate, iron [...] Read more.

Crystalline hematite nanoparticles as adsorbents for anionic Congo red dye were prepared by a hydrothermal process using urea hydrolysis. To examine the effects of coexisting anions in a solution on the formation of hematite nanoparticles, different iron(III) salts, including iron chloride hexahydrate, iron nitrate nonahydrate, iron sulfate n-hydrate, ammonium iron sulfate dodecahydrate, and basic ferric acetate, were employed as iron-ion sources. After the hydrothermal treatment of the solution, consisting of an iron salt and urea at 423 K for 20 h, a single phase of hematite was formed from the iron-nitrate solution. The results suggested that the hydrothermal formation of hematite depended on the stability of iron complexes formed in the starting solution. The average crystallite size and median diameter of hematite nanoparticles also depended on the coexisting anions, suggesting that the appropriate selection of the coexisting anions in the starting solution can allow for control of the crystallite size and particle diameter of hematite nanoparticles. The Congo red adsorption kinetics and isotherms of the hematite nanoparticles were described by the Elovich model and Langmuir model, respectively. The adsorption thermodynamics parameters were estimated, which suggested an exothermic and spontaneous process. The results demonstrated good adsorption properties for Congo red adsorption. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

27 pages, 2850 KiB

Open AccessFeature PaperArticle

Analysis of the Influence of Process and Formulation Properties on the Drying Behavior of Pharmaceutical Granules in a Semi-Continuous Fluid Bed Drying System

by Tuur Vandeputte, Michael Ghijs, Michiel Peeters, Alexander De Man, Daan Van Hauwermeiren, Eduardo Dos Santos Schultz, Tamas Vigh, Fanny Stauffer, Ingmar Nopens and Thomas De Beer

Powders 2023, 2(2), 232-258; https://doi.org/10.3390/powders2020016 - 4 Apr 2023

Cited by 3 | Viewed by 2601

Abstract

In the last decade, twin-screw wet granulation became an essential technology for continuous pharmaceutical tablet production. Consequently, interest in (semi-)continuous fluidized bed drying systems as a subsequent processing unit has grown. In parallel, it has become pivotal to fully understand and control manufacturing [...] Read more.

In the last decade, twin-screw wet granulation became an essential technology for continuous pharmaceutical tablet production. Consequently, interest in (semi-)continuous fluidized bed drying systems as a subsequent processing unit has grown. In parallel, it has become pivotal to fully understand and control manufacturing processes in line with in the quality-by-design paradigm. Formulation-generic prediction models would enormously facilitate digitally enhanced process development and require dedicated experimental data collection and process knowledge. To obtain this knowledge, three experimental campaigns were performed in this work. Firstly, an investigation into the effect of dryer process settings on drying behavior is presented. Secondly, the effect of active pharmaceutical ingredient properties on drying was assessed by producing granules of similar particle size and porosity and evaluating their drying and breakage behavior. Finally, additional experiments with varying active pharmaceutical ingredients and drug load were conducted to increase the genericity of the data set. This knowledge can be used in mathematical process modelling. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

20 pages, 10044 KiB

Open AccessArticle

Experimental Investigation of the Flow Conditions in Spiral Jet Mills via Particle Image Velocimetry—Influence of Product Outlet Diameter and Gas Flow Rate

by Lisa Marie Radeke, Niklas Jongebloed, Mathias Ulbricht and Heyko Jürgen Schultz

Powders 2023, 2(1), 169-188; https://doi.org/10.3390/powders2010012 - 13 Mar 2023

Cited by 2 | Viewed by 1668

Abstract

Spiral jet mills used for fine and colloid grinding have an enormously high energy consumption resulting in a great potential for optimization. In order to increase their efficiency, it is essential to precisely understand the flow conditions within the grinding chamber and the [...] Read more.

Spiral jet mills used for fine and colloid grinding have an enormously high energy consumption resulting in a great potential for optimization. In order to increase their efficiency, it is essential to precisely understand the flow conditions within the grinding chamber and the influencing parameters. In this work, the experimental method of particle image velocimetry is applied, which is optimized to the extent that the velocity fields of the grinding gas flow can be determined in the entire mill cross-section. Additionally, the influence of the product outlet diameter and the grinding gas flow rate on the flow profiles are investigated. With decreasing outlet diameter, significantly higher velocities are obtained in the inner mill region resulting in higher classifying efficiencies. At the same time, as the outlet diameter declines, an overpressure builds up in the mill, causing a deceleration of the entire flow in the outer region, preventing the complete formation of the nozzle jets and leading to worse comminution efficiencies. Therefore, there is an optimum between the competing comminution and classifying processes regarding the effect of the product outlet diameter. In contrast, increasing the gas flow rate can consistently achieve a gain in velocity, improving both comminution and classifying efficiency. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

11 pages, 3134 KiB

Open AccessArticle

An Experimental Study on the Dilute Phase Pneumatic Conveying of Fat-Filled Milk Powders: Particle Breakage

by Fuweng Zhang, James A. O’Mahony, Song Miao and Kevin Cronin

Powders 2023, 2(1), 124-134; https://doi.org/10.3390/powders2010009 - 17 Feb 2023

Cited by 1 | Viewed by 2067

Abstract

Powder breakage during pneumatic conveying negatively affects the properties of dairy products and causes increased dusting, reduced wettability, and decreased product performance. In particular, particle breakage is a serious issue for fat-filled milk powder (FFMP) which, if it breaks, releases fat that causes [...] Read more.

Powder breakage during pneumatic conveying negatively affects the properties of dairy products and causes increased dusting, reduced wettability, and decreased product performance. In particular, particle breakage is a serious issue for fat-filled milk powder (FFMP) which, if it breaks, releases fat that causes odours and leads to sticky blocked pipes. In this work, a conveying rig (dilute phase, positive pressure) with 50 mm diameter food grade stainless steel pipes (1.5 m high and 5 m conveying distance with three 90° bends, two in the vertical plane and one in the horizontal plane) was built as the test system. The effects of operating conditions (conveying air velocity and solid loading rate) on the attrition of FFMP in a dilute phase conveying system were experimentally studied. Four quality characteristics were measured before and after conveying: bulk density, particle size distribution, wettability, and solubility, to access the influence of particle breakage. Conveying air speed shows a significant impact on powder breakage. As air speed increased, more breakage occurred, and the volume mean diameter D[4,3] decreased by around 50%, using the largest conveying air speed of 38 m/s. Bulk density increased accordingly whereas wettability decreased with an increase in air speed, resulting from the higher breakage rate. On other hand, improving the solid loading rate can further reduce the breakage level, but the positive effect is not as good as decreasing air speed. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

22 pages, 4259 KiB

Open AccessArticle

Investigation of the Influence of the Mixing Process on the Powder and Component Properties during Cyclic Reuse of a Polyamide 12 Sinter Material in Selective Laser Sintering

by Tom Eggers and Frank von Lacroix

Powders 2023, 2(1), 75-96; https://doi.org/10.3390/powders2010006 - 6 Feb 2023

Cited by 3 | Viewed by 2295

Abstract

Selective laser sintering (SLS) with polymers is currently in transition to the production of functional components. Nevertheless, the potential to revolutionize conventional production processes is confronted by newly imposed requirements regarding reliability and reproducibility. To ensure that the requirements are fulfilled, the aging [...] Read more.

Selective laser sintering (SLS) with polymers is currently in transition to the production of functional components. Nevertheless, the potential to revolutionize conventional production processes is confronted by newly imposed requirements regarding reliability and reproducibility. To ensure that the requirements are fulfilled, the aging mechanisms occurring in polymers are compensated by recycling strategies, such as fraction-based mixing of a defined ratio of new with recycled powder. Although various mixing ratios for the reuse of the material in SLS have been investigated, there is insufficient knowledge of suitable mixing parameters for homogeneous and gentle mixing of the powder fractions. This work therefore focused on the influence of potentially suitable mixing parameters identified in a previous study on the ongoing powder and component properties in SLS using polyamide 12 and a constant refreshing rate. Regarding the powder properties, the intrinsic properties and density of the powders were investigated. Regarding the component properties, mechanical properties, sinter density, and surface quality were investigated. Decreases in the powder density and the component properties were measured by increasing the number of process cycles. Taking into account the determined powder and component properties, the selected mixing parameters enabled a homogeneous and gentle mixing of the powder fractions. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Graphical abstract

16 pages, 6909 KiB

Open AccessArticle

Powder Production via Atomisation and Subsequent Laser Powder Bed Fusion Processing of Fe+316L Steel Hybrid Alloy

by Sudipta Pramanik, Anatolii Andreiev, Kay-Peter Hoyer, Jan Tobias Krüger, Florian Hengsbach, Alexander Kircheis, Weiyu Zhao, Jörg Fischer-Bühner and Mirko Schaper

Powders 2023, 2(1), 59-74; https://doi.org/10.3390/powders2010005 - 16 Jan 2023

Viewed by 2867

Abstract

The current investigation shows the feasibility of 316L steel powder production via three different argon gas atomisation routes (closed coupled atomisation, free fall atomisation with and without hot gas), along with subsequent sample production by laser powder bed fusion (PBF-LB). Here, a mixture [...] Read more.

The current investigation shows the feasibility of 316L steel powder production via three different argon gas atomisation routes (closed coupled atomisation, free fall atomisation with and without hot gas), along with subsequent sample production by laser powder bed fusion (PBF-LB). Here, a mixture of pure Fe and atomised 316L steel powder is used for PBF-LB to induce a chemical composition gradient in the microstructure. Optical microscopy and μ-CT investigations proved that the samples processed by PBF-LB exhibit very little porosity. Combined EBSD-EDS measurements show the chemical composition gradient leading to the formation of a local fcc-structure. Upon heat treatment (1100 °C, 14 h), the chemical composition is homogeneous throughout the microstructure. A moderate decrease (1060 to 985 MPa) in the sample’s ultimate tensile strength (UTS) is observed after heat treatment. However, the total elongation of the as-built and heat-treated samples remains the same (≈22%). Similarly, a slight decrease in the hardness from 341 to 307 HV1 is observed upon heat treatment. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

15 pages, 5424 KiB

Open AccessArticle

Investigation of the Influence of the Mixing Process on the Powder Characteristics for Cyclic Reuse in Selective Laser Sintering

by Tom Eggers, Hendrik Rackl and Frank von Lacroix

Powders 2023, 2(1), 32-46; https://doi.org/10.3390/powders2010003 - 10 Jan 2023

Cited by 5 | Viewed by 3390

Abstract

Selective laser sintering (SLS) with polymers is currently at the transition to the production of functional components and thus holds great potential to revolutionize conventional production processes. Nevertheless, the application capability is confronted by newly defined requirements regarding reliability and reproducibility. In order [...] Read more.

Selective laser sintering (SLS) with polymers is currently at the transition to the production of functional components and thus holds great potential to revolutionize conventional production processes. Nevertheless, the application capability is confronted by newly defined requirements regarding reliability and reproducibility. In order to fulfil the requirements and to increase the process stability, the ageing mechanisms in polymers are compensated by recycling strategies. This involves fraction-based mixing of a defined ratio of new powder with recycled powder. Basically, fraction-based mixing must be preceded by the selection of suitable mixing parameters. The work focused on the influence of the mixing process on the powder characteristics for cyclic reuse in SLS. With regard to the powder characteristics, the particle shape and particle size distribution as well as the bulk and tap density of the powder were investigated. The authors found an influence of the mixing process with increasing mixing time on the powder characteristics of a black polyamide 12 sintering material. A mixing time of 1 h and a mixing intensity of 15 rpm proved to be potentially effective for achieving a gentle and homogeneous mixing of the powders. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

11 pages, 6787 KiB

Open AccessArticle

Direct Powder Forging—A New Approach for near Net Shape Processing of Titanium Powders

by Sébastien Germain Careau, Elena Ulate-Kolitsky and Bernard Tougas

Powders 2023, 2(1), 21-31; https://doi.org/10.3390/powders2010002 - 4 Jan 2023

Cited by 2 | Viewed by 2569

Abstract

This study investigates direct powder forging (DPF) as a new approach for near-net-shape processing of titanium alloys using a coarse particle size distribution (PSD) between 90 and 250 μm. This route was utilised to takes advantage of DPF’s enclosed nature to make near-net-shape [...] Read more.

This study investigates direct powder forging (DPF) as a new approach for near-net-shape processing of titanium alloys using a coarse particle size distribution (PSD) between 90 and 250 μm. This route was utilised to takes advantage of DPF’s enclosed nature to make near-net-shape components with conventional forging equipment, making it attractive and viable even for reactive powder such as titanium. In this study, the uncompacted Ti-6Al-4V ELI powder was sealed under vacuum in a stainless-steel canister and hot forged in air to produce a fully dense titanium femoral stem. After the final forging stage, the excess material in the flash region was cut, which efficiently released the canister, revealing the forged part with minimal surface contamination. The as-forged microstructure comprises coarse β grains with a martensitic structure. The subsequent annealing was able to generate a fine and homogenous lamellar microstructure with mechanical properties that respects the surgical implant standard, showing that DPF offers significant potential for forged titanium parts. Therefore, the DPF process provides a suitable alternative to produce titanium components using basic equipment, making it more available to the industry. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

29 pages, 5065 KiB

Open AccessArticle

On Efficient Powder Manufacturing Using Process Control Methods and Cybernetics: A Background, Results and Policy Case Study

by Ejay Nsugbe

Powders 2022, 1(4), 273-301; https://doi.org/10.3390/powders1040019 - 16 Dec 2022

Cited by 1 | Viewed by 2635

Abstract

Powder manufacturing processes involve a systematic processing of particulate material towards forming a final product which needs to meet specific quality standards. A means towards ensuring that standards are met in a manufacturing plant is to apply self-regulating intelligent machinery that can take [...] Read more.

Powder manufacturing processes involve a systematic processing of particulate material towards forming a final product which needs to meet specific quality standards. A means towards ensuring that standards are met in a manufacturing plant is to apply self-regulating intelligent machinery that can take mitigatory actions in the presence of a process deviation or unsatisfactory process behavior. Given a case study of an open-loop batch powder agglomeration process, this work synthesizes the process of how a feedback element can be applied towards the powder manufacturing plant in order to allow for self-regulation and process optimization which, in turn, would increase process efficiency, minimize waste and ensure that the overall product quality meets production targets. Focusing on a proposed cybernetic loop with a feedback element, a vital component is the ability to measure key quality attributes of the powder mixture, which is crucial towards ensuring the control algorithm is able to implement the most reflective and appropriate control strategy on the powder process; thus, this work discusses heavily the sensing and associated signal processing component of the cybernetic loop. The results from the reviewed signal processing scenarios which comprised the in-process material spanned estimation accuracies of 3–10%, depending on the scenario that was considered. This paper also addresses the feared dystopian view of mass redundancy and job losses in the age of the introduction of enhanced automation technology within a manufacturing process, where it is distilled what kinds of knock-on effects can be expected as a result of the technology, in addition to means by which policy makers can contribute towards ensuring that the adaptation and transition process is as smooth as possible. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

11 pages, 3186 KiB

Open AccessFeature PaperArticle

60% IACS Conductive Metal Coating on a Polymer Surface: Achievement of a Highly Efficient Additive Processing by Cold Spraying

by Libin Lalu Khoitara, Rija Nirina Raoelison and Sophie Costil

Powders 2022, 1(4), 262-272; https://doi.org/10.3390/powders1040018 - 8 Dec 2022

Cited by 3 | Viewed by 1918

Abstract

This paper investigates a current challenge that enables the hybridization of different materials using a solid-state additive principle. We investigate the suitability of such a principle to easily and efficiently grow a metallic electrically conductive coating on a polymer substrate. The additive principle [...] Read more.

This paper investigates a current challenge that enables the hybridization of different materials using a solid-state additive principle. We investigate the suitability of such a principle to easily and efficiently grow a metallic electrically conductive coating on a polymer substrate. The additive principle is obtained using the high-pressure cold spraying (CS) method whose literature does not include an achievement as suggested in this paper, that is, to obtain a good conductive copper coating onto polymer with a very high deposition efficiency by tuning the effect of the stand-off distance, transverse speed of the nozzle, and temperature of the carrier gas on the deposition efficiency (DE) in order to overcome delamination and erosion, and thus to improve the DE. A good coating formation up to 400 µm can be obtained, which implies that a standoff distance higher than 100 mm is needed, since both a high gas temperature (400–500 °C) and high gas pressure (30 bars) are required. A nozzle scanning velocity in the range of 200–300 mm/s gives the highest DE. The results reveal that the Cu coating on PEEK reaches a DE up to 91%, leading to an electrical conductivity up to 60% IACS (International Annealed Copper Standard). Thus, parametric analysis, along with the deposition optimization, promises to be feasible for the future in terms of DE improvement along with a good electrical conductivity in CS. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Graphical abstract

19 pages, 4296 KiB

Open AccessArticle

Evaluation of Approximate Expressions to Calculate the Area of the Intersection between a Sphere and a Cylindrical Plane

by Charl Gabriël Du Toit

Powders 2022, 1(4), 243-261; https://doi.org/10.3390/powders1040017 - 2 Dec 2022

Cited by 1 | Viewed by 1343

Abstract

Cylindrical packed beds of spheres are found in many industrial and practical applications where heat and mass transfer and fluid flow occur. A proper understanding of the porous structure is imperative for the analysis and design of the performance of packed beds. The [...] Read more.

Cylindrical packed beds of spheres are found in many industrial and practical applications where heat and mass transfer and fluid flow occur. A proper understanding of the porous structure is imperative for the analysis and design of the performance of packed beds. The porosity of the packed bed and in particular the radial variation in porosity is of interest. When the positions and sizes of the spheres in the packed bed are known, the areas of the intersections between the spheres and selected cylindrical planes can be used to obtain the radial variation in porosity. The aim of the study is to evaluate the performance of approximate expressions that had been derived to calculate the intersection areas. Firstly, the ability of the approximate expressions to calculate the intersection area is evaluated by considering several typical sphere–cylindrical plane configurations. Secondly, the application of the approximate expressions to obtain the radial variation in porosity for a selection of cylindrical packed beds is evaluated. It is concluded that the approximate expressions should only be applied to packed beds with aspect ratios larger than 6 and for radial positions larger than 1.5 sphere diameters from the centre line of the cylindrical packed bed. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

12 pages, 2284 KiB

Open AccessFeature PaperArticle

Improving the Powder Properties of an Active Pharmaceutical Ingredient (Ethenzamide) with a Silica Nanoparticle Coating for Direct Compaction into Tablets

by Tatsuki Tadauchi, Daiki Yamada, Yoko Koide, Mayumi Yamada, Yasuhiro Shimada, Eriko Yamazoe, Takaaki Ito and Kohei Tahara

Powders 2022, 1(4), 231-242; https://doi.org/10.3390/powders1040016 - 21 Nov 2022

Cited by 5 | Viewed by 5136

Abstract

To improve the powder properties of active pharmaceutical ingredients (APIs), we coated APIs with silica nanoparticles using a dry process that allowed for direct compression into tablets. The dry coating performed with different apparatuses (a batch-type high-speed shear mixer (Mechanomill) and a continuous [...] Read more.

To improve the powder properties of active pharmaceutical ingredients (APIs), we coated APIs with silica nanoparticles using a dry process that allowed for direct compression into tablets. The dry coating performed with different apparatuses (a batch-type high-speed shear mixer (Mechanomill) and a continuous conical screen mill (Comil)) and properties of the resulting dry-coated APIs were compared. Ethenzamide (ETZ), which has low powder flowability, was selected as the host particle to be improved and the colloidal silicas Aerosil 200 and R972 were used as the guest particles. Both coating processes and types of silica nanoparticles improved the powder flowability (angle of repose) of ETZ under unstressed conditions. Inverse gas chromatography demonstrated that dry coating with silica nanoparticles reduced the surface free energy and improved the homogeneity of the surface energy distribution of ETZ particles. Under the stress conditions of a shear cell test, the Mechnomill-based treatment improved the powder flowability of ETZ from that of untreated ETZ; however, the Comil-based treatment did not improve the flowability. The mechanical shear force exerted by Comil was apparently insufficient for interactions between host and guest particles. However, the properties of tableted ETZ were enhanced even when the silica nanoparticles were coated using Comil. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

10 pages, 5450 KiB

Open AccessFeature PaperArticle

A Novel Method to Formulate Pigmented Powder Coatings by Ultrafine Powders

by Lang Li, Liyi Xu, Marshall Shuai Yang, Jinbao Huang, Hui Zhang and Jesse Zhu

Powders 2022, 1(4), 221-230; https://doi.org/10.3390/powders1040015 - 17 Nov 2022

Viewed by 2564

Abstract

Powder coatings are a green alternative to conventional solvent-borne liquid coatings, but they have the intrinsic drawback of color-matching and adjustment in production with the conventional extrusion process. In this study, an industrially applicable approach to formulate color powder coatings utilizing ultrafine powders, [...] Read more.

Powder coatings are a green alternative to conventional solvent-borne liquid coatings, but they have the intrinsic drawback of color-matching and adjustment in production with the conventional extrusion process. In this study, an industrially applicable approach to formulate color powder coatings utilizing ultrafine powders, i.e., a powdery blending and pressing method, was invented. This novel method was validated by comparing samples prepared by the Method 1 conventional extrusion method with an extra ultramarine pigment at 3%; Method 2 powdery blending and pressing of the original coatings and the same coating with 6% ultramarine pigment utilizing regular (coarse) powder coatings; and Method 3 utilizing ultrafine powder coatings for the two coatings with the same formulations as Method 2. The coating powders were prepared to have similar particle sizes and particle size distributions, with three commonly used coating binders, namely polyester-epoxy hybrid, polyester/TGIC (triglycidyl isocyanurate), and polyurethane (PU). The powders prepared by Methods 1 and 3 had similar flow abilities in terms of angle of repose (AOR) and avalanche angle (AVA). The performance of the new coatings by Method 3 was close to or better than the ones prepared by Method 1 in terms of the specular gloss, DOI (distinctness-of-image), reflection haze and color values, being superior to Method 2. The coatings via ultrafine powders also exhibited a comparable ultramarine particle distribution in the coating cross-sections as the conventional ones, whereas the ones via regular powders had an inferior pigment dispersion. The new method can greatly enhance the production efficiency and reduce the cost of powder coatings with compound colors, especially for small batch manufacturing. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

14 pages, 7135 KiB

Open AccessFeature PaperArticle

Fabrication of Cu-CNT Composite and Cu Using Laser Powder Bed Fusion Additive Manufacturing

by Leila Ladani, Jafar Razmi and Maryam Sadeghilaridjani

Powders 2022, 1(4), 207-220; https://doi.org/10.3390/powders1040014 - 12 Oct 2022

Cited by 4 | Viewed by 2517

Abstract

Additive manufacturing (AM) as a disruptive technique has offered great potential to design and fabricate many metallic components for aerospace, medical, nuclear, and energy applications where parts have complex geometry. However, a limited number of materials suitable for the AM process is one [...] Read more.

Additive manufacturing (AM) as a disruptive technique has offered great potential to design and fabricate many metallic components for aerospace, medical, nuclear, and energy applications where parts have complex geometry. However, a limited number of materials suitable for the AM process is one of the shortcomings of this technique, in particular laser AM of copper (Cu) is challenging due to its high thermal conductivity and optical reflectivity, which requires higher heat input to melt powders. Fabrication of composites using AM is also very challenging and not easily achievable using the current powder bed technologies. Here, the feasibility to fabricate pure copper and copper-carbon nanotube (Cu-CNT) composites was investigated using laser powder bed fusion additive manufacturing (LPBF-AM), and 10 × 10 × 10 mm³ cubes of Cu and Cu-CNTs were made by applying a Design of Experiment (DoE) varying three parameters: laser power, laser speed, and hatch spacing at three levels. For both Cu and Cu-CNT samples, relative density above 90% and 80% were achieved, respectively. Density measurement was carried out three times for each sample, and the error was found to be less than 0.1%. Roughness measurement was performed on a 5 mm length of the sample to obtain statistically significant results. As-built Cu showed average surface roughness (R_a) below 20 µm; however, the surface of AM Cu-CNT samples showed roughness values as large as 1 mm. Due to its porous structure, the as-built Cu showed thermal conductivity of ~108 W/m·K and electrical conductivity of ~20% IACS (International Annealed Copper Standard) at room temperature, ~70% and ~80% lower than those of conventionally fabricated bulk Cu. Thermal conductivity and electrical conductivity were ~85 W/m·K and ~10% IACS for as-built Cu-CNT composites at room temperature. As-built Cu-CNTs showed higher thermal conductivity as compared to as-built Cu at a temperature range from 373 K to 873 K. Because of their large surface area, light weight, and large energy absorbing behavior, porous Cu and Cu-CNT materials can be used in electrodes, catalysts and their carriers, capacitors, heat exchangers, and heat and impact absorption. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

13 pages, 5113 KiB

Open AccessFeature PaperArticle

Particulate Matter Characterization in a Hospital’s Underground Car Park

by Hector Garcia-Gonzalez, Maida Domat, Teresa Lopez-Pola, Pilar Fernandez-Rubio and Pablo Fernandez-Rodriguez

Powders 2022, 1(4), 194-206; https://doi.org/10.3390/powders1040013 - 30 Sep 2022

Cited by 4 | Viewed by 2113

Abstract

The air quality in a hospital’s underground car park is a concern because diesel fumes from cars impact upon vulnerable people attending medical consultations. This research aims to quantify the potential health risk associated with a particular hospital car park. Particulate matter was [...] Read more.

The air quality in a hospital’s underground car park is a concern because diesel fumes from cars impact upon vulnerable people attending medical consultations. This research aims to quantify the potential health risk associated with a particular hospital car park. Particulate matter was evaluated in the area with direct reading devices for particle numbers and mass concentrations (CPC 3007, EEPS 3090, Trolex Air XD, Nanozen, and Grimm 1109). Elemental and total carbon concentrations were measured following the NIOSH 5040 method, while volatile organic compounds (VOCs), and polycyclic aromatic hydrocarbons (PAHs) were measured through laboratory analysis and Scanning Electron Microscopy and Energy Dispersive using X-Ray Analysis SEM-EDX microscopy. The nanoparticle levels reached over 80,000 nanoparticles/cm³ (double the German Institut für Arbeitsschutz (IFA) benchmark levels). Diesel particulate matter levels measured as elemental carbon were around 35% of the occupational limit, and from the 49 VOCs analyzed only 13 were detected in quantities below the 0.1% of the occupational limit, while levels of the 13 PAHs analyzed, were below the laboratory limit of quantification. The study concludes that particulate matter in the underground car park can easily exceed nanoparticles benchmark levels and could be harmful, mainly to vulnerable people. It is therefore recommended that they use the outdoor car park or minimize their time in the underground one. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

10 pages, 4153 KiB

Open AccessArticle

Influence of Process Parameters on Porosity and Hot Cracking of AISI H13 Fabricated by Laser Powder Bed Fusion

by Siyuan Qin, Yutao Bo, Simone Herzog, Bengt Hallstedt, Anke Kaletsch and Christoph Broeckmann

Powders 2022, 1(3), 184-193; https://doi.org/10.3390/powders1030012 - 9 Sep 2022

Cited by 14 | Viewed by 2694

Abstract

Laser powder bed fusion is an attractive manufacturing technology promising novel components for the aircraft, automobile, and medical industries. However, depending on the material, some defects in the parts, especially pores or microcracks, cannot be avoided in the LPBF process. To achieve a [...] Read more.

Laser powder bed fusion is an attractive manufacturing technology promising novel components for the aircraft, automobile, and medical industries. However, depending on the material, some defects in the parts, especially pores or microcracks, cannot be avoided in the LPBF process. To achieve a part with low defect density, the optimal parameter sets must be determined. Many investigations have focused on how laser speed and laser power influence the melting process and the relative density of as-built parts. In this study, we considered laser and heated powder beds as two energy input sources, represented by volume energy density and preheating temperature, respectively. The interaction of these two energy inputs for the fabrication of AISI H13 was investigated. It was found that high preheating temperatures shifted the optimal parameter sets from the low energy density area to the high energy density area. In addition, high preheating also led to hot cracking, which was confirmed with Scheil solidification simulations. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

18 pages, 4609 KiB

Open AccessFeature PaperArticle

Understanding Morphology, Bulk Properties, and Binding of Silk Particles for 3D Printing

by Daniel Whyte, Benjamin J. Allardyce, Abbas Z. Kouzani, Xungai Wang and Rangam Rajkhowa

Powders 2022, 1(2), 111-128; https://doi.org/10.3390/powders1020009 - 18 Jun 2022

Viewed by 2638

Abstract

Silk fibroin has emerged as a leading biomaterial for biomedical applications. 3D printing has been successfully used for printing with silk fibroin, albeit in the form of a bioink, in direct-write 3D printers. However, in the form of bioinks, stability and mechanical attributes [...] Read more.

Silk fibroin has emerged as a leading biomaterial for biomedical applications. 3D printing has been successfully used for printing with silk fibroin, albeit in the form of a bioink, in direct-write 3D printers. However, in the form of bioinks, stability and mechanical attributes of silk are lost. An innovative alternative to producing 3D printed solid silk constructs is silk milled into powder for printing in a binder jetting printer. In this work, we focus on characteristics of silk powder to determine suitability for use in 3D printing. Two different silk powders are compared with hydroxyapatite powder, a known biomaterial for biomedical constructs. We have investigated powder size and shape by Camsizer X2 and Scanning Electron Microscope and bulk behaviour, dynamic flow behaviour, and shear behaviour by FT4 powder rheometer. Preliminary printing tests were conducted in an in-house custom-built printer designed for silk powder. It was found that silk powder has low flowability and stability. Therefore, to print solely out of silk powder, a 3D printer design will need sophisticated techniques to produce flow to ensure even distribution and consistent thickness of powder layers during the printing process. It was also found that high concentrations of formic acid (>75 to 99 wt.%) can fuse particles and therefore be used as a binder ink for 3D printing. The printer design challenges for silk powder are discussed. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

23 pages, 3910 KiB

Open AccessFeature PaperArticle

A Combined Isolation and Formulation Approach to Convert Nanomilled Suspensions into High Drug-Loaded Composite Particles That Readily Reconstitute

by Alexander Coelho, Luke Schenck, Gulenay Guner, Ashish Punia and Ecevit Bilgili

Powders 2022, 1(2), 88-110; https://doi.org/10.3390/powders1020008 - 3 May 2022

Cited by 3 | Viewed by 3580

Abstract

The advantage of nanoparticles to improve bioavailability of poorly soluble drugs is well known. However, the higher-energy state of nanoparticles beneficial for bioavailability presents challenges for both the stability of nanosuspensions and preventing irreversible aggregation if isolated as dry solids. The aim of [...] Read more.

The advantage of nanoparticles to improve bioavailability of poorly soluble drugs is well known. However, the higher-energy state of nanoparticles beneficial for bioavailability presents challenges for both the stability of nanosuspensions and preventing irreversible aggregation if isolated as dry solids. The aim of this study is to explore the feasibility of an evaporation isolation route for converting wet media milled nanosuspensions into high drug-loaded nanocomposites that exhibit fast redispersion in aqueous media, ideally fully restoring the particle size distribution of the starting suspension. Optimization of this approach is presented, starting from nanomilling conditions and formulation composition to achieve physical stability post milling, followed by novel evaporative drying conditions coupled with various dispersant types/loadings. Ultimately, isolated nanocomposite particles reaching 55–75% drug load were achieved, which delivered fast redispersion and immediate release of nanoparticles when the rotary evaporator drying approach was coupled with higher concentration of hydrophilic polymers/excipients. This bench-scale rotary evaporation approach serves to identify optimal nanoparticle compositions and has a line of sight to larger scale evaporative isolation processes for preparation of solid nanocomposites particles. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

13 pages, 1786 KiB

Open AccessFeature PaperArticle

Infrared Spectroscopy Studies of Aluminum Oxide and Metallic Aluminum Powders, Part II: Adsorption Reactions of Organofunctional Silanes

by Bellamarie Ludwig

Powders 2022, 1(2), 75-87; https://doi.org/10.3390/powders1020007 - 1 Apr 2022

Cited by 13 | Viewed by 7084

Abstract

A gas phase, probe molecule doser was fabricated and connected to a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reaction chamber to study the reactions and stability of two organosilanes with the surfaces of metallic aluminum and boehmite powders in situ. Two metallic [...] Read more.

A gas phase, probe molecule doser was fabricated and connected to a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reaction chamber to study the reactions and stability of two organosilanes with the surfaces of metallic aluminum and boehmite powders in situ. Two metallic aluminum powder surfaces were studied, including an as-received, native oxide layer surface, and a laboratory prepared, boehmite-like surface. Neat boehmite powder was also used for reference and comparison to the laboratory prepared surface. We found that the metalloxane bond (Al-O-Si) was observed in the 1100–950 cm⁻¹ region for all surfaces, which indicates chemisorption between the adsorbate and available surface hydroxyls. We were also able to draw correlations between the loss of surface –OH and the subsequent growth of –CH for additional confirmation of adsorbate retention. Hydrothermal stability was probed through intentional exposure to water after chlorotrimethyl silane dosing, which showed adsorbate loss through fractional decreases in intensity of the –CH stretches. These results provide clear evidence of metalloxane bonds formed on aluminum powder and insight into their stability, supporting the identification of these bonds on bulk scale silane treated powders. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

15 pages, 3135 KiB

Open AccessFeature PaperArticle

Infrared Spectroscopy Studies of Aluminum Oxide and Metallic Aluminum Powders, Part I: Thermal Dehydration and Decomposition

by Bellamarie Ludwig and Taryn T. Burke

Powders 2022, 1(1), 47-61; https://doi.org/10.3390/powders1010005 - 10 Mar 2022

Cited by 9 | Viewed by 5513

Abstract

In this work, we study three aluminum oxides (alpha, gamma, boehmite) and various oxidized metallic aluminum powders to observe their dehydration and decomposition behavior using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and scanning electron microscopy (SEM). We find that a [...] Read more.

In this work, we study three aluminum oxides (alpha, gamma, boehmite) and various oxidized metallic aluminum powders to observe their dehydration and decomposition behavior using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and scanning electron microscopy (SEM). We find that a temperature increase to the aluminum oxides (aluminas) reduces physically adsorbed water molecules to reveal the presence of hydroxyl groups. All three aluminas contained bridged hydroxyls located at 3670 cm⁻¹; we found additional surface hydroxyls, which varied based on the oxidation state of the aluminum atom. Oxidized metallic aluminum powders that were aged resulted in similar behavior; however, the results differed depending on the method of aging. We find that naturally aged aluminum (NA-Al) powders with heavy oxidation in the form of the tri-hydroxide decomposed and did not reveal any detectable surface hydroxyl peaks. When aged using artificial methods (AA-Al), we find both surface hydroxyls, including bridged hydroxyls at 3670, 3700, and 3730 cm⁻¹, and a remaining boehmite-like surface. These results show that metallic aluminum powders can be tailored for specific applications, regardless of age. It also elucidates different ways to pre-process the powders to control the surface oxide layer, corroborated by comparison with the models oxides studied herein. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

14 pages, 18666 KiB

Open AccessFeature PaperArticle

Sugar as an Analogue for Snow in Penetration Testing: A Preliminary Comparison

by Adrian B. McCallum, Damon Kent and Denham Lee

Powders 2022, 1(1), 33-46; https://doi.org/10.3390/powders1010004 - 24 Feb 2022

Viewed by 2626

Abstract

Snow is a sintered matrix of ice, the strength of which is determined by the number and size of bonds between ice grains. However, because snow is a thermally unstable material, it is problematic to transport and store samples for accurate ex situ [...] Read more.

Snow is a sintered matrix of ice, the strength of which is determined by the number and size of bonds between ice grains. However, because snow is a thermally unstable material, it is problematic to transport and store samples for accurate ex situ testing of mechanical behaviour. As an analogue for snow, we examined the sintering behaviour of different types of granular sugar at different humidities over different temporal periods and then assessed the extent of sintering and resistance to penetration of these samples. Like snow, increased sintering occurs in sugar over time. Sintering extent and rate are affected by the humidity environment and penetration resistance generally increases after increased sintering time. This preliminary examination suggests that in the absence of snow testing facilities, humidity-controlled sintered sugar may serve as a valuable proxy for examining the temporal variation of penetration resistance in snow. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

15 pages, 8896 KiB

Open AccessFeature PaperArticle

A Carbon-Free Way for Obtaining Nanoscale Silicon

by Nikolay Lyakhov, Tatiana Grigoreva, Tatiana Talako, Tatyana Udalova, Sergey Vosmerikov and Evgeniya Devyatkina

Powders 2022, 1(1), 18-32; https://doi.org/10.3390/powders1010003 - 17 Feb 2022

Cited by 2 | Viewed by 2542

Abstract

The nanosized silicon powder has been produced by reduction of silica with magnesium in an argon medium using both the mechanically activated self-propagating high-temperature synthesis and the direct mechanochemical synthesis and has been investigated by X-ray phase analysis, Infrared spectroscopy, electron scanning microscopy, [...] Read more.

The nanosized silicon powder has been produced by reduction of silica with magnesium in an argon medium using both the mechanically activated self-propagating high-temperature synthesis and the direct mechanochemical synthesis and has been investigated by X-ray phase analysis, Infrared spectroscopy, electron scanning microscopy, and energy dispersive X-ray spectroscopy. The optimal Mg:SiO₂ ratio has been found to provide the minimum content of contaminant impurities of magnesium silicide and silicate in mechanically activated self-propagating high-temperature synthesis. For the first time, direct mechanochemical synthesis of Si via reduction of silica with magnesium has been implemented. Optimal component ratio and mechanical activation parameters have been determined, yielding Si/MgO composites without impurity phases (magnesium silicide and silicate). A purification procedure has been proposed for separating silicon obtained from magnesium oxide and other impurity phases. The ratio of initial components has been determined, at which purified silicon has the least amount of impurities. The particle size of silicon powder obtained was 50–80 nm for the mechanically activated self-propagating high-temperature synthesis, and 30–50 nm for the direct mechanochemical synthesis. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Graphical abstract

15 pages, 3018 KiB

Open AccessFeature PaperArticle

Mechanical, Corrosion, and Ion Release Studies of Ti-34Nb-6Sn Alloy with Comparable to the Bone Elastic Modulus by Powder Metallurgy Method

by Mariana Correa-Rossi, Liliana Romero-Resendiz, Daniel Leal-Bayerlein, Ana Liz Garcia-Alves, Francisco Segovia-López and Vicente Amigó-Borrás

Powders 2022, 1(1), 3-17; https://doi.org/10.3390/powders1010002 - 25 Jan 2022

Cited by 16 | Viewed by 3448

Abstract

The development of a Ti-34Nb-6Sn alloy by the powder metallurgy method, employing two different compaction conditions, A (100 MPa) and B (200 MPa), was carried out. To evaluate the feasibility of the Ti-34Nb-6Sn alloy as an implant biomaterial, microstructural and mechanical characterizations, as [...] Read more.

The development of a Ti-34Nb-6Sn alloy by the powder metallurgy method, employing two different compaction conditions, A (100 MPa) and B (200 MPa), was carried out. To evaluate the feasibility of the Ti-34Nb-6Sn alloy as an implant biomaterial, microstructural and mechanical characterizations, as well as corrosion susceptibility and ion release tests, were performed. Results indicated microstructures dominated by the presence of β-Ti phase and a lower percentage of α-Ti and Nb phases. The porosity percentage decreased when the compaction pressure increased. Both conditions presented a good match between the elastic moduli of the alloy (14.0 to 18.8 GPa) and that reported for the bone tissue. The Ti, Nb and Sn ions released for both compaction conditions were within the acceptable ranges for the human body. Condition B showed higher corrosion resistance in comparison with condition A. Based on the obtained results, the produced porous Ti-34Nb-6Sn alloys are feasible materials for orthopedic implant applications. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

Review

Jump to: Research

16 pages, 1865 KiB

Open AccessFeature PaperReview

Application of Electric Field Technologies in the Manufacture of Food Powders and the Retention of Bioactive Compounds

by Doll Chutani, Thom Huppertz and Eoin Murphy

Powders 2023, 2(1), 135-150; https://doi.org/10.3390/powders2010010 - 22 Feb 2023

Cited by 3 | Viewed by 3747

Abstract

Electric fields have been used in the manufacturing of powders in a number of ways, including to enhance drying rates and retain heat-sensitive materials. Electrohydrodynamic drying and electrostatic spray drying use electric fields to accelerate the evaporation of liquid from a surface, resulting [...] Read more.

Electric fields have been used in the manufacturing of powders in a number of ways, including to enhance drying rates and retain heat-sensitive materials. Electrohydrodynamic drying and electrostatic spray drying use electric fields to accelerate the evaporation of liquid from a surface, resulting in faster drying times and improved product quality. These technologies are used in the food and pharmaceutical industries to manufacture powders from liquid feed materials. In addition to enhancing drying rates, the use of electric fields in powder manufacturing can also help to retain the bioactivity of compounds in the final product. Many bioactive compounds are sensitive to heat and can be degraded or destroyed during conventional drying processes. By using electric fields to dry powders, it is possible to reduce the amount of heat applied and therefore preserve the bioactive compounds in the final product. This article reviews the different mechanisms of various electric field assisted technologies, i.e., electrohydrodynamic atomization, electrohydrodynamic drying, pulsed electric fields and a new approach of electrostatic spray drying, along with their potential food industry applications. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Figure 1

29 pages, 4316 KiB

Open AccessReview

Advances in Microfluidic Synthesis of Solid Catalysts

by Huihui Chen, Zhenhua Dong and Jun Yue

Powders 2022, 1(3), 155-183; https://doi.org/10.3390/powders1030011 - 4 Aug 2022

Cited by 3 | Viewed by 3490

Abstract

Heterogeneous catalysis plays a central role in the chemical and energy fields, owing to the high and tunable activities of solid catalysts that are essential to achieve the favorable reaction process efficiency, and their ease of recycle and reuse. Numerous research efforts have [...] Read more.

Heterogeneous catalysis plays a central role in the chemical and energy fields, owing to the high and tunable activities of solid catalysts that are essential to achieve the favorable reaction process efficiency, and their ease of recycle and reuse. Numerous research efforts have been focused on the synthesis of solid catalysts towards obtaining the desired structure, property and catalytic performance. The emergence and development of microfluidic reactor technology provide a new and attractive platform for the controllable synthesis of solid catalysts, primarily because of its superior mixing performance and high heat/mass transfer efficiency. In this review, the recent research progress on the synthesis of solid catalysts based on microfluidic reactor technology is summarized. The first section deals with the synthesis strategies for solid catalysts, including conventional methods in batch reactors and microfluidic alternatives (based on single- and two-phase flow processing). Then, different kinds of solid catalysts synthesized in microflow are discussed, especially with regard to the catalyst type, synthetic process, structure and property, and catalytic performance. Finally, challenges in the microreactor operation and scale-up, as well as future perspectives in terms of the synthesis of more types of catalysts, catalyst performance improvement, and the combination of catalyst synthesis process and catalytic reaction in microreactors, are provided. Full article

(This article belongs to the Special Issue Feature Papers in Powders)

► Show Figures

Graphical abstract

Journal Menu

Journal Browser

Feature Papers in Powders

Share This Special Issue

Special Issue Editor

Special Issue Information

Keywords

Benefits of Publishing in a Special Issue

Published Papers (26 papers)

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI