Dry Powder Processing Research Articles

Physical Properties of Paste Synthesized from Wet- and Dry-Processed Silver Powders.

This study compares the characteristics and low-temperature curing properties of pastes prepared from silver (Ag) powders synthesized by either wet powder (WP) or dry powder (DP) processing. The WP synthesis of electrode particles has the advantage of controlling the average particle size and particle size distribution but the disadvantage of producing low-purity, crystalline particles because they are synthesized through chemical reduction at less than 100 °C. Conversely, the DP synthesis of electrode particles has the advantage of producing pure, highly crystalline particles (due to synthesis at high temperatures) but the disadvantage of a high processing cost. WP and DP were used to manufacture pastes for low-temperature curing, and the physical properties of the pastes and the electrode characteristics after low-temperature curing were compared between powder types. Shear stress as a function of the shear rate shows that the WP paste is a plastic fluid, whereas the DP paste is a pseudoplastic fluid, closer to a Newtonian fluid. Screen printing the Ag pastes and curing for 30 min at 130 °C produces a nonconductive WP paste, whereas it produces a DP paste with a conductivity of 61 mΩ/sq, indicating that the highly crystalline DP paste is advantageous for low-temperature curing.

Synthesis and Characterization of Hematite Fe2O3 Nanofiller for Enhanced Dielectric and Microwave-Absorbing Properties in PTFE Composites

This paper presents the synthesis of hematite Fe2O3 nanofiller from mill scales and its application in polytetrafluoroethylene (PTFE) composites for enhanced dielectric and microwave-absorbing properties. The nanofiller was obtained through 9 hours of high-energy ball milling, resulting in a particle size reduction 43.6 to 11.05 nm. The PTFE/Fe2O3 composites were fabricated by dispersing different concentration of Fe2O3 nanofillers using the dry powder processing technique. The structural and morphological characterization of the nanofiller and PTFE/Fe2O3 composites was carried out using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The composites’ microwave absorption properties were analyzed utilizing vector network analyzer (VNA) measurements in the 8–12 GHz frequency range. Based on the findings from the results, as the percentage of filler increased from 5 to 15%wt, the composites' loss tangent and dielectric constant increased from 0.0272 to 0.0478 and 2.12 to 3.25, respectively, while their reduced signal transmission speed was between 2.21 and 2.07 x 108 m/s at 8 GHz and from 2.24 to 2.11 x 108 m/s at 12 GHz. These findings demonstrate that Fe2O3 nanoparticles are a suitable material for developing microwave-absorbing polymer composites within the 8–12 GHz frequency range.

Developing a method for dry-stressed Cronobacter spp. cells for subsequent sanitiser efficacy testing

Cronobacter spp. are opportunistic foodborne pathogens in dry dairy powder processing plants, where they may occur in a viable, desiccated form. This study designed a model testing system that identified the most desiccation tolerant cell form of Cronobacter spp. and that could then be used for further studies in cleaning and sanitation efficacy. Colonies of cells scraped from plates (colony cells) represented a worst-case scenario model for the most desiccation tolerant form of Cronobacter spp., followed by biofilms on stainless steel surfaces, planktonic cells, and cells mechanically dispersed from a biofilm. This model colony cell testing scheme was then used to evaluate the efficacy of two powder-based sanitisers against desiccated Cronobacter spp. on flooring materials (resin-coated concrete and stainless steel). Results indicated that powder-based sanitisers may be useful adjuncts in dairy processing plants to aid in keeping levels of Cronobacter spp. on floors low (<10 cfu).

A multivariate methodology for material sparing characterization and blend design in drug product development

This study developed a material and time saving method for powder characterization. Building on an earlier developed raw material property database for use towards development of pharmaceutical dry powder processes, blends were selected in an efficient way to include maximal variability of the underlying raw material dataset. For both raw materials and blends, powder characterization methods were kept to a minimum by selecting the testing methods that described the highest amount of variability in physical powder properties based on principal component analysis (PCA). This method selection was made by identifying the overarching properties described by the principal components of the PCA model. Ring shear testing, powder bed compressibility, bulk/tapped density, helium pycnometry, loss on drying and aeration were identified as the most discriminating characterization techniques from this dataset to detect differences in physical powder properties. This ensured a workload reduction while most of the powder variability that could be detected was still included. The methodology proposed in this paper could be used as a material-saving alternative to the current “Design of Experiment” approach, which will be investigated further for applicability to speed up the development of formulations and processes for new drug products and building an end-to-end predictive platform.

Effects of Particle Size on the Dielectric, Mechanical, and Thermal Properties of Recycled Borosilicate Glass-Filled PTFE Microwave Substrates.

Low dielectric loss and low-cost recycled borosilicate (BRS) glass-reinforced polytetrafluoroethylene (PTFE) composites were fabricated for microwave substrate applications. The composites were prepared through a dry powder processing technique by dispersing different micron sizes (25 µm, 45 µm, 63 µm, 90 µm, and 106 µm) of the recycled BRS filler in the PTFE matrix. The effect of the filler sizes on the composites’ thermal, mechanical, and dielectric properties was studied. The dielectric properties of the composites were characterised in the frequency range of 1–12 GHz using an open-ended coaxial probe (OCP) connected to a vector network analyser (VNA). XRD patterns confirmed the phase formation of PTFE and recycled BRS glass. The scanning electron microscope also showed good filler dispersion at larger filler particle sizes. In addition, the composites’ coefficient of thermal expansion and tensile strength decreased from 12.93 MPa and 64.86 ppm/°C to 7.12 MPa and 55.77 ppm/°C when the filler size is reduced from 106 μm to 25 μm. However, moisture absorption and density of the composites increased from 0.01% and 2.17 g/cm3 to 0.04% and 2.21 g/cm3. The decrement in filler size from 106 m to 25 m also increased the mean dielectric constant and loss tangent of the composites from 2.07 and 0.0010 to 2.18 and 0.0011, respectively, while it reduced the mean signal transmission speed from 2.088 × 108 m/s to 2.031 × 108 m/s. The presented results showed that PTFE/recycled BRS composite exhibited comparable characteristics with commercial high-frequency laminates.

Cold Plasma Process for Lithium-Ion Electrode Manufacturing

Conventional slurry-cast manufacturing of Lithium-ion battery (LIB) cathode containing active materials, conductive carbon, binders, and organic solvents is expensive and environmental unfriendly due to the long drying process (solvents evaporation). Here, we apply a new, completely dry powder process to manufacturing (LIB) cathodes which includes the use of multiple atmospheric plasma streams to activate cathodes particles for manufacturing high-density and thick LIB cathodes. In this presentation, we use Lithium iron phosphate (LFP) as an example to elaborate this drying process and discuss the effectiveness of the cold-plasma process on electrode manufacturing. During the cold-plasma process, LFP power together with a metallic binder (aluminum herein) were directly co-deposited on the current collector with a superb control of thickness. This presentation will discuss the effects of loading LFP thickness, particles size, and surface chemistry on the electrochemical properties and the cycling performance. XPS and in situ XRD analysis are also used here to better understand the LFP phase evolution and surface chemistry at different electrochemical states.

Dry Processing and Recycling of Thick Nacre–Mimetic Nanocomposites

AbstractBioinspired nanocomposites with high levels of reinforcement hold great promise for future, green lightweight, and functional engineering materials, but they suffer from slow, tedious, and nonscalable preparation routes, that typically only lead to very thin films. A rapid and facile dry powder processing technique is introduced to generate bioinspired nanocomposite materials at high fractions of reinforcements (50 wt%) and with millimeter scale thickness. The process uses powder drying of vitrimer‐coated nanoplatelets (nanoclay and MXene) from aqueous solution and subsequent hot‐pressing. As a method of choice in industrial lightweight composite materials engineering, hot‐pressing underscores a high potential to translate this approach to actual products. The use of the vitrimer chemistry with temperature‐activated bond shuffling is important to facilitate smooth integration into the nanocomposite design, leading to layered nacre‐inspired nanocomposites with nanoscale hard/soft order traced by X‐ray diffraction and excellent mechanical properties investigated using flexural tests. Recycling by grinding and hot‐pressing is possible without property loss. The compatibility with existing composite processing techniques, scalable thickness and dimensions, and recyclability open considerable opportunities for translating bioinspired nanocomposites to real‐life applications.

Effect of CNT on microstructural properties of Zn2SiO4/CNT composite via dry powder processing

This work focused on the influence of carbon nanotubes (CNT) to the microstructural properties of Zn2SiO4/CNT (ZSO/CNT) composite. CNT was synthesized via alcohol catalytic chemical vapor deposition (ACCVD) using cobalt oxide as catalyst and ethanol as carbon source. Zinc silicate (ZSO) glass was prepared from quenching the melted commercial waste glass bottle with zinc oxide powder. ZSO/CNT-x composites with various CNT concentration (0, 1, 2 and 3 wt%) was prepared through introducing CNT into ZSO glass via dry processing technique followed by sintering process in Argon gas (Ar) environment and atmospheric (atm) environment, respectively. FESEM, XRD and EDS were employed to determine the surface morphology, phase composition and elemental distribution of sintered sample. Crystallite trigonal willemite (Zn2SiO4) phase was observed from argon sintered sample and the crystallite size of willemite phase in ZSO/CNT-3/Ar showed the most reduced lattice strain of 22.85% compared to ZSO/CNT-0/Ar. In contrast, semi-crystalline phase exhibited in atmospheric sintered sample resulted in high lattice strain. It is concluded that dry powder processing and inert gas thermal treatment can be an effective technique in fabricating strain-reduced ceramics/CNT composite without alternating the domain phase. Least internal strain in crystal lattice have potential on enhancing the luminescence properties of phosphor material and lattice thermal conductivity of thermoelectric material.

Design of swellable ordered-mixed spherical drug particles (Swell-OM-spheres) using a dry powder milling and coating technique to improve dissolution behavior

A novel dry powder milling/ordered-mixing technique using a mechanical powder processor was previously developed to improve the dissolution properties of poorly water-soluble drugs. Mecanofused composite particles with an ordered-mixing principle, named OM particles, were designed using corn starch (CS) as a core particle and drug as a coating layer. In the present study this dry powder processing technique was modified to improve the dissolution behavior further by means of two approaches. First, wettable composite particles were produced by co-formulating the water-soluble waxy additive to enhance the hydrophilicity of the outer drug layer. Second, swellable composite particles were designed by replacing CS with a modified starch having expanding property as the core particle. It was found that the latter (swellable) approach was more effective than the former (wettable) one to improve the dissolution behavior of poorly water-soluble model drug. The swellable OM particles promptly expanded on contact with water and induced the effective detachment of fine drug particles from the core particles, resulting in rapid drug release. The present research suggests that the proposed contamination-free dry milling technique, which does not use hard milling balls or beads, can generate spherical drug particles with improved dissolution characteristics.

Ceramic dies selection for electrical resistance sintering of metallic materials

Abstract Processing metallic powders by electrical resistance sintering requires the use of insulating ceramics dies. Selecting the appropriate ceramic material according to the electrical, thermal and mechanical properties is a need. Dies produced with several ceramic materials have been tested during the production of cemented carbide in order to check their behaviour in the process and final product properties. Tialite/mullite, zircon/mullite, zirconium phosphate based ceramic, yttria-stabilized zirconia and sialon, in most cases with modified compositions and shaping processes in order to achieve a high density, have been tested. Dry powder processing by cold isostatic pressing and furnace sintering resulted to be the better process for dies production. The effect of die properties on the produced cemented carbide, and the behaviour and life of the die during the production have been analysed. Very smooth die surface increases the number of cycles withstood during metallic parts production, because of lower extraction stresses, as checked for sialon dies. Zirconium phosphate based dies, with low thermal conductivity, show the most densified hard metal parts surface.

A multivariate raw material property database to facilitate drug product development and enable in-silico design of pharmaceutical dry powder processes

In current study a holistic material characterization approach was proposed and an extensive raw material property database was developed including a wide variety of APIs and excipients with different functionalities. In total 55 different materials were characterized and described by over 100 raw material descriptors related to particle size and shape distribution, specific surface area, bulk, tapped and true density, compressibility, electrostatic charge, moisture content, hygroscopicity, permeability, flowability and wall friction. Principal component analysis (PCA) was applied to reveal similarities and dissimilarities between materials and to identify overarching properties. The developed PCA model allows to rationalize the number of critical characterization techniques in routine characterization and to identify surrogates for use during early drug product development stages when limited amounts of active pharmaceutical ingredients are available. Additionally, the developed database will be the basis to build predictive models for in silico process and formulation development based on (a selection of) property descriptors.

Mechanical Alloying of Ti-Based Materials

Mechanical alloying (MA) is a simple and versatile dry powder processing technique that has been used for the manufacture of both equilibrium and metastable phases of commercially useful and scientifically interesting materials. It owes its origin to an industry need to develop a nickel-based super alloy for gas turbine applications that had both oxide dispersion strengthening and precipitation hardening. This far-from equilibrium powder metallurgy processing technique involves fracturing, welding and re-welding of powder particles in a High Energy Ball Mill (HEBM). MA is an economically viable process with important technical advantages. Its utmost advantage is in the synthesis of novel alloys, e.g., alloying of ordinarily immiscible elements, that is not possible by any other technique. As MA is a completely solid-state processing technique, the limitations imposed by phase diagrams do not apply to it. The MA process is capable of producing different types of metastable effects in a variety of alloy systems. Some of the metastable effects achieved by MA are solid solution formation and amorphisation. MA has the possibility of producing superior and enhanced materials than those produces by conventional methods. In this work a review of MA and its present and potential applications for Ti-based materials are presented.

Influence of process parameters on the preparation of pharmaceutical films by electrostatic powder deposition

Electrostatic powder deposition (ESPD) has been developed as a solvent-free method to prepare pharmaceutical films. The aim of this work was to investigate the influence of process parameters during (1) electrostatic powder deposition, (2) curing, and (3) removal of the film from the substrate on the properties of the film. Polyethylene oxide (PEO) was used as the model polymer and stainless steel 316 as the substrate. Deposition efficiency (i.e. deposited weight) was measured with varying charging voltage, gun tip to substrate distance, and environmental humidity. Scanning electron microscopy was utilized to assess film formation, and adhesive and mechanical strength of films were measured with varying cure temperature and time. Adhesive strength was measured for films prepared on substrates of varying surface roughness. When deposition was performed at low humidity conditions, 25%RH, process parameters did not significantly affect deposition behavior. At 40%RH, increasing deposition efficiency with decreasing gun tip to substrate distance and increasing voltage (up to 60kV) was observed. Complete film formation was seen by 30min at 80°C, compared to lower curing temperatures and times. All films were readily removed from the substrates. The results show the ESPD process can be modified to produce films with good mechanical properties (e.g. tensile strength>0.06MPa), suggesting it is a promising dry powder process for preparing pharmaceutical films.

Facile preparation of core@shell and concentration-gradient spinel particles for Li-ion battery cathode materials

Core@shell and concentration-gradient particles have attracted much attention as improved cathodes for Li-ion batteries (LIBs). However, most of their preparation routes have employed a precisely-controlled co-precipitation method. Here, we report a facile preparation route of core@shell and concentration-gradient spinel particles by dry powder processing. The core@shell particles composed of the MnO2 core and the Li(Ni,Mn)2O4 spinel shell are prepared by mechanical treatment using an attrition-type mill, whereas the concentration-gradient spinel particles with an average composition of LiNi0.32Mn1.68O4 are produced by calcination of their core@shell particles as a precursor. The concentration-gradient LiNi0.32Mn1.68O4 spinel cathode exhibits the high discharge capacity of 135.3 mA h g−1, the wide-range plateau at a high voltage of 4.7 V and the cyclability with a capacity retention of 99.4% after 20 cycles. Thus, the facile preparation route of the core@shell and concentration-gradient particles may provide a new opportunity for the discovery and investigation of functional materials as well as for the cathode materials for LIBs.

Technical Terms Related to Feature Articles: Electrification of Particles during Dry Powder Processes and Its Applications

Technical Terms Related to Feature Articles: Electrification of Particles during Dry Powder Processes and Its Applications

Introduction to the Feature Articles: Electrification of Particles during Dry Powder Processes and Its Applications

Introduction to the Feature Articles: Electrification of Particles during Dry Powder Processes and Its Applications

Maximum electrostatic charge of powder in pipe flow

In dry powder process, particles collide against each other and onto wall, and normally, electrostatic charge is generated. Such a process is called trioelectrification or tribo-/contact-/impact-charging of particles. In this paper, the amount of maximum (or saturated or equilibrium) charge on a particle in a powder flow of a pneumatic conveyer with a metal pipe was discussed. A theoretical discussion involving the space charge effect with the basis of ‘charge relaxation model,’ in which the maximum charge is limited to cause gas break down, is shown. The result showed two regions in which the space charge does not affect on, and dominates the amount of the charge. The charge was proportional to the particle size raised to the power 1.5 in the region of no space charge effect, whilst power 3 in the other region of the space charge dominant. Empirically a well approximated analytical formula was found, for all over the range including these two regions. The maximum charge as a function of particle size, pipe size, and volume fraction of the powder, was given as: q / C = 1.10 × 10 - 4 ( d p / m ) 3 { ϕ ( D / m ) } 2 + { 17.1 ( d p / m ) 1.5 } . A comparison showed that the theory gives a certain overestimation to the data cited from literatures. Additional discussions were given in details.

Designing with Pores - Synthesis and Applications

Environment, energy, health and transport issues are dominating our modern daily live. The complex interactions of these problems can only be solved by sustainable processing and the development of improved components. Materials science will play an important role in this new approach. One domain with specific relevance are porous ceramics and metals. It are substrates with pores sizes ranging from vacancies at the atomic level to macro pores with sizes of millimeters. There are plenty of emerging applications for porous components in different industrial sectors. Each application will specify the window of properties of the porous material. This review is limited to inorganic porous materials which can be synthesized by dry and wet powder processing methods. In order to cope with this large application domain and window of properties, several processing and coating routes and related characterization techniques have been developed. The overview of applications for porous inorganic materials is focused on macro porous components with a designed functional coating. Examples of applications include catalytic supports, diesel particulate filters, molten metal filters, biomedical scaffolds for tissue engineering and ceramic membranes for different separation purposes.

管内流における粉体の最大帯電量について

In dry powder processes, particles collide against each other and onto walls, and normally, electrostatic charge is generated. Such process is called triboelectrification or tribo-/contact-/impact- charging of particles. In this paper, the amount of maximum (or saturated, or equilibrium) charge on a particle in a powder flow of a pneumatic conveyer with a metal pipe was discussed. A theoretical discussion involving the space charge effect on the basis of ‘charge relaxation model, ’ in which the maximum charge is limited by the gas break down, is given. The result showed two regions, i. e., the region in which the space charge does not have any effect, and the other region where the space charge dominates the amount of the charge. The charge was proportional to the particle size to the power of 1.5 in the region of no space charge effect, and the power of 3 in the other region. An approximated analytical formula was empirically found, for the whole range, including these two regions. The maximum charge as a function of particle size pipe size and volume fraction of the powder, was given as: q/C=1.1×10-4 (dp/m)3/√[{Φ(D/m)}2+{17.1(dp/m)1.5}2], when the relative dielectric constant of the particle is 2. A comparison showed that the theory gives a certain overestimation to the data cited from literature. Additional detailed discussions are given in the paper.

Dry Powder Processing of Fibrous Fumed Silica Compacts for Thermal Insulation

This study proposes a new dry powder processing method to produce fiber reinforced fumed silica compacts for highly efficient thermal insulation. First, mechanical forces such as shear stress and compression were applied into a fumed silica powder (BET SSA 300 m2/g) and glass fibers (3 mm length, 11 μm diameter) using an attrition type milling apparatus without any media balls. In the resultant powder mixture, fumed silica porously coated glass fiber composites were successfully prepared. SiC particles were also integrated as opacifiers. Then, the fibrous fumed silica porous compact was formed by dry pressing of the powder mixture and exhibited fracture strength of 1.58 MPa at room temperature and thermal conductivity of 0.0282 W/mK at 400°C, when its porosity was 80.1%.