Car tires, sealing caulk and high-voltage cable insulators are prime examples of commercially available and widely used composites of polymers containing nanostructured particles. In fact, myriads of applications can be realized but the usefulness of such nanocomposites depends heavily on composition, morphology, concentration and dispersion homogeneity of the nanoparticle filler in the polymer matrix. Optimizing these characteristics while ensuring economically feasible fabrication, determines the extent to which new products integrate nanocomposites. This review discusses challenges and manufacturing options of polymer nanocomposites and, in particular, which and how much nanoparticle fillers improve electrical/thermal conductivity, dielectric permittivity, gas permeability, magnetization and mechanical stability by critically reviewing and classifying over 280 peer-reviewed articles. Lastly, the economic, environmental and health implications associated with these materials are highlighted.

Recent studies evaluating the flowability and floodability of cohesive powder under conditions of consolidation, mechanical force, vibrating force, fluid force, and floodability are reviewed. The ball indentation test is an effective method for evaluating the flowability of a small amount of cohesive powder at very low stress under consolidation conditions. The environmental conditions such as temperature and humidity play an important role in the flow of cohesive powder. With regard to cohesive powder flowing under mechanical force, the FT4 powder rheometer can evaluate the powder flowability using the total energy which is related to the shear stress on the impeller blade. The vibrating capillary method and the vibrating shear tube method are effective for the measurement of the flowability of strongly cohesive powder. The test using powder discharge by air flow can assess the flowability of cohesive powder which Carr’s flowability index is an equivalent level by using mass flow rate and interstitial air pressure. Finally, the flushing of cohesive powder occurs when the interstitial air pressure and the void fraction are high. The pressure difference between the interstitial air pressure and the outside of an orifice are the dominant factors in the spouting of powder.

Emulsion—a liquid dispersed in another liquid—is in many respects very similar to granular matter. In the early 2000s a new technology—droplet microfluidics—began emerging from the wider field of microfluidics. Droplet microfluidics was quickly established as a discipline of science and engineering and has been used for the generation of highly uniform emulsions. The last few years have brought significant advances to the field, directed towards a wide range of applications in material sciences—from synthesis of nanoparticles in droplets to assembling complex droplets and using droplets as templates for ordered materials, with applications in food, cosmetic and diagnostic industries. Droplet microfluidic platforms are also successfully used as analytical tools in molecular biology and biochemistry, in e.g. high-throughput screening, digital assays, encapsulation of single cells, sequencing technologies, and in point-of-care diagnostic applications. This article provides an accessible overview of the physical phenomena observed in multiphase flow at the microscale and the techniques in droplet microfluidics systems. We also present the most interesting applications and potential further directions of research in this fascinating young field of science and engineering.

Nanostructures in solar cells are used both for the active layers and for light management techniques. Particularly thin-film solar cells will benefit strongly from such nanoscale approaches as the light absorption needs to be improved. Nanoparticles produced by wet chemical techniques, sometimes in the form of quantum dots, are currently used to fabricate thin-film solar cells for research purposes. Light management studies use nanostructures that are often created by lithographic methods but which are too expensive for an industrial realisation. In this review paper, the opportunities for using nanoparticles as a bottom-up approach for both the active layer and light management nanostructures is discussed. Since both the wet chemical method and lithographic techniques have considerable limitations, the use of gas aggregation cluster sources is proposed as a promising method to advance the use of bottom-up nanoparticles for solar cells. Plasmonics, Mie scattering, quantum dots and new materials are reviewed with respect to the nanoparticle potential. The increase of solar cell efficiency by using ultra-clean and crystalline nanoparticles which are produced with a vacuum-compatible technique at low temperatures should be very interesting for science and technology, ultimately leading to industrial products.

Researches relating dust collector using fiber as particle collection body i.e., air filter, cartridge filter and nonwoven bag filter, were reviewed. Their filtration process was classified into 3 stages, i.e., Stage 1. inner filtration I, Stage 2. inner filtration II and Stage 3. surface filtration. Collection mechanisms of fresh circular fiber have been well understood and so-called classic filtration theory is applicable except single nano-particle, where discussion about the possibility of thermal rebound is necessary. In Stage 1, effects of shape of both fiber and particle, and filter structure, non-uniformity are the important issues. In Stages 2 and 3, filtration process becomes very complicated because of many affecting parameters. Main target in Stage 2 is to develop effective scheme to describe the phenomena and to find filter structure having a large holding capacity. Most important issue in Stage 3 is to develop the effective cleaning technique to minimize the dust emission based on rational but not empirical scheme.

Ceramics with highly controlled microstructures at all levels from micrometer to nanometer order are required to improve their properties. To realize such ceramics, advances in powder processing are indispensable. Powder processing involves the preparation of fine particles, surface modification, consolidation, and sintering. The colloidal processing using fine particles has received particular attention as a means of achieving ceramics with highly controlled microstructures. Here, the preparation of fine-grained ceramics through a well-dispersed suspension and the preparation of porous ceramics and nanocomposites through heterocoagulated suspensions are demonstrated. Then novel colloidal processing under an external field such as a strong magnetic field and/or an electric field and the fabrication of textured ceramics and laminated composites are demonstrated.

Significant progress has been made over the last half-century in delivering therapeutics by the pulmonary route. Inhaled therapeutics are administered to humans using metered-dose inhalers, nebulizers, or dry powder inhalers, and each device requires a different formulation strategy for the therapeutic to be successfully delivered into the lung. In recent years, there has been a shift to the use of dry powder inhalers due to advantages in the consistency of the dose delivered, ease of administration, and formulation stability. Numerous preclinical studies, involving small and large animals, have evaluated dry powder drugs, vaccines, and immunotherapeutics delivered by the pulmonary route. These studies used different dry powder delivery devices including nose-only, whole-body, and intratracheal administration systems, each of which works with different aerosolization mechanisms. Unfortunately, these delivery platforms usually lead to variable powder deposition in the respiratory tract of animals. In this review, we will discuss obstacles and variables that affect successful pulmonary delivery and uniform powder deposition in the respiratory tract, such as the type of delivery device, dry powder formulation, and the animal model used. We will conclude by outlining factors that enhance the reproducible deposition of dry powders in the respiratory tract of preclinical animal models and identifying knowledge and technology gaps within the field. We will also outline the important factors necessary for successful translation of studies performed in preclinical models to humans.

Magnetite (Fe₃O₄) is one of the most important iron oxides due to its extensive range of application in various fields. The characteristics of magnetite can be considerably enhanced by reducing the particle size to the nanometer scale. When novel functions of nanoparticles are desired, it is necessary to have monodispersed or nearly monodispersed nanoparticles. Many synthesis methods have been proposed to produce monodispersed magnetite nanoparticles, including co-precipitation, sol-gel, hydrothermal and electrochemical methods. In this review, progress in the preparation of magnetite nanoparticles and their composites through the electrochemical method and the scale-up method are discussed.

The state of a suspension is crucial with regard to processing pathways, functionality and performance of the end product. In the past decade, substantial progress has been made in designing highly specialized and functionalized particles. In current particle technology, besides classic particle properties such as particle size distribution, shape and density, surface properties play an essential role for processing, product specification and use. For example, in medical therapy, analytical diagnostic applications, as well as in separation processing and harvesting of high-valued materials, magnetic micro- and nanoparticles play an increasing role. In addition to traditional parameters such as size, the particle magnetization has to be quantified here.

Sedimentation techniques have been used for hundreds of years to determine the geometrical characteristics of dispersed particles. Numerous national and international standards regarding these techniques have been published. Mainly due to the fast growing market share of laser scattering techniques over the past two decades, most customers these days are not aware of some advantageous features of particle characterization via a first-principle fractionating approach such as sedimentation. This is unfortunate as sedimentation techniques have made huge technological leaps forward regarding electronics, sensors and computing abilities.

This paper aims to give a short review about different cumulative and incremental sedimentation approaches to measure the particle size distribution. It focuses mainly on the in-situ visualization (STEP-Technology^®) of particle migration in gravitational and centrifugal fields. It describes the basics of the new multi-sample measuring approaches to quantify the separation kinetics by spatial and time-resolved particle concentration over the entire sample height. Based on these data, the sedimentation velocity and particle size distribution are elucidated and estimates of accuracy, precision and experimental uncertainties are discussed. Multi-wavelength approaches, correction of higher concentration, and the influence of rheological behavior of continuous phase will also be discussed. Applications beyond the traditional scope of sedimentation analysis are presented. This concerns the in-situ determination of hydrodynamic particle density and of magnetophoretic velocity distributions for magnetic particulate objects.

The stability of particle suspensions, which is important in numerous industrial processes, is generally dominated by the interaction forces between the suspended particles. Understanding the interaction forces between surfaces in liquids is therefore fundamentally important in order to evaluate and control how particulates, including fluid droplets in emulsions and air bubbles in foams, behave in various systems. The invention of the surface force apparatus (SFA) enabled the direct measurement of interaction forces in liquids with molecular level resolution and it has led to remarkable progress in understanding surface forces in detail. Following the SFA, the application of atomic force microscopy (AFM) to force measurement has further extended the possibility of force measurements to a broad field of research, mainly due to the range of materials that can be employed. This review provides an overview of developments in the investigation of interaction forces between surfaces using AFM. The properties of various interaction forces, important in particle technology, revealed by the studies using AFM are described in detail.

Semiconductor-based photocatalysis is regarded as an effective approach to harness solar energy to address the critical energy and environmental issues, such as fossil fuel shortage and climate change. The overall efficiency of the semiconductor-based photocatalysts can be further improved by creating nanocomposites with the incorporation of other functional materials, including metals, graphene, and metal-organic frameworks (MOFs). This critical review highlights the recent progress on the rational design of semiconductor-based photocatalysts via microdroplets, where the synthesis can be completed in a fast and controlled manner. Particular emphasis is given to three typical semiconductor-based composites, including semiconductor heterojunctions, crumpled graphene oxide/semiconductor composites, and MOF/semiconductor composites. The rationale behind the nanocomposite design, photocatalytic performance, and fundamental mechanisms are systematically discussed.

Formation, expansion, and breakage of bubbles in single bubble and freely bubbling fluidized beds were studied using an improved hybrid Lagrangian-Eulerian computational fluid dynamics (CFD) approach. Dense Discrete Phase Model (DDPM) is a novel approach to simulate industrial scale fluidized bed reactors with polydispersed particles. The model uses a hybrid Lagrangian-Eulerian approach to track the particle parcels (lumping several particles in one computational cell) in a Lagrangian framework according to Newton’s laws of motion. The interactions between particles are estimated by the gradient of solids stress solved in Eulerian grid. In this work, a single bubble fluidized bed and a freely bubbling fluidized bed were simulated using DDPM coupled with kinetic theory of granular flows (KTGF). The solid stress was improved to include both tangential and normal forces compared to current hybrid methods with the consideration of only normal stress or solid pressure. The results showed that solid pressure (normal forces) as the only contributor in solid stress would lead to overprediction of bubble size and overlooking of bubble breakage in a single bubble bed. Also, the results showed the improved model had a good prediction of bubble path in a freely bubbling bed compared to solid pressure-based model. It was shown that increasing the restitution coefficient increased the particle content of the bubbles and it lead to less breakage during the formation of the bubble. The probability of formation of bubbles was compared with experimental results and solid stress model showed less discrepancies compared to the solid pressure-based model.

Uniform spherical graphene/monocrystal-copper powder is fabricated by melting bulk laminated composite. Graphene, in the form of reduced graphene oxide (rGO), is uniformly dispersed on the surface of monocrystal Cu particle. A mechanism is proposed based on liquid/solid interface interaction combining the surface energy minimization of liquid Cu and low wettability of molten Cu on graphene. The rGO/Cu composite powder exhibits good sphericity, and the size distribution could be controlled by the amount of rGO.

Biomass grinds are typically non-spherical and are composed of particles with wide range of sizes that may vary up to 10× between the smallest and largest particle. Since fluidized bed system is often used to convert biomass into fuels, chemicals and products, the viscous and kinetic energy losses’ coefficients in the Ergun equation were determined to incorporate these unique characteristics of biomass grinds. The revised Ergun’s equation, validated using loblolly pine wood grinds, and data from other published work resulted in estimated Ergun’s K₁ and K₂ coefficients of 201 and 2.7 respectively. In addition, the relative mean deviation between experimental and predicted pressure drop was in general better with the modified Ergun’s equation when compared to the original Ergun’s equation.

Briquetting tests were conducted on lodgepole pine, switchgrass, and corn stover biomass. Three moisture levels (12, 15, and 18 % [w.b.]) and three-hammer mill screen sizes (4.8, 12.7, and 19.05 mm) were used to understand the impact of these variables on briquette-quality attributes such as unit and bulk density, durability rating, and briquetting energy consumption. A pilot-scale hydraulic continuous briquetting system was used in the present study. The briquette-quality attributes were measured after five days of storage. The hammer mill screen size of 4.8 and 12.7 mm and biomass moisture content of 12 and 15 % (w.b.) resulted in a higher unit and bulk density and durability rating. For the three biomasses tested, corn stover and lodgepole pine resulted in briquettes with bulk density > 480 kg/m³ whereas durability rating of corn stover was > 97.5 and lodgepole pine was about 92–93 %. A larger screen size of the hammer mill (12.7 mm) and higher moisture content of 18 % (w.b.) increased the briquetting energy consumption for both the woody and herbaceous biomass. Larger hammer mill screen size (19.05 mm) and moisture content of 15 % (w.b.) resulted in lower density and durability rating of the briquettes produced.

During biomass pelletization, the presence of activated natural binders is thought to promote the formation of solid bridges in a biomass assembly. To examine this hypothesis, bonded particles were extracted from the switchgrass compacts formed at different pressure and temperature. This study investigated the influence of these two factors on the resistance to dislocation of the particle-particle bond. The generated force-bond dislocation curves were used to calculate the slope from no load to failure from the assemblies formed at the treatments A (60 MPa and 75 °C), B (100 MPa at 75 °C), C (60 MPa and 90 °C), and D (100 MPa at 90 °C). Assemblies from the treatment B had the highest diametral tensile strength (60.9 ± 7.1 kPa) and densities (653.2 kg m⁻³), whereas, assemblies formed from the treatment C had the lowest diametral strength (7.2 ± 1.4 kPa). The resistance to dislocation of particle-particle bonds at microscale was linearly correlated to the strength (R²=0.838) and density (R²=0.981) of the densified assemblies. High pressures are documented to form stronger compacts. However, the presence of sufficient moisture at low temperature can significantly improve the densified assembly properties by lowering the glass transition temperature of lignin to form stronger bonds.

The Swirl reactor is an innovative concept for performing reactions in gas phases or solid and gas phase mixtures. It was developed during the initial boom of the solar cell industry, where the need for more energy- and cost-efficient means of producing high-purity solid silicon became important. The Swirl reactor was designed to fulfil the following requirements: continuous production of high-purity silicon; efficient energy transfer from the reactor to the gas; controlled transport of the Si-fines and the gas formed; the use of silane as feed for silicon. By employing a stainless steel tubular reactor honed on the inside and heated from the outside, and using argon as the carrier gas, the requirements were all shown to be fulfilled. The Swirl reactor throughput can be increased by having more than one injector introducing new swirls. Also, two swirls—each containing reacting agents—may form product where they mix, i.e. along the path where the swirls overlap. Thus, reactions can be controlled but still be run continuously. The possible uses of the Swirl reactor are numerous.

Experimental data on the hydrodynamic behavior of dense and circulating fluidized beds at high temperatures are scarce in the literature. This work deals with the hydrodynamic study of a Fast Internally Circulating Fluidized Bed (FICFB) used for biomass gasification. The first part of this study investigates the influence of the bed temperature (between 20 and 950 °C) and the nature of fluidizing gas (air or steam) on the hydrodynamic parameters of a dense fluidized bed of olivine particles (i.e. minimum fluidization velocity and voidage as well as average voidage). Three olivine batches are used with a mean Sauter diameter of 282, 464 and 689 μm, respectively. Experimental results are compared with different empirical correlations from the literature to evaluate their validity under elevated temperature conditions. Besides, two dimensionless correlations calculating the minimum fluidization velocity and average bed voidage are proposed. The second part of this study focuses on the hydrodynamic behavior of an FICFB operating between 20 and 850 °C. The effect of different process parameters (i.e. bed material nature, air velocity, solids inventory, bed temperature) on the solids circulation flow rate is investigated. It was found that the transport velocity U_tr is not affected by the bed temperature and the bed material inventory. It mainly depends on the terminal settling velocity U_t of bed material particles. Besides, key parameters controlling solids flow rate are the combustor gas velocity and the solids inventory. An increase in these parameters leads to a higher circulation flow rate.