Powder processing and manufacturing operations are rate processes for which the bottleneck is cohesive powder flow. Diversity of material properties, particulate form, and sensitivity to environmental conditions, such as humidity and tribo-electric charging, make its prediction very challenging. However, this is highly desirable particularly when addressing a powder material for which only a small quantity is available. Furthermore, in a number of applications powder flow testing at low stress levels is highly desirable.

Characterisation of bulk powder failure for flow initiation (quasi-static) is well established. However, bulk flow parameters are all sensitive to strain rate with which the powder is sheared, but in contrast to quasi-static test methods, there is no shear cell for characterisation of the bulk parameters in the dynamic regime. There are only a handful of instruments available for powder rheometry, in which the bulk resistance to motion can be quantified as a function of the shear strain rate, but the challenge is relating the bulk behaviour to the physical and mechanical properties of constituting particles. A critique of the current state of the art in characterisation and analysis of cohesive powder flow is presented, addressing the effects of cohesion, strain rate, fluid medium drag and particle shape.

There is an increasing demand of air filters with a high collection performance, i.e., high collection efficiency and low pressure drop, for the application to indoor air cleaning. Air filters consisting of nanofibers have attracted great interests since they may have a low pressure drop because of slip flow effect and high collection efficiency due to enhanced interception effect. Although various nanofiber filters are available on the market, their collection performance is not as high as expected by the conventional filtration theory because non-uniform packing of fibers plays a significant role in the nanofiber filtration. In the present review, the present status of development of high performance air filters are reviewed. We may use air filters not only for the removal of particles but also for the classification of particles by selecting an appropriate filter by operating it under an optimized filtration condition for classification. Other topics introduced in the present review are the applications of filters and metal screen for aerosol classification and the use of centrifugal force for enhancing collection efficiency without increasing the pressure drop.

A continuous flow reaction process in which a metal salt solution is rapidly mixed with high-temperature water was employed to achieve rapid heating up to supercritical conditions. A quarter of a century has passed since the supercritical hydrothermal method was first proposed. This paper introduces recent advances in science and technology related to the supercritical process. Process design, kinetics, reaction atmosphere (redox) control, morphology control, organic modification of particles, nanocatalysts, and organic-inorganic hybrid materials are reviewed for promising applications of the supercritical process.

Optical Coherence Tomography (OCT) is a light-based imaging method capable of simultaneously capturing the internal structure and motion (1D, 2D or 3D) of various opaque and turbid materials with a micron-level spatial resolution. Depending on the OCT technology, axial scanning rates can vary in a range of tens to hundreds of kHz. The actual imaging depth significantly depends on the optical properties of the material and can vary from micrometers to a few millimeters. From the viewpoint of industrial applications, OCT technology is very appealing. Due to its resolution, speed, and ability to deal with opaque materials, it fills an apparent gap in available measurement methods. Nonetheless, OCT has not to date seen widespread growth in the industrial field. This has been at least partly due to a lack of commercial devices compact and flexible enough to adapt to industrial needs. The recent emergence of more generic commercial OCT devices has considerably lowered the threshold for adapting the technique. The utilization of OCT for structural analysis, also outside the medical field, has been thoroughly discussed in scientific literature. Therefore, in this paper, we will mainly concentrate on applications of OCT that also utilize its capability of performing velocity measurements. The emphasis will be on industrially motivated problems such as rheology, microfluidics, fouling and turbulence.

Microorganisms are ubiquitous in the environment. Wherever their sources are present, the particles can be released into the air forming microbiological aerosols. Although most of their particles cause no harm to the exposed individuals, some of their propagules may have infectious or allergenic potential and may carry toxic or irritant substances and components. Their inhalation usually poses a significant health risk and is responsible for numerous adverse outcomes, from allergic reactions, infections and toxic responses to various nonspecific symptoms. This review article provides fundamental background information on the role of microorganisms in the environment, defines and characterizes environmental sources of microbial aerosols, describes microbial abilities for airborne transport and comments on their role in atmospheric processes, discusses their physical and biological characteristics which result in adverse health outcomes observed in exposed individuals. The paper characterizes comprehensively numerous sampling and analysis techniques involved in the quantitative and qualitative evaluation of microbial aerosols together with their practical applications, presents strategies applied in the assessment of harmful microbial agents formed by bioaerosols, explains the ways of creating hygienic standards (understood here as reference/threshold limits) for microbiological aerosols conditioned by both medical and environmental determinants, and comments on their usefulness in the control and protection of environment and health.

The salt hydrate heat storage phase change material (PCM) has a promising prospect of application and has become a research hotspot because of the advantages of high thermal storage density, high thermal conductivity, moderate phase change temperature, and low price. However, some problems have restricted the application of salt hydrate heat storage materials, such as phase separation, supercooling, and corrosion of the metal container. A microencapsulated PCM using the microencapsulated technology of solid PCM coated packaging with core-shell structure composite material is an effective method to solve the above problems. In this paper, the research situations involving microencapsulated salt hydrate are analysed. This review introduces the selection of core and shell materials, compares the different preparation methods of encapsulated salt hydrate PCMs and summarizes the application fields.

Immunization can be traced back to classical China. Modern immunization reduces the risk of infection by attenuating or killing the pathogen or using non-infectious antigens to elicit the immune response. The challenge of immunization is to raise a robust protective response without infecting the individual or overstimulating the immune response, and this can be achieved by using nanoparticle delivery systems to specifically target the innate immune system with known antigens and where necessary include an adjuvant to enhance the efficacy. These systems can be targeted to mucosal sites that are located throughout the body with the nasal and pulmonary routes of administration allowing ease of access. Macrophages are the first line of defense of the innate immune system and are the host cell for primary intracellular infection by several respiratory pathogens notably mycobacteria and streptococci. The breadth of nanoparticle technology available to deliver vaccines has been explored and consideration of its value in nasal and pulmonary delivery is addressed specifically.

The growing population and economic development globally has led to increasing resource consumption and waste generation. This has generated concern at local, national and international levels on environmental issues including air quality, resource scarcity, waste management (including plastics) and global warming. The resulting antipathy towards fossil fuels and waste landfilling has spurred the demand for alternative bioenergy and biofuels production methods, making use of abundant biomass and waste feedstock. Although not new concepts, there has been renewed impetus recently to develop advanced thermochemical processes such as pyrolysis and gasification to treat biomass and municipal solid waste (including refuse-derived fuel therefrom). This is because these processes have the potential to add value to cheap and abundant materials by converting them into advanced biofuels and chemicals. The work presented in this paper is concerned principally with the technical analysis and review of new-generation, state-of-the-art systems based on fluidised bed reactors operated with biomass and solid waste. A comprehensive assessment of fluidised bed reactor types and operations is considered, with particular attention given to those processes aimed at the production of clean syngas for the subsequent synthesis of high-value products, including bio-hydrogen, synthetic natural gas (SNG), and liquid fuels.

The discrete element method (DEM) and the moving particle semi-implicit (MPS) method are the most popular mesh-free particle methods in the discontinuum and continuum. This paper describes a state-of-the-art modeling on multi-phase flows using these mesh-free particle methods. Herein, a combinational model of the signed distance function (SDF) and immersed boundary method (IBM) is introduced for an arbitrary-shaped wall boundary in the DEM simulation. Practically, this model uses a simple operation to create the wall boundary. Although the SDF is a scalar field for the wall boundary of the DEM, it is useful for the wall boundary of the CFD through combination with the IBM. Validation tests are carried out to demonstrate the adequacy of the SDF/IBM wall boundary model. Regarding the mesh-free particle method for continuum, the phase change problem is one of the challenging topics, as the solid state is usually modeled by extremely high viscous fluid in the phase change simulation. The phase change simulation is shown to be efficiently performed through an implicit algorithm and a heat flux model in the MPS method. The adequacy of these models is verified by the numerical examples.

The scheme of DLVO theory and the concept of fractal structure of flocs applied to the suspension of montmorillonite have revealed out the unique nature of this clay dispersion. In this context, two major regimes are recognized. The first is the electrostatically dispersed regime. And the second is the coagulated regime. In the former, the formation of a diffusive electric double layer (EDL) characterized by reciprocal Debye length measured from the surface of the particle is distinctively important. Intrinsic viscosity with electroviscous effects and yield stress are interpreted by the steric presence of EDL. In the latter, the unit of transportation is a coagulated floc with finite cohesive strength. Sedimentation process reflecting these factors is carefully observed to recognize the turbulence generation by the formation of large flocs at the moment of gel collapse. Waiting time prior to gel collapse was found to be determined reflecting the pH-dependent charging behavior. By taking into account the effect pH-dependent charge, the DLVO based two regimes are further categorized into five. The developed tools can be extensively used for the system involved with different ionic species, pH, volume fraction and organic substances.

Classic crystallization describes a burst nucleation followed by a layer-by-layer atom deposition. The non-classic crystallization refers to particle mediated crystallization process. Different crystallization routes lead to the formation of diverse structured materials. Here we report a rational synthesis of silver particles by selecting the crystallization routes. Silver particles were synthesized by a solution reduction approach. The crystallization routes were regulated by adding amino acids to stabilize silver ions which leads to the decrease of the reduction rate. Without amino acids, silver dendrites were largely formed. With the addition of amino acids, flower-like (low concentration of amino acids) and spherical silver (high concentration of amino acid) particles were synthesized. Three kinds of amino acids were tested and the similar results were obtained. The time-dependent characterization on the evolution of silver particles showed that silver dendrites were formed by the classic atom deposition while the other two morphologies were formed by the combination of classic and non-classic crystallization. The silver particles synthesized were evaluated for ethylene epoxidation and the dendritic particles demonstrated a high selectivity.

Unwanted changes in powder flow behavior can unexpectedly occur when a product is exposed to certain conditions of temperature and humidity. This can happen during production, but also during transport or storage. The work reported here demonstrates the novel approach of using an amended powder rheology set-up for measuring and predicting such changes in powder flow behavior. The developed methodology makes it possible to vary in-situ the temperature and the relative humidity of the air to which the product is exposed, thereby mimicking realistic conditions of production or related unit operations. An air flow capable of fluidizing the powder particles is controlled at a specific constant temperature and its relative humidity can be altered while measuring the torque in the fluidized powder bed in real time. The fluidization is necessary for generating a homogeneous introduction of temperature and relative humidity. Results obtained using citric acid and commercial coffee whitener products have proven this methodology to provide both similar and in certain instances dissimilar results compared to the more established methodology such as measuring the vapour adsorption isotherms. These observations are explained. In this way, it can be predicted under which combinations of temperature and humidity a product does or does not become sticky. The main advantages of our approach are that the flow properties are directly assessed, the interpretation of the obtained data is more straightforward and that the measurement times are shortened substantially.

The use of vertical stirred mills in the mining industry has increased remarkably over the past few decades as a result of the growing demand for finer ore grinding. This equipment is recognized to deliver higher energy efficiency in fine grinding operations when compared to conventional tubular mills. Methods of designing vertical stirred mills involve operational experience, pilot plant tests and bench tests. An important issue is that the laboratory-scale test, conducted in the standard 8″×10″ jar, requires at least 10–20 kg of material, depending on ore density, which is not available in many cases, particularly in the early stages of greenfield projects. For regrinding of flotation concentrates, several bench scale flotation tests are required to generate such a sample. The paper describes the development and validation with six different ore samples of a simplified laboratory jar mill test using a 6″×8″ jar, which is smaller than the 8″×10″ size, the latter commonly used which requires about one-tenth of the mass required in the standard test. The proposed test indicated similar results as compared to the standard procedure.

Multiple industrial applications, including pharmaceuticals, rely on the processing of powders. The current powder characterization framework is fragmented into two general areas. One deals with understanding powders from the standpoint of its constituting agents—particles. The other deals with understanding based on the bulk— the collective behavior of particles. While complementary, the two aspects provide distinct pieces of information. Whenever possible, experimental techniques should be used to predict powder behavior. However, it is equally important to recognize that because of the natural complexity of powders, existing predictive approaches will continue to be of limited success for predicting the collective behavior of particles. This article discusses the understanding of powder properties from two perspectives. One is the effect of surface energy at the bulk level (large collections of particles), which controls interactions between powders. This aspect is most useful if studied at the bulk-powder level, not at the single-particle level. Another perspective deals with the physico-mechanical properties of individual particles, responsible for the observed behavior of powders when subjected to mechanical stress from unit operations such as milling. This aspect, which controls the failure mechanism of powders subjected to milling, is most useful if assessed at the single-particle, not at the bulk level. Therefore, in order to fully understand, and eventually predict, or at least effectively model powder behavior, a good-judgement-based combination of microscopic and bulk-level analytical methods is necessary.

In this work, composite powders of natural rubber/silica (NR-SiO₂) were prepared via sol-gel and spray drying method. The morphology and physical properties of resultant rubber composite powders were characterized by scanning electron microscopy with energy dispersive X-ray spectrometry, laser light scattering particle sizer and thermogravimetric analyzer. The results showed that spray-dried NR-SiO₂ particles were spherical in shape with diameter of less than 10 μm, with silica on the outer layer. The particle size was found to increase gradually with the increase in NR/Si mass ratio. Marginal growth in particle size was observed with increasing feed flow rate. Increasing inlet air temperature improved the latex particle encapsulation by silica layer while maintaining the final particle size. The mechanical properties of NR-SiO₂ powders-filled polylactic acid (PLA) composite increase gradually with the addition of dried particles of higher rubber content. However, the composite exhibited relatively lower or reduced tensile strength and elongation at break compared to the host PLA polymer. This could be attributed to poor filler dispersion associated with weak filler/matrix interaction effect occurring during melt-compounding process.

Gold nanoparticles (AuNPs) exhibit unique size-dependent physiochemical properties that make them attractive for a wide range of applications. However, the large-scale availability of precision AuNPs has been minimal. Not only must the required nanoparticles be of precise size and morphology, but they must also be of exceedingly narrow size distribution to yield accurate and reliable performance. The present study aims to synthesize precision AuNPs and to assess the advantages and limitations of the Turkevich method—one of the common chemical synthesis technique. Colloidal AuNPs from 15 nm to 50 nm in diameter were synthesized using the Turkevich method. The effect of the molar ratio of the reagent mixture (trisodium citrate to gold chloride), the scaled-up batch size, the initial gold chloride concentration, and the reaction temperature was studied. The morphology, optical property, surface chemistry, and chemical composition of AuNPs were thoroughly characterized. It was determined that the as-synthesized AuNPs between 15 nm and 30 nm exhibit well-defined size and shape, and narrow size distribution (PDI < 0.20). However, the AuNPs became more polydispersed and less spherical in shape as the particle size increased.

The NMR-based solvent relaxation technique, a non-invasive tool to characterize the surface of particles, which are dispersed in a liquid, was applied to characterize the nanoparticles’ aggregation structure. The liquid molecules in a dispersion undergo a rapid exchange between the bound states at the interface and highly mobile free states in a bulk liquid. The relaxation time of the liquid molecules bound on the particle surface is shorter than that of the free states liquid. By detecting how much liquid is bound on the particle surface, the wetted specific surface area (S_NMR) can be determined. In this study, it was clarified that the water adsorbed at more than a 1.138 layer from the silica surface can be detected by the NMR and the maximum limitation ranged from 2.160 and 3.336 layers. The model aggregates with an artificial solid neck among the particles were mixed with the silica nanoparticle dispersion. Although the determined S_NMR was underestimated compared to S_BET from gas adsorption, even a low ratio (5 mass%) of the model aggregates in the dispersion can be detected.

A continuous, compact and simple process was developed to synthesize micro- and nanoparticles of iron oxide. The process combines the spraying (pulverization) of an aqueous solution of iron nitrate in a fluidized bed reactor containing coarse and hot glass beads (T = 200 °C) for the production of solids and a transported bed reactor for calcination (T = 490 °C). The intermediate product formed in the fluidized bed reactor is 2-line ferrihydrite, while the calcination reactor allows the production of hematite micro- and nanoparticles. These particles are characterized by a narrow size distribution, a mean size of 0.5 μm, a specific surface area of 24 m² g⁻¹ and a density of 4499 kg m⁻³. Particles are made up of small clusters of crystallites having an average size of 47 nm and a low internal porosity (0.12). The reaction mechanism was studied using a muffle furnace and a lab convective dryer. It was found that several steps are involved leading first to the production of iron nitrate dihydrate after the removal of the solution water, as well as two and then five molecules of water of hydration. After that, the elimination of nitrate leads to the production of ferrihydrite. Finally, ferrihydrite is transformed into hematite due to the removal of residual nitrate and water of hydroxylation.

Electrodynamic sorting (EDX) is a new technology developed to sort industrial scrap metals. Under the present embodiment, an electromagnet is placed directly underneath a conveyor belt and then excited by an alternating electrical current to produce a time-varying magnetic field. As scrap particles pass through the field overhead, electrical eddy currents are induced throughout their volumes and then repelled away. If the frequency of excitation is very high (e.g., 12 kHz), then the lightweight aluminum particles tend to jump far more dramatically than heavier materials like copper, brass, and zinc. To demonstrate the principle, a small-scale prototype was assembled and tested. Using an 8-inch (20 cm) lane width, the system could process industrial scrap Zorba at a throughput of over 550 lbs/hour (225 kg/h) with an aluminum grade of 97.6 % and a recovery of 93 %.