There is great demand for nanoparticles (NPs) dispersed in liquid phases for practical applications of functional NP materials. However, it is difficult to produce NP dispersions with specific particle sizes, concentrations, viscosities, and purities on an industrial scale (large mass production rate and low energy consumption). In this review, we highlight recent developments in NP dispersion using low-energy bead mill. Such processes enable the use of small beads (7–50 μm). Smaller beads reduce the collision and shear energies of NPs during agitation. This minimizes NP breakage/damage, and retains the shape and crystallinity of the NPs, which determine the inherent NP functions. This review starts with a brief explanation of the theory and current status of NP dispersion and describes the mechanism and experimental results for low-energy bead mill processes, i.e., using uniaxial, dual-axial, and all-separator bead mills, and selection of dispersing agent. Applications of NP dispersions, including nanocomposite materials, and methods for dealing with NP dispersion coloration are also discussed, along with future research directions.
An increase in global consumption has led to an exponential increase in industrial production activities which inevitably results in overwhelming remain of industrial waste. Consequently it has driven increasing attentions of research and development teams in various countries to propose and investigate novel methodologies to utilize such industrial waste. Instead of using as alternative energy sources, usage of industrial waste for production of carbonaceous nanomaterials has been examined via various routes, such as catalytic pyrolysis, hydrothermal treatment and so on. Meanwhile, for sustainable and secure continuity of the carbonaceous nanomaterial production, broad spectra of promising applications have also been examined. Among those emerging applications, utilization of carbonaceous nanomaterials in pollution control and prevention has been focused worldwide. Therefore, in this review, relevant research works focusing on catalytic pyrolysis of carbonaceous industrial waste for carbonaceous nanomaterial production were comprehensively analyzed and summarized. In addition, promising applications involving with antibiotic removal, spilled oil handling and pollutant gas detection were also reviewed.
In this article, applications of engineered nanoparticles containing siRNA for inhalation delivery are reviewed and discussed. Diseases with identified protein malfunctions may be mitigated through the use of well-designed siRNA therapeutics. The inhalation route of administration provides local delivery of siRNA therapeutics to the lungs for various pulmonary diseases. A siRNA delivery system can be used to overcome the barriers of pulmonary delivery, such as anatomical barriers, mucociliary clearance, cough clearance, and alveolar macrophage clearance. Apart from naked siRNA aerosol delivery, previously studied siRNA carrier systems include those of lipidic, polymeric, peptide, or inorganic origin. These delivery systems can achieve pulmonary delivery through the generation of an aerosol via an inhaler or nebulizer. The preparation methodologies for these siRNA nanocarrier systems will be discussed herein. The use of inhalable nanocarrier siRNA delivery systems have barriers to their effective delivery, but overcoming these constraints while formulating a safe and effective delivery system will offer unique advances to the field of inhaled medicine.
A novel triple-bed combined circulating fluidized-bed (TB-CFB) coal gasifier, consisting of a downer (pyrolyzer), a bubbling fluidized bed (gasifier), and a riser (combustor) was proposed for realizing low-temperature coal gasification. Several key thermochemical reactions were extracted from those expected in the downer unit: the reforming of refractory tar in both the gas phase and over the char surface, and the steam gasification of the nascent char. This review highlights our recent progress, both experimental and numerical, in studies of thermochemical coal conversion including the various reaction processes, by employing a drop-tube reactor that well approximates the reaction environment in a downer reactor. This discussion can be utilized in designing TB-CFBs and optimizing their operation.
Laser ablation is a method for fabricating various kinds of nanoparticles including semiconductor quantum dots, carbon nanotubes, nanowires, and core shell nanoparticles. In this method, nanoparticles are generated by nucleation and growth of laser-vaporized species in a background gas. The extremely rapid quenching of vapor is advantageous in producing high purity nanoparticles in the quantum size range (< 10 nm). In this review, the formation mechanism of nanoparticles by laser ablation is summarized. Recent progress on the control of nanoparticle size and the challenges for functional nanoparticle synthesis by advanced laser ablation technology are then discussed.
The importance of providing safe and effective delayed- and extended-release oral formulations that can replace products requiring multiple administrations has been continually cited as an area in need of improvement for pharmaceutical companies. Such controlled release challenges become especially critical when they must be adapted for paediatrics, those suffering from dysphagia, or patients with specific dosage administration limitations. More often than not, lack of palatability and taste-masking compound this formulation challenge. Many particulate approaches show promise, but can be fraught with broad particle size distributions, initial drug burst, poor drug entrapment efficiency, low drug loading, and limited scalability. Here, we summarize the key factors that drive formulation development of format-flexible controlled-release oral powders, and the manufacturing aspects involved with some of the foremost marketed products, including next-generation single-step layered powder manufacturing (below).
In the early 1990s the discrete element method (DEM) was used for the first time to simulate media motion in tumbling mills. Although it has been over a quarter of a century since this tool was first used to predict media motion it has not yet reached maturity to be used in predicting product size distribution and throughput of tumbling mills. However, there has not been shortage of attempts to do so. The literature is relatively vast in the topic and researchers who embark in this area of research will find it difficult to understand the current status of development and also the similarities and fundamental differences that exist amongst the various approaches that have been proposed and pursued over the years. The paper reviews the literature on the application of models based on distributed collision energy information to predict size reduction in tumbling mills, in particular ball mills, analyzing critically various approaches proposed, their limitations and achievements, identifying areas that still require development until the technology becomes ready for being used for optimizing and designing ball mills. Finally, the advances recently accomplished on the approach proposed by the author and his co-workers are then reviewed in greater detail.
High Pressure Grinding Rolls (HPGR) technology is accepted as an energy-efficient and cost-effective alternative for treating specific mineral ore types. HPGR technology has been advancing within manufacturing facilities and research centers since its first installation in 1985. Over the last three decades much of the literature on HPGR have focused on the industrial applications and trade-off studies in comparison with semi-autogenous and ball milling circuits. Literature on fundamental studies of HPGR technology has been very limited. This paper aims to provide a review of the modeling of high pressure grinding rolls.
In this review article, a specific flame spray pyrolysis method, Liquid Flame Spray (LFS), is introduced to produce nanoparticles using a coflow type hydrogen-oxygen flame utilizing pneumatically sprayed liquid precursor. This method has been widely used in several applications due to its characteristic features, from producing nanopowders and nanostructured functional coatings to colouring of art glass and generating test aerosols. These special characteristics will be described via the example applications where the LFS has been applied in the past 20 years.
Fluidized bed design and scale-up depends strongly on particle characteristics such as size, shape, and for Geldart Group A particles, the level of fines (particles smaller than 44 microns). However, recent research has shown that particle clustering has a significant effect on fluidized bed hydrodynamics which impacts how these units should be designed and scaled up. This is especially true with the estimation of the solids entrainment rate and the cyclone collection efficiency. The amount of fines, particle shape and surface morphology play a role on the level of particle clustering in a fluidized bed. The fine particles are an excellent conduit for moving charge as electrons or ions which appear to be the dominant mechanism of electrostatics for Geldart Group A material in a bubbling fluidized bed. This electrostatic force trades off with particle momentum relaxation and rotational to translation momentum transfer with regard to forming a particle cluster. The issue is the quantification of this effect so more precise calculations can be made with particle entrainment rates and cyclone collection efficiency. Preliminary work on particle shear in a packed and fluidized beds, suggest that particle clustering can be measured and may provide a quantifiable metric for the level of particle clustering.
Size characterization of nanoparticles has gained wide concerns in the past decades, but it remains a challenge for measurement in suspensions up to now. The extremely small scales of particle size result in great difficulty for traditional static light scattering method and optical imaging. In addition to the electron microscopy techniques, the dynamic light scattering (DLS) method is another widely used technique for laboratory analysis of samples. Moreover, the ultrasonic attenuation spectroscopy (UAS) technique is also being developed rapidly to provide an alternative method for nanoparticle sizing. This paper focuses on the latest development in the above two technologies for nanoparticle size characterization. As for the former, advances about the image-based DLS technology in recent years are reviewed, including three different kinds of data processing methods and corresponding measuring experiments using standard polystyrene particles. Methodology principles, models and experimental setup were also reviewed for the latter UAS technology. Samples of the same nanoscale silver particles were tested by the above two methods, as well as by transmission electron microscopy. A sample of Antimony Tin Oxide (ATO) nanoparticles has also been adopted for measurements and comparisons. Relatively consistent results can be found by comparing the particle sizes or distributions with various methods. The dramatically reduced measurement time in image-based DLS indicates the potential for real-time and in-situ nanoparticle sizing. UAS also provides a suitable way for nanoparticle size characterization at high concentrations.
This study reports on the synthesis and microstructural evaluation of ZrB2/ZrO2 ceramic powders prepared by milling-assisted magnesiothermic reduction of oxide raw materials. Powder blends containing ZrO2, B2O3 and Mg reactants were milled in different type of mills at different durations and were subsequently annealed in a tube furnace under Ar atmosphere. An additional purification step (HCl leaching) was conducted on the milled and annealed samples to obtain only Zr-based products. FactSage™ thermochemical software was used in order to show a preliminary route for the experiments. The effects of milling duration (up to 100 h), milling type (a SPEX™ 8000D Mixer/Mill and a planetary ball mill), excess Mg amount (5–20 wt.%) and annealing duration (6 and 12 h) on the formation and microstructure of the products were examined. The milled, annealed and leached products were characterized using an X-ray diffractometer (XRD), stereomicroscope (SM), scanning electron microscope (SEM) and differential scanning calorimeter (DSC). Pure ZrB2/ZrO2 ceramic powders having particles in size range of 200 nm – 1 μm and containing two different crystal structures of ZrO2 phase (monoclinic and tetragonal) were obtained after milling in the SPEX™ 8000D Mixer/Mill for 30 h, annealing at 1200 °C for 12 h and leaching with 5 M HCl.
Paracetamol is well-known API (active pharmaceutical ingredient) for its bad flow and compression abilities. To improve the compressibility, a high amount of excipient is commonly mixed with paracetamol to create better compressible material. Conversely, we used modified crystallization procedures to prepare plate, irregular and spherical particles from original raw paracetamol to prepare directly compressible API. To expand our screening, several sizes of each shape were prepared and material properties analyzed, mainly the flow and compression abilities, and significant variation of the properties presented; from very poor properties of raw paracetamol to excellent properties of spherical crystals which exhibited ability to be directly compressed without excipient. The analysis also showed very small effect of the size modification on tablet compression and material behavior as the main contribution had the shape alteration and compression force.
Al5083 powder was subjected to ball milling in liquid nitrogen for 8 h using an attrition ball milling. The evolution of morphology of powder particles and the refinement of grain size were studied by scanning and transmission electron microscopies. The results showed that during cryomilling the morphology of powder particles changed from spherical to equiaxed shape. Additionally, the size of powder particles increased from ~10 μm to ~20 μm with narrower distribution. Simultaneously the cryomilling was associated with a significant reduction of grain size so that the final product after 8 h of cryomilling had a nanocrystalline microstructure (~25 nm) with well-developed high angle grain boundaries. These features were discussed in terms of severe plastic deformation, cold-welding and fracturing of powder particles which occur simultaneously during cryomilling process.
It is known that ball milling is an energy intensive process and great efforts have been made over the years to improve energy efficiency. The use of population balance models (PBMs) can assist in the design of mineral processing circuits and the scale-up of laboratory mill results to full-scale. However, since each model has its own capabilities and limitations, it is believed that a combined use will provide more accurate information for the reliable description of the process.
In this study, the simulation of grinding of quartz is investigated in order to identify the optimal mill operating parameters. With the use of population balance modeling the specific rate of breakage and the cumulative breakage parameters can be determined from mono-size, short grinding time batch tests. The determined breakage parameters were back calculated by minimizing the residual error between experimental and reproduced size distributions. By combining two software packages the back calculated breakage parameters were used for the prediction of the optimum ball filling volume. The proposed procedure can be also applied for the identification of optimal mill operating parameters for other minerals.
The objective of this study was to investigate the effect of vibration on critical pore structure parameters related to flow in porous beds. The discrete element method was used to simulate particle packing in porous beds of soybean subjected to vibration. The porous bed was simulated as an assembly of spherical particles with diameters randomly distributed between 5.5 mm and 7.5 mm. The simulated porous bed was subjected to vertical vibration at a fixed frequency of 15 Hz and multiple amplitudes from 0.5 to 4.0 mm, resulting in vibration intensities from 0.45g to 3.62g (g = gravitational acceleration). The location (coordinates) of each particle was tracked during vibration. Based on the simulated spatial arrangement of particles, critical flow-related parameters of the porous bed, including porosity, tortuosity, and pore throat width were calculated. It was found that vibration intensity of 1.81g resulted in the lowest porosity, whereas lower vibration intensity did not have enough energy to densify the bed and higher intensity produced less dense parking due to over-excitement. Local porosity fluctuated markedly during vibration, with a general trend of decrease as vibration progressed. Vibration noticeably affected the shape (tortuousness) of flow path. Tortuosity of the porous bed before vibration was higher (2 % to 9 %) than that after vibration. Vibration reduced the pore throat width by 18 % on average (from 3.3 mm before vibration to an average of 2.7 mm after vibration).
The increasing number of touch surface mediated infections has steered research to look for alternative strategies that can prevent infection transmission via pathogen inactivation on surfaces. Anatase, a crystalline form of titanium dioxide, shows strong UV induced photocatalytic properties. However, nanoparticles of anatase have been found to inactivate organic contaminants in the visible spectrum. Degradation of mordant orange and inactivation of S. aureus was evaluated on anatase surfaces under visible light band pass filters across the visible light region. Inactivation shows a strong co-relation to the absorption spectrum of the dye/microbe on the surface of the anatase coating. The phenomenon is similar to dye sensitized solar cells and was not found to exist in coatings with a higher bandgap such as amorphous silica. Photocatalytic nano-crystalline anatase coatings hold potential as a visible light active disinfectant to inactivate microbes on touch surfaces over long periods of time.
We present a novel technique for sorting nonferrous metal scrap by using eddy current separation. However, rather than vary the magnetic field with a spinning rotary drum, our system utilizes a fixed electromagnet excited by an alternating electric current. The technique requires no moving parts other than a feeding mechanism and has the capacity to operate at excitation frequencies up to 50 kHz and beyond. Sorting results are demonstrated using various combinations of metal spheres, which resulted in nearly perfect performance in terms of grade and recovery. We also demonstrate sorting of aluminum alloys from other aluminum alloys, with consistent grade and recovery between 85–95 %.
We present a study of efficient dispersion of an impact onto structured and potentially scalable granular beds. We use discrete element method based dynamical simulations of shock wave propagation and dispersion in 2D and 3D arrangements of granular spheres. The spheres are geometrically packed in a nested columnar structure, which leads to the severe attenuation and spreading of the incident energy within the structure. We further show that by incorporating inhomogeneity in material properties, or by introducing layers of a dissimilar material in the middle of the arrangement, impact mitigation can be enhanced significantly. Such an arrangement can therefore be useful in the design of effective impact decimation systems. Using a 2D arrangement we first show the basic idea behind impact dispersion in such an arrangement. With this understanding the system is scaled to 3D. The influence of the system size and material properties on the wave propagation within the packing is also presented.
Extensive experimental investigations were carried out for pressure drop and concentration profile in the flow of bi-modal slurry comprising silica sand and fly ash with mean diameter of 450 and 75 μm, respectively, at six silica sand:flyash ratios (namely, 100:0, 90:10, 80:20, 70:30, 60:40 and 0:100) in a 53 mm diameter horizontal bend. Flow velocity was varied up to 3.56 m/s (namely, 1.78, 2.67 and 3.56 m/s) at two efflux concentrations of 8.82 % and 16.28 % for each silica sand:flyash ratio. The experimental data were compared with the CFD modelling results using an Eulerian two-phase model available in the FLUENT software. Eulerian model predicted almost all the experimental data collected in the present study for pressure drop and concentration profile with fair accuracy. The bend loss coefficient kt was found to decrease with increase in percentage of flyash for silica sand:flyash ratio up to 70:30. Further increase in flyash did not show any significant change in the value of kt.
This study focuses on investigating the mixing state by different mixing indices for different pre-organized particles. We also try to propose a new mixing index and discuss the advantages and disadvantages of different cases.
The results show that the Avg. distance mixing index indicates the degree of mixing more accurately than other mixing indices for a case of complete segregation. In some cases the degree of mixing would be higher with the Lacey mixing index compared with the other indices, with the size of the cells greatly affecting this value. In other words, the use of any single specific mixing index on its own cannot accurately reflect the correct degree of mixing for all different kinds of systems. The only difference between mixing indices is which one can provide more accurate and stable results.
Characterisation of the wettability of five poor wetting food powders was performed using static immersion and contact angle measurements. The effect of temperature (20, 50 and 70 °C) on wettability showed varying effects on the powders. Higher temperatures majorly improved the wettability of chocolate and high fat powders but worsened the wettability of sodium caseinate and milk protein isolate. Rate-limiting regime testing was performed by pouring a fixed mass of powder on to the surface of water in an agitated beaker and visually assessing what was rate-limiting rehydration after 1 minute. The rate limiting regime tended to be floating at lower agitation speeds and dispersed clumps of varying sizes at higher speeds. However, there were major differences observed between the powders. Some of the powders formed strong films at powder/water interfaces, that could act as a barrier to water penetration and wettability. Consequently, force displacement testing was performed on a layer of powder on the water surface to assess the strength of any powder film formed. Some of the powders formed strong films that may in-part explain their poor wetting behaviour and their propensity to form strong clumps that were difficult to disrupt.
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