Increasing Particle Concentration Research Articles

Rheology and structure of ceramic stereolithography slurries: Role of powder nature, dispersant, and orthogonal strain

AbstractWe investigate the rheological properties of ceramic slurries designed for laser stereolithography manufacturing in relation to their formulation, including the powder morphology, their volume fraction, and the concentration of dispersing agent. By combining dynamic strain sweep and Small‐Angle X‐ray Scattering (SAXS) experiments, we first illustrate that slurry viscosity follows an exponential trend with increasing particles content, with steeper increase observed for more aggregated particles. We then show that increasing the dispersant concentration up to an optimal value decreases slurry viscosity, as SAXS measurements reveal a reduction and homogenization in agglomerate size. Finally, we evidence that applying vertical oscillatory deformation during steady shear flow induces fluidization of the slurry. The shear viscosity exhibits a time–strain rate equivalence, enabling the generalization of this effect across a wide range of formulations. This methodology holds potential for industrial applications, where introducing vibration perpendicular to the scraping blade motion could improve the surface quality of the spread slurry prior to polymerization.

Influence of particle morphology on solar thermal conversion performance and sensible heat storage capacity: A case study of TiO2@Go binary nanofluid

Photothermal catalytic hydrogen production driven by the full spectrum of outdoor solar radiation, represents a highly promising and efficient approach for hydrogen generation. This method is widely anticipated by researchers due to its potential to enhance photon utilization efficiency at the reaction source. However, limited attention has been devoted to the variations in photothermal conversion performance of particle reaction suspensions caused by objective fluctuations of solar irradiation, especially when the morphology of the nanostructure changes, which is a crucial factor for practical applications in hydrogen production. Based on this bottleneck, we prepared the typical photo-responsive TiO2@Go composite with varied dimensions (i.e., nanosphere TiO2@Go, nanorod TiO2@Go, nanosheet TiO2@Go) as research models, and systematically investigated their thermal conversion and sensible heat conversion performance under different working conditions. The results showed that at low nanofluid concentration, nanosphere TiO2@Go and nanosheet TiO2@Go exhibit better sensible heat conversion. As the particle concentration increases, the sensible heat conversion efficiency of all nanofluids decreases. It can also be found that the latent heat conversion efficiency tends to increase with the increase of concentration, but the nanorod TiO2@Go show the opposite, which should be closely related to the uniformity of the particle size in different directions. In addition, for the sensible heat storage properties of nanofluids, smaller particle size and abundant porosity due to particles aggregation were found to be more beneficial for varied shapes. The underlying functional mechanisms were elucidated associated with the analysis of particle structures, interfacial properties, and optical characteristics. We contend that our research could provide valuable insights for the large-scale implementation of solar photothermal hydrogen production and a reasonable selection of photothermal material morphology for outdoor working conditions.

Experimental Investigation on the Permeability and Fine Particle Migration of Debris-Flow Deposits with Discontinuous Gradation: Implications for the Sustainable Development of Debris-Flow Fans in Jiangjia Ravine, China

The particle size distribution (PSD) is a crucial parameter used to characterize the material composition of debris-flow deposits which determines their hydraulic permeability, affecting the mobility of debris flows and, hence, the sustainable development of debris-flow fans. Three types of graded bedding structures—normal, reverse, and mixed graded bedding structures—are characterized by discontinuous gradation within a specific deposit thickness. A series of permeability tests were conducted to study the effects of bed sediment composition, particularly coarse grain sizes and fine particle contents, on the permeability and migration of fine particles in discontinuous debris-flow deposits. An increase in fine particles within the discontinuously graded bed sediment led to a power-law decrease in the average permeability coefficient. With fine particle contents of 10% and 15% in the bed sediments, the final permeability coefficient consistently exceeded the initial value. However, this trend reversed when the fine particle contents were increased to 20%, 25%, and 30%. Lower fine particle contents indicated enhanced permeability efficiency due to more interconnected voids within the coarse particle skeleton. Conversely, an increase in fine particle content reduced the permeability efficiency, as fine particles tended to aggregate at the lower section of the seepage channel. An increase in coarse particle size decreased the formation of flow channels at the coarse–fine particle interface, causing fine particles to move slowly along adjacent or clustered slow flow channels formed by fine particles, resulting in decreased permeability efficiency. Three formulae are proposed to calculate the permeability coefficients of discontinuously graded bed sediments, which may aid in understanding the initiation mechanism of channel deposits. Based on experimental studies and field investigations, it is proposed that achieving sustainable development of debris-flow fans requires a practical approach that integrates three key components: spatial land-use planning, in situ monitoring of debris flows and the environment, and land-use adjustment and management. This comprehensive and integrated approach is essential for effectively managing and mitigating the risks associated with debris flows, ensuring sustainable development in vulnerable areas.

Influence of MWCNT/ZnO hybrid nanofluids’ thermo-physical characteristics for heat transfer applications

Hybrid nanofluids (HNF’s) can perform as promising heat transfer fluids because of their enhanced thermo-physical characteristics. However, there are certain limitations of using them at higher concentrations. Moreover, lot of works on hybrid nanofluids focussed greatly on assessing thermal conductivity and viscosity. But the other parameters like specific heat and density also play an important role in heat transfer applications in addition to the volume concentration. Also, the effect of the combination of different nano particles on heat transfer is also a crucial area. Hence in this work, it is aimed to determine the thermo-physical characteristics of MWCNT/ZnO hybrid nanofluids (70:30) at varied loading and temperatures. Two step strategy was employed to prepare the (HNF’s) at distinct loadings varying in the range of 0.01%–0.05% and at a range of temperatures of 30°C–70°C with base fluid as water. The mixture’s ratios were 30:70 of MWCNT and ZnO, respectively. HNF’s exhibited an improved thermal conductivity in comparison to the original fluid, which was 80% more than the base fluid. With the rise in the temperature, the density, viscosity and specific heat all trended downward. There is an increase in the density and viscosity with the increase in the volume concentration of the hybrid nano particles. This work suggested that the MWCNT and ZnO hybrid nanofluids are better heat transfer fluids for enhancing the heat transfer and can emerge as efficient coolants for the applications of heat transfer.

Interaction of preservatives with contact materials during filling and storage of parenteral liquid formulations

Silicone tubing is a frequently used material in pharmaceutical filling processes for parenteral formulations, as its characteristics like flexibility, chemical resistance and easy handling make it particularly suitable for these purposes. This study investigated the time-dependent interaction of phenol and m-cresol with silicone tubing and other broadly applied contact materials used during the filling and transport processes of parenteral formulations. Phenol losses could be observed after incubation in silicone tubing, depending on the inner diameter (ID). This has been demonstrated for process interruptions of up to 120 minutes. A loss of 40 % could be observed for a small ID of 3.2 mm which can be found close to filling needles, and up to 12 % for larger tubes with an ID of 9.5 mm commonly used for sterile filtration and transport processes. Analysis of tubes with varying ID revealed a linear relationship between the decrease of phenol and the surface-to-volume ratio. m-cresol showed an even more pronounced loss in silicone tubing. Fluorinated polymers and thermoplastic elastomers were also analyzed, and no loss of phenol and m-cresol was observed. Pumping tests revealed that shear forces in peristaltic pumps led to strong particle formation in selected tubing. A strong increase in particle concentration was observed in thermoplastic elastomers, particularly in PharMed® BPT tubing. In contrast, the C-Flex® tubing demonstrated minimal particle formation. Fluorinated polymers are not compatible with peristaltic pumps, which is why they were not analyzed regarding pumpability. Although silicone tubes are not impervious to preservatives such as phenol, they did not generate particles when pumped.

Investigating the compaction and the mechanical behaviors of coal gangue as subgrade filler and constructing highway subgrade in practice

Using coal gangue as subgrade filler (CGSF) can address the accumulated issues of coal mine waste, but also save the constructing costs, which has the important ecological and engineering practical value. The well-graded limit of CGSF was captured based on the fractal model grading equation (FMGE). The large-scale vibration compaction test (LCT) shows that particle grading has a remarkable influence on the compaction of CGSF, with the increase of fine particle content, the dry density of sample first increases and then decreases. On this basis, the optimal range of particle grading was obtained. A series of large-scale triaxial tests (LTT) were conducted to investigate the mechanical behaviors of CGSF. The results shown that (1) the peak deviatoric stress shows a well-quadratic correlation with the fractal dimension. The optimal grading range of CGSF captured by LTT and LCT is basically the same, hence the suggestion of acquiring the optimal grading through LCT was given. (2) Increasing the compaction degree (DC) can significantly improve the strength of CGSF if DC is smaller, while when DC is greater, the strength improved by increasing DC will not be significant. (3) The grading and DC have a significant impact on the cohesive force of CGSF, while have little effect on internal friction angle. In addition, the research results provide good guidance for the constructing of a highway subgrade in practice.

Experimental study on the unsteady evolution mechanism of centrifugal pump impeller wake under solid–liquid two-phase conditions: Impact of particle concentration

To study the spatiotemporal evolution process of particle wakes behind the impeller in the centrifugal pump, this paper utilized high-speed photography to capture the particle motion characteristics under different solid-phase particle concentrations (1%, 1.5%, and 2%). First, this paper studies the changes in hydraulic performance of the centrifugal pump under solid–liquid two-phase flow conditions. It then introduces the evolution process of the impeller particle wake, comparing the differences in particle wake evolution under varying solid-phase concentrations. Finally, the impact of the solid-phase concentration on the wear of the volute's partitions is investigated. This study found that as the solid-phase particle concentration increases, the hydraulic performance of the pump gradually declines. Under the design conditions, when the solid-phase concentration increases by 0.5%, the efficiency of the centrifugal pump decreases by 0.56% and 0.35%. There is mutual transport of particles between adjacent wakes, and the movement of particle wakes within the volute passage is not equidistant over time. As the solid-phase particle concentration increases, wake cutting occurs at the volute partitions, and there is a significant solid–liquid separation between the particle wakes. The spatial evolution of the particle wakes is significantly influenced by the solid-phase concentration. Wear at the volute partitions intensifies with increasing solid-phase concentration and is also affected by changes in the particle wakes. The research results provide a basis for further exploration of the solid–liquid two-phase flow dynamics within centrifugal pumps.

Study on the design and application of the three-electrode ionization particle sensor

Accurate detection is the foundation of haze governance. The existing particle concentration detection methods and instruments have many shortcomings, such as complex structure, high cost, easy blockage, short life, and significant impact of environmental changes. Therefore, this paper proposes a silicon micropillar three-electrode ionization particle sensor based on the gas discharge principle and studies the sensor's sensitivity to PM2.5 particles. Three-electrode comprises a cathode with micro silicon pillars grown on the surface, an extracting electrode, and a collecting electrode. It shows that the cathode current of the sensor increases linearly with extraction voltage and nonlinearly with temperature. As the cathode material of the sensor, the silicon micropillar is compared with the carbon nanotube to solve the burn problem of the nanotube rising from positive ions bombardment during gas discharge. The collecting current of the sensor shows a decreasing trend with the increase in particle concentration. The collecting current and sensitivity of the sensor are much higher in radio frequency excitation than in direct current excitation. The sensor developed in this paper displays the advantages of simple technology, high integration, low cost, and high sensitivity, and it exhibits great application potential.

Acoustic emission analysis of self-healing properties in cementitious materials with superabsorbent polymers (SAPs) during different environments

This paper studies the coupling effect of superabsorbent polymers (SAPs) and fly ash on the self-healing performance of mortar. The three-point bending test was used to evaluate the mechanical property recovery effect of mortar specimens after curing in different environments, and the relationship between crack closure rate, flexural strength and flexural stiffness recovery was established. The amplitude and energy in acoustic emission were used to evaluate the characteristics of self-healing products. The results show that compared with the control specimens, the addition of SAP improves the crack closure rate and mechanical property recovery effect of mortar specimens. With the increase of SAP particle size and content, the mechanical property recovery rate and crack closure rate increase accordingly. The order of self-healing effect of specimens in different healing environments is saturated calcium hydroxide > water >97 % RH > air. After reloading, the amplitude number and cumulative energy of samples with SAP are larger than those of the control specimens. The SEM results also prove this, and the self-healing products in the crack area of the mortar specimens with SAP are denser than those in the control specimens.

Significant annual variations of firework-impacted aerosols in Northeast China: Implications for rethinking the firework bans

Fireworks are banned in many Chinese cities but never eliminated, reflecting strong public demand on this traditional activity for festival celebrations. On the other hand, the assessment of firework contributions to air pollution remains vague, raising concerns on the necessity of the mandatory bans. Here we investigated the characteristics of firework episodes in a megacity in Northeast China, based on field campaigns conducted in four successive winters during 2018–2022. Although prohibited, the firework influences remained evident during the Chinese New Year periods, as suggested by the enhancements of water-soluble potassium (K+). In addition, significant annual variations were identified for the firework episodes, with the following features observed. First, the firework-induced enrichment ratios of K+ and chloride exhibited increasing trends across years, climbing from 4.4 to 8.6 and from 1.7 to 2.9, respectively. Second, the enrichment ratio of sulfate dropped from 2.8 to 1.6, indicating that the firework contributions to sulfate decreased but remained considerable. Third, fireworks turned into an unimportant source for organic carbon and nitrate in the most recent winter of 2021–2022, with enrichment ratios of ∼1 for both species. Fourth, the firework-driven increases in fine particle concentration were as high as ∼100% for the two winters during 2019–2021, whereas the increase dropped sharply to ∼30% for 2021–2022. These variations were in line with the promotion of environmentally friendly fireworks. Our results indicated that the air pollution caused by fireworks could be reduced substantially by advanced manufacturing technologies and thus it is time to rethink the firework bans.

Autoignition of premixed hydrogen/air mixtures with uniformly dispersed carbon particles

The autoignition of a stoichiometric hydrogen/air mixture laden with uniformly distributed coal char particles is simulated with the Eulerian-Lagrangian approach under isochoric conditions. A zero-dimensional model is adopted to assess the effects of gas temperature, pressure, particle diameter, and concentration on ignition dynamics. Increasing the initial temperature reduces the ignition time and maximum heat release rate of the homogeneous reactions, while the parameters for particle reactions stabilize after reaching a critical temperature. Initial pressure exhibits a non-monotonic influence on gas phase ignition, with higher pressures promoting particle autoignition. An increase in particle diameter decreases the ignition time for the homogeneous reaction, approaching that of particle-free conditions. Meanwhile, particle ignition time first decreases and then linearly increases. Increasing particle concentration reduces the interphase disparities of ignition times, while the two-phase ignition times rapidly rise after exceeding the critical concentration. Moreover, pre-ignition temperature equilibrium (PTE) significantly impacts the ignition parameters and processes. PTE results in a minimal ignition time disparity between the gas and particles, with coal char particles markedly influencing hydrogen ignition. Failure to reach PTE leads to significant two-phase ignition time differences, with negligible impact from the solid phase on gas phase ignition. The particle effect ratio, δ, is introduced to evaluate these effects. Notably, the evolution variations in ignition time and heat release rate are determined by the existence of the PTE under corresponding initial conditions. The findings of this study are crucial for developing strategies to mitigate explosion hazards and enhance the performance of detonation propulsion systems using hybrid fuels.

Understanding photo-thermal and melting mechanisms in optical charging of nano and micro particles laden organic PCMs

Engineering efficient optical charging process necessitates efficient photo-thermal energy conversion, transfer, as well as storage of the incident solar radiant energy. The present work is a determining step in deciphering, quantifying, and understanding the aforementioned steps involved in the optical charging of PCMs. Herein, the effect of particle size, concentration and thermochromism have been critically investigated. In particular, detailed optical characterization and photo-thermal experimentation pertinent to non-thermochromic nanoparticles laden PCM (referred to as NP-PCM) and thermochromic micro capsules laden PCM (referred to as TMCP-PCM) has been undertaken. Detailed optical analysis points out that opposed to NP-PCM, TMCP-PCM significantly scatter the incident radiations – the diffuse transmittance (at room temperature) in the two cases being approximately 2 % and 39 % respectively. Furthermore, whereas, optical properties of non-thermochromic nanoparticles are nearly invariant to temperature changes; in the case of thermochromic microcapsules, the magnitude of scattering further increases and diffuse transmittance reaches as high as 51 % at elevated temperatures. Although, thermochromism helps in enhancing the penetration depth at elevated temperatures, but, due to significant fraction of scattering, the photo-thermal energy conversion is not that effective. In terms of temperature field, spatial-temporal temperature distribution curves reveal that temperature spread (in the liquid phase) in case of optical charging of non-thermochromic particles (carbon soot nanoparticles) laden PCMs is significantly high (as high as approximately 24 °C) relative to that observed in case of thermochromic particles (microcapsules) laden PCMs (approximately, 4 °C). The magnitude of the temperature spread (being representative of the deviation from thermostatic optical charging) clearly points out that opposed to non-thermochromic laden PCMs, nearly thermostatic optical charging can be achieved in case of thermochromic particles laden PCMs.Furthermore, in case of optical charging without thermochromic assistance, the temperature spread, peak temperatures and the melting rates increase with increase in particles concentration. Whereas, in the latter case, although the temperature spread and peak temperatures are nearly independent; the melting rates do depend on the particles’ concentration. Overall, the present work is a significant step towards accelerated-thermostatic thermal energy storage.

Impact of the Source Material Gradation on the Disaster Mechanism of Underground Debris Flows in Mines

In mines where the natural caving method is used, the frequent occurrence of underground debris flows and the complex mine environments make it difficult to prevent and control underground debris flows. The source is one of the critical conditions for the formation of debris flows, and studying the impact of source material gradation on underground debris-flow disasters can effectively help prevent and control these occurrences. This paper describes a multiscale study of underground debris flows using physical model experiments and the discrete-element method (PFC3D) to understand the impact of the source material gradation on the disaster mechanism of underground debris flows from macroscopic and microscopic perspectives. Macroscopically, an increase in content of medium and large particles in the gradation will enhance the instantaneous destructive force. Large particles can more easily cause disasters than medium and fine particles with the same content, but the disaster-causing ability is minimized when the contents of medium and large particles exceed 50% and 60%, respectively. With increasing fine particle content, the long-distance disaster-causing ability and duration is increased. On the microscopic level, the source-level pairs affect the initial flow mode, concentration area of the force chain, average velocity, average runout distance, and change in energy of the underground debris flow. Among them, the proportion of large particles in the gradation significantly affects the change in kinetic energy, change in dissipative energy, time to reach the peak kinetic energy, and time of coincidence of dissipative energy and gravitational potential energy. The process of underground debris flow can be divided into a “sudden stage”, a “continuous impact stage”, and a “convergence and accumulation stage”. This work reveals the close relationship between source material gradation and the disaster mechanism of underground debris flows and highlights the necessity of considering the source material gradation in the prevention and control of underground debris flows. It can provide an important basic theory for the study of environmental and urban sustainable development.

The impact of particle size and concentration on the characteristics of solid–fluid two-phase flow in vertical pipe under pulsating flow

Vertical pipe hydraulic conveying is currently considered the most promising method for deep-sea mining. The conveying velocity at the inlet of the vertical pipe is often close to a pulsating form due to the influence of the flexible pipe and the marine environment. This study employs a combined Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) approach to investigate the impact of various particle sizes and concentrations on the flow behavior of solid–fluid two-phase flow in a vertical pipe under pulsating flow. The study reveals that fluid velocities exhibit periodic fluctuations within the vertical pipe under pulsating inlet flow. Moreover, the periodic phenomenon of local increases in particle velocity and concentration becomes more pronounced as particle size and concentration increase. Larger particle sizes increase particle inertia, reducing the ability to follow the fluid and leading to more localized particle aggregation. Therefore, the flow pattern within the vertical pipe transitions from homogeneous flow to plug flow as particle size increases. Variations in fluid–solid interaction forces and particle collision forces are explored to explain this phenomenon. When the particle size exceeds a critical threshold, the collision force surpasses the fluid–solid interaction force, leading to the transition.

Solid-liquid flow characteristics of twin-screw pump under solid-containing transportation

Abstract Twin-screw pumps have the wear risk when the fluid contains particles. In order to clarify the flow characteristics of the twin-screw pump under solid-containing transportation, the solid-liquid flow characteristics research on a twin-screw pump are carried out using numerical simulation and experimental methods in this paper. The results show that the particle concentration has a small effect on the volumetric efficiency and hydraulic efficiency of the twin-screw pump under each differential pressure, but the presence of particles could increase the volumetric efficiency limitedly. The velocity of main flow and the turbulent kinetic energy have been restrained by the particles in the tooth chamber, and the inhibition phenomenon is more significant with the increase of particle concentration. The particles in the tooth chamber are inhaled by the leakage flow at the tooth-tip clearance. Some particles hit the tooth-tip and cause the abrasion, others flow into the tip clearances, which decreases the leakage flow velocity and results in a higher volumetric efficiency than that of the pure-liquid condition. The results of the study will provide a theoretical basis for the study of solid-containing transportation and particle wear in twin-screw pumps.

Statistical analysis on the rate of heat transfer of radiative water‐based hybrid nanofluid flow over an elongating surface due to velocity slip and melting heat condition

AbstractThe performances of the heat transfer due to dissipative heat likely magnetic dissipation is a challenging field of research because of it's diversifies applications in industries and engineering. Particularly, nowadays, in biomedical field of research the implementation of dissipation along with thermal radiation is vital. Based upon the current scenario, the present investigation leading to the role of magnetic dissipation vis‐à‐vis thermal radiation on the water‐based hybrid nanofluid past an electro‐magnetized elongating surface associated with melting boundary conditions. The adaptation of the transformed rule particularly, similarity rules are useful to convert the proposed set of problems in to ordinary. Further, shooting‐based numerical technique is proposed to handle the governing equations. The interesting and novel approach in this topic is the use of robust statistical technique, that is, response surface methodology for the optimizing Nusselt number for the use of various factors. Moreover, the validation is obtained by conducting a hypothetical testing using analysis of variance (ANOVA) which conforms a best output model for appropriate response. Further, the major outcomes of the study are depicted as; the unsteadiness parameter decelerates the velocity profile of the hybrid nanofluid for the interaction. However, the increasing particle concentration favours in enhancing the heat transport phenomenon.

Comparison of aerosol number size distribution and new particle formation in summer at alpine and urban regions in the Guanzhong Plain, Northwest China

Ultrafine particles play a crucial role in understanding climate change, mitigating adverse health effects, and developing strategies for air pollution control. However, the factors influencing the occurrence and development of new particle formation (NPF) events, as well as the underlying chemical mechanisms, remain inadequately explained. This study compared number concentrations and size distributions of atmospheric ultrafine particles at Xi'an (urban area) and the summit of Mt. Hua (alpine region) in summer to investigate the NPF mechanism and particle growth in both clean and polluted areas of the Guanzhong Plain. The average particle number concentration in Xi'an was significantly higher than that at Mt. Hua. The diurnal variation of total particle number concentration differed between Xi'an and Mt. Hua indicating a divergence in influencing factors. The size distributions in Xi'an varied across different timescales and weather conditions, whereas Mt. Hua exhibited little variation. This stability at Mt. Hua is attributed to its cleaner background atmosphere and the steady influx of aging particles with larger diameters transported from the free atmosphere. In both areas, geometric mean diameters (GMDs) were inversely proportional to particle number concentrations suggesting that increase in particle numbers were primarily due to the generation of smaller particles. The potential governing factors for NPF events differed somewhat between the urban and mountainous stations. In the urban area, intense local stationary and mobile emission sources promoted the growth of newly formed nanoparticles, with ozone-oxidized condensable vapors serving as key precursors. In contrast, at the mountainous station, NPF process were significantly influenced by anthropogenic precursors from long-range transport and locally emitted biogenic organics. The rapid increase in ultrafine particle concentrations primarily poses serious health risks and degrades air quality in urban areas, while also contributing to climate-related effects in alpine regions.

Research on humidity field and freezing resistance of green recycled ceramic internal cured concrete at early age

In cold and drought environment, concrete shrinkage cracking caused by water loss is serious, and thus the freezing resistance of concrete is deteriorated. The waste ceramic particles were used as internal curing materials to prepare concrete, based on this background. Then, the influence of internal curing with ceramic particles on humidity field and temperature of concrete is analyzed by using temperature and humidity sensor. Based on the change mechanism of the internal humidity of concrete, the relationship between the curvature radius of liquid surface and the relative humidity is revealed. Taking water loss and water loss rate as the index, the water transfer law of concrete surface under ceramic particle internal curing was defined. Through the drying shrinkage test, the mechanism of improving the drying shrinkage of concrete by internal curing in ceramic particles was mastered. Finally, the effects of ceramic internal curing on cement hydration, interfacial transition zone (ITZ) and freezing resistance of concrete were studied. The results show that the relative humidity, water loss and water loss rate of concrete increase with the increase of ceramic particle content, and the dry shrinkage value decreases with the increase of ceramic particle content. Compared with ordinary concrete, when the ceramic particle content is 10 %, 15 %, 20 %, 25 % and 30 %, and the test period is 10 days, the internal relative humidity of concrete increases by 0.52 %, 0.67 %, 1.55 %, 2.55 % and 3.05 %, respectively. The drying shrinkage values decreased by 3.42 %, 7.69 %, 10.26 %, 15.17 % and 30.13 %, respectively. When the test period was 1032 h, the water loss increased by 1.08 %, 5.15 %, 7.90 %, 12.69 % and 14.49 %, respectively. Furthermore, when the ceramic particle content is 20 %, the initial normalized heat flow of concrete increases by 2.74 mW/g, and the normalized heat flow minimum increases by 0.324 mW/g. The minimum ITZ microhardness increased by 2.64 MPa, the ITZ width decreased by 5 μm, and the maximum crack width at the contact between ITZ and aggregate decreased by 0.89 μm. At the same time, when the ceramic particle content is less than 20 %, the effect of internal curing on the freezing resistance of concrete increases with an increase in ceramic particle content.

Investigation into personal exposure to ultrafine particle (UFP) in Phnom Penh, Cambodia: A pilot study

This pilot study aimed to examine personal exposure to ultrafine particles (UFP or particle smaller than 100 nm) in Phnom Penh, Cambodia through the assessment of different transportation modes, travel routes, and the comparison of indoor and outdoor activities. A handheld UFP counter was used to record the UFP size, concentration and as well as Lung Deposited Surface Area (LDSA). GPS data was recorded using a GPS watch and then combined with the UFP data before further analysis with geospatial software (QGIS) along with OpenStreetMap to generate spatial data of personal exposure to UFP. The study revealed significant differences in UFP exposure between motorbike and bus users, with average UFP concentrations of approximately 114,300 and 171,700 particles/cm³ for motorbike users, and 22,600 and 37,200 particles/cm³ for bus users on lines 3 and 4A, respectively. These concentrations exceed WHO guidelines, which consider UFP levels above 20,000 particles/cm³ per hour as high and potentially harmful. The results of our study also revealed varying amounts of exposure on different roadways, with Russian Federation Blvd consistently exhibited the highest concentrations of UFP, especially during periods of peak traffic. Furthermore, indoor environments generally presented lower UFP exposure. Specific activities or events were found to generate temporary increases in particle concentration. It was shown that weekdays had elevated levels of UFP compared to weekends. Regardless of the limitations of the study, especially its small sample size, it provides significant initial observations, highlighting the urgent need for mitigation strategies and further comprehensive studies in the region.

Effect of Fine Particle Content on Solution Flow and Mass Transfer of Ion-Adsorption-Type Rare Earth Ores

Fine particle content significantly affects the in situ leaching of ion-adsorption-type rare earth ores. This study investigated the effect of fine particle content on solution flow and mass transfer in leaching. The results showed that with the increase in fine particle content, the peak concentration and peak time of rare earth increased. When the fine particle content exceeded 20%, all ion-exchangeable-phase rare earth ions could be replaced with a low dosage of the leaching solution. The leachate flow rate exhibited multi-stage variation, influenced by solution permeation, ion exchange, and fluctuations in accumulated liquid height. A mass transfer analysis showed that a higher fine particle content corresponded to a smaller plate height and a larger plate number of theoretical plates. As fine particle content increased, the final rising height of capillary water decreased, with rising rates varying across different stages for the samples. Moreover, an increase in fine particle content from 5% to 20% resulted in a 94% decrease in the samples’ permeability coefficients. A mechanism analysis showed that when the fine particle content was higher, the fine particles were embedded in the gaps between coarse particles, and the ore particles in the sample were arranged continuously, resulting in a lower permeability coefficient. Then, the leaching solution could penetrate uniformly, which was beneficial for reducing leaching blind spots and improving leaching efficiency. However, excessive fine particle content might have detrimental effects. Based on these results and considering actual mining conditions, the optimal fine particle content for rare earth leaching is 20%.