Types Of Particles Research Articles

Investigation of the Dominant Effects of Non-Spherical Particles on Particle–Wall Collisions

A deep understanding of the particle–wall collision (PWC) behaviors of non-spherical particles is important for managing gas–solid flows in industrial applications. It is important to identify the dominant parameters and to develop the common PWC prediction models for typical non-spherical particles. In this paper, different types of non-spherical particles were used to conduct the fundamental experiments. The effects of key parameters such as particle size, non-sphericity, wall roughness, and impact angle were analyzed. The results show that the trends of the collision coefficients with the impact angle for all non-spherical particles are similar. The dominant factors of particle–wall collisions are particle sphericity and wall roughness. A model with four parameters was fitted from the experimental data. The model can predict the collisions of non-spherical particles on rough steel walls with sizes ranging from 50 to 550 microns.

Bañados-Silk-West phenomenon for near-fine-tuned particles with an external force: General classification of scenarios

If two particles moving toward a black hole collide in the vicinity of the horizon, the energy Ec.m. in the center-of-mass frame can grow indefinitely if one of the particles is fine-tuned. This is the Bañados-Silk-West (BSW) effect. One of the objections against this effect is that, for some types of horizon, fine-tuned particles cannot reach the horizon. However, this difficulty can be overcome if, instead of exact fine-tuning, one particle is nearly fine-tuned, with the value of small detuning being adjusted to the distance to the horizon. Such particles are called near-fine-tuned. We give classification of such particles and describe possible high-energy scenarios of collision in which they participate. We analyze the ranges of possible motion for each type of particle and determine under which condition such particles can reach the horizon. We analyze collision energy Ec.m. and determine under which conditions it may grow indefinitely. We also take into consideration the forces acting on particles and find when the BSW effect with nearly fine-tuned particles is possible with finite forces. We demonstrate that the BSW effect with particles under discussion is consistent with the principle of kinematic censorship. According to this principle, Ec.m. cannot be literally infinite in any event of collision (if no singularity is present), although it can be made as large as one likes. Published by the American Physical Society 2024

Nanostructured Magnetic Particles for Removing Cyanotoxins: Assessing Effectiveness and Toxicity In Vitro.

The rise in cyanobacterial blooms due to eutrophication and climate change has increased cyanotoxin presence in water. Most current water treatment plants do not effectively remove these toxins, posing a potential risk to public health. This study introduces a water treatment approach using nanostructured beads containing magnetic nanoparticles (MNPs) for easy removal from liquid suspension, coated with different adsorbent materials to eliminate cyanotoxins. Thirteen particle types were produced using activated carbon, CMK-3 mesoporous carbon, graphene, chitosan, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidised cellulose nanofibers (TOCNF), esterified pectin, and calcined lignin as an adsorbent component. The particles' effectiveness for detoxification of microcystin-LR (MC-LR), cylindrospermopsin (CYN), and anatoxin-A (ATX-A) was assessed in an aqueous solution. Two particle compositions presented the best adsorption characteristics for the most common cyanotoxins. In the conditions tested, mesoporous carbon nanostructured particles, P1-CMK3, provide good removal of MC-LR and Merck-activated carbon nanostructured particles, P9-MAC, can remove ATX-A and CYN with high and fair efficacy, respectively. Additionally, in vitro toxicity of water treated with each particle type was evaluated in cultured cell lines, revealing no alteration of viability in human renal, neuronal, hepatic, and intestinal cells. Although further research is needed to fully characterise this new water treatment approach, it appears to be a safe, practical, and effective method for eliminating cyanotoxins from water.

Microplastics in Russian Freshwater Systems: a Review

Contamination of environment by plastic debris has already become a worldwide problem due to the global production of polymers and the further accumulation of waste. Microplastic particles (<5 mm) have been found almost everywhere. Despite the significant number of publications devoted to the microplastic pollution in freshwater and marine environments, in the review articles around the world freshwater systems the Russian territory is a white spot. The article provides the summary of studies investigating microplastics (MP) in Russian lakes and rivers, the determination of concentrations, type and composition of polymer particles and also possible sources of plastic contamination. The map of the MP distribution in Russian freshwater systems is presented. The concentration of microplastics in freshwater system varies greatly, e.g., in lakes from 0,27 items/m3 in Lake Baikal to (4-26)∙103 items/m3 in the Altai lakes of Western Siberia; in large Russian rivers measured polymer content varies by three orders of magnitude, from parts of items/m3 in the Volga River to hundreds of items/m3 in the Upper Ob. Significantly higher concentrations of MP are found in the bottom sediments of rivers and lakes, exceeding polymer concentrations in surface water by several orders of magnitude. Thus, bottom sediments are able to accumulate significant amounts of MP.

Improvement of thermomechanical and dielectric properties of thermoplastic polyurethane using bismuth sodium titanate/carbon nanotube hybrid fillers

AbstractThe development of innovative composite materials through the amalgamation of thermoplastic polyurethane (TPU) with bismuth sodium titanate (BNT) and carbon nanotube (CNT) fillers was investigated. Before the composite fabrication, the fillers' surfaces were treated to enhance their compatibility with the TPU matrix. Hybrid fillers of BNT and CNTs were fabricated by mixing the two types of filler particles through ball milling and subsequently annealing the mixture at 250°C. Melt‐blending and injection molding were utilized to synthesize the composites at 210°C processing temperature. The prepared composites showed significantly enhanced thermal conductivity, dielectric constant, thermal stability, and thermomechanical properties compared with the neat TPU matrix. For instance, the dielectric constant was enhanced by 340% upon the inclusion of 40 wt.% BNT and CNT fillers compared to the neat TPU matrix (40CBNT‐TPU has 13.2). In particular, the inclusion of BNT‐CNT particles in the TPU matrix improved the thermal conductivity of the TPU matrix by 1180% tremendously as compared to neat TPU (40CBNT‐TPU has 2.6 W/(m.K)).Highlights Crystalline bismuth sodium titanate (BNT) is fabricated. Degradation of 8 wt.% of the IPDI‐treated BNT proves surface treatment. Dielectric constant (DC) improved by 340% compared to neat TPU. Thermal conductivity (TC) enhanced 11.4 times compared to neat TPU. Improvement in TC and DC will make it applicable in electronic materials.

Persistent mixed‐phase states in adiabatic cloud parcels under idealised conditions

AbstractBy assuming that liquid droplets and ice crystals within a computational grid box grow under the same conditions, mean‐field representations of mixed‐phase clouds in numerical models favour a quick cloud glaciation driven by the Wegener–Bergeron–Findeisen process. Consequently, maintenance of mixed‐phase states under the mean‐field approximation is conditioned to external dynamical forcing, such as sufficiently strong updraughts. In this work we go beyond the mean‐field representation and investigate the maintenance of mixed‐phase states in adiabatic (non‐entraining) cloud volumes by accounting for local variability in a particle's growth conditions in the turbulent cloud environment. This is done by using a Lagrangian microphysical scheme, where temperature and vapour mixing ratio are stochastic attributes attached to each cloud particle. Different dynamic scenarios show that microphysical variability and parametrised turbulence effects may significantly reduce cloud glaciation rates, resulting in much more resilient mixed‐phase states in idealised parcels containing non‐sedimenting and non‐aggregating cloud particles. We have stated a more refined criterion for the Wegener–Bergeron–Findeisen process activity in the bulk of a mixed‐phase cloud parcel (or computational grid box). This criterion is stated in terms of the conditional average supersaturations that are experienced by specific cloud particle types (liquid or ice), and not in terms of unconditional averages corresponding to parcel‐ or grid‐mean values of supersaturations. Formulation of a relation between conditional and unconditional average supersaturations poses an interesting closure problem in mixed‐phase cloud microphysics. Our stochastic microphysical model provides a Lagrangian closure to this problem and gives insights towards the development of a prognostic stochastic subgrid‐scale scheme for condensation/deposition in numerical models of mixed‐phase clouds.

Responses of colonization and development of periphytic biofilms to three typical tire wear particles with or without incubation-aging in migrating aqueous phases

Understanding the behavior of tire wear particles (TWPs) and their impact on aquatic environments after aging is essential. This study explored the characteristics of TWPs generated using different methods (rolling friction, sliding friction, and cryogenic milling) and their transformation after exposure to environmental conditions mimicking runoff and sewage, focusing on their effects on river water and periphytic biofilms. Laboratory experiments indicate that at low exposure levels (0.1 mg/L), TWPs promoted biofilm growth, likely due to zinc release acting as a nutrient and the aggregation of particles serving as biofilm scaffolds. However, at higher concentrations (100 mg/L), TWPs inhibited biofilm development. This inhibition is linked to toxic byproducts like N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone and environmentally persistent free radicals, which reduce biofilm biomass, alter algal diversity, and decrease the production of essential biofilm components such as proteins and polysaccharides, consistent with the inhibitory behavior of TWPs on bis-(3′-5′)-cyclic diguanosine monophosphate and quorum sensing signals, including acyl-homoserine lactone and autoinducer-2. Aging processes, particularly after simulated sewage treatment, further affect ecological impacts of TWPs, reducing the benefits observed at low concentrations and intensifying the negative effects at high concentrations. Contribution of here lies in systematically revealing the impact of TWPs on the development of aquatic biofilms, emphasizing the logical relationship between their aging characteristics, environmental behavior, and ecological risks. It assesses not only the release effects of typical additives and conventional size effects but also highlights the emerging photochemical toxicity (persistent free radicals), thus providing valuable insights into the aquatic ecological risk assessment of TWPs.

Effect of total content of Zn and Mg on microstructure and mechanical properties of Al-3.2xZn-xMg-1.66Cu-0.15Zr aluminum alloy sheet

The effects of total Zn and Mg content on the microstructure, tensile properties, and fatigue properties of Al-3.2xZn-xMg-1.66Cu alloy sheets were systematically investigated after aging at 120 °C for 24 h. As the total content of Zn and Mg increased, the recrystallized grains were gradually refined, and the types of precipitate particles did not change, all of which comprised Guinier Preston (GP) zones and η′ metastable-phase particles, whereas both the number and volume fraction of η′-phase particles increased gradually, where the particles were first coarsened and then refined. The η′-phase particles were largest (∼8.2 nm) in the alloy with the total Zn and Mg content of 5.15 wt.%. The grain boundary precipitate (GBP) gradually coarsened and the width of the precipitates free zone (PFZ) gradually decreased. When the total content of Zn and Mg was increased from 2.61 to 11.40 wt.%, the yield strength and tensile strength increased from 173 and 309 MPa to 554 and 620 MPa, respectively, whereas the elongation decreased from 29.9% to 8.5%. However, the fatigue strength of the alloy sheet first decreased from 149 to 119 MPa and then increased to 183 MPa under the condition of R = 0.1. The fatigue strength of the alloy sheet with total Zn and Mg contents of 5.15 and 11.40 wt.% were the lowest one and the highest one, respectively, and the latter was 54% higher than the former.

Anisotropic remixing of a phase separated binary colloidal system with particles of different sizes in an external modulation.

We explore the phase behavior of a binary colloidal system under external spatially periodic modulation. We perform Monte Carlo simulations on a binary mixture of big and small repulsive Lennard-Jones particles with a diameter ratio of 2:1. We characterize structure by isotropic and anisotropic pair correlation functions, cluster size distribution, bond angle distribution, order parameter, and specific heat. We observe the demixing of the species in the absence of external modulation. However, the mixing of the species gets enhanced with increasing potential strength along with the alignment of the particles transverse to the modulation. The de-mixing order parameter shows discontinuity with increasing modulation strength, characterizing a first order phase transition. The peak in specific heat increases linearly with the size of the system. We also look into the dynamical behavior of the system via computing Mean Square Displacement (MSD) along both parallel and perpendicular directions to the modulation. We observe a decrease in the diffusion coefficient for both types of particles as we increase the strength of the modulation.

Simulation of particle-laden flows and erosion in an axial fan stage considering the relative position of the blades

Abstract Axial fans are vital accessories in aircraft ventilation systems, but, they may experience erosion from particulate flows, causing a decline in effectiveness over time. This study investigated the trajectories of two types of sand particles and erosion in an axial fan stage, considering the relative position of the blades facing the inlet guide vanes. The movement of particles was simulated using an in-house code that implements a Lagrangian approach along with a stochastic particle-eddy interaction model. The flow field was solved separately and the flow data was transferred to the particle trajectory code. The finite element method allowed for the tracking of particles through the computational cells and accurate determination of their impact positions. A semi-empirical erosion correlation was used to evaluate the local erosion rates, mass removal, and geometry deterioration. As a result, the rotor exhibits a high frequency of impacts and significant erosion on the leading edge of the blade, extending to the upper corner of the pressure side and blade tip, as well as the front of the suction side. In the inlet guide vane, the erosion is spread out along the entire pressure side but at lower erosion rates compared to the rotor blade. The erosion patterns obtained at different pitch-wise positions were cumulated to get better representation of erosion patterns. After being exposed to MIL-E5007E sand (0–1000 $\unicode{x03BC}$ m) at the highest concentration for 10 hours, the blade experienced a reduction of a 0.29% in mass, a 0.45% decrease in tip chord, and a 0.23% increase in tip clearance. On the other hand, AC-coarse sand (0–200 μm) resulted in a 0.23% decrease in blade mass, a 0.4% reduction in tip chord, and a 0.16% increase in tip clearance. The data that is available can be used to monitor the lifespan of axial fans of similar design and select appropriate coatings to protect against erosion.

Influence of thermal denaturation on whey protein isolates in combination with chitosan for fabricating Pickering emulsions: a comparison study.

Composite natural emulsifiers such as whey protein isolate (WPI) and chitosan (CS) are commonly used in Pickering emulsions to address the effect of thermal deformation of proteins before complexation with CS and heating after complexation. In this study, the properties of WPI and CS composites were investigated by complexing CS with either unmodified WPI or thermally denatured WPI (DWPI). Three types of composite particles were prepared, WPI-CS, DWPI-CS, and D(WPI-CS). Atomic force microscopy revealed that the composite particles formed larger aggregates with increased contour size and surface roughness compared to CS and WPI, whereas the interfacial tension decreased, indicating improved emulsifying abilities. Fourier-transform infrared analysis revealed differences in the hydrogen bonds between CS and WPI/DWPI. All three composite particles formed stable emulsions with droplet sizes of 20.00 ± 0.15, 27.80 ± 0.35, and 16.77 ± 0.51 μm, respectively. Thermal stability experiments revealed that the curcumin emulsion stabilized with WPI-CS and DWPI-CS exhibited relatively better thermal stability than that stabilized with D(WPI-CS). In vitro experiments results indicated that the bioaccessibility of the curcumin emulsion stabilized with WPI-CS was 61.18 ± 0.16%, significantly higher than that of the emulsions prepared with the other two composite particles (p < 0.05). This study will enable the customized design of WPI composite-based Pickering emulsions for application in the food and nutrition industries.

Microstructure, cracking susceptibility and abrasive wear resistance of core-shell ceramic particles reinforced laser cladding coatings

In this study, the typical core-shell ceramic particles were synthesized in-situ in the Fe-based composite coating using the laser cladding technology. The core-shell ceramic particles were composed of a pure TiC core and a (Ti,Nb,W)C multiple carbide shell, exhibiting fine cubic morphologies with particle sizes ranging from 0.5 μm to 1.0 μm rather than coarse dendritic morphologies. These core-shell ceramic particles were uniformly distributed in the entire coating with no obvious gradient distribution from the upper to the bottom. With the formation of the core-shell ceramic particles, the clad coating showed a more stable microhardness distribution along the depth direction and a lower cracking susceptibility than the original coating, and its average microhardness value (about 410 HV0.5) was only about 64 % of that of the original coating (about 640 HV0.5). Besides, the introduction of the core-shell ceramic particles caused the clad coating to possess the excellent abrasive wear resistance, which was approximately 10 times higher than that of the original coating. This significant improvement was attributed to the outstanding dispersion strengthening effect provided by the core-shell ceramic particles.

Hydrodynamic behavior of Janus particles in a finite inertial flow

Hydrodynamic behavior of Janus particles in a finite inertial flow is studied numerically using the lattice Boltzmann method (LBM) in the range of Reynolds number 0.05 ⩽ Re⩽ 10 and swimming parameter −3 ⩽ β ⩽ 3. Some results are validated by comparing with the existing results. The effects of Re, β on the hydrodynamic behavior of Janus particles are analyzed. The results show that the velocity of a pusher (a type of Janus particles) monotonically increases with the increase of Re, while the velocity of a puller (another type of Janus particles) exhibits a non-monotonic change. At high Re, the puller is unstable and presents a lateral displacement, while the pusher remains stable. The power consumption for the pusher and puller, the hydrodynamic efficiency for the pusher increase monotonically with increasing Re, while the hydrodynamic efficiency for the puller exhibits a non-monotonic change. At low Re, the power consumption and hydrodynamic efficiency of Janus particles exhibit symmetry with the variation of surface velocity distribution. This symmetry is disrupted with the increase of Re, similar to the velocity changing with the surface angle.

Discrete element simulations to predict the response of bio-cemented sands

Discrete element method (DEM)-based numerical models in the YADE environment are used to simulate the constitutive response of uncemented and bio-cemented sands to investigate the influence of boundary conditions, loading and testing conditions, and material types. Both the classical DEM model and the pore scale finite volume (PFV)-coupled DEM model are used to simulate the response of saturated uncemented and lightly cemented sands with a rigid wall boundary under both drained and undrained triaxial compression. A DEM model with flexible boundaries created using particle facet (PFacet) elements is used to simulate undrained triaxial compression of moderately cemented sands, including the influence of confining stress. The PFacet-based model is used to predict the transition from barreling failure to shear banding when the confining stress or the cementation degree increases. The classical DEM model with cohesive bonds of uniform strength is also used to successfully simulate the uniaxial compression response of a sand with an extremely high degree of cementation. Finally, this paper presents a particle-packing model consisting of multiple solid phases for cemented sands based on the understanding that not all particle types will have the same cohesive properties. This multiple solid-phase model is a refinement of the classical DEM model that represents the particle physics more realistically, especially for heterogeneous systems. A preliminary parametric study is carried out considering varying cohesive properties and volume fractions for the different solid phases.

Knowledge Gaps in Quantifying the Climate Change Response of Biological Storage of Carbon in the Ocean

AbstractThe ocean is responsible for taking up approximately 25% of anthropogenic CO2 emissions and stores &gt;50 times more carbon than the atmosphere. Biological processes in the ocean play a key role, maintaining atmospheric CO2 levels approximately 200 ppm lower than they would otherwise be. The ocean's ability to take up and store CO2 is sensitive to climate change, however the key biological processes that contribute to ocean carbon storage are uncertain, as are how those processes will respond to, and feedback on, climate change. As a result, biogeochemical models vary widely in their representation of relevant processes, driving large uncertainties in the projections of future ocean carbon storage. This review identifies key biological processes that affect how ocean carbon storage may change in the future in three thematic areas: biological contributions to alkalinity, net primary production, and interior respiration. We undertook a review of the existing literature to identify processes with high importance in influencing the future biologically‐mediated storage of carbon in the ocean, and prioritized processes on the basis of both an expert assessment and a community survey. Highly ranked processes in both the expert assessment and survey were: for alkalinity—high level understanding of calcium carbonate production; for primary production—resource limitation of growth, zooplankton processes and phytoplankton loss processes; for respiration—microbial solubilization, particle characteristics and particle type. The analysis presented here is designed to support future field or laboratory experiments targeting new process understanding, and modeling efforts aimed at undertaking biogeochemical model development.

Low energy alpha particles dose mapping with a combination of CR-39 detector and a high resolution flatbed scanner

The potential of a combination of the well-known CR-39 detector and a high-resolution flatbed scanner for low energy alpha particles dose mapping is investigated. The CR-39 detectors were irradiated with perpendicular incident 4 MeV alpha particles of doses 0.009, 0.018, 0.033, 0.051, 0.067, 0.134, and 0.164 Gy, thereafter, etched in 6.25 N NaOH at 70 °C. The CR-39 detectors were scanned with Canon CanScan 9000F Mark II of spatial resolution of 9600 dpi and color depth of 48 bit. The measurements reveal that the pixel values for different color channels are correlated linearly with 4 MeV alpha particles dose at the etching times of 2 h, 3 h, and 4 h. For blue channel, the maximum sensitivity was −53178 ± 1463 pixel value/Gy at etching time of 4 h, compared to −15290 ± 2004 pixel value/Gy, and −42255 ± 840 pixel value/Gy at 2 h and 3 h respectively, the negative sign indicates the pixel values decrease as the 4 MeV alpha particles dose increases. While for etching times, 5 h and 6 h, the pixel values decrease exponentially as the 4 MeV alpha particles dose increases. For prolonged etching time, the pixel values are non-monotonic function of alpha particles dose. The optical density was evaluated as a function of etching time (removal thickness) of CR-39 irradiated with different doses. For 0.009 Gy, and 0.018 Gy doses of alpha particles, the optical density is linearly correlated with the etching time; for other doses, the optical density is not a monotonic function of the etching time. These new findings pave the way to use the combination of the CR-39 detector and high-resolution flatbed scanner for dose mapping of alpha particles and heavy ions over large-scale areas, applying etching conditions for each particle type and corresponding energy, that produce maximum sensitivity and linearity.

Identification and Root Cause Analysis of the Visible Particles Commonly Encountered in the Biopharmaceutical Industry.

Visible particle is an important issue in the biopharmaceutical industry, and it may occur across all the stages in the life cycle of biologics. Upon the occurrence of visible particles, it is often necessary to conduct chemical identification and root cause analysis to safeguard the safety and efficacy of the biotherapeutic products. In this article, we present a number of typical particles and relevant root cause analysis in the categories of extrinsic, intrinsic and inherent particles that are commonly encountered in the biopharma industry. In particular, the optical images of particles obtained both in situ and after isolation are provided, along with the spectral and elemental information. The particle identification was carried out with multiple microscopic and microspectroscopic techniques, including stereo optical microscopy, Fourier transform infrared microscopy, confocal Raman microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. Both commercial and in-house spectral databases were used for comparison and identification. In addition to particle identification, our significant efforts are placed on the root cause analysis of the addressed particles with the intention to provide a relatively whole picture of the particle related issues and practical references to particle mitigation for our peers in the biopharmaceutical industry.

Synthesis and Characterization of Grewia asiatica-Stabilized Silver Nanoparticle as a Selective Probe for Al+3 in Tap, Deionized, Industrial Waste Water and Human Blood Plasma

Aluminum can be found in water and vegetables in the form of the trivalent ion (Al3+), which can potentially contaminate food and water. Overconsumption of aluminum can lead to serious health problems in humans. Therefore, there is a need for an economical and simple procedure to detect the presence of aluminum. In this study, we synthesized a conjugate of Grewia asiatica extract with silver nanoparticles. The nanoparticle-stabilized fruit extract of Grewia asiatica was found to be an extremely selective sensor of Al3+ in tap water, DI water, industrial wastewater, and human blood plasma. We characterized the Grewia asiatica-conjugated silver nanoparticles (GA-AgNPs) using UV-visible, SEM, and AFM techniques and found that they were stable in an extensive pH range and different electrolyte concentrations up to 10 M NaCl. The GA-AgNPs were circular in shape with typical particle sizes of 65–97 nm. We inspected the photo physical properties of GA-AgNPs concerning metallic ions using UV-visible spectroscopy and found that they were highly selective for Al3+ ions, with no interfering ions detected in competitive experimentation. The absorption intensity of GA-AgNPs was directly related to Al3+ concentration over a wide range of concentrations (6.25–500 μM). Jobs plot experiment displayed 1 : 1 binding stoichiometry between GA-AgNPs, and Al3+. Additionally, GA-AgNPs were effectively utilized for the recognition of Al3+ in laboratory tap water, DI water, industrial wastewater, and human blood plasma.

Effect of heat treatment on microcracking behaviors and Mode-I fracture characteristics of granite: An experimental and numerical investigation

Combining thermal stimulation and tensile fracture induced by cold water injection can synergistically enhance hydraulic fracturing, improving geothermal reservoir connectivity. To investigate the heat effect on the Mode-I fracture characteristics of granite, notched semi-circular bend (SCB) granite specimens were prepared and heat-treated at five temperatures ranging from 25 to 600 ℃. Mineralogical analysis and three-point bending tests were performed on the SCB specimens, and a grain-based model (GBM) incorporating four types of mineral particles was developed. The model was simulated for heat treatment and Mode-I loading and then validated against experimental results. The behavior and evolution of intra- and intergranular microcracks in the SCB specimens during heating, cooling, and mechanical loading were analyzed. Moreover, the fracture surface morphology and microcracking mechanisms observed in the SCB specimens at different heat-treatment temperatures were discussed. The results reveal a nonlinear trend in the Mode-I fracture toughness of the SCB specimens, initially increasing and then decreasing with heat-treatment temperature. The number of thermally induced cracks escalates with increasing heat-treatment temperature, predominantly as intergranular tensile cracks, followed by intragranular tensile cracks. Under Mode-I loading, the SCB specimens heat-treated below 450 ℃ predominantly exhibit intergranular cracks, while intragranular tensile cracks become more prevalent at 600 ℃. Thermally induced cracks can alter the propagation direction and path of mechanically induced cracks, causing macrocracks to deviate from the initial straight propagation path. Scanning electron microscope (SEM) analysis illustrates that at 300 ℃ and above, the fracture surface morphology becomes more fragmented and longer microcracks appear.

Differences and similarities in optical properties of coated fractal soot and its surrogates

Atmospheric soot (or black carbon, BC) affects climate through solar light absorption and scattering, which depend strongly on the particle morphology and composition. Initially, soot particles are fractal aggregates of spherules made of elemental carbon (EC), but condensation of atmospheric trace vapors adds non-EC materials and often results in particle compaction. The optical properties of such processed soot differ from those of fractal soot, and the changes are caused both by particle volume increase from coating addition and by restructuring of the EC backbone. In laboratory studies of soot optics, surrogates such as carbon black (CB) and nigrosin are often used in place of flame-generated soot. Our goal was to investigate if compositional and morphological differences between these surrogates and soot may produce different processing rates and optical responses. In our experiments, we generated fractal soot, compact CB, agglomerated CB (via coagulation of compact CB), and spherical nigrosin aerosol particles, subjected them to supersaturated vapor of dioctyl sebacate (DOS) to form a coating layer, and investigated the morphological response of these four particle types to coating addition and removal. Using coated and coated-denuded aerosol particles with known composition and morphology, we quantified the contributions of volume increase and restructuring to light scattering and absorption enhancements. By comparing experimental measurements against different particle optics models we show that it is crucial to account for larger, multiply charged particles present in the mobility-classified aerosol. Producing a disproportionately high contribution to absolute values of optical cross sections, such larger particles also result in lesser optical enhancements due to slower growth by vapor condensation. Scattering increases for all particle types due to the addition of a coating layer, and also due to restructuring for fractal soot (strongly) and agglomerated CB (weakly). Absorption increases only due to coating addition caused by the coating layer for all particle types. We find that simple optical models, such as Mie, are often sufficient to provide reasonable closure with experimental results for bare and coated aerosols, but only after accounting for the contributions from multiply charged particles, both in terms of their stronger optical cross sections and slower condensational growth. We conclude that CB is an appropriate surrogate for soot in aerosol aging studies where the effects of restructuring do not need to be considered and that nigrosin can be used as a general model for light-absorbing aerosols but is not representative of optical properties of soot.