50-μm Particles Research Articles

Maximizing the Processing of Polymetallic Concentrates via Actinide Separation and Rare Earth Retrieval

During the last decades, the growing demand for rare earth elements (REEs) has led to numerous recent studies to recover these elements from various bearing ores and wastes. Therefore, the recovery of REEs from Ras Baroud polymetallic concentrate has been investigated in the current study. Physical beneficiation for the Ras Baroud pegmatite sample was carried out, yielding a concentrate for euxenite (Y), fergusonite (Y), xenotime (Y), monazite (Ce), allanite, thorite, uranothorite, and Hf-zircon, which resulted in raising the concentrations of rare earth elements, Th, Zr, U, and Ti in the sample. Fusion digestion processes with sodium hydroxide were studied using the Conceived Predictive Diagonal (CPD) technique. The three experimental digestion groups proved the dissolution of 99.9, 95.6, 99.9, 52.5, and 0.47% for REEs, Th, U, Ti, and Zr, respectively, under fusion conditions of 723 K, 120 min, 1/1.5 ore/alkali ratio, and − 100-μm particle sizes. Fusion kinetics, isotherms, and thermodynamics were investigated using several suggested models, namely, pseudo reversible first order, uptake general model, and shrinking core model which matched well with the experimental digestion results. Selective recovery of actinide content from REE content of the digested concentrate chloride solutions was accomplished using solvent extraction with di-2-ethyl hexyl phosphoric acid. About 99.9, 99.9, and 4.2% extraction efficiencies for Th, U, and REEs were performed, respectively, using 0.3 mol/L solvent concentration in kerosene as a diluent, 1/2 organic to aqueous ratio, an aqueous pH of 0.2, and 15-min contact time. Thorium and uranium ions were stripped with sulfuric acid solution 2.5 mol/L with 94 and 98% stripping efficiency, respectively. A highly purified REE precipitate was obtained from the raffinate solutions. Zircon mineralization tailings were obtained as a by-product through the alkaline digestion process.

DEVELOPMENT OF COMPOSITE MATERIALS FOR TRICYCLE BRAKE PADS

Coconut fiber and rice dust are locally sourced, developed, and evaluated as agro-waste materials to replace carcinogenic asbestos fibers in brake pad production. The process involves crushing, grinding, and sieving coconut fiber into a powder, mixing it with steel dust, carbon black, and epoxy resin, filling a mould, adding hardener, and pressing and curing samples at 250 °C. The produce is tested for mechanical properties, with optimal brake pad properties achieved using a 100μm sieve grade, enhancing interfacial bonding between resin and coconut shell particles. The hardness, compressive strength, ash content, specific gravity, wear rate, and water absorption values were found to be 258, 113 N/mm2, 40%, 1.91, 3.23 mg/m, and 0.63%. The study found that coconut shell has qualities similar to those needed for brake pad material and asbestos replacement in brake pad production. Coconut shell, with its 100μm particle size, has the potential to replace asbestos-based brake pad manufacturing, reducing harmful components and environmental impact.

Crystallographic and Topographic Analysis of Ultra-Translucent Zirconia After Various Surface Treatments

The aim of the present study was to analyze the effects of 4 different surface treatments, on the crystallographic characteristics of Ultra-Translucent Zirconia. Fully sintered zirconia specimens of highly translucent yttria partially stabilized zirconia (Y-PSZ) (KATANA UTML) were divided into four experimental groups and a control group (n=10). Each group received one of the following surface treatments: sandblasting with 50µm alumina particles (Al₂O₃), sandblasting with 110µm alumina particles, and grinding with a rotary high-speed turbine with and without water irrigation. For each sample, x-ray diffraction was carried out to analyze peak intensity, calculate the crystallite size, and detect the presence of compressive and tensile stress. Surface roughness was measured on all specimens using a standard scanning profilometer. Additionally, scanning electron microscopy (SEM) was performed to qualitatively analyze the surfaces of the specimens. Statistical analysis included repeated measures analysis of variance and post hoc Tukey test (p≤0.05). The control group exhibited the highest crystallite size (323nm). All surface treatments led to a reduction in the crystallite size, with the most significant reduction observed in the groups subjected to sandblasting with 110µm alumina particles and high-speed grinding with irrigation. Sandblasting with 50µm alumina particles resulted in less transformation of the crystallite size. A general tendency of the diffraction peaks to shift to a lower angle can be observed in the experimental groups, indicating the presence of compressive stress on the samples. Profilometry revealed higher roughness in the ground samples (6,14µm and 6,57µm) compared to the sandblasted groups (2,93µm and 2,02µm). The crystal domain size showed a tendency to decrease after the surface treatments. Sandblasted samples, as well as ground samples without irrigation, exhibited compressive stress. Sandblasted samples had lower surface roughness compared to the ground samples. Sandblasting with 50µm alumina particles caused the least decrease in crystallite size.

Increasing aggregate size reduces single-cell organic carbon incorporation by hydrogel-embedded wetland microbes.

Microbial degradation of organic carbon in sediments is impacted by the availability of oxygen and substrates for growth. To better understand how particle size and redox zonation impact microbial organic carbon incorporation, techniques that maintain spatial information are necessary to quantify elemental cycling at the microscale. In this study, we produced hydrogel microspheres of various diameters (100, 250, and 500μm) and inoculated them with an aerobic heterotrophic bacterium isolated from a freshwater wetland (Flavobacterium sp.), and in a second experiment with a microbial community from an urban lacustrine wetland. The hydrogel-embedded microbial populations were incubated with 13C-labeled substrates to quantify organic carbon incorporation into biomass via nanoSIMS. Additionally, luminescent nanosensors enabled spatially explicit measurements of oxygen concentrations inside the microspheres. The experimental data were then incorporated into a reactive-transport model to project long-term steady-state conditions. Smaller (100μm) particles exhibited the highest microbial cell-specific growth per volume, but also showed higher absolute activity near the surface compared to the larger particles (250 and 500μm). The experimental results and computational models demonstrate that organic carbon availability was not high enough to allow steep oxygen gradients and as a result, all particle sizes remained well-oxygenated. Our study provides a foundational framework for future studies investigating spatially dependent microbial activity in aggregates using isotopically labeled substrates to quantify growth.

Chemo-Mechanical Durability of Reinforced Fuel Cell Membranes in the Presence of Metallic Foreign Particles

High-throughput production is vital to achieve cost-effective proton exchange membrane fuel cells (PEMFCs) at scale1. The high-volume mass production of PEMFCs using industrial manufacturing machinery may however introduce unwanted material in the final product due to the wear and tear of the machinery. As an example, roll-to-roll processes applied to the manufacture of catalyst coated membrane (CCM) generally use Fe alloys such as stainless steel2 components that could release fine metallic particles or related debris that may affect the product quality3,4. Therefore, it is important to understand the fundamental impact of such non-uniformities on PEMFC performance and durability.This work focusses on the impact of slightly oxidized iron (Fe) and stainless steel 316L (SS316L) micro-particles entrapped between the cathode catalyst layer (CCL) and a GORE-SELECT® Membrane A. Fe cations are considered as Fenton’s catalyst/reagent which enhance harmful radical generation and ionomer attack, known to weaken its mechanical strength and ionic conductivity5. Therefore, membrane electrode assemblies (MEAs) containing solid Fe and SS316L particles were prepared to conduct in-situ PEMFC experiments and identify their impact on membrane degradation and durability. The chosen particles were placed carefully on the bare membrane at selected locations based on the flow field design of the graphite bipolar plates. Later, the assembled MEAs were tested using a small-scale fixture (SSF) fuel cell in a combined chemical and mechanical AST after beginning-of-life (BOL) conditioning and diagnostics6.X-ray computed tomography (XCT) has been shown to be a powerful and non-invasive 3D characterization tool for analyzing membrane degradation7,8. Thus, periodic same-location XCT visualization of the CCL-membrane interface was performed after every 10 AST cycles. According to the Fe Pourbaix diagram9, Fe oxidizes to Fe2+ at 0.77 V and indeed, in this work, complete dissolution of the Fe-50µm particles was observed leaving cavities at the CCL-membrane interface. This dissolution manifested as a distinct black spot in CT imaging, as highlighted by the enclosed red circle in Figure 1. In contrast, corrosion of SS316L particles is usually prevented by a native oxide layer formation during fuel cell operational conditions10. The Fe particle laden AST reached membrane failure within 30 cycles and indicates an escalation of degradation by global membrane thinning. This is substantially lower than the baseline AST without particles. The XCT images for Fe-50µm AST seen in Figure 1 show that severe global membrane thinning occurred in the Fe-50µm MEA, which contributed to a high electrochemical leak detection (ELDT) signal exceeding test failure criteria. In contrast, the SS316L MEA did not reach the threshold failure criteria for the AST duration, however, the average OCV remained lower as compared to the baseline MEA AST. XCT imaging showed that the SS316L- 50µm particles did not dissolve throughout the AST duration and the membrane thinning was more pronounced near the particle rather than globally. Additionally, we have evaluated whether chemically and mechanically mitigated GORE-SELECT Membrane® B could enable more robustness and minimize impact of multiple metallic particles. Analysis of combined chemo-mechanical AST with a larger dimension SS316L-500µm present on mitigated GORE-SELECT® Membrane B suggest that chemical and mechanical mitigation can reduce impact of large particles and enable lifetime response at the level close to baseline. In conclusion, the membrane lifetime and failure mode were found to be strongly dependent on the particle chemical composition and membrane degradation mitigation strategies, which are therefore should be considered at PEM design stages to reduce risks and improve CCM and MEA production quality. Keywords: PEM durability, quality control, cost reduction, XCT Acknowledgments This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Ballard Power Systems, and W.L. Gore & Associates. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program. References H. Tsuchiya and O. Kobayashi, Int. J. Hydrogen Energy, 29, 985–990 (2004).J. Chen, H. Liu, Y. A. Huang, and Z. Yin, J. Manuf. Process., 23, 175–182 (2016).A. Phillips et al., Fuel Cells, 20, 60–69 (2020).A. Phillips, M. Ulsh, K. C. Neyerlin, J. Porter, and G. Bender, Int. J. Hydrogen Energy, 43, 6390–6399.J. G. Goodwin, K. Hongsirikarn, S. Greenway, and S. Creager, J. Power Sources, 195, 7213–7220 (2010).Y. Chen et al., J. Power Sources, 520, 230673 (2022).Y. Chen et al., J. Power Sources, 520, 230674 (2022).Y. Singh et al., J. Power Sources, 412, 224–237 (2019).R. Tolouei et al., Phys. Chem. Chem. Phys., 18, 19637–19646 (2016).N. Kumar et al., Int. J. Energy Res., 44, 6804–6818 (2020). Figure 1

One-step sintering process for high-performance SiC membranes for efficient filtration of dust-laden gas

Silicon carbide (SiC) ceramic membranes are known for their remarkable attributes, including resistance to acid and alkali corrosion, exceptional tolerance to thermal shock, and high mechanical strength. These properties have garnered considerable attention for dust-laden gas filtration. However, large-scale applications of SiC membranes are limited because of the high sintering energy consumption in membrane formation. In this study, a preparation method for high-performance and low-cost SiC membranes using a co-sintering process was proposed. In this method, SiC particles with a 100-μm average particle size were uniformly mixed with sintering aids and SiC green supports were prepared via a dry pressing process. Subsequently, SiC dispersion was coated on the SiC green supports via a spray coating method to prepare membrane layer. Through optimization of the sintering process and sintering atmosphere, the sintering stress difference during co-sintering was released. Finally, a defect-free membrane surface was fabricated. The carbon powder in the green supports was utilized as a pore-forming agent and to prevent small particles in the SiC membrane layers from infiltrating the SiC green supports, decreasing the mass transfer resistance in the application process. The SiC ceramic membrane had a mean pore size and a gas permeance of 3.90 μm and 246.33 m3 m−2 h−1. In addition, when subjected to identical average pore size and porosity conditions, it exhibited a high Darcy's permeability coefficient, indicating favorable structural characteristics for the membrane. Additionally, the membrane was optimized to have a 99.9 % rejection of solid particles in dusty gases, including nanometer (0.3 μm) and micron (2.5 μm) solid particles. This study has introduced a preparation method for low-cost and high-performance SiC membranes for industrial dust-laden gas filtration.

Comparison of retention of monolithic zirconia crowns with alumina airborne-particle abraded and nonabraded intaglio using three different cements: A clinical simulation

The necessity of roughening the intaglio surface of zirconia crowns to achieve adequate retention is unclear. The purpose of this clinical simulation study was to evaluate the retention of airborne-particle-abraded and nonabraded monolithic zirconia crowns using 3 different cement types. Extracted human molars were used and prepared with a 10-degree taper. Impressions were made of the prepared teeth with a polyvinyl siloxane (PVS) material, and dies were made with Type 4 gypsum. Each die was scanned with a NobelProcera 1G Scanner, and the standard tessellation language (STL) files were transferred electronically to the Nobel Biocare production site, where a bar was added virtually on top of each crown and parameters were set for milling. Seventy-two Procera zirconia crowns were generated, of which half were airborne-particle abraded on the intaglio surface with 50-µm alumina particles at 400 to 500 kPa for 15 seconds. The other 36 received no intaglio treatment other than cleaning. Both groups of 36 crowns were divided into 3 subgroups of 12 specimens. The area of each preparation was calculated using a computer-aided design software program. The specimens were distributed to attain similar mean surface areas among the cementation groups. The crowns were cemented onto the specimen with a controlled force of 196N. The 3 cements used were self-adhesive, modified resin RelyX Unicem Aplicap, resin-modified glass ionomer RelyX Luting, and a composite resin, Panavia F2.0 with ED Primer A & B. All specimens were thermocycled (5 °C to 55 °C) for 5000 cycles and then removed axially with a universal testing machine (Instron Model 5585H) at a crosshead speed of 0.5mm/min. The removal force was recorded, and stress of dislodgement was calculated for each crown. A 2-way analysis of variance was used for statistical analyses. The type of failure was analyzed with the chi-squared test of association for independent samples (α=.05 for all tests). The mean dislodging force for crowns with airborne-particle abraded intaglio was 5.4MPa, which was statistically greater than the mean of 3.2MPa for nonabraded specimens (P<.001). No significant differences related to the dislodging stresses were detected among the 3 cements (P=.109). The mode of failure was similar whether abraded or not, with 50% of specimens retaining cement in the crown after separation. Alumina airborne-particle abrasion of the intaglio of zirconia to create surface roughness is beneficial in retaining the crowns, regardless of the cement type. The nonabraded crowns demonstrated significantly lower retentive stress with crown removal. The principal mode of failure was similar whether the zirconia intaglio was airborne-particle abraded or not. The most common mode of failure (>50% of specimens) was at least three-fourths of the cement remaining within the crown.

Influence of engineered roughness microstructures on adhesion and turbulent resuspension of microparticles

From microplastics resuspending into the atmosphere to earth particles left behind during extraterrestrial explorations, the resuspension of microparticles by a turbulent gas flow occurs in many natural, environmental and industrial systems. Wall surfaces, onto which particles initially adhere, are rarely smooth and this surface roughness affects particle resuspension. Available experimental data on particle resuspension have been obtained with substrates, whose surfaces are either unaltered or manually abraded with, for instance, sand blasting. In these experiments, the roughness elements span a wide size range and are in-homogeneously distributed in space. Surface functionalization is a modern technique allowing the precise fabrication of a wall surface with well-characterized microstructures, hence reducing the asperity randomness associated with conventional abrasion techniques. Taking advantage of surface functionalization, we present here a new set of reference data, where the wall asperities are represented by a structured arrangement of micropillars and microcubes. Adhesion force measurements and particle remaining fraction against gas velocity, at Reynolds number up to 8000, are reported for one reference and two artificially roughened substrates. Laboratory measurements show that the microasperities have little to moderate effect on the mean adhesion force and the threshold velocity, at which half of the 100-μm particles resuspend. The standard deviations are, however, much more affected. The presented results will primarily contribute to the improvement of resuspension models, which until now rely on a simplified representation of the surface roughness elements. The presented measurements are highly compatible with such models, which involve elementary roughness features, such as hemispherical asperities superimposed with a flat plate.

Fracture strength of anterior cantilever resin-bonded fixed partial dentures fabricated from high translucency zirconia with different intaglio surface treatments.

To compare the fracture resistance and failure modes of anterior cantilever resin-bonded fixed partial dentures (RBFPDs) fabricated from high translucency zirconia with different intaglio surface treatments. Sound-extracted canines (N=50) were randomly divided into five groups (n=10) to be restored with high translucency zirconia RBFBDs of different intaglio surface treatments. The RBFPD was designed using exocad software and fabricated using a CAM milling machine. The RBFPDs were treated differently: abrasion with 50µm alumina particles (Group 1); abrasion with 30µm silica-coated alumina particles (Group 2); abrasion with silica-coated alumina particles (30µm) and silane application (Group 3); abrasion with silica-coated alumina particles (30µm) and 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) primer application (Group 4); abrasion with silica-coated alumina particles (30µm) and silane, and 10-MDP primer application. All RBFPDs were cemented using dual-cured resin cement. The RBFPDs underwent 6000 thermal cycles with distilled water at 5/55°C for 2min per cycle and then mechanical cyclic loading with 1200,000 cycles of 50N at a 1.7Hz frequency at an angle of 135° to the abutment's long axis. Then, RBFPDs were loaded to fracture using a universal testing machine at 1mm/min. Maximum fracture forces and failure modes were recorded. Fractured specimens and uncemented specimens were examined using a scanning electron microscope. Data was analyzed using ANOVA and Games-Howell post hoc tests at p<0.05. Mean fracture load results showed a statistically significant difference between the research groups (p<0.0001) and it ranged from 69.78 to 584N. Group 4 exhibited the highest fracture load mean (p<0.0001) which was significantly different from all other groups. Group 2 recorded a significantly higher fracture load mean than Group 3 (p=0.029). Three modes of failure were observed: prosthesis debonding, prosthesis fracture, and abutment fracture. Abrasion of zirconia surface with 30µm silica-coated alumina particles and application of 10-MDP primer yielded the highest mean fracture loads of monolithic high translucency zirconia RBFPD. The mode of fracture of the RBFPDs was influenced by the type of surface treatments.

Characterization of trace elements in coal fly ash by extraction, micro-PIXE, TOF-SIMS, and XAFS

Coal fly ash (CFA) contains considerable amounts of potentially hazardous trace elements. Characterization of trace elements in CFA is essential for the safe disposal and recycle of CFA. The objectives of this study were i) to determine and predict the solubility of trace elements in CFA in relation to their chemical and mineralogical properties, and ii) to characterize trace elements using the surface chemical analysis including time-of-flight secondary ion mass spectrometry (TOF-SIMS) and accelerator-based micro particle induced X-ray emission (PIXE) analysis, in combination with X-ray absorption fine structure (XAFS) spectroscopy with a primary focus on As and Cr. The CFA samples from 12 thermal power plants contained B (ave. 203 mg kg−1), F (90 mg kg−1), Cr (63 mg kg−1), As (21 mg kg−1), and Se (3.2 mg kg−1), in which the water soluble fraction relative to the total concentration decreased in the order B (24 %) > Se (23 %) > F (20 %) > As (1.7 %) > Cr(IV) (0.71 %). A regression model indicated that water extractable As and Cr(VI) from CFA increased linearly with increasing SiO2 and CaO in CFA, respectively. The SIMS images showed that B was finely and heterogeneously distributed on CFA, whereas F was distributed homogeneously on CFA. The combined results from micro-PIXE and XAFS revealed that i) As was distributed on about 50-μm particles in the form of As(V) associated with Al and Ca, and ii) Cr was co-located with Fe and Ca on about 50-μm particles and was present as Cr(III). This study demonstrated that the combined results from TOF-SIMS, micro-PIXE, and XAFS techniques enable trace elements in CFA to be better characterized in terms of spatial distribution and chemical speciation.

Quality Implications of Foreign Metallic Particles in the Membrane Electrode Assembly of a Fuel Cell

Hydrogen-based polymer electrolyte membrane fuel cells (PEMFCs) are advantageous in terms of high efficiency, zero emissions, and low-temperature operation in both stationary and transportation sectors. Recently, efforts to reduce the cost by developing novel materials used in the membrane electrode assembly (MEA) and its design are underway. Besides the materials, the other factor that could contribute to cost reduction is the high volume production of MEA components with a high yield1. Additionally, during MEA assembly, certain abnormal process conditions or external contaminants may negatively affect the quality of the MEA and its compatibility with scalable high-volume manufacturing. The durability of the perfluorosulfonic acid (PFSA) ion exchange membrane is a major concern for the fuel cell industry, especially under Fenton’s cations such as Fe2+ 2–5.Stainless steel instruments used during the production of catalyst coated membranes (CCMs) may be considered as a possible source contributor of contamination. Micron sized metallic particles of SS316L (or Fe) could attach themselves on to the membrane during fabrication; thus, potentially cause MEA structural damage by perforation, rupture, or electrode delamination. Additionally to structural damage, there is also a possibility that Fe2+ cations leaching from metal corrosion would reduce the membrane proton conductivity, cause backbone chain scission, etc2,6. Whereas the presence of cations has been studied extensively in ex-situ Fenton’s reagent testing of ion-exchanged membranes, controlling, and understanding the role of such cations in the in-situ fuel cell environment is much more challenging. In such an instance, membrane thinning and degradation are anticipated due to the presence of cations which act as a catalyst for radical generation during fuel cell operation6; therefore, it is essential to understand the effect of such metallic particles on the membrane and by extension, improving the fundamental understanding of the effects of various irregular features and foreign contaminants is desirable7,8. The present work focuses on understanding the effect of unintended solid metallic particles in the MEA during and after the conditioning phase of a fuel cell. Stainless steel 316L (SS316L) and pure iron (Fe) particles are located conveniently at the interface of the cathode catalyst layer (CCL) and membrane (M) inside an MEA using a robust and controlled method. During the conditioning phase, the MEA is subjected to a sequential order of air starves, cyclic voltammetry, and constant current hold procedures. After each conditioning procedure, cell imaging is performed using the X-ray computed tomography (XCT) method, which has been proven to provide relevant information without damaging the integrity of the fuel cell9,10. Figure 1(a) &(c) shows the position of SS316L and Fe 50µm particles, respectively located at the CCL/M interface before conditioning, as originally planned. Initializing the air starve cycles, the MEAs containing particles indicates that the SS316L-50µm remains intact, as seen in Figure 1(c), and the Fe-50µm tends to dissolve and leave behind a void directly exposing the membrane as shown in Figure 1(d). The dissolution of Fe particles also leaves behind an ion concentration of more than 50 ppm in the active area. It is believed that Fe2+ leaches from SS316L corrosion as well; however, the process is delayed by the native oxide layer formation on its surface and the concentration of Fe2+ is lower. Therefore, it is important to know the response of such particles when conditioning an MEA so that better quality control processes can be identified prior to fuel cell assembly. Acknowledgments This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Ballard Power Systems, and W.L. Gore & Associates. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program. References G. Bender, W. Felt, and M. Ulsh, J. Power Sources, 253, 224–229 (2014) http://dx.doi.org/10.1016/j.jpowsour.2013.12.045.J. G. Goodwin, K. Hongsirikarn, S. Greenway, and S. Creager, J. Power Sources, 195, 7213–7220 (2010) http://dx.doi.org/10.1016/j.jpowsour.2010.05.005.J. Qi et al., J. Power Sources, 286, 18–24 (2015) http://dx.doi.org/10.1016/j.jpowsour.2015.03.142.A. Tavassoli et al., J. Power Sources, 322, 17–25 (2016) http://dx.doi.org/10.1016/j.jpowsour.2016.05.016.N. Kumar et al., Int. J. Energy Res., 44, 6804–6818 (2020).S. Kundu, L. C. Simon, and M. W. Fowler, Polym. Degrad. Stab., 93, 214–224 (2008).S. Komini Babu et al., J. Electrochem. Soc., 168, 024501 (2021).A. Phillips, M. Ulsh, K. C. Neyerlin, J. Porter, and G. Bender, Int. J. Hydrogen Energy, 43, 6390–6399 (2018) https://doi.org/10.1016/j.ijhydene.2018.02.050.D. Ramani et al., Int. J. Hydrogen Energy, 45, 10089–10103 (2020) https://doi.org/10.1016/j.ijhydene.2020.02.013.Y. Singh et al., J. Power Sources, 412, 224–237 (2019). Figure 1

Micro-Explosion mechanism of iron hybrid Methane-Air premixed flames

Compared to gaseous hydrocarbon flame, a metal hybrid flame has higher energy and even has a higher flame temperature. This study explored the micro-explosion mechanisms of iron particles in methane-air premixed flames. Four different particle sizes were used in this experiment, that is 2–10 μm, 50 μm, 100 μm, and 150 μm. A conical methane-air premixed flame was fixed in a stoichiometric condition and doped with iron particles at various feeding rates. The 50- and 100-μm iron particles had a 20% and 500% higher micro-explosion probability than the 2–10-μm particles. The micro-explosion probability would increase with the increase of particle size. In addition, the micro-explosion probability of the 2–10 μm iron particles was 125% higher under 10% CO addition than under no CO addition. CO plays a critical role in increasing the micro-explosion probability of iron particles smaller than 50 µm.Regarding the mechanism of the micro-explosion of iron particles, the oxidizer diffuses into iron particles and produces iron oxide in a thin shell. However, limited oxygen heterogeneously reacts over the surface of the iron particles and produces Fe3O4. Fe3O4 comprises FeO and Fe2O3. However, when CO reacts Fe3O4, this reaction makes Fe3O4 redox into fresh Fe particles, whereas it will lead to FeO while Fe reacts with O2 predominantly. The presence of FeO brings about iron particles blinking and shrinking right after passing the flame front. When CO was dominated in the reaction, it gave rise to the formation of Fe(CO)5 gas bubbles in the film of iron particles. During the agglomeration of the bubbles, incorporating Fe(CO)5, CO, O2, and N2, the iron particles expand gradually and become hollow spherical particles eventually. However, under special conditions, this particle expansion will deteriorate the micro-explosion of the iron particles.

Intervention of personalized ventilation on interpersonal airborne disease transmission

Personalized ventilation (PV) has been integrated to reduce the risk of interpersonal infection exposure in the office environment. Some studies showed that PV systems may increase occupants’ risk of airborne infection. Therefore, the aim of this study is to investigate the intervention of PV on interpersonal airborne disease transmission in office environment. A three-dimensional computational fluid dynamics model (CFD) was developed and experimentally validated in a clean chamber. Then the validated CFD model was used to calculate the diffusion of exhaled droplets under different particle size. Results showed at the size of 0.7μm particles, compared to pure mixing ventilation, the personal ventilation of 6L/s reduced the inhalation fraction （IF）from 0.121% to 0.092%，and the reduction ratio of IF is 23.96%. As of 5μm, the IF also decreased from 0.165% to 0.102%, and the reduction ratio of IF is 38.18%. The percentage of 50μm particles deposited on the ground rises from 6.29% to 43.22% of exhaled particles. Therefore, the personalized ventilation can reduce the risk of inhalation in exposed person, and for large size particles, the number of particles falling on the floor increased greatly, which lead to the risk of resuspension increases. The results may be helpful for maximizing the effect of PV in interpersonal airborne disease control.

Genicular Artery Embolization for the Treatment of Symptomatic Knee Osteoarthritis.

Background:Genicular artery embolization (GAE) is a novel therapy to treat patients with symptomatic knee osteoarthritis (OA) by reducing synovial arterial hypervascularity. This study evaluates the safety and efficacy of GAE for the treatment of symptomatic knee OA.Methods:A prospective, single-center, open-label U.S. Food and Drug Administration-approved investigational device exemption study was conducted. Patients enrolled in the study were 40 to 80 years old, with moderate or severe knee OA (Kellgren-Lawrence grade 2, 3, or 4), who previously had failure of conservative therapy. Baseline pain (visual analog scale [VAS]) and symptom scores (Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC]) were assessed. After femoral arterial access was achieved, GAE of 1, 2, or 3 genicular arteries supplying the location of the subject’s pain, as determined by digital subtraction angiography and cone-beam computed tomography, was performed using 100-μm particles. Adverse events and symptoms scores were assessed at 1 week, 1 month, 3 months, 6 months, and 1 year after GAE.Results:Over a 10-month period, 40 subjects were enrolled. The median age was 69 years (range, 49 to 80 years). The median body mass index was 29 kg/m2 (range, 19 to 44 kg/m2). Knee OA severity was grade 2 in 18% of the patients, grade 3 in 43%, and grade 4 in 40%. Technical success was achieved in 100% of the subjects. Transient skin discoloration and transient mild knee pain after the procedure were common and expected. Treatment-related adverse events included a groin hematoma requiring overnight observation in 1 subject, self-resolving focal skin ulceration in 7 subjects, and an asymptomatic small bone infarct on magnetic resonance imaging at 3 months in 2 subjects. The WOMAC total and VAS pain scores decreased by 61% and 67% at 12 months from a median baseline of 52 (of 96) and 8 (of 10), respectively. Twenty-seven patients (68%) had a reduction of ≥50% in both WOMAC total and VAS pain scores.Conclusions:This prospective trial demonstrates that GAE is effective and durable in reducing pain symptoms from moderate or severe knee OA that is refractory to other conservative therapy, with an acceptable safety profile.Level of Evidence:Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Abstract No. 16 Genicular artery embolization for the treatment of knee osteoarthritis: final results from a prospective investigational device exemption trial

Genicular artery embolization (GAE) is a promising therapy to treat patients with symptomatic knee osteoarthritis (OA) by reducing synovial arterial hypervascularity. This study evaluates the safety and efficacy of GAE for the treatment of symptomatic knee OA. A prospective, single-center, open-label FDA-approved IDE study was conducted to evaluate the safety and efficacy of GAE for the treatment of symptomatic knee OA. Included patients were age 40-80 years, with moderate or severe focal knee pain and osteoarthritis on knee radiograph (Kellgren-Lawrence 2-4), had no prior knee surgery, and were not candidates or not willing to undergo total knee replacement surgery. Patients had to have failed conservative therapy, including NSAIDs and/or joint injections. Baseline pain (visual analog scale) and symptom scores (WOMAC) were assessed. Median age was 69 years (range 49-80). Median BMI was 28 (range 18-44). Knee OA severity based on Kellgren-Lawrence scale: 18% with grade 2, 43% with grade 3, and 40% with grade 4. After obtaining femoral arterial access, genicular artery embolization was performed using 100-μm particles (Embozene, Varian) of 1-3 genicular arteries supplying the location of the subject’s pain, as determined by digital subtraction angiography and cone-beam CT. Adverse events and symptoms scores were assessed at 1 week, 1 month, 3 months, 6 months, and 1 year after GAE. Over a 9-month period, 40 patients were treated with GAE. The left knee was treated in 25/40 (62%) subjects, and the right knee was treated in 15/40 (38%) subjects. Medial knee pain was treated in 27/40 (68%) and lateral knee pain was treated in 13/40 (32%). Technical success was achieved in 100% of subjects. Transient skin discoloration and transient mild post-procedure knee pain were common and expected. Treatment-related adverse events included: 1 subject with a groin hematoma requiring overnight observation, 7 subjects with self-resolving focal skin ulceration, and 2 subjects with asymptomatic small bone infarct on MRI at 3 months. WOMAC and pain scores decreased from median of 52 (of 96) and 8/10 at baseline to 21/96 (60% decrease) and 3/10 (63% decrease) at 12 months, respectively. 27/40 (67.5%) and 28/40 (70%) had greater than 50% reduction in WOMAC and pain scores, respectively. This prospective trial demonstrates that GAE is highly effective and durable in reducing symptoms due to moderate to severe knee OA that is refractory to other conservative therapy and has an acceptably low toxicity profile.

Use of Acid for Oxide Layer Removal of Overcast UCLA Abutments: Influence on Fit and Roughness.

The objective of this study was to evaluate the influence of the oxide layer removal procedure using acid on the roughness and internal fit of overcast universal castable long abutments (UCLAs) for a taper connection. For this, maxillary first premolars were waxed on the plastic sleeve of 15 UCLAs with a premachined interface. The specimens were overcast using the NiCr alloy, and the frameworks were randomly distributed to undergo one of two different oxide layer removal methods: blasting with 100-μm particles of aluminum oxide at 0.60-MPa pressure or bathing for 5 hours in 0.5% hydrofluoric acid. The surface roughness was evaluated by a light interferometer at the subcritical contour of each abutment. Next, the frameworks were attached to the respective analogs for internal fit evaluation. The central cross section of each assembly was exposed, and three regions were visualized by scanning electron microscopy (SEM): taper interface, axial wall, and index region. The premachined base was used as the control. The groups were compared using analysis of variance (ANOVA) and Tukey post hoc test (α = .05). The results showed that acid bathing produced intermediary roughness between premachined and blasted surfaces (P < .05). SEM images showed a sealed interface at the taper region of all groups, despite some irregularities after alumina blasting. Increased discrepancies at the axial wall and index region were found after the alumina blasting procedure (P < .05). It was concluded that acid bathing should be used, instead of blasting to remove the oxide layer, to produce a better fit and smoother surface on UCLAs.

Comparative Study of Chemical and Mechanical Surface Treatment Effects on The Shear Bond Strength of Polyether-Ether-Ketone to Veneering Resin.

To assess the shear bond strength of composite resin to polyether ether ketone (PEEK) after mechanical and chemical surface treatments. A total of 48 PEEK discs were fabricated and divided equally into four surface treatment groups (n = 12 each): (1) airborne particle abrasion with 50-μm alumina particles at 2 MPa pressure for 10 seconds; (2) 98% sulfuric acid etching for 1 minute; (3) airborne particle abrasion and sulfuric acid etching; and (4) no surface treatment. Specimens were conditioned, then Gradia composite veneer (GC) was applied to the PEEK surfaces and polymerized. Bond strength was measured with shear bond test using a universal testing machine. One-way analysis of variance and Tukey post hoc tests were applied for statistical analysis. The mean shear bond strength values of the sulfuric acid-etched group were higher than that of the airborne particle abrasion + acid etching, airborne particle abrasion, and control groups (P < .05). Mean shear bond strength values for the airborne particle abrasion + acid etching samples were higher than for the control and airborne particle abrasion groups (P < .05). There was no significant difference between the samples treated with airborne particle abrasion and the control group.

Design of taste-masked swellable drug particles using dry-coating technology with mechanical curing

A novel dry coating technique for fine particles that does not require any liquids has been developed. Swellable ordered-mixed drug particles (Swell-OM-spheres, SOS), using a modified starch as the core particle and a drug coating layer have been previously developed. In the present work, SOS particles were further processed to generate 100-μm taste-masking particles using an all dry coating processes. SOS particles were coated with a gastric-soluble powder using a mechanical powder processor. The coated particles (CPs) were subsequently heated while rotating in the same powder processor, completing film formation by a process termed dynamic curing. As a control, conventional film formation (static curing) was performed using a drying oven. The CPs obtained by these two curing processes had distinct appearances, but exhibited equivalent dissolution suppression effects in a medium at pH 6.8 (the pH of the oral cavity). The suppression effect was further improved by adding a plasticizer to the coating powder, even though a lower heating temperature was required. Orally disintegrating tablets incorporating these CPs exhibited excellent taste-masking performance, i.e., suppressing taste in saliva while accelerating dissolution in gastric juice. The dissolution behavior indicated that the CPs can provide an ON/OFF switching function in drug release.

Development and uncertainty estimation of cryogenic homogenization and static headspace–gas chromatography–mass spectrometry method for the simultaneous determination of twelve toxic volatiles in disposable menstrual products

Volatile organic compounds (VOCs) threaten the health of women who use disposable menstrual products (DMPs). In this study, we aimed to develop a simple and reliable analytical method using a cryogenic mill and static headspace–gas chromatography–mass spectrometry (HS-GC-MS) for the simultaneous determination of twelve toxic VOCs in DMPs, and estimate the measurement uncertainty of the method using the bottom-up approach to ensure the quality of analytical results. Static HS conditions for the direct thermal extraction of the target VOCs from the cryogenically ground sample powders were optimized in terms of extraction temperature and equilibrium time. The separation was achieved using a GC-MS equipped with a VF-624ms column. Cryogenic mill homogenized DMP into powder with 100-μm particles in scanning electron microscopy study. Sample powder was demonstrated to be homogenous as assessed by the homogeneity test. Validation studies showed that the method has reliable performance characteristics: linearity (R2 ≥ 0.9994), limit of quantification (LOQ, 8.4–50.5 ng g−1), precision (relative standard deviation ≤ 18.7%), and accuracy (recovery = 83.4–114.2%) for all the analytes. The proposed method was successfully applied to the commercial products of disposable sanitary pads and tampons. The content of styrene was the highest, followed by those of toluene, hexane, and ethylbenzene. The quantitative data exhibited acceptable precision, as evaluated using the intra-laboratory Horwitz ratio. The expanded uncertainties estimated at three concentration levels ranged from 6.4% to 77.9%. Our simple and reliable method will be useful for quality control testing or quantitative risk assessment and will contribute to resolving the safety issues associated with the risk of human exposure to trace volatile residues in DMPs.

Human and ecological risk assessment of heavy metals in different particle sizes of road dust in Muscat, Oman.

Heavy metal contamination of Hg, As, Cu, Cr, Zn, and Pb was investigated in three different fractions 45, 125, and 200μm of road dust in Muscat, Oman. Dust samples were collected from three different traffic roads, viz. high, medium, and low based on traffic volume and then sieved individually before they analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES). Cu has the highest level among the analyzed metals while the lowest amount was for Hg. Most of the metals in all traffic sites have higher concentration in finer fraction and the concentrations of Cu, Pb, and Zn in HT road dust decreased significantly from finer fraction (45μm) to bigger fraction size (200μm). The risks of analyzed heavy metals to the urban ecosystem and human health were calculated by the potential ecological risk index and human exposure model, respectively. Risk index levels of studied metals in the three fractions and roads vary from strong to very strong potential. Hg found to have the greatest contribution in risk index in the three different fractions and roads. The values of risk levels for individual metal contamination in the dust street samples from different roads and fractions were ranked in the following order: Hg > Cu > Pb > Cr > Zn. Ingestion is the main pathway of exposure to road dust particles for both children and adults, followed by dermal contact absorption. The HI for children and adults exposed to 45- and 125-μm particles were higher than exposed to 200-μm particles, which indicated that finer particles tend to have higher non-carcinogenic risk. The non-carcinogenic risks of the studied heavy metals to children and adults are within safe threshold value; however, health risks of Cr, Pb, and Cu were relatively high for children.