| 1. |
- Bergman, Fanny, et al.
(författare)
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Physicochemical metamorphosis of re-aerosolized urban PM2.5
- 2024
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Ingår i: Journal of Aerosol Science. - : Elsevier Ltd. - 0021-8502 .- 1879-1964. ; 181
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Tidskriftsartikel (refereegranskat)abstract
- The toxicity of particulate matter (PM) is dependent on particle physical and chemical properties and is commonly studied using in vivo and in vitro approaches. PM to be used for in vivo and in vitro studies is often collected on filters and then extracted from the filter surface using a solvent. During extraction and further PM sample handling, particle properties change, but this is often neglected in toxicology studies, with possible implications for health effect assessment. To address the current lack of knowledge and investigate changes in particle properties further, ambient PM with diameter less than 2.5 μm (PM2.5) was collected on filters at an urban site and extracted using a standard methanol protocol. After extraction, the PM was dried, dispersed in water and subsequently nebulized. The resulting aerosol properties were then compared to those of the ambient PM2.5. The number size distribution for the nebulized aerosol resembled the ambient in terms of the main mode diameter, and >90 % of particle mass in the nebulized size distribution was still in the PM2.5 range. Black carbon made up a similar fraction of PM mass in nebulized as in ambient aerosol. The sulfate content in the nebulized aerosol seemed depleted and the chemical composition of the organic fraction was altered, but it remains unclear to what extent other non-refractory components were affected by the extraction process. Trace elements were not distributed equally across size fractions, neither in ambient nor nebulized PM. Change in chemical form was studied for zinc, copper and iron. The form did not appear to be different between the ambient and nebulized PM for iron and copper, but seemed altered for zinc. Although many of the studied properties were reasonably well preserved, it is clear that the PM2.5 collection and re-aerosolization process affects particles, and thus potentially also their health effects. Because of this, the effect of the particle collection and extraction process must be considered when evaluating cellular and physiological outcomes upon PM2.5 exposure. © 2024 The Authors
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| 2. |
- Bergman, Fanny, et al.
(författare)
-
Physicochemical metamorphosis of re-aerosolized urban PM2.5
- 2024
-
Ingår i: Journal of Aerosol Science. - : Elsevier Ltd. - 0021-8502 .- 1879-1964. ; 181
-
Tidskriftsartikel (refereegranskat)abstract
- The toxicity of particulate matter (PM) is dependent on particle physical and chemical properties and is commonly studied using in vivo and in vitro approaches. PM to be used for in vivo and in vitro studies is often collected on filters and then extracted from the filter surface using a solvent. During extraction and further PM sample handling, particle properties change, but this is often neglected in toxicology studies, with possible implications for health effect assessment. To address the current lack of knowledge and investigate changes in particle properties further, ambient PM with diameter less than 2.5 μm (PM2.5) was collected on filters at an urban site and extracted using a standard methanol protocol. After extraction, the PM was dried, dispersed in water and subsequently nebulized. The resulting aerosol properties were then compared to those of the ambient PM2.5. The number size distribution for the nebulized aerosol resembled the ambient in terms of the main mode diameter, and >90 % of particle mass in the nebulized size distribution was still in the PM2.5 range. Black carbon made up a similar fraction of PM mass in nebulized as in ambient aerosol. The sulfate content in the nebulized aerosol seemed depleted and the chemical composition of the organic fraction was altered, but it remains unclear to what extent other non-refractory components were affected by the extraction process. Trace elements were not distributed equally across size fractions, neither in ambient nor nebulized PM. Change in chemical form was studied for zinc, copper and iron. The form did not appear to be different between the ambient and nebulized PM for iron and copper, but seemed altered for zinc. Although many of the studied properties were reasonably well preserved, it is clear that the PM2.5 collection and re-aerosolization process affects particles, and thus potentially also their health effects. Because of this, the effect of the particle collection and extraction process must be considered when evaluating cellular and physiological outcomes upon PM2.5 exposure.
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| 3. |
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| 4. |
- Gren, Louise, et al.
(författare)
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Effects of renewable fuel and exhaust aftertreatment on primary and secondary emissions from a modern heavy-duty diesel engine
- 2021
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 156
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Tidskriftsartikel (refereegranskat)abstract
- Compared to petroleum diesel, renewable diesel fuels and exhaust aftertreatment systems can reduce primary exhaust emissions that are hazardous to human health and the environment. Secondary aerosol emissions which form upon atmospheric processing have, however, been less studied. This study aimed to quantify the impacts of replacing petroleum diesel with renewable fuels (hydrotreated vegetable oil [HVO] and rapeseed methyl ester [RME]) on primary and secondary aerosol emissions from a heavy-duty diesel engine at different stages of an exhaust aftertreatment system. Emission characterization was obtained by combining a battery of physical characterization techniques with chemical characterization using aerosol mass spectrometry. At engine-out measurements, RME and HVO reduced primary particulate matter (PM) emissions (for example equivalent black carbon [eBC]) and secondary aerosol production (studied with an oxidation flow reactor [OFR]) by mass compared to petroleum diesel. The diesel oxidation catalyst (DOC) reduced primary nucleation mode emissions, reduced the effective density of soot mode emissions, and reduced secondary particle production by mass. The DOC + a diesel particulate filter removed >99% of the particle number and eBC emissions. Volatile PM emissions (for example organic aerosol) were found to be distributed between the nucleation mode and soot mode for both primary and secondary emissions, to a degree that depends on both fuel type and aftertreatment. A high mass concentration of condensable species and a low condensation sink in the soot mode led to increased fractions of condensable species present in the nucleation mode. Aging in the OFR led to increases in particle effective density. Motoring the engine (running without combustion) showed that the nucleation mode originated primarily from lubricating oil, and nonvolatile nanoparticle emissions were identified down to 1.2 nm in particle size. In conclusion, replacing petroleum diesel with HVO and RME changes emission characteristics and can help reduce key aerosol emissions of relevance for adverse health and climate impact, especially for diesel engines with no or limited exhaust aftertreatment.
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| 5. |
- Hazeri, Mohammad, et al.
(författare)
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Regional deposition of the allergens and micro-aerosols in the healthy human nasal airways
- 2021
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502 .- 1879-1964. ; 152
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Tidskriftsartikel (refereegranskat)abstract
- The nasal cavity is the inlet to the human respiratory system and is responsible for the olfactory sensation, filtering pollutant particulate matter, and humidifying the air. Many research studies have been performed to numerically predict allergens, contaminants, and/or drug particle deposition in the human nasal cavity; however, the majority of these investigations studied only one or a small number of nasal passages. In the present study, a series of Computed Tomography (CT) scan images of the nasal cavities from ten healthy subjects were collected and used to reconstruct accurate 3D models. All models were divided into twelve anatomical regions in order to study the transport and deposition features of different regions of the nasal cavity with specific functions. The flow field and micro-particle transport equations were solved, and the total and regional particle deposition fractions were evaluated for the rest and low activity breathing conditions. The results show that there are large variations among different subjects. The standard deviation of the total deposition fraction in the nasal cavities was the highest for 5 x 10(4) impaction parameter (IP)<1.125 x 10(5) with a maximum of 20%. The achieved results highlighted the nasal cavity sections that are more involved in the particle deposition. Particles with IP = 30,000 deposit more in the middle turbinate and nasopharynx areas, while for particles with IP = 300,000, deposition is mainly in the anterior parts (kiesselbach and vestibule regions). For small IP values, the amounts of deposition fractions in different regions of the nasal cavity are more uniform.
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| 6. |
- Jönsson, Linnéa, et al.
(författare)
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The effect of electrode composition on bimetallic AgAu nanoparticles produced by spark ablation
- 2024
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Ingår i: Journal of Aerosol Science. - 0021-8502. ; 177
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Tidskriftsartikel (refereegranskat)abstract
- A flexible way to generate bimetallic nanoparticles with high control of their composition is to use spark ablation of alloyed electrodes. It has been generally accepted and stated that particles produced using spark ablation of alloyed electrodes obtain the same chemical composition as the electrodes. However, we identify a lack of studies fully supporting the connection between electrode and particle composition, presented in a small literature survey. The aim of the study is, hence, to explore the validity of the statement by analysing the relation between alloyed electrodes and their resulting particle composition using three sets of AgAu electrodes containing Au and 25, 50, and 75 atomic % Ag, respectively. The resulting composition is thoroughly investigated using both single particle (scanning- and transmission electron microscopy) and ensemble particle techniques (inductive coupled plasma-mass spectroscopy, x-ray photoelectron spectroscopy, x-ray fluorescence, and optical measurements of surface plasmon resonance. We also investigate how sample size (e.g., the number of particles analysed) affects the reliability of the resulting sample mean. For single-particle measurements of a sample with a compositional standard deviation of a few atomic percentage points, a sample size of 20 particles is a good benchmark for obtaining reliable results of the sample mean. Furthermore, this article aims to challenge the practice in which the composition of nanoparticles is measured, presented, and interpreted, to improve and facilitate future research related to this topic. From the results of this study, it could be concluded that for the investigated Ag–Au material system, the particles obtained a composition very similar to the alloyed AgAu electrodes.
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| 7. |
- Karlsson, Anders, et al.
(författare)
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Numerical scattering simulations for estimating soot aggregate morphology from nephelometer scattering measurements
- 2022
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 159
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Tidskriftsartikel (refereegranskat)abstract
- Nephelometers are regularly used for air quality monitoring through scattering measurements of aerosols in the atmosphere. Less attention has been paid to the potential of estimating soot morphological parameters from nephelometer measurements in combination with scattering theory. In this work, we perform a fundamental laboratory study where an Ecotech Aurora 3000 nephelometer is used for measuring the scattering properties of soot with different characteristics. The nephelometer monitors the forward and backward scattering at three wavelengths (450 nm, 525 nm, and 635 nm) to retrieve information on the ratio of forward and backward scattering intensities, as well as the scattering wavelength dependence. An inverse scattering method, based on the Rayleigh–Debye–Gans theory, for determination of the equivalent fractal dimension (Df) and radius of gyration (Rg) of soot particles from the experimental scattering data was developed. It is shown that the inverse method can estimate Rg and Df when Rg<185nm and from the wavelength dependence, information on the relative amount of organic soot could be obtained. For validation, estimated parameters are compared with the morphological parameters of soot sampled from the mini-CAST soot generator and evaluated using transmission electron microscopy (TEM). Uncertainties and limitations of the procedure are discussed.
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| 8. |
- Lu, Junjing, et al.
(författare)
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An improved sectional model to simulate multi-component aerosol dynamics in a containment of pressurized water reactor
- 2021
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502 .- 1879-1964. ; 157
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Tidskriftsartikel (refereegranskat)abstract
- Simulating an evolving aerosol population in a reactor containment is essential for estimating the radioactivity that is possible to leak to the environment. In this study, a sectional model is developed to simulate multi-component aerosol dynamics in the containment during severe ac-cidents of a pressurized water reactor by improving the widely used MAEROS (Multicomponent AEROSol) model. An important advantage of the improved model is its simplified calculation method by introducing a series of correction factors to the equation coefficients when the thermal boundary conditions and the aerosol particle density in the containment change continuously. In addition, the restriction of the maximum section number in the MAEROS model is removed. The reliability of the model is validated against four analytical solutions and three sets of test data. Moreover, the improvements in the model are also proven to be necessary to effectively capture the influences of thermal boundary conditions and aerosol particle density on aerosol dynamics.
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| 9. |
- Lyu, Yezhe, 1987-, et al.
(författare)
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On black carbon emission from automotive disc brakes
- 2020
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502 .- 1879-1964. ; 148
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Tidskriftsartikel (refereegranskat)abstract
- Black carbon, as a series of light-absorbing carbonaceous material, contributes significantly to current global warming. Black carbon has always been considered a product of incomplete combustion of fossil fuels and vegetation. In the road transport sector, combustion exhaust is thought to be the primary source of black carbon. This study uses a pin-on-disc tribometer to simulate automotive disc brake system and investigate its black carbon emission. The results verified the existence of black carbon emission from disc brake system. Brake pad surface treatment and graphite content also have strong influence on black carbon emission of disc brake contact. A scorched brake material features lower black carbon and particulate matter emissions than non-scorched brake materials. Meanwhile, high graphite content in the brake material tends to expedite black carbon emission. Black carbon emission shows a proportional correlation with PM1 levels from disc brake system. The fraction of black carbon in PM1 depends on the surface condition and graphite content of the brake materials. Future studies on the emission levels of black carbon under different traffic conditions and morphology of non-exhaust black carbon is suggested, which is essential for the enactment of relevant legislations and reduce its impact on global warming.
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| 10. |
- Middelburg, Luke M., et al.
(författare)
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Exploring the response of a resistive soot sensor to AC electric excitation
- 2020
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502 .- 1879-1964. ; 146
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Tidskriftsartikel (refereegranskat)abstract
- The resistive particulate matter sensor is a simple device that transduces the presence of soot through impedance change across inter-digital electrodes (IDEs). We investigate the information provided by impedance spectroscopy over the frequency range from 100 Hz to 10 kHz for two purposes. The first is to investigate the opportunities for an improved sensor response to particulate matter (PM), based on the additional information provided by the measurement of both the in-phase (resistive) and out-of-phase (capacitive) components of the change in impedance over this frequency range as compared to DC resistance measurement only. Secondly, the origin of the capacitive response of the device is investigated from the perspective that soot on the device is in the form of bendable dendrites that grow in three dimensions. An IDE structure with the housing acting as an additional suspended electrode for introducing a controllable vertical electric field component has been used for this purpose. The formation of dipoles, due to bending of the charged dendrites, is found to be the source of the capacitive response. Simulation of electrostatic soot deposition reinforces dendritic self-assembly mechanisms, driven by charged particle trajectories along electric field lines. Optical microscopy confirms that dendrites growing out of the substrate plane are sensitive to electric and flow forces, bending when force balances are appropriate. We also apply impedance spectroscopy under varying electric field strengths, showing that capacitive response is only observed when conditions are conducive to dendrite bending in response to the applied AC electric fields.
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| 11. |
- Misiulia, Dzmitry, et al.
(författare)
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Performance characteristics of a small scale cyclone separator operated in different flow regimes
- 2022
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502 .- 1879-1964. ; 163
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Tidskriftsartikel (refereegranskat)abstract
- The flow pattern, cyclone pressure drop and particle penetration through a sampling cyclone have been studied at a wide range of flow rate 0.22–7.54 LPM using the LES simulations that have been validated based on experimental penetration data. The cyclone performance has been described by three dimensionless characteristics, the Euler number Eustatout, cut-size ψ50 and slope of the transformed penetration curve κ1. Three main flow regimes and four sub-regimes have been revealed. The effects of the flow rate (Reynolds number) on the dimensionless cyclone performance characteristics have been described and a one-term power series model has been proposed. Additionally, the effect of the aspiration efficiency on the cyclone cut-size has been determined.
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| 12. |
- Roth, Adrian, et al.
(författare)
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High-speed scattered-light imaging for sizing respiratory droplets
- 2023
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Ingår i: Journal of Aerosol Science. - 0021-8502. ; 174
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Tidskriftsartikel (refereegranskat)abstract
- The COVID-19 pandemic has illuminated the lack of knowledge regarding the airborne transmission pathway of disease. The pathway consists of pathogens contained in small particles ejected when speaking and coughing. A crucial characteristic of these particles is their size that is connected to the their suspension longevity in the air as well as the location of generation and deposition within a subject’s respiratory system. Sizing of particles launched from the respiratory system is a challenge for a number of reasons: (1) the size of ejected particles varies over a wide range, between sub- to several hundreds of microns, (2) particles are ejected at various speeds in different directions, (3) each single event is unique where for example the number of particles can vary greatly between two occurrences of the same event and subject, (4) the size of the particles vary significantly as they evaporate over time. To overcome these challenges and categorize full coughing and speaking events, new measuring methods are needed. In this work, we present, in detail, high-speed scattered light imaging to size liquid particles (droplets) in unique respiratory events. A high-speed camera records scattered laser light at 16 000 frames per second in a semi-forward scattering direction. The illumination is close to the ejection source which means that the particles are sized before evaporation. The measurement can size stationary droplets from 3.4 to 44 µm and moving droplets from 4 to 80 µm resolved in both time and space. To get a reliable estimation, careful calibration of scattering angles and calibration uncertainty has been performed showing a general uncertainty of 8%. Thus, the approach proposed in this article can provide valuable and accurate data to improve the understanding of the airborne transmission pathway.
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| 13. |
- Snellman, Markus, et al.
(författare)
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A thermal evaporator for aerosol core-shell nanoparticle synthesis
- 2024
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Ingår i: Journal of Aerosol Science. - 0021-8502. ; 175
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Tidskriftsartikel (refereegranskat)abstract
- Segregated bimetallic nanoparticles like core-shell nanoparticles are of interest in various fields including biomedicine, catalysis, and optoelectronics. Aerosol technology is an optimal platform to control nanoparticle size, structure, and composition, which are some of the most important parameters tuning the material performance for the intended applications. Here, we develop a novel evaporator design to coat core particles on-line with a shell directly in the gas phase. The evaporator employs a local heater that decouples heating the evaporating material from the aerosol particles to limit core-shell alloying. We characterize the system by evaporating Zn onto core particles of Au, Sn, and Bi and demonstrate the core-shell particle formation with controllable shell thickness in each material system. We discuss simple models to explain the observed growth process inside the evaporator and the resulting shell formation.
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| 14. |
- Snellman, Markus, et al.
(författare)
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On-line compositional measurements of AuAg aerosol nanoparticles generated by spark ablation using optical emission spectroscopy
- 2022
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 165
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Tidskriftsartikel (refereegranskat)abstract
- Spark ablation is an established technique for generating aerosol nanoparticles. Recent demonstrations of compositional tuning of bimetallic aerosols have led to a demand for on-line stoichiometry measurements. In this work, we present a simple, non-intrusive method to determine the composition of a binary AuAg nanoparticle aerosol on-line using the optical emission from the electrical discharges. Machine learning models based on the least absolute shrinkage and selection operator (LASSO) were trained on optical spectra datasets collected during aerosol generation and labelled with X-ray fluorescence spectroscopy (XRF) compositional measurements. Models trained for varying discharge energies demonstrated good predictability of nanoparticle stoichiometry with mean absolute errors <10 at. %. While the models utilized the emission spectra at different wavelengths in the predictions, a combined model using spectra from all discharge energies made accurate predictions of the AuAg nanoparticle composition, showing the method's robustness under variable synthesis conditions.
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| 15. |
- Ternero, Pau, et al.
(författare)
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Effect of the carrier gas on the structure and composition of Co–Ni bimetallic nanoparticles generated by spark ablation
- 2023
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Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502. ; 170
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Tidskriftsartikel (refereegranskat)abstract
- Spark ablation is a versatile technique for producing pure size-selected nanoparticles. The carrier gas used in spark ablation affects the nanoparticles’ generation, crystalline structure, and chemical composition. The comprehension of this phenomenon can contribute to the design of nanoparticles with tailored properties. In this paper, we evaluate the effects of reducing (95%N2 + 5%H2), inert (N2), and oxidative (air) carrier gases in a spark ablation setup with Co–Ni alloyed electrodes. The agglomerates’ particle size distribution, morphology, structure, and composition were highly dependent on the carrier gas, especially its relative oxygen content. The agglomerates were then sintered into compacted particles. Three different crystalline structures and chemical compositions were observed with X-ray diffraction and confirmed with transmission electron microscopy for the compacted particles. For 95%N2 + 5%H2 and air, single-phase (Co,Ni) and (Co,Ni)O particles were identified, respectively, whereas for N2, two-phase (Co,Ni) and (Co,Ni)O particles were obtained. This work opens up new possibilities of tuning the structure and composition, i.e., distribution of metallic and oxide phases, of the produced particles and thus tailor their properties for specific applications by simply changing the carrier gas.
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