| 1. |
- Elmroth Nordlander, Jonas, et al.
(författare)
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Mo3Ni2N Nanoparticle Generation by Spark Discharge
- 2023
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 16:3
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Tidskriftsartikel (refereegranskat)abstract
- Spark ablation is an advantageous method for the generation of metallic nanoparticles with defined particle sizes and compositions. The reaction of the metal particles with the carrier gas during the synthesis and, therefore, the incorporation of those light elements into structural voids or even compound formation was confirmed for hydrides and oxides but has only been suspected to occur for nitrides. In this study, dispersed nanoparticles of Mo3Ni2N and Mo with Janus morphology, and defined particle sizes were obtained by spark discharge generation as a result of carrier gas ionization and characterized using transmission electron microscopy and powder X-ray diffraction. Metal nitrides possess beneficial catalytic and thermoelectric properties, as well as high hardness and wear resistance. Therefore, this method offers the possibility of controlled synthesis of materials which are interesting for numerous applications.
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| 2. |
- 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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| 3. |
- Wahlqvist, David
(författare)
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Taming of Oxygen in the Electron Microscope : Effects of High Energy Electron Irradiation on O2 and Oxides
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transmission electron microscopy (TEM) is an atomic resolution technique that allows for in depth analysis of the properties of different materials by passing high energy electrons through a thin sample and detecting how they are affected. However, due to the strong interaction between electrons and matter, the probability of the sample remaining unperturbed by the electron irradiation is small. This is an issue as there can be ambiguity about if the effects seen in TEM are inherent for the material or induced, fully or in part, by electron irradiation.One especially useful application of TEM is to observe dynamic processed by introducing external stimuli such the introduction of reactive gases into close proximity of the sample, referred to as Environmental TEM (ETEM). ETEM allows for the observation of morphological, elemental, atomic, and chemical changes in a solid in a solid–gas reaction, providing insight into the function of the solid during the reaction. However, during dynamic processes, due to the increased complexity of the interactions, it is even more difficult to deconvolve the inherent effects from the ones induced by electron irradiation. When a reactive gas is introduced into the TEM, it will be affected by the electron irradiation and may become even more reactive. The gas may also interact with defects in the sample caused by electron irradiation. Both these interactions generally lack equivalents in applications outside the ETEM, resulting in further ambiguity.Herein I discuss the ramifications of electron irradiation in TEM, both in vacuum and with reactive gases present, especially as they pertain to carbon black oxidation and the electron irradiation induced oxidation of cobalt nickel nanoparticles. In both of these cases there is a substantial effect from electron irradiation. For carbon black oxidation, the oxidation rate is highly dependent on the electron flux and in observations of cobalt nickel nanoparticles, electron irradiation induces surface oxidation of the particles. In this thesis I provide some suggestions for how the interpretative problems arising from electron irradiation can be compensated for, and how to best mitigate the effects in the first place.
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