Nanomaterialer for hydrogenlagring - Framstilling og karakterisering av MgH2-nanopartikler

Hvis de fornybare og CO2-frie alternativene til fossilt brensel som sol-, vind- og vannkraft skal forsyne verden med energi, må denne konverteres fra elektrisitet til et energimedium. Hydrogen er en lovende kandidat som et slikt medium. Men for at hydrogen skal kunne erstatte fossilt drivstoff for transportformål, må det utvikles egnede lagringsmetoder. Lagring i faste materialer som metall- og komplekshydrider er en lovende tilnærming fordi det muliggjør svært kompakt lagring av hydrogen. Men flere problemer, som utilstrekkelig vektmessig lagringskapasitet og/eller uegnet termodynamikk for mange av materialene, må løses. MgH2 er et av metallhydridene med høyest lagringskapasitet, men er begrenset av treg kinetikk og uegnet termodynamikk. Nanometerstore MgH2-partikler har bedret kinetikk, og teoretiske beregninger indikerer at termodynamikken deres endres fordelaktig under en viss partikkelstørrelse. Denne masteroppgaven omfatter framstilling av MgH2-nanopartikler og studier av deres mikrostruktur og kinetikk. Det var også planlagt å gjøre termodynamiske studier, men det var det i praksis ikke mulig å gjennomføre i den begrensede prosjektperioden. MgH2-partiklene ble forsøkt framstilt med kulemalingsmetoder og ved inkorporering i karbonnanorør. Med kulemaling og metatesereaksjon mellom MgCl2 og alkalihydrider ble det framstilt saltkompositter bestående av homogent blandede MgH2- og LiCl- eller NaCl-nanopartikler. Det ble observert forskjeller i dekomponeringstemperatur og aktiveringsenergi for de forskjellige saltkomposittene. I den ene prøven ble MgH2-nanopartiklene separert fra LiCl, og partikkelstørrelsen ble målt til å ligge i området 6-30 nm med den største andelen i intervallet 10-20 nm. Det ble observert kornstørrelser ned til 6 nm. Ved inkorporering av Mg i karbonnanorør ble det forsøkt å smelte Mg inn i rørene ved inerte betingelser. Dette resulterte i oksidasjon av Mg til MgO, som indikerte at betingelsene ikke var inerte. Det ble også forsøkt å dampe Mg inn i rørene i en evakuert kvartsampulle, men dette førte igjen til dannelse av MgO, både som nanopartikler og større krystaller. Nanopartiklene forelå som flak i størrelsesområdet 10-30 nm. Årsaken til oksideringen var trolig at Mg-damp reagerte med kvartsampullen ved å redusere SiO2. Det ble ikke påvist signifikante mengder Mg eller MgO inne i nanorørene

Dipolar ordering of clay particles in various carrier fluids

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Dipolar ordering of clay particles in various carrier fluids

We investigate here examples of complexity in composite materials. The objective of the paper is to show that clay particles can be aligned in different hosting media, such as: silicone oil, paraffin-wax, polystyrene and ambient air. The use of an electric field is an easily controllable, non-intrusive manner of inducing such an alignment. Depending on the medium used, a large span in time constants for the orientation and reorganization has been observed. Furthermore, the reorientation may be frozen into the material, thus permanently changing its properties

Oxygen-Controlled Phase Segregation in Poly(N‑isopropylacrylamide)/Laponite Nanocomposite Hydrogels

The combination of nanoparticles and polymers into nanocomposite gels has been shown to be a promising route to creating soft materials with new or improved properties. In the present work, we have made use of Laponite nanoparticles in combination with a poly(N-isopropylacrylamide) (PNIPAAM)polymer and describe a phenomenon taking place during the polymerization and gelling of this system. The presence of small amounts of oxygen in the process induces two distinctly separated phases, one polymer-rich and one polymer-deficient water−clay phase. Complex interactions among clay, oxygen, and the polymer are found to govern the behavior of these phases. It is also observed that the initial clay concentration can be used to control the volume fraction of the polymer-deficient phase directly. The dynamics of the phase boundary is found to be dependent on water penetration and in general to exhibit non-Fickian behavior. An approach using video recording to monitor hydrogel swelling is also presented, and its advantages are addressed

Effect of Clay Surface Charge on the Emerging Properties of Polystyrene−Organoclay Nanocomposites

A series of polystyrene-clay nanocomposites, based on two natural clay types (Na-Montmorillonite and Hectorite) and two synthetic clays (Laponite and Li- Fluorohectorite), were prepared via in situ intercalative polymerization after surface modification with an organic ammonium cation (CTAB). The structural characteristics of the organically modified clays as well as the nanocomposites were investigated by means of wide-angle X-ray scattering (WAXS), and the thermal properties were studied with TGA. In the organically modified clays, the silicate interlayer spacing increases, and the magnitude seems to be directly correlated with the amount of clay surface charge. In the nanocomposites, polymer intercalation is also observed, but partial exfoliation is present, modifying significantly the morphology of the material. The degree of dispersion of the clay platelets, as well as the resulting properties of the nanocomposites, were found again to be systematically, and almost linearly, correlated with the intrinsic surface charge of the clays, which varied between 44 and 120 meq/100 g. Increased dispersion was seen in the nanocomposites made from clays with low surface charge, here Hectorite and Laponite, suggesting that these can be suitable alternatives to the more employed Montmorillonite for enhancement of thermal properties. The thermal stability was found to be better for the nanocomposites than for the pure polystyrene

Short-Range Structure of Ti0.63V0.27Fe0.10D1.73 from Neutron Total Scattering and Reverse Monte Carlo Modelling

Ti-V-based body-centered cubic (BCC) alloys have potential for large-scale hydrogen storage if expensive vanadium is substituted with much cheaper Fe-containing ferrovanadium. Use of ferrovanadium reduces the alloys’ hydrogen storage capacity. This is puzzling since the amount of Fe is low and hydrogen atoms are accommodated in interstitial sites which are partly coordinated by Fe in many intermetallic compounds. The present work is aimed at finding a structural explanation for Fe-induced capacity loss in Ti-V alloys. Since such alloys and their hydrides are highly disordered without long-range occupational order of the different metal species, it was necessary to employ a technique which is sensitive to local structure. Neutron total scattering coupled with reverse Monte Carlo modelling was thus employed to elucidate short-range atomic correlations in Ti0.63V0.27Fe0.10D1.73 from the pair distribution function. It was found that Fe atoms form clusters and that the majority of the vacant interstitial sites are within these clusters. These clusters take the same face-centered cubic structure as the Ti-V matrix in the deuteride and thus they are not simply unreacted Fe which has a BCC structure. The presence of Fe clusters is confirmed by transmission electron microscopy. Density functional theory calculations indicate that the clustering is driven by thermodynamics