Induction plasma synthesis of Mg-Ni nanoparticles

---

Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Metalurji ve Malzeme Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2013

Öğrenci: BURAK AKTEKİN

Danışman: TAYFUR ÖZTÜRK

Özet:

There is a considerable interest in developing magnesium and magnesium alloys in the form of nanoparticles for hydrogen storage purposes. In the current study, induction thermal plasma was used to synthesize Mg-Ni nanoparticles. In this technique, precursors, which are normally powders, are fed to the thermal plasma where they are evaporated and nanoparticles are derived from condensation of this vapor in the quenching zone. RF induction plasma system used in the current work was operated at 25 kW and the reactor incorporated two injectors axially located in the torch, one from above and the other from below. This allowed injection of precursor powder in different temperature zones. Precursors used were mainly elemental Ni and Mg powders, but experiments were also carried out with pre-alloyed Mg2Ni. The study has shown that Mg, Ni, Mg2Ni with the additional amount of MgO phase could be synthesized in the form of nanopowders less than 100 nm in size. Upon feeding elemental powders Mg and Ni, Mg2Ni could be synthesized; but, its fraction was quite low. The fraction was maximized and reached a weight fraction of 0.55 when Ni was fed from the top and Mg from the bottom injector the tip of which was located just below the quenching gas inlet. Hydrogenation of these powders showed fast kinetics, but there was no significant decrease in the dehydrogenation temperature. So as to further reduce the particle size and also to prevent oxidation, additional experiments were carried out where a fraction of argon used as carrier gas was replaced with methane. This has led to a core-shell structure in derived nanopowders. In the case of Ni, nanoparticles of varying sizes, e.g. 5-200 nm were encapsulated by 3-9 graphitic layers. For Mg, core-shell structure with a comparable clarity was not observed. Instead, nanoparticles which had been embedded in carbonaceous matrix were obtained. The size of these particles could be as small as 5 nm.