Carine Rongeat

Synthesis of LiNH2 + LiH by reactive milling of Li3N

The hydrogen sorption properties of Li3N under reactive milling conditions have been investigated in- and ex-situ as a function of polytype structure (alpha vs. beta), focusing on the influence of the micro-structure and/or the crystal structure upon hydrogen uptake. LiNH2 and LiH were synthesized by reactive milling of Li3N at 20 bar hydrogen pressure for 4 h. Reactive milling represents a quick and effective technique to produce LiNH2 by hydrogenation of Li3N at low hydrogen pressure and without any need for heating. As to our knowledge, we present a full hydrogenation of Li3N under the aforementioned conditions for the first time. The (de)hydrogenation and rehydrogenation behaviour of milled amides was evaluated using a combination of powder X-ray diffraction, differential scanning calorimetry, thermogravimetry and in situ Raman spectroscopy. In situ Raman spectroscopy showed a shift in the lithium amide stretching modes upon hydrogenation supporting a non-stoichiometric storage mechanism consistent with the literature. The microstructure and polytype composition of the Li3N dehydrogenated materials had no effect on the hydrogenation products and only minor effects on the hydrogen uptake profile during milling.

Influence of the carbon content on the microstructure and properties of heat-resistant cast steels

Abstract Two heat-resistant ferritic cast steels, 1.4476 and 1.4777 with a similar high Cr concentration, have been analyzed regarding their microstructures, mechanical properties, corrosion resistance and aging behavior. The differences observed between the grades are related to their different C contents. A higher C concentration ensures a higher mechanical resistance, in particular at high temperature (850°C) and also a better high-temperature (850°C) corrosion resistance. This is related to the formation of numerous carbides. However, this study also reveals that the microstructure of these steels is greatly affected by aging. In particular, the precipitation of the sigma phase and the formation of nitride precipitates could lead to failure during service at high temperature.

Characterisation of complex hydrides synthesised or modified by ball milling

Abstract Ball milling is an effective method for the synthesis and modification of light complex hydrides by changing the milling conditions. Using specially designed vials, in-situ variations of the hydrogen pressure and vial temperature taking place during the milling of LiAlH4, with and without dopants, and of LiBH4 + MgCl2 were monitored. This provided information about the efficiency of the reactions before removing the powder from the vial. The thermodynamic properties of the milled hydrides were analysed by differential scanning calorimetry and intelligent gravimetric analysis. Additional structural characterisation was carried out by X-ray diffraction and Raman spectroscopy. The results showed that the decomposition of LiAlH4 during milling is strongly affected by the use of TiCl3 as dopant. The partial formation of Mg(BH4)2 from LiBH4 + MgCl2 was demonstrated by Raman spectroscopy.