Marek Polanski

Mechano-chemical activation of the (3LiBH4 + TiF3) system, its dehydrogenation behavior and the effects of ultrafine filamentary Ni and graphene additives

The influence of milling energy input, QTR (kJ g−1), during ball milling and additives such as ultrafine filamentary Ni and graphene (reduced graphene oxide), on the occurrence of the solid-state mechano-chemical reaction and resulting microstructure, were investigated for the (3LiBH4 + TiF3) system. The new phases LiF and Ti are observed after injecting the energy input QTR = 72.8 kJ g−1 (1 h ball milling). A mechanical dehydrogenation phenomenon occurs during mechano-chemical reaction. The ultrafine filamentary Ni additive does not measurably accelerate the rate of mechanical dehydrogenation while the rate of mechanical dehydrogenation with graphene is initially slow and then dramatically increases up to 5 h ball milling (QTR = 364 kJ g−1). Thermal desorption of ball milled samples occurs at a very low temperature of 60 °C. The addition of 5 wt% filamentary Ni mildly reduces the apparent average activation energy for desorption. The highest average apparent activation energy of 95.2 ± 1.9 kJ mol−1 is exhibited by a sample with 5 wt% graphene milled for 1 h which dramatically decreases after 5 h ball milling. The X-ray diffraction intensity of the LiF and Ti peaks greatly increases after thermal dehydrogenation. The principal gas released during thermal dehydrogenation is hydrogen although the 1 h ball milled (QTR = 72.8 kJ g−1) sample shows a very small quantity of diborane gas, B2H6, which ceased to be released after 5 h ball milling. It clearly shows that the release of B2H6 during thermal dehydrogenation depends on the quantity of milling (mechanical) energy injected into the powder mixture. Differential scanning calorimetry measurements show exothermic peaks for all samples regardless of the milling energy input. The ball milled samples release H2 during long term storage at room temperature.

Synthesis of Fe-Al-Ti Based Intermetallics with the Use of Laser Engineered Net Shaping (LENS)

The Laser Engineered Net Shaping (LENS) technique was combined with direct synthesis to fabricate L21-ordered Fe-Al-Ti based intermetallic alloys. It was found that ternary Fe-Al-Ti alloys can be synthesized using the LENS technique from a feedstock composed of a pre-alloyed Fe-Al powder and elemental Ti powder. The obtained average compositions of the ternary alloys after the laser deposition and subsequent annealing were quite close to the nominal compositions, but the distributions of the elements in the annealed samples recorded over a large area were inhomogeneous. No traces of pure Ti were observed in the deposited alloys. Macroscopic cracking and porosity were observed in all investigated alloys. The amount of porosity in the samples was less than 1.2 vol. %. It seems that the porosity originates from the porous pre-alloyed Fe-Al powders. Single-phase (L21), two-phase (L21-C14) and multiphase (L21-A2-C14) Fe-Al-Ti intermetallic alloys were obtained from the direct laser synthesis and annealing process. The most prominent feature of the ternary Fe-Al-Ti intermetallics synthesized by the LENS method is their fine-grained structure. The grain size is in the range of 3–5 μm, indicating grain refinement effect through the highly rapid cooling of the LENS process. The Fe-Al-Ti alloys synthesized by LENS and annealed at 1000 °C in the single-phase B2 region were prone to an essential grain growth. In contrast, the alloys annealed at 1000 °C in the two-phase L21-C14 region exhibited almost constant grain size values after the high-temperature annealing.

Hydriding properties of Mg- -Al- -Zn quasicrystal powder produced by mechanical alloying

Abstract The stable quasicrystal belonging to the Bergman class based on Mg–Al–Zn (Mg44Al15Zn41) was prepared by the mechanical alloying of elemental powders. The phase structure, chemical composition and hydriding properties of the obtained quasicrystal were investigated by XRD, SEM, EDS, DSC and the volumetric Sievert method. Our results have shown that the Mg44Al15Zn41 quasicrystal is unstable while hydriding above 200 °C and decomposes irreversibly into different Mg–Zn based intermetallic compounds. While being hydrided at 200 °C, where the quasicrystal is stable, Mg44Al15Zn41 decomposes mainly into the MgZn2 based intermetallic compound with MgH2 but above 300 °C, where the 2/1 approximant is stable, Mg44Al15Zn41 transforms mainly into the Frank-Kasper phase with MgH2.

Sulfurized metal borohydrides

The reactions between metal borohydrides and elemental sulfur are investigated in situ during thermal treatment and are found to be highly exothermic (up to 700 J g(-1)). These reactions are exceptionally rapid, occurring below 200 °C, also resulting in the sudden release of substantial quantities of hydrogen gas. For NaBH4 this hydrogen release is pure, with no detectable levels of H2S or B2H6. The reaction results in the formation of an array of metal-boron-sulfur compounds. These MBH4-S compounds are interesting for possible uses in high energy applications (fuels or explosives), hydrogen generation, and metal-boron-sulfur precursors.