Structural and hydrogen storage characterization of nanocrystalline magnesium synthesized by ECAP and catalyzed by different nanotube additives

Ball-milled nanocrystalline Mg powders catalyzed by TiO2 powder, titanate nanotubes and carbon nanotubes were subjected to intense plastic deformation by equal-channel angular pressing. Microstructural characteristics of these nanocomposites have been investigated by X-ray diffraction. Microstructural parameters, such as the average crystallite size, the average dislocation density and the average dislocation distance have been determined by the modified Williamson–Hall analysis. Complementary hydrogen desorption and absorption experiments were carried out in a Sieverts’ type apparatus. It was found that the Mg-based composite catalyzed by titanate nanotubes exhibits the best overall H-storage performance, reaching 7.1 wt% capacity. The hydrogenation kinetic curves can be fitted by the contracting volume function for all the investigated materials. From the fitted parameters, it is confirmed that the titanate nanotube additive results in far the best kinetic behavior, including the highest hydride front velocity

Hydrogen storage of nanocrystalline Mg-Ni alloy processed by equal-channel angular pressing and cold rolling

Ball-milled nanocrystalline Mg2Ni powders were subjected to intense plastic straining by cold rolling or equal-channel angular pressing. Morphological and microstructural evolution during these processes has been investigated by scanning electron-microscopy and X-ray diffraction line profile analysis, respectively. Complementary hydrogen absorption experiments in a Sieverts’ type apparatus revealed that there exists some correlation between the micro- and nanostructure and hydrogen storage properties of the severely deformed materials

Gelatinization of industrial starches studied by DSC and TG

The microstructure and thermal behaviour of industrial starches with different origin were characterized by X-ray diffraction and thermal analyses (DSC, TG). Some of the studied starches revealed crystalline structure (type A and type B), while others were predominantly amorphous, having only about 15 % crystallinity. The moisture content of the pristine starches correlated with their microstructure: starches with a higher amount of amorphous phase showed larger water content. The thermal behaviour of the starches with different amount of additional water was also studied by DSC. In a starch-water paste at higher water content the gelatinization started earlier and gelatinization enthalpy change was greater, than what was observed at lower water content. At certain starch to water ratio two distinguished endothermic peaks denoted the gelatinization and melting processes. The determined enthalpies of gelatinization were in the range of 5-15 J/g and did not correlate with the initial crystallinity of the starches. The activation energies of gelatinization in the range 40-100 kJ/mol, obtained by the Kissinger method, were found not to depend on the initial crystallinity of the starch either. At starch concentrations of 20-35% after the gelatinization endothermic peaks a clear exothermic effect could also be observed, which could be described by the formation of internal hydrogen-bonded association

Synergetic Effect of FeTi in Enhancing the Hydrogen-Storage Kinetics of Nanocrystalline MgH₂

High-energy ball milling was applied to produce nanocrystalline MgH2-FeTi powder composites. In order to achieve a remarkable synergetic effect between the two materials, the amount of the FeTi catalyst was chosen to be 40 wt.%, 50 wt.% and 60 wt.%. The morphology and microstructure of the as-milled powders were characterized by scanning electron microscopy and X-ray diffraction, respectively. The evaluation of the diffraction profiles by the Convolutional Multiple Whole Profile fitting algorithm provided a detailed microstructural characterization of the coherently scattering α-MgH2 crystallites. Differential scanning calorimetry experiments revealed two overlapping endotherms corresponding to the dehydrogenation of metastable γ-MgH2 and stable α-MgH2 hydrides. Isothermal hydrogen-sorption experiments were carried out in a Sieverts-type apparatus. It was established that the MgH2-40 wt.% FeTi powder is capable of absorbing 5.8 wt.% hydrogen, while extraordinary absorption kinetics were observed for the MgH2-50 wt.% FeTi alloy, i.e., 3.3 wt.% H2 is absorbed after 100 s

Novel mechanochemical approach for wheat starch-LPC complex formation

Amylose-LPC inclusion complexes are acquired by a novel mechanochemical method and by hydrothermal method. The new synthetic method includes mechanical milling of suspension of LPC and starch under controlled conditions. Both methods applied resulted in similar microstructure of the complexes, studied by x-ray diffraction (XRD). Furthermore, Solid-state 13C NMR spectroscopy and differential scanning calorimetry (DSC) also confirm the efficient complexation by the new approach.</p

Facilitated Synthesis of Mg2Ni Based Composites with Attractive Hydrogen Sorption Properties

Composites based on Mg2Ni with 5% activated carbon from apricot stones (ACAP) have been prepared by ball milling and subsequent annealing in hydrogen atmosphere. The purpose of the primary metal (Mg, Ni, and V) milling was to reduce the particle size and achieve a good contact between them, without forming intermetallic compounds. During hydriding/dehydriding at 300 °C the amount of the Mg2Ni phase progressively increased, and after 10 cycles about 50% Mg2(Ni,V) was achieved. The hydrogenation produced mainly Mg2NiH4, but small amounts of MgH2 and VHx were also detected in the powder mixture. Relatively high hydrogen storage capacity and fast hydriding/dehydriding kinetics of the Mg2.1Ni0.7V0.3—5 wt.% ACAP composite were determined both from hydrogen gas phase and electrochemically

Static and Dynamic Thermal Properties of a Pd40Ni40Si20 Glassy Alloy

The thermal properties of a Pd40Ni40Si20 glassy alloy with the largest supercooled liquid region among the glassy alloys containing Si as a metalloid element are studied using static and dynamic measurement methods. The relatively wide supercooled liquid region of 45 K, defined by the temperature interval between the glass transition temperature (Tg) and the onset temperature of crystallization (Tx), and the viscosity of the supercooled liquid, varying from 2.7 &times; 1010 to 3.2 &times; 1011 Pa&middot;s, make this glass suitable for the introduction of controlled pores by a viscous flow in the temperature range Tg~Tx. The obtained activation energy for crystallization, 272 &plusmn; 19 kJ/mol, is slightly higher than that of Tg (228 &plusmn; 11 kJ/mol), indicating the dominant contribution of the atomic transport barrier in the overall energy barrier for crystallization

Luminescence of Binary-Doped Silica Aerogel Powders: A Two-Step Sol-Gel Approach

In this study, we report a novel synthesis of hydrophobic silica aerogel powder composites, functionalized and binary-doped with [Tb(phen)2](NO3)3 and [Eu(phen)2](NO3)3 nanocrystals, employing a two-step sol-gel methodology. The investigation delves into the structural elucidation, optical properties and thermal conductivity of these functionalized Tb(III)-Eu(III) composites. Our analysis includes diffuse reflectance spectra and excitation and luminescence spectra, highlighting the quantum yields of composites with varying chemical compositions. Remarkably, these samples exhibit a strong luminescence, with distinct hues of red or green based on the specific doping type and level. The detailed examination of excitation spectra and quantum yields establishes robust energy-transfer mechanisms from the 1,10-phenanthroline molecule to the lanthanide ions. Notably, our study uncovers a Tb3⁺→Eu3⁺ energy-transfer phenomenon within the binary functionalized samples, providing compelling evidence for a structural formation process occurring within the mesoporous framework of the aerogel powders