Structure of a seeded palladium nanoparticle and its dynamics during the hydride phase transformation

Palladium absorbs large volumetric quantities of hydrogen at room temperature and ambient pressure, making the palladium hydride system a promising candidate for hydrogen storage. Here, we use Bragg coherent diffraction imaging to map the strain associated with defects in three dimensions before and during the hydride phase transformation of an individual octahedral palladium nanoparticle, synthesized using a seed-mediated approach. The displacement distribution imaging unveils the location of the seed nanoparticle in the final nanocrystal. By comparing our experimental results with a finite-element model, we verify that the seed nanoparticle causes a characteristic displacement distribution of the larger nanocrystal. During the hydrogen exposure, the hydride phase is predominantly formed on one tip of the octahedra, where there is a high number of lower coordinated Pd atoms. Our experimental and theoretical results provide an unambiguous method for future structure optimization of seed-mediated nanoparticle growth and in the design of palladium-based hydrogen storage systems.

Study of the hydrogenation effect on the structure and flattening of tubular samples of PT-7M titanium alloy

In this work, we analyze the effect of hydrogen embrittlement on the performance of PT-7M titanium alloy products. The above examples show that PT-7M titanium alloy products with a high hydrogen content are prone to cracking, the probability of their destruction increases. In the initial state, the samples were annealed in vacuum at 680 о. Hydrogenation of the samples was carried out by the diffusion method at room temperatures to concentrations of 0.002, 0.005 and 0.01 % (by mass) in a Siverts laboratory setup. The hydrogen content in the samples was determined on a highly sensitive G8 Galileo gas analyzer. To assess the effect of hydrogen embrittlement on the plastic properties and tendency to crack formation, the samples were tested for flattening. The structural state of the alloy was analyzed, which showed that hydride phases were observed to increase with increasing hydrogen concentration. The effect of structural changes in the alloy on the microhardness was studied. The X-ray diffraction analysis also showed the presence of hydride precipitates in the PT-7M alloy. Using the CAE ANSYS engineering complex, a numerical simulation of the stress-strain state of samples was carried out during a flattening test. The simulation results showed that the maximum stresses during flattening exceed the tensile strength. One of the reasons for the hydride phase precipitation is high stresses, which is also confirmed by the results of flattening tests and metallographic analysis: in local zones with an increased level of stresses in the material structure, a higher concentration of the TiHx hydride phase. Flattening tests also showed that the cause of cracking during flattening testing is the presence of brittle hydrides in the structure of the material: cracks are formed by the destruction of hydride phases. In the initial state and with a low hydrogen content (up to 0.002 mass %) no cracks were found in the samples. Thr research was conducted within the framework of the grant RNF No. 19-19-00332 "Development of scientifically substantiated approaches, hardware and software facilities for monitoring of damage of construction materials, based on the artificial intellect approaches to provide safe operation of technical objects in the Arctic conditions".

The Thermodynamic Way of Assessing Reversible Metal Hydride Volume Expansion: Getting a Grip on Metal Hydride Formation Overpotential

<p>The relative volume expansion of reversible metal hydride crystals upon formation is determined by means of the van’t Hoff reaction entropy and STP ideal gas parameters, the development of this approach leads to a general method for calculating metal hydride single-crystal density. These results allow highlighting the pressure requirement to hydride phase formation, shown by the example of Ti-NaAlH₄.</p>

Structure of a single palladium nanoparticle and its dynamics during the hydride phase transformation

Palladium absorbs large volumetric quantities of hydrogen at room temperature and ambient pressure, making the Pd-H system a promising candidate for hydrogen storage. Here, we use Bragg coherent diffraction imaging to map the strain associated with defects in three dimensions before and during the hydride phase transformation of an individual octahedral palladium nanoparticle, synthesized by using the seed-mediated approach. The displacement distribution imaging unveils the location of the seed nanoparticle in the final nanocrystal. By comparing our experimental results with a finite-element model, we verify that the seed nanoparticle causes a characteristic displacement distribution of the larger nanocrystal. During the hydrogen exposure, the hydride phase is predominantly formed on one tip of the octahedra, where there is a high number of lower coordinated Pd atoms. Our experimental and theoretical results provide an unambiguous method for future structure optimization of seed-mediated nanoparticles growth and in the design of palladium-based hydrogen storage systems.

Watching in situ the hydrogen diffusion dynamics in magnesium on the nanoscale

Active plasmonic and nanophotonic systems require switchable materials with extreme material contrast, short switching times, and negligible degradation. On the quest for these supreme properties, an in-depth understanding of the nanoscopic processes is essential. Here, we unravel the nanoscopic details of the phase transition dynamics of metallic magnesium (Mg) to dielectric magnesium hydride (MgH2) using free-standing films for in situ nanoimaging. A characteristic MgH2 phonon resonance is used to achieve unprecedented chemical specificity between the material states. Our results reveal that the hydride phase nucleates at grain boundaries, from where the hydrogenation progresses into the adjoining nanocrystallites. We measure a much faster nanoscopic hydride phase propagation in comparison to the macroscopic propagation dynamics. Our innovative method offers an engineering strategy to overcome the hitherto limited diffusion coefficients and has substantial impact on the further design, development, and analysis of switchable phase transition as well as hydrogen storage and generation materials.

Hydrogen Sorption Properties, Thermal Stability and Kinetics of Hydrogen Desorption From the Hydride Phase of The MgH2 of a Mechanical Alloys of Magnesium with Ti, Ni and Y

The mechanical alloys-composite MАs (Mg +10 % wt.Ti + 5 % wt.Y and Mg +10 % wt.Ni + 5 % wt.Y) were synthesized. The phase content, microstructure, the thermal stability, kinetics of hydrogen desorption from the MgH2 hydride phase of the obtained MAs were studiedby using XRD, SEM, TDS methods. It has been established that the addition of Ti + Y and Ni + Y to magnesium leads to significant improvement in the kinetics of hydrogen desorption from the MgH2 hydride phase, which is evidenced by a significant reduction (in 6 and 15 times)in the time of release of all hydrogen from MA1 and MA2, respectively. Due to, Ti, Ni,Y alloying, the decrease in the thermodynamic stability of MgH2 is not found.