Adsorption-Based Hydrogen Storage in Activated Carbons and Model Carbon Structures

The experimental data on hydrogen adsorption on five nanoporous activated carbons (ACs) of various origins measured over the temperature range of 303–363 K and pressures up to 20 MPa were compared with the predictions of hydrogen density in the slit-like pores of model carbon structures calculated by the Dubinin theory of volume filling of micropores. The highest amount of adsorbed hydrogen was found for the AC sample (ACS) prepared from a polymer mixture by KOH thermochemical activation, characterized by a biporous structure: 11.0 mmol/g at 16 MPa and 303 K. The greatest volumetric capacity over the entire range of temperature and pressure was demonstrated by the densest carbon adsorbent prepared from silicon carbide. The calculations of hydrogen density in the slit-like model pores revealed that the optimal hydrogen storage depended on the pore size, temperature, and pressure. The hydrogen adsorption capacity of the model structures exceeded the US Department of Energy (DOE) target value of 6.5 wt.% starting from 200 K and 20 MPa, whereas the most efficient carbon adsorbent ACS could achieve 7.5 wt.% only at extremely low temperatures. The initial differential molar isosteric heats of hydrogen adsorption in the studied activated carbons were in the range of 2.8–14 kJ/mol and varied during adsorption in a manner specific for each adsorbent.

Synthesis and Stability of Hydrogen Storage Material Aluminum Hydride

Aluminum hydride (AlH3) is a binary metal hydride with a mass hydrogen density of more than 10% and bulk hydrogen density of 148 kg H2/m3. Pure aluminum hydride can easily release hydrogen when heated. Due to the high hydrogen density and low decomposition temperature, aluminum hydride has become one of the most promising hydrogen storage media for wide applications, including fuel cell, reducing agents, and rocket fuel additive. Compared with aluminum powder, AlH3 has a higher energy density, which can significantly reduce the ignition temperature and produce H2 fuel in the combustion process, thus reducing the relative mass of combustion products. In this paper, the research progress about the structure, synthesis, and stability of aluminum hydride in recent decades is reviewed. We also put forward the challenges for application of AlH3 and outlook the possible opportunity for AlH3 in the future.

Analysis of hydrogen behavior by crystallization of secondary aluminum alloy

Methodology. There was conducted the process modeling of hydrogen by crystallization of secondary aluminum alloy. Findings. There was conducted an analysis of hydrogen behavior by indurating secondary aluminum alloy castings. There were obtained expressions for calculation of the current value in the process of secondary aluminum alloy crystallization of the hydrogen density in the boundary diffused layer, on the crystallization front, in the volume of the remaining melt, and the effective hydrogen distribution coefficient. Originality. For the first time, there was obtained an arithmetic model for the forecasting of hydrogen behavior by indurating secondary aluminum alloy castings. Practical value. The results of the study can be implemented with the purpose of the flow optimization process and the more efficient use of expensive equipment for getting high-quality secondary aluminum alloy castings. Keywords: aluminum, secondary aluminum alloys, indurating, hydrogen, crystallization front, distribution coefficient, boundary diffusion layer.

Detecting multiple DLAs per spectrum in SDSS DR12 with Gaussian processes

ABSTRACT We present a revised version of our automated technique using Gaussian processes (GPs) to detect damped Lyman α absorbers (DLAs) along quasar (QSO) sightlines. The main improvement is to allow our GP pipeline to detect multiple DLAs along a single sightline. Our DLA detections are regularized by an improved model for the absorption from the Lyman α forest that improves performance at high redshift. We also introduce a model for unresolved sub-DLAs that reduces misclassifications of absorbers without detectable damping wings. We compare our results to those of two different large-scale DLA catalogues and provide a catalogue of the processed results of our GP pipeline using 158 825 Lyman α spectra from SDSS data release 12. We present updated estimates for the statistical properties of DLAs, including the column density distribution function, line density (dN/dX), and neutral hydrogen density (ΩDLA).

Unusually high thermospheric hydrogen density prior to severe storm of September 8, 2017 and its impact on the storm manifestations

<p>Atomic hydrogen plays a key role for the plasmasphere, exosphere, and the nighttime ionosphere. It directly impacts the rate of plasmasphere refilling after strong magnetic storms as atomic hydrogen is the primary source of hydrogen ions. It is the source of the geocorona, which significantly affects ring current decay during the recovery phase of magnetic storms.</p><p>Our previous studies with the Kharkiv incoherent scatter radar (49.6 N, 36.3 E), Arase and DMSP satellite missions, and FLIP physical model showed that during magnetically quiet periods of 2016–2018 the hydrogen density was generally a factor of 2 higher than from the NRLMSIS00-E model (Kotov et al., 2018).</p><p>Even larger values of thermospheric hydrogen density were detected prior to the severe storm of September 8, 2017. With Kharkiv IS radar, AWDANet whistler receivers, Arase satellite, and TEC data we found that during the nights of September 5 to 6 and September 6 to 7, the thermospheric hydrogen density had to be at least a factor of 4 higher than the values from NRLMSIS00-E model i.e. ~100% higher than expected from our previous studies. We discuss the possible mechanisms that could lead to the increased hydrogen density.</p><p>Such high hydrogen densities may be the reason for very quick recovery of inner plasmasphere after the severe depletion by the storm of September 8, 2017 (Obana et al., 2019).</p><p><strong>References:</strong></p><p>1. Kotov, D. V., Richards, P. G., Truhlík, V., Bogomaz, O. V., Shulha, M. O., Maruyama, N., et al. ( 2018). Coincident observations by the Kharkiv IS radar and ionosonde, DMSP and Arase (ERG) satellites, and FLIP model simulations: Implications for the NRLMSISE‐00 hydrogen density, plasmasphere, and ionosphere. Geophysical Research Letters, 45, 8062– 8071. https://doi.org/10.1029/2018GL079206</p><p>2. Obana, Y., Maruyama, N., Shinbori, A., Hashimoto, K. K., Fedrizzi, M., Nosé, M., et al. (2019). Response of the ionosphere‐plasmasphere coupling to the September 2017 storm: What erodes the plasmasphere so severely? Space Weather, 17, 861–876. https://doi.org/10.1029/2019SW002168</p>

Photoionization modelling of quiescence-phase spectra of novae and a symbiotic star

ABSTRACT Using observed and published spectra in the optical region, we have studied a handful of novae and symbiotic stars that show novae-like variability in the quiescence phase. We present results for the novae T Coronae Borealis, GK Persei, RS Ophiuchi, V3890 Sagittarii and V745 Scorpii, and for a symbiotic star BX Monocerotis. Observations were carried out at the 2-m Himalayan Chandra Telescope (HCT). Generally, the spectra show prominent low-ionization emission features of hydrogen, helium, iron and oxygen and TiO absorption features resulting from the cool secondary component; T Coronae Borealis and GK Persei show higher ionization lines. We used the photoionization code cloudy to model these spectra. From the best-fitting models, we have estimated the physical parameters (e.g. temperature, luminosity and hydrogen density), the elemental abundances and other parameters related to the system. By matching the spectra of various giants with the absorption features and using the best fit, we have determined the types of secondaries and also their contribution to the spectra.