Effect of the Process Parameters on the Energy Transfer during the Synthesis of the 2LiBH4-MgH2 Reactive Hydride Composite for Hydrogen Storage

Abstract

Several different milling parameters (additive content, rotation velocity, ball-to-powder ratio, degree of filling, and time) affect the hydrogen absorption and desorption properties of a reactive hydride composite (RHC). In this paper, these effects were thoroughly tested and analyzed. The milling process investigated in such detail was performed on the 2LiH-MgB2 system doped with TiCl3. Applying an upgraded empirical model, the transfer of energy to the material during the milling process was determined. In this way, it is possible to compare the obtained experimental results with those from processes at different scales. In addition, the different milling parameters were evaluated independently according to their individual effect on the transferred energy. Their influence on the reaction kinetics and hydrogen capacity was discussed and the results were correlated to characteristics like particle and crystallite size, specific surface area, presence of nucleation sites and contaminants. Finally, an optimal value for the transferred energy was determined, above which the powder characteristics do not change and therefore the RHC system properties do not further improve.

Efficient Synthesis of Alkali Borohydrides from Mechanochemical Reduction of Borates Using Magnesium–Aluminum-Based Waste

“…The milling energy per gram of powder changes with the milling time varying from 1 to 36 h. According to Equation (1), the transferred energy depends on the filling vial coefficient, which is related to the number of balls and reactor volume, as well as to the volume of powder [54]. In this study, the number of balls and reactor volume were the same for all experiments; therefore, the energy transferred was mainly related to the volume occupied by each powder sample [55]. Taking into account that the densities of the initial reagents were not so different, the energy transferred for NBOM and LBOM materials was almost the same (Figure 8).…”

“…The results of this calculation correlated to the results of the experimental techniques allow the energy that is transferred to the system in order to reach the maximum yield to be obtained. The influence of every different process parameter on the energy transferred during the milling processes was also recently studied in a methodical analysis based on Equation 1for hydrogen storage materials [55].…”

Modeling the kinetic behavior of the Li-RHC system for energy-hydrogen storage: (I) absorption

“…For each milling, an amount of 5 g of powder was inserted into the milling vial. These parameters were chosen based on analyses developed and thoroughly discussed in previous work [31].…”

Metals in Hydrogen Technology

“…Among the possible RHC systems containing borohydrides, in the last decade, 2LiBH 4 + MgH 2 /2LiH + MgB 2 has been one of the most investigated due to its high hydrogen storage capacity and expected low operating conditions. In their contribution, Capurso et al [11] report on the improvement of the hydrogen storage properties of 2LiBH 4 + MgH 2 /2LiH + MgB 2 via the tuning of both the synthesis parameter as well as type and quantity of used additives. For the preparation of this system, an optimal set of additive content and of milling parameters (i.e., milling time, milling velocity, and degree of filling of the milling vials) were determined.…”