**5. Conclusion**

In this study, focusing on the formation of MgH2 in the Mg core, the effects of Al concentration in Mg for microstructure of hydrogenated Mg and Mg-Al-Zn alloys were investigated. MgH2(int) formed at Mg grain boundary and the growth rate of MgH2(int) was investigated including plastic deformed condition. From three-dimensional analysis, it was found that the MgH2(int) was surrounded by metallic Mg or Mg-Al-Zn alloys and they had not interfaced with H2 gas and MgH2 on the surface area(sur). The time when the surface covered with MgH2(sur) was described as time of halt, *τ*h. Comparing growth rate of MgH2(sur) and MgH2(int)

**113**

*Magnesium-Based Materials for Hydrogen Storage: Microstructural Properties*

before and after *τ*h, the growth rate of both MgH2 were higher before *τ*h than after *τ*h. The growth of MgH2(sur) and MgH2(int) were observed to stop after *τ*h because H supply route change from in Mg to MgH2. After *τ*h, the thickness of MgH2(sur) decreased and particle size of MgH2(int) increased with increasing Al concentration. This result could be explained by increase of supplied H amount to MgH2(int) due to the shifting *τ*h to longer time and small diffusion distance of MgH2(sur)

• Hydrogenated Mg plate formed MgH2 on surface(sur) and in internal

• The thickness of MgH2(sur) decreased with increase of Al concentrations in Mg.

• The particle size of MgH2(int) increased with increase of Al concentrations in Mg.

This is a product of research which was financially supported by JSPS KAKENHI

Development Fund (2RF-1801) of the Environmental Restoration and Conservation

Grant Number 19K15278, and the Environment Research and Technology

Department of Chemistry and Materials Engineering, Faculty of Chemistry,

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Materials and Bioengineering, Kansai University Suita, Osaka, Japan

\*Address all correspondence to: rkondo@kansai-u.ac.jp

*DOI: http://dx.doi.org/10.5772/intechopen.88679*

which had low value of diffusion coefficient.

area(int).

**Acknowledgements**

Agency of Japan.

**Author details**

Ryota Kondo\* and Takeshita T. Hiroyuki

provided the original work is properly cited.

Findings from this research point out in following:

## *Magnesium-Based Materials for Hydrogen Storage: Microstructural Properties DOI: http://dx.doi.org/10.5772/intechopen.88679*

before and after *τ*h, the growth rate of both MgH2 were higher before *τ*h than after *τ*h. The growth of MgH2(sur) and MgH2(int) were observed to stop after *τ*h because H supply route change from in Mg to MgH2. After *τ*h, the thickness of MgH2(sur) decreased and particle size of MgH2(int) increased with increasing Al concentration. This result could be explained by increase of supplied H amount to MgH2(int) due to the shifting *τ*h to longer time and small diffusion distance of MgH2(sur) which had low value of diffusion coefficient.

Findings from this research point out in following:

