Magnesium and magnesium alloys have high strength/weight ratios and are frequently utilized in various structures to reduce weight. However, due to the activity of Mg, magnesium alloys are prone to be corroded in marine atmosphere.

The powder thermal diffusion alloying method, or pack cementation, is frequently employed to enhance the corrosion resistance of magnesium alloys. Traditionally, it is crucial to change the diffusion source between two successive pack cementation processes.

Recently, a research team led by Prof. HUANG Yanliang from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) proposed a new diffusion source that could be utilized in multiple pack cementation processes, i.e., a recyclable diffusion source.

The study was published in Journal of Cleaner Production on Feb. 23.

The recyclable character of this diffusion source is mainly attributed to reversible chemical reactions related to a compound called zinc hydroxide chloride. When heated, the compound will decompose, and active metal ions will emerge. Upon cooling, zinc hydroxide chloride will form again. Then a cycle forms.

"This cycle indicates that the diffusion source could be utilized repeatedly for coating fabrication on magnesium alloys," said Dr. LU Dongzhu, first author of the study.

"Between two adjacent pack cementation processes, there is no need to change the diffusion source for a new one or add other materials into the diffusion source," said Prof. HUANG.

Promotion of such a recyclable diffusion source would save materials in the pack cementation industry. "Meanwhile, the omitted reloading of powders between two adjacent pack cementation processes can protect related workers' health and the environment," said Dr. LU.

This work was supported by the National Natural Science Foundation of China for Exploring Key Scientific Instrument, the Nantong Science and Technology Development Funds, and the Central Government Guiding Funds for Local Science and Technology Development.

Comparation of the utilization of the classical diffusion source and the recyclable diffusion source (Image by IOCAS)