Hydrogen absorption and electrochemical properties of Mg _2-xNi (x=0-0.5) alloys prepared by bulk mechanical alloying

Thermodynamic properties of hydrides of Mg _2-xNi alloys produced by bulk mechanical alloying were determined from the pressure-composition isotherms for absorption over the temperatures from 623 to 423 K. The van't Hoff plots for the plateau pressures of the isotherms clearly indicated the existence of high- and low-temperature hydrides with different entropy and enthalpy for hydride formation. The phase transition temperature was 525 K for Mg _2.0Ni and decreased with increasing value of x. Chemical and electrochemical behaviors of Mg _2-xNi alloys in an alkaline solution were precisely determined. It was found that hydrogen absorption in Mg _2-xNi alloys takes place by only immersing the alloys in 6 M KOH solution. On the other hand, during electrical charging hydrogen content increased with the quantity of charged electricity and reached the maximum value. However, the hydrogen content decreased afterwards because the corrosion of the alloys in the alkaline solution is significant.