Increase In Reaction Area Research Articles

Design of Al–Fe alloys for fast on-board hydrogen production from hydrolysis

On-board hydrogen production from the hydrolysis of Al in alkaline water has received great attention because it eliminates the need for hydrogen storage. The Al powder, though providing high reaction rate in the hydrolysis, causes a serious problem of explosive danger when in contact with air or moisture, etc. Since the hydrogen generation rate increases linearly with the corrosion rate of Al to Al3+, an Al–Fe alloy, in which an electrochemically noble Al3Fe phase precipitates along grain boundaries, is designed, and hence causes fast hydrogen generation from the hydrolysis of Al in alkaline water by combined action of galvanic and intergranular corrosion. The Al alloy containing 1 wt% Fe increases the hydrogen generation rate 3.7 times compared with that of pure Al, in which 65% of the increase is due primarily to the galvanic corrosion between Al and Al3Fe phase, and 35% due to the increase in reaction area by intergranular corrosion.

Ｍｇ２Ｎｉ合金の均質化処理およびプロチウム吸・脱蔵特性

The Mg2Ni alloy was homogenized by a multi-stage heat treatment to assure the single phase, and its protium absorption and desorption characteristics were investigated. The results show that the Mg2Ni alloy containing a small amount of MgNi2 phase can be obtained by the heat treatment just below the peritectic temperature. The PCT curve shows two plateaus of Mg and Mg2Ni in the as-cast specimen. However, the plateau pressure of Mg solid solution is hard to appear in the heat-treated specimen because it is homogenized during the multi-stage heat treatment. Both activated as-cast and heat-treated specimens absorb protium at room temperature. They have higher protium contents than before activation. This phenomenon is caused by new surface formation and an increase in reaction area due to activation. As the elapsed time after taking specimens out from hydrogen atmosphere increases, the protium desorption temperature decreases and desorbed protium content increases. The decrease in desorption temperature is caused by a decrease in microtwinning in Mg2NiH4 low temperature phase. Also, grinding the powder of the hydride leads to similar improvement of hydrogen desorbing characteristics.