Research On Reaction Of Aluminum-based Alloys With Water

Aluminum is widely used in the field of hydro-reactive metal fuel and hydrogen generated because of its high volume energy density and hydrogen carrying capacity.However,the oxide produced on the surface of the Al powder leads to high start-up temperature and low conversion efficiency when reacting with water.To solve these problems,in this paper the elements including Li,Mg and Zr were added to Al,and the binary,ternary and quaternary aluminum-based alloy powders with different compositions were prepared by close-coupled gas atomization（CCGA）.The reaction activity and weight gain process of each alloy powders under the atmosphere of pure vapor were studied by steam-synchronous thermal analyzer.Further by monitoring the temperature variation in the process of the alloy/water reaction in the closed vessel,the effect of the mole ratio of water to fuel（W/F）and the different ions added into water on the reaction characteristics in the high-pressure environment were investigated.The products of the alloy/water reaction with different water-fuel ratios were characterized by XRD and SEM,and the hydrogen production and conversion rate of the reaction under each condition were measured by quantitative methods.The results showed that the starting temperature of the reaction with water was significantly reduced after alloying Li,Mg and Al,the start-up temperature of the reaction of Al-37Mg-3Li or Al-50Mg-5Li-5Zr with water was as low as 330℃at normal pressure,and the process was very intensive and complete.The start-up temperature of the alloy/water reaction was lower in the closed self-pressurized system（especially for Al-37Mg-3Li,whose reaction with steam started at 155℃when the pressure of the system reached 10.3bar）,and the reaction process of Zr-containing alloy with water was more concentrated and stable.Under the condition of the W/F was 1.5:1,both the two materials showed the best exothermic performance.Adding different kinds of ions to water could effectively reduce the start-up temperature of the alloy powders and water reaction,on the whole,a certain concentration of ions such as NO₃^—、SO₄^2—、Cl^—、K⁺、Na⁺could promote the reaction of alloy/water,in which the promotion effect of KNO₃ was the best.The starting temperature of the reaction of Al-50Mg-5Li-5Zr powders with this salt solution was decreased to 165.8℃（reducing by 20.1℃compared to the pure water）,and the exothermic temperature rise increased to 199.7℃（nearly 60℃higher than water）,the average heat-rising rate reached 6.657℃·s^-1（more than twice as much as water）.On the contrary,the same concentration of fluoride salts showed inhibition obviously.The priority order of the reaction between water and each phase in the aluminum-based alloy powder wasα-Al（Li）>Mg₂Al₃(Al₁₂Mg₁₇)>Al>Al₃Zr,and the hydrogen generation and conversion rate of the alloy/water reaction both grew with the W/F further increasing.Al-50Mg-5Li-5Zr reacted with water more effectively,when the W/F was 12:1,no combustible substance was found in the reaction product and the particles broke completely,with the conversion rate running up to 96.21%.