| Hydrogen energy, being an environmental friendly and sustainable new energy,has attracted increasing attentions. Splitting water using Al to produce hydrogen isbecoming more and more interested, for Al abundance in nature, higher energycapacity and mild temperature of reaction with water. Particularly, the resultant ofreaction can be fully recycled. In fact, Al will not react with water directly because athin layer Al oxide forms on Al surfaces due to high chemical activity of Al.Alloying Al with low melting point metals like Ga, In and Sn, the influence of oxidefilm on Al-water reaction can be avoided effectively, resulting in the prepared alloyreacts with water quickly and continuously.Some key questions still need to be solved before practical application of thiskind of alloy in the future. These mainly contain:（1） relations among microstructure,chemical composition and preparation techniques of Al-rich alloy.（2） interfacialreaction of Al with Ga-In-Sn phase.（3） relations between hydrogen generation rateand microstructure of Al alloy together with key factors controlling the reaction ofAl-water.（4） mechanism of Al to split water. In order to solve these questions, manyinvestigations have been conducted by the present dissertation concerning the issuesof preparation technique, microstructure, reaction mechanism. To prepare Al alloyswith different chemical compositions, methods of arc melting and induction meltingwere carried out. SEM, and XRD were use to characterize the microstructure, phaseconstitutes of alloys, and DSC was performed to measure the melting point ofGa-In-Sn. The splitting water reactions of Al-water were measured using a waterdisplacement method. The obtained important results are:（1） The phases of Al-Ga-In-Sn alloy depend on the compositions of alloy. Thealloy only contains Al（Ga）solid solution and In3Sn（Ga） intermetallic compound twophases with a larger weight ratio of In:Sn of15:7; a new phase InSn4（Ga）was formedwhen the weight ratio of In:Sn was19:11.（2） The Al grain size, size and number of Ga-In-Sn are connected with the preparation techniques. Al grains are large and columnar shape as the alloy solidifiedat lower cooling rates. Their surfaces are covered with small amount of plate-likeGa-In-Sn phase. The Al grains are refined with the increase of cooling rate and thenumber of granular Ga-In-Sn phase increases.（3） The results of DSC experiment confirm that Al alloy contains Ga-In-Snphase with low melting point, which reacts with Al at Al grain boundaries.（4） The formation of Al-Ga-In-Sn eutectic by the interfacial reaction of Al withGa-In-Sn, is the origin of Al being capable of splitting water continuously.（5） the hydrogen generation rate strongly depends on the microstructure of alloy.The Al grain size, composition, size and number of Ga-In-Sn phase are key factorsgoverning the reactivity of Al-water. Based on measurements, an analyticalexpression was found to correlate those relations.（6） The finer the Al grain size, the smaller the activation energy of Al-waterreaction. In another words, Al reacts with water fast.（7） When the amount of low melting point metals was fixed to6wt%andIn:Sn=15:7, the alloy exhibits a maximum hydrogen generation rate with a Gacontent of3.8wt%. The hydrogen generation rates are smaller as the Ga content inalloy is either too much lower or higher. The presence of new phase InSn4（Ga）enhances the reactivity of Al with water.From the above studies, the relationships among microstructures, compositions,preparation techniques and reactivity of alloy are well understood, and themechanism of Al-water reaction is clear. The works have made experiment andtheoretical fundamentals for the applications of alloys. |
