Investigations On Design And Hydrolysis Properties Of Al-Bi-Zn Based Composite Powders

As a kind of energy,hydrogen has the characteristics of high calorific value,non-pollution and wide sources.There are many methods to prepare hydrogen,such as fossil fuels and electrolysis of water.Compared with these methods,the hydrogen generation by the Al-H2O reaction has drawn a lot of attentions due to its low cost,high efficiency,safety and environment-friendship.Therefore,the method of hydrogen generation by the Al-H2O reaction exhibits good prospect.However,some challenges exist for Al-based hydrolysis materials in practical applications.For example,Al-based hydrolysis materials are easily oxidized by O2 to form dense Al2O3 oxide layer,and this passivation layer reduces the reaction activity of composite powders.Another problem is that the reaction rate of Al-H2O reaction is too fast to control.In this study,based on CALPHAD and gas atomization methods,Al-Bi-Zn and Al-Bi-Zn-Sn composite powders were designed and prepared.Furthermore,the hydrogen production performances were studied in detail,and the reaction mechanism was explained.The results of this study are as follows:(1)In this study,Al-Bi-Zn and Al-Bi-Zn-Sn composite powders were designed by CALPHAD method.These designed composite povwders were successfully prepared by gas atomization method.The results show that both Al-Bi-Zn and Al-Bi-Zn-Sn composite powders exhibit liquid phase separation.These composite powders show a special microstructure,in which the Bi-rich or(Bi,Sn)-rich phase discontinuously wrapped Al-rich phase.(2)The hydrolysis properties of Al-Bi-Zn and Al-Bi-Zn-Sn composite powders were investigated.The effects of reaction temperature,reaction medium,alloy composition and stirring on hydrogen production performance were investigated experimentally.The results show that the Al-Bi-Zn-Sn composite powder has good hydrogen production performances,and the reaction rate can be controlled by changing reaction conditions.Among them,when the(Al,Bi,Zn)-6Sn(wt.%)composite powders react with 50℃ distilled water under stirring conditions,the final conversion rate can be close to 100%within 30 minutes.Even if composite powders react with distilled water at 30℃,a conversion rate of 80%within 170 minutes can be also achieved.(3)The Al-H2o reaction mechanism of composite powders was studied.The outer Bi-rich and(Bi,Sn)-rich phase ensure that some Al-rich phase are not oxidized,and the internal Bi-rich and(Bi,Sn)-rich phase could effectively activate composite powder.Both Al-H2O reaction and Al-Zn electrochemical reaction exist during the reaction process of composite powder with water.These two reactions are competitive,and the Al-H2O reaction rate is faster.