Thermodynamic Study On Ti-V-Zr/Co Hydrogen Storage Alloys Systems

Based on the concerns about the energy crisis and global warming,researchers have paid much attention to investigate and develop a renewable energy source.Hydrogen energy involves the use of hydrogen as a fuel,which is a zero-emission fuel when burned with oxygen and is a kind of unlimited energy reserves,has long been seen as an alternative energy source with high potential,but it has not been pursued due to difficulties with hydrogen production and storage.In order to use hydrogen energy more widely,these technological difficulties should be overcome.Since the Ti-V-based hydrogen storage alloys with body-centered cubic(bcc)structure is a new type of high-capacity hydrogen storage alloys,the development of the Ti-V-based hydrogen storage alloys has become a hot topic in recent years.Although the hydrogen capacity of Ti-V alloys itself is already high,this kind of alloys does not have the reversible electrochemical ability of absorption hydrogen.However,the existence of the second phase in Ti-V-based hydrogen storage alloys can improve the hydrogen absorption performance,it can make this kind of hydrogen alloys have a good dynamic hydrogen sorption property under the atmospheric pressure.Therefore,alloying has become the main method to conquer the weakness of the Ti-V hydrogen storage alloys at present.With the addition of the third elements such as Zr,Co,Ni,Mn and so on,laves phase is formed in the Ti-V-based hydrogen storage alloys,leading to the formation of bcc+laves two phases region to improve the properties of hydrogen storage.The present work is mainly focused on the binary and ternary systems composed of the alloying elements Zr and Co and the basic elements Ti and V.The phase-equilibrium experimental measurements and the thermodynamic optimizations are performed,in the meantime,Se-Sn-Te ternary system has been optimized.A set of self-consistent thermodynamic parameters of the individual ternary system is obtained,which are of importance reference to the composition design and the process control.The main research work is listed in the following.Firstly,the phase equilibrium experimental measurements have been worked.By the comprehensive consideration of the microstructure observation,the phase identification and the composition measurement of the V-Zr binary alloys,the solidification processes are analyzed.And combined with the experimental data of the literature,V-Zr binary phase diagram has been completed.Furthermore,with the comprehensive consideration of the means of the microstructure observation,the phase identification and the composition measurement of the as-cast Ti-V-Zr and Co-Ti-V ternary alloys,their solidification processes are analyzed.On the basis of the experimental data of the literature and present work,the liquidus projections of Ti-V-Zr and Co-Ti-V ternary system are constructed respectively.In addition,through the study of the equilibrium microstructure,the phase identification and the composition measurement of the Ti-V-Zr ternary alloys after the isothermal heat treatment at 1073 and 1273 K,the phase equilibrium relations and the isothermal sections at 1073 and 1273 K in the Ti-V-Zr system over the entire composition range are determined.Secondly,CALPHAD technique is used in the process of the thermodynamic assessments.According to the crystalline structures,the reasonable and unified thermodynamic models of all phases are selected.In consideration of the literature reported phase equilibrium data and the thermochemical data,as well as the present,obtained experimental results,the V-Zr binary systems is re-assessed.Moreover,the Ti-V-Zr and Co-Ti-V ternary systems are optimized based on the experimental liquidus projection and isothermal sections constructed by the literature and this work.In the process of Ti-V-Zr and Co-Ti-V ternary systems optimization.Ti-Zr and Co-V binary systems are revised.Besides the above systems,the Se-Sn-Te ternary system is optimized according to the experimental date in the literature and present work.The calculation results agree with the experimental data well.