Research Progress of Dual-Phase Hydrogen Separation Alloy Films
Hydrogen has the characteristics of high combustion calorific value,the product of its combustion is water,is one of the world's cleanest energy,and hydrogen resources are rich,can be sustainable development.In the context of"carbon peak,carbon neutral",hydrogen energy has become the focus of scientific research in recent years.Hydrogen energy is a sustainable secondary ener-gy source,and the increasing demand for reliable renewable energy sources has stimulated the development of a hydrogen economy.Hydrogen production,storage,transportation and application technologies have also become the focus of attention in the 21st century.The importance of hydrogen production is self-evident,traditional hydrogen production methods such as fossil fuel reforming often con-tain varying degrees of impurity gas,so hydrogen separation and purification is an essential part of the production of high purity hydro-gen,hydrogen separation membrane is an important hydrogen purification material.The membrane described here is a kind of function-al material with special selectivity in the form of film,which can be separated by screening or controlling the relative rate of different components passing through the membrane in the mixing system.Membrane separation technology has the advantages of environmental friendliness,economic feasibility and strong adaptability.Starting from the types of membranes,separation mechanism and prepara-tion method,the transport mechanism of hydrogen in dense membranes based on the atomic dissolve-diffusion mechanism was de-scribed in combination with the schematic diagram,and then the research progress of dual-phase alloy hydrogen separation membranes was reviewed.Firstly,the types of dual-phase hydrogen separation alloy membranes with metal solid solution and oxide particles as the second phase particles were introduced respectively.As the second phase,the solid solution could be divided into two types:ordinary casting and eutectic structure.The metal solid solution played a key role in hydrogen penetration,and the resistance to hydrogen em-brittlement was regulated by the eutectic structure.During high-temperature treatment,the metal underwent atomic interdiffusion be-tween thin palladium(Pd)/Pd alloy layers and metal components.In order to inhibit the interdiffusion of atoms,a ceramic layer must be introduced as a diffusion barrier.The common methods for forming interdiffusion barrier layers included coating thin ceramic lay-ers,such as oxide materials such as ZrO2,TiO2,Al2O3,and SiO2.Then the process,characteristics and shortcomings of the prepara-tion of hydrogen separation film by ordinary casting process were describe.Ordinary casting could obtain a large number of equiaxed crystals,and pointout that the traditional casting process such as arc melting method had a fast-cooling speed,resulting in uneven in-ternal structure of the alloy,a large number of defects,and the prepared alloy film was thicker and had higher fatigue strength.It was necessary to homogenize annealing treatment in the later stage,which was difficult to achieve large-scale production applications.This led to the special process of directional solidification,because the directional solidification technology was to establish a specific direc-tion of the temperature gradient in the mold,so that the melt alloy along the opposite direction of the heat flow,according to the re-quired crystallization orientation of the solidification casting process,could greatly improve the comprehensive properties of superal-loys.This technique could control the grain orientation of the solidified structure,eliminate the transverse grain boundary,and greatly improve the longitudinal mechanical properties of the material.Then,the effects of directional solidification process on the microstruc-ture,hydrogen permeability and hydrogen brittleness resistance of the membrane of the dual-phase hydrogen separation alloy were summarized,and the reported alloy systems with both excellent hydrogen permeability and good hydrogen brittleness resistance were listed.On this basis,the hydrogen permeability properties of the dual-phase alloys with common hydrogen separation pure metals and different processes were compared.It then concluded that by adjusting the solidification conditions,it was possible to control the micro-structure over a wide range,from well-arranged sheets to finely dispersed particles or fibers.Directional solidification of binary or pseu-do-binary eutectic could produce well-aligned regular structures composed of fibrous rod-like or lamellar components.Such structures might offer significant improvements in high temperature strength,fracture properties or creep resistance compared to conventional cast alloys.The appropriate directional solidification process could change the microstructure and phase distribution of the alloy,and increase the hydrogen diffusivity and permeability of the alloy.More importantly,it could also enhance its resistance to hydrogen brit-tleness.Crystallization and solidification were the core of the casting formation process,which determined the formation of the struc-ture and defects of the casting,and also determined the performance and quality of the casting.At last,it was pointed out that although scholars in various countries had conducted in-depth exploration and research on hydrogen separation alloy system,outstanding results had been achieved at present,but it was far from large-scale commercial application.The dual-phase hydrogen separation alloy film had high catalytic performance,reasonable hydrogen permeation performance and good durability,and had a good application pros-pect.By further adjusting the alloying element content and controlling the phase composition,the hydrogen separation alloy film with excellent comprehensive properties could be obtained,and was expected to become a reliable material for hydrogen separation and pu-rification in the future.
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