First-principles Study On Hydrogen Permeation Characteristics Of Vanadium Based Solid Solution Alloy

VB-group metal vanadium?V? is an important material for hydrogen separation and purification.Arising from its low cost,high hydrogen permeability and good mechanical strength,it is favored by people.However,pure V is prone to hydrogen embrittlement and oxidation,and the dissociation and recombination efficiency of hydrogen is slow,which is very restricted in practical application.Studies have shown that V alloying can change the hydrogen embrittlement effect,surface oxidation,hydrogen dissociation and recombination,thereby improving the hydrogen permeability and mechanical properties of vanadium-based alloys.For this reason,the effects of H on V?1 0 0?surface and in the bulk as well as the doping of transition metal elements?M=Mo,W,Pd,and Ni?on their thermodynamic stabilities and hydrogen permeation properties are systematically studied by using first-principles calculation.1.In the low-miller exponential crystal plane of V,the V?1 0 0?surface is the most stable,and in the range of H coverage of 0.25-1 ML,the most stable configuration of H atoms or molecules adsorbed on the surface is hollow site?HS?>bridge site?BS?>top site?TS?.Among them,H atoms and molecules belong to chemisorption and physical adsorption respectively,and H molecules are adsorbed on the surface in a vertical way,with a bond length,dissociation energy and the vibration frequency of 0.752?,4.511 e V and 4262 cm^-1,respectively.The preferred path of H atom diffusion from the surface to the second subsurface is BS?TIS?1??TIS?2??TIS?3?.For adsorption in intrinsic V,single H atom preferentially occupies the tetrahedral interstitial site?TIS?,then the diagonal interstitial site?DIS?,finally the octahedral interstitial site?OIS?.The optimal diffusion path of H in the interstitial is TIS?DIS?TIS.In addition,H dissolution and diffusion depend on the concentration of doping elements and H,and are influenced by the lattice distortion and the electronic structure.2.When the doping amount of Mo and W is 25%,the V-based solid solutions not only have excellent mechanical and thermodynamic properties,but also yield the best resistance to hydrogen brittleness and permeability.Among them,V_0.75Mo_0.25 and V_0.75W_0.25have better hydrogen permeability,while V_0.5Mo_0.25W_0.25has better hydrogen brittleness resistance.3.Pd doping reduces the adsorption capacity of hydrogen on V?1 0 0?surface and the diffusion barrier on the surface to the subsurface,and improves the hydrogen permeability.At ?=0.25 ML,the diffusion barrier from surface to subsurface of hydrogen atoms is minimal.The calculation of the electronic structure of the surface is shown that the Pd-H bond is weaker than the V-H bond,which is favorable for the hydrogen dissociation of the surface.4.Ni doping reduces the hydrogen solubility in the monovacancy of vanadium solid,which helps to inhibit the generation of hydrogen embrittlement.The H atom preferentially occupies the nearby OIS rather than the center of the vacancy.A single vacancy can capture six H atoms.The concentration of a single vacancy and vac-n H cluster is largely dependent on the temperature and H concentration,respectively.Finally,the diffusion of H in the vacancy is mainly along the OIS?OIS path,and the H diffusion energy barrier rises,indicating that the presence of a vacancy is not conducive to H diffusion.This thesis systematically studied the effect of alloying elements on Mo,W,Pd and Ni doping on the penetration behavior of H in V metal through the first-principles calculation method.The basic physical data of the project of this research group were completed,and the necessary theoretical basis was provided for the material design and preparation of hydrogen permeable alloy membranes.