Microstructures And Hydrogen Transport Properties Of Nb-Ti(Hf)-Co Alloys

As a new source of clean,pollution-free new energy,hydrogen has great potential for development.Palladium and its alloy have the advantages of high hydrogen permeability,good mechanical stability and high catalytic activity,and are currently used hydrogen separation alloy membranes.However,palladium is scarce,and has high cost for hydrogen separation,not suitable for large-scale industrial applications.Group 5B metals（such as Nb,V,Ta）have high hydrogen permeability and abundant resources.The formation of multiphase and functional sharing by alloy design is one of the important research directions in the development of hydrogen separation alloys with high hydrogen permeability and hydrogen embrittlement resistance.The Nb₄₀Ti₃₀Co₃₀ alloy with excellent performance is selected to adding hafnium.The microstructure and hydrogen permeation properties of Nb-Ti（Hf）-Co alloy are studiedNb₄₀Ti_30-xHf_xCo₃₀（x=0,5,10,15,20,30）hydrogen separation alloy was prepared by element substitution method,and the alloy membrane was subjected to microstructure analysis and hydrogen permeation performance test.The alloy Nb₄₀Ti₃₀Co₃₀ consists of Bcc-（Nb,Ti）phase and B₂-TiCo phase;with the increase of hafnium content,the phase composition of the alloy becomes Bcc-（Nb,Ti,Hf）and B₂-（Ti,Hf）Co phase;when x=30,the phase composition of the alloy is Bcc-（Nb,Hf）and Bf-HfCo phase.The Nb-Ti（Hf）-Co alloy consists of the primary Bcc-Nb phase and the eutectic[Bcc-Nb+（Ti,Hf）Co]phase.With the increase of hafnium content,the volume fraction of Bcc-Nb phase in the alloy increases gradually,which is conducive to improve the hydrogen permeability of the alloy.The hydrogen permeation flux of the alloy increases with increasing temperature and upstream pressure.The hydrogen permeation flux of Nb₄₀Ti_30-xHf_xCo₃₀ alloy increases with the increase of hafnium content.When the upstream pressure is 0.2-0.4MPa,the hydrogen permeation flow rate J?L of the alloy is linearly related to the pressure difference?P^0.5,and the hydrogen permeability coefficientФdoes not change with pressure.When the upstream pressure is greater than 0.4MPa,the hydrogen permeability coefficient of the alloy varies with pressure.The hydrogen permeability coefficient of the alloy increases with increasing temperature.The hydrogen permeability coefficient of the alloy increases with the increase of hafnium content,and the substitution of hafnium for titanium can improve the hydrogen permeation performance of the alloy.The hydrogen solubility of the Nb-Ti（Hf）-Co alloy increases as the equilibrium pressure increases.At 673 K,the hydrogen solubility of the alloy is significantly higher at pressures less than 0.01 MPa.The hydrogen solubility of the alloy increases with the decrease of temperature,and the influence of temperature is especially obvious when the pressure is less than 0.01 MPa.The substitution of hafnium for titanium does not change the shape of the alloy PCT curve.The hydrogen solubility and PCT factor of the alloy increase with the increase of hafnium content,which can improve the hydrogen permeation performance of the alloy.The relationship between the hydrogen concentration and the equilibrium pressure P^0.5 in the alloy can be expressed by the modified Sievert’s law,but there is still an error,and the hydrogen permeability coefficientФcannot accurately describe the hydrogen permeation performance of the alloy.According to the hydrogen permeation model driven by the chemical potential gradient,the hydrogen permeation flow rate J*L is proportional to the PCT factor.The hydrogen atom mobility B of the alloy can be determined from the slope of the fitted straight line.The hydrogen atom mobility of the Nb-Ti（Hf）-Co hydrogen separation alloy increases with increasing temperature.The atomic mobility of the alloy increases as the hafnium content increases.The substitution of hafnium for titanium helps to increase the hydrogen atom mobility B in the Nb-Ti（Hf）-Co hydrogen separation alloy and enhance the hydrogen diffusion properties of the alloy.