Investigation On The Fabrication And Properties Of The Porous Ni-Cr-Fe Materials

With the rapid development of industry,the negative social and environmental consequences that come from energy over-consumption are become serious.The application of porous materials makes great contribution to enhance the efficiency of industry production,energy conservation and recycle resources.There are some features in Ni based materals:high strength and low density and low weight.Widely applications based on areospace and energy source have gained widely attention.Therefore,it is necessary to study the Ni based porous materials.The porous Ni-Cr-Fe alloys were prepared by reactive powder synthesis method,which used the principle of partial diffusion in solid phase sintering in this paper.The expansion rate,changes of pore structure and phase composition of porous Ni-Cr-Fe alloys under different sintering temperature were characterized to research the pore forming process and explore the mechanism of pore.The pore formation mechanism of porous Ni-Cr-Fe materials by reactive powder synthesis method is that the infinite solid solution of Ni matrix was formed,with the partial diffusion of Cr and Fe.The Fe atoms can solubilize firstly in Ni and the(Ni,Fe)solid solution was formed in process of sintering.When the temperature reached 1100?,the Fe had all reacted.Then part of the Cr atoms further dissolved in the(Ni,Fe)solid solution.Until 1380?,the reaction was complete.Eventually,Cr,Fe atoms dissolvesd completely into the Ni to form homogeneous solid solution.According to the different rate of pore formation,the pore formation of porous Ni-Cr-Fe materials are divided into two periods: Pore formative period belong to low temperature region(under 800?),the open porosity of porous Ni-Cr-Fe materials is about 20% in this period: Sintering temperature between 940? to 1380? is pore growth sharply period and the open porosity is about 32.5%.With the increase of temperature,open porosity maintaining stablility.The variation tendency of maximum pore size and the permeability are consistent with open porosity of porous Ni-Cr-Fe materials.Reaching the final sintering temperature,the mean pore size and permeability of porous Ni-Cr-Fe materials is 90?m,990m3m-2KP-1h-1,respectively.The oxidation behavior and mechanism of porous Ni-Cr-Fe materials in air from 600? to 1000? were studied.The differences of surface morphology,phase and pore structure paraments between material oxidized and non-oxidized were characterized by SEM,XRD and mercury intrusion.The results show that,oxidationregularity of porous materials are in parabolic rule under the oxidation temperature600?,800? and 1000?.The oxidation products are Ni Fe2O4,Ni Cr2O4,NiO,(Ni,Cr,Fe)at the temperature 600?and 800?,then the final oxidation products are NiFe2O4,NiCr2O4,NiO under 1000?.The differences of surface morphology,phase and pore structure paraments between Ni-Cr-Fe oxidized and before oxidized were slightly which oxidized 560 h at the temperature 1000 ?,and there were abundant pores remained in the surface of Ni-Cr-Fe.The oxidation products of Ni-Cr-Fe porous are tiny particles and closely attached to the substrate,so as to prevent the further oxidation,showing excellent high temperature oxidation resistance.The objective of this work is to investigate the electrocatalytic efficiency and stability using cyclic voltammetry,cathodic polarization and impedance spectroscopy techniques of the porous Ni-Cr-Fe cathode materials.The kinetic parameters are determined by electrochemical steady-state polarization and electrochemical impedance spectroscopy technology in 6mol/L KOH.The results show that porous Ni-Cr-Fe cathode material has excellent corrosion resistance in 6 mol/L KOH.The Tafel slope of best-performing porous Ni-Cr-Fe alloy is-130 m V dec-1 at high temperature,implying that the rate determining step for the HER(Hydrogen Evolution Reaction)is the proton discharge electrosorption(Volmer reaction).The value for the exchange current density is 7 x10-4A cm-2 at elevated temperature.The apparent energy of activation obtained from an Arrhenius plot for the porous Ni-Cr-Fe cathode material has been calculated to be-21 kJ mol-1.The results suggest that the significant catalytic performance is not only from the increase of the real surface area of the cathode material,but also from the intrinsic catalytic effect.After hydrogen evolution 8 hours at-1.5V,the current density fluctuation is slightly.SEM images show that the surface morphology and the pore structure of the porous Ni-Cr-Fe alloy unchanged after polarization,which reveals a good stability of the electrocatalytic performance of the electrode.