Investigation On The Corrosion Resistance And Gradient Of Porous Ni-Cr-Fe Materials

There are some features in metal porous materials: high strength,low density and weldable.The application of porous materials makes great contribution to enhance the efficiency of industry production,energy conservation and recycle resources.Due to porous alloys are senior to superficial area,one of the key problems that retardded their industry applicantion is poor corrosion resistance.With the rapid development of industry,in industrial production and environmental protection,more high-level are required.The gradient porous materials have both good filtration precision and excellent filtration seepage flow,especially in the field of filtration and separation.It can largely improve the production efficiency of industrial and save energy.Therefore,it is necessary to study on the corrosion activity and the gradient of porous alloys.The porous Ni-Cr-Fe alloys were prepared by reactive powder synthesis method.The objective of this work is to investigate the electrocatalytic corrosion behavior and corrosion mechanism of the porous Ni-Cr-Fe alloys obtained by reactive synthesis of Ni,Cr and Fe elemental powders in the 2 mol/L KOH solution by using electrochemical and immersion corrosion method.Polarization resistance indicate that porous Ni-Cr-Fe alloys has more positive free corrosion potential and lower corrosion current than porous Ni.The results of open circuit potential(OCP)indicates that the corrosion resistance of porous Ni-Cr-Fe alloys with a lower porosity is better.The immersion test reveals,that the weight change of porous Ni-Cr-Fe alloy stayed stable in KOH solution after 600 h immersion.X-ray photoelectron spectroscopy(XPS)results revealed that the corrosion products of porous Ni-Cr-Fe alloys are NiO,NiOOH,Ni(OH)2,Cr2O3,FeCr2O4 and the corrosion products of porous Ni are NiO,NiOOH,Ni(OH)2.In addition,the corrosion mechanism of porous Ni-Cr-Fe alloys is also discussed.The corrosion behavior of porous Ni-Cr-Fe alloys which prepared by reactive powder synthesis method is studied at 400 ? in pure chlorine corrosion of 720 h.porous Ni-Cr-Fe alloys shows excellent corrosion resistance.Porosity change about13.4% and the largest aperture drop about 4.3%.XRD and XPS analysis shows that the corrosion products of porous Ni-Cr-Fe alloys are NiCl3,Cr2O3,CrCl3 and FeCl2.The corrosion products of porous Ni-Cr-Fe alloys have higher melting point and lower vapor pressure.The structure of the corrosion products has high density and good stability.It can repress the metal corrosion.The gradient porous Ni-Cr-Fe alloys were prepared by powder metallurgy method and powder brush techniques,which used the principle of partial diffusion in solid phase sintering in this paper.The layer thickness,changes of pore structure and the bonding strength of layer of the gradient porous Ni-Cr-Fe alloys are characterized to research its properties.Results are presented to show that the alloy powder with different sizes and layer thickness have a significant impact on pore structure properties of the gradient porous Ni-Cr-Fe alloys.When the size of powder varies greatly,membrane layer can easily collapse,and fine powders will plug up support body.so that the permeability decrease greatly.When the membrane layer thickness is thinner,the structure of layer is incomplete.Instead,it can seriously affects the flux of filtration.Therefore,it is necessary to add the transition layer.When thickness of transition layer is 80 ?m and thickness of surface membrane layer is 30?m,the gradient porous Ni-Cr-Fe alloys has the maximum pore size of 6?m,the porosity of 936 m3·m-2·h-1·KPa-1and porosity descended of 22.64%.In addition,the support body and membrane layer are homogeneous,so a first order and second order gradient porous Ni-Cr-Fe alloys has good bond strength and thermal shock resistance.It is a ideal material for various severe environment.