Fabrication Of Porous Ni-Cr-Mo-Cu Materials And Its Application

The research purpose of this paper is to prepare porous Ni-Cr-Mo-Cu filtration material which is suitable for this harsh environment by combining with the complicated conditions of hydrometallurgy and wet phosphoric acid,and to conduct in-depth study on the pore structure performance,high temperature oxidation resistance and corrosion resistance of porous Ni-Cr-Mo-Cu filtration materials by various means.The diffusion rate of each atom is calculated by combining the diffusion equation.The effect of Cr content on porous Ni-Cr-Mo-Cu materials was investigated,and the pore formation mechanism of porous Ni-Cr-Mo-Cu materials was discussed,and the oxidation and corrosion mechanism of porous materials under high temperature and acid environment were studied.Finally,the hydrogen evolution performance of porous Ni-Cr-Mo-Cu materials in alkaline environment was discussed,and the phosphating was carried out to improve its hydrogen evolution performance,and good experimental results were obtained.The main contents and conclusions of this study are as follows:(1)Porous Ni-Cr-Mo-Cu materials were fabricated by reactive synthesis sintering technique with Ni,Cr,Mo and Cu element powders as raw materials.Phase composition,the volume expansion ratio,pore structures and pore morphology were characterized and the pore forming mechanism was discussed.The results indicate that the pore size,porosity and volume expansion rate of porous materials increase with the increase of Cr amount.When the Cr content is 30 wt.%,the open porosity reaches 42.10%,the total porosity is48.36%,the volume expansion rate is 12.60%,the average pore size and permeability are13.32?m and 96.3 m³·m^-2·kpa^-1·h^-1,respectively.The diffusion rates of Cr,Mo,Cu atoms in different matrix elements at 1150?are calculated,and the calculation results illustrate that the diffusion rates of Cr atoms in Ni and Cu atoms are 1.61×10^-14m²·s^-1and8.22××10^-13m²·s^-1,respectively,which is higher than the diffusion rates of Mo and Cu atoms.The pore forming mechanism is explored and it is mainly based on the inter-connected pores in the green compacts and the Kirkendall effect due to the different diffusion rates of Cr,Mo and Cu atoms in the nickel substrate.(2)The oxidation kinetic curve was measured by the static weight method,and X-ray diffraction(XRD),scanning electron microscope(SEM),X-ray photoelectron spectroscope(XPS),energy dispersive spectroscopy(EDS)and pore size tester have characterized the surface oxide composition,structure and morphology of porous Ni-Cr-Mo-Cu material at600-800?.The experimental results show that the oxidation kinetics of the porous material is pseudo-parabolic type,and the oxidation mass increases rapidly at the initial stage,as the oxidation time goes on,it becomes slower gradually.The surface of the alloy is composed of dense oxide film,the oxidation products are mainly Cr₂O₃and Ni O.The maximum pore size and permeability decreases as the exposure time increases and the temperature rises,but the permeability reduction rate is controlled within a certain range.(3)The effects of Cr content varied from 10 to 30 wt%on the corrosion performance of porous Ni-Cr-Mo-Cu materials in 10 wt%H₂SO₄solution were evaluated using a weight-loss method and electrochemical techniques.The structural morphology,phase constitution and elemental distribution were characterized by scanning electron microscopy,X-Ray diffraction analysis,energy dispersive spectrometer and X-ray photoelectron spectroscopy.The results indicate that porous Ni-Cr-Mo-Cu materials possess excellent corrosion performance,which exhibit better corrosion resistance than dense Ni and Cu.With incremental changes in Cr contents,the porous alloys anti-corrosion ability increases as well.Electrochemical measurements illustrate results similar to that of weight-loss method,with the increment of Cr content,the double capacitive loops for the porous Ni-Cr-Mo-Cu materials in electrochemical impedance spectroscopy tests increases as well,which illustrate that the corrosion procedure is controllable by electrochemical reaction.Moreover,the charge transfer resistance of Ni30wt%Cr10wt%Mo5wt%Cu is 49.2 times bigger than that of Ni10wt%Cr10wt%Mo5wt%Cu.The corrosion mechanism was explored by X-ray photoelectron spectroscopy,and the results revealed that the main corrosion products were Cr₂O₃,Ni OH,Ni(OH)₂and Mo O₂,especially with a passive Cr₂O₃film that prevented further corrosion in acid solution.(4)The electrochemical characterization for hydrogen evolution reaction(HER)was investigated by cyclic voltammetry curves,electrochemical impedance spectroscopy,and linear sweep voltammetry.Different parameters,including Cr content,temperature,and solution concentration that affected electrocatalytic activity for HER were also considered.The results illustrated that porous Ni-Cr-Mo-Cu electrodes possessed excellent hydrogen evolution performance,and the Cr content within a certain range 15?25 wt.%improved hydrogen evolution catalytic activity.The surface roughness Rf of porous Ni25wt.%Cr10wt.%Mo5wt.%Cu alloy electrodes was 8718.4,and the electrochemical activation energy is determined to be 7.46 k J·mol^-1,compared with 53.44 k J·mol^-1for porous Ni15wt.% Cr10wt.% Mo5wt.% Cu alloy electrodes.