The Effect Of Rare Earth Lanthanum On The Corrosion Resistance Of Copper And Copper-nickel Alloys

As common corrosion resistant materials,copper and copper-nickel alloys have been widely used in marine transportation,petrochemical industry and seawater desalination,The addition of rare earth elements can greatly improve the corrosion resistance of copper and copper-nickel alloys.At present,the application of rare earth in aluminum and magnesium alloys is relatively mature,but the application of rare earth in copper and copper-nickel alloy is deficient,There are also few publication about the application of rare earth in copper and copper-alloys.Therefore,this paper studies the effect of lanthanum on the corrosion resistance of copper and copper-nickel alloys,and provides a strong basis for the development of high performance copper and copper-nickel alloys.The morphology and composition of corrosion products on the surface of the samples were studied by sem scanning electron microscope and xrd phase analysis;the electrochemical impedance of the sample is measured by means of electrochemical test,compare the electrochemical corrosion properties of copper and copper-nickel alloys before and after the addition of lanthanum;the composition of passivation film is studied by X-ray electron spectroscopy,calculate the parameters of anodic passivation film based on the Mott-Schottky curve and the point defect model,disscuss the effect of lanthanum addition on semiconductor properties of passivation film of B10 copper-nickeli alloy.The results show that:(1)The corrosion product of pure copper is composed of Cu2O and Cu2(OH)3Cl after immersing in 3.5%NaCl solution,the Cu2(OH)3C1 corrosion product is triangular granular;the addition of lanthanum results in the formation of lamellar La2O3 corrosion product;the mesophase of CuLa with grid distribution in the matrix of copper alloy containing lanthanum has a large volume fraction,which can form a barrier layer,effectively improve the corrosion resistance of pure copper.(2)The corrosion product film on the surface of B10 copper-nickel alloy is composed of Cu2O and Cu2(OH)3Cl,at the beginning of soaking,a protective Cu2O product film is formed and the arc diameter of electrochemical impedance increases,at the later stage of soaking,the oxidation film reacts with Cl-,which leads to the reduction of electrochemical impedance arc diameter.(3)In addition to Cu2O,the corrosion prodcuct on the surface of B10 copper-nickel alloy containing lanthanum also conclud lamellar LaOOH and spherical Cu2(OH)3Cl,electrochemical impedance arc diameter of samples in solution increases and becomes stable later;electrochemical impedance fitting results of impedance at different time periods displays the increase amplitude of charge transfer resistance of B10 copper-nickel with lanthanum is larger than that of B10 copper-nickel alloy;under the same immersion time,the charge transfer resistance of B10 copper-nickel with lanthanum is larger than that of B10 copper-nickel alloy.The addition of lanthanum can improve the stability of product film on B10 copper-nickel alloy surface and increase the corrosion resistance of alloy.(4)B10 copper-nickel alloy and B10 copper-nickel alloy with lanthanum both have a good passivation performance in NaOH solution.the electrochemical impedance arc diameter of the sample in solution is increasing with the increasing of anodic passivation potential,as the anode potential is the same,the charge transfer resistance of B10 copper-nickel with lanthanum is larger than that of B10 copper-nickel alloy.The results of XPS show that the surface passivation film of B10 copper-nickel alloy is a double-layer structure,the inner layer is the compact Cu2O,the outer layer is CuO/Cu(OH)2/Ni(OH)2,after addition of lanthanum,La2O3 is doped in passivation film of B10 copper-nickel alloy;the passivation film on the surface of B10 copper-nickel alloy before and after addition of lanthanum are all p-type semiconductor;the addition of lanthanum can improve the resistivity of the passive film on the surface of B10 copper-nickel alloy,which impedes the diffusion of ions and electrons in the passivation film,thus improving the electrochemical corrosion resistance of B10 copper-nickel alloy.