A method of calculating a theoretical polarization curve of an inhibitor on a metal surface

Abstract

The application provides a method for calculating a theoretical polarization curve of an inhibitor on a metal surface, obtaining a pure Fe (110) surface from an iron body phase, constructing a 4*3*1 Fe (110) surface and performing structural optimization to obtain a stable Fe (110) surface; placing an inhibitor molecule on a top position of the Fe (110) surface in sequence and performing structural optimization to obtain a stable adsorption structure; adding a water molecule layer on the inhibitor molecule and performing structural optimization to obtain a stable co-adsorption system; calculating a planar average electron potential energy of the co-adsorption system to obtain an electrode potential of the system and surface charge information of the co-adsorption system; taking the co-adsorption system as a cathode and an anode, simulating anode electron loss and cathode electron gain processes in a corrosion process, calculating electrode potentials of the system in different charge states, linearly fitting the obtained electrode potentials, and obtaining a theoretical polarization curve. The application can preferably give polarization curves of various inhibitors on different metal surfaces.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal corrosion, in particular to a method for calculating the theoretical polarization curve of corrosion inhibitor on the surface of metal. BACKGROUND

[0002] Corrosion of metals has always been an extremely important scientific and social problem, and how to improve the corrosion resistance of metals has always been an urgent problem in materials science. Among various protective measures for resisting corrosion problems, corrosion inhibition is widely used due to its economy, high efficiency and high feasibility. By adsorbing corrosion inhibitors on the surface of metal, the corrosion of metal by corrosion factors in the water environment can be effectively resisted. Corrosion inhibitors are mainly adsorbed on the surface of metal to form a protective film to resist the corrosion effect of corrosion agents in the environment. The effectiveness of organic inhibitors in providing corrosion protection depends largely on the interaction between the corrosion inhibitor and the surface. At room temperature, the corrosion of metal in solution is carried out through two mutually coupled electrochemical half-cell reactions, i.e. anodic dissolution reaction and cathodic hydrogen evolution reaction. Adsorbed corrosion inhibitors can affect the corrosion reaction by physically blocking the surface or changing the activation barrier of the anodic and cathodic parts during the corrosion process.

[0003] At present, the corrosion inhibition performance of corrosion inhibitors is usually detected by experiment, which relies on the polarization curve of constant current or constant potential method. The polarization curve is the relationship curve between electrode potential and current density, which can simply and directly describe the polarization degree of electrode reaction, so that we can determine the strength of the corrosion resistance performance of various corrosion inhibitors by comparing the corrosion potential and corrosion current. However, although the experimental method and the characterization of the instrument can characterize the type, rate of corrosion and corrosion inhibition efficiency of corrosion inhibitors, the characterization of the atomic changes between corrosion inhibitors, metal and solution in the corrosion process is still insufficient. The theoretical research of corrosion inhibitors is also limited to the characterization of the corrosion inhibition performance of corrosion inhibitors by the thermodynamic parameters of corrosion inhibitor molecules and the adsorption strength on the surface of metal, and the research on the interaction between corrosion inhibitors and metal / solution interface is not much. However, the double-layer structure of metal / solution interface is an important structure of corrosion behavior, and the addition of corrosion inhibitors will directly change the electrochemical surface potential between water and metal, and then change the electrode potential of the system. Therefore, it is very important for us to understand the corrosion inhibition mechanism of corrosion inhibitors to study the co-adsorption form of corrosion inhibitor molecules and water molecules on the surface of metal from the atomic scale, and then analyze the interaction between corrosion inhibitors and metal / solution interface to reveal the corrosion inhibition behavior of corrosion inhibitors in the process of metal electrochemical corrosion. SUMMARY

[0004] The application aims to provide a method for calculating a theoretical polarization curve of an inhibitor on a metal surface.

[0005] The technical solution for achieving the object of the application is as follows: a method for calculating a theoretical polarization curve of an inhibitor on a metal surface, which realizes the calculation of a material polarization curve by establishing an electrochemical corrosion model, and the specific steps are as follows:

[0006] Step 1: obtaining a pure Fe (110) surface from an iron body phase, constructing a 4×3×1 Fe (110) surface and performing structure optimization to obtain a stable Fe (110) surface;

[0007] Step 2: placing the inhibitor molecules in the top position of the Fe (110) surface in turn, and optimizing the structure to obtain a stable adsorption structure;

[0008] Step 3: on the basis of the adsorption model obtained in the previous step, adding a water molecule layer on the inhibitor molecule, and optimizing the structure to obtain a stable co-adsorption system;

[0009] Step 4: calculating the planar average electron potential energy of the co-adsorption system, obtaining the electrode potential of the system according to the potential difference between the metal layer and the water molecule layer, and obtaining the surface charge information of the co-adsorption system;

[0010] Step 5: taking the co-adsorption system as a cathode and an anode respectively, introducing a series of excess surface charges into the co-adsorption system, calculating the electrode potential of the system under different charge states by adding or reducing 0.5-2 electrons, and linearly fitting the obtained electrode potential to obtain the theoretical polarization curve.

[0011] Further, in step 1, a pure Fe (110) surface is obtained from an iron body phase, a 4×3×1 Fe (110) surface is constructed and structure optimization is performed to obtain a stable Fe (110) surface, and the specific method is as follows: using the Materials studio software, importing the iron unit cell structure, cutting the iron unit cell, cutting out the Fe (110) surface and setting it to 3 layers, using the supercell function to expand the cut Fe (110) surface to 4×3×1, and using the PBE+vdW surf DFT method in VASP for structure optimization to obtain a stable 4×3×1 Fe (110) surface.

[0012] Further, in step 2, the inhibitor molecules are placed in the top position of the Fe (110) surface in turn, and the structure is optimized to obtain a stable adsorption structure, and the specific method is as follows: using the Materials studio software to construct imidazole or benzimidazole molecules, and using the PBE+vdWsurf The DFT method of PBE+vdW is used to optimize the structure; the optimized molecule is placed on the top position of the Fe (110) surface, and the PBE+vdW surf The DFT method of PBE+vdW is used to optimize the structure, and a stable adsorption structure is obtained.

[0013] Further, in step 3, a water molecule layer is added to the inhibitor molecule, and the structure is optimized to obtain a stable co-adsorption system. The specific method is: on the basis of the adsorption structure obtained in step 2, a water molecule layer is added above the inhibitor molecule, and the PBE+vdW surf The DFT method of PBE+vdW is used to optimize the structure, and a stable metal / inhibitor / water co-adsorption system is obtained.

[0014] Further, in step 4, the plane average electron potential energy of the co-adsorption system is calculated, the electrode potential of the system is obtained according to the potential difference between the metal layer and the water molecule layer, and the surface charge information of the co-adsorption system is obtained. The specific method is: using VASP software, the DFT method of PBE functional is used to calculate the plane average electron potential energy of the co-adsorption system formed by the inhibitor and the Fe (110) surface and the water molecules, and the surface potential E M of the metal and the potential E sol of the water molecule layer near the metal surface are obtained. The absolute value of the difference between E M and E sol is calculated, that is, the electrode potential of the system is obtained, and the calculation formula is: ΔE=|E M -E sol |, ΔE represents the electrode potential of the system.

[0015] Further, in step 5, the co-adsorption system is taken as a cathode and an anode respectively, a series of excess surface charges are introduced into the co-adsorption system, and the electrode potential of the system under different charge states is calculated by adding or reducing 0.5-2 electrons. The obtained electrode potential is linearly fitted to obtain the theoretical polarization curve. The specific method is: using VASP software, the DFT method of PBE functional is used to calculate the plane average electron potential energy of the co-adsorption system under different numbers of surface charges. When the system is taken as an anode, a series of loss surface charges are introduced into the co-adsorption system to calculate the potential, and then the electrode potential under different loss surface charges is obtained. When the system is taken as a cathode, a series of excess surface charges are introduced into the co-adsorption system to calculate the potential, and then the electrode potential of the co-adsorption system under different excess surface charges is obtained. The obtained electrode potential is linearly fitted to obtain the theoretical polarization curve of the system.

[0016] Compared with the prior art, the present application has the advantages that a method for calculating the theoretical polarization curve of an inhibitor on a metal surface without using empirical parameters is provided by using a first principle calculation method, and the polarization curve of various inhibitors on different metal surfaces can be better given, which has a good guiding effect on the research of new inhibitors. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a top view and a side view of imidazole and benzimidazole adsorbed on the Fe(110) surface.

[0018] Figure 2 is a front view of the co-adsorption configuration of imidazole / H2O on the Fe(110) surface.

[0019] Figure 3 is a side view of the co-adsorption configuration of imidazole / H2O on the Fe(110) surface.

[0020] Figure 4 is a front view of the co-adsorption configuration of benzimidazole / H2O on the Fe(110) surface.

[0021] Figure 5 is a side view of the co-adsorption configuration of benzimidazole / H2O on the Fe(110) surface.

[0022] Figure 6 is a planar average electron potential energy diagram of imidazole / H2O adsorbed on a receptor metal system.

[0023] Figure 7 is a planar average electron potential energy diagram of benzimidazole / H2O adsorbed on a receptor metal system.

[0024] Figure 8 is a theoretical polarization curve of imidazole / H2O adsorbed on a receptor metal system.

[0025] Figure 9 is a theoretical polarization curve of benzimidazole / H2O adsorbed on a receptor metal system. DETAILED DESCRIPTION

[0026] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0027] A method for calculating a theoretical polarization curve of an inhibitor on a metal surface, by establishing a general electrochemical corrosion model to realize calculation of material polarization curves, and the specific steps are as follows:

[0028] (1) Obtain a pure Fe (110) surface from an iron body phase, construct a 4*3*1 Fe (110) surface and perform structure optimization to obtain a stable Fe (110) surface;

[0029] (2) Place the imidazole or benzimidazole molecule on the top position of the Fe (110) surface in turn, and perform structure optimization to obtain a stable adsorption structure;

[0030] (3) On the basis of the adsorption model obtained in the previous step, add a layer of water molecules to the imidazole or benzimidazole molecule, and perform structure optimization to obtain a stable co-adsorption system;

[0031] (4) Calculate the plane average electron potential energy of the two co-adsorption systems, obtain the electrode potential of the system according to the potential difference between the metal layer and the water molecule layer, and obtain the surface charge information of the co-adsorption system;

[0032] (5) To simulate the anodic electron loss and cathodic electron gain process in the corrosion process, the co-adsorption system containing the imidazole or benzimidazole molecule is used as the cathode and anode respectively, a series of excess surface charges are introduced into the co-adsorption system, and the electrode potential of the system under different charge states is calculated by adding or reducing 0.5-2 electrons. Linear fitting of the obtained electrode potential can obtain the theoretical polarization curve.

[0033] Further, in step 1, the specific method is: using Materials studio software, importing iron unit cell structure, cutting the iron unit cell, cutting out Fe (110) surface and setting it to 3 layers, using supercell function to expand the cut Fe (110) surface to 4*3*1, and using PBE+vdW surf DFT method in Vienna Ab-initio Simulation Package (VASP) software for structure optimization to obtain stable 4*3*1 Fe (110) surface.

[0034] Further, in step 2, the specific method is: using Materials studio software to construct imidazole or benzimidazole molecule, and using PBE+vdW surf DFT method in VASP for structure optimization; place the optimized molecule on the top position of the Fe (110) surface in turn, and use PBE+vdW surf DFT method in VASP for structure optimization to obtain a stable adsorption structure.

[0035] Further, in step 3, the specific method is: on the basis of the adsorption structure obtained in step 2, a water molecule layer is added above the imidazole or benzimidazole molecule, and a DFT method of PBE+vdW surf is used in VASP to perform structure optimization, so as to obtain a stable metal / inhibitor / water co-adsorption system.

[0036] Further, in step 4, the specific method is: using VASP software, a DFT method of PBE function is used to calculate the plane average electron potential energy of the co-adsorption system formed between imidazole or benzimidazole and Fe (110) surface and water molecules respectively, so as to obtain the metal surface potential E M and the potential E sol of the water molecule layer near the metal surface, the absolute value of the difference between E M and E sol is calculated, and then the electrode potential of the system is obtained. The calculation formula is: ΔE=|E M -E sol |, and ΔE represents the electrode potential of the system.

[0037] Further, in step 5, the specific method is: using VASP software, a DFT method of PBE function is used to calculate the plane average electron potential energy of the co-adsorption system under the introduction of different amounts of surface charges. When the system is used as an anode, a series of loss surface charges are introduced into the co-adsorption system to calculate the potential, and then the electrode potential under different loss surface charges is obtained; when the system is used as a cathode, a series of excess surface charges are introduced into the co-adsorption system to calculate the potential, and then the electrode potential of the co-adsorption system under different excess surface charges is obtained. The obtained electrode potential is linearly fitted, so as to obtain the theoretical polarization curve of the system.

[0038] In order to verify the effectiveness of the present application, the following experiments are carried out. Embodiment

[0039] (1) Using Materials studio software, import the iron unit cell structure, cut the iron unit cell, cut out the Fe (110) surface and set it to 3 layers, use the supercell function to expand the cut Fe (110) surface to 4×3×1, and use a DFT method of PBE+vdW surf in Vienna Ab-initio Simulation Package (VASP) software to perform structure optimization, so as to obtain a stable 4×3×1 Fe (110) surface.

[0040] (2) Using Materials studio software to construct imidazole molecules, and using PBE+vdW surfDFT method of PBE+vdW surf The optimized structure of the adsorption structure is obtained by the DFT method of PBE+vdW Figure 1 .

[0041] (3) On the basis of the adsorption structure obtained in the previous step, 2 layers of water molecules are added above the imidazole molecule, and the structure is optimized by the DFT method of PBE+vdW surf in VASP, to obtain a stable metal / inhibitor / water co-adsorption system, as shown in Figures 2-3 .

[0042] (4) The plane average electron potential energy of the co-adsorption system is calculated by the DFT method of PBE functional using VASP software, as shown in Figure 6 . The metal surface potential E M and the potential of the water molecule layer near the metal surface E sol are obtained, and the electrode potential of the system is obtained by calculating the absolute value of the difference between E M and E sol . The calculation formula is: ΔE = |E M -E sol |, ΔE represents the electrode potential of the system.

[0043] (5) The loss of surface charge is introduced into the co-adsorption system to simulate the loss of electrons of the anode. The plane electron potential energy of the co-adsorption system under the introduction of-0.5 e, -1.0 e, -1.5 e, and -2.0 e is calculated, and a series of electrode potentials are obtained, as shown in Table 1. The excess surface charge is introduced into the co-adsorption system to simulate the gain of electrons of the cathode. The plane electron potential energy of the co-adsorption system under the introduction of 0.5 e, 1.0 e, 1.5 e, and 2.0 e is calculated, and a series of electrode potentials are obtained, as shown in Table 1.

[0044] (7) The electrode potentials under different charge states obtained are linearly fitted, and the theoretical polarization curve of the co-adsorption system is obtained, as shown in Figure 8 .

[0045] Table 1 Electrode potentials of Fe(110) / imidazole / H2O co-adsorption system under the introduction of different surface charges

[0046] Example

[0047] This example is basically the same as Example 1, the only difference is that the imidazole molecule is replaced by a benzimidazole molecule, and the obtained adsorption structure is as shown in Figure 1The co-adsorption system of metal / inhibitor / water is shown as Figures 4-5 The planar average electron potential energy of the co-adsorption system is shown as Figure 6 The electrode potential of the Fe(110) / benzimidazole / water co-adsorption system under different charge states is shown in Table 2, and the theoretical polarization curve is shown as Figure 9

[0048] Table 2 Electrode potential of Fe(110) / benzimidazole / water co-adsorption system under introduction of different surface charges

[0049]

[0050] The technical features of the above embodiments can be combined in any manner. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, but as long as the combinations of the technical features do not contradict, they should be considered as the scope of the present disclosure.

[0051] The above embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.​

Claims

1. A method of calculating the theoretical polarization curve of an inhibitor on a metal surface, characterized in that, The material polarization curve is calculated by establishing an electrochemical corrosion model, and the specific steps are as follows: Step 1: Obtain a pure Fe(110) surface from the iron body phase, construct a 4x3x1 Fe(110) surface and optimize the structure to obtain a stable Fe(110) surface; Step 2: Place the corrosion inhibitor molecules on the top position of the Fe(110) surface in turn, and optimize the structure to obtain a stable adsorption structure; Step 3: On the basis of the adsorption model obtained in the last step, add a layer of water molecules to the corrosion inhibitor molecules, and optimize the structure to obtain a stable co-adsorption system; Step 4: Calculate the plane average electron potential energy of the co-adsorption system, obtain the electrode potential according to the potential difference between the metal layer and the water molecule layer, and obtain the surface charge information of the co-adsorption system; Step 5: Introduce a series of excess surface charges to the co-adsorption system by applying or reducing 0.5-2 electrons to calculate the electrode potential of the system under different charge states, and the obtained electrode potential is linearly fitted to obtain the theoretical polarization curve; Among them, the co-adsorption system is taken as the cathode and anode respectively, and the electrode potential of the system under different charge states is calculated by applying or reducing 0.5-2 electrons, the specific method is: When the co-adsorption system is taken as the cathode, the loss of surface charge is introduced to the co-adsorption system to simulate the loss of electrons of the anode, the plane electron potential energy of the co-adsorption system under the introduction of-0.5 e, -1.0 e, -1.5 e, -2.0 e is calculated, and then the electrode potential of the co-adsorption system under different loss of surface charge is calculated; When the co-adsorption system is taken as the anode, the excess surface charge is introduced to the co-adsorption system to simulate the process of getting electrons of the cathode, the plane electron potential energy of the co-adsorption system under the introduction of 0.5 e, 1.0 e, 1.5 e, 2.0 e is calculated, and the electrode potential of the co-adsorption system under different excess surface charge is calculated.

2. The method for calculating the theoretical polarization curve of a corrosion inhibitor on a metal surface according to claim 1, characterized in that, In step 1, a pure Fe (110) surface is obtained from an iron body phase, a 4x3x1 Fe (110) surface is constructed, and structural optimization is performed to obtain a stable Fe (110) surface. The specific method is as follows: using the Materials studio software, importing the iron unit cell structure, cutting the iron unit cell, cutting out the Fe (110) surface and setting it to 3 layers, using the supercell function to expand the cut Fe (110) surface to 4x3x1, and using the PBE+vdW surf DFT method in VASP for structural optimization to obtain a stable 4x3x1 Fe (110) surface.

3. The method for calculating the theoretical polarization curve of a corrosion inhibitor on a metal surface according to claim 1, characterized in that, In step 2, the inhibitor molecules are placed in turn on the top position of the Fe(110) surface, and the structure is optimized to obtain a stable adsorption structure. The specific method is as follows: the imidazole or benzimidazole molecule is constructed by using the Materials studio software, and the PBE+vdW surf DFT method is used for structure optimization in VASP; the optimized molecule is placed in turn on the top position of the Fe(110) surface, and the PBE+vdW surf DFT method is used for structure optimization in VASP to obtain a stable adsorption structure.

4. The method for calculating the theoretical polarization curve of a corrosion inhibitor on a metal surface according to claim 1, characterized in that, In step 3, a layer of water molecules is added to the inhibitor molecule, and the structure is optimized to obtain a stable co-adsorption system. The specific method is as follows: on the basis of the adsorption structure obtained in step 2, a layer of water molecules is added above the inhibitor molecule, and the PBE+vdW surf DFT method in VASP is used for structure optimization to obtain a stable metal / inhibitor / water co-adsorption system.

5. The method for calculating the theoretical polarization curve of a corrosion inhibitor on a metal surface according to claim 1, characterized in that, In step 4, the planar average electron potential energy of the co-adsorption system is calculated, the electrode potential of the system is obtained according to the potential difference between the metal layer and the water molecule layer, and the surface charge information of the co-adsorption system is obtained, and the specific method is as follows: the planar average electron potential energy of the co-adsorption system formed by the corrosion inhibitor, the Fe (110) surface and the water molecules is calculated by using the VASP software and the DFT method of the PBE functional, the metal surface potential E M and the potential E sol of the water molecule layer near the metal surface are obtained, the absolute value of the difference between E M and E sol is calculated, that is, the electrode potential of the system is obtained, and the calculation formula is: ΔE = |E M -E sol |, and ΔE represents the electrode potential of the system.

6. The method of claim 1, wherein the theoretical polarization curve of the corrosion inhibitor on the metal surface is calculated by, In step 5, the co-adsorption system is taken as the cathode and anode respectively, a series of excess surface charges are introduced to the co-adsorption system, and the electrode potential of the system under different charge states is calculated by applying or reducing 0.5-2 electrons, and the obtained electrode potential is linearly fitted to obtain the theoretical polarization curve, the specific method is: using VASP software, using DFT method of PBE functional to calculate the plane average electron potential energy of the co-adsorption system under the introduction of different number of surface charges, when the system is taken as the anode, a series of loss of surface charge is introduced to the co-adsorption system to calculate the potential, and then the electrode potential under different loss of surface charge is obtained; When the system is taken as the cathode, a series of excess surface charges are introduced to the co-adsorption system to calculate the potential, and then the electrode potential of the co-adsorption system under different excess surface charge is obtained; The obtained electrode potential is linearly fitted to obtain the theoretical polarization curve of the system.

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