Method for evaluating insulation characteristics of c4f7n gas in high voltage insulation device

Abstract

The application provides a method for evaluating the insulation characteristics of C4F7N gas in a high-voltage insulation device. The method comprises the following steps: introducing initial parameters of SnSe material; performing geometric optimization on the SnSe layer; establishing a molecular model of C4F7N gas decomposition products; performing geometric optimization and energy calculation on the C4F7N gas decomposition products; constructing a calculation function of the SnSe layer; constructing a density functional theory calculation model of SnSe; establishing an adsorption model of the C4F7N gas decomposition products; deriving the state density of SnSe and the C4F7N gas decomposition products; calculating the work function change of the SnSe adsorption system in the C4F7N gas decomposition products; and evaluating the ability of the SnSe material to desorb gas. The method provided by the application can accurately evaluate the C4F7N decomposition products and their influence on the insulation performance, thereby effectively diagnosing the health status of the high-voltage insulation device and realizing early warning of insulation failure.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-voltage electricity and insulation, and particularly relates to a method for evaluating insulation characteristics of C4F7N gas in a high-voltage insulation device. BACKGROUND

[0002] Due to the excellent insulation performance and arc extinguishing ability of sulfur hexafluoride (SF6), SF6 has been widely used in high-voltage electrical equipment such as gas-insulated substations for a long time. However, as a greenhouse gas, the greenhouse effect potential of SF6 is much higher than that of CO2, so under the background of increasingly strict environmental protection regulations, the research on replacing SF6 has become increasingly urgent.

[0003] As a potential environmentally friendly alternative gas, C4F7N has gradually attracted widespread attention due to its lower global warming potential and good insulation performance.

[0004] However, the application of C4F7N in high-voltage insulation devices still faces many technical bottlenecks, such as the need for research on its insulation performance, breakdown characteristics, and the impact of decomposition products generated under insulation on the stability and safety of the equipment. In particular, C4F7N may decompose to generate various gas products under the action of an electric field, and these decomposition products may affect the insulation characteristics and thus the safety of the device. Therefore, studying the decomposition products of C4F7N and their impact on insulation performance is crucial to evaluating the application potential of C4F7N.

[0005] By monitoring the decomposition products of C4F7N, the health status of high-voltage equipment can be effectively diagnosed, thereby achieving early warning of insulation faults. Therefore, research on the gas-sensitive characteristics of C4F7N decomposition products will help develop online monitoring and fault diagnosis technologies. However, current research on C4F7N mainly focuses on basic insulation performance testing, and the decomposition characteristics of C4F7N under high-voltage and the impact of various gases generated on the insulation system have not been fully revealed. Whether these decomposition products will accumulate in the equipment or have a negative impact on the long-term reliability of the system needs further exploration. SUMMARY

[0006] In view of the deficiencies in the prior art, the purpose of the present application is to provide a method for evaluating the insulation characteristics of C4F7N gas in a high-voltage insulation device. The insulation characteristic evaluation method provided by the present application can accurately evaluate the influence of sensing materials on C4F7N decomposition products and insulation performance, thereby effectively diagnosing the health status of high-voltage insulation devices and achieving early warning of insulation faults, which provides a new approach for accurate diagnosis and online monitoring of environmentally friendly insulation gases in high-voltage insulation devices.

[0007] To achieve the purpose of the present application, the following technical solutions are adopted:

[0008] The application provides a method for evaluating the insulation characteristics of C4F7N gas in a high-voltage insulation device.

[0009] (1) The initial parameters of the SnSe material are imported from the Materials Studio material library, and after cutting the (001) crystal plane, the minimum unit cell structure of the SnSe layer is established.

[0010] (2) After geometric optimization of the SnSe layer, the system energy and charge of the SnSe layer are determined.

[0011] (3) The molecular model of the C4F7N gas decomposition product is established, and the C4F7N gas decomposition product is geometrically optimized to determine the system energy, charge, molecular bond length and bond angle of the SnSe layer.

[0012] (4) The single-chain adsorption structure of the C4F7N gas decomposition product is geometrically optimized and energy calculated.

[0013] (5) The calculation functions of the adsorption energy, doping energy and charge transfer amount of the SnSe layer are constructed, and the required calculation formulas and physical quantities are defined.

[0014] (6) The parameters of the self-defined adsorption calculation formula are set, and the density functional theory calculation model of SnSe based on the 7x7x1 Monkhorst-Pack k-point grid is constructed.

[0015] (7) The adsorption model of the C4F7N gas decomposition product is established on the top, hole and bridge positions of the Sn atoms and Se atoms on the surface of the SnSe layer, and then according to the overall energy and charge transfer of each adsorption structure, the SnSe-based composite adsorption structure with the smallest deformation, the largest charge transfer amount and the largest adsorption energy of the different target molecules is found by combining the self-defined adsorption calculation formula.

[0016] (8) The density of states of SnSe and the C4F7N gas decomposition product is exported and analyzed, and then the conductivity of the adsorption system is analyzed according to the energy curve integral and change degree near the Fermi level.

[0017] (9) The work function change of the SnSe adsorption system in the C4F7N gas decomposition product is calculated.

[0018] (10) The recovery time The desorption gas capacity of the SnSe material is evaluated to evaluate the effectiveness of the high-voltage insulation device, and the gas transmission capacity of the SnSe layer is evaluated.

[0019] The insulating property evaluation method provided by the application can accurately evaluate the influence of the sensing material (namely, the SnSe material) on the C4F7N decomposition product and the insulating performance, thereby effectively diagnosing the health state of the high-voltage insulating device and realizing early warning of insulating failure, which provides a new idea for accurate diagnosis and online monitoring of the insulating environment-friendly gas in the high-voltage insulating device.

[0020] It should be noted that the "7x7x1 Monkhorst-Pack k-point grid" is a parameter setting expression for sampling the Brillouin zone when performing first-principle calculations in the fields of material science and physics. The specific meaning is as follows:

[0021] Monkhorst-Pack method: This is a method for selecting discrete k-points in reciprocal space (Brillouin zone), which aims to efficiently sample the Brillouin zone as much as possible while ensuring calculation accuracy, in order to obtain information related to the electronic structure of materials. This method is widely used in first-principle calculations such as density functional theory (DFT).

[0022] Specific parameters of 7x7x1: The three numbers here correspond to the number of k-point divisions in three directions (usually the three coordinate axis directions of a three-dimensional crystal). For "7x7x1", 7x7 k-points are selected in two dimensions (such as the plane direction of the crystal), and only 1 k-point is selected in the third dimension (such as the vertical direction of the crystal). This asymmetric division is usually determined according to the structural characteristics of the crystal and the calculation requirements. For example, if the periodicity in a certain direction of the crystal is weak or the physical properties in that direction have little effect on the whole, fewer k-points can be selected in that direction to reduce the amount of calculation while ensuring the accuracy of the calculation results.

[0023] In summary, the 7x7x1 Monkhorst-Pack k-point grid is a way to sample the Brillouin zone of a crystal under a specific calculation method, which can effectively obtain information about the electronic structure of the crystal in first-principle calculations, providing a basis for studying the physical properties of materials.

[0024] Preferably, after the SnSe layer in step (2) is geometrically optimized, a Sn on the surface of the SnSe layer is removed to form a vacancy structure and is geometrically optimized, and then the system energy and charge of the SnSe layer are determined.

[0025] Preferably, step (3) establishes a molecular model of the C4F7N gas decomposition product and also establishes a model of a single transition metal atom; and when the C4F7N gas decomposition product in step (3) is geometrically optimized, the single transition metal atom is also geometrically optimized.

[0026] Preferably, the transition metal atom comprises a Ni atom.

[0027] Preferably, between step (6) and step (7), the following step is performed:

[0028] The single Ni atom of the geometry optimization is placed at the Sn vacancy of the SnSe layer to form a Ni-SnSe layer, and then the Ni-SnSe layer is re-geometry optimized.

[0029] In the present application, the Ni atom and the SnSe layer with Sn vacancy can form a reliable chemical bond, and during the adsorption process, obvious orbital hybridization is generated with the C4F7N gas decomposition product, so that the adsorption capacity of the SnSe layer can be significantly improved and optimized, and the theoretical recovery time and work function of the SnSe material at room temperature are obviously improved.

[0030] Preferably, the C4F7N gas decomposition product in step (3) comprises CF3CN, COF2 and C2F5CN.

[0031] Preferably, when the adsorption model of the C4F7N gas decomposition product is established in step (7), the distance between the C4F7N gas decomposition product and the SnSe layer is controlled to be 1.7-1.9 Å, for example, it can be 1.7 Å, 1.8 Å or 1.9 Å, etc.

[0032] Preferably, after step (7), the adsorption energy calculation formula of the C4F7N gas decomposition product on the SnSe layer is obtained:

[0033] E Ads =E Gas / SnSe -E SnSe -E Gas .

[0034] Wherein, E Gas / SnSe is the energy of the SnSe layer after adsorbing the C4F7N gas decomposition product, E SnSe is the energy of the SnSe layer, and E Gas is the energy of a single C4F7N gas decomposition product.

[0035] Preferably, after step (7), the charge transfer amount Q Tra of the SnSe adsorption system is obtained: a -Q b .

[0036] Wherein, Q a is the charge amount of the SnSe layer after adsorbing the C4F7N gas decomposition product, and Q b is the charge amount of the SnSe layer before adsorbing the C4F7N gas decomposition product.

[0037] Preferably, the formula used in step (9) for calculating the change of work function of the SnSe adsorption system in the C4F7N gas decomposition product is:

[0038] φ = E vacuum -E fermi .

[0039] wherein E vacuum is the potential far from the surface of the SnSe layer, and E fermi is the energy of the highest occupied state in the system.

[0040] It should be noted that the work function (WF) is defined as the energy required for an electron to escape from the surface of a material.

[0041] It should be noted that the above system refers to a doped system and an adsorption system.

[0042] In the present application, the work function can be used to further analyze the adsorption characteristics of the SnSe adsorption system, and can reveal the influence of transition metal atom doping on the electronic properties of the SnSe material surface and its interaction with gas molecules.

[0043] Preferably, the formula for calculating the recovery time in step (10) is:

[0044] = v0 -1 exp(-E a / kT).

[0045] wherein v0 -1 is the attempt frequency, which is 10 12 s -1 ; k is 1.38x10 -23 J / K; and T is the actual temperature, in K.

[0046] It should be noted that the recovery time refers to the time required for the gas to return to the original state from the adsorbed state.

[0047] By calculating the recovery time , the response speed and recovery ability of the material in the sensing process can be predicted, which helps to optimize material selection and sensor design, making the actual test more targeted and efficient.

[0048] The numerical range described in the present application not only includes the point values listed above, but also includes any point values between the above numerical ranges that are not listed, and for the sake of brevity and simplicity, the present application does not exhaustively list the specific point values included in the range.

[0049] Compared with the prior art, the present application has the following beneficial effects:

[0050] The insulation property evaluation method provided by the present application can accurately evaluate the influence of the sensing material (i.e. SnSe material) on the decomposition products of C4F7N and the insulation performance, thereby effectively diagnosing the health state of the high-voltage insulation device and realizing early warning of insulation failure, which provides a new idea for accurate diagnosis and online monitoring of the insulation environment-friendly gas in the high-voltage insulation device. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 The front view and the left view of the SnSe layer provided by the present application in one specific embodiment after geometric optimization of a 7x7x1 Monkhorst-Pack k-point grid.

[0052] Figure 2 The geometric model of the SnSe layer provided by the present application in one specific embodiment after adsorption of the decomposition products of C4F7N gas.

[0053] Figure 3 The theoretical recovery time diagram of the SnSe layer provided by the present application in one specific embodiment in the process of adsorption of the decomposition products of C4F7N gas.

[0054] Figure 4 The front view and the left view of the Ni-SnSe layer provided by the present application in one specific embodiment after geometric optimization of a 7x7x1 Monkhorst-Pack k-point grid.

[0055] Figure 5 The geometric model of the Ni-SnSe layer provided by the present application in one specific embodiment after adsorption of the decomposition products of C4F7N gas.

[0056] Figure 6 The density of states distribution diagram of the SnSe layer and the Ni-SnSe layer provided by the present application in one specific embodiment respectively adsorbing the decomposition products of C4F7N gas.

[0057] Figure 7 The work function change curve of the SnSe layer and the Ni-SnSe layer provided by the present application in one specific embodiment respectively in the decomposition products of C4F7N gas.

[0058] Figure 8 The theoretical recovery time of the Ni-SnSe layer provided by the present application in one specific embodiment in the process of adsorption of the decomposition products of C4F7N gas. DETAILED DESCRIPTION

[0059] The technical solutions of the present application are further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations to the present application.

[0060] In one specific embodiment, the present application provides a method for evaluating the insulation properties of C4F7N gas in a high-voltage insulation device, comprising the following steps:

[0061] (1) Import the initial parameters of the SnSe material from the Materials Studio material library, and after cutting the (001) crystal plane, establish the minimum unit cell structure of the SnSe layer.

[0062] (2) After geometric optimization of the SnSe layer, determine the system energy and charge of the SnSe layer.

[0063] (3) Establish a molecular model of the decomposition products of C4F7N gas, and perform geometric optimization on the decomposition products of C4F7N gas to determine the system energy, charge, bond length and bond angle of the SnSe layer.

[0064] Among them, the decomposition products of C4F7N gas include CF3CN, COF2 and C2F5CN.

[0065] (4) Geometric optimization and energy calculation of the single-chain adsorption structure of the decomposition products of C4F7N gas.

[0066] (5) Construct the calculation function of the adsorption energy, doping energy and charge transfer amount of the SnSe layer, and define the required calculation formula and physical quantity.

[0067] Select the generalized gradient approximation method GGA and the PBE function, and establish a SnSe layer containing 18 Sn atoms and 18 Se atoms, with the size of the vacuum layer being 12Å×12Å×18Å. Considering the static electronic structure, set the atomic orbital basis set to double numerical polarization (DNP), the self-consistent ring energy to 10 -6 Ha, and the global orbital cutoff radius to 5.0Å.

[0068] (6) Set the parameters of the self-defined adsorption calculation formula, and construct the density functional theory calculation model of SnSe based on the 7×7×1 Monkhorst-Pack k-point grid.

[0069] Based on the density functional theory and the first principle, the Grimme correction rule is adopted to correct the van der Waals force and the long-range interaction. In order to avoid the nuclear relative effect, the DFT functional semi-nuclear pseudo-potential (DSSP) is adopted, and the 7*7*1 Monkhorst-Pack k-point grid is adopted in the convergence analysis of the geometric structure optimization and electronic characteristics, and the self-consistent accuracy, the maximum stress accuracy and the displacement accuracy of the electronic energy are set to 10 -6 Ha, 2*10 -3 Ha / Å and 5*10 -3 Å.

[0070] (7) The Sn atoms and Se atoms on the surface of the SnSe layer are respectively established as the adsorption model of the C4F7N gas decomposition product, and the distance between the C4F7N gas decomposition product and the SnSe layer is controlled to be 1.7 Å, then according to the overall energy and the charge transfer of each adsorption structure, the SnSe-based composite adsorption structure with the smallest deformation, the largest charge transfer and the largest adsorption energy of the target molecule SnSe layer is found by combining the self-defined adsorption calculation formula.

[0071] The adsorption energy calculation formula of the C4F7N gas decomposition product on the SnSe layer is:

[0072] E Ads =E Gas / SnSe -E SnSe -E Gas .

[0073] Wherein, E Gas / SnSe is the energy of the SnSe layer after adsorbing the C4F7N gas decomposition product, E SnSe is the energy of the SnSe layer, and E Gas is the energy of a single C4F7N gas decomposition product.

[0074] The charge transfer amount of the SnSe adsorption system

[0075] Q Tra =Q a -Q b .

[0076] Wherein, Q a is the charge amount of the SnSe layer after adsorbing the C4F7N gas decomposition product, and Q b is the charge amount of the SnSe layer before adsorbing the C4F7N gas decomposition product.

[0077] (8) The state density of SnSe and C4F7N gas decomposition product is derived and analyzed, and then the conductivity of the adsorption system is analyzed according to the energy curve integral and the change degree near the Fermi level.

[0078] (9) Calculate the work function change of the SnSe adsorption system in the C4F7N gas decomposition products.

[0079] The formula used to calculate the work function change of the SnSe adsorption system in the C4F7N gas decomposition products is:

[0080] φ = E vacuum - E fermi .

[0081] Where E vacuum is the potential far from the surface of the SnSe layer, and E fermi is the energy of the highest occupied state in the system.

[0082] (10) Use the recovery time to evaluate the ability of SnSe material to desorb gas, to evaluate the effectiveness of high-voltage insulation devices, and to evaluate the gas transmission ability of the SnSe layer.

[0083] The formula for calculating the recovery time is:

[0084] = v0 -1 exp(-E a / kT).

[0085] Where v0 -1 is the attempt frequency, which is 10 12 s -1 ; k is 1.38 x 10 -23 J / K; and T is the actual temperature in K.

[0086] Figure 1 The front view and left view of the SnSe layer after geometric optimization using a 7 x 7 x 1 Monkhorst-Pack k-point grid are shown, where the left image is the front view and the right image is the left view. From the Figure 1 it can be seen that the bond lengths of Sn-Se bonds in the horizontal and vertical directions are 2.905 Å and 2.841 Å, respectively, and a single unit cell is a planar monolayer repeat structure with high symmetry.

[0087] Figure 2The geometric model of SnSe layer after adsorbing C4F7N gas decomposition products is shown, and it can be seen from the figure that the SnSe layer will deform to different degrees as the adsorption process is completed. It can be observed that the gas adsorption distance of the SnSe layer is greater than 3Å, and the far adsorption distance means that there is a weak interaction between the SnSe material and the gas molecules, so it shows a small level of charge transfer. F atoms play a dominant role in the adsorption process due to their high electronegativity and polarity. In the adsorption process, the three gas molecules all act as electron acceptors to obtain electrons from the SnSe material, and the adsorption performance of the three gas molecules is ranked as: CF3CN > COF2 > C2F5CN.

[0088] In another specific embodiment, the application also provides a method for evaluating the insulation properties of C4F7N gas in a high-voltage insulation device, comprising the following steps:

[0089] (1) Import the initial parameters of the SnSe material from the Materials Studio material library, and after cutting the (001) crystal plane, establish the minimum unit cell structure of the SnSe layer.

[0090] (2) After geometric optimization of the SnSe layer, first remove one Sn on the surface of the SnSe layer to form a vacancy structure and perform geometric optimization, and then determine the system energy and charge of the SnSe layer.

[0091] (3) Establish a molecular model of C4F7N gas decomposition products, and at the same time establish a molecular model of a single Ni atom, and perform geometric optimization on C4F7N gas decomposition products and a single Ni atom to determine the system energy, charge, bond length and bond angle of the SnSe layer.

[0092] Among them, C4F7N gas decomposition products include CF3CN, COF2 and C2F5CN.

[0093] (4) Geometric optimization and energy calculation of single-chain adsorption structure of C4F7N gas decomposition products.

[0094] (5) Construct the calculation function of the adsorption energy, doping energy and charge transfer amount of the SnSe layer, and define the required calculation formula and physical quantity.

[0095] Select the generalized gradient approximation method GGA and the PBE function, and establish a SnSe layer containing 18 Sn atoms and 18 Se atoms, and the size of the vacuum layer is 12Å×12Å×18Å. Considering the static electronic structure, set the atomic orbital basis set to double numerical polarization (DNP), the self-consistent ring energy to 10 -6 Ha, and the global orbital cutoff radius to 5.0Å.

[0096] (6) Set the parameters of the self-defined adsorption calculation formula, and construct a density functional theory calculation model of SnSe based on a 7x7x1 Monkhorst-Pack k-point grid.

[0097] Based on the density functional theory and the first principle, the Grimme correction rule is adopted to correct the van der Waals force and the long-range interaction. In order to avoid the nuclear relative effect, the DFT functional semi-nuclear pseudo-potential (DSSP) is adopted, and in the convergence analysis of the geometric structure optimization and the electronic characteristics, a 7x7x1 Monkhorst-Pack k-point grid is adopted, and the self-consistent accuracy, the maximum stress accuracy and the displacement accuracy of the electronic energy are set to 10 -6 Ha, 2x10 -3 Ha / Å and 5x10 -3 Å.

[0098] (7) Place the single Ni atom of the geometric optimization at the Sn vacancy of the SnSe layer to form a Ni-SnSe layer, and then re-optimize the geometry of the Ni-SnSe layer;

[0099] (8) Establish an adsorption model of the C4F7N gas decomposition product on the top site, hole site and bridge site of the Sn atom and Se atom on the surface of the Ni-SnSe layer, and control the distance between the C4F7N gas decomposition product and the Ni-SnSe layer to be 1.7 Å, and then according to the overall energy and charge transfer of each adsorption structure, combined with the self-defined adsorption calculation formula, find the Ni-SnSe-based composite adsorption structure with the smallest deformation, the largest charge transfer and the largest adsorption energy of the target molecule Ni-SnSe layer.

[0100] The adsorption energy calculation formula of the C4F7N gas decomposition product on the Ni-SnSe layer is:

[0101] E Ads =E Gas / Ni-SnSe -E Ni-SnSe -E Gas .

[0102] Wherein, E Gas / Ni-SnSe is the energy of the Ni-SnSe layer after adsorbing the C4F7N gas decomposition product, E Ni-SnSe is the energy of the Ni-SnSe layer, and E Gas is the energy of a single C4F7N gas decomposition product.

[0103] The charge transfer amount calculation formula of the Ni-SnSe adsorption system is:

[0104] Q Tra =Q a -Q b .

[0105] wherein Q a is the amount of charge carried by the Ni-SnSe layer after adsorbing the C4F7N gas decomposition product, Q b is the amount of charge carried by the Ni-SnSe layer before adsorbing the C4F7N gas decomposition product.

[0106] (9) The density of states of Ni-SnSe and the C4F7N gas decomposition product is derived and analyzed, and then the conductivity of the adsorption system is analyzed according to the energy curve near the Fermi level and the degree of change.

[0107] (10) The work function change of the Ni-SnSe adsorption system in the C4F7N gas decomposition product is calculated.

[0108] The formula used to calculate the work function change of the Ni-SnSe adsorption system in the C4F7N gas decomposition product is:

[0109] φ = E vacuum -E fermi .

[0110] wherein E vacuum is the potential far from the surface of the Ni-SnSe layer, and E fermi is the energy of the highest occupied state in the system.

[0111] (11) The recovery time is used to evaluate the ability of the Ni-SnSe material to desorb gas, to evaluate the effectiveness of the high-voltage insulation device, and to evaluate the gas transmission ability of the Ni-SnSe layer.

[0112] The formula for calculating the recovery time is:

[0113] = v0 -1 exp(-E a / kT).

[0114] wherein v0 -1 is the attempt frequency, which is 10 12 s -1 ; k is 1.38×10 -23 J / K; and T is the actual temperature in K.

[0115] Figure 4 are the front view and the left view of the Ni-SnSe layer after geometric optimization by the 7×7×1 Monkhorst-Pack k-point grid, wherein the left figure is the front view and the right figure is the left view, from Figure 4As can be seen from the figure, the Ni-SnSe material after geometric optimization has undergone geometric deformation, which is due to the strong metallic property of the transition metal Ni atom activating the SnSe material, making the Sn-Se bond near the Ni atom stretch. The A, B and C bonds (A, B and C are self-defined to distinguish different bonds with the doping atom) are changed to 2.587 Å, 2.594 Å and 2.616 Å, respectively. Moreover, the Q Dop (doping energy) is -6.294 eV, which means that the interaction between the Ni atom and the SnSe material is more intense. In addition, the Q Tra (charge transfer amount) is 0.064 e, which further proves that the Ni atom can act as an electron donor to transport electrons to the SnSe material, proving the success of the process of modifying the Sn vacancy SnSe layer by the transition metal Ni atom.

[0116] Figure 5 The figure is the geometric model of the Ni-SnSe layer after adsorbing the decomposition products of C4F7N gas. As can be seen from the figure, the gas molecules have undergone deformation before and after adsorption, which is due to the chemical adsorption between the Ni-SnSe layer and the gas molecules. The adsorption effect is more obvious, and the adsorption energy of various C4F7N gas decomposition products is increased by 76.5%, 65.8% and 55.8%, respectively. Moreover, the interaction between C atoms and Ni atoms is more obvious during the adsorption process, so in the three adsorption configurations, the C atoms and Ni atoms are significantly close to each other, and the adsorption distance is significantly reduced. The Ni-SnSe layer still behaves as an electron donor in the adsorption process of CF3CN, COF2 and C2F5CN, and the electron transport capacity of the Ni-SnSe layer is significantly higher than that of the SnSe layer, and the charge transfer amount is changed to 13.13 times, 15.16 times and 11.19 times, respectively. This is because the transition metal Ni atom can improve the energy band structure of the SnSe layer, thereby reducing the energy required in the transmission process.

[0117] Figure 6The density of states distribution diagram of SnSe layer and Ni-SnSe layer respectively adsorbing C4F7N gas decomposition products is shown, wherein the dashed line is the Fermi level, and the energy distribution level of the Fermi level determines the sensing sensitivity and conductivity of the sensing system to the greatest extent. As can be seen from the figure, the SnSe layer has obvious energy distribution at-1.5 eV, -2.7 eV and -7 eV. For the Ni-SnSe layer, the energy distribution of each energy level is displaced towards the side close to the Fermi level, which means that electrons can occupy the interval close to the Fermi level more, and thus the large electron state can promote the conductivity of the doped system to improve the adsorption sensing potential of the system. At the same time, it can be observed that there is a significant overlap of energy peaks between the gas molecules and the adsorption substrate near the Fermi level, which is due to the high hybridization between the outermost orbitals of the gas molecules and the outermost orbitals of the adsorption substrate, thereby showing the same energy peak position.

[0118] Figure 7 The work function change curve of SnSe layer and Ni-SnSe layer in C4F7N gas decomposition products is shown. As can be seen from the figure, after the process of Ni atom doping on the SnSe layer is completed, the work function energy of the Ni-SnSe system is further reduced, which means that the energy required for electrons to cross the energy level is less, that is, the conductivity of the Ni-SnSe system is increased, and the resistance is decreased, so that the Ni-SnSe material has more potential for gas sensitive sensing. With the completion of the gas adsorption process, the work function of the SnSe adsorption system and the Ni-SnSe adsorption system further rises and shows the same change trend. The change rate of the work function of the Ni-SnSe adsorption system after adsorbing C4F7N gas decomposition products is higher than that of the SnSe adsorption system.

[0119] Figure 3 and Figure 8 The theoretical recovery time diagrams of SnSe layer and Ni-SnSe layer in the C4F7N gas decomposition product adsorption process are shown, respectively. As can be seen from the figure, the SnSe layer adsorption shows a lower order of magnitude of gas theoretical recovery time, which means that the desorption occurs before the gas is completely adsorbed, which is not easy for actual sensing signal collection and sensing analysis. The use of Ni-SnSe layer adsorption can observe that under normal temperature (298 K) working conditions, the response recovery time of C4F7N gas decomposition products has been significantly improved, which is related to the improvement of the surface active sites of the sensing material and the structure and morphology of the material, so that the Ni-SnSe material can be used as a good sensing material and applied to the reliable detection of CF3CN, COF2 and C2F5CN.

[0120] Applicants declare that the process of the present application is illustrated by the above examples, but the present application is not limited to the above process steps, i.e. it does not mean that the present application must rely on the above process steps to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the raw materials selected by the present application, addition of auxiliary ingredients, selection of specific modes, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for evaluating the insulation characteristics of C4F7N gas in a high-voltage insulation device, characterized in that, Includes the following steps: (1) Import the initial parameters of SnSe material from the Materials Studio material library, and after cutting the (001) crystal plane, establish the minimum cell structure of the SnSe layer; (2) After performing geometric optimization on the SnSe layer, determine the system energy and charge of the SnSe layer; (3) Establish a molecular model of the C4F7N gas decomposition products and perform geometric optimization on the C4F7N gas decomposition products to determine the system energy, charge status, bond length and bond angle of each molecule in the SnSe layer; (4) Perform geometric optimization and energy calculation on the single-chain adsorption structure of C4F7N gas decomposition products; (5) Construct calculation functions for the adsorption energy, doping energy, and charge transfer of the SnSe layer, and define the required calculation formulas and physical quantities; (6) Set the parameters of the custom adsorption calculation formula and construct a density functional theory calculation model of SnSe based on a 7×7×1 Monkhorst-Packk point grid. (7) Adsorption models of C4F7N gas decomposition products were established at the top, hole and bridge sites of Sn and Se atoms on the SnSe layer surface. Then, based on the overall energy and charge transfer of each adsorption structure, the SnSe-based composite adsorption structure with the smallest SnSe layer deformation, the largest charge transfer and the largest adsorption energy was found by combining the custom adsorption calculation formula. (8) Derive the density of states of SnSe and C4F7N gas decomposition products and analyze them. Then, analyze the conductivity of the adsorption system based on the energy curve integral and the degree of change near the Fermi level. (9) Calculate the change in work function of the SnSe adsorption system in the decomposition products of C4F7N gas; (10) Using recovery time The ability of SnSe materials to desorb gases was evaluated to assess the effectiveness of high-voltage insulation devices and to evaluate the gas sensing capability of the SnSe layer.

2. The insulation characteristic evaluation method according to claim 1, characterized in that, After the SnSe layer in step (2) is geometrically optimized, a Sn on the surface of the SnSe layer is removed to form a vacancy structure and geometric optimization is performed. Then the system energy and charge of the SnSe layer are determined.

3. The insulation characteristic evaluation method according to claim 2, characterized in that, In step (3), while establishing the molecular model of the C4F7N gas decomposition products, a model of a single transition metal atom is also established. When performing geometric optimization on the C4F7N gas decomposition products in step (3), geometric optimization is also performed on individual transition metal atoms.

4. The insulation characteristic evaluation method according to claim 3, characterized in that, The transition metal atoms include Ni atoms.

5. The insulation characteristic evaluation method according to claim 4, characterized in that, Between step (6) and step (7), the following steps are performed: The geometry-optimized single Ni atom is placed at the Sn vacancy in the SnSe layer to form a Ni-SnSe layer, and then the Ni-SnSe layer is geometry-optimized again.

6. The insulation characteristic evaluation method according to claim 1, characterized in that, The C4F7N gas decomposition products in step (3) include CF3CN, COF2 and C2F5CN.

7. The insulation characteristic evaluation method according to claim 1, characterized in that, When establishing the adsorption model of C4F7N gas decomposition products in step (7), the distance between the C4F7N gas decomposition products and the SnSe layer is controlled at 1.7-1.9 Å.

8. The insulation characteristic evaluation method according to claim 1, characterized in that, After step (7), the formula for calculating the adsorption energy of the C4F7N gas decomposition products on the SnSe layer is obtained: AND Ads =E Gas / SnSe -AND SnSe -AND Gas ; Among them, E Gas / SnSe E represents the energy released after the SnSe layer adsorbs the decomposition products of C4F7N gas. SnSe E represents the energy of the SnSe layer. Gas The energy of a single C4F7N gas decomposition product.

9. The insulation characteristic evaluation method according to claim 1, characterized in that, After step (7), the charge transfer amount Q of the SnSe adsorption system is obtained. Tra =Q a -Q b ; Among them, Q a Q represents the charge carried by the SnSe layer after adsorbing the decomposition products of C4F7N gas. b The charge on the SnSe layer before adsorbing the decomposition products of C4F7N gas is denoted as .

10. The insulation characteristic evaluation method according to claim 1, characterized in that, The formula used in step (9) to calculate the change in work function of the SnSe adsorption system in the C4F7N gas decomposition products is as follows: φ=E vacuum -AND fermi ; Among them, E vacuum It is the potential away from the surface of the SnSe layer, while E fermi It is the energy of the highest occupied state in the system; The recovery time mentioned in step (10) The calculation formula is: =v0 -1 exp(-E a / kT); Among them, v0 -1 This is the frequency of attempts, which is 10. 12 s -1 k is 1.38 × 10 -23 J / K; T is the actual temperature, in K.

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