Method for Measuring Corrosion Rate of Metal Material in a Graphite-Metal Composite Grounding Structure

Abstract

The present application discloses a method for measuring the corrosion rate of a metal material in a graphite-metal composite grounding structure, comprising the following steps: measuring the release rate and release speed of sulfur elements in the graphite composite grounding material. Obtaining the equivalent concentration of sulfate radicals in the medium around the graphite composite grounding material according to the release rate and release speed. Preparing a simulated soil solution according to the equivalent concentration, then placing the metal material in the simulated soil solution for a corrosion rate measurement test, and then obtaining the corrosion rate of the metal material according to formula (D): #imgabs0# In formula (D), V W is the corrosion rate. S is the contact area between the metal material and the simulated soil solution. t is the contact time between the metal material and the simulated soil solution. w0 is the mass of the metal material before the corrosion rate measurement test, and w is the mass of the metal material after the corrosion rate measurement test. The present application realizes more scientific and accurate measurement of the corrosion rate of the metal material.

Description

Technical Field

[0001] This application relates to the field of high-voltage tests, and particularly to a method for measuring the corrosion rate of metal materials in a graphite-metal composite grounding structure. Background Art

[0002] Graphite composite grounding materials, due to their characteristics of being not easily corroded and having good current dissipation performance, have gradually replaced metal materials and are widely used in the grounding design of power systems. Whether it is a graphite / metal composite grounding material designed by using metal as the skeleton or protective material, or a graphite composite grounding material without metal materials itself, in engineering applications, it is necessary to connect it with the metal grounding downlead of the power system to achieve effective grounding. In this way, in actual applications, a macroscopic or microscopic graphite / metal composite environment is inevitably formed, which will cause or accelerate the corrosion of the connected metal materials. In actual engineering, there have been a large number of corrosion phenomena of the connected metal materials. According to the investigation of a newly built UHV line by the China Electric Power Research Institute, the above-mentioned corrosion problems occurred 2 months after the completion of the grounding construction of the line towers. After rechecking, among the 11 towers installed with graphite grounding devices randomly selected, the grounding devices of 3 towers remained intact without corrosion, while the grounding devices of the other 8 towers were corroded to varying degrees at certain parts, and the probability of the corrosion phenomenon was as high as 72.7%. Moreover, from the positions where the corrosion occurred, it all appeared at the metal joints such as the crimping plates, galvanized bolts, small connecting plates, and downleads connected to the graphite grounding devices.

[0003] However, at present, relevant domestic scholars in the research on the corrosion resistance of flexible graphite composite grounding materials often only conduct a large number of experimental studies on the graphite materials themselves, while ignoring the corrosion problems of the metal at the graphite / metal connection positions. In addition, in the preparation process of flexible graphite, it is necessary to use concentrated sulfuric acid to react with natural flake graphite under the action of an oxidant to carry out an intercalation reaction. A large number of hydrogen sulfate anions enter the graphite interlayer and combine with the oxidized carbon ions to form graphite intercalation compounds, which makes a large amount of sulfur elements remain in the graphite material products. And the sulfur content in the graphite / metal composite grounding materials will affect the soil acidity, and the acidic soil environment will accelerate the corrosion process of the metal materials in the graphite / metal composite grounding materials.

[0004] Application Content

[0005] This application provides a method for measuring the corrosion rate of metal materials in a graphite-metal composite grounding structure, which can measure the corrosion rate of metal materials more scientifically and accurately, provide a theoretical basis for the corrosion situation assessment and service life design of the graphite-metal composite grounding structure, and avoid power accidents caused by the corrosion of the graphite-metal composite grounding structure.

[0006] In a first aspect, an embodiment of the present application provides a method for measuring the corrosion rate of a metal material in a graphite-metal composite grounding structure, including the following steps:

[0007] Measure the release rate and release speed of sulfur elements in the graphite composite grounding material.

[0008] Obtain the equivalent concentration of sulfate radicals in the medium around the graphite composite grounding material based on the release rate and release speed.

[0009] Prepare a simulated soil solution according to the equivalent concentration, then place the metal material in the simulated soil solution for a corrosion rate measurement test, and then obtain the corrosion rate of the metal material according to formula (D):

[0010]

[0011] In formula (D), V W is the corrosion rate. S is the contact area between the metal material and the simulated soil solution. t is the contact time between the metal material and the simulated soil solution. w0 is the mass of the metal material before the corrosion rate measurement test, and w is the mass of the metal material after the corrosion rate measurement test.

[0012] In some of these embodiments, measure the release rate and release speed of sulfur elements in the graphite composite grounding material according to formula (A) and formula (B) respectively:

[0013]

[0014] In formula (A), D t is the release rate. X is the sulfur content of the graphite material sample obtained from the graphite material used in the graphite composite grounding material. H t is the content of sulfate radicals in the extract obtained after the extraction of the graphite material sample.

[0015]

[0016] In formula (B), V D is the release speed. t1 and t2 are both the extraction times of the graphite material sample, and t2 is greater than t1. H t1 is the content of sulfate radicals in the extract obtained after the extraction of the graphite material sample for t1 time. H t2 is the content of sulfate radicals in the extract obtained after the extraction of the graphite material sample for t2 time.

[0017] In some of these embodiments, H t is the content of sulfate radicals in the extract obtained after the extraction of the graphite material sample for 24 hours.

[0018] In some of these embodiments, H t is V DThe content of sulfate in the extract obtained after extracting a graphite material sample for t2 hours when it is less than 10 micrograms per hour.

[0019] In some of these embodiments, a graphite material sample is weighed, distilled water is used as the extraction agent, and a Soxhlet extraction device is used to extract for a preset time to obtain an extract. Then, the extract is reacted with a hydrochloric acid acidified barium chloride solution, followed by filtration, washing, drying, and weighing to obtain the content of sulfate.

[0020] In some of these embodiments, the equivalent concentration of sulfate in the medium around the graphite composite grounding material is obtained according to formula (C) based on the release rate and release speed:

[0021] m1 = m0·X·10 -6 ·D,

[0022]

[0023]

[0024]

[0025] In formula (C), m1 is the sulfur content of all the graphite materials in the graphite composite grounding material. m0 is the mass of the graphite material. X is the sulfur content per unit mass of the graphite material. D is the release rate. m2 is the mass of sulfuric acid converted from all the sulfides in the graphite material according to the release rate. n2 is the amount of substance of sulfuric acid. C is the equivalent concentration. Y is the water absorption rate of the graphite composite grounding material.

[0026] In some of these embodiments, a simulated solution is prepared according to the equivalent concentration, and then the simulated solution is mixed with cleaned and dried fine sand to obtain a simulated soil solution.

[0027] In some of these embodiments, during the corrosion rate measurement test, first, the bottom of a graphite-metal composite grounding structure is inserted into the simulated soil solution, or the bottoms of a graphite composite grounding material and a steel product are both inserted into the simulated soil solution, and a copper product is used to connect the tops of the graphite composite grounding material and the steel product. After a set time, then the graphite-metal composite grounding structure or the steel product is taken out, and then rust removal, cleaning, drying, and weighing are carried out.

[0028] In some of these embodiments, it is carried out for a set time under the condition that the container containing the simulated soil solution is sealed.

[0029] In some of these embodiments, during the set time, pay attention to the liquid level change of the simulated soil solution and timely replenish the liquid level of the simulated soil solution to the initial volume.

[0030] A method for measuring the corrosion rate of a metal material in a graphite-metal composite grounding structure provided by an embodiment of the present application includes the following steps: measuring the release rate and release speed of sulfur elements in the graphite composite grounding material. Obtaining the equivalent concentration of sulfate radicals in the medium around the graphite composite grounding material according to the release rate and release speed. Preparing a simulated soil solution according to the equivalent concentration, then placing the metal material in the simulated soil solution for a corrosion rate measurement test, and then obtaining the corrosion rate of the metal material according to Equation (D): In Equation (D), V W is the corrosion rate. S is the contact area between the metal material and the simulated soil solution. t is the contact time between the metal material and the simulated soil solution. w0 is the mass of the metal material before the corrosion rate measurement test, and w is the mass of the metal material after the corrosion rate measurement test. In the method for measuring the corrosion rate of the metal material in the graphite-metal composite grounding structure provided by the present application, not only the metal corrosion caused by the electrochemical reaction of graphite metal in the soil is considered, but also the influence of the release of sulfur elements in the graphite material on the soil acidity and the metal corrosion environment is considered, which can more scientifically and accurately evaluate the corrosion situation of the graphite-metal composite grounding structure, can provide a more scientific and reasonable theoretical basis for calculating the service life of the graphite-metal composite grounding structure, and effectively reduce power accidents caused by the corrosion of the graphite-metal composite grounding structure. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained according to these drawings.

[0032] Figure 1 It is a schematic diagram of the corrosion rate measurement test in the embodiment of the present application;

[0033] Figure 2 It is a graph showing the relationship between the corrosion rate and time of the same metal material in different simulated soil solutions in the embodiment of the present application;

[0034] Figure 3 It is a graph showing the relationship between the corrosion rate of different metal materials and the equivalent sulfuric acid concentration in the embodiment of the present application.

[0035] Specific Embodiments

[0036] In order to make the purpose, technical solutions and advantages of the present application clearer, the following will further describe the present application in detail with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0037] In the preparation process of flexible graphite, concentrated sulfuric acid is required for the intercalation reaction. Although most of the hydrogen sulfate anions will be converted into sulfur dioxide and sulfur trioxide and escape during the subsequent processes of water washing, drying, and high-temperature expansion due to the decomposition of graphite intercalation compounds, sulfur dioxide and sulfur trioxide decomposed may be adsorbed on the graphite surface due to insufficient water washing, low expansion temperature, or short time in the production process. In addition, trace impurity elements present in the raw materials react with sulfuric acid and may also exist in the form of sulfates, which results in the presence of a small amount of sulfur in the flexible graphite material. Currently, the sulfur content in domestic-produced flexible graphite materials is in the range of 1000 - 6000 ppm. When the flexible graphite grounding material is applied in engineering, sulfur-containing compounds in the graphite material penetrate into the surrounding soil through diffusion, react with water and oxygen, and are oxidized to form sulfurous acid and sulfuric acid, reducing the local pH value of the soil and promoting the chemical corrosion and electrochemical corrosion reaction rates between the flexible graphite grounding material and its connected metal.

[0038] Considering the impact of the release of sulfur elements in the graphite material on soil acidity and the metal corrosion environment, as well as the metal corrosion caused by the electrochemical reaction of graphite metal in the soil, the embodiments of the present application provide a method for measuring the corrosion rate of the metal material in a graphite-metal composite grounding structure, including the following steps:

[0039] (1) Measure the release rate and release speed of sulfur elements in the graphite composite grounding material.

[0040] Specifically, measure the release rate and release speed of sulfur elements in the graphite composite grounding material according to formula (A) and formula (B) respectively:

[0041]

[0042] In formula (A), D t is the release rate. X is the sulfur content of the graphite material sample obtained from the graphite material used in the graphite composite grounding material. H t is the content of sulfate radicals in the extraction solution obtained after extraction of the graphite material sample.

[0043]

[0044] In formula (B), V D is the release speed. t1 and t2 are both the extraction times of the graphite material sample, and t2 is greater than t1. H t1 is the content of sulfate radicals in the extraction solution obtained after extraction of the graphite material sample for t1 time. H t2 is the content of sulfate radicals in the extraction solution obtained after extraction of the graphite material sample for t2 time.

[0045] Among them, Ht is the content of sulfate radical in the extract obtained after extracting the graphite material sample for 24 hours. Or, H t is V D is the content of sulfate radical in the extract obtained after extracting the graphite material sample for t2 hours when it is less than 10 μg / hour.

[0046] In addition, by weighing the graphite material sample, using distilled water as the extractant and extracting for a preset time with a Soxhlet extraction device to obtain an extract, then reacting the extract with a hydrochloric acid acidified barium chloride solution, followed by filtration, washing, drying, and weighing to obtain the content of sulfate radical.

[0047] Specifically, 1) Weigh 4 groups of 5 g of flexible graphite (sulfur content is X ppm) or scrape 4 groups of 5 g of flexible graphite products (sulfur content is X ppm), wrap the obtained 4 groups of samples separately with filter paper, fold and seal the open end, tie it with a rubber band, and put it into the extraction cylinder. 2) Install a 250 mL round-bottom flask on an electric heating mantle, put in 2 pieces of zeolite, measure 100 mL of distilled water, pour it from the extraction cylinder into the flask, install the Soxhlet extraction device, turn on the power, control the temperature at 100 - 110 °C, and heat and reflux. 3) Extract the 4 groups of samples for 4 h, 8 h, 16 h, and 24 h respectively. After cooling the 4 obtained flask extracts, measure the pH value, prepare a hydrochloric acid acidified barium chloride solution, and measure the content of sulfate radical in the 4 extracts after filtration, washing, drying, and weighing with an analytical balance.

[0048] The measurement results are shown in Table 1 below.

[0049] Table 1 Measurement Table of Sulfate Radical Release Amount of Flexible Graphite

[0050]

[0051] Release rate V D Generally, it will decrease significantly with the increase of the extraction time of t hours.

[0052] When t ≥ 24 hours, or the release rate V in the most recent 4 hours D is less than 10 μg / hour, then the release rate D of sulfur element at this moment t is taken as the value for subsequent calculation.

[0053] (2) Obtain the equivalent concentration of sulfate radical in the medium (soil) around the graphite composite grounding material according to the release rate and the release rate.

[0054] Specifically, according to Equation (C) and based on the release rate and the release rate, obtain the equivalent concentration of sulfate radical in the medium around the graphite composite grounding material:

[0055] m1 = m0 · X · 10 -6 · D,

[0056]

[0057]

[0058]

[0059] In formula (C), m1 is the sulfur content of all the graphite materials in the graphite composite grounding material. m0 is the mass of the graphite material. X is the sulfur content per unit mass of the graphite material. D is the release rate. m2 is the mass of sulfuric acid converted from all the sulfides in the graphite material according to the release rate. n2 is the amount of substance of sulfuric acid. C is the equivalent concentration. Y is the water absorption rate of the graphite composite grounding material.

[0060] (3) Prepare the simulated soil solution according to the equivalent concentration, then place the metal material in the simulated soil solution for the corrosion rate measurement test, and then obtain the corrosion rate of the metal material according to formula (D):

[0061]

[0062] In formula (D), V W is the corrosion rate. S is the contact area between the metal material and the simulated soil solution. t is the contact time between the metal material and the simulated soil solution. w0 is the mass of the metal material before the corrosion rate measurement test, and w is the mass of the metal material after the corrosion rate measurement test.

[0063] Among them, the simulated soil solution is obtained by preparing the simulated solution according to the equivalent concentration and then mixing the simulated solution with the cleaned and dried fine sand.

[0064] And, during the corrosion rate measurement test, first insert the bottom of a graphite-metal composite grounding structure into the simulated soil solution, or insert the bottoms of a graphite composite grounding material and a steel product into the simulated soil solution, connect the top of the graphite composite grounding material and the top of the steel product with a copper product, then after a set time, take out the graphite-metal composite grounding structure or the steel product, and then carry out rust removal, cleaning, drying, and weighing. Among them, it is under the condition that the container containing the simulated soil solution is sealed for the set time. And pay attention to the liquid level change of the simulated soil solution within the set time, and timely replenish the liquid level of the simulated soil solution to the initial volume. The container is made of brown glass.

[0065] Specifically, 1) Pretreat the metal material in the graphite-metal composite grounding structure by sanding, polishing, cleaning, and drying with fine sandpaper to prefabricate a test piece with a length of 150 mm. 2) Calculate the SO4 in the local microenvironment according to step (2). 2-Prepare a simulated solution with an equivalent concentration C. 3) Use 60-mesh fine sand, clean and dry it, and mix the fine sand with the simulated solution at a ratio of 4:1 to prepare a simulated soil solution. 4) Insert the graphite-metal composite grounding structure into the simulated soil with a depth of not less than 100 mm, and seal the container with plastic film. During this period, pay attention to the liquid level change of the soil simulated solution, and replenish the soil simulated solution in each container to the initial volume in a timely manner. Perform measurements when the measurement time is reached. Among them, conduct multiple groups of experiments. The depth of insertion into the simulated soil solution is the same for all groups, and the surface area in contact with the simulated soil solution is the same. And set the experimental observation period: The observation period is 24 hours for one cycle. The corrosion rate is relatively fast in the early stage, so intensive measurements are carried out. Measure one group for each cycle, and continue for seven cycles. In the later stage, measure one group every three cycles, with a total of thirty groups measured, so it takes 97 days. 5) Measurement scheme: Clean the graphite-metal composite grounding structure specimen with deionized water, use a rust remover to wipe off the corrosion layer on the surface of the metal part of the specimen, clean it again with acetone and put it in an oven to dry or air-dry naturally. Weigh the specimen using an analytical balance to calculate the corrosion rate of the metal material in the specimen (that is, the weight loss rate per unit surface area per unit cycle).

[0066] Or, 1) Calculate the equivalent concentration C of SO4 in the local microenvironment according to step (2) to prepare a simulated solution. 2) Use 60-mesh fine sand, clean and dry it, and mix the fine sand with the simulated solution at a ratio of 4:1 to prepare a simulated soil solution; 3) Prepare 3 Q235 flat steel specimens with a length of 150 mm and 1 graphite composite grounding material and insert them into the simulated soil solution 2 respectively, and the tops of the two materials are connected by a copper strip 4, as 2- shown. The depth of insertion into the simulated soil is not less than 100 mm, and seal the container with plastic film. During this period, pay attention to the liquid level change of the soil simulated solution, and replenish the soil simulated solution in each container to the initial volume in a timely manner. Perform measurements when the measurement time is reached. Among them, conduct multiple groups of experiments. The depth of insertion into the simulated soil solution is the same for all groups, and the surface area in contact with the simulated soil solution is the same. And set the experimental observation period: The observation period is 24 hours for one cycle. The corrosion rate is relatively fast in the early stage, so intensive measurements are carried out. Measure one group for each cycle, and continue for seven cycles. In the later stage, measure one group every three cycles, with a total of thirty groups measured, so it takes 97 days. 4) Measurement scheme: Clean the steel specimen 3 with deionized water, use a rust remover to wipe off the corrosion layer on the surface of the metal part of the specimen, clean it again with acetone and put it in an oven to dry or air-dry naturally. Weigh the specimen using an analytical balance to calculate the corrosion rate of the specimen (that is, the weight loss rate per unit surface area per unit cycle). Figure 1 shown. The depth of insertion into the simulated soil is not less than 100 mm, and seal the container with plastic film. During this period, pay attention to the liquid level change of the soil simulated solution, and replenish the soil simulated solution in each container to the initial volume in a timely manner. Perform measurements when the measurement time is reached. Among them, conduct multiple groups of experiments. The depth of insertion into the simulated soil solution is the same for all groups, and the surface area in contact with the simulated soil solution is the same. And set the experimental observation period: The observation period is 24 hours for one cycle. The corrosion rate is relatively fast in the early stage, so intensive measurements are carried out. Measure one group for each cycle, and continue for seven cycles. In the later stage, measure one group every three cycles, with a total of thirty groups measured, so it takes 97 days. 4) Measurement scheme: Clean the steel specimen 3 with deionized water, use a rust remover to wipe off the corrosion layer on the surface of the metal part of the specimen, clean it again with acetone and put it in an oven to dry or air-dry naturally. Weigh the specimen using an analytical balance to calculate the corrosion rate of the specimen (that is, the weight loss rate per unit surface area per unit cycle).

[0067] According to the above technical solution, a relationship graph of the corrosion rate and time of the same metal material in different simulated soil solutions is obtained, as Figure 2as shown, and the relationship diagram between the corrosion rate of different metal materials and the equivalent sulfuric acid concentration, such as Figure 3 shown.

[0068] In addition, the technical solution of this application can also be described as follows:

[0069] The embodiment of this application provides a method for measuring the corrosion rate of metal materials in a graphite-metal composite grounding structure, including the following steps:

[0070] (1) Measure the release rate and release speed of sulfur elements in the graphite material through experiments

[0071] During the preparation process of flexible graphite, concentrated sulfuric acid is required for the intercalation reaction. Although most of the hydrogen sulfate anions will be converted into sulfur dioxide and sulfur trioxide and escape during the subsequent processes of water washing, drying, and high-temperature expansion due to the decomposition of graphite intercalation compounds. However, due to insufficient water washing or low expansion temperature and short time in the production process, the decomposed sulfur dioxide and sulfur trioxide may be adsorbed on the graphite surface. In addition, trace impurity elements in the raw materials react with sulfuric acid and may also exist in the form of sulfates, which makes a small amount of sulfur still present in the flexible graphite material. Currently, the sulfur content in domestic-produced flexible graphite materials is within the range of 1000 - 6000 ppm.

[0072] In order to master the process of oxidation and diffusion of sulfur-containing substances in graphite composite grounding materials in the soil, high-temperature extraction experiments were conducted on graphite composite grounding materials with different sulfur contents. During the measurement, distilled water was used as the extractant, and the pH value of the extract was measured every 8 hours to obtain the release rate D and release speed V of sulfur-containing substances in graphite composite grounding materials with different sulfur contents in the electrolyte solution D .

[0073] The steps for determining the release rate and release speed of sulfur elements in flexible graphite materials are as follows:

[0074] 1) Weigh 4 groups of 5 g of flexible graphite or 5 g of scraped flexible graphite products (sulfur content is X ppm), wrap the obtained samples with filter paper, fold and seal the open end, and fasten with a rubber band, then put them into the extraction cylinder;

[0075] 2) Install a 250 mL round-bottom flask on an electric heating mantle, put in 2 zeolites, measure 100 mL of distilled water, pour it from the extraction cylinder into the flask, install the Soxhlet extraction device, turn on the power, control the temperature at 100 - 110 °C, and heat under reflux;

[0076] 3) The four groups of samples were extracted for 4h, 8h, 16h, and 24h respectively. After the obtained flask extracts were cooled, the pH value was measured. A barium chloride solution acidified with hydrochloric acid was prepared to measure the sulfate content in the extract. After filtration, washing, and drying, the sulfate content was measured using an analytical balance;

[0077] 4) According to the measured sulfate content, calculate the release rate V of sulfur elements in the graphite material in the soil D and the release rate D.

[0078] Calculate the release rate V of sulfur elements according to the following formula D , H t is the sulfate content at this moment when the extraction time is t hours, with the unit of ppm. The release rate V D has the unit of micrograms per hour.

[0079]

[0080] Calculate the release rate D of sulfur elements according to the following formula. D t is the release rate of sulfur elements at this moment when the extraction time is t hours.

[0081]

[0082] The results measured in the laboratory are shown in Table 1 below.

[0083] Table 1 Measurement Table of Sulfate Release Amount of Flexible Graphite

[0084]

[0085] When the release rate V D generally decreases significantly with the increase of the extraction time of t hours.

[0086] When t ≥ 24 hours, or the release rate V in the most recent 4 hours D is less than 10 micrograms per hour, then use the release rate D of sulfur elements at this moment t as the value for subsequent calculations.

[0087] (2) Calculate the equivalent concentration C of SO4 2- in the medium (soil) around the graphite material

[0088] After the flexible graphite grounding material is applied in the project, the sulfur-containing compounds in the graphite material penetrate into the surrounding soil through diffusion, react with water and oxygen, and are oxidized to form sulfurous acid and sulfuric acid, reducing the local pH value of the soil and promoting the chemical corrosion and electrochemical corrosion reaction rates between the flexible graphite grounding material and its connected metal.

[0089] In order to simulate the oxidation, diffusion, and penetration processes of sulfides in flexible graphite grounding materials, in the study, after considering a certain release rate and release ratio, the sulfur content in the unit graphite rope material was equivalently calculated as the SO4 2- concentration in the surrounding medium (soil).

[0090] The equivalent calculation method is as follows:

[0091] Let the mass of the graphite material be m0 (g), and the sulfur content be m1 (X micrograms of sulfur per gram of graphite material). Assuming that its sulfide is finally completely converted into sulfuric acid at the release ratio D measured in the first step, the mass of the converted sulfuric acid is m2 (g), and the amount of substance is n2 (mol). The molar mass of S is 32 g / mol, and the molar mass of H2SO4 is 98 g / mol. Then:

[0092] m1 = m0·X·10 -6 ·D

[0093]

[0094]

[0095] In order to study the influence of the local microenvironment of the graphite conductor in the soil on the connected metal, the equivalent sulfuric acid concentration in the local microenvironment of the graphite conductor and the connected metal was calculated according to the water absorption of the graphite wire per unit mass and the amount of sulfuric acid released.

[0096] Let the water absorption rate of the graphite wire be Y%, the water absorption of m0 (g) graphite wire be m3 (g), and the density of the environmental solution ρ = 103 g / L. Then the equivalent sulfuric acid concentration C (mol / L) in the local microenvironment is:

[0097]

[0098] According to the above formula, it can be seen that the equivalent sulfuric acid concentration in the local microenvironment of the graphite conductor and the connected metal is directly proportional to the sulfur content X in the unit graphite wire and inversely proportional to the water absorption rate of the material.

[0099] (3) Measuring the corrosion rate of the metal material in the graphite-metal composite grounding structure

[0100] According to the equivalent sulfuric acid concentration C calculated in the second step, an equivalent electrolyte solution was prepared with 60-mesh sand to simulate the soil and placed in a 1000-ml capacity brown glass wide-mouth bottle.

[0101] The specific test plan is as follows:

[0102] 1) The metal material was pretreated by polishing with fine sandpaper, cleaning, and drying, and prefabricated into test pieces with a length of 150 mm.

[0103] 2) Configure the simulated solution according to the equivalent concentration C of SO4 in the local microenvironment calculated in step 2; 2- in the simulated solution;

[0104] 3) Use 60-mesh fine sand, clean and dry it. Mix the fine sand with the above simulated solution according to a ratio of 4:1 to prepare a simulated soil solution;

[0105] 4) Insert the graphite / metal composite grounding material into the simulated soil, and the insertion depth into the simulated soil shall not be less than 100 mm; when there is no metal material in the graphite composite grounding material, a Q235 flat steel specimen with a length of 150 mm can be prepared for the test, as shown below Figure 1 shown, the tops of the two materials are connected by a copper strip. The insertion depth of all groups into the simulated soil is the same, the contact surface area with the simulated soil is the same, and the container is sealed with a plastic film. During this period, pay attention to the liquid level change of the soil simulated solution, and timely supplement the soil simulated solution in each container to the initial volume. Measure when the measurement time arrives.

[0106] 5) Measurement plan: Clean the specimen with deionized water, use a rust remover to wipe off the corrosion layer on the surface of the metal part of the specimen, clean it again with acetone and put it in the oven to dry / natural air dry, weigh the specimen with an analytical balance, and calculate the corrosion rate of different specimens (that is, the weight loss rate per unit surface area per unit cycle).

[0107] 6) Set the experimental observation period: The observation period is 24 hours as a cycle. Since the corrosion rate is relatively fast in the early stage, measure intensively, measure once every cycle, and continue for seven cycles. Measure once every three cycles in the later stage, and measure a total of thirty times, so it lasts for 97 days.

[0108] 7) Calculate the corrosion rate of the metal material in the graphite-metal composite grounding structure

[0109] Let w0 be the mass of the metal sample before the test, w be the mass of the metal sample cleaned after the test, S be the area of the sample in contact with the simulation, t be the test time, and V w be the corrosion rate of the specimen. Then, calculate the corrosion rate of the metal material in the graphite-metal composite grounding structure according to the following formula:

[0110]

[0111] The parameters to be recorded for the measurement are shown in the following table.

[0112] Table 2 Corrosion Rate Measurement Record Table

[0113]

[0114] According to the above technical solution, the relationship diagram of the corrosion rate and time of the same metal material in different simulated soil solutions is obtained, as shown in Figure 2 shown, and the relationship diagram of the corrosion rate of different metal materials and the equivalent sulfuric acid concentration, as shown in Figure 3 shown.

[0115] In the accompanying drawings of this embodiment, the same or similar reference numerals correspond to the same or similar components; in the description of this application, it should be understood that if there are terms such as "upper", "lower", "left", "right", etc. indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, it is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the accompanying drawings are only for illustrative purposes and cannot be understood as a limitation of this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to the specific situation.

[0116] The above is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims

1. A method for measuring the corrosion rate of a metal material in a graphite-metal composite grounding structure, characterized in that, Including the following steps: Measuring the release rate of sulfur element in the graphite composite grounding material; wherein, the release rate of sulfur element in the graphite composite grounding material is measured according to formula (B): （B）； In formula (B), V D is the release rate; t1 and t2 are the extraction times of the graphite material sample obtained from the graphite material used in the graphite composite grounding material, and t2 is greater than t1; H t1 is the content of sulfate radical in the extract obtained after the graphite material sample is extracted for t1 time; H t2 is the content of sulfate radical in the extract obtained after the graphite material sample is extracted for t2 time; Obtaining the release rate of sulfur element in the graphite composite grounding material according to the release rate; wherein, the release rate of sulfur element in the graphite composite grounding material is measured according to formula (A): （A）； In formula (A), D t is the release rate; X is the sulfur content of the graphite material sample obtained from the graphite material used in the graphite composite grounding material; H t is V D is the content of sulfate radical in the extraction solution obtained after extracting the graphite material sample for t2 hours when it is less than 10 μg / hour; Obtaining the equivalent concentration of sulfate radical in the medium around the graphite composite grounding material according to the release rate; wherein, the equivalent concentration of sulfate radical in the medium around the graphite composite grounding material is obtained according to formula (C) and the release rate: ， ， ， （C）； In formula (C), m1 is the sulfur content of all graphite materials in the graphite composite grounding material; m0 is the mass of the graphite material; X is the sulfur content per unit mass of the graphite material; D is the release rate; m2 is the mass of sulfuric acid converted from all sulfides in the graphite material according to the release rate; n2 is the amount of substance of the sulfuric acid; C is the equivalent concentration; Y is the water absorption rate of the graphite composite grounding material; Preparing a simulated soil solution according to the equivalent concentration, then placing the metal material in the simulated soil solution for a corrosion rate measurement test, and then obtaining the corrosion rate of the metal material according to formula (D): （D）； In formula (D), V W is the corrosion rate; S is the contact area between the metal material and the simulated soil solution; t is the contact time between the metal material and the simulated soil solution; w0 is the mass of the metal material before the corrosion rate measurement test, and w is the mass of the metal material after the corrosion rate measurement test.

2. The corrosion rate measurement method according to claim 1, characterized in that By weighing a graphite material sample, using distilled water as an extractant and extracting for a preset time with a Soxhlet extraction device to obtain an extract, then reacting the extract with a hydrochloric acid acidified barium chloride solution, and then filtering, washing, drying, and weighing to obtain the content of sulfate radical.

3. The corrosion rate measurement method according to claim 1, characterized in that By preparing a simulated solution according to the equivalent concentration and then mixing the simulated solution with cleaned and dried fine sand to obtain the simulated soil solution.

4. The corrosion rate measurement method according to claim 1, characterized in that During the corrosion rate measurement test, first insert the bottom of a graphite-metal composite grounding structure into the simulated soil solution, or insert the bottoms of a graphite composite grounding material and a steel product into the simulated soil solution, and connect the top of the graphite composite grounding material and the top of the steel product with a copper product. After a set time, then take out the graphite-metal composite grounding structure or the steel product, and then carry out rust removal, cleaning, drying, and weighing.

5. The corrosion rate measurement method according to claim 4, characterized in that Under the condition that the container containing the simulated soil solution is sealed for a set time.

6. The corrosion rate measurement method according to claim 5, characterized in that Pay attention to the liquid level change of the simulated soil solution within the set time and timely replenish the simulated soil solution to the initial volume.

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