Preparation method of graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating

Abstract

The present invention discloses a preparation method of a graphite-like carbon nitride-yttrium-stabilized zirconium oxide composite hydrogen barrier coating. First, a low-carbon steel substrate is pretreated to obtain a pretreated substrate; then zirconium n-propyl alcohol, n-propyl alcohol, acetylacetone and yttrium nitrate are mixed and reacted, aged to obtain a yttrium-stabilized zirconium oxide sol; the sol is coated on the pretreated substrate and dried, and the coating, drying and repeated treatments are followed by pre-sintering, followed by repeated coating, drying, and finally heat treatment to obtain a yttrium-stabilized zirconium oxide coating YSZ; melamine and thiourea are mixed, calcined and ground to obtain powdered graphite-like carbon nitride g-C3N4; finally, g-C3N4 powder and a coating coated with YSZ are sintered to obtain a graphite-like carbon nitride-yttrium-stabilized zirconium oxide g-C3N4 / YSZ composite coating. The hydrogen barrier coating prepared by the present invention can solve the problem that hydrogen embrittlement is prone to occur when current steel equipment is used in a hydrogen environment, and improve the safety of steel equipment during hydrogen energy utilization.

Description

1. Technical Field:

[0001] The present invention belongs to the technical field of hydrogen barrier coating protection, and in particular relates to a method for preparing a graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating for protecting steel equipment in a hydrogen environment. 2. Background technology:

[0002] As the most widely distributed substance in nature, hydrogen is hailed as the cleanest energy source with the greatest development potential in the 21st century due to its high calorific value, pollution-free nature, and abundant resources. Hydrogen energy is conducive to promoting the clean and efficient utilization of traditional fossil energy and supporting the large-scale development of renewable energy. However, for metal materials exposed to hydrogen, due to the small atomic radius and high permeability of hydrogen atoms, hydrogen can enter the metal and cause a degradation of its mechanical properties, particularly a reduction in plasticity, leading to hydrogen-induced damage and even fracture, resulting in significant economic losses and even disasters.

[0003] Currently, hydrogen barrier coatings applied to substrates through surface coating techniques can slow the diffusion of hydrogen into steel, reduce the incidence of hydrogen embrittlement, and effectively alleviate a range of issues caused by hydrogen permeation. Therefore, research into the design of hydrogen permeation barrier coating material systems and the development of related technologies to optimize and improve the performance and controllability of hydrogen barrier coatings is crucial for extending the service life of hydrogen-prone equipment. Zirconia coatings, as a traditional hydrogen barrier coating, offer advantages such as excellent stability, high hardness, and low thermal conductivity. However, zirconia exhibits crystal phase transitions, which can cause volume changes, leading to cracking in the coating material and a decrease in hydrogen barrier properties.

[0004] There are also many patent literature reports on hydrogen barrier coatings in China. For example: 1. CN 202110194529.1 discloses a zirconium hydride composite hydrogen barrier coating structure and its preparation method. It includes a zirconium hydride substrate, the outer layer of the zirconium hydride substrate is coated with a layer of micro-arc oxidation coating; the outer layer of the micro-arc oxidation coating is also coated with a layer of graphene. After the zirconium hydride substrate is surface pretreated, a zirconium oxide film layer is prepared on the surface of the zirconium hydride by a micro-arc oxidation process, and then a graphene film layer is deposited by solution to prepare a composite hydrogen barrier coating on the surface of the zirconium hydride. 2. CN 202010629507.9 discloses a zirconium oxide-graphite-like phase carbon nitride composite hydrogen barrier coating and its preparation method. The patent application of the present invention first prepares a Zr precursor solution and powdered g-C3N4; then the Zr precursor solution is applied to a substrate to obtain a wet film, which is dried and calcined, and then zirconium oxide is deposited again on the sample surface by electrochemical deposition; finally, g-C3N4 is covered on the sample in a porcelain boat to obtain the zirconium oxide-graphite-like carbon nitride composite hydrogen barrier coating of the present invention. 3. Summary of the invention:

[0005] The present invention addresses the technical problem of zirconia hydrogen-barrier coatings. By addressing the challenges of existing technologies, the present invention provides a method for preparing a graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen-barrier coating. This hydrogen-barrier coating, prepared using the present method, can address the hydrogen embrittlement issue currently associated with steel equipment used in hydrogen environments, thereby improving the safety of steel equipment during hydrogen energy utilization.

[0006] In order to solve the above problems, the technical solution adopted by the present invention is:

[0007] The present invention provides a method for preparing a graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating, the preparation method comprising the following steps:

[0008] a. Using low carbon steel as a substrate, the substrate is polished with sandpaper, and then the substrate surface is polished with a polishing agent. The substrate is then placed in acetone and anhydrous ethanol for ultrasonic cleaning (to remove oil and impurities on the substrate surface), and then dried to obtain a pretreated substrate;

[0009] b. Using zirconium n-propoxide as a zirconium source, n-propanol as a solvent, acetylacetone as a complexing agent, and yttrium nitrate as a stabilizer; first dissolving zirconium n-propoxide in the n-propanol solvent, then sequentially adding acetylacetone and deionized water, and then adding yttrium nitrate, mixing evenly, and stirring at room temperature for 24 to 36 hours; after the reaction, sealing the resulting sol at room temperature and allowing it to age for 36 to 48 hours to obtain an yttrium-stabilized zirconia sol;

[0010] c. The sol obtained in step b is evenly coated on the pretreated substrate obtained in step a, and then placed in a drying oven at 85° C. for drying; after drying, the sample is taken out and the coating and drying processes are repeated 3 to 5 times; then the sample is placed in a muffle furnace and pre-sintered at 300° C.; after pre-sintering, the sample is taken out and the coating and drying processes are repeated 5 to 11 times, and finally the sample is placed in a muffle furnace and heat-treated by programmed temperature increase to 550° C. to obtain a yttrium-stabilized zirconia coating YSZ;

[0011] d. Weigh melamine and thiourea, mix them evenly, add the resulting mixture into an alumina crucible, and place it in a muffle furnace and calcine it at 550° C. for 3 to 5 hours. After calcination, cool it to room temperature to obtain a pale yellow or yellow blocky graphite-like carbon nitride g-C3N4, which is fully ground to obtain powdered g-C3N4;

[0012] e. Evenly spread the obtained powdered g-C3N4 in a porcelain boat, place the yttrium-stabilized zirconia coating YSZ obtained in step c on top of the powder, and cover the porcelain boat with a glass plate. Then, place the porcelain boat in a muffle furnace and heat it to 550°C for constant temperature sintering. After sintering, cool it to room temperature to obtain a graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating.

[0013] According to the above-mentioned method for preparing the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating, when the substrate is polished with sandpaper in step a, the substrate is polished in sequence with 800# silicon carbide sandpaper, 1200# silicon carbide sandpaper and 2400# silicon carbide sandpaper respectively; the polishing agent is a diamond polishing agent with a diameter of 1 to 5 μm.

[0014] According to the above-mentioned method for preparing a graphite-like carbon nitride-yttrium-stabilized zirconium oxide composite hydrogen barrier coating, the molar ratio of zirconium n-propoxide, acetylacetone and deionized water in step b is 0.9-1.1:1.9-2.1:2.3-2.7; the molar ratio of zirconium n-propoxide and n-propanol is 1:5-40; and the molar ratio of zirconium n-propoxide and yttrium nitrate is 1:0.01-0.15.

[0015] According to the above-mentioned preparation method of the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating, the drying process in step c is set as: heating to 85°C at a heating rate of 3°C / min, and keeping warm for 10 to 30 minutes; the pre-sintering process is set as: heating to 300°C at a heating rate of 1°C / min, and keeping warm for 30 to 40 minutes; the heat treatment process is set as: heating to 200°C at a rate of 1°C / min, keeping warm for 30 to 40 minutes, then maintaining the heating rate at 1°C / min, heating from 200°C to 300°C, keeping warm for 40 to 70 minutes, then heating to 400°C at 3°C / min, and finally maintaining the heating rate unchanged and heating to 550°C, keeping warm for 100 to 150 minutes, and then cooling to room temperature with the furnace.

[0016] According to the above-mentioned method for preparing the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating, the mass ratio of melamine and thiourea added in step d is 6 to 15:1.

[0017] According to the above-mentioned method for preparing the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating, during the calcination in step d, the rate of the temperature increase process is 2° C. / min.

[0018] According to the above-mentioned preparation method of the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating, the ratio of the mass of the powdered g-C3N4 added in step e to the coating area is 0.2 to 0.8 g / cm 2 .

[0019] According to the above-mentioned method for preparing the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating, during the constant temperature sintering in step e, the heating rate is 2° C. / min, and the constant temperature sintering time is 2 to 4 hours.

[0020] The technical solution of the present invention first prepares a Zr precursor solution and powdered g-C3N4; then, the Zr precursor solution is applied to a substrate to obtain a wet film, which is dried and calcined, and then zirconium oxide is deposited again on the sample surface by electrochemical deposition; finally, the g-C3N4 is covered on the sample in a porcelain boat to obtain the zirconium oxide-graphite-like carbon nitride composite hydrogen barrier coating of the present invention.

[0021] The positive beneficial effects of the present invention are:

[0022] 1. The graphite-like carbon nitride-yttrium-stabilized zirconia coating prepared by the technical solution of the present invention has a dual structure of an outer layer that blocks hydrogen and an inner layer that stores hydrogen. Graphite-like carbon nitride (g-C3N4) has a two-dimensional layered structure, and its basic structure is composed of layered carbon and nitrogen six-membered rings. These six-membered rings form a planar structure by sharing nitrogen atoms. Such a planar structure can effectively block the passage of H atoms and H2 molecules. Therefore, the graphite-like carbon nitride-yttrium-stabilized zirconia composite layer prepared by the present invention is very suitable as a hydrogen barrier layer on the outer layer of the coating.

[0023] 2. Zirconia, as a metal oxide, is a dense physical barrier. When hydrogen diffuses in the oxide coating, on the one hand, it needs to overcome the bonds between MM and MO, and the bond energy is much greater than the energy required for hydrogen diffusion and penetration. On the other hand, after hydrogen dissociates into hydrogen atoms at a certain temperature, it will be adsorbed by O atoms or metal atoms in the oxide lattice to form hydrides. The diffusion of hydrogen in metal oxides is affected by both the lattice barrier effect and the atomic capture effect. Therefore, it has a lower permeability and a slower diffusion rate, which makes zirconium oxide very suitable as a hydrogen storage layer in the inner layer of the coating. However, the crystal transformation problem of the zirconium oxide coating will cause volume changes, resulting in cracking of the material, which greatly reduces the hydrogen barrier performance of the coating. Doping with the crystal stabilizer yttrium nitrate and optimizing its doping amount is an effective method to stabilize the zirconium oxide crystal form. Therefore, the graphite-like carbon nitride-yttrium stabilized zirconia composite coating prepared by the present invention has excellent hydrogen barrier performance and high use value.

[0024] 3. The composite hydrogen barrier coating prepared by the present invention has excellent hydrogen barrier capability. Compared with the low carbon steel substrate, the sample coated with the coating of the present invention has a steady-state current density reduced by 86.6%, which means that the hydrogen permeation flux is greatly reduced. The sample coated with the coating prepared by the present invention has a steady-state current density reduced by 81.6% and 80.4% respectively. This shows that the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating prepared by the present invention has excellent hydrogen barrier capability, can greatly reduce the amount of hydrogen diffusion into steel in a hydrogen environment, and avoid the occurrence of hydrogen-induced damage (see Appendix Figure 1and Table 1). Meanwhile, from Comparative Examples 1-2, it can be seen that the addition of yttrium and graphite-like carbon nitride plays a crucial role in improving the hydrogen barrier performance of the coating. The addition of yttrium reduces the hydrogen permeation flux of the coating by 51.59%, and the addition of graphite-like carbon nitride reduces the hydrogen permeation flux of the coating by 49.94%.

[0025] 4. The composite hydrogen barrier coating prepared by the present invention has good bonding with the substrate, the coating is evenly distributed on the substrate, the surface is smooth and continuous, and there are no obvious depressions, protrusions and cracks (see the attached Figure 2-4 ). 4. Description of the accompanying drawings:

[0026] Figure 1 Electrochemical hydrogen permeation curves of the hydrogen barrier coatings prepared in Examples 1-3, Comparative Examples 1-2, and the blank example;

[0027] Figure 2 Scanning electron microscope (SEM) morphology of the hydrogen barrier coating prepared in Example 1 of the present invention;

[0028] Figure 3 Scanning electron microscope (SEM) morphology of the hydrogen barrier coating prepared in Example 2 of the present invention;

[0029] Figure 4 Scanning electron microscope (SEM) morphology of the hydrogen barrier coating prepared in Example 3 of the present invention. V. Specific implementation methods:

[0030] The present invention is further described below with reference to the embodiments, but the scope of protection of the technical solution of the present invention is not limited. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the technical solution of the present invention.

[0031] Example 1:

[0032] The preparation method of the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating of the present invention comprises the following detailed steps:

[0033] a. Using low carbon steel as the substrate, the substrate was polished in sequence using 800# silicon carbide sandpaper, 1200# silicon carbide sandpaper, and 2400# silicon carbide sandpaper, and then the substrate surface was polished using a 5μm diamond polishing agent. The substrate was then ultrasonically cleaned in acetone and anhydrous ethanol in sequence (to remove oil and impurities on the substrate surface), and then dried to obtain a pretreated substrate;

[0034] b. Using zirconium n-propoxide as a zirconium source, n-propanol as a solvent, acetylacetone as a complexing agent, and yttrium nitrate as a stabilizer; first dissolving zirconium n-propoxide in the n-propanol solvent and stirring evenly, then sequentially adding acetylacetone and deionized water, adding yttrium nitrate after 30 minutes and mixing evenly, and then stirring and reacting at room temperature for 24 hours; after the reaction, the resulting sol is sealed at room temperature and aged for 48 hours to obtain yttrium-stabilized zirconia sol;

[0035] The molar ratio of zirconium n-propoxide, n-propanol, acetylacetone, deionized water and yttrium nitrate is 1:10:2:2.5:0.06;

[0036] c. The sol obtained in step b is evenly coated on the pretreated substrate obtained in step a, and then placed in a drying oven, heated to 85°C at a heating rate of 3°C / min, and kept dry at this temperature for 20 minutes; after drying, the sample is taken out and the coating and drying process is repeated three times; then the sample is placed in a muffle furnace, heated to 300°C at a heating rate of 1°C / min, and pre-sintered at this temperature for 35 minutes; after pre-sintering, the sample is taken out and the coating and drying process is repeated six times; finally Then, it was placed in a muffle furnace and subjected to heat treatment by program heating to 550°C (the heat treatment process was set as follows: at room temperature, the temperature was increased to 200°C at a rate of 1°C / min and kept at that temperature for 35 minutes, then the temperature was increased from 200°C to 300°C at a rate of 1°C / min and kept at that temperature for 60 minutes, then the temperature was increased to 400°C at a rate of 3°C / min, and finally the temperature was increased to 550°C at a rate of constant heating and kept at that temperature for 120 minutes) to obtain a yttrium-stabilized zirconia coating (YSZ);

[0037] d. Weigh 6.5 g of melamine and 0.6 g of thiourea, mix the two, add the resulting mixture into an alumina crucible, and place it in a muffle furnace. Heat it to 550 ° C at a rate of 2 ° C / min and calcine it for 4 h. After calcination, cool it to room temperature to obtain a pale yellow block of graphite-like carbon nitride (g-C3N4), which is fully ground in a mortar to obtain powdered g-C3N4;

[0038] e. Evenly spread 0.6 g of powdered g-C3N4 on a porcelain boat, place the yttrium-stabilized zirconia coating YSZ obtained in step c on top of the powder, and cover the porcelain boat with a glass plate. Then, place the porcelain boat in a muffle furnace, heat it to 550°C at a rate of 2°C / min, and sinter it at a constant temperature for 3 hours. After sintering, cool it to room temperature to obtain a graphite-like carbon nitride-yttrium-stabilized zirconia g-C3N4 / YSZ composite coating.

[0039] Example 2:

[0040] The preparation method of the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating of the present invention comprises the following detailed steps:

[0041] a. Using low carbon steel as the substrate, the substrate was polished using 800# silicon carbide sandpaper, 1200# silicon carbide sandpaper, and 2400# silicon carbide sandpaper, respectively. The substrate surface was then polished using a 3μm diamond polishing agent. The substrate was then ultrasonically cleaned in acetone and anhydrous ethanol in sequence (to remove oil and impurities on the substrate surface), and then dried to obtain a pretreated substrate.

[0042] b. Using zirconium n-propoxide as a zirconium source, n-propanol as a solvent, acetylacetone as a complexing agent, and yttrium nitrate as a stabilizer, dissolving zirconium n-propoxide in the n-propanol solvent and stirring evenly, then sequentially adding acetylacetone and deionized water, adding yttrium nitrate after 30 minutes and mixing evenly, and then stirring and reacting at room temperature for 24 hours; after the reaction, the obtained sol is sealed at room temperature and aged for 48 hours to obtain yttrium-stabilized zirconia sol;

[0043] The molar ratio of zirconium n-propoxide, n-propanol, acetylacetone, deionized water and yttrium nitrate is 1:20:2:2.5:0.03;

[0044] c. The sol obtained in step b is evenly coated on the pretreated substrate obtained in step a, and then placed in a drying oven, heated to 85°C at a heating rate of 3°C / min, and kept dry at this temperature for 10 minutes; after drying, the sample is taken out and the coating and drying process is repeated 5 times; then the sample is placed in a muffle furnace, heated to 300°C at a heating rate of 1°C / min, and pre-sintered at this temperature for 30 minutes; after pre-sintering, the sample is taken out and the coating and drying process is repeated 5 times; finally Then, it was placed in a muffle furnace and subjected to heat treatment by program heating to 550°C (the heat treatment process was set as follows: at room temperature, heating to 200°C at a rate of 1°C / min, holding for 30 minutes, then maintaining a heating rate of 1°C / min, heating from 200°C to 300°C, holding for 45 minutes, then heating to 400°C at a rate of 3°C / min, and finally maintaining a constant heating rate to 550°C, holding for 100 minutes) to obtain a yttrium-stabilized zirconia coating (YSZ);

[0045] d. Weigh 5.5 g of melamine and 0.7 g of thiourea, mix the two, add the resulting mixture into an alumina crucible, place it in a muffle furnace, heat it to 550 ° C at a rate of 2 ° C / min, and calcine it for 3 h. After calcination, cool it to room temperature to obtain a pale yellow block of graphite-like carbon nitride (g-C3N4), which is fully ground in a mortar to obtain powdered g-C3N4;

[0046] e. Evenly spread 0.4 g of powdered g-C3N4 on a porcelain boat, place the yttrium-stabilized zirconia coating YSZ obtained in step c on top of the powder, and cover the porcelain boat with a glass plate. Then, place the porcelain boat in a muffle furnace, heat it to 550°C at a rate of 2°C / min, and sinter it at a constant temperature for 3 hours. After sintering, cool it to room temperature to obtain a graphite-like carbon nitride-yttrium-stabilized zirconia g-C3N4 / YSZ composite coating.

[0047] Example 3:

[0048] The preparation method of the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating of the present invention comprises the following detailed steps:

[0049] a. Using low carbon steel as the substrate, the substrate was polished in sequence using 800# silicon carbide sandpaper, 1200# silicon carbide sandpaper, and 2400# silicon carbide sandpaper, and then the substrate surface was polished using a 1μm diamond polishing agent. The substrate was then ultrasonically cleaned in acetone and anhydrous ethanol in sequence (to remove oil and impurities on the substrate surface), and then dried to obtain a pretreated substrate;

[0050] b. Using zirconium n-propoxide as a zirconium source, n-propanol as a solvent, acetylacetone as a complexing agent, and yttrium nitrate as a stabilizer, dissolving zirconium n-propoxide in the n-propanol solvent and stirring evenly, then sequentially adding acetylacetone and deionized water, adding yttrium nitrate after 30 minutes and mixing evenly, and then stirring and reacting at room temperature for 24 hours; after the reaction, the resulting sol is sealed and allowed to stand at room temperature for 48 hours to obtain an yttrium-stabilized zirconia sol;

[0051] The molar ratio of zirconium n-propoxide, n-propanol, acetylacetone, deionized water and yttrium nitrate is 1:5:2:2.5:0.12;

[0052] c. The sol obtained in step b is evenly coated on the pretreated substrate obtained in step a, and then placed in a drying oven, heated to 85°C at a heating rate of 3°C / min, and kept dry at this temperature for 30 minutes; after drying, the sample is taken out and the coating and drying process is repeated 4 times; then the sample is placed in a muffle furnace, heated to 300°C at a heating rate of 1°C / min, and pre-sintered at this temperature for 40 minutes; after pre-sintering, the sample is taken out and the coating and drying process is repeated 7 times; finally Then, it was placed in a muffle furnace and subjected to heat treatment by program heating to 550°C (the heat treatment process was set as follows: at room temperature, the temperature was increased to 200°C at a rate of 1°C / min and kept at that temperature for 40 minutes, then the temperature was increased from 200°C to 300°C at a rate of 1°C / min and kept at that temperature for 60 minutes, then the temperature was increased to 400°C at a rate of 3°C / min, and finally the temperature was increased to 550°C at a rate of constant heating and kept at that temperature for 140 minutes) to obtain a yttrium-stabilized zirconia coating (YSZ);

[0053] d. Weigh 7.5 g of melamine and 0.65 g of thiourea, mix the two, add the resulting mixture into an alumina crucible, place it in a muffle furnace, heat it to 550 ° C at a rate of 2 ° C / min, and calcine it for 3 h. After calcination, cool it to room temperature to obtain a light yellow block of graphite-like carbon nitride (g-C3N4), which is fully ground in a mortar to obtain powdered g-C3N4;

[0054] e. Evenly spread 0.8 g of powdered g-C3N4 on a porcelain boat, place the yttrium-stabilized zirconia coating YSZ obtained in step c on top of the powder, and cover the porcelain boat with a glass plate. Then, place the porcelain boat in a muffle furnace, heat it to 550°C at a rate of 2°C / min, and sinter it at a constant temperature for 4 hours. After sintering, cool it to room temperature to obtain a graphite-like carbon nitride-yttrium-stabilized zirconia g-C3N4 / YSZ composite coating.

[0055] Comparative Example 1:

[0056] The coating of this comparative example is a coating sample to which no yttrium nitrate is added during the preparation process, and the preparation process of this comparative example is based on Example 1.

[0057] Comparative Example 2:

[0058] The coating of this comparative example is a coating sample in which no g-C3N4 is added during the preparation process and no subsequent related treatment is performed. The preparation process of this comparative example is based on Example 1.

[0059] Blank example:

[0060] This comparative example refers to a mild steel substrate, a blank sample without any coating to protect it.

[0061] The specific analysis of the product prepared by the present invention is as follows:

[0062] The present invention uses an electrochemical hydrogen permeation test method to evaluate the hydrogen barrier performance of the coating. The specific operation is as follows:

[0063] The Devanathan–Stachurski double electrolytic cell serves as the cathode chamber and the anode chamber respectively. The sample to be tested is clamped between the two chambers and fixed with gaskets and clamps. The electrolyte in the cathode chamber is a mixed solution of 0.2 mol / L NaOH and 1 g / L Na2S, and the electrolyte in the anode chamber is a 0.2 mol / L NaOH solution. The platinum electrode serves as the counter electrode of the two chambers, and the mercury / mercury oxide electrode serves as the reference electrode of the anode chamber. The sample acts as a dual working electrode, acting as both the anode and the cathode. During the experiment, the coated side faced the cathode chamber, the cathode chamber was connected to a constant current meter, and the anode chamber was connected to an electrochemical workstation. The test adopted the non-steady-state current time lag method. First, 10 mA / cm 2A constant current of 0.25V is applied to the anode chamber to instantly ionize the hydrogen atoms on the other side of the sample into hydrogen ions, making the hydrogen concentration on that side zero. The curve of current change over time is recorded by the electrochemical workstation and computer connected to it.

[0064] During the entire experiment, the current density will increase with time and eventually reach a steady state. When the current reaches a dynamic equilibrium, it is the steady-state current density (steady-state permeation current density: I ss ), indicating that the hydrogen permeation process has reached a steady state and the reaction hydrogen permeation flux has reached a stable state. The lower the steady-state current density, the lower the hydrogen diffusion amount per unit time and the better the hydrogen barrier effect of the coating. ∞ (mol / m 2 s) can be calculated by the following formula, where i∞ is the steady-state current density, A / m 2 ; n is the charge number; F is the Faraday constant (96500C / mol).

[0065]

[0066] Therefore, the present invention uses steady-state current density and hydrogen permeation flux to evaluate the hydrogen barrier performance of the coating. At the same time, the surface state of the sample and the hydrogen present in the sample itself will cause certain interference to the sample. To avoid the interference of these factors, it is necessary to apply a constant potential to the anode chamber before starting hydrogen charging, that is, before applying a constant current, so that the background current of the anode chamber is reduced to zero or close to zero, generally less than 0.1μA / cm 2 The entire electrochemical hydrogen permeation test was conducted at room temperature.

[0067] During the entire test experiment, the current density will increase with time and eventually reach a steady state. When the current reaches dynamic equilibrium, it is the steady-state current density (Steady-State Permeation Current Density: I ss ). This indicates that the hydrogen permeation process has reached a steady state and the reaction hydrogen permeation flux has reached a stable state. The lower the steady-state current density, the lower the hydrogen diffusion amount per unit time and the better the hydrogen barrier effect of the coating. The hydrogen permeation flux through the sample J ∞ It can also be calculated by steady-state current density. The experimental results are detailed in the attached Figure 1 and Table 1.

[0068] Table 1 Steady-state hydrogen current density Iss and corresponding hydrogen permeation flux J∞ detection data of Examples 1-3, Comparative Examples 1-2 and Blank Example

[0069] Sample Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Blank example <![CDATA[I ss (μA / cm 2 )]]> 4.41 6.05 6.46 9.11 8.81 32.96 <![CDATA[J ∞ (mol / cm 2 ·s)]]> 0.46E-6 0.63E-6 0.67E-6 0.94E-6 0.91E-6 3.42E-6

[0070] By the attached Figure 1 As can be seen from Table 1, the composite hydrogen barrier coatings prepared in Examples 1-3 of the present invention have excellent hydrogen barrier capabilities. Compared with the low-carbon steel substrate, the sample coated with the coating of Example 1 of the present invention has a steady-state current density reduced by 86.6%, which means that the hydrogen permeation flux is greatly reduced. The samples coated with the coatings of Examples 2 and 3 of the present invention have steady-state current densities reduced by 81.6% and 80.4% respectively. This shows that the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating prepared by the present invention has excellent hydrogen barrier capabilities, can greatly reduce the amount of hydrogen diffusion into steel in a hydrogen environment, and avoid the occurrence of hydrogen-induced damage. At the same time, it can be seen from Comparative Examples 1-2 that the addition of yttrium element and the addition of graphite-like carbon nitride play a vital role in improving the hydrogen barrier performance of the coating. The addition of yttrium reduces the hydrogen permeation flux of the coating by 51.59%, and the addition of graphite-like carbon nitride reduces the hydrogen permeation flux of the coating by 49.94%.

[0071] By the attached Figure 2-4 It can be seen that the composite hydrogen barrier coatings prepared in Examples 1-3 of the present invention are well bonded to the substrate, the coatings are evenly distributed on the substrate, the surface is smooth and continuous, and there are no obvious depressions, protrusions or cracks.

Claims

1. A method for preparing a graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating, characterized in that: The preparation method comprises the following steps: a. Using low carbon steel as a substrate, the substrate is polished with sandpaper, and then the surface of the substrate is polished with a polishing agent. The substrate is then ultrasonically cleaned in acetone and anhydrous ethanol in sequence, and then dried to obtain a pretreated substrate; b. Using zirconium n-propoxide as a zirconium source, n-propanol as a solvent, acetylacetone as a complexing agent, and yttrium nitrate as a stabilizer; first dissolving zirconium n-propoxide in the n-propanol solvent, then sequentially adding acetylacetone and deionized water, and then adding yttrium nitrate, mixing evenly, and stirring at room temperature for 24 to 36 hours; after the reaction, sealing the resulting sol at room temperature and allowing it to age for 36 to 48 hours to obtain an yttrium-stabilized zirconia sol; The molar ratio of the zirconium n-propoxide, acetylacetone and deionized water is 0.9-1.1:1.9-2.1:2.3-2.7; the molar ratio of the zirconium n-propoxide and n-propanol is 1:5-40; the molar ratio of the zirconium n-propoxide and yttrium nitrate is 1:0.01-0.15; c. The sol obtained in step b is evenly coated on the pretreated substrate obtained in step a, and then placed in a drying oven at 85° C. for drying; after drying, the sample is taken out and the coating and drying processes are repeated 3 to 5 times; then the sample is placed in a muffle furnace and pre-sintered at 300° C.; after pre-sintering, the sample is taken out and the coating and drying processes are repeated 5 to 11 times, and finally the sample is placed in a muffle furnace and heat-treated by programmed temperature increase to 550° C. to obtain a yttrium-stabilized zirconia coating YSZ; The drying process is set as follows: heating to 85°C at a heating rate of 3°C / min and holding for 10 to 30 minutes; the pre-sintering process is set as follows: heating to 300°C at a heating rate of 1°C / min and holding for 30 to 40 minutes; the heat treatment process is set as follows: heating to 200°C at a rate of 1°C / min and holding for 30 to 40 minutes, then heating from 200°C to 300°C at a heating rate of 1°C / min and holding for 40 to 70 minutes, then heating to 400°C at a heating rate of 3°C / min, finally heating to 550°C at a constant heating rate, holding for 100 to 150 minutes, and then cooling to room temperature with the furnace; d. Weigh melamine and thiourea, mix them evenly, add the resulting mixture into an alumina crucible, and place it in a muffle furnace and calcine it at 550° C. for 3 to 5 hours. After calcination, cool it to room temperature to obtain a pale yellow or yellow blocky graphite-like carbon nitride g-C3N4, which is fully ground to obtain powdered g-C3N4; e. Evenly spread the obtained powdered g-C3N4 on a porcelain boat, place the yttrium-stabilized zirconia coating YSZ obtained in step c on top of the powder, and cover the porcelain boat with a glass plate. Then, place the porcelain boat in a muffle furnace, heat it to 550°C, and sinter it at a constant temperature. After sintering, cool it to room temperature to obtain a graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating. The ratio of the added mass of the powdered g-C3N4 to the coating area is 0.2 to 0.8 g / cm 2 .

2. The method for preparing the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating according to claim 1, characterized in that: When the substrate is polished with sandpaper in step a, 800# silicon carbide sandpaper, 1200# silicon carbide sandpaper and 2400# silicon carbide sandpaper are used to polish the substrate in sequence; the polishing agent is a diamond polishing agent with a diameter of 1 to 5 μm.

3. The method for preparing the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating according to claim 1, characterized in that: The mass ratio of melamine and thiourea added in step d is 6 to 15:

1.

4. The method for preparing the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating according to claim 1, characterized in that: During the calcination in step d, the rate of the temperature increase process is 2°C / min.

5. The method for preparing the graphite-like carbon nitride-yttrium-stabilized zirconia composite hydrogen barrier coating according to claim 1, characterized in that: During the constant temperature sintering process in step e, the heating rate is 2° C. / min, and the constant temperature sintering time is 2 to 4 hours.

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