Electrode material and preparation method thereof

Abstract

The invention provides an electrode material and a preparation method thereof, and belongs to the technical field of electrolytic bath electrodes, the preparation method comprises the following steps: S1, pretreating a stainless steel substrate to obtain a pretreated substrate; s2, chromium chloride, sodium phosphate and sodium molybdate are sequentially added into water and stirred until the chromium chloride, the sodium phosphate and the sodium molybdate are completely dissolved, then the pH value is adjusted to 2.5-3.0 through a hydrochloric acid solution with the mass concentration being 3.2-3.8%, and an electroplating solution is obtained; s3, the pretreated matrix obtained in the step S1 serves as a cathode, graphite serves as an anode, the cathode and the anode are put into the electroplating solution obtained in the step S2 for electroplating treatment, and the composite coating stainless steel is obtained; and S4, the composite coating stainless steel obtained in the S3 is cleaned and dried, and the electrode material is obtained. The pitting corrosion resistance of the cathode can be effectively improved, so that the service life of the cathode is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolytic cell electrodes, and particularly relates to an electrode material and a preparation method thereof. Background Art

[0002] In the electrolytic preparation of sodium perchlorate, the cathode material uses stainless steel with a chromium oxide coating on its surface. A large amount of ClO3 exists in the electrolyte. - To enhance conductivity, hydrochloric acid solution is generally added to make the electrolyte acidic.

[0003] In the acidic electrolyte, ClO3 - combines with H + to form HClO3 as a strong oxidant, which causes oxidative corrosion to the coating. Due to the micropores, grain boundary defects and low density of the chromium oxide coating, the oxidative erosion at the micropores of the chromium oxide coating will be aggravated, resulting in pitting corrosion. In this way, the corrosion products accumulate and cause stress, damaging the chromium oxide coating locally, causing local warping or peeling of the coating, and shortening the service life of the cathode. Summary of the Invention

[0004] To solve the problems in the background art, the present invention provides an electrode material and a preparation method thereof, which can effectively improve the pitting corrosion resistance of the prepared electrode material (cathode), and further improve the service life of the cathode.

[0005] To achieve the above object, in the first aspect, the present invention provides a preparation method of an electrode material, including the following steps: S1. Pretreat the stainless steel substrate to obtain a pretreated substrate; S2. Add chromium chloride, sodium phosphate and sodium molybdate to water in sequence, stir until completely dissolved, and then adjust the pH value to 2.5 - 3.0 with a hydrochloric acid solution with a mass concentration of 3.2 - 3.8% to obtain an electroplating solution; S3. Use the pretreated substrate obtained in S1 as the cathode and graphite as the anode, and put them into the electroplating solution obtained in S2 for electroplating treatment to obtain stainless steel with a composite coating; S4. Clean and dry the stainless steel with a composite coating obtained in S3 to obtain the electrode material.

[0006] Further, in S1, the specific operation of the pretreatment is: first, alkali-wash the stainless steel substrate with an alkali solution to remove the oil on the surface of the stainless steel substrate; then, perform acid-washing with a mixed acid solution to obtain the pretreated substrate.

[0007] Further, the temperature of the alkali-washing is 55 - 62 °C, and the temperature of the acid-washing is 23 - 26 °C.

[0008] Further, the alkali solution is an aqueous sodium hydroxide solution, and its concentration is 50 ± 5 g / L.

[0009] Further, in the mixed acid solution, the volume concentration of nitric acid is 10 ± 1%, and the volume concentration of hydrofluoric acid is 2 ± 0.2%.

[0010] Further, in the electroplating solution, the concentration of chromium chloride is 80 - 85 g / L, the concentration of sodium molybdate is 15 - 18 g / L, and the concentration of sodium phosphate is 30 - 35 g / L.

[0011] Further, in S3, the current density is 4 - 6 A / dm 2 , the temperature is 45 - 48 °C, and the electroplating time is 25 - 30 min.

[0012] Further, in S4, the specific operations of the cleaning and drying are as follows: After washing the composite coating stainless steel with deionized water multiple times, it is dried at a temperature of 50 - 55 °C for 60 - 80 min.

[0013] In the second aspect, the present invention provides an electrode material prepared by the above preparation method.

[0014] The present application has the following beneficial effects: In the present invention, the electroplating solution includes chromium chloride, sodium phosphate, and sodium molybdate. On the one hand, the phosphate radical (PO4 3- ) in sodium phosphate selectively adsorbs on the active sites on the cathode surface (such as the Cr 3+ enrichment region), preferentially occupies the grain boundary growth sites, inhibits the disordered accumulation of chromium oxide crystals, thereby reducing the formation of grain boundary cracks and micropores, the compactness of the coating is good, blocking the ClO 3- diffusion channels, thereby improving the pitting corrosion resistance of the cathode.

[0015] On the other hand, the phosphate radical (PO4 3- ) in sodium phosphate and the molybdate ion (MoO4 2- ) in sodium molybdate co-deposit in the coating to form a dense oxide film with a doped Mo - P - O composite structure, significantly reducing the porosity of the coating, synergistically improving the pitting corrosion resistance of the cathode, and further achieving the effect of synergistically increasing the service life of the cathode. Specific Embodiments

[0016] The following further describes the present application in detail with reference to the embodiments.

[0017] The raw materials in the embodiments and comparative examples of the present application are all commercially available except as otherwise specified.

[0018] Example 1: This example provides a preparation method of an electrode material, including the following steps: S1. Pretreat the stainless steel substrate. The specific operations are as follows: First, alkali wash the stainless steel substrate with an alkali solution. Then, pickle it with a mixed acid solution to obtain a pretreated substrate. The alkali solution is an aqueous sodium hydroxide solution with a concentration of 50 g / L. The temperature of the alkali wash is 60 °C, and the stainless steel substrate is soaked in a constant temperature water bath for 30 minutes to achieve the alkali washing effect of removing the oil stain on the surface of the stainless steel substrate. After alkali washing, ultrasonic clean (20 KHz) three times with deionized water at 60 °C, 5 minutes each time. In the mixed acid solution, the volume concentration of nitric acid is 10%, the volume concentration of hydrofluoric acid is 2%, and the balance is deionized water. The temperature of the pickling is 25 °C, and it can be soaked in a constant temperature water bath for 15 minutes. After pickling, ultrasonic clean (20 KHz) with deionized water at 25 °C until neutral (detected with pH test paper), and dry with nitrogen.

[0019] S2. Add chromium chloride to deionized water and stir mechanically at 300 rpm for 30 minutes. Then add sodium phosphate and stir mechanically at 300 rpm for 20 minutes. Then add sodium molybdate and stir mechanically at 300 rpm for 15 minutes until completely dissolved. Then, while continuously stirring, adjust the pH value to about 2.8 by slowly dripping a hydrochloric acid solution with a mass concentration of 3.5% to prevent precipitation and obtain an electroplating solution. In this electroplating solution, the concentration of chromium chloride is 82 g / L, the concentration of sodium molybdate is 16 g / L, and the concentration of sodium phosphate is 32 g / L.

[0020] S3. Use the pretreated substrate obtained in S1 as the cathode (size 50×50×1 mm, effective area 0.5 dm 2 ), and use a high-purity graphite plate as the anode (purity ≥ 99.9%, size 60×60×5 mm). Put them into the electroplating solution obtained in S2 for electroplating treatment. The electrode spacing is 50 mm (fixed by a polytetrafluoroethylene fixture) to obtain stainless steel with a composite coating. Specific process parameters: The current density is about 5.0 A / dm 2 (using a DC regulated power supply with a ripple factor ≤ 5%), the temperature is controlled at about 46 °C (controlled by a circulating water bath), the electroplating time is 28 minutes (accurate to ±10 seconds), and the plating solution is magnetically stirred at 200 rpm (rotor size Φ15×50 mm).

[0021] S4. Clean and dry the stainless steel with a composite coating obtained in S3. The specific operations are as follows: After cleaning the stainless steel with a composite coating three times with deionized water, dry it in a hot air circulation drying oven at a constant drying temperature of about 52 °C for 70 minutes, with a wind speed of 1.5 m / s to obtain the electrode material. The specific cleaning procedure is three-stage countercurrent cleaning: First, use deionized water at the first stage (25 °C), then, use deionized water at the second stage (40 °C), and then, use deionized water at the third stage (25 °C). The cleaning time for each time is 5 minutes, and the water flow rate is 2 L / min.

[0022] Example 2: The difference between this example and Example 1 is that this example provides a method for preparing an electrode material, which includes the following steps: S1. Pretreat the stainless steel substrate. The specific operation is as follows: First, alkali-wash the stainless steel substrate with an alkali solution to remove the oil stain on the surface of the stainless steel substrate; then perform acid-washing with a mixed acid solution to obtain a pretreated substrate. The alkali solution is an aqueous sodium hydroxide solution with a concentration of 45 g / L; the temperature of the alkali-washing is 55 °C. In the mixed acid solution, the volume concentration of nitric acid is 9%, and the volume concentration of hydrofluoric acid is 1.8%; the temperature of the acid-washing is 23 °C.

[0023] S2. Add chromium chloride, sodium phosphate, and sodium molybdate to water in sequence and stir until completely dissolved, and then adjust the pH value to 2.5 with a hydrochloric acid solution with a mass concentration of 3.2% to obtain an electroplating solution. In this electroplating solution, the concentration of chromium chloride is 80 g / L, the concentration of sodium molybdate is 15 g / L, and the concentration of sodium phosphate is 30 g / L.

[0024] S3. Use the pretreated substrate obtained in S1 as the cathode and graphite as the anode, and put them into the electroplating solution obtained in S2 for electroplating treatment to obtain stainless steel with a composite coating. The current density is 5.0 A / dm 2 , the temperature is 45 °C, and the electroplating time is 25 min.

[0025] S4. Clean and dry the stainless steel with a composite coating obtained in S3. The specific operation is as follows: After washing the stainless steel with a composite coating three times with deionized water, dry it at a temperature of 50 °C for 80 min to obtain the electrode material.

[0026] Example 3: The difference between this example and Example 1 is that this example provides a method for preparing an electrode material, which includes the following steps: S1. Pretreat the stainless steel substrate. The specific operation is as follows: First, alkali-wash the stainless steel substrate with an alkali solution to remove the oil stain on the surface of the stainless steel substrate; then perform acid-washing with a mixed acid solution to obtain a pretreated substrate. The alkali solution is an aqueous sodium hydroxide solution with a concentration of 55 g / L; the temperature of the alkali-washing is 62 °C. In the mixed acid solution, the volume concentration of nitric acid is 11%, and the volume concentration of hydrofluoric acid is 2.2%; the temperature of the acid-washing is 26 °C.

[0027] S2. Add chromium chloride, sodium phosphate, and sodium molybdate to water in sequence and stir until completely dissolved, and then adjust the pH value to 3.0 with a hydrochloric acid solution with a mass concentration of 3.8% to obtain an electroplating solution. In this electroplating solution, the concentration of chromium chloride is 85 g / L, the concentration of sodium molybdate is 18 g / L, and the concentration of sodium phosphate is 35 g / L.

[0028] S3. Take the pretreated substrate obtained in S1 as the cathode and graphite as the anode, and place them in the electroplating solution obtained in S2 for electroplating treatment to obtain stainless steel with a composite coating. The current density is 5.0 A / dm 2 , the temperature is 48 °C, and the electroplating time is 30 min.

[0029] S4. Clean and dry the stainless steel with a composite coating obtained in S3. The specific operation is as follows: After cleaning the stainless steel with a composite coating three times with deionized water, dry it at a temperature of 55 °C for 60 min to obtain the electrode material.

[0030] Example 4: The difference between this example and Example 1 is that this example provides a method for preparing an electrode material, which includes the following steps: S1. Pretreat the stainless steel substrate. The specific operation is as follows: First, alkali-wash the stainless steel substrate with an alkali solution to remove the oil stains on the surface of the stainless steel substrate; then perform pickling with a mixed acid solution to obtain a pretreated substrate. The alkali solution is an aqueous sodium hydroxide solution with a concentration of 53 g / L; the temperature of the alkali-washing is 58 °C. In the mixed acid solution, the volume concentration of nitric acid is 10.5%, and the volume concentration of hydrofluoric acid is 2%; the temperature of the pickling is 25 °C.

[0031] S2. Add chromium chloride, sodium phosphate, and sodium molybdate to water in sequence, and stir until completely dissolved. Then adjust the pH value to 2.8 with a hydrochloric acid solution with a mass concentration of 3.5% to obtain an electroplating solution. In this electroplating solution, the concentration of chromium chloride is 84 g / L, the concentration of sodium molybdate is 16 g / L, and the concentration of sodium phosphate is 34 g / L.

[0032] S3. Take the pretreated substrate obtained in S1 as the cathode and graphite as the anode, and place them in the electroplating solution obtained in S2 for electroplating treatment to obtain stainless steel with a composite coating. The current density is 5.0 A / dm 2 , the temperature is 46 °C, and the electroplating time is 28 min.

[0033] S4. Clean and dry the stainless steel with a composite coating obtained in S3. The specific operation is as follows: After cleaning the stainless steel with a composite coating three times with deionized water, dry it at a temperature of 55 °C for 70 min to obtain the electrode material.

[0034] Comparative Example 1: The difference between this comparative example and Example 1 is only that: Sodium molybdate and sodium phosphate in the electroplating solution are deleted. That is, the electroplating solution only contains chromium chloride.

[0035] Specifically, this comparative example provides a method for preparing an electrode material, which includes the following steps: S1. Pretreat the stainless steel substrate. The specific operations are as follows: First, alkali-wash the stainless steel substrate with an alkali solution. Then, pickle it with a mixed acid solution to obtain a pretreated substrate. The alkali solution is an aqueous sodium hydroxide solution with a concentration of 50 g / L. The temperature for alkali-washing is 60 °C, and soaking in a constant-temperature water bath for 30 minutes can achieve the effect of removing the oil stain on the surface of the stainless steel substrate. After alkali-washing, ultrasonically clean it three times with deionized water at 60 °C (20 KHz), 5 minutes each time. In the mixed acid solution, the volume concentration of nitric acid is 10%, the volume concentration of hydrofluoric acid is 2%, and the balance is deionized water. The temperature for pickling is 25 °C, and soaking in a constant-temperature water bath for 15 minutes is sufficient. After pickling, ultrasonically clean it with deionized water at 25 °C (20 KHz) until neutral (detected with pH test paper), and then dry it with nitrogen.

[0036] S2. Add chromium chloride to deionized water and mechanically stir it at 300 rpm for 30 minutes until completely dissolved. Then, adjust the pH value to 2.8 with a hydrochloric acid solution with a mass concentration of 3.5% to obtain an electroplating solution. In this electroplating solution, the concentration of chromium chloride is 82 g / L.

[0037] S3. Use the pretreated substrate obtained in S1 as the cathode (size 50×50×1 mm, effective area 0.5 dm 2 ), and a high-purity graphite plate as the anode (purity ≥ 99.9%, size 60×60×5 mm). Place them in the electroplating solution obtained in S2 for electroplating treatment. The electrode spacing is 50 mm (fixed by a polytetrafluoroethylene fixture) to obtain stainless steel with a composite coating. The specific process parameters are as follows: The current density is about 5.0 A / dm 2 (using a DC regulated power supply with a ripple factor ≤ 5%), the temperature is controlled at about 46 °C (controlled by a circulating water bath), the electroplating time is 28 minutes (accurate to ±10 seconds), and the plating solution is magnetically stirred at 200 rpm (rotor size Φ15×50 mm).

[0038] S4. Clean and dry the stainless steel with a composite coating obtained in S3. The specific operations are as follows: After cleaning the stainless steel with a composite coating three times with deionized water, dry it at a constant drying temperature of about 52 °C in a hot air circulation drying oven for 70 minutes with a wind speed of 1.5 m / s to obtain the electrode material. The specific cleaning procedure is three-stage countercurrent cleaning: First, use deionized water at the first stage (25 °C), then, use deionized water at the second stage (40 °C), and then, use deionized water at the third stage (25 °C). The cleaning time for each time is 5 minutes, and the water flow rate is 2 L / min.

[0039] Comparative Example 2: The only difference between this comparative example and Example 1 is that sodium phosphate in the electroplating solution is deleted. That is, the electroplating solution contains chromium chloride and sodium molybdate.

[0040] Comparative Example 3: The only difference between this comparative example and Example 1 is that sodium molybdate in the electroplating solution is deleted. That is, the electroplating solution contains chromium chloride and sodium phosphate.

[0041] Test Example: Test Subject: Electrode material samples prepared in Examples 1 - 4 and Comparative Examples 1 - 3.

[0042] Test Method: The salt spray test method was used to test the corrosion resistance of the coating. An acidic salt spray test solution (containing 5% NaCl) was prepared, and the pH of the acidic salt spray test solution was about 3.2. Each sample was continuously sprayed for 72 hours, and the acidic salt spray test temperature was set at 25 ± 2°C. After the test, the surface was inspected with a 10 - fold magnifying glass to obtain the pitting area and conduct grading. The grading reference standard is shown in Table 1.

[0043] Test Results: See Table 2.

[0044] Table 1. Grading Reference Standard

[0045] Table 2. Test Results of Test Examples

[0046] Result Analysis: Analyzing Examples 1 - 4 in combination with the data in Table 1, it can be seen that the electrode materials (cathodes) prepared in the present invention (Examples 1 - 4) have excellent pitting resistance.

[0047] Analyzing Example 1 and Comparative Examples 1 - 3 in combination with the data in Table 1, by comparing Comparative Example 1 and Comparative Example 2, it can be known that adding sodium molybdate to the electroplating solution containing chromium chloride will cause the pitting resistance of the prepared electrode material (cathode) to decrease instead of increase. This is because when there is only chromium chloride in the electroplating solution, the chromium oxide coating formed by chromium chloride has a passivation effect, but there are grain boundary defects and pores in its microstructure, which are easily penetrated by ClO3 - through the defects and cause local corrosion. When sodium molybdate is added alone to the electrolyte, MoO4 introduced by sodium molybdate 2- , forms a MoO2 or MoO3 film, and its compatibility with the chromium - based coating is poor, resulting in an increase in the internal stress of the coating and an increase in the porosity instead. ClO3 - diffuses through the pores to the substrate surface and causes more serious pitting.

[0048] By comparing Comparative Example 1 and Comparative Example 3, it can be known that adding sodium phosphate to the electroplating solution containing chromium chloride can improve the pitting resistance of the prepared electrode material (cathode). This is because the phosphate group (PO4 3- ) in sodium phosphate selectively adsorbs on the active sites on the cathode surface (such as the Cr 3+ enrichment area), preferentially occupies the grain boundary growth sites, inhibits the disordered accumulation of chromium oxide crystals, thereby reducing the formation of grain boundary cracks and micropores, the coating has good compactness, and blocks the ClO 3- diffusion channels, thus improving the pitting resistance of the cathode.

[0049] Combined with Example 1 for comparison, it can be seen that adding sodium molybdate and sodium phosphate to the electroplating solution containing chromium chloride can produce a synergistic effect, synergistically improving the pitting corrosion resistance of the prepared electrode material (cathode). This is because the phosphate group (PO4 3- of sodium phosphate) and the molybdate ion (MoO4 2- of sodium molybdate) co-deposit in the coating to form a composite oxide film with a doped Mo-P-O structure. The Mo-P-O composite fills the grain boundary gaps, reduces the porosity, and the chemical stability of the composite film is better than that of a single oxide, inhibiting the penetration of ClO3 - and the expansion of pitting corrosion, thereby synergistically improving the pitting corrosion resistance of the cathode.

[0050] In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0051] In addition, any combination can be made between various different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing an electrode material, characterized in that, It includes the following steps: S1. Pretreat the stainless steel substrate to obtain a pretreated substrate; S2. Add chromium chloride, sodium phosphate and sodium molybdate to water in sequence, stir until completely dissolved, and then adjust the pH value to 2.5 - 3.0 with a hydrochloric acid solution with a mass concentration of 3.2 - 3.8% to obtain an electroplating solution; S3. Use the pretreated substrate obtained in S1 as the cathode and graphite as the anode, and place them in the electroplating solution obtained in S2 for electroplating treatment to obtain stainless steel with a composite coating; S4. Clean and dry the stainless steel with a composite coating obtained in S3 to obtain the electrode material.

2. The preparation method of the electrode material according to claim 1, characterized in that In S1, the specific operation of the pretreatment is: first, alkali-wash the stainless steel substrate with an alkali solution; then, acid-wash it with a mixed acid solution to obtain the pretreated substrate.

3. The preparation method of the electrode material according to claim 2, characterized in that, The temperature of the alkali-washing is 55 - 62°C, and the temperature of the acid-washing is 23 - 26°C.

4. The preparation method of the electrode material according to claim 2 or 3, characterized in that, The alkali solution is an aqueous sodium hydroxide solution with a concentration of 50 ± 5 g / L.

5. The preparation method of the electrode material according to claim 2 or 3, characterized in that, In the mixed acid solution, the volume concentration of nitric acid is 10 ± 1%, and the volume concentration of hydrofluoric acid is 2 ± 0.2%.

6. The preparation method of the electrode material according to claim 1, characterized in that In the electroplating solution, the concentration of chromium chloride is 80 - 85 g / L, the concentration of sodium molybdate is 15 - 18 g / L, and the concentration of sodium phosphate is 30 - 35 g / L.

7. The preparation method of the electrode material according to claim 1, characterized in that, In S3, the current density is 4 - 6 A / dm 2 , the temperature is 45 - 48 °C, and the electroplating time is 25 - 30 min.

8. The preparation method of the electrode material according to claim 1, characterized in that, In S4, the specific operation of the cleaning and drying is: after washing the stainless steel with a composite coating with deionized water multiple times, dry it at a temperature of 50 - 55°C for 60 - 80 min.

9. An electrode material, characterized in that, It is prepared by the preparation method according to any one of claims 1 - 8.

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