Boric acid quality detection method

Abstract

The invention provides a boric acid quality detection method, and belongs to the technical field of chemical analysis and detection. Comprising the following steps: S1, preprocessing an electronic foil; s2, placing the pre-treated electronic foil in a boric acid solution to be detected, connecting the pre-treated electronic foil with a positive electrode of a power supply, connecting a negative electrode of the power supply with another conductive material in contact with the boric acid solution to be detected, and setting a constant voltage value; s3, starting a power-up reaction, and turning off a power supply after the reaction is carried out for 30 seconds to 2 minutes; s4, taking out the electronic foil, and observing the surface of the electronic foil; judging whether the boric acid to be detected is qualified or not according to whether corrosion spots and snowflake spots exist on the surface of the electronic foil; in the step S2, when the boric acid is capacitance-level boric acid, the constant voltage of the power supply is 550-800V; and when the boric acid is nuclear power grade boric acid, the constant voltage of the power supply is 800-900V. The detection method provided by the invention can quickly and accurately judge the content of impurities in boric acid, is simple and convenient to operate, short in detection reaction time and low in cost, and does not need complex separation operation.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical analysis and detection, and particularly relates to a method for detecting the quality of boric acid. Background Art

[0002] Boric acid is widely used in the production of electrode foil for aluminum electrolytic capacitors, neutron shielding in nuclear reactors, medical applications (such as cancer neutron therapy), and glass production. However, impurities in boric acid can affect its effectiveness. For example, when boric acid is used as an electrolyte component during electrode foil formation, impurities such as sulfates, chlorides, and fluorides can affect the quality of the oxide film and the performance of the electrode foil. Impurity control in nuclear boric acid is also crucial for neutron absorption performance and reactor safety. The standard GB-T 538-2018 for industrial boric acid requires that the sodium, calcium, and magnesium contents in nuclear boric acid be ≤10 mg / kg. Sulfates, chlorides, and fluorides can also cause equipment corrosion or interfere with neutron absorption efficiency. When boric acid is used to prepare high-borosilicate glass, impure metal ions such as iron and sodium can reduce the glass's light transmittance.

[0003] Existing methods for detecting boric acid impurities include atomic absorption spectroscopy for heavy metal content, ion chromatography for metal ion impurities, high-performance liquid chromatography for sulfate, chloride, and other compounds. Ion chromatography coupled with ICP-MS can cover the full spectrum of anions, light metals, and heavy metals. However, these methods suffer from expensive instrumentation, cumbersome testing procedures, and lengthy testing times.

[0004] CN 109342538 A discloses a method for testing the quality of boric acid used in aluminum capacitor electrolytes. Boric acid is mixed with a dopant to form a test medium. Then, electricity is applied to two aluminum foils placed in the test medium. Under constant current conditions, the rate and quality of oxide layer growth can be determined by measuring the duration of the voltage increase. This test method uses ammonium water, borax, and ammonium pentaborate as dopants, introducing ammonium ions and sodium ions into the test medium. However, boric acid prepared using processes such as the borax-sulfuric acid neutralization method, the carbon-ammonia method, and the sodium polyborate-sulfuric acid method is prone to containing impurities such as ammonium ions and sodium ions. This test method cannot eliminate the effects of ammonium and sodium ions, as well as impurities on the aluminum foil surface, on the quality of the boric acid, nor can it evaluate the quality of the boric acid prepared using these processes. Furthermore, this test method is limited to boric acid used in aluminum capacitor electrolytes, making it unsuitable for use in other fields such as the nuclear industry and optical glass. Summary of the Invention

[0005] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for detecting the quality of boric acid.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: A method for detecting the quality of boric acid comprises the following steps: S1. Pretreatment of the electronic foil: Soak the electronic foil in a nitric acid solution and then boil it in boiling water. S2. The pretreated electronic foil is placed in a boric acid solution to be tested, connected to the positive electrode of the power supply, the negative electrode of the power supply is connected to another conductive material in contact with the boric acid solution to be tested, and a constant voltage value is set; S3. Start the power-on reaction, and turn off the power after 30 seconds to 2 minutes. S4. Remove the electronic foil and observe the surface of the electronic foil; when there are no corrosion points or snowflakes on the surface of the electronic foil, the boric acid to be tested is determined to be qualified; when there are corrosion points and / or snowflakes on the surface of the electronic foil, the boric acid to be tested is determined to be unqualified; In step S2, when the boric acid is capacitor-grade boric acid, the constant voltage of the power supply is 550-800V; when the boric acid is nuclear-grade boric acid, the constant voltage of the power supply is 800-900V.

[0007] The present invention applies a constant voltage to the electronic foil, causing it to undergo an electrical reaction under high voltage. If the boric acid to be tested contains low impurities, is of high purity, and is of qualified quality, the breakdown voltage of the system to be tested is high. As the electrical reaction proceeds, the resistance of the detection system increases, the current continuously decreases, and no corrosion spots and / or snowflakes form on the surface of the aluminum foil. If the boric acid to be tested contains too much impurities, the impurity ions lower the breakdown voltage of the system to be tested. Therefore, under high voltage conditions, the electronic foil can be rapidly broken down in a boric acid solution to be tested with excessive impurities, easily forming corrosion spots and / or snowflakes on the surface of the electronic foil, and the current does not continuously decrease after the electronic foil breaks down. Therefore, the present invention can determine whether the impurity content in the boric acid to be tested is qualified based on the surface condition of the electronic foil after a short period of time when a constant voltage is applied.

[0008] Since any impurity ions can cause the breakdown voltage of the system to be tested to decrease, the present invention can accurately eliminate the influence of most impurity ions including ammonium ions and sodium ions on the quality of boric acid.

[0009] The system to be tested refers to the system to be tested consisting of the boric acid solution to be tested and the electronic light foil.

[0010] The present invention uses a boric acid solution as the medium and an applied voltage as a reference to test whether aluminum foil breaks down under a high-voltage electric field. Higher-quality boric acid increases the flashover voltage (i.e., breakdown voltage) of the boric acid solution. Therefore, the present invention can meet varying requirements for boric acid quality by applying different voltages.

[0011] The boric acid to be tested in the present invention does not require the introduction of other dopants. Although dopants can increase the conductivity of the solution to be tested, they will introduce impurity ions, which can easily reduce the flash voltage (i.e., breakdown voltage) of the solution to be tested. This is not conducive to the quality evaluation of boric acid containing impurity ions and limits the application of boric acid.

[0012] In the pretreatment process, the nitric acid solution is used to remove impurities from the electronic foil surface and dissolve the oxide film, which is then corroded to expose the new aluminum substrate. The boiling water is used to form an oxide film on the aluminum foil surface, optimizing the oxide film structure through thermodynamic conditions and facilitating the electrical reaction.

[0013] The electronic foil used in the present invention is a bare foil, that is, a high-voltage electronic foil that has been annealed.

[0014] Specifically, the purity of the electronic foil is ≥99.998%.

[0015] Preferably, in step S2, when the boric acid is capacitor-grade boric acid, the voltage is 590V~800V.

[0016] More preferably, in step S2, when the boric acid is capacitor-grade boric acid, the voltage is 590V~620V.

[0017] More preferably, in step S2, when the boric acid is capacitor-grade boric acid, the voltage is 610V-620V.

[0018] Specifically, the content of boric acid in the boric acid solution to be tested is 9-12 wt %.

[0019] Specifically, the temperature of the boric acid solution to be tested is 83-87°C.

[0020] Specifically, the conductive material is a conductive metal or a carbon material.

[0021] Specifically, in step S2, the boric acid solution to be tested is placed in a stainless steel container, and a pretreated electronic foil is placed in the boric acid solution to be tested and connected to the positive electrode of a constant voltage power supply. The electronic foil does not contact the stainless steel container, and the negative electrode of the power supply is connected to the wall of the stainless steel container.

[0022] Preferably, in step S3, the maximum starting current of the power supply is set to 0.8-1.2A.

[0023] Preferably, in step S3, the power supply is turned off after reacting for 1 to 2 minutes.

[0024] Specifically, in step S1, the content of nitric acid in the nitric acid solution is 40-50 wt%.

[0025] Specifically, in step S1, the soaking temperature is 50-55°C.

[0026] Specifically, in step S1, the boiling time is 3 to 10 minutes.

[0027] Compared with the prior art, the present invention has the following beneficial effects: By applying a constant voltage to the electronic foil, causing it to undergo an electrical reaction at high voltage, the present invention can determine the impurity content of the boric acid being tested based on the surface condition of the electronic foil after the electrical reaction. Since most impurity ions can reduce the breakdown voltage of the system being tested, the present invention can accurately eliminate the effects of most impurity ions, including ammonium and sodium ions, on the quality of the boric acid.

[0028] The detection method provided by the present invention can quickly and accurately judge the impurity content in boric acid, and is simple to operate, has a short detection reaction time, is low in cost, does not require complex separation operations, and has high practical value and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a surface image of the electronic foil after the electrical reaction in Example 4.

[0030] Figure 2 This is the surface image of the electronic foil after the electrical reaction in Example 6.

[0031] Figure 3 This is a surface image of the electronic foil after the electrical reaction in Example 8. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0033] The boric acid samples in the Examples and Comparative Examples of the present invention were tested for impurities and their contents using the national standard GB / T 12684-2018, "Analysis of Industrial Borides," using methods such as spectrophotometry and turbidimetry. The impurities and their contents in the boric acid samples are shown in Table 1.

[0034] High-purity boric acid sample 1: capacitor-grade boric acid, boric acid content ≥99.5%.

[0035] High-purity boric acid sample 2: nuclear-grade boric acid, boric acid content ≥ 99.9% (Class II standard in national standard GB / T 538-2018), total impurities strictly controlled below 3 ppm.

[0036] The electronic foil used in the present invention is a bare foil, that is, a high-voltage electronic foil that has been annealed.

[0037] Example 1 This embodiment provides a method for detecting the quality of boric acid, comprising the following steps: S1. Cut a 5cm x 15cm square of annealed high-voltage electronic foil into a 50% nitric acid solution at 50°C for 60 seconds. Remove the foil, rinse it with pure water, and then boil it in boiling water for 5 minutes. S2. Weigh 100 g of high-purity boric acid sample 1 and place it in a stainless steel pot. Add 900 g of pure water and heat with stirring until the boric acid is completely dissolved. Clamp the pretreated electronic foil and immerse it in the boric acid solution to be tested. The temperature of the test boric acid solution is 85°C, and the immersion area is 5 x 8 cm². The electronic foil should not contact the stainless steel tank. Connect the positive terminal of the power supply to the tank wall, and the negative terminal to the stainless steel tank wall. Set the constant voltage to 580 V and the maximum starting current to 1 A. S3. Turn on the power supply to start the power-on reaction. After 1 minute of reaction, turn off the power supply. S4. Remove the electronic foil and observe its surface. Determine whether the impurity content in the boric acid sample meets the requirements based on the corrosion and snowflake spots on the surface.

[0038] Example 2 This embodiment provides a method for detecting the quality of boric acid, comprising the following steps: S1. Cut a 5cm x 15cm square of annealed high-voltage electronic foil into a 55°C x 50wt% nitric acid solution for 120 seconds. Remove the foil, rinse it with pure water, and then boil it in boiling water for 10 minutes. S2. Weigh 100 grams of high-purity boric acid sample 1 into a stainless steel pot. Add 900 grams of pure water and heat with stirring until the boric acid is completely dissolved. Clamp the pretreated electronic foil and immerse it in the boric acid solution to be tested. The solution temperature is 85°C, and the immersion area is 5 x 8 square centimeters. The electronic foil should not touch the stainless steel tank. Connect the positive terminal of the power supply to the tank wall, and the negative terminal to the stainless steel tank wall. Set the constant voltage to 620V and the maximum starting current to 1A. S3. Turn on the power supply to start the power-on reaction. After 1 minute of reaction, turn off the power supply. S4. Remove the electronic foil and observe its surface. Determine whether the impurity content in the boric acid sample meets the requirements based on the corrosion and snowflake spots on the surface.

[0039] Example 3 This embodiment provides a method for detecting the quality of boric acid, comprising the following steps: S1. Cut a 5cm x 15cm square of annealed high-voltage electronic foil into a 55°C x 50wt% nitric acid solution for 120 seconds. Remove the foil, rinse it with pure water, and then boil it in boiling water for 10 minutes. S2. Weigh 100 g of high-purity boric acid sample 1 and place it in a stainless steel pot. Add 900 g of pure water and heat with stirring until the boric acid is completely dissolved. Clamp the pretreated electronic foil and immerse it in the boric acid solution to be tested. The solution temperature is 85°C and the immersion area is 5 x 8 cm². The electronic foil should not touch the stainless steel tank. Connect the positive terminal of the power supply to the tank wall, and the negative terminal to the stainless steel tank wall. Set the constant voltage to 800 V and the maximum starting current to 1 A. S3. Turn on the power supply to start the power-on reaction. After 2 minutes of reaction, turn off the power supply. S4. Remove the electronic foil and observe its surface. Determine whether the impurity content in the boric acid sample meets the requirements based on the corrosion and snowflake spots on the surface.

[0040] Example 4 This embodiment provides a method for detecting the quality of boric acid, comprising the following steps: S1. Cut a 5cm x 15cm square of annealed high-voltage electronic foil into a 55°C x 50wt% nitric acid solution for 120 seconds. Remove the foil, rinse it with pure water, and then boil it in boiling water for 10 minutes. S2. Weigh 100 grams of high-purity boric acid sample 1 and place it in a stainless steel pot. Add 900 grams of pure water and heat and stir until the boric acid is completely dissolved. Clamp the pretreated electronic foil and immerse it in the boric acid solution to be tested. The temperature of the test boric acid solution is 85°C, and the immersion area is 5 × 8 square centimeters. The electronic foil should not touch the stainless steel tank. Connect the positive terminal of the power supply to the tank wall, and the negative terminal to the stainless steel tank wall. Set the constant voltage to 900V and the maximum starting current to 1A. S3. Turn on the power supply to start the power-on reaction. After 2 minutes of reaction, turn off the power supply. S4. Remove the electronic foil and observe its surface. Determine whether the impurity content in the boric acid sample meets the requirements based on the corrosion and snowflake spots on the surface.

[0041] Example 5 This embodiment provides a method for testing the quality of boric acid, which differs from that of Example 4 in that, in step S2, the boric acid solution to be tested uses a high-purity boric acid sample 2. The rest is the same as that of Example 4.

[0042] Example 6 This embodiment provides a method for detecting the quality of boric acid. The difference from Example 2 is that in step S2, a standard hydrochloric acid solution is added to a stainless steel pot until the Cl in the solution is - The content is 4ppm, and the rest is the same as Example 2.

[0043] Example 7 This embodiment provides a method for detecting the quality of boric acid. The difference from Example 2 is that in step S2, a standard solution of iron ions is added to a stainless steel pot until the Fe 3+ The content is 4ppm, and the rest is the same as Example 2.

[0044] Example 8 This embodiment provides a method for detecting the quality of boric acid. The difference from embodiment 2 is that in step S2, a standard ammonium pentaborate solution is added to a stainless steel pot until the NH 4+ The content is 5ppm, and the rest is the same as Example 2.

[0045] Example 9 This embodiment provides a method for detecting the quality of boric acid. The difference from Example 2 is that in step S2, a borax standard solution is added to a stainless steel pot until the Na + The content is 5ppm, and the rest is the same as Example 2.

[0046] Example 10 This embodiment provides a method for detecting the quality of boric acid. The difference from Example 2 is that in step S2, a sulfate ion standard solution is added to a stainless steel pot until the SO 4- The content is 6ppm, and the rest is the same as Example 2.

[0047] Comparative Example 1 This comparative example provides a method for detecting the quality of boric acid, which is different from Example 8 in that, in step S2, the constant voltage is 500 V and the maximum starting current is set to 1 A.

[0048] The impurity contents and test results of the examples and comparative examples are shown in Table 1.

[0049] Table 1 Impurity content and test results of Examples and Comparative Examples

[0050] As can be seen from Examples 1 to 3, for capacitor-grade boric acid, as the constant voltage increases, there are no corrosion spots or snowflakes on the surface of the plain foil. However, slight snowflakes appear in Example 4. This may be because the applied constant voltage is slightly higher than the breakdown voltage of the system to be tested, which in turn causes slight snowflakes to form on the surface of the electronic foil.

[0051] It can be seen from Examples 4 and 5 that the lower the impurity content in the boric acid, the higher the purity of the boric acid. Even under a high voltage of 900V, the electronic foil is not broken down. This shows that the higher the quality of the boric acid, the higher the flash voltage of the boric acid solution.

[0052] It can be seen from Examples 2 and 6 to 10 that the increase in the impurity ion content in boric acid leads to a decrease in the breakdown voltage of the system to be tested, which in turn causes a large number of snowflakes to be easily generated on the surface of the aluminum foil.

[0053] It can be seen from Example 8 and Comparative Example 1 that when the applied constant voltage is lower than 550 V, even if the impurity ion content in the boric acid increases, the electronic foil will not be broken down, and thus the quality of the boric acid cannot be accurately evaluated.

[0054] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for detecting the quality of boric acid, characterized in that: The following steps are involved: S1. Pretreatment of the electronic foil: Immerse the electronic foil in a nitric acid solution and then boil it in boiling water. S2. The pretreated electronic foil is placed in a boric acid solution to be tested, connected to the positive electrode of the power supply, the negative electrode of the power supply is connected to another conductive material in contact with the boric acid solution to be tested, and a constant voltage value is set; S3. Start the power-on reaction, and turn off the power after 30 seconds to 2 minutes. S4. Remove the electronic foil and observe the surface of the electronic foil; when there are no corrosion points or snowflake points on the surface of the electronic foil, the boric acid to be tested is determined to be qualified; when there are corrosion points and / or snowflake points on the surface of the electronic foil, the boric acid to be tested is determined to be unqualified; In step S2, when the boric acid is capacitor-grade boric acid, the constant voltage of the power supply is 550-800V; when the boric acid is nuclear-grade boric acid, the constant voltage of the power supply is 800-900V.

2. The detection method according to claim 1, characterized in that In step S2, when the boric acid is capacitor-grade boric acid, the voltage is 590V to 800V.

3. The detection method according to claim 1, characterized in that In step S2, the content of boric acid in the boric acid solution to be tested is 9-12 wt %.

4. The detection method according to claim 1, characterized in that In step S2, the temperature of the boric acid solution to be tested is 83-87°C.

5. The detection method according to claim 1, characterized in that: The conductive material is a conductive metal or a carbon material.

6. The detection method according to claim 1, characterized in that: In step S2, the boric acid solution to be tested is placed in a stainless steel container, a pretreated electronic foil is placed in the boric acid solution to be tested, the positive electrode of a constant voltage power supply is connected, and the negative electrode of the power supply is connected to the wall of the stainless steel container.

7. The detection method according to claim 1, characterized in that: In step S3, the power supply is turned off after reacting for 1 to 2 minutes.

8. The detection method according to claim 1, characterized in that: In step S1, the content of nitric acid in the nitric acid solution is 40-50 wt%.

9. The detection method according to claim 1, characterized in that: In step S1, the soaking temperature is 50-55°C.

10. The detection method according to claim 1, characterized in that: In step S1, the boiling time is 3 to 10 minutes.

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