Method for determining hypophosphite in electrode foil forming liquid

Abstract

The invention relates to a method for determining hypophosphite in an electrode foil forming solution, which comprises the following steps: adding an oxidizing agent into a to-be-detected electrode foil forming solution containing hypophosphite, and carrying out oxidation reaction to obtain a solution containing orthophosphate radicals; the oxidizing agent is selected from at least one of perchloric acid, hydrogen peroxide, sodium hypochlorite and nitric acid; determining the concentration of the phosphorus element in the solution containing orthophosphate radicals by adopting a molybdenum blue method; and obtaining the content of hypophosphite in the formation liquid of the electrode foil to be detected according to the concentration of phosphorus in the solution containing orthophosphate radicals. According to the method, the content of hypophosphite in the electrode foil forming liquid can be accurately measured, and the method is simple.

Description

Technical Field

[0001] The invention relates to the technical field of detection and analysis, and in particular to a method for determining hypophosphite in an electrode foil forming solution. Background Art

[0002] The service life of aluminum electrolytic capacitors is determined by many factors. The chemical foil used for anodes is the most critical material for aluminum electrolytic capacitors. It affects the capacity, volume, leakage, loss, ripple resistance, equivalent impedance, withstand voltage and temperature characteristics of the capacitor. In order to improve the service life of aluminum electrolytic capacitors, the anode foil is required to have the characteristics of low leakage, low loss, dense oxide film on the surface of the anode foil, and few defects, so as to reduce the failure of the capacitor. In the process of forming the oxide film of the anode foil, in order to improve the quality of the oxide film and reduce the loss and leakage current after the oxide film is prepared into a capacitor, a small amount of hypophosphite-containing additives are usually added to the anode foil forming liquid, and multi-stage phosphoric acid treatment is added. Among them, the small amount of hypophosphite-containing additives added to the forming liquid can effectively reduce the defects generated during the formation of the anode foil, and make the oxide film more dense, which can effectively reduce the leakage current and loss of the anode foil. However, because the content of hypophosphite additives in the forming liquid is low, the content of hypophosphite additives cannot be detected using traditional capacity analysis methods. Summary of the invention

[0003] Based on this, it is necessary to provide a method for accurately measuring the hypophosphite in the electrode foil forming solution.

[0004] The first aspect of the present application provides a method for determining hypophosphite in an electrode foil forming solution, comprising the following steps:

[0005] An oxidant is added to the electrode foil forming solution to be tested containing hypophosphite to carry out an oxidation reaction to obtain a solution containing orthophosphate; the oxidant is selected from at least one of perchloric acid, hydrogen peroxide, sodium hypochlorite and nitric acid;

[0006] The concentration of phosphorus in the solution containing orthophosphate is determined by the molybdenum blue method;

[0007] The content of hypophosphite in the electrode foil forming solution to be tested is obtained according to the concentration of phosphorus element in the solution containing orthophosphate.

[0008] The above-mentioned method for determining hypophosphite in the electrode foil forming liquid first uses an oxidant of a specific component to oxidize the hypophosphite in the electrode foil forming liquid to be tested into orthophosphate to obtain a solution containing orthophosphate; then the molybdenum blue method is used to determine the concentration of phosphorus in the solution containing orthophosphate, and then the content of hypophosphite in the electrode foil forming liquid to be tested is obtained based on the phosphorus concentration. Among them, the electrode foil forming liquid has a complex composition and a low content of hypophosphite, and it is difficult to determine an accurate result using a traditional volumetric analysis method. The present application uses an oxidant component of a specific component to fully oxidize the hypophosphite in the hypophosphite in the electrode forming liquid to form orthophosphate; further, the molybdenum blue method can be used to accurately measure the phosphorus concentration in a solution with a complex composition and a low phosphorus concentration, and the content of hypophosphite in the electrode forming liquid can be accurately obtained through the phosphorus concentration. Based on the large number of components in the electrode foil forming liquid, the above-mentioned specific type of oxidant is selected, which can oxidize hypophosphite into orthophosphate, and inhibit the generation of other by-products, thereby reducing the reaction between the oxidant and other components in the electrode foil forming liquid except hypophosphite, which affects the accuracy of the test results. In addition, compared with the traditional volumetric analysis method, the above method is simple and has a high measurement accuracy.

[0009] Furthermore, the above detection method can effectively monitor the changes in the content of the hypophosphite additive in the formation solution during the production process of the anode foil, improve the stability and consistency of the anode foil production process, and ensure the performance and life of the capacitor.

[0010] In some embodiments, the conditions of the oxidation reaction include: adding an oxidant to the electrode foil forming solution to be tested, heating to boiling and maintaining the boiling temperature for 5 minutes to 20 minutes.

[0011] In some embodiments, the concentration of hypophosphite in the electrode foil forming solution to be tested is 0.05 g / L to 2.0 g / L.

[0012] In some embodiments, the ratio of the volume of the electrode foil forming liquid to the volume of the oxidant is (2-4):1.

[0013] In some embodiments, the method of determining the concentration of phosphorus in the solution containing orthophosphate using the molybdenum blue method comprises:

[0014] A variety of standard phosphomolybdenum blue solutions with different phosphorus concentrations were prepared using phosphorus standard solution, ammonium molybdate potassium antimony tartrate solution, ascorbic acid solution and water;

[0015] The absorbance intensities of the plurality of standard phosphomolybdenum blue solutions with different phosphorus concentrations are measured by a spectrophotometer to obtain a relationship between the absorbance intensities of the standard phosphomolybdenum blue solutions and the phosphorus concentrations;

[0016] Adding ammonium molybdate, potassium antimony tartrate, ascorbic acid and sulfuric acid to the solution containing orthophosphate to obtain a phosphomolybdenum blue test solution, and obtaining an absorbance intensity test value of the phosphomolybdenum blue test solution by a spectrophotometer;

[0017] According to the relationship between the absorbance intensity of the standard phosphomolybdenum blue solution and the concentration of phosphorus element and the absorbance intensity test value of the phosphomolybdenum blue test solution, the concentration of phosphorus element in the phosphomolybdenum blue test solution is obtained.

[0018] In some embodiments, the molar ratio of orthophosphate to ammonium molybdate, potassium antimony tartrate and ascorbic acid in the phosphomolybdenum blue test solution is 1:(12-13):(1-2).

[0019] In some embodiments, the volume proportion of the sulfuric acid in the phosphomolybdenum blue test solution is 25% to 35%.

[0020] In some embodiments, the step of obtaining the absorbance intensity test value of the phosphomolybdenum blue test solution by using a spectrophotometer includes diluting the phosphomolybdenum blue test solution and then testing the absorbance intensity test value of the diluted phosphomolybdenum blue test solution by using a spectrophotometer.

[0021] In some embodiments, the concentration of phosphorus in the diluted phosphomolybdenum blue test solution is 0.01 ppm to 0.5 ppm.

[0022] In some embodiments, the method for obtaining the content of hypophosphite in the electrode foil forming solution to be tested according to the concentration of phosphorus in the solution containing orthophosphate includes using the following calculation formula (I) to obtain the content of hypophosphite in the electrode foil forming solution to be tested:

[0023] C = (M × C1 / Mp) × d (I)

[0024] Wherein, C is the content of hypophosphite in the electrode foil forming solution to be tested, in g / L;

[0025] M is the relative molecular mass of the hypophosphite in the electrode foil forming solution to be tested;

[0026] C1 is the measured value of phosphorus concentration in the diluted phosphomolybdenum blue test solution, in mg / L;

[0027] Mp is the relative atomic mass of phosphorus;

[0028] d is the dilution factor of the phosphomolybdenum blue test solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the drawings required for use in the embodiments or the conventional technology descriptions are briefly introduced below. Obviously, the drawings described below are merely embodiments of the present application, and ordinary technicians in this field can obtain other drawings based on the disclosed drawings without paying any creative work.

[0030] FIG. 1 is a standard curve diagram of absorbance intensity and phosphorus concentration obtained in an example of the present application. DETAILED DESCRIPTION

[0031] In order to facilitate the understanding of the present invention, the present invention is described more comprehensively below. And preferred embodiments of the present invention are given. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. It should be understood that the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0033] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0034] The weight of the relevant components mentioned in the description of the embodiments of the present invention may not only refer to the specific content of each component, but also indicate the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the description of the embodiments of the present invention, it is within the scope disclosed in the description of the embodiments of the present invention. Specifically, the weight described in the description of the embodiments of the present invention may be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0035] In one embodiment of the present application, a method for determining hypophosphite in an electrode foil forming solution is provided, comprising the following steps S10 to S30:

[0036] S10, adding an oxidant to the electrode foil forming solution to be tested containing hypophosphite to carry out an oxidation reaction to obtain a solution containing orthophosphate; the oxidant is selected from at least one of perchloric acid, hydrogen peroxide, sodium hypochlorite and nitric acid.

[0037] S20, using the molybdenum blue method to measure the concentration of phosphorus in the solution containing orthophosphate;

[0038] S30. Obtain the content of hypophosphite in the electrode foil forming solution to be tested according to the concentration of phosphorus element in the solution containing orthophosphate.

[0039] The above-mentioned method for determining hypophosphite in the electrode foil forming liquid first uses an oxidant of a specific component to oxidize the hypophosphite in the electrode foil forming liquid to be tested into orthophosphate to obtain a solution containing orthophosphate; then uses the molybdenum blue method to determine the concentration of phosphorus in the solution containing orthophosphate, and then obtains the content of hypophosphite in the electrode foil forming liquid to be tested based on the phosphorus concentration. Among them, the electrode foil forming liquid has a complex composition and a low content of hypophosphite, and it is difficult to determine an accurate result using a traditional volumetric analysis method. However, the present application uses an oxidant component of a specific component to fully oxidize the hypophosphite in the hypophosphite in the electrode forming liquid to form orthophosphate, and further cooperates with the molybdenum blue method to accurately measure the phosphorus concentration in a solution with a complex composition and a low phosphorus concentration, and the content of hypophosphite in the electrode forming liquid can be accurately obtained through the phosphorus concentration. Based on the large number of components in the electrode foil forming liquid, the above-mentioned specific type of oxidant is selected, which can oxidize hypophosphite into orthophosphate, and inhibit the generation of other by-products, thereby reducing the reaction between the oxidant and other components in the electrode foil forming liquid except hypophosphite, which affects the accuracy of the test results. In addition, compared with the traditional volumetric analysis method, the above method is simple and has a high measurement accuracy.

[0040] Furthermore, the above detection method can effectively monitor the changes in the content of the hypophosphite additive in the formation solution during the production process of the anode foil, improve the stability and consistency of the anode foil production process, and ensure the performance and life of the capacitor.

[0041] The electrode foil forming solution to be tested containing hypophosphite does not contain orthophosphate.

[0042] In some embodiments, the oxidizing agent is preferably perchloric acid.

[0043] In some embodiments, the conditions of the oxidation reaction include: after adding an oxidant to the electrode foil forming liquid to be tested, heating to boiling and maintaining for 5 minutes to 20 minutes. As an example, the holding time for heating to boiling can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes. After adding an oxidant to the electrode foil forming liquid to be tested, heating to boiling and maintaining a certain boiling time can make the hypophosphite fully react under the action of the oxidant.

[0044] In some embodiments, in the above oxidation reaction conditions, the heating temperature is 90°C~100°C.

[0045] In some embodiments, the concentration of hypophosphite in the electrode foil forming liquid to be tested is 0.05 g / L to 2.0 g / L. As an example, the concentration of hypophosphite in the electrode foil forming liquid to be tested can be 0.05 g / L, 0.10 g / L, 0.20 g / L, 0.30 g / L, 0.40 g / L, 0.50 g / L, 0.60 g / L, 0.70 g / L, 0.80 g / L, 0.90 g / L, 1.0 g / L, 1.2 g / L, 1.4 g / L, 1.5 g / L, 1.6 g / L, 1.8 g / L or 2.0 g / L. Further, the concentration of hypophosphite in the electrode foil forming liquid to be tested can be a range value consisting of any two of the above point values ​​as end values. Preferably, the concentration of hypophosphite in the electrode foil forming liquid to be tested is 0.05 g / L to 1.0 g / L.

[0046] In some embodiments, the ratio of the volume of the electrode foil forming liquid to the volume of the oxidant is (2-4):1. As an example, the ratio of the volume of the electrode foil forming liquid to the volume of the oxidant can be 2:1, 2.5:1, 2.8:1, 3:1, 3.5:1 or 4:1. Further, the ratio of the volume of the electrode foil forming liquid to the volume of the oxidant can be a range value consisting of any two of the above point values ​​as end values. By controlling the volume ratio between the electrode foil forming liquid and the oxidant, the ratio of the hypophosphite to the oxidant in the electrode foil forming liquid can be controlled, while ensuring that the amount of the oxidant is excessive and that all the hypophosphites are oxidized to orthophosphates.

[0047] In some embodiments, the method for determining the concentration of phosphorus in a solution containing orthophosphate using the molybdenum blue method in step S20 includes the following steps S201 to S204:

[0048] S201, prepare a plurality of standard phosphomolybdenum blue solutions with different phosphorus concentrations using phosphorus standard solution, ammonium molybdate potassium antimony tartrate solution, ascorbic acid solution and water.

[0049] S202. Determine the absorbance intensity of a plurality of standard phosphomolybdenum blue solutions having different phosphorus concentrations using a spectrophotometer to obtain a relationship between the absorbance intensity of the standard phosphomolybdenum blue solution and the phosphorus concentration.

[0050] S203. Add ammonium molybdate, potassium antimony tartrate, ascorbic acid and sulfuric acid to a solution containing orthophosphate to obtain a phosphomolybdenum blue test solution, and obtain an absorbance intensity test value of the phosphomolybdenum blue test solution by a spectrophotometer.

[0051] S204. According to the relationship between the absorbance intensity of the standard phosphomolybdenum blue solution and the phosphorus concentration and the absorbance intensity test value of the phosphomolybdenum blue test solution, the concentration of the phosphorus in the phosphomolybdenum blue test solution is obtained.

[0052] In some embodiments, the relationship between the absorbance intensity of the standard phosphomolybdenum blue solution obtained in step S202 and the phosphorus concentration satisfies the following formula (II):

[0053] Y=a·Xb (II)

[0054] Wherein, Y is the concentration of phosphorus;

[0055] X is the absorbance intensity, with the unit being 1;

[0056] a is a constant;

[0057] b is a constant.

[0058] In some embodiments, Y=2.049X-0.0007, and the unit of Y is mg / L.

[0059] In some embodiments, the molar ratio of orthophosphate to ammonium molybdate, potassium antimony tartrate and ascorbic acid in the phosphomolybdenum blue test solution obtained in step S203 is 1:(12-13):(1-2).

[0060] In some embodiments, the phosphomolybdenum blue test solution also includes sulfuric acid, and the volume proportion of sulfuric acid in the phosphomolybdenum blue test solution is 25% to 35%. Sulfuric acid is added to the phosphomolybdenum blue test solution to provide an acidic environment for the reaction system. In the acidic environment, orthophosphate reacts with ammonium antimony molybdenum and potassium antimony tartrate to generate phosphomolybdic heteropoly acid, which is then reduced by ascorbic acid to generate a blue complex phosphomolybdenum blue.

[0061] In some embodiments, the method of obtaining the phosphomolybdenum blue test solution in step S203 comprises the following steps:

[0062] A mixed aqueous solution of ammonium molybdate, potassium antimony tartrate and sulfuric acid and an aqueous solution of ascorbic acid are respectively prepared, and then the mixed aqueous solution of ammonium molybdate, potassium antimony tartrate and sulfuric acid and the aqueous solution of ascorbic acid are added to a solution containing orthophosphate; wherein the step of preparing the mixed aqueous solution of ammonium molybdate, potassium antimony tartrate and sulfuric acid comprises: dissolving ammonium molybdate and potassium antimony tartrate in water respectively to obtain an aqueous solution of ammonium molybdate and an aqueous solution of potassium antimony tartrate; adding the aqueous solution of ammonium molybdate to sulfuric acid, mixing evenly, and then adding the aqueous solution of potassium antimony tartrate.

[0063] In some embodiments, the step of obtaining the absorbance intensity test value of the phosphomolybdenum blue test solution using a spectrophotometer includes diluting the phosphomolybdenum blue test solution and then testing the absorbance intensity test value of the diluted phosphomolybdenum blue test solution using a spectrophotometer.

[0064] In some embodiments, the concentration of phosphorus in the diluted phosphomolybdenum blue test solution is 0.01ppm to 0.5ppm. The phosphomolybdenum blue test solution is diluted so that the substance can fully react at a low concentration and the color of the liquid is lighter, thereby improving the accuracy of the test.

[0065] In some embodiments, the method for obtaining the content of hypophosphite in the electrode foil forming solution to be tested according to the concentration of phosphorus in the solution containing orthophosphate includes using the following calculation formula (I) to obtain the content of hypophosphite in the electrode foil forming solution to be tested:

[0066] C = (M × C1 / Mp) × d (I)

[0067] Wherein, C is the content of hypophosphite in the electrode foil forming solution to be tested, in g / L;

[0068] M is the relative molecular mass of the hypophosphite in the electrode foil forming solution to be tested;

[0069] C1 is the measured value of phosphorus concentration in the diluted phosphomolybdenum blue test solution, in mg / L;

[0070] Mp is the relative atomic mass of phosphorus;

[0071] d is the dilution factor of the phosphomolybdenum blue test solution.

[0072] In some embodiments, the hypophosphite is sodium hypophosphite.

[0073] In order to make the purpose, technical solutions and advantages of the present invention more concise and clear, the present invention is described with the following specific embodiments, but the present invention is by no means limited to these embodiments. The embodiments described below are only preferred embodiments of the present invention, which can be used to describe the present invention and cannot be understood as limiting the scope of the present invention. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0074] In order to better illustrate the present invention, the present invention is further described below in conjunction with the embodiments. The following are specific embodiments.

[0075] Example of preparation of test solution:

[0076] Preparation of ammonium molybdate and potassium antimony tartrate solution: weigh 6.5g of ammonium molybdate and dissolve it in 50mL of pure water, and dissolve 0.175g of potassium antimony tartrate in 50mL of pure water. Then pour the dissolved ammonium molybdate into 150mL of sulfuric acid solution (the volume ratio of concentrated sulfuric acid to water is 1:1), cool it, stir it evenly, and finally add the dissolved potassium antimony tartrate into the above solution. After the liquid cools, move it to a 250mL volumetric flask.

[0077] Preparation of ascorbic acid solution: Weigh 5 g of ascorbic acid and dissolve it in 50 mL of pure water to prepare an ascorbic acid solution with an ascorbic acid concentration of 1 g / mL.

[0078] The ammonium molybdate potassium antimony tartrate solution and ascorbic acid solution used in the following examples and embodiments are all prepared by the preparation method of this example.

[0079] Drawing of standard curve:

[0080] 0, 1mL, 2mL, 3mL, 4mL, and 5mL of 10ppm phosphorus standard solution (prepared from potassium dihydrogen phosphate) were respectively drawn into 6 100ml volumetric flasks, and 4mL of ammonium molybdate potassium antimony tartrate solution and 2mL of ascorbic acid solution were added to each flask in turn, and pure water was added to make the volume to 100ml, shaken well, and left for 10 minutes to obtain the test solution. The absorbance was detected using a 7230 spectrophotometer, and the wavelength was set to 750nm. The test results are shown in Table 1:

[0081] Table 1

[0082]

[0083] The standard curve is drawn with the measured absorbance as the horizontal axis and the corresponding phosphorus concentration as the vertical axis, as shown in Figure 1. From the regression equation, we can know that the standard curve is: Y = 2.049X-0.0007, R 2 =0.9999, where X is the absorbance of the test solution, and Y is the concentration of phosphorus in the test solution, in mg / L.

[0084] The following is an example of determining the sodium hypophosphite content in the test solution:

[0085] Example 1

[0086] This embodiment simulates the composition of the anode foil forming solution to verify whether other components in the forming solution affect the detection amount of sodium hypophosphite. The steps are as follows:

[0087] (1) Solution preparation: Weigh 0.3452 g of sodium hypophosphite, 0.5 g of citric acid, 0.5 g of ammonium pentaborate and 0.5 g of boric acid into a small beaker and then dilute to a 500 ml volumetric flask to obtain a simulated solution with a sodium hypophosphite concentration of 0.6904 g / L.

[0088] (2) Transfer 20 mL of the simulated solution prepared in step (1) into a small beaker, add 4 small glass beads, and then add an appropriate amount of perchloric acid. Heat and boil on an electric stove for about 10 minutes.

[0089] (3) When the liquid volume in step (1) is 3mL~4mL, stop heating, wait for the white smoke in the beaker to evaporate, cool down, add 20mL~30mL pure water to completely dissolve the substance in the beaker, transfer to a 1000mL volumetric flask, and add pure water to make up the volume. Then transfer 10mL of the solution to a 100mL volumetric flask, add 4mL of the prepared ammonium molybdate potassium antimony tartrate solution and 2mL of ascorbic acid solution, add pure water to make up the volume to 100mL, shake well, and place in a water bath at a constant temperature of 25℃-30℃ for 10min to obtain the test solution. Use a 7230 spectrophotometer to detect the absorbance, set the wavelength to 750nm, obtain the absorbance value, and then substitute the absorbance value into the standard curve equation to obtain the phosphorus concentration in the test solution.

[0090] The test and calculation results are shown in Table 2:

[0091] Table 2

[0092]

[0093] Note: The measured concentration of phosphorus in the test solution in Table 2, C1, is calculated by the standard curve equation Y=2.049·X-0.0007. The calculation formula for the measured concentration of sodium hypophosphite in the simulated solution to be tested is: C=M×C1 / 31×d, in this embodiment, M is 106 and d is 500. The calculation formula for the relative error is: relative error=(measured concentration of sodium hypophosphite in the simulated solution to be tested-sodium phosphite configuration concentration in the simulated solution) / sodium phosphite configuration concentration in the simulated solution×100%.

[0094] From Table 2, we can see that adding 5 mL of perchloric acid is enough to oxidize all the sodium hypophosphite into orthophosphate. The main reason may be that the higher the concentration of perchloric acid, the stronger the oxidizing power, which can more fully oxidize the sodium hypophosphite. At the same time, adding other raw materials such as citric acid, ammonium pentaborate and boric acid, which are conventional raw materials, has no obvious effect on the detection of sodium hypophosphite content.

[0095] Analysis of test results: When the amount of simulated liquid is constant, increasing the amount of perchloric acid can completely oxidize the sodium hypophosphite and improve the accuracy of the test results.

[0096] Example 2

[0097] This embodiment simulates the composition of the anode foil forming solution to verify whether other components in the forming solution affect the detection amount of sodium hypophosphite. The steps are as follows:

[0098] (1) Solution preparation: Weigh a certain amount of 0.3450 g sodium hypophosphite, 0.5 g ammonium carbonate, 0.5 g triammonium citrate, 0.5 g adipic acid and 1 g boric acid and dissolve them in a small beaker. Then make up to the volume in a 500 mL volumetric flask to obtain a simulated solution with a sodium hypophosphite concentration of 0.6900 g / L.

[0099] (2) Transfer 20 mL of the simulated solution prepared in step (1) into a small beaker, add 4 small glass beads, and then add an appropriate amount of perchloric acid. Heat and boil on an electric stove for about 10 minutes.

[0100] (3) Stop heating when 3mL~4mL of the liquid remains. After the white smoke in the beaker evaporates and cools, add 20mL~30mL of pure water to dissolve the substance in the beaker completely, then transfer it to a 1000mL volumetric flask and add pure water to make up the volume. Then transfer 10mL of the solution to a 100mL volumetric flask, add 4mL of the prepared ammonium molybdate potassium antimony tartrate solution and 2mL of ascorbic acid solution, add pure water to make up the volume to 100mL, shake well, and place in a water bath at a constant temperature of 25℃-30℃ for 10 minutes to obtain the test solution. Use a 7230 spectrophotometer to detect the absorbance, set the wavelength to 750nm, obtain the absorbance value, and then substitute the absorbance value into the standard curve equation to obtain the phosphorus concentration in the test solution.

[0101] The test and calculation results are shown in Table 3:

[0102] Table 3

[0103]

[0104] Note: The measured concentration C1 of the orthophosphorus element in the test solution in Table 3 is calculated by the standard curve equation Y=2.049X-0.0007. The calculation formula for the measured concentration of sodium hypophosphite in the simulated solution to be tested is: C=M×C1 / 31×d, in this embodiment, M is 106 and d is 500.

[0105] Example 3

[0106] This embodiment simulates the composition of the anode foil forming solution to verify whether other components in the forming solution affect the detection amount of sodium hypophosphite. The steps are as follows:

[0107] (1) Solution preparation: Weigh 0.3447 g sodium hypophosphite, 0.5 g ammonium adipate, 0.5 g ammonium carbonate, 0.5 g citric acid and 1 g boric acid and dissolve them in a small beaker. Then dilute to a 500 ml volumetric flask to obtain a simulated solution with a sodium hypophosphite concentration of 0.6894 g / L.

[0108] (2) Transfer 20 mL of the simulated solution prepared in step (1) into a small beaker, add 4 small glass beads, and then add 5 mL of sodium hypochlorite solution. Heat on an electric stove and boil for about 12 minutes.

[0109] (3) Stop heating when 3mL~4mL of the solution remains, cool it down and transfer it to a 1000mL volumetric flask, and add pure water to make up the volume. Then transfer 10mL of the solution to a 100mL volumetric flask, add 4mL of ammonium molybdate potassium antimony tartrate solution and 2mL of ascorbic acid solution, add pure water to make up the volume to 100mL, shake well, and place it in a water bath at a constant temperature of 25℃-30℃ for 10 minutes to obtain the test solution. Use a 7230 spectrophotometer to detect the absorbance, set the wavelength to 750nm, obtain the absorbance value, and then substitute the absorbance value into the standard curve equation to obtain the phosphorus concentration in the test solution.

[0110] The test and calculation results are shown in Table 4:

[0111] Table 4

[0112]

[0113] Note: The measured concentration C1 of the orthophosphorus element in the test solution in Table 4 is calculated by the standard curve equation Y=2.049·X-0.0007. The calculation formula for the measured concentration of sodium hypophosphite in the simulated solution to be tested is: C=M×C1 / 31×d, in this embodiment, M is 106 and d is 500.

[0114] Comparative Example 1

[0115] This comparative example uses a volumetric analysis method to measure the concentration of sodium hypophosphite in the simulated liquid. The specific steps are:

[0116] Using the JM iodine titration method, iodine is used to oxidize hypophosphite and phosphite to phosphite in an acidic system, and then the excess iodine is titrated with sodium thiosulfate to calculate the total amount of hypophosphite.

[0117] 1. Configuration of the test solution

[0118] (1) Preparation of potassium dichromate solution (0.01 mol / L): Weigh 1.4709 g of the standard substance K2Cr2O7 dried to constant weight at 120°C into a small beaker using the fixed weight weighing method. Add water to dissolve it. Transfer the solution quantitatively to a 500 mL volumetric flask. Add water to the mark, mix well, and set aside.

[0119] (2) Preparation of sodium thiosulfate solution (0.05 mol / L): Weigh 6.2042 g of Na2S2O3·5H2O into a small beaker and weigh 0.02 g of anhydrous Na2CO3. Dissolve the two solid samples in cooled distilled water and use the cooled distilled water to make up the volume in a 500 mL brown volumetric flask. Add water to the mark, mix well, and place in a dark place for 7 to 10 days for calibration.

[0120] (3) Preparation of iodine solution (0.05 mol / L): Use the fixed weight weighing method to weigh 3.1726 g of solid standard I2 into a small beaker. At the same time, weigh 9 g of solid KI and add it to the solid iodine. Dissolve it in pure water and make up to a 500 mL brown volumetric flask. Add water to the mark, mix well, and set aside.

[0121] (4) Preparation of 1% starch indicator: Weigh 1 g of soluble starch, add 100 mL of pure water, mix well, and set aside.

[0122] 2. Standardization of sodium thiosulfate solution

[0123] (1) Use a single-marked pipette to measure 10.00 mL of 0.01 mol / L K2Cr2O7 solution into an iodine bottle, add 1 g of KI, 15 mL of distilled water, and 4 mL of HCl solution with a volume ratio of 1:1 between concentrated hydrochloric acid and pure water. Seal the bottle, shake well, seal with water, and place in a dark place for 10 min.

[0124] (2) Dilute with 30 mL of distilled water, titrate with Na2S2O3 solution until it is close to the end point, add 2 mL of starch indicator solution, and continue titrating until the blue color disappears and bright green appears, which means the end point has been reached.

[0125] (3) Repeat the calibration twice, and the relative deviation should not exceed 0.2%. To prevent the volatilization loss of the reaction product I2, the potassium iodide reagents for parallel tests should not be added at the same time, but should be added one at a time.

[0126] (4) Calculation results of the molar concentration of sodium thiosulfate:

[0127]

[0128] In the formula, is the molar concentration of sodium thiosulfate; the unit is mol / L;

[0129] is the mole number of potassium dichromate; the unit is mol;

[0130] is the volume of sodium thiosulfate, in ml;

[0131] 3. Determination of hypophosphite in the preparation solution

[0132] (1) Use a graduated pipette to accurately transfer 20 mL of the preparation solution into a 250 mL conical flask, add 10 mL of 0.05 mol / L iodine solution, then add 20 mL of hydrochloric acid (the volume ratio of concentrated hydrochloric acid to pure water is 1:1), and place in a dark place for 30 min.

[0133] (2) Add 2 to 3 drops of 1% starch indicator and titrate with 0.05 mol / L sodium thiosulfate solution. The titration endpoint is when the solution changes from blue to colorless.

[0134] The calculation formula of hypophosphite molar concentration is:

[0135]

[0136] In the formula, is the molar concentration of hypophosphite; the unit is mol / L;

[0137] is the number of moles of I2; the unit is mol;

[0138] is the mole number of sodium thiosulfate; the unit is mol;

[0139] is the volume of hypophosphite; the unit is mL;

[0140] 4. Main reaction equation:

[0141] (1) Calibration of sodium thiosulfate: Cr2O7 2- +6I - +14H + =2Cr 3+ +3I2+7H2O

[0142] I2+2S2O3 2- =S4O6 2- +2I -

[0143] (2) Titration of hypophosphite: H2PO2 - +I2+H2O= H2PO3 2- +2I - +3H +

[0144] I2+2S2O3 2- =S4O6 2- +2I -

[0145] The concentration of sodium hypophosphite in the prepared solution is 0.6900 g / L. The detection result using this method is 0.7325 g / L, with a relative error of 6.16%. The relative error is large and cannot truly reflect the content of sodium hypophosphite in the tank liquid.

[0146] Comparative Example 2

[0147] This comparative example uses a volumetric analysis method to measure the concentration of sodium hypophosphite in the simulated liquid. The specific steps are:

[0148] Using the Rao method, potassium dichromate is used to oxidize hypophosphite and phosphite to orthophosphate in a sulfuric acid system, and then the excess potassium dichromate is titrated with ammonium ferrous sulfate to calculate the total amount of hypophosphite.

[0149] 1. Configuration of the test solution

[0150] (1) Preparation of potassium dichromate solution (0.01 mol / L): Weigh 1.4709 g of the standard substance K2Cr2O7 dried to constant weight at 120°C into a small beaker using the fixed weight weighing method. Add water to dissolve it. Transfer the solution quantitatively to a 500 mL volumetric flask. Add water to the mark, mix well, and set aside.

[0151] (2) Preparation of ammonium ferrous sulfate solution (0.05 mol / L): Weigh 9.8033 g of FeSO4·(NH4)2SO4·6H2O into a small beaker, add water to dissolve it, and add a few drops of concentrated sulfuric acid (to prevent the precipitation of ferrous and ferric hydroxides) to make the solution acidic or weakly acidic. Transfer the solution quantitatively to a 500 mL brown volumetric flask, add water to the mark, mix well, and set aside.

[0152] (3) Preparation of 1.5% o-phenanthroline indicator: Weigh 1.5 g o-phenanthroline and add 100 mL pure water. O-phenanthroline is not easily soluble in water. During the preparation process, add 1 mL of concentrated sulfuric acid, mix well, and set aside.

[0153] 2. Calibration of ammonium ferrous sulfate solution concentration

[0154] (1) Use a single-mark pipette to accurately transfer 10 mL of the prepared 0.01 mol / L K2Cr2O7 solution into a 250 mL conical flask, and then add 5 mL of 1:1 hydrochloric acid (the volume ratio of concentrated hydrochloric acid to pure water is 1:1) to keep the solution acidic.

[0155] (2) Add 2 to 3 drops of 1.5% phenanthroline indicator and titrate with the prepared ammonium ferrous sulfate solution. The titration endpoint is when the solution changes from orange to bright green.

[0156] (3) Repeat the calibration twice, and the relative deviation cannot exceed 0.2%.

[0157] (4) The calculation formula for the molar concentration of ferrous sulfate is:

[0158]

[0159] In the formula, is the molar concentration of ferrous sulfate, in mol / L;

[0160] is the mole number of potassium dichromate, in mol;

[0161] is the volume of ferrous sulfate, in mL.

[0162] 3. Determination of hypophosphite in the preparation solution

[0163] (1) Use a graduated pipette to accurately transfer 20 mL of the preparation solution into a 250 mL conical flask, add 20 mL of 0.01 mol / L K2Cr2O7 solution, then add 8 mL of concentrated sulfuric acid, let stand for 10 min and cool.

[0164] (2) Add 2 to 3 drops of 1.5% o-phenanthroline indicator and titrate with 0.05 mol / L ammonium ferrous sulfate solution. The titration endpoint is when the solution changes from orange to bright green.

[0165] The formula for calculating the molar concentration of hypophosphite is:

[0166]

[0167] In the formula, is the molar concentration of hypophosphite; the unit is mol / L;

[0168] is the mole number of potassium dichromate; the unit is mol;

[0169] is the number of moles of ferrous sulfate; the unit is mol;

[0170] is the volume of hypophosphite solution; the unit is mL.

[0171] 5. Main reaction equation: 3H2PO2 - +2Cr2O7 2- +10H + = 3PO4 3- +4Cr 3+ +8H2O

[0172] 3H2PO3 2- +Cr2O7 2- +5H + = 3PO4 3- +2Cr 3+ +4H2O

[0173] Cr2O7 2- +6Fe 2+ +14H + = 6Fe 3+ +2Cr 3+ +7H2O

[0174] The concentration of sodium hypophosphite in the prepared solution is 0.6904 g / L. The detection result using this method is 0.7319 g / L, with a relative error of 6.01%. The relative error is large and cannot truly reflect the content of sodium hypophosphite in the tank liquid.

[0175] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0176] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims, and the description can be used to interpret the content of the claims.

Claims

1. A method for determining hypophosphite in an electrode foil forming solution, characterized in that: The steps include: An oxidant is added to the electrode foil forming solution to be tested containing hypophosphite to carry out an oxidation reaction to obtain a solution containing orthophosphate; the oxidant is selected from at least one of perchloric acid, hydrogen peroxide, sodium hypochlorite and nitric acid; The concentration of phosphorus in the solution containing orthophosphate is determined by the molybdenum blue method; The content of hypophosphite in the electrode foil forming solution to be tested is obtained according to the concentration of phosphorus element in the solution containing orthophosphate.

2. The measuring method according to claim 1, characterized in that The conditions of the oxidation reaction include: adding an oxidant to the electrode foil forming solution to be tested, heating to boiling and maintaining the boiling temperature for 5 minutes to 20 minutes.

3. The measuring method according to claim 1, characterized in that The concentration of the hypophosphite in the electrode foil forming solution to be tested is 0.05 g / L to 2.0 g / L.

4. The measuring method according to claim 1, characterized in that The ratio of the volume of the electrode foil forming liquid to the volume of the oxidant is (2-4):

1.

5. The measuring method according to any one of claims 1 to 4, characterized in that The method for determining the concentration of phosphorus in the solution containing orthophosphate using the molybdenum blue method comprises: A variety of standard phosphomolybdenum blue solutions with different phosphorus concentrations were prepared using phosphorus standard solution, ammonium molybdate potassium antimony tartrate solution, ascorbic acid solution and water; The absorbance intensities of the plurality of standard phosphomolybdenum blue solutions with different phosphorus concentrations are measured by a spectrophotometer to obtain a relationship between the absorbance intensities of the standard phosphomolybdenum blue solutions and the phosphorus concentrations; Adding ammonium molybdate, potassium antimony tartrate, ascorbic acid and sulfuric acid to the solution containing orthophosphate to obtain a phosphomolybdenum blue test solution, and obtaining an absorbance intensity test value of the phosphomolybdenum blue test solution by a spectrophotometer; According to the relationship between the absorbance intensity of the standard phosphomolybdenum blue solution and the concentration of phosphorus element and the absorbance intensity test value of the phosphomolybdenum blue test solution, the concentration of phosphorus element in the phosphomolybdenum blue test solution is obtained.

6. The assay method according to claim 5, wherein The molar content ratio of orthophosphate, ammonium molybdate potassium antimony tartrate and ascorbic acid in the phosphomolybdenum blue test solution is 1:(12-13):(1-2).

7. The assay method according to claim 5, wherein The volume proportion of the sulfuric acid in the phosphomolybdenum blue test solution is 25% to 35%.

8. The assay method according to claim 5, wherein The step of obtaining the absorbance intensity test value of the phosphomolybdenum blue test solution by using a spectrophotometer includes diluting the phosphomolybdenum blue test solution and then testing the absorbance intensity test value of the diluted phosphomolybdenum blue test solution by using a spectrophotometer.

9. The assay method according to claim 8, wherein The concentration of phosphorus in the diluted phosphomolybdenum blue test solution is 0.01ppm~0.5ppm.

10. The measuring method according to any one of claims 8 to 9, characterized in that The method for obtaining the content of hypophosphite in the electrode foil forming solution to be tested according to the concentration of phosphorus in the solution containing orthophosphate includes using the following calculation formula (I) to obtain the content of hypophosphite in the electrode foil forming solution to be tested: C = (M × C1 / Mp) × d (I) Wherein, C is the content of hypophosphite in the electrode foil forming solution to be tested, in g / L; M is the relative molecular mass of the hypophosphite in the electrode foil forming solution to be tested; C1 is the measured value of phosphorus concentration in the diluted phosphomolybdenum blue test solution, in mg / L; Mp is the relative atomic mass of phosphorus; d is the dilution factor of the phosphomolybdenum blue test solution.

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