Method for detecting content of nitric acid and hydrofluoric acid in titanium alloy pickling solution

Abstract

The present application relates to the technical field of titanium alloy surface chemical pickling solution component concentration testing, in particular to a method for detecting the content of nitric acid and hydrofluoric acid in a titanium alloy pickling solution. The method comprises the following steps: adding a polar solvent diluent to the titanium alloy pickling solution or its diluent, masking the undissociated hydrofluoric acid, and then titrating to obtain the molar content of nitric acid; adding a hydrofluoric acid dissociation agent to another portion of the titanium alloy pickling solution or its diluent to completely dissociate the hydrofluoric acid, release H + and generate strong acid, and then titrate to obtain the total molar content of acid; subtract the molar content of nitric acid from the total molar content of acid to obtain the molar content of hydrofluoric acid. The technical problems of long time consumption and large metal ion interference in the determination of the content of nitric acid and hydrofluoric acid in the titanium alloy pickling solution are solved, the rapid determination of the content of nitric acid and hydrofluoric acid in the titanium alloy pickling solution is realized, which is conducive to the maintenance of the titanium alloy pickling solution and the extension of the service life of the pickling solution, reduces pollution, and protects the environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of testing the concentration of components in a titanium alloy surface chemical pickling solution, and particularly relates to a method for detecting the content of nitric acid and hydrofluoric acid in a titanium alloy pickling solution. BACKGROUND

[0002] The commonly used pickling solution for titanium alloy surface chemical processing is a mixed acid solution of nitric acid and hydrofluoric acid. Rapid determination of the content of nitric acid and hydrofluoric acid in the mixed acid solution is of great significance for maintaining the titanium alloy pickling solution, prolonging the service life of the pickling solution, reducing pollution, and protecting the environment.

[0003] Currently, the determination of the components of the titanium alloy pickling solution mainly uses the lead nitrate precipitation method in QJ1574-1988 "Titanium Alloy Chemical Pickling Solution Analysis Method" to determine the content of hydrofluoric acid and the ferrous sulfate method to determine the content of nitric acid. In addition, there are also studies that first measure the total acid of the mixed acid solution, and then determine the content of fluoride ions by the standard curve potential method to determine the content of hydrofluoric acid by fluoride ions. The difference between the two is the content of nitric acid. The above methods have large errors in test results due to the lack of shielding of metal ion interference.

[0004] In the prior art, the patent technical solution with publication number CN117571917A uses silicon dioxide powder to react with the mixed acid to remove hydrofluoric acid, and then calculates the content of nitric acid and hydrofluoric acid in the mixed acid by determining the acid value of the solution before and after the reaction. However, the reaction of silicon dioxide powder with mixed acid takes 12-24 hours, which is time-consuming and has poor detection effect when the content of hydrofluoric acid in the mixed acid is high. It does not shield the interference of metal ions on the detection.

[0005] In the patent technical solution with publication number CN107796912A, non-protic polar organic solvents are used to dilute the mixed acid to form titration mixed acid, and continuous titration is performed. The titration end point of hydrofluoric acid and the titration end point of nitric acid are obtained through the potential change in the titration process, and then the concentration of hydrofluoric acid and the concentration of nitric acid in the test mixed acid are obtained. However, there are flaws in the mechanism description of the non-protic polar organic solvents because the mixed acid of nitric acid and hydrofluoric acid belongs to a strong acid-weak acid system. The dissociation constant Ka of hydrofluoric acid is 6.61×10 -4 , and the corresponding pKa is approximately 3.18. When the pH of the mixed acid is less than pKa, hydrofluoric acid mainly exists in the form of molecules. The bond energy of hydrofluoric acid molecules is about 500 kJ / mol, and the bond energy of the carbonyl group combined with the hydrogen of hydrofluoric acid is only about 40 kJ / mol. When the pH is less than 3.18, the non-protic polar organic solvents are associated or complexed with the hydrofluoric acid molecules through solvation, rather than dissociating the hydrofluoric acid molecules. Since the potential function relationship between the potential value of the titration mixed acid and the titration volume of the titrant is used, the process of testing the content of nitric acid and hydrofluoric acid is relatively complex, and the interference of metal ions on the test results is large.

[0006] In summary, how to quickly determine the composition of mixed acid, maintain titanium alloy pickling solution, prolong the service life of pickling solution, reduce pollution, protect the environment, and urgently need to seek a fast and effective method for analyzing the composition of titanium alloy chemical pickling solution. SUMMARY

[0007] The application provides a method for detecting the content of nitric acid and hydrofluoric acid in a titanium alloy pickling solution, solves the technical problems of long time consumption and large metal ion interference in the determination of the content of nitric acid and hydrofluoric acid in the titanium alloy pickling solution, realizes the rapid determination of the content of nitric acid and hydrofluoric acid in the titanium alloy pickling solution, is conducive to the maintenance of the titanium alloy pickling solution and the prolongation of the service life of the pickling solution, the reduction of pollution, and the protection of the environment.

[0008] A method for detecting the content of nitric acid and hydrofluoric acid in a titanium alloy pickling solution, comprising the following steps:

[0009] 1) Determination of the content of nitric acid: adding a polar solvent diluent to the titanium alloy pickling solution or its diluent, masking the undissociated hydrofluoric acid, and titrating to determine the molar content of nitric acid; wherein the volume ratio of the titanium alloy pickling solution to the polar solvent diluent is 1:10; the volume concentration of the polar solvent in the polar solvent diluent is 10%;

[0010] 2) Determination of the total acid content: adding a hydrofluoric acid dissociation agent to another portion of the titanium alloy pickling solution or its diluent to completely dissociate the hydrofluoric acid, release H + and generate strong acid, and titrate to determine the total acid molar content;

[0011] 3) Calculation of the content of hydrofluoric acid: subtracting the molar content of nitric acid determined in step 1) from the total acid molar content determined in step 2) to obtain the molar content of hydrofluoric acid.

[0012] In one specific embodiment of the application, in steps 1) and 2), the pH value of the titanium alloy pickling solution or its diluent is 0.5-2.

[0013] In one specific embodiment of the application, in step 1), the polar solvent is at least one selected from acetone, methyl ethyl ketone, acetylacetone, dimethyl sulfoxide, and N,N-dimethylformamide.

[0014] In one specific embodiment of the application, in step 1), the titration determination is titrated with sodium hydroxide standard solution using thymol blue as an indicator, and the titration end point is from red to yellow and pH=3.

[0015] In one specific embodiment of the application, in step 2), the hydrofluoric acid dissociation agent is selected from any one of aluminum chloride and boric acid.

[0016] In one specific embodiment of the present invention, in step 2), the titration determination is performed using thymol blue as an indicator and sodium hydroxide standard solution as a titration endpoint, where the color changes from red to yellow.

[0017] In one specific embodiment of the present invention, the titration endpoint is determined by titrating with a potentiometric titrator and measuring pH=3 as the titration endpoint.

[0018] In one specific embodiment of the present invention, the concentration of the sodium hydroxide standard solution is 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, or 0.5 mol / L.

[0019] The ions or ion groups coexisting in the titanium alloy pickling solution of this invention mainly include H. + , , HF, F - , , , , with F - The content of hydrofluoric acid in the mixed acid will be biased.

[0020] In the titanium alloy pickling solution of this invention, hydrofluoric acid is a weak acid with a dissociation constant Ka = 6.61 × 10⁻⁶. -4 The corresponding pKa is 3.18; therefore, theoretically, when pH < pKa, HF mainly exists in molecular form; when pH ≈ pKa, HF molecules and F... - The concentrations are approximately equal; when pH > pKa, F - Hydrofluoric acid is primarily present in its active form. Therefore, during acid-base titration of titanium alloy pickling solutions, as the pH of the solution increases, hydrofluoric acid molecules gradually and continuously decompose, without a fixed pH dissociation point. Furthermore, based on the principle of equilibrium shift and the fact that HF ​​molecules form more stable associated structures through hydrogen bonds, hydrofluoric acid generally exists in molecular form in strongly acidic titanium alloy pickling solutions when pH ≤ 3.1. Therefore, when determining the content of nitric acid and hydrofluoric acid in titanium alloy pickling solutions using acid-base titration, it is preferable to remove or inhibit the dissociation of hydrofluoric acid. Using thymol blue as an indicator and controlling the pH value at the titration endpoint to around 3 allows for the analysis and detection of nitric acid content in the titanium alloy pickling solution.

[0021] The present application is directed to the titanium alloy pickling solution after use, in the acid-base titration process, with the increase of the solution pH value, in addition to the neutralization reaction of hydrogen ion and sodium hydroxide, the metal ion fluoride complex will also react with sodium hydroxide. The test is as follows: take 1 mL of titanium alloy pickling solution after use, with methyl orange and phenolphthalein as double indicator, titrate with sodium hydroxide standard solution; when titrated to pH 5, the solution is turbid, and precipitate appears after standing. The above test shows that the metal ion fluoride complex in the titanium alloy pickling solution reacts with sodium hydroxide standard solution to generate precipitate, consumes the amount of sodium hydroxide, and causes the total acid determination value of mixed acid to be high, and the pH value at which the precipitate appears is related to the type and content of metal ions in the titanium alloy pickling solution after use.

[0022] In the detection method of the content of nitric acid and hydrofluoric acid in the titanium alloy pickling solution, the "solvation effect" of the polar solvent is used to mainly inhibit the dissociation of hydrofluoric acid molecules in the titanium alloy pickling solution, and at the same time, due to the association structure formed by the polar solvent and the hydrofluoric acid molecules, the inhibition of nitric acid dissociation by the hydrofluoric acid molecules is broken, so that the content of nitric acid can be determined at the titration end point pH value of 3, and the interference of metal ions in titration is avoided.

[0023] In the test method, aluminum chloride or boric acid is used for the determination of total acid to promote the dissociation of hydrofluoric acid in the titanium alloy pickling solution, convert the reaction of the weak acid hydrofluoric acid into a strong acid, and then titrate with sodium hydroxide standard solution as an indicator until the pH value is 3 to obtain the total acid content of the titanium alloy pickling solution; the content of hydrofluoric acid is obtained by subtracting the content of nitric acid from the total acid content.

[0024] Boric acid (H3BO4) mainly exists in molecular form at pH < 7, and during the acid-base titration of the titanium alloy pickling solution to the titration end point pH value of 3, the excess boric acid hardly dissociates and does not interfere with the titration of sodium hydroxide. Boric acid reacts with hydrofluoric acid to generate fluoroboric acid (HBF4), which is another strong acid and completely dissociates and releases H + During the acid-base titration process, the chemical reaction formula for generating fluoroboric acid is: 4HF + H3BO4 → HBF4 + 3H2O; in step 2) total acid content determination, if boric acid is used, the total acid content minus the content of nitric acid, and then multiplied by 4 is the content of hydrofluoric acid; the use of boric acid in the total acid content determination process is suitable for titanium alloy pickling solution systems with high hydrofluoric acid content.

[0025] Aluminum chloride is suitable for titanium alloy pickling solution systems with low hydrofluoric acid content, because the stability constant of fluorine aluminum complex is 1.44×10 -20There is a strong complexation trend in any environment, and there is a dynamic balance between the fluoroaluminum complex and the fluoride ion and the aluminum ion. When there are enough aluminum ions, the reaction will proceed to the fluoroaluminum complex direction according to the Le Chatelier principle, thereby consuming the fluoride ion and promoting the decomposition of hydrofluoric acid to release hydrogen ions. The hydrolysis and complexation reactions of aluminum chloride occur simultaneously, and the hydrolysis reaction is broken and re-complexed during the reaction, which takes a long time. The water and aluminum chloride are added in the afternoon of the test day, and the results detected the next day are more accurate. The longest time is 12h. Therefore, when determining the content of nitric acid, aluminum chloride is added first, and then water is added (the amount of water added is such that the pH value after adding water is not higher than 2), and the water is added while shaking.

[0026] The amount of aluminum chloride is determined according to the content of hydrofluoric acid in the pickling solution, which is 40-50%. In actual production, the concentration of hydrofluoric acid in titanium alloy pickling solution is about 10%, and the concentration of hydrofluoric acid in the strong corrosion liquid of titanium alloy in the Soviet Union is 20%. At this concentration, the reaction of titanium alloy is violent, with yellow smoke rolling and the solution temperature rising sharply, and the production is easy to lose control. In order to ensure the dissociation of hydrofluoric acid and the safety of testing, when the content of hydrofluoric acid is high, the dissociation agent is boric acid.

[0027] The beneficial effects of the present application are:

[0028] 1. The present application uses polar solvent association to inhibit the dissociation of hydrofluoric acid, solving the defect of interference of hydrofluoric acid dissociation on the determination of nitric acid content;

[0029] 2. The present application uses a hydrofluoric acid dissociation agent to solve the defect that weak acid hydrofluoric acid exists in molecular form at pH<3 and is difficult to titrate to obtain total acid;

[0030] 3. The titration end point pH value of the present application is 3, which on the one hand has little interference on the determination results of nitric acid content and total acid content in strong acid titanium alloy pickling solution, and on the other hand avoids the interference of metal ions on the titration results when the acid-base titration is to weak acid (pH>3).

[0031] 4. The test method of the present application realizes the determination of the content of hydrofluoric acid in strong acid titanium alloy pickling solution by inhibiting the dissociation of hydrofluoric acid to determine the content of nitric acid and promoting the dissociation of hydrofluoric acid to determine the content of total acid.

[0032] 5. The test method of the present application is simple and low in cost, short in time and high in efficiency for determining the content of nitric acid and hydrofluoric acid in titanium alloy pickling solution, and can effectively serve the production.

[0033] 6. The test method of the present application has significant economic value and social benefits in maintaining titanium alloy pickling solution, prolonging the service life of pickling solution, reducing pollution and protecting the environment. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present application.

[0035] A detection method of nitric acid and hydrofluoric acid content in titanium alloy pickling solution, comprising the following steps:

[0036] 1) Nitric acid content determination: add polar solvent diluent to the titanium alloy pickling solution or its diluent, mask the undissociated hydrofluoric acid, and then titrate to determine the molar content of nitric acid; wherein the volume ratio of titanium alloy pickling solution to polar solvent diluent is 1:10; the volume concentration of polar solvent in polar solvent diluent is 10%;

[0037] 2) Total acid content determination: add hydrofluoric acid dissociating agent to another portion of titanium alloy pickling solution or its diluent to completely dissociate the hydrofluoric acid, release H + and generate strong acid, and titrate to determine the total acid molar content;

[0038] 3) Hydrofluoric acid content calculation: subtract the molar content of nitric acid determined in step 1) from the total acid molar content determined in step 2) to obtain the molar content of hydrofluoric acid.

[0039] In some examples, in steps 1) and 2), the pH value of the titanium alloy pickling solution or its diluent is 0.5-2.

[0040] In some examples, in step 1), the polar solvent is at least one selected from acetone, methyl ethyl ketone, acetylacetone, dimethyl sulfoxide, and N,N-dimethylformamide.

[0041] In some examples, in step 1), the titration determination is titrated with sodium hydroxide standard solution using thymol blue as an indicator, and the titration end point is from red to yellow and pH=3.

[0042] In some examples, in step 2), the hydrofluoric acid dissociating agent is selected from any one of aluminum chloride and boric acid; wherein aluminum chloride and boric acid are both used in excess relative to the molar amount of hydrofluoric acid in the aluminum alloy pickling solution; wherein boric acid is used in excess and white insoluble substances appear in the solution; preferably, the amount of aluminum chloride and boric acid is 0.5-1.0g.

[0043] In some examples, in step 2), the titration determination is titrated with sodium hydroxide standard solution using thymol blue as an indicator, and the titration end point is from red to yellow.

[0044] In some examples, in order to avoid the color interference of thymol blue in the acid-base titration process, the titration end point is titrated and determined by a potential titrator with pH = 3 as the titration end point to assist in determining the titration end point of the acid-base titration.

[0045] In some examples, the concentration of the sodium hydroxide standard solution is 0.05 mol / L, 0.1 mol / L, 0.2 mol / L or 0.5 mol / L.

[0046] Since the interference of metal ions on the acid-base titration process is concentrated after the acid-base titration end point (pH = 3), metal ions will not interfere with the determination of the content of nitric acid and hydrofluoric acid in the original titanium alloy pickling solution and the titanium alloy pickling solution after use. The following examples use the configured, original titanium alloy pickling solution to analyze the accuracy and feasibility of the test method.

[0047] Example 1

[0048] The present embodiment provides a method for detecting the content of nitric acid and hydrofluoric acid in a titanium alloy pickling solution, comprising the following steps:

[0049] 1. Prepare a titanium alloy pickling solution standard solution and 10% polar solvent;

[0050] Titanium alloy pickling solution standard solution A: Take hydrofluoric acid, nitric acid and water to prepare a titanium alloy pickling standard solution A with a nitric acid concentration of 1.44 mol / L and a total acid concentration of 1.83 mol / L, 100 mL, for standby;

[0051] 10% (v / v) polar solvent: 1 volume part of acetone, methyl ethyl ketone, dimethyl sulfoxide and N, N-dimethylformamide, respectively, 9 volume parts of four distilled water, respectively, to prepare 10% (v / v) acetone diluent, methyl ethyl ketone diluent, dimethyl sulfoxide diluent and N, N-dimethylformamide diluent, standby.

[0052] 2. Nitric acid content determination: take 1 mL of titanium alloy pickling solution standard solution A, slowly add to 10 mL of acetone diluent, add 5 drops of thymol blue as indicator, shake well; titrate with sodium hydroxide standard solution with a concentration of c 氢氧化钠 = 0.1 mol / L, when the solution color changes from red to yellow and the yellow color is obvious (when the pH value of the titration process is measured online by a potential titrator, pH = 3), it is the titration end point; record the volume V1 (mL) of sodium hydroxide consumed in titration, calculate the nitric acid content c 硝酸 :

[0053] Formula 1: .

[0054] Total acid content determination: 1 mL of titanium alloy pickling solution standard solution A was taken, 0.523 g of aluminum chloride was added into it, and 10 mL of distilled water was added into it, and 5 drops of thymol blue were added as an indicator, and it was shaken well; the sodium hydroxide standard solution with a concentration c 氢氧化钠 of 0.1 mol / L was used for titration, and when the solution color changed from red to yellow and the yellow color was obvious (the pH value of the titration process was measured online by a potential titrator = 3), it was the titration end point; the volume V2 (mL) of sodium hydroxide consumed in titration was recorded, and the total acid content c 总酸 was calculated by the following formula 2.

[0055] Formula 2: .

[0056] 4, Hydrofluoric acid content calculation: the total acid content c 总酸 minus the nitric acid content c 硝酸 , that is, the hydrofluoric acid content c 氢氟酸 .

[0057] According to the test method of the present embodiment, the titanium alloy pickling standard solution A was titrated in parallel for 3 times, and the determination results of the nitric acid content and the total acid content are shown in Table 1.

[0058] Table 1 Determination results of nitric acid content and total acid content of Example 1

[0059]

[0060] Example 2

[0061] The present embodiment provides a method for detecting the contents of nitric acid and hydrofluoric acid in a titanium alloy pickling solution, comprising the following steps:

[0062] 1. Preparation of titanium alloy pickling solution standard solution B: hydrofluoric acid, nitric acid and water are prepared into 100 mL of titanium alloy pickling standard solution B with a nitric acid concentration of 2.16 mol / L and a total acid concentration of 3.13 mol / L, for standby;

[0063] 2. Nitric acid content determination: 10 mL of "N,N-dimethylformamide diluent" is used instead of "acetone diluent" in Example 1, and the nitric acid content in the titanium alloy pickling standard solution B is determined according to the nitric acid content determination method of Example 1;

[0064] 3. Total acid content determination: the total acid content of the titanium alloy pickling solution B is determined according to the same method of Example 1;

[0065] 4. Hydrofluoric acid content calculation: the total acid content minus the nitric acid content, that is, the hydrofluoric acid content.

[0066] The titanium alloy pickling standard solution B was titrated in parallel for 3 times in the present embodiment, and the determination results of the nitric acid content and the total acid content are shown in Table 2.

[0067] Table 2 Determination results of nitric acid content and total acid content of Example 2

[0068]

[0069] Example 3

[0070] The embodiment provides a detection method of nitric acid and hydrofluoric acid content in a titanium alloy pickling solution, comprising the following steps:

[0071] 1. Preparation of titanium alloy pickling solution standard solution C containing interfering ions: 100 mL of titanium alloy pickling standard solution B of Example 2, and then potassium fluoride, aluminum chloride hexahydrate, and iron chloride hexahydrate hydrofluoric acid are added to prepare titanium alloy pickling standard solution C containing 3.5 wt% of potassium fluoride, 4.8 wt% of aluminum chloride hexahydrate, and 5.4 wt% of iron chloride hexahydrate, which is ready for use;

[0072] 2. Determination of nitric acid content: the determination method of Example 1 is used to determine the nitric acid content of the titanium alloy pickling solution standard solution C;

[0073] 3. Determination of total acid content: the determination method of Example 1 is used to determine the total acid content of the titanium alloy pickling solution standard solution C;

[0074] 4. Calculation of hydrofluoric acid content: the total acid content is subtracted by the nitric acid content, and the hydrofluoric acid content is obtained.

[0075] In this embodiment, the titanium alloy pickling standard solution B is tested by parallel titration for three times, and the determination results of nitric acid content and total acid content are shown in Table 3.

[0076] Table 3 Determination results of nitric acid content and total acid content

[0077]

[0078] According to Tables 1-3, it can be seen that the dissociation of hydrofluoric acid is masked when the nitric acid content is determined, and the complete dissociation of hydrofluoric acid is promoted when the total acid content is determined, the acid-base titration end point is controlled at pH value = 3, the test results of nitric acid content and hydrofluoric acid content are accurate and reliable, the acid-base titration process is simple, low in cost, short in time, high in efficiency, and can effectively serve the production.

[0079] The above only describes the preferred embodiments of the present application, and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for detecting the content of nitric acid and hydrofluoric acid in a titanium alloy pickling solution, characterized in that, The method comprises the following steps: 1) nitric acid content determination: adding a polar solvent diluent to the titanium alloy pickling solution or its diluent, masking undissociated hydrofluoric acid, and titrating to determine the molar content of nitric acid; wherein the volume ratio of the titanium alloy pickling solution to the polar solvent diluent is 1:10; the volume concentration of the polar solvent in the polar solvent diluent is 10%; the polar solvent is at least one selected from acetone, methyl ethyl ketone, acetylacetone, dimethyl sulfoxide, and N,N-dimethylformamide; 2) Total acid content determination: To another portion of the titanium alloy pickling solution or its dilution, add hydrofluoric acid dissociation agent, so that the hydrofluoric acid is completely dissociated, H + is released, and strong acid is generated, and the total acid molar content is determined by titration; 3) hydrofluoric acid content calculation: subtracting the molar content of nitric acid measured in step 1) from the total acid molar content measured in step 2) to obtain the molar content of hydrofluoric acid.

2. The method for detecting the content of nitric acid and hydrofluoric acid in titanium alloy pickling solution according to claim 1, characterized in that: In steps 1) and 2), the pH value of the titanium alloy pickling solution or its diluent is 0.5-2.

3. The method for detecting the content of nitric acid and hydrofluoric acid in titanium alloy pickling solution according to claim 1, characterized in that: In step 1), the titration determination is performed with thymol blue as the indicator, using a sodium hydroxide standard solution for titration, and the titration end point is when the color changes from red to yellow and the pH is 3.

4. The method for detecting the content of nitric acid and hydrofluoric acid in titanium alloy pickling solution according to claim 1, characterized in that: In step 2), the hydrofluoric acid dissociation agent is selected from any one of aluminum chloride and boric acid.

5. The method for detecting the content of nitric acid and hydrofluoric acid in titanium alloy pickling solution according to claim 1, characterized in that: In step 2), the titration determination is performed with thymol blue as the indicator, using a sodium hydroxide standard solution for titration, and the titration end point is when the color changes from red to yellow.

6. The method for detecting the content of nitric acid and hydrofluoric acid in titanium alloy pickling solution according to claim 3 or 5, characterized in that: The titration end point is determined by using a potentiometric titrator to titrate and measure the pH=3 as the titration end point.

7. The method for detecting the content of nitric acid and hydrofluoric acid in titanium alloy pickling solution according to claim 3 or 5, characterized in that: The concentration of the sodium hydroxide standard solution is 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, or 0.5 mol / L.

Images