A method for determining the phosphorus content in steel

Abstract

The present invention provides a method for determining the phosphorus content in steel. The ethyl violet-phosphovanadomolybdic heteropolyacid-surfactant system is used to determine the phosphorus content in steel. After dissolving the steel to be tested, a masking agent, sulfuric acid, ammonium molybdate solution, and vanadium base solution are added for reaction to obtain a phosphovanadomolybdic heteropolyacid solution. Ethyl violet is complexed with the phosphovanadomolybdic heteropolyacid solution to obtain a phosphovanadomolybdenum violet complex system. A surfactant is peptized with the phosphovanadomolybdenum violet complex system to obtain a test solution. The absorbance of the test solution is measured by spectrophotometry, and the phosphorus content in the steel to be tested is obtained through calculation. In the method for determining the phosphorus content in steel of the present invention, the ethyl violet-phosphovanadomolybdic heteropolyacid-surfactant system has strong stability, a short stable time, and a fast measurement speed; moreover, the determination interference is small, there are few interfering ions, the detection limit is low, and the measurement accuracy is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of detection methods for phosphorus content, and particularly relates to a method for determining phosphorus content in steel and iron. Background Art

[0002] Phosphorus is a harmful and highly segregating element in steel and iron. Excessive phosphorus content can easily increase the cold brittleness of steel and the sensitivity of steel to crack formation. Therefore, the determination of phosphorus content in steel and iron is of great significance for controlling product quality.

[0003] Currently, the methods for determining phosphorus in steel and iron include the phosphovanadomolybdic yellow spectrophotometry and the phosphomolybdenum blue spectrophotometry.

[0004] In the phosphovanadomolybdic yellow color development system, phosphoric acid reacts with ammonium vanadate and ammonium molybdate to form a phosphovanadomolybdic yellow heteropolyacid complex (P205V205·22MoO3·nH2O). The suitable complexation acidity is 0.5 - 1 mol / L. In a nitric acid medium, this complex is more stable than phosphomolybdic yellow, with a maximum absorption wavelength of 315 nm, ε 315 = 2.0×10 4 , and it is stable for more than 24 hours. In actual measurement, using a 72-type spectrophotometer can only measure in the visible light region at 420 - 470 nm, resulting in a decrease in sensitivity. In addition, colored ions such as Fe 3+ , Cu 2+ , Cr 3+ etc. will interfere with the determination, F will destroy the complex, and will also reduce pentavalent vanadium to fade the complex. Si and As can also form ternary heteropolyacids with molybdenum and vanadium, and only when As ≤ 25 mg does it not interfere with the measurement result.

[0005] In the phosphomolybdenum blue color development system, phosphoric acid reacts with ammonium molybdate to form a phosphomolybdic acid complex, which is masked with fluoride - stannous chloride or sodium sulfite - hydrazine sulfate to reduce interfering elements and reduce the complex to phosphomolybdic heteropoly blue, and the absorbance is measured at 680 - 700 nm; the suitable acidity for the formation of phosphomolybdic heteropolyacid is 0.3 - 1.4 mol / L, the maximum absorption of phosphomolybdic heteropolyacid < 400 nm, already at the 10 order of magnitude, the maximum absorption of heteropoly blue > 750 nm, already at the 10 order of magnitude. To enhance the ability of the central ion phosphorus to form heteropolyacid with molybdate ions, the dosage of ammonium molybdate must be more than 3.5 times the theoretical value. The commonly used reducing agents in the phosphomolybdenum blue spectrophotometry are stannous chloride - sodium fluoride, hydrazine sulfate, and ascorbic acid.

[0006] CN102539426A discloses a method for determining phosphorus in ferrosilicon manganese alloy. After dissolving the sample with nitric acid and hydrofluoric acid, perchloric acid is added to convert the phosphorus in the sample into orthophosphoric acid, obtaining a first mixed solution; sodium sulfite is added to the first mixed solution to reduce the manganese in the ferrosilicon manganese alloy, obtaining a second mixed solution; bismuth nitrate solution, ammonium molybdate solution, sodium potassium tartrate solution, sodium fluoride solution and stannous chloride are added to the second mixed solution, wherein ammonium molybdate converts the orthophosphoric acid in the first mixed solution into phosphomolybdic heteropolyacid, and stannous dichloride is used to reduce the formed phosphomolybdic heteropolyacid to blue phosphomolybdenum blue, and then the content of phosphorus is determined by spectrophotometry; this method uses stannous chloride as a reducing agent, and has the characteristics of fast reduction speed and good reduction effect.

[0007] CN110873695A discloses a method for determining the phosphorus content in ferroniobium, including the following steps: 1) Mix nitric acid, hydrofluoric acid and the sample to obtain a decomposition solution; 2) Mix the decomposition solution with perchloric acid solution, sulfuric acid, water and sodium tartrate solution to obtain a mixed solution; 3) Mix the mixed solution with ascorbic acid solution, bismuth salt solution, gum arabic solution, sodium thiosulfate solution and ammonium molybdate solution and place it in a water bath to obtain a test solution; 4) Measure the absorbance of the test solution, and obtain the mass content of phosphorus in the sample according to the absorbance value. This method decomposes the sample with nitric acid-hydrofluoric acid, removes nitric acid and hydrofluoric acid with a mixed acid of sulfuric acid and perchloric acid, adds sodium tartrate solution to complex niobium, uses sodium thiosulfate solution to mask arsenic, and directly determines the phosphorus content in ferroniobium.

[0008] However, when using stannous chloride-sodium fluoride for detection, the detection process is unstable and difficult to master, and it is only suitable for rapid in-furnace analysis. The disadvantage of using hydrazine sulfate for detection is that the color development speed is slow, it needs to be heated in a boiling water bath, and it cannot develop color in a nitric acid solution, so it is less used in China. Using ascorbic acid for detection will be interfered by other ions, and sodium thiosulfate needs to be added for masking. These methods are relatively cumbersome to operate, have a long cycle, and the organic reagents used are toxic to the human body.

[0009] Therefore, there is still a need to establish a method for determining the phosphorus content in steel that is fast, sensitive and easy to operate. Summary of the Invention

[0010] The purpose of the present invention is to provide a method for determining the phosphorus content in steel, which uses an ethyl violet-phosphomolybdovanadic heteropolyacid-surfactant system to determine the phosphorus content in steel; in the method for determining the phosphorus content in steel of the present invention, the ethyl violet-phosphovanadomolybdic heteropolyacid-surfactant system has strong stability, short stable time and fast measurement speed; and the determination interference is small, there are few interfering ions, the detection limit is low, and the measurement accuracy is high.

[0011] To achieve the purpose of this invention, the following technical solutions are adopted by the present invention:

[0012] The object of the present invention is to provide a method for determining the phosphorus content in steel, and the phosphorus vanadium molybdenum purple spectrophotometry is used to determine the phosphorus content in steel; the phosphorus vanadium molybdenum purple spectrophotometry uses an ethyl violet - phosphorus molybdenum vanadium heteropolyacid - surfactant system to determine the phosphorus content in steel.

[0013] In the method for determining the phosphorus content in steel according to the present invention, the ethyl violet - phosphorus molybdenum vanadium heteropolyacid - surfactant system has strong stability, short stable time, and fast measurement speed; and the determination interference is small, the interfering ions are few, the detection limit is low, and the measurement accuracy is high.

[0014] As a preferred technical solution of the present invention, the determination method includes the following steps:

[0015] (1) After dissolving the steel to be measured, the initial solution containing phosphate is obtained through the first volume fixation.

[0016] (2) A masking agent, sulfuric acid, ammonium molybdate solution, and vanadium bottom solution are added to the initial solution in step (1) for reaction to obtain a phosphorus molybdenum vanadium heteropolyacid solution.

[0017] (3) Ethyl violet is complexed with the phosphorus molybdenum vanadium heteropolyacid solution in step (2) to obtain a phosphorus vanadium molybdenum purple complex system.

[0018] (4) A surfactant is peptized with the phosphorus vanadium molybdenum purple complex system in step (3), and the test solution is obtained through the second volume fixation.

[0019] (5) The absorbance of the test solution in step (4) is measured by spectrophotometry, and the phosphorus content in the steel to be measured is obtained through calculation of the absorbance.

[0020] As a preferred technical solution of the present invention, the dissolution in step (1) is carried out under the condition of heating to boiling.

[0021] Preferably, the dissolution in step (1) includes acid dissolution and oxidation carried out in sequence.

[0022] Preferably, the dissolution reagent used for acid dissolution is nitric acid with a concentration of more than 8 mol / L, such as 8 mol / L, 8.5 mol / L, 9 mol / L, etc., but is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0023] Preferably, the oxidation reagent used for oxidation includes potassium permanganate solution.

[0024] Preferably, the method for oxidation is: the potassium permanganate solution is slowly added dropwise to the solution after acid dissolution, and when brown precipitate starts to form in the solution, the addition of the potassium permanganate solution is stopped.

[0025] It should be noted that in the present invention, when nitric acid is added in excess and the steel to be tested is dissolved by nitric acid, most of the phosphorus is in the state of orthophosphoric acid, and the remaining small part forms phosphorous acid. The chemical reaction equations are as follows:

[0026] 3Fe3P + 41HNO3 = 3H3PO4 + 9Fe(NO3)3 + 16H2O + 14NO↑

[0027] Fe3P + 13HNO3 = H3PO3 + 3Fe(NO3)3 + 5H2O + 4NO↑

[0028] Adding potassium permanganate can oxidize phosphorous acid into orthophosphoric acid. The chemical reaction equation is as follows:

[0029] 5H3PO3 + 2KMnO4 + 6HNO3 = 5H3PO4 + 2KNO3 + 2Mn(NO3)2 + 3H2O

[0030] In the present invention, hydrochloric acid or sulfuric acid is not selected to dissolve the steel because phosphorus can react with hydrochloric acid or sulfuric acid to generate phosphine gas and escape, which will lead to a low measured phosphorus content. The chemical reaction equations for the reaction of phosphorus with hydrochloric acid or sulfuric acid are as follows:

[0031] 2Fe3P + 12HCl = 6FeCl2 + 2H3P↑ + 3H2↑

[0032] 2Fe3P + 6H2SO4 = 6FeSO4 + 2H3P↑ + 3H2↑

[0033] Preferably, the method for judging the end point of the dissolution in step (1) is: no more gas is generated in the solution.

[0034] It should be noted that in step (1), an excessive amount of nitric acid is added, and the H in nitric acid + will affect the reaction for generating heteropolyacid in step (2). Therefore, the excess nitric acid must be removed; since nitric acid will be decomposed into nitrogen dioxide, oxygen and water during heating, when no more gas is generated in the solution, it proves that all the excess nitric acid has been decomposed.

[0035] As a preferred technical solution of the present invention, in step (2), based on 4 mL of the initial solution, the masking agent is 5 - 6% sodium fluoride.

[0036] Preferably, the dosage of the masking agent in step (2) is 1 - 3 mL. For example, it can be 1 mL, 1.5 mL, 2 mL, 2.5 mL, 3 mL, etc., but it is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0037] As a preferred technical solution of the present invention, the concentration of sulfuric acid in step (2) is 2.5 - 3.5 mol / L, for example, it can be 2.5 mol / L, 2.6 mol / L, 2.7 mol / L, 2.8 mol / L, 2.9 mol / L, 3.1 mol / L, 3.2 mol / L, 3.3 mol / L, 3.4 mol / L, 3.5 mol / L, etc., and further preferably 3.0 mol / L. However, it is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0038] Preferably, in step (2), based on 4 mL of the initial solution, the amount of sulfuric acid used is 5.2 - 9.6 mL, for example, it can be 5.2 mL, 5.3 mL, 5.5 mL, 5.7 mL, 8.1 mL, 8.3 mL, 8.5 mL, 8.7 mL, 9 mL, 9.2 mL, 9.6 mL, etc., and further preferably 6 - 8 mL, for example, it can be 6 mL, 6.2 mL, 6.5 mL, 6.8 mL, 7 mL, 7.3 mL, 7.5 mL, 7.7 mL, 8 mL, etc. However, it is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0039] As a preferred technical solution of the present invention, the concentration of ammonium molybdate solution in step (2) is 0.15 - 0.25 mol / L, for example, it can be 0.15 mol / L, 0.17 mol / L, 0.19 mol / L, 0.21 mol / L, 0.23 mol / L, 0.25 mol / L, etc., and further preferably 0.20 mol / L. However, it is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0040] Preferably, in step (2), based on 4 mL of the initial solution, the amount of ammonium molybdate solution used is 3.2 - 8 mL, for example, it can be 3.2 mL, 3.5 mL, 3.8 mL, 6.2 mL, 6.5 mL, 6.7 mL, 7 mL, 7.3 mL, 7.8 mL, 8 mL, etc., and further preferably 4 - 6 mL, for example, it can be 4 mL, 4.3 mL, 4.5 mL, 4.8 mL, 5 mL, 5.2 mL, 5.6 mL, 6 mL, etc. However, it is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0041] As a preferred technical solution of the present invention, the preparation method of the vanadium bottom solution in step (2) includes: mixing 1 mg of vanadium pentoxide with 20 mL of sulfuric acid solution with a concentration of 3 mol / L and then heating. After the vanadium pentoxide is completely dissolved, it is diluted to obtain the vanadium bottom solution.

[0042] Preferably, calculated as vanadium pentoxide, the mass concentration of the vanadium bottom solution in step (2) is 2.0 - 2.5 g / L. For example, it can be 2 g / L, 2.1 g / L, 2.2 g / L, 2.3 g / L, 2.4 g / L, 2.5 g / L, etc. Further preferably, it is 2.0 g / L, but it is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0043] Preferably, in step (2), based on 4 mL of the initial solution, the dosage of the vanadium bottom solution is 1.2 - 3 mL. For example, it can be 1.2 mL, 1.3 mL, 1.5 mL, 1.8 mL, 2.0 mL, 2.2 mL, 2.5 mL, 2.7 mL, 3 mL, etc. Further preferably, it is 1.5 - 3 mL, but it is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0044] As a preferred technical solution of the present invention, the ethyl violet in step (3) is prepared into an ethyl violet solution with a concentration of (1.0 - 1.5) × 10 - 3 mol / L. For example, it can be 1.0 × 10 -3 mol / L, 1.1 × 10 -3 mol / L, 1.2 × 10 -3 mol / L, 1.3 × 10 -3 mol / L, 1.4 × 10 -3 mol / L, 1.5 × 10 -3 mol / L. Further preferably, it is 1.0 × 10 -3 mol / L, but it is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0045] Preferably, based on 4 mL of the initial solution, the dosage of the ethyl violet solution is 2 - 4 mL. For example, it can be 2 mL, 2.3 mL, 2.5 mL, 2.8 mL, 3 mL, 3.2 mL, 3.4 mL, 3.7 mL, 4 mL, etc. Further preferably, it is 3 - 4 mL, but it is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0046] As a preferred technical solution of the present invention, the surfactant in step (4) includes any one or a combination of at least two of gelatin, PVA, gum arabic, or microemulsion. Typical but non-limiting examples of the combination include the combination of gelatin and gum arabic, the combination of microemulsion and gelatin, and the combination of PVA and microemulsion.

[0047] Preferably, the surfactant in step (4) is microemulsion and gum arabic.

[0048] Preferably, the solutes of the microemulsion include polyethylene glycol octyl phenyl ether, n-pentanol, and n-heptane.

[0049] Preferably, in the microemulsion, the volume ratio of polyethylene glycol octyl phenyl ether, n-pentanol, and n-heptane is (6.4 - 7.5):(4.6 - 5.4):1. For example, it can be 6.4:4.6:1, 6.4:5:1, 6.4:5.2:1, 6.4:5.4:1, 6.8:4.7:1, 6.8:5:1, 6.8:5.4:1, 7:4.6:1, 7:4.8:1, 7:5.2:1, 7.2:4.6:1, 7.2:5.4:1, 7.5:4.6:1, 7.5:4.9:1, 7.5:5.1:1, 7.5:5.4:1, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0050] Preferably, the solvent of the microemulsion includes water.

[0051] Preferably, in the microemulsion, the volume percentage of the solute is 6 - 8%. For example, it can be 6%, 6.2%, 6.5%, 6.8%, 7%, 7.3%, 7.5%, 7.7%, 8%, etc., and the rest is the solvent.

[0052] Preferably, based on 4 mL of the initial solution, the dosage of the microemulsion is 0.6 - 0.8 mL. For example, it can be 0.6 mL, 0.63 mL, 0.65 mL, 0.68 mL, 0.7 mL, 0.72 mL, 0.75 mL, 0.77 mL, 0.8 mL, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0053] Preferably, the gum arabic is formulated into a gum arabic solution with a concentration of 5 - 6 g / L. For example, it can be 5 g / L, 5.2 g / L, 5.4 g / L, 5.6 g / L, 5.8 g / L, 6 g / L, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0054] Preferably, based on 4 mL of the initial solution, the dosage of the gum arabic solution is 0.65 - 0.75 mL. For example, it can be 0.65 mL, 0.66 mL, 0.67 mL, 0.68 mL, 0.69 mL, 0.70 mL, 0.71 mL, 0.72 mL, 0.73 mL, 0.74 mL, 0.75 mL, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0055] Preferably, after the second constant volume in step (4), the content of phosphate ions in the test solution is 0.4 - 20 μg / 50 mL. For example, it can be 0.4 μg / 50 mL, 0.7 μg / 50 mL, 1 μg / 50 mL, 2 μg / 50 mL, 4 μg / 50 mL, 6 μg / 50 mL, 10 μg / 50 mL, 12 μg / 50 mL, 15 μg / 50 mL, 18 μg / 50 mL, 20 μg / 50 mL, etc. However, it is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0056] As a preferred technical solution of the present invention, before the measurement in step (5), the test solution in step (4) is allowed to stand for 13 - 21 min. For example, it can be 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, etc. However, it is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0057] Preferably, the instrument used in the spectrophotometry in step (5) is a spectrophotometer.

[0058] Preferably, the test wavelength of the absorbance in step (5) is 610 - 615 nm. For example, it can be 610 nm, 611 nm, 612 nm, 613 nm, 614 nm, 615 nm, and further preferably 612 nm.

[0059] As a preferred technical solution of the present invention, the steps of the calculation in step (5) include: substituting the absorbance into the calibration curve regression equation to obtain the phosphorus content of the test solution, and substituting the phosphorus content of the test solution into the conversion formula to obtain the phosphorus content in the steel to be tested.

[0060] Preferably, the calibration curve regression equation is A = 0.0516X - 0.0021, where A is the absorbance; X is the phosphorus content in the test solution, with the unit of μg / 50 mL.

[0061] Preferably, the conversion formula is X0 = (X × V2 × V1) / (50 × V x × M), where X0 is the phosphorus content in the steel to be tested, with the unit of ppm; X is the phosphorus content in the test solution, with the unit of μg / 50 mL; V1 is the volume of the initial solution, with the unit of mL; V2 is the volume of the test solution, with the unit of mL; V x is the volume of the initial solution taken when preparing the test solution, with the unit of mL; M is the mass of the steel to be tested, with the unit of g.

[0062] It should be noted that the content of phosphate ions in the test solution described in step (4) of the present invention is 0.4 - 20 μg / 50 mL. That is to say, the detection limit of the method of the present invention is 0.4 - 20 μg / 50 mL. If the test result obtained in step (5) exceeds the range of the detection limit, the initial solution should be diluted and measured again.

[0063] As a preferred technical solution of the present invention, the phosphorus content in steel is determined by the phosphovanadomolybdic acid purple spectrophotometry method; the phosphovanadomolybdic acid purple spectrophotometry method uses an ethyl violet - phosphomolybdovanadic heteropolyacid - surfactant system to determine the phosphorus content in steel; the determination method includes the following steps:

[0064] (1) The steel to be tested is acid - dissolved with nitric acid above 8 mol / L under the condition of heating to boiling, and then potassium permanganate solution is slowly added dropwise to the solution. When brown precipitate begins to form in the solution, the addition of potassium permanganate solution is stopped; when no more gas is generated in the solution, heating is stopped; after the first constant volume, an initial solution containing phosphate ions is obtained;

[0065] (2) Sodium fluoride, sulfuric acid, ammonium molybdate solution, and vanadium bottom solution are added to the initial solution described in step (1) for reaction to obtain a phosphomolybdovanadic heteropolyacid solution;

[0066] Among them, based on 4 mL of the initial solution, the dosage of 5 - 6% sodium fluoride is 1 - 3 mL, the dosage of 2.5 - 3.5 mol / L sulfuric acid is 5.2 - 9.6 mL, the dosage of 0.15 - 0.25 mol / L ammonium molybdate solution is 3.2 - 8 mL, and the dosage of vanadium bottom solution is 1.2 - 3 mL; the preparation method of the vanadium bottom solution is: 1 mg of vanadium pentoxide is mixed with 20 mL of sulfuric acid solution with a concentration of 3 mol / L and then heated. After the vanadium pentoxide is completely dissolved, it is diluted to obtain the vanadium bottom solution; calculated based on vanadium pentoxide, the mass concentration of the vanadium bottom solution is 2.0 - 2.5 g / L;

[0067] (3) An ethyl violet solution with a concentration of (1.0 - 1.5)×10 -3 mol / L is complexed with the phosphomolybdovanadic heteropolyacid solution described in step (2) to obtain a phosphovanadomolybdic acid purple complex system;

[0068] Among them, based on 4 mL of the initial solution, the dosage of the ethyl violet solution is 2 - 4 mL;

[0069] (4) A microemulsion and a gum arabic solution with a concentration of 5 - 6 g / L are used to peptize the phosphovanadomolybdic acid purple complex system described in step (3), and after the second constant volume, a test solution is obtained;

[0070] Among them, the solutes of the microemulsion include polyethylene glycol octyl phenyl ether, n-pentanol, and n-heptane with a volume ratio of (6.4 - 7.5):(4.6 - 5.4):1; in the microemulsion, the volume proportion of the solutes is 6 - 8%, and the rest is the solvent; based on 4 mL of the initial solution, the dosage of the microemulsion is 0.6 - 0.8 mL, and the dosage of the gum arabic solution is 0.65 - 0.75 mL;

[0071] (5) Use a spectrophotometer to measure the absorbance of the test solution described in step (4) at 610 - 615 nm, substitute the absorbance into the calibration curve regression equation to obtain the phosphorus content of the test solution; substitute the phosphorus content of the test solution into the conversion formula to obtain the phosphorus content in the steel to be tested;

[0072] Among them, the calibration curve regression equation is A = 0.0516X - 0.0021, where A is the absorbance; X is the phosphorus content in the test solution, with the unit of μg / 50 mL; the conversion formula is X0 = (X × V2 × V1) / (50 × V x × M), where X0 is the phosphorus content in the steel to be tested, with the unit of ppm; X is the phosphorus content in the test solution, with the unit of μg / 50 mL; V1 is the volume of the initial solution, with the unit of mL; V2 is the volume of the test solution, with the unit of mL; M is the mass of the steel to be tested, with the unit of g.

[0073] The numerical ranges described in the present invention not only include the point values exemplified above, but also any point values between the above numerical ranges not exemplified. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the ranges.

[0074] Compared with the prior art, the present invention has the following beneficial effects:

[0075] (1) In the method for determining the phosphorus content in steel described in the present invention, the ethyl violet - phosphovanadomolybdophosphoric acid - surfactant system has strong stability, short stable time, and fast measurement speed;

[0076] (2) The method for determining the phosphorus content in steel described in the present invention has less measurement interference, fewer interfering ions, low detection limit, and high measurement accuracy. Description of the Drawings

[0077] Figure 1 It is the calibration curve graph of the calibration curve regression equation described in the present invention;

[0078] Figure 2 It is the absorbance curve of the phosphovanadomolybdenum purple complex at 20°C with different color development times in the present invention. Detailed Embodiments

[0079] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0080] In the specific embodiment of the present invention, the method for determining the calibration curve regression equation is as follows:

[0081] (1) Prepare a phosphorus standard solution: After drying potassium dihydrogen phosphate at 105 °C for 1 h, weigh 4.3936 g of potassium dihydrogen phosphate, dissolve it, and make up the volume to 1000 mL in a volumetric flask to obtain a phosphorus stock solution of 1.0 mg / mL; and gradually dilute the phosphorus stock solution to a phosphorus standard solution of 4.0 μg / mL.

[0082] (2) Take k mL of the phosphorus standard solution, where k = 1; add 7 mL of sulfuric acid with a concentration of 3 mol / L, 5 mL of ammonium molybdate solution with a concentration of 0.20 mol / L, and 2.5 mL of vanadium bottom solution to the phosphorus standard solution for reaction to obtain a phosphovanadomolybdic heteropolyacid solution.

[0083] Among them, the preparation method of the vanadium bottom solution is: Mix 1 mg of vanadium pentoxide with 20 mL of sulfuric acid solution with a concentration of 3 mol / L and heat it. After the vanadium pentoxide is completely dissolved, dilute it to obtain the vanadium bottom solution; calculated based on vanadium pentoxide, the mass concentration of the vanadium bottom solution is 2.0 g / L.

[0084] (3) Complex 3.5 mL of ethyl violet solution with a concentration of 1.0×10 -3 mol / L with the phosphovanadomolybdic heteropolyacid solution to obtain a phosphovanadomolybdenum purple complex system.

[0085] (4) Add 0.7 mL of microemulsion and 0.7 mL of gum arabic solution with a concentration of 5 g / L to the phosphovanadomolybdenum purple complex system for peptization, and make up the volume to 50 mL in a volumetric flask to obtain a phosphorus standard test solution.

[0086] Among them, the solute of the microemulsion includes polyethylene glycol octyl phenyl ether, n-pentanol, and n-heptane with a volume ratio of 6.4:4.6:1; in the microemulsion, the volume ratio of the solute is 6%, and the rest is the solvent.

[0087] (5) Measure the absorbance of the phosphorus standard test solution at 612 nm using a spectrophotometer.

[0088] (6) Adjust the value of k, repeat steps (2)-(5), measure the absorbances when k = 2, 3, 4, 5, 6, 7, and fit them into a calibration curve graph as Figure 1 shown, and then obtain the calibration curve regression equation.

[0089] The regression equation of the calibration curve measured by the above method is A = 0.0516X - 0.0021, where A is the absorbance; X is the phosphorus content in the test solution, with the unit of μg / 50 mL; its correlation coefficient is 0.9980, and the apparent molar absorption coefficient ε 612 is 1.5×10 5 L·mol -1 ·cm -1 . The phosphorus content shows a good linear relationship with the ΔA value (ΔA = A - A0) in the range of 1.0 - 20.0 μg / 50 mL, conforming to Beer's law. Its detection limit is 0.4 μg / 50 mL, and the precision is high.

[0090] In addition, in order to verify the stability of the ethyl violet - phosphomolybdovanadic heteropolyacid - surfactant system described in the present invention, the absorbance of the phosphovanadomolybdenum purple complex in the phosphorus standard test solution obtained in step (4) at different color development times at 20°C was measured. The results are as Figure 2 shown. The results show that the absorbance value of the phosphovanadomolybdenum purple complex starts to stabilize and is also the largest after 13 minutes of color development, and its stable time is 7 minutes. In all embodiments of the present invention, the absorbance is measured 15 minutes after color development.

[0091] Example 1

[0092] This example provides a method for determining the phosphorus content in steel. The steel type is carbon colorimetric standard steel 75 - 105. The determination method includes the following steps:

[0093] (1) Acid - dissolve 996.7 mg of the steel to be tested with 50 mL of 8 mol / L nitric acid under the condition of heating to boiling, and then slowly dropwise add potassium permanganate solution to the solution. When brown precipitate begins to form in the solution, stop adding potassium permanganate solution; stop heating when no more gas is generated in the solution; perform the first volume - fixing in a 100 - mL volumetric flask to obtain an initial solution containing phosphate.

[0094] (2) Take 4 mL of the initial solution, add sodium fluoride, sulfuric acid, ammonium molybdate solution, and vanadium bottom solution to the initial solution for reaction to obtain a phosphomolybdovanadic heteropolyacid solution;

[0095] Among them, the dosage of 5% sodium fluoride is 1 mL, the dosage of 3 mol / L sulfuric acid is 7 mL, the dosage of 0.20 mol / L ammonium molybdate solution is 5 mL, and the dosage of vanadium bottom solution is 2.5 mL; the preparation method of the vanadium bottom solution is: mix 1 mg of vanadium pentoxide with 20 mL of sulfuric acid solution with a concentration of 3 mol / L and heat. After all the vanadium pentoxide is dissolved, it is diluted to obtain the vanadium bottom solution; calculated based on vanadium pentoxide, the mass concentration of the vanadium bottom solution is 2.0 g / L;

[0096] (3) Add the solution with a concentration of 1.0×10-3 The ethyl violet solution with a concentration of [[mol / L]] is complexed with the phosphovanadomolybdic heteropolyacid solution described in step (2) to obtain a phosphovanadomolybdenum violet complex system;

[0097] Among them, the dosage of the ethyl violet solution is 3.5 mL;

[0098] (4) The microemulsion and the gum arabic solution with a concentration of 5 g / L are peptized with the phosphovanadomolybdenum violet complex system described in step (3), and second volume fixation is carried out in a 50 mL volumetric flask to obtain a test solution;

[0099] Among them, the solutes of the microemulsion include polyethylene glycol octyl phenyl ether, n-pentanol and n-heptane with a volume ratio of 6.4:4.6:1; in the microemulsion, the volume ratio of the solutes is 6%, and the rest is the solvent; the dosage of the microemulsion is 0.7 mL, and the dosage of the gum arabic solution is 0.7 mL;

[0100] (5) The absorbance of the test solution described in step (4) is measured at 612 nm using a spectrophotometer, and the phosphorus content in the steel to be measured is obtained through calculation of the absorbance.

[0101] Example 2

[0102] This example provides a method for determining the phosphorus content in steel. The steel model is 8098 low alloy steel, and the determination method includes the following steps:

[0103] (1) 624.8 mg of the steel to be measured is acid-dissolved with 30 mL of 8 mol / L nitric acid under the condition of heating to boiling, and then a potassium permanganate solution is slowly added dropwise to the solution. When brown precipitate begins to form in the solution, the addition of the potassium permanganate solution is stopped; when no more gas is generated in the solution, the heating is stopped; first volume fixation is carried out in a 100 mL volumetric flask to obtain an initial solution containing phosphate ions;

[0104] (2) Take 4 mL of the initial solution, add sodium fluoride, sulfuric acid, ammonium molybdate solution, and vanadium bottom solution to the initial solution for reaction to obtain a phosphovanadomolybdic heteropolyacid solution;

[0105] Among them, the dosage of 5% sodium fluoride is 1 mL, the dosage of 3 mol / L sulfuric acid is 7 mL, the dosage of 0.20 mol / L ammonium molybdate solution is 5 mL, and the dosage of the vanadium bottom solution is 2.5 mL; the preparation method of the vanadium bottom solution is: 1 mg of vanadium pentoxide is mixed with 20 mL of sulfuric acid solution with a concentration of 3 mol / L and then heated. After the vanadium pentoxide is completely dissolved, it is diluted to obtain the vanadium bottom solution; calculated based on vanadium pentoxide, the mass concentration of the vanadium bottom solution is 2.0 g / L;

[0106] (3) The concentration is 1.0×10 -3The ethyl violet solution at mol / L is complexed with the phosphovanadomolybdic heteropolyacid solution described in step (2) to obtain a phosphovanadomolybdenum violet complex system;

[0107] Among them, the dosage of the ethyl violet solution is 3.5 mL;

[0108] (4) The microemulsion and the gum arabic solution at 5 g / L are peptized with the phosphovanadomolybdenum violet complex system described in step (3), and a second volume fixation is carried out in a 50 mL volumetric flask to obtain a test solution;

[0109] Among them, the solutes of the microemulsion include polyethylene glycol octylphenyl ether, n-pentanol and n-heptane with a volume ratio of 6.4:4.6:1; in the microemulsion, the volume fraction of the solutes is 6%, and the rest is the solvent; the dosage of the microemulsion is 0.7 mL, and the dosage of the gum arabic solution is 0.7 mL;

[0110] (5) The absorbance of the test solution described in step (4) is measured at 612 nm using a spectrophotometer, and the phosphorus content in the steel to be measured is obtained through calculation of the absorbance.

[0111] (I) In the above-mentioned embodiment, the calculation steps in step (5) include: substituting the absorbance into the calibration curve regression equation to obtain the phosphorus content X of the test solution i (i = 1, 2, 3 or 4); substituting the phosphorus content of the test solution into the conversion formula to obtain the phosphorus content X in the steel to be measured 0-i (i = 1, 2, 3 or 4); measuring 4 times in total, and the absorbance is A i (i = 1, 2, 3 or 4), and its average value is A AVE , the phosphorus content of the test solution is denoted as X i (i = 1, 2, 3 or 4) and its average value is X AVE , the phosphorus content in the steel to be measured is X 0-i (i = 1, 2, 3 or 4), and its average value is X 0-AVE ;

[0112] The calibration curve regression equation is:

[0113] A = 0.0516X - 0.0021

[0114] In the formula, A is the absorbance; X is the phosphorus content in the test solution, and the unit is μg / 50 mL;

[0115] The conversion formula is:

[0116] X0 = (X × V2 × V1) / (50 × V x × M)

[0117] Wherein, X0 is the phosphorus content in the steel to be measured, with the unit of ppm; X is the phosphorus content in the test solution, with the unit of μg / 50mL; V1 is the volume of the initial solution, with the unit of mL; V2 is the volume of the test solution, with the unit of mL; V x is the volume of the initial solution taken when preparing the test solution, with the unit of mL; M is the mass of the steel to be measured, with the unit of g;

[0118] The measurement results of the phosphorus content in the above-mentioned examples are listed in Table 1.

[0119] (2) Conduct a standard addition recovery experiment on the above-mentioned examples, and the steps are as follows:

[0120] Based on the test result X AVE in the above-mentioned (1), conduct a standard addition recovery experiment;

[0121] Take 4 mL of the initial solution obtained in step (1), add 1 mL of a phosphorus standard solution with a concentration of 4.0 μg / mL, repeat steps (2) to (4) to obtain a spiked test solution, and measure the absorbance of the spiked test solution at 612 nm using a spectrophotometer. Test three times, denoted as A i '(i = 1, 2, or 3), substitute it into the calibration curve regression equation to obtain the phosphorus content X i ' (i = 1, 2, or 3) of the spiked test solution, and its average value is X AVE ';

[0122] Recovery rate = (X AVE ' - X AVE ) / added standard phosphorus content × 100%; wherein, X AVE ' is the phosphorus content of the spiked test solution, with the unit of μg / 50mL; X AVE is the phosphorus content of the test solution, with the unit of μg / 50mL; the added standard phosphorus content is 4 μg / 50mL.

[0123] The results of the standard addition recovery experiment of the above-mentioned examples are listed in Table 2.

[0124] Table 1

[0125]

[0126]

[0127] Table 2

[0128]

[0129]

[0130] As can be seen from Table 1 and Table 2, in the specific implementation of the method for determining the phosphorus content in steel according to the present invention, the standard deviation is less than 2%, and the spiked recovery rate is 96.98% or 103.55%, meeting the requirement that the recovery rate is between 95% and 105%, and the measurement results are accurate.

[0131] The applicant declares that the above is only the specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for determining the phosphorus content in steel, characterized in that, The phosphorus content in steel is determined by the phosphovanadomolybdic acid violet spectrophotometry; the phosphovanadomolybdic acid violet spectrophotometry uses an ethyl violet-phosphomolybdovanadic heteropolyacid-surfactant system to determine the phosphorus content in steel; The determination method includes the following steps: (1) After dissolving the steel to be measured, the initial solution containing phosphate is obtained through the first volume fixing; (2) A masking agent, sulfuric acid, ammonium molybdate solution, and vanadium bottom solution are added to the initial solution in step (1) for reaction to obtain a phosphomolybdovanadic heteropolyacid solution; (3) Ethyl violet is complexed with the phosphomolybdovanadic heteropolyacid solution in step (2) to obtain a phosphovanadomolybdic acid violet complex system; (4) A surfactant is peptized with the phosphovanadomolybdic acid violet complex system in step (3), and the test solution is obtained through the second volume fixing; (5) The absorbance of the test solution in step (4) is measured by spectrophotometry, and the phosphorus content in the steel to be measured is obtained through calculation from the absorbance; Among them, the dissolution in step (1) is carried out under the condition of heating to boiling; The dissolution in step (1) includes acid dissolution and oxidation carried out in sequence; The dissolution reagent used for the acid dissolution is nitric acid with a concentration of more than 8 mol / L; The oxidation reagent used for the oxidation includes potassium permanganate solution; The method of oxidation is: the potassium permanganate solution is slowly added dropwise to the solution after acid dissolution, and when brown precipitate begins to form in the solution, the addition of the potassium permanganate solution is stopped; The method for judging the end point of the dissolution in step (1) is: no gas is generated in the solution.

2. The measurement method according to claim 1, characterized in that, The masking agent in step (2) is 5-6% sodium fluoride.

3. The measurement method according to claim 1, characterized in that, In step (2), based on 4 mL of the initial solution, the dosage of the masking agent is 1-3 mL.

4. The measurement method according to claim 1, wherein The concentration of the sulfuric acid in step (2) is 2.5-3.5 mol / L.

5. The measurement method according to claim 4, wherein The concentration of the sulfuric acid in step (2) is 3.0 mol / L.

6. The measurement method according to claim 1, wherein In step (2), based on 4 mL of the initial solution, the dosage of the sulfuric acid is 5.2-9.6 mL.

7. The measurement method according to claim 6, characterized in that In step (2), based on 4 mL of the initial solution, the dosage of the sulfuric acid is 6-8 mL.

8. The measurement method according to claim 1, wherein The concentration of the ammonium molybdate solution in step (2) is 0.15-0.25 mol / L.

9. The measurement method according to claim 8, characterized in that, The concentration of the ammonium molybdate solution in step (2) is 0.20 mol / L.

10. The measurement method according to claim 1, characterized in that, In step (2), based on 4 mL of the initial solution, the dosage of the ammonium molybdate solution is 3.2-8 mL.

11. The measurement method according to claim 10, wherein In step (2), based on 4 mL of the initial solution, the dosage of the ammonium molybdate solution is 4-6 mL.

12. The measurement method according to claim 1, characterized in that, The preparation method of the vanadium bottom solution in step (2) includes: 1 mg of vanadium pentoxide is mixed with 20 mL of sulfuric acid solution with a concentration of 3 mol / L and then heated. After the vanadium pentoxide is completely dissolved, it is diluted to obtain the vanadium bottom solution.

13. The measurement method according to claim 12, characterized in that, Calculated based on vanadium pentoxide, the mass concentration of the vanadium bottom solution in step (2) is 2.0-2.5 g / L.

14. The measurement method according to claim 13, characterized in that, Calculated based on vanadium pentoxide, the mass concentration of the vanadium bottom solution in step (2) is 2.0 g / L.

15. The measurement method according to claim 1, characterized in that, In step (2), based on 4 mL of the initial solution, the dosage of the vanadium bottom solution is 1.2-3 mL.

16. The measurement method according to claim 15, wherein In step (2), based on 4 mL of the initial solution, the dosage of the vanadium bottom solution is 1.5-3 mL.

17. The measurement method according to claim 1, characterized in that, The ethyl violet described in step (3) is prepared into an ethyl violet solution with a concentration of (1.0 - 1.5)×10 -3 mol / L.

18. The measurement method according to claim 17, characterized in that, The ethyl violet described in step (3) is prepared into a concentration of 1.0×10 -3 mol / L.

19. The measurement method according to claim 17, characterized in that, Based on 4 mL of the initial solution, the dosage of the ethyl violet solution is 2 - 4 mL.

20. The measurement method according to claim 19, characterized in that, Based on 4 mL of the initial solution, the dosage of the ethyl violet solution is 3 - 4 mL.

21. The measurement method according to claim 1, characterized in that, The surfactant in step (4) includes any one or a combination of at least two of gelatin, PVA, gum arabic, or microemulsion.

22. The measurement method according to claim 21, wherein, The surfactant in step (4) is microemulsion and gum arabic.

23. The measurement method according to claim 21, wherein The solute of the microemulsion includes polyethylene glycol octyl phenyl ether, n-pentanol, and n-heptane.

24. The measurement method according to claim 23, wherein In the microemulsion, the volume ratio of polyethylene glycol octyl phenyl ether, n-pentanol, and n-heptane is (6.4 - 7.5):(4.6 - 5.4):

1.

25. The measurement method according to claim 21, characterized in that, The solvent of the microemulsion includes water.

26. The measurement method according to claim 21, characterized in that, In the microemulsion, the volume percentage of the solute is 6 - 8%, and the rest is the solvent.

27. The measurement method according to claim 21, characterized in that, Based on 4 mL of the initial solution, the dosage of the microemulsion is 0.6 - 0.8 mL.

28. The measurement method according to claim 21, wherein The gum arabic is formulated into a gum arabic solution with a concentration of 5 - 6 g / L.

29. The measurement method according to claim 21, wherein Based on 4 mL of the initial solution, the dosage of the gum arabic solution is 0.65 - 0.75 mL.

30. The measurement method according to claim 1, wherein After the second volume fixation in step (4), the content of phosphate ions in the test solution is 0.4 - 20 μg / 50 mL.

31. The measurement method according to claim 1, characterized in that, Before the measurement in step (5), the test solution in step (4) is left standing for 13 - 21 min.

32. The measurement method according to claim 1, characterized in that, The instrument used in the spectrophotometry in step (5) is a spectrophotometer.

33. The measurement method according to claim 1, characterized in that, The test wavelength of the absorbance in step (5) is 610 - 615 nm.

34. The measurement method according to claim 33, characterized in that, The test wavelength of the absorbance in step (5) is 612 nm.

35. The measurement method according to claim 1, characterized in that The steps of the calculation in step (5) include: substituting the absorbance into the calibration curve regression equation to obtain the phosphorus content of the test solution, and substituting the phosphorus content of the test solution into the conversion formula to obtain the phosphorus content in the steel to be tested.

36. The measurement method according to claim 35, wherein The calibration curve regression equation is A = 0.0516X - 0.0021, where A is the absorbance; X is the phosphorus content in the test solution, with the unit of μg / 50 mL.

37. The determination method according to claim 35, characterized in that, The conversion formula is X0 = (X × V2 × V1) / (50 × V x × M), where X0 is the phosphorus content in the steel to be measured, in ppm; X is the phosphorus content in the test solution, in μg / 50mL; V1 is the volume of the initial solution, in mL; V2 is the volume of the test solution, in mL; V x is the volume of the initial solution taken when preparing the test solution, in mL; M is the mass of the steel to be measured, in g.

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