Method for detecting phosphorus elution in phosphating film of non-oriented silicon steel

Abstract

The application discloses a method for detecting the phosphorus dissolution amount in a phosphating film of non-oriented silicon steel, and belongs to the technical field of non-oriented silicon steel surface phosphating film performance detection. The method adopts a Φ48mm standard circular sample, and after being purified by anhydrous ethanol, the phosphorus element is dissolved out by constant temperature extraction with ultrapure water at 100 DEG C, and after being oxidized and impurity-removed by concentrated nitric acid and being concentrated at low temperature, the volume is fixed; a standard solution matched with the nitric acid matrix is prepared, determination is carried out by using an inductively coupled plasma emission spectrometer, and the dissolution amount per unit area is converted by a fixed area correction coefficient 0.922. The whole process parameter of the method is standardized, the linear correlation coefficient of a working curve is greater than or equal to 0.999, the relative standard deviation of parallel determination is less than 1.5%, the matrix interference is small, the detection precision is high, the repeatability is good, the method can be adapted to chromium-free environmental protection phosphating film detection, and is suitable for performance characterization of coating corrosion resistance, process curing effect and the like.

Description

Technical Field

[0001] This invention relates to the field of performance testing technology for phosphate films on the surface of non-oriented silicon steel, and specifically to a method for detecting the amount of phosphorus leaching in phosphate films on non-oriented silicon steel. Background Technology

[0002] Non-oriented silicon steel is a core material used in drive motors for new energy vehicles, high-efficiency variable frequency home appliances, and special industrial motors. To improve the insulation performance, corrosion resistance, and stamping performance of the sheet metal, a phosphate-based insulating coating is applied to the surface of the silicon steel during the production process. The amount of phosphorus leached from the coating directly determines the insulation reliability, weather resistance, and long-term storage stability of the phosphate film, and is a core technical indicator for controlling the coating formulation, curing process, and product quality upon delivery.

[0003] Current industry testing technologies have many shortcomings: 1. Traditional chemical titration methods have lengthy procedures, high reagent consumption, and weak resistance to matrix interference. They cannot achieve accurate quantification of trace amounts of phosphorus in phosphating films, resulting in low detection efficiency and large human error.

[0004] 2. Conventional ICP testing lacks a unified and standardized pretreatment process, resulting in inconsistent sample specifications, arbitrary extraction temperatures and times, and no fixed oxidation and concentration parameters. This can easily lead to insufficient element dissolution or volatilization loss, poor test repeatability, and large data dispersion, which cannot meet production quality control requirements.

[0005] 3. Conventional testing did not use the nitric acid matrix matching method. Impurities leached from the silicon steel substrate and the water substrate would cause spectral interference, resulting in poor linearity of the working curve and large systematic deviation of the quantitative results.

[0006] 4. Existing temporary testing procedures for enterprises lack a fixed sample area conversion model, making it impossible to compare results for samples of different sizes in a unified manner. The industry lacks standardized testing methods that can be adapted to Φ48mm standard samples and directly output industry-standard units.

[0007] 5. As chromium-free environmentally friendly phosphate coatings for new energy vehicles gradually replace traditional chromium-containing coatings, existing testing methods cannot simultaneously detect and evaluate the performance of both types of coatings, thus hindering the optimization of new product processes and quality upgrades.

[0008] Therefore, developing an ICP testing method with standardized sample specifications, solidified pretreatment parameters, minimal matrix interference, high linearity, good repeatability, and compatibility with chromium-free phosphating films is of great practical significance for quality control of non-oriented silicon steel products, research and development of environmentally friendly coatings, and enhancing market competitiveness. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of existing technologies, such as non-standard detection process for phosphorus leaching of non-oriented silicon steel phosphate films, large matrix interference, poor repeatability, lack of a unified area conversion system, and inability to adapt to the characterization of environmentally friendly coatings. This invention provides a method for detecting phosphorus leaching in non-oriented silicon steel phosphate films, achieving standardized detection process, accurate and stable data, and wide applicability, thus meeting the dual needs of routine industrial quality inspection and scientific research performance characterization.

[0010] To achieve the above objectives, the present invention is implemented through the following technical solution: This invention provides a method for detecting the amount of phosphorus leaching in a phosphate coating on non-oriented silicon steel, comprising the following steps: S1. Sample preparation: Take a non-oriented silicon steel phosphate film coated plate, make it into a circular sample piece, and clean the sample piece to remove surface oil and impurities. S2. Extraction: Place the sample piece treated in step S1 in a container, add the extraction solvent, and perform constant temperature extraction under heating conditions to fully dissolve the phosphorus element in the phosphating film into the extraction solvent. After the extraction is completed, take out the sample piece, collect the extraction liquid, and rinse the surface of the sample piece. The rinsing liquid is added to the extraction liquid. S3. Oxidation and concentration: Add an oxidant to the extract collected in step S2 to oxidize and decompose organic impurities and stabilize phosphorus in the solution, and then heat and concentrate to a predetermined volume. S4. Volume adjustment: Transfer the concentrated solution from step S3 to a volumetric flask, adjust the volume to the mark with ultrapure water, shake well, and prepare the test solution. S5. Plotting the working curve: Prepare a series of standard solutions containing phosphorus, add matrix matching reagents to the standard solutions, and use an inductively coupled plasma atomic emission spectrometer to measure the spectral intensity of each standard solution. Plot the working curve with elemental concentration as the abscissa and spectral intensity as the ordinate. S6. Detection and Quantitative Calculation: The spectral intensity of phosphorus in the test solution is determined by inductively coupled plasma atomic emission spectrometry. The phosphorus content in the test solution is obtained by substituting it into the working curve. Then, the phosphorus content is converted into the leaching amount per unit area based on the area of ​​the sample piece, which gives the phosphorus leaching amount in the non-oriented silicon steel phosphate film.

[0011] As a preferred embodiment of the present invention, in step S1, the diameter of the circular sample piece is Φ48mm; the purification process involves wiping the surface of the sample piece with anhydrous ethanol and then air-drying it.

[0012] As a preferred embodiment of the present invention, in step S2, the extraction solvent is ultrapure water, the heating condition is constant temperature boiling at 100°C, the extraction time is 8-15 minutes, and the boiling process is carried out under a lid.

[0013] As a preferred embodiment of the present invention, in step S3, the oxidant is concentrated nitric acid, the volume ratio of the added concentrated nitric acid to the extract is 1:(15-20), the heating and concentration temperature is not higher than 120°C, and the predetermined volume is 30-40 mL.

[0014] As a preferred embodiment of the present invention, in step S4, the volumetric flask is 50 mL in size; the inner wall of the extraction container is washed with ultrapure water 2-3 times, and all washing liquid is transferred to the volumetric flask.

[0015] As a preferred embodiment of the present invention, in step S5, the matrix matching reagent is concentrated nitric acid; the working curve is set with blank sample and intermediate concentration confirmation sample, the gradient concentration covers the entire range of phosphorus leaching amount of conventional phosphating film, and the linear correlation coefficient of the working curve is ≥0.999.

[0016] As a preferred embodiment of the present invention, in step S5, the operating parameters of the inductively coupled plasma atomic emission spectrometer are: radio frequency power 1300-1400W, nebulizing gas flow rate 0.6-0.8L / min, cooling gas flow rate 12-15L / min, and sample lift rate 0.8-1.2mL / min.

[0017] As a preferred embodiment of the present invention, in step S6, when the sample piece is a Φ48mm circular sample piece, the area conversion uses a fixed area correction coefficient of 0.922, and the calculation formula is as follows: The dissolution rate of P per unit area = the measured content of P × 0.922; Wherein, the unit of dissolution amount of P per unit area is μg / 100cm². 2 .

[0018] As a preferred technical solution of the present invention, in steps S2-S4, the vessel used is a phosphorus-free quartz glass vessel.

[0019] As a preferred technical solution of the present invention, the detection method is applicable to the detection of phosphorus leaching of chromium-free phosphate environmentally friendly thin-coated non-oriented silicon steel sheets for new energy vehicles, and is also used for performance characterization tests of coating corrosion resistance, storage stability and process curing effect.

[0020] Compared with existing detection technologies, this invention effectively solves the technical shortcomings of existing methods, such as non-standard procedures, large matrix interference, poor data repeatability, lack of a unified quantification system, and narrow applicability. The specific beneficial effects are as follows: 1. This invention ensures the full dissolution of phosphorus from the phosphating film through isothermal extraction, combined with controlled low-temperature concentration to avoid elemental volatilization loss, and with standardized on-machine detection procedures, significantly improving the stability of the detection results. The relative standard deviation (RSD) of parallel determinations is <1.5%, and the overall repeatability error is controlled within ±5%, far superior to non-standardized temporary detection processes; it can achieve accurate quantification of trace and ultra-trace phosphorus in the phosphating film, fully meeting the precision requirements of industrial production quality control.

[0021] 2. This invention standardizes and solidifies the entire process, including sample size specifications, surface cleaning methods, extraction temperature and duration, oxidant dosage, concentration temperature range, volume adjustment system, instrument operating parameters, and result conversion model. This eliminates the result fluctuations caused by arbitrary parameter settings in conventional testing. Operators can directly follow the standardized procedures without having to figure out the test conditions themselves, effectively reducing human error. The method is highly reproducible and easy to promote and apply in large-scale production and quality inspection processes.

[0022] 3. This invention uses concentrated nitric acid for matrix matching and prepares a standard working curve. At the same time, it selects low-interference characteristic analysis spectral lines and combines them with the pretreatment process of nitric acid oxidation and decomposition of organic impurities and low-temperature concentration and purification of the matrix. This can effectively shield the spectral interference caused by leaching impurities from silicon steel substrates, water substrates and organic matter in coatings. The resulting working curve has a linear correlation coefficient ≥0.999, with high linearity, which avoids systematic bias in quantitative results from the root and significantly improves the sensitivity of trace element detection.

[0023] 4. This invention sets a fixed area correction coefficient of 0.922 for standard circular samples with a diameter of 48mm, which can directly convert the measured values ​​of elements in the solution into the industry-standard μg / 100cm³. 2 The leaching amount per unit area does not require additional area conversion or unit conversion. Test results from different batches and under different production conditions can be directly compared horizontally, facilitating production process adjustment, product quality traceability, and technical benchmarking within the industry.

[0024] 5. This method is applicable to the testing requirements of chromium-free phosphate environmentally friendly thin coatings for new energy vehicles; it can also be used for performance characterization tests of coating corrosion resistance, storage stability, and process curing effect, supporting the research and development of environmentally friendly coatings, optimization of production processes, and upgrading of product quality, and adapting to the iterative development direction of silicon steel coating technology.

[0025] 6. The reagent dosage of this method is controllable, the heating process temperature is controlled, and the operation risk is low. At the same time, it is clear that phosphorus-free quartz glassware is used throughout the experiment to avoid background pollution. Experimental waste liquid and waste reagents are collected separately and centrally treated in a harmless manner, which complies with the relevant regulations on laboratory safety management and environmental protection control. Detailed Implementation

[0026] To make the technical solution, operation process, and technical effects of the present invention clearer and more complete, the present invention will be further described in detail below with reference to specific embodiments and experimental verification data. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention; conventional parameter adjustments and equivalent substitutions made by those skilled in the art based on the core technical solution of the present invention are all within the protection scope of the present invention.

[0027] Experimental instruments and reagents: 1. Main instruments and equipment Inductively coupled plasma optical emission spectrometer (ICP-OES); programmable temperature-controlled constant temperature electric heating plate; Φ48mm standard round silicon steel punching die; 200mL phosphorus-free quartz beaker, with matching quartz watch glass; 50mL A-grade quartz volumetric flask; several single-mark pipettes and graduated pipettes; electronic analytical balance with an accuracy of 0.1mg.

[0028] 2. Test reagents Phosphorus standard solution: concentration 1000 μg / mL, national standard material; superior grade concentrated nitric acid (mass fraction 65%-68%); analytical grade anhydrous ethanol; ultrapure water.

[0029] This embodiment uses industrially produced non-oriented silicon steel phosphate film samples as the testing object, and strictly follows the following steps: S1 Sample Preparation Take the non-oriented silicon steel phosphate coating sheet to be tested, and cut it into circular sample pieces using a Φ48mm standard punching die. Prepare no less than 3 samples in parallel for each group. Wipe both sides of the sample piece with anhydrous ethanol cotton balls to thoroughly remove surface oil, dust and attached impurities. After wiping, place it in a clean and dust-proof environment to air dry at room temperature. Select qualified samples with flat surfaces, no scratches, no coating peeling and no oxidation rust spots for later use, and reject samples with surface defects.

[0030] S2 Extraction After drying, place the sample pieces in a 200mL quartz beaker with gaps between them, ensuring that the samples do not stick together or have large-area contact with the inner wall of the beaker. Add pre-boiled ultrapure water to the beaker, and completely submerge all the sample pieces. After covering with a quartz watch glass, place the beaker on a constant temperature heating plate and boil at 100℃ for 8-15 minutes. In this embodiment, the preferred extraction time is 10 minutes, so that the phosphorus element in the phosphating film can be fully dissolved into the extraction solvent.

[0031] After extraction, remove the sample piece with clean polytetrafluoroethylene tweezers, rinse the surface of the sample piece with a small amount of hot ultrapure water to remove any remaining extract, and add all the rinsing solution back into the original beaker of extract. Collect a total of 75-100 ml of extract.

[0032] S3 Oxidation and Concentration Add 5 mL of high-purity concentrated nitric acid as an oxidant to the collected extract to oxidize and decompose the organic impurities dissolved in the coating, while simultaneously complexing and stabilizing phosphorus ions in the solution to avoid detection deviations caused by changes in elemental form. Place the beaker back on a constant-temperature heating plate for heating and concentration, controlling the heating temperature not to exceed 120°C. After concentrating the solution to 30-40 mL, remove it and allow it to cool naturally to room temperature.

[0033] This step and subsequent solution processing steps all use phosphorus-free quartz glassware to avoid interference from background elements in the glassware on trace detection results.

[0034] S4 Volume Adjustment Transfer the cooled concentrated solution to a 50 mL quartz volumetric flask; wash the inner wall of the extraction beaker 2-3 times with a small amount of ultrapure water, and transfer all the washings to the same volumetric flask; finally, add ultrapure water to make up to the mark of the volumetric flask, cap and shake well, and let stand to obtain the test solution.

[0035] S5 Working Curve Plotting (1) Preparation of standard series solutions Accurately transfer 1000 μg / mL phosphorus standard solution into 50 mL volumetric flasks, adding concentrated nitric acid as a matrix matching reagent to each set of standard solutions. Dilute to the mark with ultrapure water, shake well, and prepare a series of standard solutions of different concentrations. Simultaneously, prepare blank standard solutions (without phosphorus standard solution, only concentrated nitric acid added and diluted to volume) and intermediate concentration confirmation samples. The proportion of concentrated nitric acid added to each set of standard solutions is equal.

[0036] The standard series solution concentration gradients in this embodiment are shown in Table 1 below, and the gradient range covers the entire range of phosphorus leaching amount of conventional phosphating films: Table 1. Proportions for Phosphorus Standard Series Solutions Note: If the content of the sample to be tested exceeds the range of the working curve, the gradient range of the working curve can be extended proportionally.

[0037] (2) ICP determination and curve establishment P 213.618nm was selected as the interference-free characteristic spectral line. The operating parameters of the inductively coupled plasma atomic emission spectrometer were set as follows: RF power 1300-1400W, nebulizer flow rate 0.6-0.8L / min, cooling gas flow rate 12-15L / min, and sample lift rate 0.8-1.2mL / min. In this embodiment, the preferred sample lift rate is 1.0mL / min.

[0038] After the instrument is ignited and stabilized, the spectral intensities of each standard series solution are measured sequentially. A working curve is plotted with elemental concentration as the abscissa and the corresponding spectral intensity as the ordinate. The linear correlation coefficient of the working curve is required to be ≥0.999. The accuracy of the curve is verified by using an intermediate concentration confirmation sample. If the deviation exceeds the allowable range, the standard series must be prepared again and the curve plotted.

[0039] S6 Detection and Quantitative Calculation Under instrument parameters that are completely consistent with those used in the working curve determination, the spectral intensity of the characteristic phosphorus spectral lines in the test solution is measured, and the total mass of phosphorus in the test solution is calculated by substituting it into the working curve; then, the amount of phosphorus dissolved per unit area is converted based on the sample area.

[0040] This method uses a standard Φ48mm circular sample piece, with a fixed area correction factor of 0.922. The calculation formula is as follows: Dissolution rate of P per unit area (μg / 100cm²) 2 = P measured value × 0.922.

[0041] The area correction factor of 0.922 is derived as follows: 0.922 = 100cm² 2 / [3.14×(4.8 / 2) 2 ×6cm 2 (The sample diameter is 48.0 mm). Based on the calculation logic of this method, which involves simultaneous extraction of three parallel samples per group and a unified 50 mL volumetric system, the corresponding 100 cm³ sample diameter is derived. 2 The fixed conversion factor for sample area is 0.922, allowing for direct output of industry-standard μg / 100cm². 2 Unit results.

[0042] Take the arithmetic mean of the test results of 3 parallel samples in the same group, round it to one decimal place in accordance with GB / T8170, and take it as the final test result.

[0043] Method Performance Verification Examples Example 1: Repeatability verification of chromium-free phosphating film samples Since the detection of phosphorus leaching in the phosphate coating of non-oriented silicon steel is a destructive test, the repeatability verification method is as follows: five groups of samples are prepared from different parts of the same batch of samples with uniform coating and no scratches on the surface. Five independent parallel tests are performed continuously according to the above steps. The results of the phosphorus leaching detection are shown in the table below: Table 2 Parallel test results of chromium-free phosphating film The results show that the relative standard deviation (RSD) of phosphorus leaching is less than 1.5%, indicating excellent repeatability of the method. The overall detection error is controlled within ±5%, and the data is stable and reliable, meeting the requirements of daily industrial quality control.

[0044] Operating Precautions 1. Phosphorus-free quartz glassware was used throughout the experiment. Newly used glassware was pretreated by soaking in 10% dilute nitric acid for more than 24 hours to avoid background contamination affecting trace detection results. Standard solutions were prepared fresh and stored in the dark at low temperature.

[0045] 2. During the heating and concentration process, the temperature must be strictly controlled not to exceed 120℃. Boiling of the solution is prohibited to prevent the loss of phosphorus elements with water vapor, which would lead to lower results.

[0046] 3. Before ICP testing, the sample inlet tubing should be thoroughly flushed to eliminate the memory effect of high-concentration samples; wavelength calibration and sensitivity checks should be performed regularly to ensure the instrument is in stable condition.

[0047] 4. Experimental waste liquids and discarded reagent bottles must be collected separately and handed over to professional institutions for centralized harmless treatment, in accordance with laboratory safety and environmental protection management requirements.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for detecting the amount of phosphorus leaching in a phosphated film on non-oriented silicon steel, characterized in that, Includes the following steps: S1. Sample preparation: Take a non-oriented silicon steel phosphate film coated plate, make it into a circular sample piece, and clean the sample piece to remove surface oil and impurities. S2. Extraction: Place the sample piece treated in step S1 in a container, add the extraction solvent, and perform constant temperature extraction under heating conditions to fully dissolve the phosphorus element in the phosphating film into the extraction solvent. After the extraction is completed, take out the sample piece, collect the extraction liquid, and rinse the surface of the sample piece. The rinsing liquid is added to the extraction liquid. S3. Oxidation and concentration: Add an oxidant to the extract collected in step S2 to oxidize and decompose organic impurities and stabilize phosphorus in the solution, and then heat and concentrate to a predetermined volume. S4. Volume adjustment: Transfer the concentrated solution from step S3 to a volumetric flask, adjust the volume to the mark with ultrapure water, shake well, and prepare the test solution. S5. Plotting the working curve: Prepare a series of standard solutions containing phosphorus, add matrix matching reagents to the standard solutions, and use an inductively coupled plasma atomic emission spectrometer to measure the spectral intensity of each standard solution. Plot the working curve with elemental concentration as the abscissa and spectral intensity as the ordinate. S6. Detection and Quantitative Calculation: The spectral intensity of phosphorus in the test solution is determined by inductively coupled plasma atomic emission spectrometry. The phosphorus content in the test solution is obtained by substituting it into the working curve. Then, the phosphorus content is converted into the leaching amount per unit area based on the area of ​​the sample piece, which gives the phosphorus leaching amount in the non-oriented silicon steel phosphate film.

2. The detection method according to claim 1, characterized in that, In step S1, the diameter of the circular sample piece is Φ48mm; the purification process involves wiping the surface of the sample piece with anhydrous ethanol and then air-drying it.

3. The detection method according to claim 1, characterized in that, In step S2, the extraction solvent is ultrapure water, the heating conditions are constant temperature boiling at 100℃, the extraction time is 8-15 minutes, and the boiling process is carried out under a lid.

4. The detection method according to claim 1, characterized in that, In step S3, the oxidant is concentrated nitric acid, the volume ratio of the added concentrated nitric acid to the extract is 1:(15-20), the heating and concentration temperature is not higher than 120℃, and the predetermined volume is 30-40mL.

5. The detection method according to claim 1, characterized in that, In step S4, the volumetric flask is 50 mL in size; the inner wall of the extraction container is washed 2-3 times with ultrapure water, and all washing liquid is transferred to the volumetric flask.

6. The detection method according to claim 1, characterized in that, In step S5, the matrix matching reagent is concentrated nitric acid; the working curve is set with blank sample and intermediate concentration confirmation sample, the gradient concentration covers the entire range of phosphorus leaching amount of conventional phosphating film, and the linear correlation coefficient of the working curve is ≥0.

999.

7. The detection method according to claim 1, characterized in that, In step S5, the operating parameters of the inductively coupled plasma atomic emission spectrometer are: radio frequency power 1300-1400W, nebulizing gas flow rate 0.6-0.8L / min, cooling gas flow rate 12-15L / min, and sample lift rate 0.8-1.2mL / min.

8. The detection method according to claim 1, characterized in that, In step S6, when the sample piece is a Φ48mm circular sample piece, the area conversion uses a fixed area correction factor of 0.922, and the calculation formula is as follows: The dissolution rate of P per unit area = the measured content of P × 0.922; The unit of dissolution per unit area of ​​P is μg / 100cm². 2 .

9. The detection method according to claim 1, characterized in that, In steps S2-S4, the vessels used are phosphorus-free quartz glass vessels.

10. The detection method according to any one of claims 1-9, characterized in that, The detection method is applicable to the detection of phosphorus leaching in non-oriented silicon steel sheets with chromium-free phosphate environmentally friendly thin coatings used in new energy vehicles, and is also used for performance characterization tests of coating corrosion resistance, storage stability, and process curing effect.

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