Method for determining silicon content in manganese-silicon alloys using spectrophotometry

Abstract

This invention belongs to the field of metallurgical analysis technology, specifically relating to a method for determining the silicon content in manganese-silicon alloys using spectrophotometry. The method involves decomposing the manganese-silicon alloy sample with acid to convert the silicon into soluble silicic acid or fluorosilicic acid. A masking agent is added to eliminate the influence of interfering ions, resulting in a clear test solution. This solution is then reacted with a colorimetric reagent to generate a colored complex with characteristic absorption in the visible light region, facilitating quantitative detection by a spectrophotometer. The absorbance of the colorimetric solution is measured at a characteristic wavelength to obtain an optical signal positively correlated with the silicon content. Based on a pre-established linear regression equation, the measured absorbance value is converted into the mass fraction of silicon, thus achieving quantitative analysis of the silicon content. The method provided in this application offers significantly shorter processing time for a single sample compared to traditional titration methods, is simpler to operate, and reduces human error.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical analysis technology, specifically relating to a method for determining the silicon content in manganese-silicon alloys using spectrophotometry. Background Technology

[0002] Manganese-silicon alloys are important deoxidizers and alloying additives in steel smelting, and silicon content is one of the key indicators for evaluating their quality. Currently, the determination of silicon content in manganese-silicon alloys mainly relies on the potassium fluorosilicate titration method specified in GB / T 5686.2-2022 "Determination of Silicon Content in Ferromanganese, Manganese-Silicon Alloys, Ferromanganese Nitride and Metallic Manganese". The basic principle of this method is as follows: the sample is decomposed with nitric acid and hydrofluoric acid, converting silicon into fluorosilicic acid. Potassium fluoride and potassium nitrate are added to form potassium fluorosilicate precipitate. After filtration and washing, the free acid is neutralized with alkali, and then boiling water is added to hydrolyze the potassium fluorosilicate to release hydrofluoric acid. Using phenolphthalein as an indicator, the solution is titrated to the endpoint with a standard sodium hydroxide solution. The mass fraction of silicon is calculated based on the amount of sodium hydroxide consumed.

[0003] However, this traditional titration method has the following drawbacks: the analytical steps are cumbersome, and manual operation is time-consuming; the precipitation, filtration, and washing processes are complex, and the waste liquid contains flocculent pulp that requires special treatment; the standard solution needs to be specially prepared and calibrated, which is labor-intensive; and the detection results are easily affected by human factors, resulting in limited repeatability and accuracy. Therefore, developing a rapid, accurate, and environmentally friendly method for determining the silicon content of manganese-silicon alloys is of significant practical importance. Summary of the Invention

[0004] In view of this, the present invention provides a method for determining the silicon content in manganese silicon alloys by spectrophotometry, so as to solve the above-mentioned technical problems arising from the determination of silicon content in manganese silicon alloys by potassium fluorosilicate titration in the prior art.

[0005] To achieve the above objectives, this application adopts the following approach:

[0006] A method for determining the silicon content in manganese-silicon alloys using spectrophotometry includes the following steps:

[0007] S10. Decompose the manganese silicon alloy sample to be tested with acid to convert the silicon in the manganese silicon alloy into soluble silicic acid or fluorosilicic acid, and add a masking agent to eliminate the influence of interfering ions to obtain a clear test solution.

[0008] S20. The test solution is reacted with a colorimetric reagent to generate a colored complex with characteristic absorption in the visible light region, so as to facilitate quantitative detection by a spectrophotometer;

[0009] S30. The absorbance of the colorimetric solution at a characteristic wavelength is measured using a spectrophotometer to obtain an optical signal that is positively correlated with the silicon content;

[0010] S40. Based on the pre-established linear regression equation, the measured absorbance value is converted into the mass fraction of silicon, thereby realizing the quantitative analysis of silicon content.

[0011] Preferably, the linear regression equation is:

[0012] y = 58.274x - 3.4016

[0013] In the formula, x represents absorbance; y represents silicon content, in units of %.

[0014] Preferably, the acids used to decompose the manganese silicon alloy sample to be tested are nitric acid and hydrofluoric acid. The amount of nitric acid used is 4-6 mL per 0.05 g of manganese silicon alloy sample to be tested, and the amount of hydrofluoric acid used is 1-2 mL per 0.05 g of manganese silicon alloy sample to be tested.

[0015] Preferably, the masking agent comprises urea and boric acid, wherein the urea is used to reduce and eliminate interference from excess hydrofluoric acid and nitrogen oxides, and the boric acid is used to complex excess fluoride ions. The concentration of the urea is 3%-8% and the amount used is 4-6 mL, and the concentration of the boric acid is 3%-8% and the amount used is 40-60 mL.

[0016] Preferably, the colorimetric agent includes ammonium molybdate and oxalic acid. The ammonium molybdate is used to form silicic molybdate heteropoly acid with silicic acid, and the oxalic acid is used to mask interfering elements such as phosphorus and arsenic and adjust the colorimetric conditions. The concentration of the ammonium molybdate is 3%-8% and the amount used is 4-6 mL. The concentration of the oxalic acid is 1%-3% and the amount used is 15-25 mL.

[0017] Preferably, a reducing agent is further added after the colorimetric reaction. The reducing agent is ferrous ammonium sulfate, which is used to reduce silicomolybdenum yellow to silicomolybdenum blue to enhance the detection sensitivity and stability. The concentration of the ferrous ammonium sulfate is 0.5%-2%, and the amount used is 20-30 mL.

[0018] Preferably, after decomposing the manganese-silicon alloy sample to be tested with acid, the method further includes a step of adjusting the volume to obtain a mother liquor, transferring the mother liquor to carry out the colorimetric reaction, wherein the amount of mother liquor transferred is 2-5 mL, so as to control the silicon concentration of the colorimetric system within a suitable detection range.

[0019] Preferably, the color development reaction is carried out under water bath conditions for 20-40 seconds to accelerate the color development reaction and ensure complete color development.

[0020] Preferably, the detection wavelength of the spectrophotometer is 670-690 nm, the optical path of the cuvette is 1 cm, and the wavelength is the characteristic absorption peak of the silicomolybdenum blue complex, which can avoid spectral interference from other components.

[0021] In the above-mentioned method for determining the silicon content in manganese-silicon alloys using spectrophotometry, the manganese-silicon alloy sample to be tested is first decomposed with acid to convert the silicon in the manganese-silicon alloy into soluble silicic acid or fluorosilicic acid. A masking agent is added to eliminate the influence of interfering ions, resulting in a clear test solution. The test solution is then reacted with a colorimetric reagent to generate a colored complex with characteristic absorption in the visible light region, facilitating quantitative detection by a spectrophotometer. The absorbance of the colorimetric solution is measured at a characteristic wavelength using a spectrophotometer to obtain an optical signal positively correlated with the silicon content. Based on a pre-established linear regression equation, the measured absorbance value is converted into the mass fraction of silicon, thereby achieving quantitative analysis of the silicon content. The method provided in this application takes significantly less time for the entire detection process of a single sample compared to traditional titration methods, greatly increasing the number of samples that can be detected per unit time, enabling batch detection. It eliminates the need for cumbersome operations such as precipitation, filtration, washing, and titration, simplifying the operation and reducing human error and subjective errors caused by human judgment of the endpoint. Attached Figure Description

[0022] Figure 1 This is a standard curve of silicon content in an embodiment of the present invention. Detailed Implementation

[0023] To facilitate understanding of this application, a more comprehensive description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are also given. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to enable a more thorough and complete understanding of the disclosure of this application.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0025] Please refer to Figure 1 This application provides a method for determining the silicon content in manganese-silicon alloys using spectrophotometry, comprising the following steps:

[0026] S10. Decompose the manganese silicon alloy sample to be tested with acid to convert the silicon in the manganese silicon alloy into soluble silicic acid or fluorosilicic acid, and add a masking agent to eliminate the influence of interfering ions to obtain a clear test solution.

[0027] S20. The test solution is reacted with a colorimetric reagent to generate a colored complex with characteristic absorption in the visible light region, so as to facilitate quantitative detection by a spectrophotometer;

[0028] S30. The absorbance of the colorimetric solution at a characteristic wavelength is measured using a spectrophotometer to obtain an optical signal that is positively correlated with the silicon content;

[0029] S40. Based on the pre-established linear regression equation, the measured absorbance value is converted into the mass fraction of silicon, thereby realizing the quantitative analysis of silicon content.

[0030] Specifically, the steps for establishing a linear regression equation are as follows:

[0031] Step 1: Weigh approximately 0.05 g of standard manganese-silicon alloy samples (at least five standard manganese-silicon alloy samples with different silicon contents) to an accuracy of 0.0001 g and perform the subsequent steps accordingly. In a 500 mL plastic beaker, add 4-6 mL, preferably 5 mL, of nitric acid and shake gently. Add 1.4-1.6 mL, preferably 1.5 mL, of hydrofluoric acid and shake gently until the nitric acid fumes cease to appear.

[0032] Step 2: Add 4-6 mL, preferably 5 mL, of 5% urea and shake well; then add 40-60 mL, preferably 50 mL, of 5% boric acid.

[0033] Step 3: After the sample has dissolved, transfer it to a 250 mL plastic volumetric flask that has been pre-filled with 50 mL of distilled water, add 40-60 mL, preferably 50 mL, of 5% boric acid, and make up to volume and shake well to obtain the mother liquor.

[0034] Step 4: Quickly transfer 3 mL of the mother liquor into a 100 mL plastic volumetric flask, add 4.5-5.5 mL, preferably 5 mL, of 1% dilute sulfuric acid, 4.5-5.5 mL, preferably 5 mL, of 5% ammonium molybdate, and incubate in a water bath for 25-35 seconds, preferably 30 seconds. Then add 15-25 mL, preferably 20 mL, of 2% oxalic acid, and 20-30 mL, preferably 25 mL, of 1% ferrous ammonium sulfate. Make up to volume and shake well.

[0035] Step 5: At a wavelength of 670-690 nm, preferably 680 nm, use a 1 cm cuvette to measure the absorbance of at least five sets of standard materials with silicon content, calculate the linearity using a function calculator, obtain the slope, and get the linear regression equation.

[0036] Take the manganese-silicon alloy sample to be tested and perform the above steps S10 to S40. Substitute the measured absorbance value into the above linear regression equation to obtain the mass fraction of silicon, thereby realizing the quantitative analysis of silicon content.

[0037] The method provided in this application takes significantly less time than traditional titration for the entire detection process of a single sample, greatly increasing the number of samples that can be detected per unit time, enabling batch testing. It eliminates the need for cumbersome operations such as precipitation, filtration, washing, and titration, simplifying operation and reducing human error, particularly subjective errors caused by human judgment of the endpoint. It does not use a precipitation system containing filter paper, resulting in no flocculent pulp in the waste liquid and simplifying treatment. The reagent volume is extremely small (milliliters), reducing the risk of exposure to toxic reagents (such as potassium nitrate) and the amount of waste liquid generated. The shift from traditional titration to spectrophotometric detection aligns with the modern trend of laboratory automation and digitalization.

[0038] Furthermore, the linear regression equation is as follows:

[0039] y = 58.274x - 3.4016

[0040] In the formula, x represents absorbance; y represents silicon content, in units of %.

[0041] Furthermore, the acids used to decompose the manganese silicon alloy sample to be tested are nitric acid and hydrofluoric acid. The amount of nitric acid used is 4-6 mL per 0.05 g of manganese silicon alloy sample to be tested, preferably 5 mL. The amount of hydrofluoric acid used is 1-2 mL per 0.05 g of manganese silicon alloy sample to be tested, preferably 1.5 mL.

[0042] Furthermore, the masking agent includes urea and boric acid. The urea is used to reduce and eliminate interference from excess hydrofluoric acid and nitrogen oxides, and the boric acid is used to complex excess fluoride ions. The concentration of the urea is 3%-8%, preferably 5%, and the amount used is 4-6 mL, preferably 5 mL. The concentration of the boric acid is 3%-8%, preferably 5%, and the amount used is 40-60 mL, preferably 50 mL.

[0043] At this concentration and dosage, interference from excess hydrofluoric acid, nitrogen oxides, and free fluoride ions can be completely eliminated without affecting subsequent colorimetric reactions (e.g., without changing the solution pH to a level unsuitable for the formation of silicomolybdenum blue).

[0044] Furthermore, the colorimetric agent includes ammonium molybdate and oxalic acid. The ammonium molybdate is used to form silicomolybdate heteropoly acid with silicic acid, and the oxalic acid is used to mask interfering elements such as phosphorus and arsenic and adjust the colorimetric conditions. The concentration of the ammonium molybdate is 3%-8%, preferably 5%, and the amount used is 4-6 mL, preferably 5 mL. The concentration of the oxalic acid is 1%-3%, preferably 2%, and the amount used is 15-25 mL, preferably 20 mL.

[0045] At this concentration and dosage, silicic acid and ammonium molybdate react sufficiently to generate adequate silicomolybdenum yellow, ensuring sufficient absorbance intensity after subsequent reduction to silicomolybdenum blue and improving detection sensitivity. The optimized dosage and concentration of oxalic acid effectively mask common interfering elements in manganese-silicon alloys (such as phosphorus and arsenic), preventing them from causing positive deviations in absorbance, thus ensuring the selectivity and accuracy of the measurement results. Stable colorimetric conditions enable the linear correlation coefficient of the standard curve to reach R≥0.999, meeting the requirements for quantitative analysis.

[0046] Furthermore, a reducing agent is added after the colorimetric reaction. The reducing agent is ferrous ammonium sulfate, which is used to reduce silicomolybdenum yellow to silicomolybdenum blue to enhance the detection sensitivity and stability. The concentration of the ferrous ammonium sulfate is 0.5%-2%, preferably 1%, and the amount used is 20-30 mL, preferably 25 mL.

[0047] This embodiment reduces yellow silicomolybdenum yellow to blue silicomolybdenum blue, significantly increasing its molar absorptivity. This allows the spectrophotometer to detect a stronger absorbance signal at the same silicon content, thereby improving the method's sensitivity to silicon detection, especially suitable for the accurate determination of low-content silicon. The optimized concentration and amount of ferrous ammonium sulfate ensures a complete and controllable reduction reaction. The resulting silicomolybdenum blue is stable in this system, reducing absorbance fluctuations caused by factors such as color development time and temperature changes, ensuring the stability and reliability of data during batch testing. These reduction conditions do not introduce interfering substances and effectively eliminate interference from potential residual oxidizing agents, allowing the measured absorbance to accurately and linearly reflect the silicon content, thus guaranteeing the linear correlation coefficient (R≥0.999) of the standard curve and the accuracy of the sample determination results.

[0048] Furthermore, after decomposing the manganese-silicon alloy sample to be tested with acid, the process also includes a step of adjusting the volume to obtain a mother liquor, transferring the mother liquor to carry out the colorimetric reaction, wherein the amount of mother liquor transferred is 2-5 mL, preferably 3 mL, in order to control the silicon concentration of the colorimetric system within a suitable detection range.

[0049] Manganese-silicon alloys have a high silicon content (typically 14%-20%). If the stock solution is used directly for color development, the silicon concentration may exceed the linear response range of the spectrophotometer (absorbance > 0.8 or the instrument's detection limit). By diluting the stock solution and controlling the transfer volume to 2-5 mL, the absolute silicon content in the color development system can be adjusted to the optimal detection range of the silicomolybdenum blue method (typically corresponding to absorbance 0.2-0.7), ensuring that the measured value falls within the linear range of the standard curve. Directly using the stock solution may introduce excessive acids, masking agents, metal ions, etc., interfering with the color development reaction. Diluting the stock solution and controlling the transfer volume reduces the matrix effect, making the color development conditions more stable and the formation and reduction of silicomolybdenum blue more controllable.

[0050] Furthermore, the colorimetric reaction is carried out in a water bath for 20-40 seconds to accelerate the colorimetric reaction and ensure complete color development.

[0051] The reaction rate of silicic acid with ammonium molybdate to form silicomolybdate yellow is slow at room temperature, typically requiring several minutes to tens of minutes. Water bath heating can significantly increase the reaction rate, shorten the color development time, and substantially improve detection efficiency, meeting the needs of rapid analysis of batch samples. Furthermore, under heating conditions, the reaction between silicic acid and ammonium molybdate is more complete, with the formation rate of silicomolybdate yellow approaching 100%, resulting in a stronger final color signal (higher absorbance of silicomolybdate blue) and improved sensitivity of the method for silicon detection.

[0052] Furthermore, the spectrophotometer has a detection wavelength of 670-690 nm and a cuvette optical path of 1 cm. The wavelength is the characteristic absorption peak of the silicomolybdenum blue complex, which can avoid spectral interference from other components.

[0053] The absorbance of silicomolybdenum blue is highest at the characteristic absorption peak wavelength (670-690 nm), meaning it produces the strongest signal per unit concentration of silicon. This makes the method more sensitive to minute changes in silicon content, lowers the detection limit, and is suitable for accurate determination of silicon content over a wide range. The manganese-silicon alloy matrix is ​​complex, containing multiple elements such as iron, manganese, phosphorus, and arsenic. Selecting the characteristic absorption peak of silicomolybdenum blue for determination effectively avoids spectral interference from other components (such as the absorption of iron ions in the visible light region and the different absorption peaks of phosphomolybdenum blue), achieving selective determination of silicon without complex separation steps.

[0054] The following specific experimental examples further illustrate the technical solution and effects of the present invention. It should be noted that the following experimental examples are only for further explanation of the present invention and do not limit the technical solution of the present invention.

[0055] Example

[0056] Weigh approximately 0.05 g of standard manganese-silicon alloy samples (at least five standard manganese-silicon alloy samples with different silicon contents, such as 14.33%, 17.19%, 18.96%, and 19.34% silicon contents), accurate to 0.0001 g, and perform the subsequent steps on each sample in a 500 mL plastic beaker. Add 5 mL of nitric acid, shake gently, add 1.5 mL of hydrofluoric acid dropwise, and shake gently until the nitric acid fumes cease. Add 5 mL of 5% urea solution, shake well, and then add 50 mL of 5% boric acid solution. After the sample dissolves, transfer it to a 250 mL plastic volumetric flask pre-filled with 50 mL of distilled water, add 50 mL of 5% boric acid solution, dilute to volume, and shake well to obtain the mother liquor. Quickly transfer 3 mL of the mother liquor to a 100 mL plastic volumetric flask, add 5 mL of 1% dilute sulfuric acid and 5 mL of 5% ammonium molybdate solution, incubate in a water bath for 30 seconds, then add 20 mL of 2% oxalic acid solution and 25 mL of 1% ferrous ammonium sulfate solution, and dilute to volume and mix well. Perform colorimetric determination at 680 nm using a 1 cm cuvette in a spectrophotometer. Record the absorbance of the silicon content standard substances (silicon contents of 14.33%, 17.19%, 18.96%, and 19.34%, respectively), as shown in Table 1. Calculate the linear relationship using a function calculator. A linear relationship R ≥ 0.999 is required for sample determination. The linear equation obtained in this example is: y = 58.274x - 3.4016, where x is absorbance and y is silicon content (%). The standard curve is shown below. Figure 1 As shown.

[0057]

[0058] The manganese-silicon alloy sample was weighed again according to the above method and steps, and its absorbance was measured. The absorbance was then substituted into the above linear equation to obtain the y value, i.e. the silicon content, as shown in Table 2 (three sets of parallel experiments).

[0059]

[0060] The results show that the determination results of the method of the present invention are in high agreement with the theoretical values, with a relative error of ≤0.21%, which meets the quality requirements of metallurgical analysis.

[0061] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions should be covered within the scope of protection of the present invention.

Claims

1. A method for determining the silicon content in manganese-silicon alloys using spectrophotometry, characterized in that, Includes the following steps: S10. Decompose the manganese silicon alloy sample to be tested with acid to convert the silicon in the manganese silicon alloy into soluble silicic acid or fluorosilicic acid, and add a masking agent to eliminate the influence of interfering ions to obtain a clear test solution. S20. The test solution is reacted with a colorimetric reagent to generate a colored complex with characteristic absorption in the visible light region, so as to facilitate quantitative detection by a spectrophotometer; S30. The absorbance of the colorimetric solution at a characteristic wavelength is measured using a spectrophotometer to obtain an optical signal that is positively correlated with the silicon content; S40. Based on the pre-established linear regression equation, the measured absorbance value is converted into the mass fraction of silicon, thereby realizing the quantitative analysis of silicon content.

2. The method for determining the silicon content in manganese-silicon alloys by spectrophotometry according to claim 1, characterized in that, The linear regression equation is as follows: y = 58.274x - 3.4016 In the formula, x represents absorbance; y represents silicon content, in units of %.

3. The method for determining the silicon content in manganese-silicon alloys using spectrophotometry according to claim 1, characterized in that, The acids used to decompose the manganese silicon alloy sample to be tested are nitric acid and hydrofluoric acid. The amount of nitric acid used is 4-6 mL per 0.05 g of manganese silicon alloy sample to be tested, and the amount of hydrofluoric acid used is 1-2 mL per 0.05 g of manganese silicon alloy sample to be tested.

4. The method for determining the silicon content in manganese-silicon alloys by spectrophotometry according to claim 3, characterized in that, The masking agent includes urea and boric acid. The urea is used to reduce and eliminate interference from excess hydrofluoric acid and nitrogen oxides, and the boric acid is used to complex excess fluoride ions. The concentration of the urea is 3%-8% and the dosage is 4-6 mL. The concentration of the boric acid is 3%-8% and the dosage is 40-60 mL.

5. The method for determining the silicon content in manganese-silicon alloys by spectrophotometry according to claim 3, characterized in that, The colorimetric agent includes ammonium molybdate and oxalic acid. The ammonium molybdate is used to form silicic molybdate heteropoly acid with silicic acid. The oxalic acid is used to mask interfering elements such as phosphorus and arsenic and to adjust the colorimetric conditions. The concentration of the ammonium molybdate is 3%-8% and the amount used is 4-6 mL. The concentration of the oxalic acid is 1%-3% and the amount used is 15-25 mL.

6. The method for determining the silicon content in manganese-silicon alloys by spectrophotometry according to claim 5, characterized in that, After the colorimetric reaction, a reducing agent, namely ferrous ammonium sulfate, is added to reduce silicomolybdenum yellow to silicomolybdenum blue, thereby enhancing the detection sensitivity and stability. The concentration of the ferrous ammonium sulfate is 0.5%-2%, and the amount used is 20-30 mL.

7. The method for determining the silicon content in manganese-silicon alloys by spectrophotometry according to claim 6, characterized in that, The process of decomposing the manganese-silicon alloy sample to be tested with acid also includes a step of adjusting the volume to obtain a mother liquor, and then transferring the mother liquor to carry out the colorimetric reaction. The amount of mother liquor transferred is 2-5 mL, so as to control the silicon concentration of the colorimetric system within a suitable detection range.

8. The method for determining the silicon content in manganese-silicon alloys by spectrophotometry according to claim 1, characterized in that, The colorimetric reaction is carried out in a water bath for 20-40 seconds to accelerate the reaction and ensure complete color development.

9. The method for determining the silicon content in manganese-silicon alloys by spectrophotometry according to claim 1, characterized in that, The spectrophotometer has a detection wavelength of 670-690 nm and a cuvette optical path of 1 cm. The wavelength is the characteristic absorption peak of the silicomolybdenum blue complex, which can avoid spectral interference from other components.

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