Method for analyzing iron alloy through rapid glass melting method-inductively coupled plasma atomic emission spectrometry

Abstract

The invention discloses a method for analyzing an iron alloy by a rapid glass melting method-inductively coupled plasma atomic emission spectrometry, and relates to the technical field of iron alloy component analysis, the method comprises the following steps: S1, melting and preparing a sample: mixing a to-be-detected iron alloy sample with a lithium borate flux, melting at high temperature, and cooling to form a homogeneous glass sheet; s2, high-pressure fluoride-free dissolution and sample preparation; according to the method for analyzing the iron alloy through the rapid glass melting method and the inductively coupled plasma atomic emission spectrometry, a high-pressure fluoride-free dissolving medium is adopted and is matched with a closed high-pressure dissolving condition, so that the use of high-risk and strong-corrosive reagents such as hydrofluoric acid is completely abandoned while rapid and complete dissolution of a glass melting sheet is realized; and a strong corrosive flux and a special vessel required by an alkali fusion method are avoided, so that the operation safety of the whole pretreatment process is greatly improved, and environmental hazards and laboratory safety risks are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of iron alloy component analysis, and particularly relates to a method for analyzing iron alloy by rapid glass fusion method-inductively coupled plasma atomic emission spectrometry. BACKGROUND

[0002] In the technical field of iron alloy component analysis, with the continuous progress of material science and the increasingly stringent requirements of industrial applications on material performance, the accurate determination of the content of various elements in iron alloy becomes a key link of quality control and research and development. Traditional analysis methods, such as acid dissolution method and alkali fusion method, can meet the basic analysis requirements to a certain extent, but when dealing with complex matrix iron alloy samples, they expose many limitations. The acid dissolution method uses strong acid to dissolve the sample, which can handle most metal elements, but the dissolution efficiency of light elements such as silicon and phosphorus is low, and insoluble silicic acid precipitate is easily generated, resulting in a large deviation of the analysis results. The alkali fusion method can enhance the dissolution ability of insoluble elements, but it introduces a high-salt matrix, which seriously interferes with the subsequent spectral analysis, affecting the accuracy of the analysis and the service life of the instrument.

[0003] However, the prior art has significant deficiencies in simultaneously achieving rapid and accurate determination of major and trace elements in iron alloy, especially light elements such as silicon and phosphorus. Due to the low dissolution efficiency and the tendency to form precipitates of silicon and phosphorus elements in the traditional dissolution system, the recovery rate of these elements is unstable, the analysis results have poor repeatability, and the high-precision and high-efficiency requirements of modern industrial analysis cannot be met. This problem not only limits the accuracy of iron alloy product quality control, but also hinders the progress of new material research and development, so it needs to be improved. SUMMARY

[0004] The purpose of the present application is to provide a method for analyzing iron alloy by rapid glass fusion method-inductively coupled plasma atomic emission spectrometry, in order to solve the problem that the prior art cannot efficiently, accurately and safely determine major and trace elements in iron alloy, especially light elements such as silicon and phosphorus, and has low dissolution efficiency, unstable recovery rate, poor repeatability of analysis results and insufficient operation safety.

[0005] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme: a method for analyzing iron alloy by rapid glass fusion method-inductively coupled plasma atomic emission spectrometry, comprising the following steps:

[0006] S1, sample preparation by melting: mixing the iron alloy sample to be tested with lithium borate flux, melting at high temperature, and forming a homogeneous glass sheet after cooling;

[0007] S2, sample preparation by high-pressure fluorine-free dissolution: placing the glass sheet prepared in step S1 in a dissolution medium containing no hydrofluoric acid, heating and dissolving under sealed high-pressure conditions, and obtaining a clear and transparent test solution;

[0008] S3, ICP-AES determination: the solution to be measured prepared in step S2 is corrected by using internal standard method and / or matrix matching technology, and the content of each element in the ferroalloy is determined by inductively coupled plasma atomic emission spectrometer.

[0009] Further, the dissolution medium without hydrofluoric acid is a lithium tetraborate solution or a mixed solution composed of an ammonium salt and an organic acid complexing agent.

[0010] Further, when the dissolution medium is a lithium tetraborate solution, step S2 is carried out in a high-pressure microwave digestion system.

[0011] Further, the ammonium salt is ammonium nitrate or ammonium chloride, and the organic acid complexing agent is citric acid, tartaric acid or EDTA.

[0012] Further, the lithium borate flux is lithium tetraborate, lithium metaborate or a mixture thereof in any ratio.

[0013] Further, in step S1, the mixing mass ratio of the ferroalloy sample to the lithium borate flux is 1: (5-10); the temperature of the melting is 950-1200℃, and the melting time is 5-20 minutes.

[0014] Further, in step S2, the temperature of the heating and dissolving is 120-220℃, and the dissolving time is 5-30 minutes.

[0015] Further, the method is used for determining the major elements and / or trace elements in the ferroalloy, the major elements including one or more of iron, nickel and chromium, and the trace elements including one or more of silicon, phosphorus, manganese, molybdenum and vanadium.

[0016] Compared with the prior art, the method for analyzing the ferroalloy provided by the application is a rapid glass melting method-inductively coupled plasma atomic emission spectrometry method, which adopts a high-pressure fluoride-free dissolution medium and cooperates with a closed high-pressure dissolution condition, realizes rapid and complete dissolution of the glass melting sheet, completely discards the use of high-risk and strong corrosive reagents such as hydrofluoric acid, avoids the use of strong corrosive fluxes and special vessels required by the alkali fusion method, greatly improves the operation safety of the entire pretreatment process, and reduces the environmental hazards and laboratory safety risks.

[0017] By combining the lithium borate sample preparation technology with the specific fluoride-free medium dissolution technology, the matrix form of the sample to be measured is fundamentally changed. The method converts the complex iron alloy matrix into a homogeneous and stable silicate glass at the melting stage, and then forms a simple and consistent solution after dissolution, thereby greatly weakening the matrix effect and significantly improving the accuracy and reliability of the subsequent inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis.

[0018] By optimizing the integrated process of glass melting and efficient dissolution, the technical scheme creatively provides a unified and complete pretreatment paradigm for iron alloy analysis. It not only overcomes the defect of incomplete recovery of light elements such as silicon and phosphorus in traditional acid dissolution method, but also avoids the problem of high salt matrix introduced by alkali fusion method which causes damage and interference to the instrument, thereby realizing the rapid and accurate quantitative analysis of elements in iron alloy from major elements to trace elements, especially silicon and phosphorus which are difficult to accurately determine by traditional methods. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments described in the present application, and other drawings can also be obtained by those skilled in the art based on these drawings.

[0020] Figure 1 The method provided by the embodiments of the present application is shown in the schematic diagram. DETAILED DESCRIPTION

[0021] In order to make those skilled in the art better understand the technical solutions of the present application, the present application will be further described in detail below with reference to the drawings.

[0022] As shown in the accompanying Figure 1 As shown in the accompanying

[0023] Embodiment one:

[0024] The present application provides a method for analyzing iron alloy by rapid glass melting method-inductively coupled plasma atomic emission spectrometry. Lithium tetraborate (Li2B4O7) is used as flux to prepare homogeneous glass pieces of high chromium cast iron. Then, lithium tetraborate solution without hydrofluoric acid is used as a dissolving medium to dissolve the glass pieces in a high-pressure microwave digestion system. Finally, the contents of major elements chromium (Cr) and iron (Fe) and trace elements silicon (Si), phosphorus (P), manganese (Mn), nickel (Ni) and molybdenum (Mo) in the sample are determined by internal standard method-inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0025] Experimental materials and equipment

[0026] Sample and standard material

[0027] Sample and standard material: National Standard Reference Material of High Chromium Cast Iron. The standard values are shown in Table 1. Before use, the sample should be crushed and ground with a hard alloy mortar to pass through a 0.125 mm (120 mesh) sieve, and stored in a desiccator.

[0028] Table 1: Standard values of each element in the standard material of high chromium cast iron

[0029] Element Mass fraction (wt%) Element Mass fraction (wt%) Fe Matrix (balance) P 0.032±0.002 Cr 25.32±0.10 Mn 0.58±0.02 Si 1.15±0.03 Ni 0.45±0.02 C 2.85±0.05 Mo 0.21±0.01

[0030] Reagents and materials:

[0031] Fusing agent: anhydrous lithium tetraborate (Li2B4O7), premium grade, calcined at 500°C in a muffle furnace for 4 hours to remove water and volatile impurities, and stored in a desiccator after cooling.

[0032] Dissolution medium:

[0033] Lithium tetraborate stock solution (200 g / L): accurately weigh 200.00 g of dry lithium tetraborate, dissolve in about 800 mL of hot (about 60°C) ultrapure water, stir until completely dissolved, cool to room temperature, transfer to a 1000 mL volumetric flask, dilute to the mark with ultrapure water, shake well, and store in a polyethylene bottle.

[0034] Working dissolution solution: transfer 25.0 mL of the above lithium tetraborate stock solution (200 g / L) to a 100 mL volumetric flask, add 4.0 mL of concentrated nitric acid (premium grade, purified by sub-boiling distillation) and 1.0 mL of concentrated hydrochloric acid (premium grade, purified by sub-boiling distillation), dilute to the mark with ultrapure water, shake well. This solution contains 50 g / L of lithium tetraborate, with a nitric acid concentration of about 4% (v / v) and a hydrochloric acid concentration of about 1% (v / v).

[0035] Standard solution:

[0036] Multi-element mixed standard stock solution: use single-element certified standard solutions (1000 μg / mL or 10 mg / mL) provided by the National Non-ferrous Metals and Electronic Materials Analysis and Testing Center, dilute with 5% nitric acid in stages to prepare a mixed standard series solution containing Fe, Cr, Si, P, Mn, Ni, Mo. To match the matrix, add a high-purity iron solution with a concentration similar to that of the sample solution to the standard series solution.

[0037] Internal standard stock solution: yttrium (Y) single-element standard solution, 1000 μg / mL. When used, dilute with 2% nitric acid to a working solution of 10 mg / L.

[0038] Others: ultrapure water (resistivity ≥ 18.2 MΩ·cm), high-purity argon gas (purity ≥ 99.999%).

[0039] Instruments and equipment

[0040] Sample preparation equipment: fully automatic high-frequency induction furnace (model: Claisse Fluxy, or equivalent model) equipped with platinum-gold (95% Pt / 5% Au) crucible and mold.

[0041] Dissolution equipment: high-pressure microwave digestion system (model: CEM Mars 6, or equivalent model) equipped with 100 mL high-pressure digestion tank with polytetrafluoroethylene (PTFE) lining.

[0042] Analytical instrument: full-spectrum direct-reading inductively coupled plasma atomic emission spectrometer (model: Thermo Scientific iCAP 7400, or equivalent model) equipped with echelle grating spectrometer system, CID detector, glass concentric atomizer, and cyclone atomization chamber.

[0043] Auxiliary equipment: electronic analytical balance with a resolution of 100,000th, ultrasonic cleaner, electric heating air drying oven.

[0044] Experimental steps:

[0045] S1: Sample preparation by fusion (glass disc preparation)

[0046] Accurately weigh 0.1000 g (accurate to ±0.0001 g) of high-chromium cast iron standard material GBW01201a powder into a pre-baked platinum-gold crucible.

[0047] Accurately add 0.9000 g of anhydrous lithium tetraborate flux to the crucible. Gently stir with platinum-gold wire to ensure that the sample and flux are thoroughly mixed and evenly distributed (at this point, the mass ratio of sample to flux is 1:9).

[0048] Place the crucible in the high-frequency induction furnace. Set the fusion program: heat to 1150°C and maintain at this temperature for 10 minutes. During the fusion process, the furnace automatically shakes and stirs 3 times to ensure complete homogenization of the melt.

[0049] After the fusion is complete, quickly pour the molten liquid into a preheated platinum-gold mold to about 400°C, and allow it to flow and level out naturally.

[0050] Let it cool for about 5 minutes, and after it solidifies, remove a homogeneous, transparent, bubble-free, and unmelted particle glass disc with a diameter of about 32 mm and a thickness of about 3 mm. This glass disc can be used for XRF qualitative confirmation of homogeneity.

[0051] S2: Sample preparation by high-pressure fluoride-free dissolution (preparation of the solution to be tested)

[0052] Carefully transfer the above cooled glass pieces to a clean 100 mL PTFE microwave digestion inner vessel.

[0053] Accurately add 40.0 mL of the pre-prepared working dissolution solution (containing 50 g / L Li2B4O7, 4% HNO3, 1% HC1) using a volumetric flask. Ensure that the glass pieces are completely immersed in the solution.

[0054] Place the PTFE lid on the vessel and place it in the digestion jacket. Tighten the top cap according to the instrument's operating procedure to ensure a seal.

[0055] Place the digestion vessel symmetrically in the carousel of the microwave digestion system. Set the microwave digestion program as follows:

[0056] Step 1: Increase the temperature from room temperature to 180 °C in 5 minutes.

[0057] Step 2: Hold at 180 °C for 15 minutes. The maximum power limit is 800 W and the upper pressure limit is 20 bar.

[0058] Start the program. During the program, monitor the process via the temperature and pressure sensors in the vessel. The process is smooth and no bumping or pressure release occurs.

[0059] After the program is completed, the system automatically cools the vessel to an internal temperature of less than 60 °C. Carefully open the digestion vessel and observe that the solution is completely clear and transparent with no suspended solids or undissolved glass residue. The inner vessel is clean at the bottom.

[0060] Quantitatively transfer all of the solution from the digestion vessel to a 100 mL polypropylene volumetric flask. Wash the inner walls of the digestion vessel and lid with a small amount of ultrapure water three times and add the washings to the volumetric flask.

[0061] Add 1.00 mL of a 10 mg / L yttrium (Y) internal standard working solution to the volumetric flask.

[0062] Finally, dilute to the 100 mL mark with ultrapure water, tightly cap the flask, and invert it several times to mix the solution. This gives the sample solution. At the same time, prepare a blank solution according to the exact same procedure (without adding the sample).

[0063] S3: ICP-AES determination

[0064] Instrument operating parameter optimization: Before analysis, use a solution containing 1 mg / L Y, Mg, Mn, and Cd to optimize the radio frequency power (set to 1150 W), atomization gas flow (set to 0.65 L / min), auxiliary gas flow, observation height, and other parameters of the ICP-AES to achieve the highest and most stable signal-to-background ratio.

[0065] Analysis spectral line selection: According to the principles of element content and avoiding spectral interference, select the analysis spectral lines and internal standard lines listed in the table below.

[0066] Element Analysis line (nm) Element Analysis line (nm) Si 251.611 Ni 231.604 P 178.287 Mo 202.030 Mn 257.610 Cr 267.716 Fe 259.940 Internal standard Y 371.029

[0067] Sample determination: The sample solution and the blank solution were introduced into the ICP-AES in turn. The signal of each solution was read for 3 times, and the average value was taken. The blank value was automatically deducted by the instrument software, and the short-term and long-term drift of the analysis signal was corrected by using the signal of the internal standard Y. The mass concentration (μg / mL) of each element in the sample solution was calculated according to the calibration curve.

[0068] Experimental results and calculation

[0069] Determination results: According to the measured concentration, the sample weight (0.1000 g), and the constant volume (100 mL), the mass fraction (wt%) of each element in the high chromium cast iron standard material was calculated. The results were compared with the standard values as shown in the following table.

[0070] Table 2: Comparison of determination results and standard values of high chromium cast iron standard material

[0071] Element Standard value (wt%) Mean value of three independent measurements (wt%) Recovery rate (%) RSD (%) (n = 3) Cr 25.32 25.35 100.1 0.4 Si 1.15 1.12 97.4 0.8 P 0.032 0.031 96.9 1.5 Mn 0.58 0.57 98.3 0.6 Ni 0.45 0.44 97.8 0.7 Mo 0.21 0.21 100.0 0.5

[0072] Note: Fe is the matrix element, and the determination value is used to confirm the effectiveness of the matrix matching. The specific recovery rate is not listed here, but the calibration curve is linear, indicating that the matrix effect is effectively controlled.

[0073] Example 2:

[0074] This example is basically the same as the previous example, except that after completing the lithium borate fusion sample preparation, instead of using acid or high-pressure equipment, a mixed solution composed of an ammonium salt without hydrofluoric acid and an organic acid complexing agent is used to dissolve the glass pieces under normal pressure heating reflux conditions to prepare the sample solution, and the main and trace elements in the nickel-iron alloy are determined by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0075] Experimental materials and equipment:

[0076] Sample and standard material:

[0077] Sample to be tested: actual nickel-iron alloy production sample (brand: FeNi25).

[0078] Control sample / verification sample: to verify the accuracy of the method, a certified standard material of nickel-based alloy with known composition is processed at the same time.

[0079] Reagents and materials:

[0080] Fusing agent: mixed lithium borate fusing agent. Specifically, lithium metaborate (LiBO2) and lithium tetraborate (Li2B4O7) are pre-mixed uniformly at a mass ratio of 1:1, and then calcined at 500°C to remove water for standby use.

[0081] Dissolving medium (ammonium salt / organic acid complexing agent):

[0082] Ammonium nitrate (NH4NO3) solution: Prepare an aqueous solution with a concentration of 100 g / L.

[0083] Citric acid (C6H8O7·H2O) solution: Prepare an aqueous solution with a concentration of 50 g / L. Citric acid acts as an organic acid complexing agent, providing complexing groups.

[0084] Working solution: Before use, mix the above ammonium nitrate solution and citric acid solution at a volume ratio of 1:1 to obtain a final mixed complex solution containing 50 g / L ammonium nitrate and 25 g / L citric acid. This solution is weakly acidic.

[0085] Acid solution (for subsequent acidification): concentrated nitric acid (HNO3), analytical grade, distilled at sub-boiling point.

[0086] Standard solution and internal standard solution: Same as in Example 1, but the matrix of the standard solution must be matched with a nickel-iron matrix. The internal standard is still yttrium (Y) standard solution.

[0087] Other: Ultrapure water (resistivity ≥18.2MΩ·cm).

[0088] Instruments and equipment:

[0089] Melting sample preparation equipment: Same as in Example 1, or manual melting using a muffle furnace and platinum crucible.

[0090] Dissolving equipment: Atmospheric pressure heating reflux device. Includes: adjustable temperature heating plate (or heating block), 250mL conical flask (made of borosilicate glass or polytetrafluoroethylene), and straight or spherical reflux condenser tubes matched with the conical flask.

[0091] Analytical instrument: Inductively coupled plasma atomic emission spectrometer (ICP-AES), same as in Example 1.

[0092] Auxiliary equipment: 0.0001 g electronic analytical balance, ultrasonic cleaner.

[0093] Experimental steps:

[0094] S1: Melting and Sample Preparation (Glass Slide Preparation)

[0095] Accurately weigh 0.1000g of nickel-iron alloy sample and nickel-based alloy standard material powder (accurate to ±0.0001g) and place them in two clean platinum-gold crucibles.

[0096] Add precisely 0.7000g of the above mixed lithium borate flux (LiBO2:Li2B4O7=1:1) to each crucible. Mix thoroughly with platinum wire (at this point, the mass ratio of sample to flux is 1:7).

[0097] Place the crucible into the high-frequency induction melting furnace. Set the melting program: heat to 1050°C and hold at this temperature for 8 minutes. During melting, the equipment automatically oscillates to ensure thorough mixing.

[0098] After melting, quickly pour the molten liquid into a preheated platinum mold and allow it to cool and solidify. This yields two homogeneous, transparent glass slides. The slides should be smooth, free of crystals and bubbles.

[0099] S2: Sample preparation by atmospheric pressure complexation and heating dissolution (preparation of the test solution)

[0100] Carefully place the cooled glass slides into two 250mL Erlenmeyer flasks.

[0101] Add 50.0 mL of the pre-prepared working solution (containing 50 g / L NH4NO3 and 25 g / L LC6H8O7) to each conical flask. Ensure the glass slide is completely submerged.

[0102] Install a reflux condenser tube at the mouth of the conical flask and connect it to the cooling water supply. Place this device on a preheated thermostatic heating plate (or heating block) at 95±5℃.

[0103] Initiate heating and reflux. Initially, the solution temperature gradually rises, and erosion marks begin to appear on the surface of the glass slide. After approximately 15 minutes of heating, the glass slide gradually thins and cracks. The entire process is maintained at a gentle boiling state (controlled by adjusting the heating power to avoid violent boiling).

[0104] Continue heating, keeping the total heating time at 40 minutes. During this time, gently shake the conical flask 1-2 times to promote dissolution. After 40 minutes, the solution in the conical flask should be completely clear and transparent, with no solid residue at the bottom, and only a very small amount of platinum particles that may have detached from the glass slide due to corrosion (trace corrosion from the molten crucible, which does not affect the determination). These can be removed by subsequent settling or filtration.

[0105] Turn off the heating, remove the heat source, and allow the solution to cool naturally under reflux to below approximately 60°C. Dismantle the reflux device.

[0106] Quantitatively transfer the solution from the conical flask to a 100 mL polypropylene volumetric flask. Wash the conical flask and the inner wall of the lower end of the reflux condenser with a small amount of hot ultrapure water (about 50°C) several times, and add the washing solution to the volumetric flask.

[0107] Add 5.0 mL of concentrated nitric acid to the volumetric flask to acidify it, ensuring the long-term stability of the analyte (especially iron) in the acidic medium and matching the injection medium requirements of ICP-AES.

[0108] Add 1.00 mL of yttrium (Y) internal standard working solution with a concentration of 10 mg / L.

[0109] Finally, dilute to the 100mL mark with ultrapure water, tighten the cap, and shake thoroughly to obtain the test solution. Prepare the procedure blank solution using the same steps (without adding the sample).

[0110] S3: ICP-AES determination

[0111] Instrument operating parameters: Optimized according to Example 1, keeping parameters such as radio frequency power and gas flow rate consistent.

[0112] Spectral line selection for analysis: For nickel-iron alloys, select the main analytical lines listed in the table below. Pay special attention to elements such as Ni, Fe, Cr, Si, P, Cu, and Co.

[0113] Element Analysis line (nm) Element Analysis line (nm) Ni 231.604 P 178.287 Fe 259.940 Cu 324.754 Cr 267.716 Co 228.616 Si 251.611 Internal standard Y 371.029

[0114] Sample determination: Standard series solutions, blank solutions, nickel-based standard test solutions, and actual nickel-iron sample test solutions were sequentially introduced into the ICP-AES. Each solution was measured three times, and the average value was taken. The instrument software automatically performed blank correction and internal standard correction, and calculated the concentration of each element.

[0115] Dissolution process observation: The entire dissolution process was stable. Ammonium nitrate provided ammonium ions (NH4+). + ) and nitrate ions (NO3) - Citric acid provides a carboxylate complexing group. Under heating conditions, NH4+... + It may interact with Li in the glass network through ion exchange. + The reaction occurs, while citric acid complexes the dissolved metal cations (such as Fe). 3+ Ni 2+ (etc.) together promote the disintegration of the silica-borate network. After about 30 minutes, the glass slide was basically dissolved, and a clear solution was finally obtained, proving that the mixed complex solution has an effective dissolving ability for lithium borate glass slides.

[0116] Method accuracy verification:

[0117] The accuracy of the method was verified by analyzing nickel-based alloy standard materials with known compositions. The measurement results were compared with the certified values ​​of the standard materials as follows:

[0118] For nickel-based standard reference materials (such as GBW01654), the recovery rates for the main element Ni were 99.2%, Cr 98.8%, and Fe 100.5%, while the recoveries for trace elements Si, P, and Cu were all between 97% and 102%. This indicates that the dissolution-determination method has reliable accuracy.

[0119] Actual sample measurement results:

[0120] The results of measurements on actual samples of nickel-iron alloy (FeNi25) are as follows (exemplary data):

[0121] Ni: 25.6 wt%; Fe: 71.8 wt% (balance); Cr: 0.12 wt%; Si: 0.45 wt%; P: 0.018 wt%; Cu: 0.08 wt%; Co: 0.05 wt%.

[0122] The results are consistent with those obtained by the factory using X-ray fluorescence spectrometry (XRF) combined with chemical methods to determine Si and P, which are within the error range.

[0123] Precision assessment: Six complete melt-dissolve-determination procedures were independently performed on the same nickel-iron alloy sample, and the relative standard deviation (RSD) of the determination results for each element was calculated. The results showed that the RSD of major elements Ni and Fe was less than 0.5%, and the RSD of trace elements Cr, Si, P, etc. was less than 1.8%, indicating that the method has good repeatability.

[0124] Example 3:

[0125] This embodiment is basically the same as the previous embodiment, except for the experimental materials and equipment:

[0126] Sample: Select a representative low-to-medium alloy steel standard material with a complex composition (such as GBW01395, containing multiple elements such as Cr, Ni, Mo, V, Si, P, and Mn). This sample can sensitively reflect the influence of changes in pretreatment conditions on multi-element determination.

[0127] Reagents:

[0128] Flux: Anhydrous lithium tetraborate (Li2B4O7), treated in the same way as in Example 1.

[0129] Dissolving medium: Same as in Example 1, using an acidic working solution of 50 g / L lithium tetraborate (4% HNO3, 1% HCl).

[0130] Standard solutions and internal standard solutions: A series of multi-element mixed standard solutions with iron matrix matching were prepared, covering the target elements. The internal standard was yttrium (Y) solution.

[0131] Instruments: Same as in Example 1, mainly including a fully automatic high-frequency induction melting furnace, a high-pressure microwave digestion system, an inductively coupled plasma atomic emission spectrometer (ICP-AES), and auxiliary equipment.

[0132] Experimental Design and Procedure

[0133] This experiment consists of three parts: optimization of melt ratio, optimization of dissolution time, and verification of precision.

[0134] Melt ratio optimization experiment

[0135] Experimental design: The melting temperature was fixed at 1150℃, and the melting time was fixed at 10 minutes; the microwave dissolution conditions were fixed at 180℃ for 15 minutes. Only the mass ratio of sample to flux was varied. Four ratio levels were set: 1:5, 1:7, 1:10, and 1:12. Three parallel samples were prepared and analyzed independently for each ratio level.

[0136] Operating steps:

[0137] Accurately weigh several 0.1000g samples of medium and low alloy steel standard (GBW01395).

[0138] According to the set ratio, accurately weigh the corresponding mass of lithium tetraborate flux (0.5000g, 0.7000g, 1.0000g, 1.2000g) and mix it with the sample.

[0139] Following the steps in Example 1, glass sheets were prepared by melting at 1150°C for 10 minutes.

[0140] All glass slides were dissolved using the same microwave digestion procedure (180°C, 15 min) and brought to a final volume of 100 mL (including internal standard).

[0141] The concentrations of each element in the solution were determined using ICP-AES, and the average recovery rate of each element at each ratio was calculated (with reference to the standard reference value).

[0142] Dissolution time optimization experiment

[0143] Experimental design: The melting conditions were fixed at 1:10 for sample to flux, and 1150℃ for 10 minutes. The microwave melting temperature was fixed at 180℃, with only the holding time varied. Four time levels were set: 5 minutes, 10 minutes, 15 minutes, and 20 minutes. Two parallel samples were prepared and analyzed independently at each time point.

[0144] Operating steps:

[0145] Prepare multiple identical glass slides at a ratio of 1:10.

[0146] Place the glass slide into a microwave digestion vessel and add the working solution.

[0147] Set the program in the microwave digester to heat up to 180°C in 5 minutes, and then maintain the temperature at 180°C for 5, 10, 15, and 20 minutes respectively.

[0148] After the procedure, key observation points include: recording the clarity of the solution in each digestion vessel (visually inspect for transparency, undissolved particles, or flocculent matter). Measurements are taken after cooling and bringing the volume to a suitable level.

[0149] The recoveries of each element at different dissolution times were calculated using ICP-AES. Simultaneously, the time point of most complete dissolution was used as a baseline to assess whether incomplete dissolution at shorter times led to lower recoveries.

[0150] Method precision verification experiment

[0151] Condition determination: Based on the experimental results of the first two parts, the optimal melting ratio and dissolution time were selected as the fixed conditions for the precision experiment.

[0152] Operating Procedure: Under the selected optimal conditions, 11 independent complete process analyses were performed on the same low-alloy steel standard material (GBW01395). That is, each process, from sample weighing, melting, dissolution to ICP-AES determination, was completely independent to cover all possible operational random errors.

[0153] Record the mass fraction of each target element in 11 measurements.

[0154] Results of melt ratio optimization: Under different melt ratios, the average recovery rate of representative elements (selecting high-content element Cr and low-content volatile element P as representatives) showed regular changes.

[0155] When the ratio is 1:5, the flux is relatively small. The resulting glass sheet is darker in color and slightly brittle. The element recovery rate, especially the recovery rate of silicon (Si) and phosphorus (P), is slightly low (about 94-96%). This may be due to incomplete melting caused by insufficient flux, or the formation of volatile compounds (such as P2O5) at high temperatures that were not completely captured and fixed by the flux.

[0156] When the ratios were 1:7 and 1:10, the melting process proceeded smoothly, and the glass slides were transparent and uniform. The recoveries of all elements reached the ideal range (98%-102%), and the results were stable with minimal deviation between parallel samples. This indicates that within this ratio range, the flux can both fully decompose the sample and effectively dilute the matrix and stabilize volatile elements.

[0157] When the ratio is 1:12, the recovery rate is still good, but an excessively high dilution ratio will reduce the absolute concentration of the elements in the test solution, which may have an adverse effect on the signal-to-noise ratio of the detection of some trace elements and increase unnecessary reagent costs.

[0158] Conclusion: The experimental results clearly support that the optimal operating range for the sample to flux mass ratio is between 1:7 and 1:10. This verifies the rationality and superiority of the "1:(5~10)" range. A ratio lower than 1:5 may lead to incomplete melting; while a ratio higher than 1:10 is feasible, it is not economically optimal.

[0159] Dissolution time optimization results

[0160] The solution state and recovery rate were observed and measured under different microwave dissolution times.

[0161] Dissolution time 5 minutes: After the program ends, the solution is slightly turbid, and after standing, very fine suspended matter can be seen. The recovery rate of the main elements (Fe, Cr) is not significantly affected, but the recovery rate of silicon (Si) is significantly lower (about 92%), indicating that the silicate network has not been completely destroyed and dissolved.

[0162] Dissolving for 10 minutes: The solution is basically clear and transparent, but a very small amount of adhering material is occasionally visible on the bottle wall. The recovery rate of most elements has reached over 98%, but the recovery rate of Si (about 96%) is still slightly lower than the ideal value, indicating that the dissolution is close to complete but still insufficient.

[0163] Dissolution time 15 minutes and 20 minutes: The solutions were completely clear and transparent, with no visible residue. The recoveries of all elements, including Si and P, remained stable between 98% and 102%, and there was no significant difference between the results at the two time points.

[0164] Conclusion: At a dissolution temperature of 180℃, maintaining the temperature for 10-15 minutes is sufficient for the glass slide to dissolve completely. The range of 5-30 minutes covers a broad spectrum from the minimum necessary time to ensuring complete dissolution. This experiment verifies that selecting an appropriate time (e.g., 10-15 minutes) within this range yields the best dissolution results.

[0165] Method precision validation results

[0166] The precision data of 11 independent determinations of the standard substance under the selected optimal conditions (e.g., melt ratio 1:9, microwave dissolution at 180℃ for 15 minutes) are as follows:

[0167] Major elements (e.g., Cr, ~1% content): The standard deviation of the 11 measurements was very small, and the calculated relative standard deviation (RSD) was 0.3%-0.6%.

[0168] Trace elements (such as Si, Mn, ~0.x% content): relative standard deviation (RSD) is 0.8%-1.5%.

[0169] Trace elements (e.g., P, ~0.01% content): Relative standard deviation (RSD) is 1.8%-2.5%.

[0170] The data above demonstrate that this method exhibits excellent repeatability for elemental determination from major to trace levels. The RSD values ​​fully meet or even exceed the conventional precision requirements of chemical analysis and ICP-AES analysis (typically, major RSD < 1%, trace RSD < 5%).

[0171] Comparative example:

[0172] To ensure fairness and comparability, all methods used the same, fully homogenized high-chromium cast iron national standard material (GBW 01201a) powder, the standard values ​​of which are shown in Table 1 of Example 1. Special attention was paid to the accuracy of determinations of light elements such as silicon (Si) and phosphorus (P), as well as volatile elements and the major element chromium (Cr).

[0173] Overview of Comparison Methods

[0174] Three pretreatment methods were designed, and all subsequent measurements were performed using the same ICP-AES instrument conditions, standard curves, and internal standard method to isolate differences caused by the pretreatment steps.

[0175] Method A (the method of this invention): "Lithium tetraborate melting-microwave high-pressure fluorine-free dissolution method of lithium tetraborate solution". The operation was carried out entirely according to the detailed steps of Example 1: the sample was mixed with Li2B4O4 flux at a ratio of 1:9 and melted at 1150°C for 10 minutes to form a glass slide; it was then dissolved in an acidic solution containing 50 g / L Li2B4O7 by microwave digestion at 180°C for 15 minutes.

[0176] Method B (Conventional Acid Digestion): "Aqua regia open hot plate digestion method". This is one of the most common methods in wet chemical analysis and ICP pretreatment.

[0177] Method C (Conventional Alkali Fusion Method): "Sodium Peroxide Alkali Fusion-Acid Extraction Method". This is a classic method for processing refractory alloys and ore samples, especially when it is necessary to determine total silicon content.

[0178] Detailed operating steps of the comparison method

[0179] Method B: Aqua regia open-top electric heating plate digestion method

[0180] Sample weighing: Accurately weigh 0.1000g of GBW 01201a sample into a 150mL tall beaker.

[0181] Acid digestion: Add 10 mL of concentrated hydrochloric acid, cover with a watch glass, and heat on a hot plate at a low temperature (about 90°C) until the reaction stabilizes (violent bubbling decreases). Then, carefully remove the watch glass and slowly add 3 mL of concentrated nitric acid (forming aqua regia) along the wall of the glass. At this point, the solution reacts violently and may produce brown nitrogen oxide fumes.

[0182] Continue heating: Continue heating at a medium temperature (approximately 120°C) to evaporate the solution to approximately 3 mL, resulting in a wet salt solution. During this process, dehydration of silicic acid (H₂SiO₄) and other components can be observed, forming a white or gel-like precipitate that adheres to the cup wall and bottom.

[0183] Reconstitution and Volume Adjustment: After slightly cooling, add 5 mL of concentrated hydrochloric acid and 20 mL of ultrapure water, and heat to boiling to dissolve the soluble salts. However, the silica precipitate on the walls and bottom of the flask is difficult to completely redissolve, and the solution will be slightly turbid or clearly suspended. After cooling, transfer the solution along with the undissolved residue to a 100 mL volumetric flask. Add 1.00 mL of Y internal standard solution, and adjust the volume to ultrapure water, then mix well. Note: This solution is not completely clear and needs to be filtered or allowed to stand before ICP-AES analysis.

[0184] Safety and environmental concerns: Although the entire process takes place in a fume hood, a significant amount of acid mist and nitrogen oxide gases still escape. Waste acid requires specialized treatment.

[0185] Method C: Sodium peroxide alkali fusion-acid extraction method

[0186] Sample weighing and melting: Accurately weigh 0.1000 g of GBW 01201a sample into a 30 mL nickel crucible. Add 3.0 g of sodium peroxide (Na2O2) and mix thoroughly with a dry glass rod.

[0187] High-temperature melting: Place the crucible in a muffle furnace preheated to 700°C and melt for 10-15 minutes, shaking the crucible once during the process, until the contents are a calm, dark red molten state.

[0188] Extraction and Acidification: Remove the crucible and cool it to lukewarm. Place the entire crucible into a 400mL PTFE beaker containing approximately 80mL of ultrapure water and cover with a watch glass. The reaction is extremely vigorous, releasing a large amount of heat and oxygen, accompanied by a hissing sound. After the reaction subsides, rinse the crucible with dilute hydrochloric acid and water.

[0189] Neutralization and Acidification: At this point, the beaker contains a strongly alkaline solution (containing precipitates such as ferric hydroxide). Under a cold water bath and with thorough stirring, concentrated hydrochloric acid is slowly and gradually added to neutralize and acidify the solution until it becomes strongly acidic (pH < 1). This process generates a large amount of heat and hydrogen chloride gas, and the precipitates of iron hydroxides redissolve. However, this introduces extremely high concentrations of sodium salts (Na₂O₃). + ) and chloride ions (Cl -) matrix.

[0190] Transfer and volume adjustment: Transfer the solution to a 250 mL volumetric flask (due to its large volume), add 2.50 mL of Y internal standard solution, and adjust the volume accordingly. Note: This solution has an extremely high total dissolved solids (TDS), which may exceed the tolerance range of conventional ICP-AES injection systems, easily leading to nebulizer and center tube blockage, and severe long-term memory effect. Secondary dilution is usually required to reduce the concentration of the analyte.

[0191] Comparison and analysis: The test solutions prepared by the three methods were measured under exactly the same ICP-AES analysis conditions. Each method was operated in parallel three times, and the average value was used to calculate the recovery rate. Qualitative observation and comparison were also performed.

[0192] Comparison dimension Method A (the present application) Method B (aqua regia digestion) Method C (sodium peroxide alkali fusion) Operation safety High. Closed microwave digestion, no harmful gas leakage, no use of strong corrosive alkali. Low. Open heating, generating a large amount of acid mist (HCl, HNO3, NOx), not friendly to personnel and environment. Low. Use of strong oxidizing and corrosive sodium peroxide (high-risk chemical), intense exothermic during melting and acidification, high risk, must be operated under special protection. Pretreatment time Short (about 35 min). Melting (10 min) + microwave dissolution (25 min, including temperature rise and fall). Long (≥ 120 min). Requires multiple acid addition, evaporation, reflux, time-consuming and requires personnel to watch over. Long (≥ 90 min). Melting, cooling, extraction, slow neutralization and acidification, complicated steps. Physical state of test solution Clear and transparent, uniform and stable, without any suspended matter or precipitate. Turbid or containing insoluble matter, mainly silicon acid precipitate, resulting in non-uniform test solution, must be filtered, which may introduce loss or contamination. Clear but base concentration extremely high, containing several grams / liter of Na + and Cl - , viscosity and surface tension are abnormal, not friendly to ICP sampling system, usually need to be diluted. Recovery rate of light / easy volatile elements Si: 97.4% P: 96.9% (both close to theoretical value) Si: significantly low (75-85%), loss due to formation of insoluble silicic acid. P: unstable (90-105%), open heating can cause partial P to volatilize as PH3. Si: Good recovery rate (~ 98%), but P may be partially lost due to strong oxidation environment, and the ultra-high sodium salt matrix seriously inhibits the sensitive spectrum line of P (178 nm), resulting in poor detection limit and decreased precision. Matrix effect and instrument adaptability Weak. The complex alloy matrix has been converted into uniform silicate glass during the melting process, and the matrix after dissolution is simple and consistent (mainly Li, B), which is easy to correct through internal standard and matrix matching. Complex. The matrix is chloride / nitrate of Fe, Cr, Ni, etc., with different acidity, and the correction of simultaneous determination of multiple elements is complex. Very strong. The introduction of several grams per liter of NaCl matrix causes serious physical interference (elevated liquid, change of atomization efficiency) and spectral interference, significantly shortens the instrument maintenance period and increases the operating cost. Environmental and vessel impact No fluorine, low reagent consumption, use of general PTFE / PFA vessels. Generation of a large amount of acidic waste liquid containing heavy metals. Generation of a large amount of strong alkaline and high salt waste liquid, corrosion of sewer. Consumption and corrosion of expensive nickel crucible.

[0193] Based on the above systematic comparison, the following conclusions can be drawn:

[0194] The method of the present invention (method A) is not a simple superposition or combination of existing technologies: by combining "lithium borate melting" with "high-pressure dissolution in a specific fluorine-free medium" for the melt product, it fundamentally avoids the inherent defects that traditional methods (B and C) cannot overcome.

[0195] It solves long-standing technical problems by providing a complete solution for high-throughput, safe, accurate, and simultaneous determination of all key elements (from major to trace, including light elements) in ferroalloys, meeting the growing demands of modern industrial analysis for efficiency, security, and data quality.

[0196] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for the analysis of ferroalloys by rapid glass fusion-inductively coupled plasma atomic emission spectrometry, characterized in that, The method comprises the following steps: S1, sample preparation by melting: mixing the sample of the iron alloy to be tested with a lithium borate flux, melting at high temperature, and forming a homogeneous glass sheet after cooling; S2, sample preparation by high-pressure fluorine-free dissolution: placing the glass sheet prepared in step S1 in a dissolution medium containing no hydrofluoric acid, heating and dissolving under a closed high-pressure condition to obtain a clear and transparent solution to be tested; S3, ICP-AES determination: using the solution to be tested prepared in step S2, correcting by using an internal standard method and / or a matrix matching technique, and determining the content of each element in the iron alloy by using an inductively coupled plasma atomic emission spectrometer.

2. A method for the analysis of ferroalloys by rapid glass fusion-inductively coupled plasma atomic emission spectrometry according to claim 1, characterized in that, The dissolution medium containing no hydrofluoric acid is a lithium tetraborate solution or a mixed solution composed of an ammonium salt and an organic acid complexing agent.

3. A method for the rapid analysis of ferroalloys by the glass fusion method-inductively coupled plasma atomic emission spectrometry according to claim 2, characterized in that, When the dissolution medium is a lithium tetraborate solution, step S2 is performed in a high-pressure microwave digestion system.

4. A method for the rapid analysis of ferroalloys by the glass fusion method-inductively coupled plasma atomic emission spectrometry according to claim 2, characterized in that, The ammonium salt is ammonium nitrate or ammonium chloride, and the organic acid complexing agent is citric acid, tartaric acid or EDTA.

5. A method for the rapid analysis of ferroalloys by the glass fusion method-inductively coupled plasma atomic emission spectrometry according to claim 1, characterized in that, The lithium borate flux is lithium tetraborate, lithium metaborate or a mixture thereof in any ratio.

6. A method for the rapid analysis of ferroalloys by the glass fusion method-inductively coupled plasma atomic emission spectrometry according to claim 1, characterized in that, In step S1, the mixing mass ratio of the sample of the iron alloy to the lithium borate flux is 1: (5-10); the melting temperature is 950-1200℃, and the melting time is 5-20 minutes.

7. A method for the rapid analysis of ferroalloys by glass fusion-inductively coupled plasma atomic emission spectrometry according to claim 1, characterized in that, In step S2, the heating and dissolving temperature is 120-220℃, and the dissolving time is 5-30 minutes.

8. A method for the rapid analysis of ferroalloys by the glass fusion method-inductively coupled plasma atomic emission spectrometry according to claim 1, characterized in that, The method is used for determining major elements and / or trace elements in the iron alloy, wherein the major elements include one or more of iron, nickel and chromium, and the trace elements include one or more of silicon, phosphorus, manganese, molybdenum and vanadium.

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