A method for analyzing the content of impurity elements in a neodymium iron boron material by fusion sample preparation-X-ray fluorescence spectrometry

Abstract

The application specifically relates to a method for analyzing the content of impurity elements in a neodymium iron boron material by a fusion sample preparation-X-ray fluorescence spectrometry, and belongs to the technical field of analytical chemistry and material detection. The method comprises the following steps: after grinding, a sample is pre-fused in a platinum-gold crucible by using anhydrous lithium tetraborate to form a protective layer; lithium carbonate is added as an oxidant and vanadium pentoxide is added as an internal standard, and after pre-oxidation in stages, the sample is high-temperature fused to prepare a glass sheet; under optimized instrument conditions, a working curve is established by using a series of standard fusion sheets, a to-be-measured fusion sheet is measured, and the content of each element is calculated. Through the synergistic technology of the "flux protective layer-dry pre-oxidation-internal standard correction", two major problems of corrosion of active metals on the crucible and correction of the complex matrix effect are solved, and 10 kinds of elements such as Al, Cu, Co, Ga, Dy and Tb can be simultaneously and accurately measured. The method is safe in operation, high in efficiency and good in reproducibility, and is suitable for quality control and composition analysis of a neodymium iron boron permanent magnet material.

Description

Technical Field

[0001] This invention belongs to the field of analytical chemistry and materials testing technology, specifically relating to a method for analyzing the content of impurity elements in neodymium iron boron materials using fusion sample preparation-X-ray fluorescence spectrometry. Background Technology

[0002] Neodymium iron boron (NdFeB) is currently the most powerful permanent magnet material, and precise control of its chemical composition is crucial to ensuring its magnetic properties and long-term stability. However, NdFeB materials have a complex composition, containing high levels of various rare earth elements and iron and boron matrices, as well as trace impurities, posing a significant challenge to rapid and accurate analysis of its chemical composition. Analytical methods for NdFeB materials generally employ classical chemical methods, inductively coupled plasma atomic emission spectrometry (ICP-AES), and X-ray fluorescence spectrometry-filter paper methods. Classical chemical methods are cumbersome, time-consuming, and inefficient, failing to meet the demands of rapid industrial testing. While ICP-AES can achieve simultaneous multi-element determination, it faces challenges such as difficult sample digestion, severe interference from rare earth element spectral lines, and significant matrix effects, leading to inconsistent accuracy and complex pretreatment processes. X-ray fluorescence spectrometry (XRF) using filter paper methods or powder compression methods suffers from inherent defects such as sample inhomogeneity, instrument corrosion, and the inability to eliminate mineral and particle size effects, limiting analytical precision.

[0003] Melt preparation is considered an ideal pretreatment method for high-precision XRF analysis, as it transforms the sample into a homogeneous glassy state, completely eliminating the influence of particle size, mineral composition, and surface condition. However, applying melt preparation to highly reactive alloy materials like NdFeB faces two major technical bottlenecks: First, the risk of crucible corrosion: when the metallic elements in the sample melt at high temperatures, they can form a eutectic alloy with expensive platinum (or platinum-gold alloy) crucibles, leading to rapid corrosion or even crucible breakdown. Second, the difficulty in correcting complex matrix effects: the NdFeB matrix is ​​complex, with strong absorption-enhancement effects between elements, making it difficult for traditional calibration models to stably and accurately correct multiple elements from trace to major amounts simultaneously. While there are reports of using wet oxidation methods such as nitric acid for other alloy materials, directly applying these methods to NdFeB results in incomplete oxidation, lengthy processes, the introduction of interference, and potential corrosion risks, failing to provide a complete, reliable, and crucible-protective solution. Summary of the Invention

[0004] To address the technical problems of cumbersome procedures, poor accuracy, high risk, and low efficiency in existing methods for analyzing the chemical composition of NdFeB materials, this invention aims to provide a method for analyzing the content of impurity elements in NdFeB materials using fusion sample preparation and X-ray fluorescence spectrometry. This method successfully solves the problems of crucible corrosion risk and complex matrix effect correction in NdFeB fusion sample preparation by employing an innovative "solid lithium carbonate dry pre-oxidation" technique and a unique "vanadium pentoxide internal standard method." It achieves rapid, accurate, and stable simultaneous determination of elements such as aluminum, copper, cobalt, gallium, dysprosium, terbium, neodymium, praseodymium, niobium, and zirconium.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention discloses a method for analyzing the content of impurity elements in neodymium iron boron materials using melt-sample preparation-X-ray fluorescence spectrometry, comprising the following steps:

[0007] (1) Sample preparation: Grind the neodymium iron boron sample until it passes through a 200-mesh sieve;

[0008] (2) Crucible bottom preparation: Add anhydrous lithium tetraborate and release agent to the platinum-gold crucible, melt at high temperature and rotate to form a protective layer that evenly covers the inner wall of the crucible, and then cool;

[0009] (3) Pre-oxidation and melting sample preparation: Place the sample obtained in step (1) in a crucible with a bottom, add the oxidant lithium carbonate and the internal standard reagent vanadium pentoxide, mix and cover with anhydrous lithium tetraborate and release agent, then carry out the pre-oxidation and melting process to obtain glass flakes;

[0010] (4) X-ray fluorescence spectroscopy analysis: Using neodymium iron boron standard samples, standard fused plates are prepared according to steps (1)-(3), and working curves for aluminum, copper, cobalt, gallium, dysprosium, terbium, neodymium, praseodymium, niobium and zirconium are established. The standard fused plates are measured under the same conditions as the working curves are established, and the content of each element is calculated.

[0011] Preferably, in step (2), the amount of anhydrous lithium tetraborate used is 6-8 g, the high temperature melting temperature is 950-1050℃, and the high temperature melting time is 8-15 min.

[0012] In step (2), anhydrous lithium tetraborate is used as a flux and laid at the bottom of the crucible. Its primary function is to form a physical isolation layer during the pre-oxidation stage, preventing the active metal sample from directly contacting the platinum crucible, thereby effectively avoiding alloying corrosion and protecting the expensive crucible from damage. The melting point of anhydrous lithium tetraborate is 917℃, so the selected heating temperature must be higher than this value (usually set in the range of 950–1050℃) to ensure complete melting and good fluidity. Experiments show that 1000℃ is a relatively ideal heating temperature. Heating at this temperature for 8–15 minutes (preferably 10 minutes) allows the flux to fully transform into a fluid state. To improve the spreadability and film-forming effect of the melt, a small amount of lithium bromide solution is added as a flux before melting, which can significantly enhance the fluidity of molten lithium tetraborate, allowing it to quickly and evenly cover about 2 / 3 of the inner wall height when the crucible is rotated, forming a dense and complete protective layer after cooling.

[0013] The present invention uses anhydrous lithium tetraborate as the main flux, based on systematic experimental verification: this flux can not only ensure that the sample melts completely at high temperature, but also form a glass slide with high transparency and uniform texture; at the same time, each element to be measured can obtain a sufficiently strong X-ray fluorescence signal in this matrix, laying the foundation for subsequent high-precision quantitative analysis.

[0014] In some embodiments, the amount of anhydrous lithium tetraborate used is 7 g, the high-temperature melting temperature is 1000°C, and the high-temperature melting time is 10 min.

[0015] Preferably, in step (3), the mass ratio of lithium carbonate to the sample is (4.5-5.5):1; and the mass ratio of vanadium pentoxide to the sample is (0.4-0.6):1.

[0016] In step (3), the addition of lithium carbonate as a solid oxidant is crucial. Its role is to react with the elemental metal in the NdFeB during the pre-oxidation stage, fully converting it into a stable oxide, thereby preventing the active metal from corroding the platinum crucible during the subsequent high-temperature melting process. Experiments have verified that controlling the mass ratio of lithium carbonate to the sample within the range of (4.5–5.5):1 (preferably 5:1) ensures complete oxidation while avoiding the introduction of excessive alkali metals that could interfere with the melt properties. If the ratio is too low, incomplete oxidation may occur; if the ratio is too high, it may affect the uniformity of the melt or increase background interference.

[0017] Meanwhile, vanadium pentoxide is introduced as an internal standard reagent to correct systematic deviations caused by weighing errors, fluctuations in the melting process, and changes in instrument conditions. The mass ratio of vanadium pentoxide to the sample should preferably be maintained in the range of (0.4–0.6):1 (preferably 0.5:1). This ratio ensures that the internal standard element is uniformly distributed in the melt and that the signal is stable, while avoiding the influence of excessive content on the matrix effect or the spectral lines of the analyte.

[0018] Preferably, the release agent is a lithium bromide solution. Lithium bromide can effectively reduce the adhesion between the melt and the crucible wall at high temperatures, significantly improving the demolding effect of the molten glass sheet, thereby obtaining a smooth surface, intact edges, and easy-to-remove molten sheet, while avoiding the corrosion of the crucible by melt residue.

[0019] Preferably, in step (3), the pre-oxidation procedure is as follows: starting from room temperature, the temperature is increased to 450°C within 30 min and held for 10 min, then increased to 850°C within 10 min and held for 30 min. This temperature range is the key stage for the solid-phase oxidation reaction between lithium carbonate and the metal components. Sufficient holding time ensures that the active metals (especially iron and rare earth elements) in NdFeB are completely and stably converted into oxides, laying a safe foundation for subsequent high-temperature melting.

[0020] Preferably, the melting process is as follows: melting temperature is 1050-1200℃, mixing time is 350-380 s, rocking time is 350-380 s, and cooling time is 240 s.

[0021] The melting stage is conducted in a high-temperature range of 1050-1200℃ (preferably 1150℃). At this temperature, the pre-oxidized sample and flux form a homogeneous and transparent melt. To ensure thorough mixing of the components, the mixing and shaking times are each set to 350-380 seconds (preferably 360 seconds). This dynamic melting process effectively eliminates microbubbles, promotes uniform distribution of internal standard elements, and reduces potential elemental segregation. After melting, controlled cooling for 240 seconds forms a structurally stable, stress-free glass flake, meeting the stringent requirements of XRF analysis for sample homogeneity and consistency.

[0022] Preferably, in step (4), the measurement conditions of the X-ray fluorescence spectrometer include:

[0023] Aluminum (Al) element: voltage 30 kV, current 120 mA, 2θ angle 144.8920°, measurement time 20 s;

[0024] Copper (Cu) element: voltage 60 kV, current 60 mA, 2θ angle 65.4988°, measurement time 12 s;

[0025] Cobalt (Co) element: voltage 60 kV, current 60 mA, 2θ angle 77.8466°, measurement time 12 s;

[0026] Gallium (Ga) element: voltage 60 kV, current 60 mA, 2θ angle 56.1448°, measurement time 12 s;

[0027] Dysprosium (Dy) element: voltage 60 kV, current 60 mA, 2θ angle 84.1846°, measurement time 12 s;

[0028] Terbium (Tb) element: voltage 60 kV, current 60 mA, 2θ angle 84.8744°, measurement time 12 s;

[0029] Neodymium (Nd) element: voltage 40 kV, current 90 mA, 2θ angle 112.7228°, measurement time 12 s;

[0030] Praseodymium (Pr) element: voltage 60 kV, current 60 mA, 2θ angle 105.0020°, measurement time 12 s;

[0031] Niobium (Nb): Voltage 60 kV, current 60 mA, 2θ angle 30.3564°, measurement time 12 s;

[0032] Zirconium (Zr) element: voltage 60 kV, current 60 mA, 2θ angle 32.1074°, measurement time 12 s.

[0033] After the molten sheet is prepared, XRF detection and quantitative analysis must be performed according to the following standardized procedure:

[0034] Preparation of standard series: Select a set of NdFeB standard samples with known chemical composition and gradient distribution, and prepare corresponding standard glass flakes in strict accordance with the aforementioned melting sample preparation process to construct a calibration system;

[0035] Spectral data acquisition: Under the pre-optimized operating conditions of the X-ray fluorescence spectrometer (including tube voltage, tube current, analytical crystal, collimator, 2θ angle, and counting time, etc.), the characteristic X-ray fluorescence intensity of the target element in each standard fused sheet was measured.

[0036] Establishment of working curves: Plot the standard content value of each element on the x-axis and the net intensity of the corresponding element in the XRF spectrum (or the ratio of the intensity to the characteristic intensity of the internal standard element vanadium) on the y-axis, perform linear or quadratic fitting, and plot the calibration working curve of each element to be measured.

[0037] Unknown sample determination and quantification: Under identical instrument conditions, the fused sheet of the NdFeB sample to be tested is measured to obtain the characteristic X-ray intensity (or intensity ratio) of each element, and the mass fraction is calculated by substituting it into the working curve of the corresponding element, thus realizing multi-element synchronous quantitative analysis.

[0038] In some embodiments, the platinum-gold crucible is an alloy crucible of 95% Pt and 5% Au.

[0039] Secondly, the present invention discloses a combined reagent for analyzing NdFeB materials for carrying out the aforementioned method, comprising:

[0040] Flux and protective layer material: anhydrous lithium tetraborate, whose functions include serving as a sample melting matrix, forming a protective layer on the inner wall of the crucible to prevent corrosion, and promoting the formation of uniform and transparent glass flakes;

[0041] Solid oxidant: Lithium carbonate, used to convert the metal components in NdFeB into stable oxides during the pre-oxidation stage, thus avoiding damage to the crucible during the melting process;

[0042] Internal standard reagent: Vanadium pentoxide, used as an internal standard for quantitative analysis, can correct systematic errors in sample preparation and measurement processes;

[0043] Release agent: Lithium bromide solution, used to improve melt flowability and release effect of molten sheet.

[0044] Thirdly, this invention discloses the application of the aforementioned method in the quality control of NdFeB permanent magnet material production or in product composition analysis.

[0045] Specifically, it includes, but is not limited to: raw material inspection upon arrival, monitoring of intermediate products in the process, and analysis of finished products upon delivery; new material formulation development, component optimization, and product quality evaluation; and component comparison and consistency verification of NdFeB materials of different batches and specifications.

[0046] With its high efficiency, accuracy, and simultaneous multi-element analysis, this method can provide reliable technical support for the quality control of NdFeB permanent magnet materials throughout their entire life cycle.

[0047] Compared with the prior art, the present invention has the following significant advantages and beneficial effects:

[0048] (1) This invention solves the crucible corrosion problem in NdFeB melting sample preparation: by combining the strategy of “flux pre-coating protective layer” and “solid dry pre-oxidation of lithium carbonate”, the active metal element is completely converted into stable oxide under mild conditions, which completely avoids the direct reaction between the sample and the crucible, perfectly protects the expensive platinum-gold vessel and reduces the analysis cost.

[0049] (2) In this invention, vanadium pentoxide is introduced as an internal standard element. The internal standard method effectively corrects the systematic errors caused by weighing error, slight inhomogeneity of the molten sheet and instrument drift, and significantly improves the analytical accuracy and long-term stability.

[0050] (3) This invention establishes a complete and optimized parameter system from sample preparation to detection. An ideal glass slide for XRF analysis can be obtained through one-time melting sample preparation. Combined with optimized XRF measurement conditions, it is possible to simultaneously determine 10 elements such as Al, Cu, Co, Ga, Dy, Tb, Nd, Pr, Nb, and Zr within a few minutes, and the measurement results have high precision.

[0051] (4) The method of this invention has a clear process, well-defined parameters, and good reproducibility. The reagents used (lithium tetraborate, lithium carbonate, lithium bromide, and vanadium pentoxide) are all common chemical reagents that are safe and readily available. The equipment used (muffle furnace, melting furnace, and XRF spectrometer) are all standard equipment used in analytical laboratories. Attached Figure Description

[0052] Figure 1 This is a working curve diagram of element Al in an embodiment of the present invention;

[0053] Figure 2 This is a working curve diagram of element Cu in an embodiment of the present invention;

[0054] Figure 3 This is a working curve diagram of element Co in an embodiment of the present invention;

[0055] Figure 4 This is a working curve diagram of element Ga in an embodiment of the present invention;

[0056] Figure 5 This is a working curve diagram of element Dy in an embodiment of the present invention;

[0057] Figure 6 This is a working curve diagram of element Tb in an embodiment of the present invention;

[0058] Figure 7 This is a working curve diagram of element Nd in an embodiment of the present invention;

[0059] Figure 8 This is a working curve diagram of element Pr in an embodiment of the present invention;

[0060] Figure 9 This is a working curve diagram of element Nb in an embodiment of the present invention;

[0061] Figure 10 This is a working curve diagram of element Zr in an embodiment of the present invention.

[0062] In the attached figure, the vertical axis “V” represents the internal standard element vanadium. Detailed Implementation

[0063] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0064] After reading the contents disclosed in this invention, those skilled in the art can make appropriate adjustments or substitutions to the process parameters of the methods and applications described in this invention without departing from the spirit and scope of this invention. Such obvious adjustments, substitutions or combinations should be included within the protection scope of this invention.

[0065] Unless otherwise specified, the materials, reagents, instruments and testing methods used in the following embodiments can be obtained commercially or prepared, operated and implemented with reference to conventional methods disclosed in the art.

[0066] It should be noted that all technical parameters described in this document as numerical ranges (such as temperature, ratio, time, content, etc.) should be understood as encompassing all possible sub-ranges and specific numerical points within that range, regardless of whether the specific numerical value or sub-range is explicitly listed. Unless otherwise specified, the technical terms used in this document have the meanings commonly understood by those skilled in the art.

[0067] The neodymium iron boron standard materials / samples (such as 1#-9#) used in this invention were purchased from Baotou Rare Earth Research Institute / Beijing Zhongke Sanhuan High-Tech Co., Ltd.

[0068] All reagents used in this invention are commercially available analytical grade or higher, and their specific sources are as follows:

[0069] Lithium tetraborate (Li₂B₄O₇), superior grade, purchased from Luoyang Tainaike High Temperature Instrument Equipment Co., Ltd.; Lithium carbonate (Li₂CO₃), superior grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Lithium bromide (LiBr), superior grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Vanadium pentoxide (V₂O₅), purity ≥99.99%, purchased from Steel Research Nake Testing Technology Co., Ltd.

[0070] The instruments and equipment used in this invention are all commercially available general-purpose analytical instruments, specifically sourced as follows:

[0071] The platinum-gold crucible, composed of 95wt% Pt + 5wt% Au, with a capacity of 50mL; the electronic analytical balance, with a range of 120g and a graduation of 0.0001g, was purchased from Mettler Toledo; the box-type muffle furnace was purchased from Tianjin Zhonghuan Electric Furnace Co., Ltd.; the fully automatic high-temperature melting furnace was purchased from Luoyang Hainan Testing Instrument Co., Ltd.; and the wavelength dispersive X-ray fluorescence spectrometer, with an end-window Rh target X-ray tube and a rated power ≥4kW, was purchased from Malvern Panaco Zetium.

[0072] The manufacturers and models of reagents, materials, and instruments listed above are merely illustrative and not intended to limit the scope of this invention. This invention can also be implemented using reagents and equipment from other brands or models with equivalent performance specifications.

[0073] Example 1: An analytical method for analyzing the impurity element content in NdFeB materials using melt-preparation X-ray fluorescence spectrometry.

[0074] 1. Melting preparation of NdFeB samples.

[0075] Step 1: Grind the neodymium iron boron standard sample until it all passes through a 200-mesh sieve (approximately 74 μm) and mix thoroughly.

[0076] Step 2: Weigh 7.0000 g of anhydrous lithium tetraborate into a platinum-gold crucible, add 5 drops of lithium bromide solution, and heat in a muffle furnace at 1000℃ for 10 min until the lithium tetraborate is completely melted and in a fluid state. Rapidly rotate the crucible to evenly cover about 2 / 3 of the inner wall with the melt, and cool to room temperature.

[0077] Step 3: Accurately weigh 0.3000 g of NdFeB standard sample powder and place it in a pre-lined crucible. Add 1.5000 g of lithium carbonate (oxidant) and 0.1500 g of vanadium pentoxide (internal standard) sequentially, and gently stir with a fine glass rod. Then cover with 2.0000 g of anhydrous lithium tetraborate and add 5 drops of lithium bromide solution.

[0078] Step 4: Place the crucible into the fully automatic melting furnace and set the pre-oxidation and melting programs as follows:

[0079] Pre-oxidation stage: Increase from room temperature for 30 min to 450℃ and hold for 10 min; then slowly increase to 850℃ and hold for 30 min.

[0080] Melting stage: Heat to 1150℃, mix for 360 s, shake for 360 s, and cool for 240 s.

[0081] After the program is completed, remove the crucible, cool it to obtain a smooth, transparent, uniform, bubble-free molten glass sheet, label it and store it in a desiccator.

[0082] 2. Determination by X-ray fluorescence spectrometry (XRF).

[0083] Step 1: Select nine NdFeB standard samples with known and accurate compositions (numbered 1# to 9#), and prepare standard fused glass slides according to the above-described melting sample preparation process. The elemental contents of each standard sample are shown in Table 1.

[0084] Table 1. Element content of standard samples (unit: mass fraction / %)

[0085]

[0086] Step 2: Based on the atomic number and spectral characteristics of the elements to be measured (Nb, Zr, Ga, Cu, Co, Dy, Tb, Nd, Pr, Al), XRF measurements are performed according to the optimized conditions in Table 2. Using the known mass fraction of each element as the abscissa and the relative signal intensity ratio as the ordinate, linear or quadratic curve fitting is performed to plot the working curves for each element (e.g., ...). Figure 1-10 As shown in Table 3, the regression coefficients of the working curves for each element are shown in Table 3, and their linear regression coefficients (R²) are also shown in Table 3. 2 The results show that the standard glass slides prepared using the method described in this embodiment exhibit good linearity in compositional response, confirming the high accuracy and reliability of this method in the analysis of NdFeB impurity elements.

[0087] Table 2 Working conditions of each element

[0088]

[0089] Table 3 Regression coefficients of each element's working curve

[0090]

[0091] Example 2: Accuracy and precision determination of analytical methods for impurity element content in NdFeB materials

[0092] (1) Accuracy determination: A neodymium iron boron standard substance was selected, and its standard value was known. The method of Example 1 of this invention was used to independently determine the value 6 times, and the average measured value was calculated and compared with the standard value. The results are shown in Table 4: the measured value and the standard value are in good agreement, and the relative error of each element is within the acceptable range, which proves the accuracy of the method of this invention.

[0093] Table 4. Accuracy verification results of the method of the present invention (quality fraction / %)

[0094]

[0095] (2) Precision determination: Two NdFeB standard samples with different compositions (1# and 2#) were selected, and seven fused plates were prepared and measured independently according to the method of Example 1 of this invention. The average value, standard deviation (SD), and relative standard deviation (RSD%) of each element were calculated, and the results are summarized in Table 5. The results in Table 5 show that for major elements (such as Nd) and most impurity elements, the RSD% is less than 2%, and for some elements it is even less than 1%, indicating that the method of this invention has excellent reproducibility and precision.

[0096] Table 5 Precision verification results of the method of the present invention

[0097]

[0098] Comparative Example 1

[0099] The difference between this comparative example and Example 1 is that 1.5000 g of lithium nitrate was used as the oxidant in the melting and sample preparation process of the NdFeB sample, while the other steps were the same as in Example 1.

[0100] Comparative Example 2

[0101] The difference between this comparative example and Example 1 is that in the melting and preparation of the NdFeB sample, 1 mL of 50% nitric acid solution was used as the oxidant, and the pre-oxidation temperature was set to 140°C. The remaining steps are the same as in Example 1.

[0102] By observing the same molten glass sheets prepared using Example 1, Comparative Example 1, and Comparative Example 2, the results (data detailed in Table 6) show that only when lithium carbonate is used as the oxidant (Example 1) can the NdFeB sample be fully oxidized at 850°C, resulting in a high-quality glass sheet with uniform texture, high transparency, and no bubbles, effectively protecting the valuable platinum-gold crucible from corrosion. This result highlights the non-obviousness of the dry oxidation technique using lithium carbonate in this invention and its significant technical advantages.

[0103] Table 6 Comparison of the effects of pre-oxidation with different oxidants

[0104]

[0105] Comparative Example 3

[0106] This comparative example aims to verify the impact of internal standard use on the performance of the analytical method. The difference from Example 1 lies in the setup of two experimental groups: the first group did not add any internal standard during the fusion sample preparation process (denoted as the "no internal standard group"), while the second group strictly followed the method of Example 1 of this invention, adding vanadium pentoxide as an internal standard (denoted as the "internal standard group"). Using the same set of standard samples, working curves for each element were established based on the two sets of conditions, and their linear fit was evaluated; simultaneously, multiple repeated measurements were performed on the same actual sample to compare the precision differences between the two methods.

[0107] Table 7. The impact of the internal standard method on regression coefficients.

[0108]

[0109] Table 8. Effect of Internal Standard Method on Precision

[0110]

[0111] The results in Tables 7 and 8 show that the addition of vanadium pentoxide as an internal standard generally improved the linear correlation of the working curves for each element, while significantly improving the precision of repeated measurements, with RSD decreasing by 25% to 65%. This fully demonstrates that the use of vanadium pentoxide as an internal standard in this invention can effectively correct for fluctuations during the melting and measurement processes, thereby improving the reproducibility and reliability of the analytical method.

[0112] Comparative Example 4

[0113] To comprehensively evaluate the reliability of the method of this invention, the fused sample preparation-X-ray fluorescence spectrometry (XRF) method established in this invention was compared with the inductively coupled plasma atomic emission spectrometry (ICP-AES) widely used in the industry. Two actual NdFeB samples (denoted as No. 10# and No. 11#) were selected, and the above two methods were used for determination. The fused sample preparation-X-ray fluorescence spectrometry (XRF) method followed the experimental steps of Example 1. The specific steps of the inductively coupled plasma atomic emission spectrometry (ICP-AES) method are as follows:

[0114] For NdFeB samples, the corresponding mass needs to be weighed according to different percentage contents, dissolved in aqua regia until clear, and then diluted to the corresponding volumetric flask. The content of each impurity is then determined by inductively coupled plasma atomic emission spectrometry.

[0115] Table 9 Comparison of the determination results of the two methods (%)

[0116]

[0117] The results are shown in Table 9. The XRF determination results of this invention are in high agreement with those obtained by ICP-AES, and the differences in the content of each element are all within the reasonable error range of conventional analytical methods. This indicates that the method of this invention is comparable to the ICP-AES method in terms of accuracy and can be used for routine chemical composition analysis of NdFeB materials. In addition, compared with the ICP-AES method, this method has significant advantages in terms of analytical efficiency, simultaneous determination of multiple elements, and avoidance of spectral interference.

[0118] In summary, this invention successfully constructs a complete, efficient, and accurate fusion sample preparation-XRF analysis method for NdFeB materials by organically combining three core technologies: "flux protection layer," "lithium carbonate dry pre-oxidation," and "vanadium pentoxide internal standard method." This method effectively overcomes two major technical challenges: crucible corrosion and complex matrix correction. It boasts advantages such as safe operation, reliable results, high throughput, and low cost, providing a powerful analytical tool for the quality control of NdFeB materials.

Claims

1. A method for analyzing the content of impurity elements in NdFeB materials using fusion-X-ray fluorescence spectrometry, characterized in that, Includes the following steps: (1) Sample preparation: Grind the neodymium iron boron sample until it passes through a 200-mesh sieve; (2) Crucible bottom preparation: Add anhydrous lithium tetraborate and release agent to the platinum-gold crucible, melt at high temperature and rotate to form a protective layer that evenly covers the inner wall of the crucible, and then cool; (3) Pre-oxidation and melting sample preparation: Place the sample obtained in step (1) in a crucible with a bottom, add the oxidant lithium carbonate and the internal standard reagent vanadium pentoxide, mix and cover with anhydrous lithium tetraborate and release agent, then carry out the pre-oxidation and melting process to obtain glass flakes; (4) X-ray fluorescence spectroscopy analysis: Using neodymium iron boron standard samples, standard fused plates are prepared according to steps (1)-(3), and working curves for aluminum, copper, cobalt, gallium, dysprosium, terbium, neodymium, praseodymium, niobium and zirconium are established. The standard fused plates are measured under the same conditions as the working curves are established, and the content of each element is calculated.

2. The method according to claim 1, characterized in that, In step (2), the amount of anhydrous lithium tetraborate used is 6-8 g, the high temperature melting temperature is 950-1050℃, and the high temperature melting time is 8-15 min.

3. The method according to claim 1, characterized in that, In step (3), the mass ratio of lithium carbonate to the sample is (4.5-5.5):1; the mass ratio of vanadium pentoxide to the sample is (0.4-0.6):

1.

4. The method according to claim 1, characterized in that, The release agent is a lithium bromide solution.

5. The method according to claim 1, characterized in that, In step (3), the pre-oxidation procedure is as follows: starting from room temperature, the temperature is raised to 450°C within 30 min and held for 10 min, and then raised to 850°C within 10 min and held for 30 min.

6. The method according to claim 1, characterized in that, The melting process is as follows: melting temperature is 1050-1200℃, mixing time is 350-380 s, rocking time is 350-380 s, and cooling time is 240 s.

7. The method according to claim 1, characterized in that, In step (4), the measurement conditions of the X-ray fluorescence spectrometer include: Aluminum (Al) element: voltage 30 kV, current 120 mA, 2θ angle 144.8920°, measurement time 20 s; Copper (Cu) element: voltage 60 kV, current 60 mA, 2θ angle 65.4988°, measurement time 12 s; Cobalt (Co) element: voltage 60 kV, current 60 mA, 2θ angle 77.8466°, measurement time 12 s; Gallium (Ga) element: voltage 60 kV, current 60 mA, 2θ angle 56.1448°, measurement time 12 s; Dysprosium (Dy) element: voltage 60 kV, current 60 mA, 2θ angle 84.1846°, measurement time 12 s; Terbium (Tb) element: voltage 60 kV, current 60 mA, 2θ angle 84.8744°, measurement time 12 s; Neodymium (Nd) element: voltage 40 kV, current 90 mA, 2θ angle 112.7228°, measurement time 12 s; Praseodymium (Pr) element: voltage 60 kV, current 60 mA, 2θ angle 105.0020°, measurement time 12 s; Niobium (Nb): Voltage 60 kV, current 60 mA, 2θ angle 30.3564°, measurement time 12 s; Zirconium (Zr) element: voltage 60 kV, current 60 mA, 2θ angle 32.1074°, measurement time 12 s.

8. The method according to claim 1, characterized in that, The platinum-gold crucible is an alloy crucible of 95% Pt and 5% Au.

9. A combined reagent for analyzing NdFeB materials for carrying out the method according to any one of claims 1-8, characterized in that, include: Anhydrous lithium tetraborate as a flux and protective layer material, lithium carbonate as an oxidant, vanadium pentoxide as an internal standard reagent, and lithium bromide solution as a release agent.

10. The application of the method according to any one of claims 1-8 in the quality control of neodymium iron boron permanent magnet material production or product composition analysis.

Images