Trace detection method for iron element in silicon monoxide

Abstract

The invention belongs to the technical field of detection of metal elements in a silicon-based negative electrode material, and particularly relates to a trace detection method of an iron element in silicon monoxide, which comprises the following steps: digesting a silicon monoxide sample by using a digestion solution composed of nitric acid and hydrofluoric acid through a proper microwave digestion procedure to fully release the Fe element, and carrying out ICP-OES on-machine detection, so that the trace detection of the iron element in the silicon monoxide sample is realized. Meanwhile, excessive Fe impurities are prevented from being introduced into the system, standard curves are constructed for Fe standard working solutions with different concentration gradients based on ICP-OES, and the content of the Fe element in the silicon monoxide sample is obtained through calculation, the detection method has excellent stability and precision, the Fe element with the content smaller than 1 ppm can be accurately quantified, the trace detection requirement of Fe in silicon monoxide is met, and the method is suitable for large-scale popularization and application. And the method shows good renewal performance in different operators and different laboratories, and has good universality.

Description

Technical Field

[0001] The present invention belongs to the field of new energy, and relates to the technical field of metal element detection in silicon-based negative electrode materials, and specifically to a method for detecting trace amounts of iron in silicon oxide. Background Art

[0002] With the vigorous development of the new energy industry, lithium-ion batteries are gradually developing towards higher energy density and longer cycle life. The theoretical capacity of existing graphite anodes is only 372 mAhg -1 , which can no longer meet the future demand for battery energy density. Silicon-based anodes are gradually becoming the next generation of lithium battery anode materials that can replace graphite due to their high theoretical specific capacity (1600-2400mAhg -1 ) and good cycle performance. Silicon oxide has the advantages of abundant reserves, environmental friendliness, simple preparation compared to nano-silicon, and low cost, which makes it closer to commercial market applications than pure silicon.

[0003] However, as a negative electrode material for lithium batteries, the impurity iron in silicon oxide has a great influence on the application performance of silicon oxide. The presence of Fe will reduce the conductivity of silicon oxide, affect the conduction efficiency of lithium batteries and the charge and discharge performance of active materials; Fe may react chemically with other components in silicon oxide to form unstable compounds, thereby reducing the chemical stability of the material. In addition, Fe may also promote side reactions in the charging and discharging process of lithium batteries, resulting in capacity decay and shortened cycle life. The reaction of iron with lithium ions may lead to more serious volume changes, aggravate the volume expansion effect of lithium batteries during the charging and discharging process, cause the electrode structure to rupture, and reduce the performance and life of lithium batteries.

[0004] Since Fe has an important influence on the application performance of silicon oxide, it is generally required that the iron content in silicon oxide be controlled below 100 ppm, or even within 30 ppm. Therefore, accurate detection and measurement of the iron content in silicon oxide is crucial for regulating the preparation process of silicon oxide, reducing the Fe content in silicon oxide, and improving the application performance of silicon oxide in new energy batteries.

[0005] At present, there is still a lack of detection methods for iron in silicon oxide. Relatively close existing technologies, such as GB / T14849.1-2020 Industrial Silicon Chemical Analysis Method Part 1 "Determination of Iron Content", are as follows: the industrial silicon sample is dissolved with hydrofluoric acid and nitric acid, and perchloric acid is added to evaporate until smoke appears to remove silicon, fluorine, etc., and the residue is dissolved with hydrochloric acid. Fe(III) is reduced to Fe(II) with hydroxylamine hydrochloride. In a pH 3-5 sodium acetate buffer medium, Fe(II) ions react with 1,10-phenanthroline to form a red complex. The absorbance of the solution is measured at a wavelength of 510nm, and the mass fraction of iron is calculated. The determination range of the iron content in industrial silicon by this method is 0.050% to 0.75%, which is difficult to meet the current demand for trace determination of iron in silicon oxide. Summary of the invention

[0006] Based on the lack of a specific detection method for Fe in silicon oxide and the difficulty of existing detection methods for Fe in industrial silicon to meet the demand for trace detection of Fe, the present invention aims to provide a method for detecting trace amounts of iron in silicon oxide. By selecting a suitable digestion solution and a digestion procedure, silicon oxide is digested and Fe therein is released, and trace detection of Fe is performed based on an inductively coupled plasma emission spectrometer. The detection method of the present invention has excellent stability and precision, and can accurately quantify Fe with a content of less than 1 ppm, thereby meeting the demand for trace detection of Fe in silicon oxide.

[0007] Based on the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A method for detecting trace amounts of iron in silicon oxide comprises the following steps:

[0009] Sample pretreatment: add excess digestion solution to the silicon oxide sample for microwave digestion, remove the acid and adjust the volume with ultrapure water to obtain the sample solution;

[0010] Preparation of blank control solution: microwave digestion of equal amount of digestion solution, remove acid and make up to volume with ultrapure water to obtain blank control solution;

[0011] Preparation of Fe standard working solution: Use nitric acid solution to prepare Fe standard working solutions with different concentration gradients;

[0012] On-machine detection: The sample solution, blank control solution and Fe standard working solution are respectively introduced into the inductively coupled plasma optical emission spectrometer (ICP-OES), and the intensity is detected at the Fe element detection wavelength. The Fe element content in the silicon oxide sample is calculated based on the standard curve obtained by the Fe standard working solution detection.

[0013] The present invention uses microwave digestion of silicon oxide to release Fe elements, and then detects the Fe content in the digestion solution based on a standard curve constructed by detecting a Fe standard working solution on an ICP-OES machine, and then calculates the content of Fe elements in the silicon oxide sample to be tested. The present invention has excellent detection stability and precision for the detection of iron elements in silicon oxide, and shows good reproducibility among different operators and different laboratories, and can accurately quantify Fe with a content of less than 1ppm, meeting the trace detection requirements of Fe in silicon oxide.

[0014] Preferably, the calculation formula for the content of iron in the silicon oxide sample is as follows:

[0015]

[0016] Among them, C X is the iron content in the silicon oxide to be tested (mg / kg); C is the concentration of iron in the test solution (mg / L); C 0 is the concentration of iron in the blank solution (mg / L); N is the dilution factor of the test solution; V is the volume of the test solution (ml); and m is the mass of the silicon dioxide sample (g).

[0017] Each time the digestion solution is tested on the machine, it is calibrated with Fe standard working solutions of different concentration gradients to obtain a real-time standard curve. At the same time, the blank control solution is used as a reference to reduce the influence of factors such as reagents and equipment in the detection system. While improving the accuracy of Fe detection in silicon dioxide samples, the precision and universality of the detection results are improved.

[0018] Preferably, the digestion solution consists of nitric acid and hydrofluoric acid; the volume ratio of the nitric acid to the hydrofluoric acid is (4-19):1.

[0019] Hydrofluoric acid can react with silicon oxide to form gaseous silicon tetrafluoride, thereby removing the matrix and releasing the Fe element. Nitric acid can react with impurity elements to reduce the interference of impurity elements on the detection of Fe content. Therefore, a mixed solution formed by nitric acid and hydrofluoric acid is selected as the digestion solution for silicon oxide samples. Experiments have found that a digestion solution composed only of nitric acid and hydrofluoric acid can meet the needs of trace detection of iron elements in silicon oxide. Since this case is a trace detection, digestion solutions with fewer reagent types are used as much as possible to achieve the effect of trace detection, avoiding the use of too many types of acids, which will lead to excessive impurities introduced into the detection system, resulting in the detection limit and quantification limit of the Fe element being too high and difficult to meet the trace detection needs.

[0020] Experiments have shown that when the volume ratio of nitric acid to hydrofluoric acid in the digestion solution is in the range of (4-19):1 and the amount of the digestion solution is excessive relative to the sample amount, the detection of Fe content in silicon oxide has good detection stability and precision.

[0021] Preferably, the volume ratio of nitric acid to hydrofluoric acid in the digestion solution is (5-9):1.

[0022] It was found during the experiment that when the volume ratio of nitric acid to hydrofluoric acid in the digestion solution was 4:1, that is, when the amount of hydrofluoric acid in the digestion solution was relatively large, white mist would be generated during the experiment. For safety reasons, the volume ratio of nitric acid to hydrofluoric acid in the digestion solution is preferably greater than 4:1.

[0023] In addition, when the volume ratio of nitric acid to hydrofluoric acid is 19:1, it can be intuitively seen that the solution after digestion is not a clear and uniform solution, but there is a certain amount of precipitate, indicating that when the amount of hydrofluoric acid in the digestion solution is relatively low, there is an incomplete digestion of the silicon oxide sample, and the detection result of Fe may be inaccurate. Therefore, the volume ratio of nitric acid to hydrofluoric acid in the digestion solution should be less than 19:1.

[0024] Preferably, the microwave digestion procedure includes: heating the solution to be digested to 160° C. to 200° C. and keeping the temperature for 20 to 60 minutes.

[0025] Preferably, the procedure of microwave digestion is as follows:

[0026] Raise the temperature of the solution to be digested to 120°C and keep it warm for 3 minutes, then continue to raise the temperature to 150°C and keep it warm for 3 minutes, then continue to raise the temperature to 180°C~200°C and keep it warm for 20~30 minutes.

[0027] Preferably, the acid removal comprises: heating the solution after microwave digestion at 180° C. to 200° C. to volatilize the solution until its volume is less than 1 mL.

[0028] Preferably, the nitric acid solution used in the preparation of the Fe standard working solution is a 2% (v / v) nitric acid aqueous solution.

[0029] Preferably, the test conditions for the Fe element by inductively coupled plasma emission spectrometer are as follows:

[0030] The plasma gas flow rate is 12.0 L / min; the auxiliary gas flow rate is 1.0 L / min; the atomization gas flow rate is 0.70 L / min; and the detection wavelength of Fe is 234.350 nm, 238.204 nm or 259.940 nm.

[0031] Preferably, nitric acid and hydrofluoric acid are both of high-grade purity.

[0032] Premium purity is the highest purity level of chemical reagents, and the impurity concentration is required not to exceed 0.01%. The nitric acid and hydrofluoric acid used in the detection system of this application are both premium purity to minimize the amount of impurities introduced into the detection system, reduce the interference with the detection of trace Fe elements in silicon oxide of this application, and improve the accuracy of the detection results.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention utilizes a digestion solution composed of nitric acid and hydrofluoric acid to digest a silicon oxide sample through a suitable microwave digestion program to fully release the Fe element, perform ICP-OES on-machine detection, and simultaneously avoid introducing too much Fe impurities into the system. Based on ICP-OES, a calibration curve is constructed for Fe standard working solutions with different concentration gradients, and the Fe element content in the silicon oxide sample is calculated. The detection method of the present invention has excellent stability and precision, can accurately quantify the Fe element with a content of less than 1 ppm, meets the trace detection demand of Fe in silicon oxide, and shows good reproducibility among different operators and different laboratories, and has good universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a photo of silicon dioxide after digestion in Example 1;

[0036] Figure 2 The detection wavelength-intensity curve and the standard curve of the Fe element standard solution in Example 1;

[0037] Figure 3 The photo is a photo of the digestion of silicon dioxide sample when the dosage of nitric acid and hydrofluoric acid is 9.5 mL and 0.5 mL respectively in Example 2;

[0038] Figure 4 This is a photograph of the digestion of silicon oxide samples using nitric acid as the digestion solution in Example 2. DETAILED DESCRIPTION

[0039] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be understood by those skilled in the art that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. The test methods used in the examples are conventional methods unless otherwise specified; the materials, reagents, etc. used can be obtained from commercial sources unless otherwise specified.

[0040] It should be noted that the reagents used in the examples, such as nitric acid and hydrofluoric acid, are all of premium grade (GR), water is ultrapure water, the model of the inductively coupled plasma emission spectrometer used is Agilent 5800ICP-OES, and the silicon dioxide sample used is from Zhengzhou Juhuang New Material Technology Co., Ltd.

[0041] Example 1

[0042] This embodiment provides a method for detecting trace amounts of iron in silicon oxide, comprising the following steps:

[0043] Weigh about 0.25g of silicon dioxide sample into a polytetrafluoroethylene digestion tank, add 8ml nitric acid, then slowly add 1.5ml hydrofluoric acid, cover the safety valve, put the digestion tank into the microwave digestion system for digestion, the microwave digestion program is shown in Table 1, after the digestion is completed, remove the digestion tank, drive the acid in the digestion tank at 180℃ until the total acid remains about 0.5ml, remove the digestion tank and add appropriate amount of ultrapure water along the wall, after cooling to room temperature, rinse several times and dilute to 25ml colorimetric tube and mix well, as the test solution, the photo of the test solution is shown in Figure 1 shown.

[0044] It should be noted that the hydrofluoric acid in the digestion solution can react with silicon oxide to form gaseous silicon tetrafluoride, thereby removing the matrix and releasing the Fe element. The nitric acid in the digestion solution can react with the impurity elements to reduce the interference of the impurity elements on the detection of the Fe content. Therefore, a mixed solution formed by nitric acid and hydrofluoric acid is selected as the digestion solution for the silicon oxide sample.

[0045] Table 1 Microwave digestion instrument digestion procedure

[0046] step Temperature(℃) Heating time (min) Insulation time (min) 1 120 0 3 2 150 0 3 3 180 0 30

[0047] The test solution was placed in an inductively coupled plasma emission spectrometer for detection, and the measurement was performed three times in parallel. At the same time, a blank control solution was prepared. The blank control solution was directly added to a polytetrafluoroethylene digestion tank with 8 ml of nitric acid, and then 1.5 ml of hydrofluoric acid was slowly added. The safety valve was covered, and the digestion tank was placed in a microwave digestion system. Digestion was performed according to the microwave digestion program in Table 1. The acid removal and volume determination steps were the same as those for the test solution.

[0048] The parameters of the inductively coupled plasma optical emission spectrometer are as follows:

[0049] Observation direction: select axial according to measurement requirements and instrument sensitivity; power: 1200w; plasma gas flow: 12.0L / min; auxiliary gas flow: 1.0L / min; atomization gas flow: 0.70L / min; wavelength: 238.204nm.

[0050] According to the spectral intensity of iron in the blank solution and the solution to be tested, the content of iron in the sample to be tested is calculated from the standard curve. The calculation formula is as follows:

[0051]

[0052] Among them, C X is the iron content in the silicon oxide to be tested (mg / kg); C is the concentration of iron in the test solution (mg / L); C 0 is the concentration of iron in the blank solution (mg / L); N is the dilution factor of the test solution; V is the volume of the test solution (ml); and m is the mass of the silicon dioxide sample (g).

[0053] The concentration of Fe in the Fe element standard solution is 100 mg / L, and the standard working solution is obtained by diluting the 100 mg / L Fe element standard solution with a 2% nitric acid aqueous solution by different dilution multiples. The concentration gradient of the Fe element standard working solution is 1 mg / L, 2 mg / L, 5 mg / L, 10 mg / L, and 20 mg / L. The standard working solution is placed in an inductively coupled plasma emission spectrometer, and the Fe element spectral intensity is detected according to the above test conditions. A standard curve of the Fe element concentration corresponding to the Fe element spectral intensity is drawn. The detection wavelength-intensity curve of the Fe element standard solution and the standard curve are shown in FIG. Figure 2 shown.

[0054] The content of iron in the silicon oxide sample determined by the method of this embodiment is shown in Table 2. The detection standard deviation of the Fe content in the three groups of parallel silicon oxide samples is 1.71, and the relative standard deviation is <5%. This result shows that the detection method of this embodiment has good detection stability and precision for the detection of the Fe content in the silicon oxide sample.

[0055] Table 2

[0056]

[0057] Example 2

[0058] The purpose of this example is to analyze the effect of the composition ratio of the acid in the digestion solution on the stability and precision of the detection of iron in silicon oxide. The silicon oxide used in this example and the silicon oxide sample in Example 1 are samples from different batches. The samples used in this example to verify the composition of different digestion solutions are silicon oxide samples from the same batch. The test method is as follows:

[0059] Referring to the detection method of the Fe element in Example 1, the difference from Example 1 is that the volumes and ratios of nitric acid and hydrofluoric acid in the digestion solution of the present embodiment are as shown in Table 3, and referring to the detection method of microwave digestion and inductively coupled plasma emission spectrometer in Example 1, the content of iron in the measured silicon dioxide sample is as shown in Table 3 and Table 4.

[0060] Table 3

[0061]

[0062]

[0063] Table 4

[0064]

[0065] It can be seen from the results of Table 3 and Table 4 that the standard deviation of the Fe content detection results in each group of samples treated with different digestion solutions is less than 4, the relative standard deviation is less than 2%, and the relative standard deviation of a total of 12 samples treated with four groups of different digestion solutions is 4.69%, that is, the coefficient of variation is less than 5%. The above shows that when the digestion solution consists of nitric acid and hydrofluoric acid, wherein the volume ratio of nitric acid to hydrofluoric acid is in the range of (4-19):1, and the amount of the digestion solution is excessive relative to the sample amount, the detection of Fe content in silicon oxide has good detection stability and precision.

[0066] In the above experiment, when the dosage of nitric acid and hydrofluoric acid was 8 mL and 2 mL respectively, white mist was generated when the two were mixed. It is speculated that this was due to the volatilization of hydrofluoric acid at a slightly higher concentration. Therefore, during the experiment, the dosage of hydrofluoric acid in the digestion solution should not be too high. Therefore, the volume ratio of nitric acid to hydrofluoric acid in the digestion solution should be no less than 4:1.

[0067] In the above experiment, when the dosage of nitric acid and hydrofluoric acid was 9.5mL and 0.5mL respectively, the silicon dioxide sample was not completely digested. Figure 3 As shown, the detection results of Fe content in the sample did not show a significant decrease. This result shows that although there is a phenomenon of incomplete digestion of some silicon oxide samples, as long as the Fe element in the sample can be completely dissolved, it does not affect the detection accuracy of the Fe content.

[0068] Based on this, this case further uses 10mL nitric acid as the digestion solution, that is, the digestion solution does not contain hydrofluoric acid, and the rest of the unmentioned parts are the same as above. The sample digestion situation is as follows: Figure 4 As shown, the 5 tubes on the left are photos of 5 parallel samples after digestion, and the 5 tubes on the right are photos of blank controls after digestion. It can be seen that there are a large number of brown undigested silicon oxide precipitates in the 5 tubes on the left. The test results of the Fe content in the silicon oxide samples are shown in Table 5. The average value of the Fe content is only 6.3928 mg / kg, which is significantly lower than the above test results (>200 mg / kg). The above results show that it is difficult to digest silicon oxide to release the iron element using nitric acid as the only digestion solution, resulting in inaccurate test results for the iron content in silicon oxide.

[0069] Table 5

[0070]

[0071] Example 3

[0072] The purpose of this example is to analyze the influence of microwave digestion parameters such as temperature and time on the detection of Fe content in silicon oxide. The specific experimental method is as follows:

[0073] Referring to the detection method of the iron content in silicon oxide in Example 1, since the temperature and time of the third stage of microwave digestion have a greater impact on the digestion effect, the temperature and time of the third stage of microwave digestion are adjusted in this embodiment, as shown in Table 6. At the same time, the test liquid after different microwave digestion treatments is detected according to the parameters of the inductively coupled plasma emission spectrometer recorded in Example 1, and the results are shown in Table 6.

[0074] Table 6

[0075]

[0076]

[0077] From the results in Table 6, it can be seen that when the digestion temperature of the third stage of microwave digestion is 180°C to 200°C and the digestion time is 30min, the content of iron in the sample detected is slightly higher than that of the sample with a digestion temperature below 180°C and a digestion time of less than 30min or more than 60min. Although the relative standard deviation of the test results of the above samples is less than 3%, based on the above results, it can be seen that when the digestion temperature is not less than 180°C and the digestion time is greater than 15min but not more than 60min, silicon dioxide can be more fully digested to release Fe elements without causing loss of iron elements. Therefore, in the detection method of the present application, the temperature of the third stage of microwave digestion can be controlled to be 180°C to 200°C, and the duration of microwave digestion is preferably 20 to 30min.

[0078] Example 4

[0079] The purpose of this example is to analyze the detection limit and quantitative limit of the iron content in silicon dioxide constructed by the present invention. The specific test method is as follows:

[0080] Nitric acid is added to a polytetrafluoroethylene digestion tank, and then hydrofluoric acid is slowly added. The amount of nitric acid and hydrofluoric acid added is shown in Table 7. The safety valve is covered, and the digestion tank is placed in a microwave digestion system for digestion. The microwave digestion program is shown in Table 1. After the digestion is completed, the digestion tank is removed, and the digestion tank is driven to acid at 180°C until the total acid remains about 0.5ml. The digestion tank is removed and an appropriate amount of ultrapure water is added along the wall. After cooling to room temperature, it is rinsed several times and fixed to a 25ml colorimetric tube and mixed to serve as a test liquid. The test liquid is placed in an inductively coupled plasma emission spectrometer for detection, and the specific parameters are the same as in Example 1.

[0081] Referring to this method, the detection results of Fe in 22 sample blank solutions were statistically analyzed as shown in Table 7, and the standard deviation was calculated. Three times the standard deviation was recorded as the detection limit of Fe, and 10 times the standard deviation was recorded as the quantitative limit concentration of Fe. The detection limit of Fe in the detection method of the present application is 0.2715 mg / L (0.2715 ppm), and the quantitative limit is 0.905 mg / L (i.e., 0.905 ppm), indicating that the detection method of the present application can meet the detection requirements for trace Fe in silicon oxide.

[0082] Table 7

[0083]

[0084] Example 5

[0085] The purpose of this example is to analyze the influence of different detection wavelengths on the detection precision of iron content in silicon oxide. The silicon oxide used in this example and the silicon oxide sample in Example 1 are samples from different batches. The specific test method is as follows:

[0086] Weigh about 0.25g of silicon dioxide sample into a polytetrafluoroethylene digestion tank, add 8ml of nitric acid, and then slowly add 1.5ml of hydrofluoric acid, cover the safety valve, and place the digestion tank into a microwave digestion system for digestion. The microwave digestion program is shown in Table 1. After the digestion is completed, remove the digestion tank, and drive the acid in the digestion tank at 180°C until the total acid remains about 0.5ml. Remove the digestion tank and add an appropriate amount of ultrapure water along the wall. After cooling to room temperature, rinse it several times, make it up to volume, and mix it in a 25ml colorimetric tube as the test solution.

[0087] The detection parameters of the inductively coupled plasma emission spectrometer in Example 1 were used for on-machine detection. The difference is that the detection wavelengths were adjusted to 234.350 nm, 238.204 nm, and 259.940 nm, respectively. The influence of the detection wavelength on the detection precision of the Fe content in the silicon oxide sample was analyzed by testing the same sample at the above three detection wavelengths, as shown in Table 8.

[0088] Table 8

[0089]

[0090] It can be seen from the results in Table 7 that for the same sample at different selected wavelengths, the detection results of Fe in silicon oxide are slightly different, and the relative standard deviation does not exceed 1.1%. The above results show that for the detection method of the present invention, the above three detection wavelengths can be used for accurate detection of Fe in silicon oxide.

[0091] Example 6

[0092] The purpose of this example is to analyze the stability of the method for detecting the content of iron in silicon dioxide constructed by the present invention. The specific test method is as follows:

[0093] Two testing engineers, A and B, tested the same sample according to the detection method for Fe content in silicon oxide recorded in Example 1, analyzed the relative standard deviation of the test results, and analyzed the influence of factors such as different testing engineers on the detection method. The results are shown in Table 9.

[0094] As can be seen from Table 9, the same sample was tested 4 times by two test engineers A and B, and the relative standard deviation of the test results of Fe content was only 0.23%, indicating that the detection method of the present invention has good stability and is minimally affected by human operation.

[0095] Table 9

[0096]

[0097]

[0098] The same silicon oxide sample was divided into three equal parts and sent to three different laboratories respectively. The Fe content was determined using the method in Example 1. The results are shown in Table 10.

[0099] It can be seen from the results in Table 10 that the relative standard deviation of the test results of Fe content in the same sample by different laboratories according to the method of this application does not exceed 5%, and the test results of different laboratories show good consistency.

[0100] Table 10

[0101]

[0102] The above results show that the method for detecting the iron content in silicon oxide of the present invention is less affected by personnel and laboratories and has good stability.

Claims

1. A method for detecting trace amounts of iron in silicon oxide, characterized in that: The steps include: Sample pretreatment: add excess digestion solution to the silicon oxide sample for microwave digestion, remove the acid, dilute with ultrapure water to obtain the sample solution; Preparation of blank control solution: microwave digestion of equal amount of digestion solution, dilution with ultrapure water to obtain blank control solution; Preparation of Fe standard working solution: Use nitric acid solution to prepare Fe standard working solutions with different concentration gradients; On-machine detection: The sample solution, blank control solution and Fe standard working solution are respectively introduced into the inductively coupled plasma emission spectrometer, and the intensity is detected at the Fe element detection wavelength. The Fe element content in the silicon oxide sample is calculated based on the standard curve obtained by the Fe standard working solution detection.

2. The method for detecting trace amounts of iron in silicon oxide according to claim 1, characterized in that: The calculation formula for the content of iron in the silicon oxide sample is as follows: Among them, C X is the iron content in the silicon oxide to be tested (mg / kg); C is the concentration of iron in the test solution (mg / L); C0 is the concentration of iron in the blank control solution (mg / L); N is the dilution factor of the test solution; V is the volume of the test solution (ml); and m is the mass of the silicon oxide sample (g).

3. The method for detecting trace amounts of iron in silicon oxide according to claim 1, characterized in that: The digestion solution is composed of nitric acid and hydrofluoric acid; the volume ratio of the nitric acid to the hydrofluoric acid is (4-19):

1.

4. The method for detecting trace amounts of iron in silicon oxide according to claim 3, characterized in that: The volume ratio of nitric acid to hydrofluoric acid in the digestion solution is (5-9):

1.

5. The method for detecting trace amounts of iron in silicon oxide according to claim 1, characterized in that: The microwave digestion procedure includes: heating the solution to be digested to 160° C. to 200° C. and keeping the temperature for 20 to 60 minutes.

6. The method for detecting trace amounts of iron in silicon oxide according to claim 5, characterized in that: The procedure of the microwave digestion is as follows: Raise the temperature of the solution to be digested to 120°C and keep it warm for 3 minutes, then continue to raise the temperature to 150°C and keep it warm for 3 minutes, then continue to raise the temperature to 180°C~200°C and keep it warm for 20~30 minutes.

7. The method for detecting trace amounts of iron in silicon oxide according to claim 1, characterized in that: The acid removal comprises: heating the solution after microwave digestion at 180° C. to 200° C. to volatilize the solution until its volume is less than 1 mL.

8. The method for detecting trace amounts of iron in silicon oxide according to claim 1, characterized in that: The nitric acid solution used in the preparation of the Fe standard working solution is a 2% (v / v) nitric acid aqueous solution.

9. The method for detecting trace amounts of iron in silicon oxide according to claim 1, characterized in that: The test conditions of the inductively coupled plasma emission spectrometer for the Fe element are as follows: The plasma gas flow rate was 12.0 L / min; the auxiliary gas flow rate was 1.0 L / min; the nebulizer gas flow rate was 0.70 L / min; and the detection wavelength of Fe was 234.350 nm, 238.204 nm or 259.940 nm.

10. The method for detecting trace amounts of iron in silicon oxide according to claim 1, characterized in that: The nitric acid and hydrofluoric acid are both of high-grade purity.

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