A method for determining trace amounts of niobium, gold, mercury and rhenium in high-purity tungsten

Abstract

The present invention discloses a method for determining the content of trace niobium, gold, mercury and rhenium in high-purity tungsten, comprising the following steps: placing a high-purity tungsten sample in a beaker, and performing a blank test together with the sample; adding nitric acid and hydrofluoric acid, heating at low temperature until the sample is completely dissolved, and cooling; transferring to a plastic volumetric flask, adding a rhodium internal standard solution, diluting with water and mixing; using an inductively coupled plasma tandem mass spectrometer in ammonia mode to determine niobium and gold, and in oxygen mode to determine mercury and rhenium, and calculating the content of niobium, gold, mercury and rhenium according to a working curve method. The present invention uses inductively coupled plasma tandem mass spectrometry technology, and by selecting a suitable reaction mode and optimizing the reaction gas flow rate, effectively eliminates the mass spectrum interference of matrix elements in pure tungsten on the mass spectrum interference of niobium, gold, mercury and rhenium.

Description

Technical Field

[0001] The present invention relates to the technical field of material detection, and more specifically, to a method for determining the contents of trace amounts of niobium, gold, mercury and rhenium in high-purity tungsten. Background Art

[0002] Tungsten is a valuable strategic metal, widely used in the national defense military industry and the mechanical industry, and has become a very important basic material. High-purity tungsten has high resistance to electron migration and high-temperature stability, and can form stable silicides. It is often used as a gate, connection and barrier metal in the form of a thin film in the electronics industry. In addition, high-purity tungsten is also often used to manufacture target materials, aviation materials, etc., and has a very broad market prospect.

[0003] The purity of metal plays a very important role in the application of metal. The presence of trace impurities will affect the characteristics of metal. With the continuous improvement of the purity requirements of high-purity tungsten in various related industries, more stringent requirements have been put forward for the types and contents of impurity elements contained in it. Accurate determination of the content of impurity elements in high-purity tungsten is of great significance. YS / T659-2007 "Tungsten and Tungsten Alloy Processing Product Brands and Chemical Composition" and YS / T 1025-2015 "High-purity Tungsten and Tungsten Alloy Sputtering Targets for Electronic Thin Films" both stipulate the composition and impurity element requirements of high-purity tungsten.

[0004] The analysis methods of impurity elements in tungsten and its compounds include atomic emission spectroscopy, atomic absorption spectroscopy, spectrophotometry, inductively coupled plasma mass spectrometry, laser induced breakdown spectroscopy and glow discharge mass spectrometry. Among them, the sample processing experimental steps of spectrophotometry are relatively cumbersome and easy to introduce new impurity elements to be measured; spectroscopy, including atomic absorption spectroscopy and inductively coupled plasma atomic emission spectroscopy, has better stability than chemical methods, but the detection sensitivity of trace impurity elements in high-purity metals generally does not meet the requirements. In solid sampling analysis technology, the detection limit of spark source atomic emission spectrometry is relatively high and cannot meet the requirements of trace element analysis; laser ablation inductively coupled plasma mass spectrometry and glow discharge mass spectrometry can only perform semi-quantitative analysis due to the limitation of standard substances. Compared with other analysis methods, although ICP-MS has many advantages such as low detection limit, simultaneous determination of multiple elements, and wide linear range, it also has serious mass number interference problems. When ICP-MS determines the content of Au, Hg, Re, and Nb in high-purity tungsten, tungsten ions easily combine with O and H elements in the solution to form WO ＋ , WOH ＋ , W ＋＋ etc., serious interference 197 Au, 93 Nb, 196 Hg~ 204 Hg, 185 Re, 187For the determination of Re, all isotopes of Au, Hg, Re and Nb are interfered by mass spectrometry and cannot be directly determined. Summary of the invention

[0005] 1. Technical problems to be solved

[0006] The object of the present invention is to provide a method for determining the content of trace niobium, gold, mercury and rhenium in high-purity tungsten to solve the problems raised in the above background technology.

[0007] 2. Technical solution

[0008] A method for determining trace amounts of niobium, gold, mercury and rhenium in high-purity tungsten comprises the following steps:

[0009] Place the high purity tungsten sample in a beaker and do a blank test along with the test material;

[0010] Add nitric acid and hydrofluoric acid, heat at low temperature until the sample is completely dissolved, and cool;

[0011] Transfer to a plastic volumetric flask, add rhodium internal standard solution, dilute with water and mix well;

[0012] Niobium and gold were determined in ammonia mode and mercury and rhenium were determined in oxygen mode using an inductively coupled plasma tandem mass spectrometer. The contents of niobium, gold, mercury and rhenium were calculated using the working curve method.

[0013] Preferably, the parameters of the inductively coupled plasma tandem mass spectrometer are as follows: sampling depth: 8.0 mm, nebulizing gas flow rate: 0.8 L / min, dilution gas flow rate 0.35 L / min, nebulizing chamber temperature of 20° C., measurement method of the peak skipping method, ammonia flow rate of 50%, and oxygen flow rate of 35%.

[0014] Isotope selection is based on the principle of high isotope abundance and no interference of impurity elements. The recommended mass number, measurement mode and internal standard element of isotopes are shown in the following table:

[0015]

[0016] Q1 is the mass number of the first mass spectrometer of the instrument, and Q2 is the mass number of the second mass spectrometer of the instrument.

[0017] 3. Beneficial effects

[0018] Compared with the prior art, the advantages of the present invention are:

[0019] The present invention uses inductively coupled plasma tandem mass spectrometry technology to effectively eliminate the mass spectrum interference of matrix elements in pure tungsten on niobium, gold, mercury and rhenium by selecting a suitable reaction mode and optimizing the reaction gas flow rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of Hg determination in MS / MS O2 on-mass mode;

[0021] Figure 2 This is the ion product scan diagram under NH3 mode - blank matrix solution;

[0022] Figure 3 This is the ion product scan diagram under NH3 mode - sample solution;

[0023] Figure 4 Schematic diagram of mass transfer determination of Nb in tungsten-rhenium alloy under NH3 mode;

[0024] Figure 5 Schematic diagram of the curve of BEC and CPS changing with O2 flow rate. DETAILED DESCRIPTION

[0025] Example:

[0026] A method for determining the content of trace niobium, gold, mercury and rhenium in high-purity tungsten, wherein the sample is digested with nitric acid and hydrofluoric acid, argon plasma is used as an ionization source, niobium and gold are determined in ammonia mode of an inductively coupled plasma tandem mass spectrometer, and mercury and rhenium are determined in oxygen mode, and the contents of niobium, gold, mercury and rhenium are calculated according to a working curve method.

[0027] The steps include:

[0028] 2.1 Reagents (Unless otherwise specified, only reagents of confirmed high purity and distilled or deionized water or water of equivalent purity were used in the analysis)

[0029] 2.1.1 Nitric acid: Up grade.

[0030] 2.1.2 Hydrofluoric acid: Up grade.

[0031] 2.1.3 Standard storage solution: Niobium, gold, mercury, rhenium and rhodium shall use valid single element standard storage solution with a certificate, with a mass concentration of 1000 μg / mL.

[0032] 2.1.4 Mixed standard solution: Pipette 10.00 mL of niobium, gold, mercury and rhenium standard stock solutions (2.1.3) into a 1000 mL volumetric flask, add 50 mL of nitric acid (2.1.1), dilute to volume with water and mix well. 1 mL of this solution contains 1 µg each of niobium, gold, mercury and rhenium.

[0033] 2.1.5 Rhodium internal standard solution: Pipette 1.00 mL of the rhodium standard stock solution (2.1.3) into a 1000 mL volumetric flask, add 50 mL of nitric acid (2.1.1), dilute to volume with water, and mix. This solution contains 1 µg of rhodium per mL.

[0034] 2.2 Instruments

[0035] 2.2.1 Inductively coupled plasma tandem mass spectrometer with a mass resolution of not less than (0.8 ± 0.1) amu; equipped with a hydrofluoric acid resistant injection system.

[0036] 2.2.2 Electronic balance, accurate to 0.0001g.

[0037] 2.3 Test materials

[0038] Weigh 0.10 g of sample to an accuracy of 0.0001 g.

[0039] 2.4 Preparation of analytical solution

[0040] Place the sample (2.3) in a 100 mL polytetrafluoroethylene beaker and perform a blank test with the sample. Add a small amount of water, 3.0 mL of nitric acid (2.1.1) and 1.0 mL of hydrofluoric acid (2.1.2), heat at low temperature until the sample is completely dissolved, cool, transfer to a 100 mL plastic volumetric flask, add 1.00 mL of rhodium internal standard solution (2.1.5), dilute to the mark with water, and mix well.

[0041] 2.5 Preparation of a series of standard solutions

[0042] Pipette 0 mL, 0.10 mL, 0.50 mL, 1.00 mL, 2.00 mL, 5.00 mL and 10.00 mL of the mixed standard solution (2.1.4) into a set of 100 mL plastic volumetric flasks, add 1.00 mL of rhodium internal standard solution (2.1.5) respectively, dilute to the scale with water and mix well.

[0043] 2.6 Determination

[0044] 2.6.1 On the ICP-MS, after the instrument is running stably, use the prepared standard series solution (2.5) to calibrate the working curve under the selected instrument working conditions. The correlation coefficient of the working curve of each element should be above 0.999. Otherwise, it is necessary to re-standardize or re-prepare the standard series solution for standardization.

[0045] 2.6.2 Determine the blank solution and analytical solution (2.4) in turn. The software automatically processes the data, calculates and outputs the mass concentration of each impurity element in the blank solution and analytical solution.

[0046] 2.7 Calculation of analysis results

[0047] The content of each element is expressed in mass fraction W x, calculated according to formula (1):

[0048]

[0049] Where:

[0050] ρ x ——The mass concentration of the element being measured in the sample solution, in nanograms per milliliter (ng / mL);

[0051] ρ 0——mass concentration of the element being measured in the blank solution, in nanograms per milliliter (ng / mL);

[0052] V——total volume of the solution, in milliliters (mL);

[0053] m – the numerical value of the sample mass, in grams (g).

[0054] The verification process of the above scheme includes the following steps:

[0055] Sample dissolution:

[0056] Add 3 mL of nitric acid and 1 mL of hydrofluoric acid, and heat at low temperature to completely dissolve 0.10 g of high-purity tungsten sample. After cooling, transfer to a 100 mL plastic volumetric flask, add internal standard, make up to volume, shake well, and wait for testing;

[0057] The instrument parameters were optimized, and the inductively coupled plasma tandem mass spectrometer parameters were selected as follows: sampling depth: 7.0~8.0 mm, nebulizing gas flow rate: 0.8~1.0 L / min, dilution gas flow rate 0.35~0.40 L / min, nebulizing chamber temperature of 20°C, ammonia flow rate of 40~50%, and oxygen flow rate of 30~40%. Table 1 is the preferred options of this embodiment.

[0058] Table 1 ICP-QQQ operating parameters

[0059]

[0060] The effect of ICP-MS / MS in eliminating the interference of polyatomic ions and doubly charged ions of matrix W on Nb and Hg was investigated. The CPS counts at mass-to-charge ratios of 93 and 202 in blank matrix solution (1000 μg / mL W) and sample solution (1000 μg / mL W~1.0 ng / mL Nb and 1.0 ng / mL Hg) were collected in different modes, and the background equivalent concentration (BEC) was used as the evaluation criterion. BEC is the ratio of the CPS counts generated by the interfering element at the element to be measured to the sensitivity of the method, that is, the CPS counts generated by 1000 μg / mL W solution at the corresponding mass number of niobium and mercury are equivalent to a certain content of niobium and mercury. The lower the BEC, the less interference the tungsten matrix has on the determination of niobium and mercury. The results are shown in Table 3.

[0061] Table 3 BEC values ​​measured under different acquisition modes

[0062]

[0063] As shown in Table 3, using single quadrupole measurement in He collision mode, 202 The BEC of Hg was high, 10.1 μg / L, indicating that the mass spectrometry interference was serious and the collision mode had limited effect on eliminating the mass spectrometry interference. In the MS / MS mode, the BECs were all reduced, but when NH3 and H2 were used as reaction gases, the BEC values ​​were still high, indicating that the NH3 or H2 reaction mode failed to completely eliminate the interfering ions; when O2 was used as the reaction gas, the BEC was reduced to 0.2 μg / L, indicating that the mass spectrometry interference was small at this time and the interfering ions were effectively eliminated.

[0064] Whether the ions in the reaction cell react with O2 depends on the reaction enthalpy change (ΔHr). When ΔHr<0, the reaction is exothermic and the ions can react with O2 spontaneously. When ΔHr>0, the reaction is endothermic and it is difficult for the reaction to occur. 202 Hg ＋ and 186 W 16 O ＋ All pass through the first set of quadrupole mass filters (Q1=202) in the reaction pool. 186 W 16 O ＋ ΔHr with O2 is less than 0, and oxidation reaction easily occurs, while Hg + ΔHr with O2>0, it is difficult to react. The reaction formula is as follows:

[0065]

[0066] Generated in the reaction pool 186 W 16 O2 ＋ (m / z=218), which cannot be removed by the second set of quadrupole mass filters (Q2=202). 202 Hg ＋ It can pass through the mass filter normally, thus achieving accurate determination of Hg.

[0067] There is a lone electron pair in the NH3 molecule, and Nb reacts with NH3 to form an ammonium cluster ion product M(NH3)n +It is relatively complicated. When using the mass-shift mode, it is necessary to first perform product ion scanning on the blank matrix solution (1000 μg / mL W) and the sample solution (1000 μg / mL W~1.0 ng / mL Nb) to determine the product M(NH3)n + The mass number of Figure 2 and Figure 3 It can be seen that the Nb element in the sample solution has an obvious intensity signal at the mass number 174, while the blank matrix solution has no obvious intensity signal at the mass number 174, so it is judged that the m / z of the ion product is 174.

[0068] Fig.3 Scanning diagram of ion products under NH3 mode-sample solution

[0069] In Mass-shift mode, set Q1=93, 93 Nb + , 93 W 2+ Through the first set of quadrupoles, it enters the collision reaction cell, where NH3 and Nb in the reaction cell generate cluster ions. 93 W 2+ Does not react with NH3, set Q2=174, 93 W 2+ The second set of quadrupoles filters out the NH3 and Nb cluster ions, while the cluster ions can pass smoothly and enter the detector, thereby eliminating the double charge interference of the matrix W and achieving accurate determination of Nb.

[0070] 2.5 Optimization of reaction gas flow rate

[0071] The reaction gas flow rate is crucial to the effect of eliminating interference. Optimization of O2 flow rate: Collect the CPS counts at the mass-to-charge ratio of 202 in the blank matrix solution (1000 μg / mL W) and the sample solution (1000 μg / mL W~1.0 ng / mL Hg) and calculate the BEC value; the results of BEC and CPS counts changing with O2 flow rate are shown in Figure 5 It can be seen that with the change of O2 flow rate, the CPS counts and corresponding BEC values ​​in the blank solution and sample solution showed a trend of obvious decrease in the early stage, stability in the middle stage, and slight decrease in the late stage. When the O2 flow rate is 0.2~0.6 mL / min, 186 W 16 O ＋ Oxidation reaction with O2 generates new ions 186 W 16 O2 ＋, the interference of matrix W on Hg was significantly eliminated; when the O2 flow rate increased to 0.6~1.0 mL / min, the reaction was complete and the interference elimination reached a dynamic equilibrium; as the O2 flow rate continued to increase to 1.0~1.4 mL / min, the flow rate was too high and the excess O2 in the reaction cell 202 Hg ＋ Collisions occur, which leads to a downward trend in CPS counts. Considering the interference elimination effect and detection sensitivity, this study selected an O2 flow rate of 0.60 mL / min. Optimization of NH3 flow rate: The effect of optimizing the reaction gas flow rate on the signal intensity of m / z=39→39 and 93→174. When the flow rate is 0.5~0.6 mL / min, the signal intensity is high and the BEC is low. This study selected an NH3-He (1:9) flow rate of 0.55 mL / min.

[0072] Mass Spectral Interference and Isotope Selection

[0073] Mass spectrometry analysis usually selects mass numbers based on the principle of no interference and high abundance of isotope mass numbers. The selection of isotopes is shown in Table 2.

[0074] Table 2 Selection of isotopes for determination

[0075]

[0076] In QQQ-O2 mode, O2 is used as the reaction gas to eliminate interference. When O2 is introduced, whether the element reacts with O2 depends on the reaction enthalpy change (ΔHr). When ΔHr<0, the reaction is a spontaneous exothermic reaction, that is, the element can undergo oxidation reaction with O2; when ΔHr>0, the reaction is an endothermic reaction, and a slight oxidation reaction or no oxidation reaction occurs. In O2 mass in-situ mode, 202 Hg ＋ and 186 W 16 O ＋ All of them can pass through the first set of quadrupole mass filters (Q1=202) in the reaction pool. 186 W 16 O ＋ The reaction enthalpy with O2 is -1.01×10 -19 J can undergo oxidation reaction, while Hg and O2 cannot react spontaneously. The same applies to the determination of Re content in QQQ-O2 mode. In QQQ-NH3 mode, NH3 is used as the reaction gas to eliminate interference. NH3 has a lone electron pair and high reaction activity. Elements often undergo charge transfer reaction with NH3 to generate M(NH3)n + Eliminate interference. Set Q1 = 197, 197 Au + , 180 W17 O + Enter the reaction pool through Q1, and in the reaction pool 197 Au + Formation of Au ( NH3 ) 2+ Cluster ions. Set Q2 = 231, 180 W 17 O + is shielded, while Au( NH3 ) 2+ The matrix interference is eliminated by entering the detector through Q2. The same principle applies to the determination of Nb content in QQQ-NH3 mode.

[0077] Matrix Effects and Selection of Internal Standard Elements

[0078] The matrix effect is mainly that when the total soluble solid content in the solution to be tested is large, the matrix elements in the solution are generally prone to inhibit the signal intensity of the measured element, thereby causing a decrease or drift in the signal intensity of the analyzed element. In the face of such a problem, the internal standard correction method can be used. The internal standard element can effectively monitor and correct the short-term and long-term drift of the analytical signal and calibrate the general matrix effect, and has a significant compensation effect on the matrix effect. In this experiment, 1.0 mg / mL of zirconium matrix solution was added to the 10 ng / mL mixed standard solution. Under the selected instrument conditions, Sc, Rh, and Cs were used as internal standards for determination, and the recovery rates of each trace element when Sc, Rh, and Cs were used as internal standard elements were calculated. As shown in Table 3, Rh and Cs have better compensation effects on the matrix inhibition effect than Sc, and Rh was selected as the internal standard in the experiment.

[0079] Table 3 Selection of internal standard elements

[0080]

[0081] Limit of detection and limit of quantification

[0082] In this embodiment, the blank solution of the whole process was continuously measured 11 times, and the value obtained by 3 times the standard deviation was the detection limit, and the value obtained by 10 times the standard deviation and then converted according to the sample weight was the quantitative limit. The results are listed in Table 4.

[0083] Table 4 Calibration curve, detection limit and quantification limit

[0084]

[0085] Precision experiment

[0086] Precision experiments were carried out on samples 1#~4#. According to the experimental method, each impurity element was independently determined 7 times. The results are shown in Tables 5~7.

[0087] Table 5 Precision data of sample 1# (high purity tungsten + 10ug / g)

[0088]

[0089] Table 6 Precision data of sample 2# (high purity tungsten + 50ug / g)

[0090]

[0091] Table 7 Precision data of sample 3# (high purity tungsten + 80ug / g)

[0092]

[0093] Accuracy experiment

[0094] The spike recovery experiment was carried out on sample 1# (high purity tungsten + 10ug / g), and the amount of each impurity element added was 10 ug / g. The determination results and spike recovery rates are shown in Table 8. The results show that the spike recovery is good and the method is accurate and reliable.

[0095] Table 8 Recovery of spiked sample 1#

[0096]

[0097] In summary, the ICP-MS / MS method for analyzing trace niobium, gold, mercury and rhenium in high-purity tungsten was established, and the mechanism of eliminating mass spectrum interference in each mode in QQQ was studied. The QQQ-O2 and QQQ-NH3 modes can eliminate the mass spectrum interference of W oxide ions, hydroxide ions, doubly charged ions and polyatomic ions on Au, Hg, Re and Nb. The relative standard deviation of this method is 0.5% to 6.0%, with good precision, and the sample spike recovery is between 93.0% and 105.0%, with accurate results.

[0098] Although examples of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for determining trace amounts of niobium, gold, mercury and rhenium in high-purity tungsten, characterized in that: The steps include: Place the high purity tungsten sample in a beaker and do a blank test along with the test material; Add nitric acid and hydrofluoric acid, heat at low temperature until the sample is completely dissolved, and cool; Transfer to a plastic volumetric flask, add rhodium internal standard solution, dilute with water and mix well; Niobium and gold were determined in ammonia mode and mercury and rhenium were determined in oxygen mode using an inductively coupled plasma tandem mass spectrometer. The contents of niobium, gold, mercury and rhenium were calculated using the working curve method.

2. The method for determining the content of trace niobium, gold, mercury and rhenium in high-purity tungsten according to claim 1, characterized in that: Inductively coupled plasma tandem mass spectrometer parameter selection: sampling depth: 7.0~8.0 mm, nebulizer gas flow rate: 0.8~1.0 L / min, dilution gas flow rate 0.35~0.40 L / min, nebulizer chamber temperature 20°C, ammonia flow rate 40~50%, oxygen flow rate 30~40%.

3. The method for determining the content of trace niobium, gold, mercury and rhenium in high-purity tungsten according to claim 2, characterized in that: Isotope selection is based on the principle of high isotope abundance and no interference of impurity elements. The recommended mass number, measurement mode and internal standard element of isotopes are shown in the following table: Q1 is the mass number of the first mass spectrometer of the instrument, and Q2 is the mass number of the second mass spectrometer of the instrument.

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