Method for measuring content of metal impurities in quartz glass

Abstract

The invention belongs to the technical field of chemical analysis, and discloses a method for measuring the content of metal impurities in quartz glass, which comprises the following steps: 1) adding ultra-pure hydrofluoric acid into a quartz glass sample, heating to dissolve the surface, ultrasonically cleaning the residual sample, and drying to obtain a pretreated sample; 2) respectively adding ultra-pure hydrofluoric acid into at least two pre-treated samples, heating and digesting, completely digesting the samples until the ultra-pure hydrofluoric acid is evaporated to dryness, and then adding ultra-pure nitric acid to obtain a parallel sample; at the same time, preparing at least two blank samples under the same condition; and 3) preparing a standard solution of the to-be-detected metal element with gradient concentration, determining and drawing a standard curve by adopting an inductively coupled plasma mass spectrometer, then determining a parallel sample and a blank sample, and calculating the content of the metal element in the quartz glass sample. On one hand, the sample is controlled not to be polluted in the sample preparation process, on the other hand, the sample is controlled not to be polluted in the testing process, and finally the real metal impurity content is tested.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical analysis, and particularly relates to a method for determining the content of metal impurities in quartz glass. Background Art

[0002] The main metal impurities in quartz glass include Li (lithium), Na (sodium), Mg (magnesium), Al (aluminum), K (potassium), Ca (calcium), Ti (titanium), Cr (chromium), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Cu (copper), Ge (germanium), Zr (zirconium), Mo (molybdenum), etc. Metal impurities have a great impact on the quality of quartz glass and are key control indicators for quartz glass. The content requirements of metal impurities vary depending on the use of the prepared quartz glass, but generally, the lower the better.

[0003] Based on the strict requirements of quartz glass for metal impurities, accurately determining the content of metal impurities in quartz glass is of great significance. Currently, the conventional determination method is to crush the quartz glass, digest it with hydrofluoric acid to prepare a sample solution, and then use instruments such as inductively coupled plasma mass spectrometry (ICP-MS) to determine the metal content in the sample solution. However, the sample preparation process involves crushing, cleaning, weighing, digestion, and the recovery of metal ions after digestion. Both the sample preparation process and the testing process are extremely vulnerable to external contamination, making it difficult to measure the true impurity content of the sample. Especially for trace metal impurities at the ppb level, the phenomenon of result distortion is more serious. Therefore, an accurate determination method is urgently needed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for determining the content of metal impurities in quartz glass in view of the deficiencies of the existing technology. This determination method controls the sample from being contaminated during the sample preparation process on the one hand and controls the sample from being contaminated during the testing process on the other hand, and finally measures the true content of metal impurities.

[0005] To solve the technical problems proposed by the present invention, the present invention provides a method for determining the content of metal impurities in quartz glass, including the following steps:

[0006] 1) Add ultra-high purity hydrofluoric acid to the quartz glass sample and heat to dissolve the surface, then ultrasonically clean the remaining sample and dry it to obtain the pre-treated sample;

[0007] 2) Take at least two pre-treated samples, add ultra-high purity hydrofluoric acid to each and heat to digest. The sample is completely digested until the ultra-high purity hydrofluoric acid evaporates to dryness, and then ultra-high purity nitric acid is added to recover metal ions to obtain parallel samples; at the same time, at least two blank samples are prepared under the same conditions;

[0008] 3) Prepare a standard solution of the metal element to be measured with a gradient concentration, measure it using an inductively coupled plasma mass spectrometer and draw a standard curve, then measure parallel samples and blank samples to calculate the content of the metal element in the quartz glass sample.

[0009] In the above solution, the quartz glass sample is a block sample with a side length of ≤5 mm and a thickness of ≤1 mm, or a granular sample with a particle size of ≤1 mm.

[0010] In the above solution, the method for preparing the quartz glass sample is to place the quartz glass on a pad and crush the quartz glass with a hammer wrapped in a dust-free cloth to obtain a quartz glass sample of a target size.

[0011] Furthermore, the dust-free cloth is a dust-free cloth with a cleanliness level of Class 100 or higher.

[0012] Furthermore, the pad is made of PFA or PTFE.

[0013] In the above scheme, the tool for taking the quartz glass sample is made of PFA or PTFE.

[0014] In the above scheme, the container for holding the quartz glass sample during heating dissolution and heating digestion is made of PFA or PTFE.

[0015] In the above scheme, before use, the container containing the quartz glass sample during heating dissolution and heating digestion is first added with 10 to 20 mL of ultra-high-purity hydrofluoric acid and evaporated to dryness. The operation is repeated 3 to 5 times, and then soaked in ultra-high-purity nitric acid for 24 to 72 hours.

[0016] In the above scheme, a heating table made of graphite or ceramic material is used for heating dissolution and heating digestion.

[0017] In the above solution, the purity of the ultra-high-purity hydrofluoric acid is ≥99.999%, and the content of a single metal impurity is <10ppt.

[0018] In the above solution, the mass fraction of the ultra-high purity hydrofluoric acid is 40-50%.

[0019] In the above solution, the purity of the ultra-high purity nitric acid is ≥99.999%, and the content of a single metal impurity is <10ppt.

[0020] In the above solution, the volume fraction of the ultra-high purity nitric acid is 2-5%.

[0021] In the above solution, the volume ratio of the mass of the quartz glass sample to the ultra-high purity hydrofluoric acid is 1 g: (10-20) mL.

[0022] In the above scheme, the temperature of the heating and dissolving is 70 to 90° C., and the time is 8 to 15 minutes.

[0023] In the above solution, the ultrasonic cleaning of the remaining samples is first carried out with ultra-high-purity nitric acid for 10 - 20 minutes, and then with ultrapure water for 10 - 20 minutes, and this is repeated 2 - 3 times.

[0024] In the above solution, the drying temperature is 80 - 100 °C.

[0025] In the above solution, when weighing the pre-treated samples, it is accurate to 0.0001 g.

[0026] In the above solution, the mass ratio of the pre-treated samples to ultra-high-purity hydrofluoric acid is 1 g : (10 - 15) mL.

[0027] In the above solution, the temperature for heating and digestion is 120 - 140 °C.

[0028] In the above solution, in step 2), the volume ratio of ultra-high-purity nitric acid to ultra-high-purity hydrofluoric acid is 1 : (1 - 1.5).

[0029] In the above solution, the standard curve contains at least 4 concentration points, preferably 4 - 6 concentration points, and the fitting index R of the standard curve 2 ≥ 0.995 can be used. If R 2 does not meet the requirements, the standard curve needs to be prepared again.

[0030] In the above solution, the detection limit of the inductively coupled plasma mass spectrometer (ICP-MS) ≤ 1 ppt.

[0031] In the above solution, the metal elements include one or more of Li, Na, Mg, Al, K, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Ge, Zr, Mo.

[0032] In the above solution, helium mode is used to detect Ti, Ge, Zr, Mo, cold flame hydrogen mode is used to detect Li, Na, Mg, Al, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, and hot flame mode is used to assist in parameter optimization.

[0033] Furthermore, the parameters of the hot flame mode are: plasma power 1400.0 - 1550.0 W, sampling depth 0.5 - 0.8 mm, nebulizer gas flow rate 0.8 - 1.1 L / min, compensation gas flow rate 0.7 - 0.9 L / min, extraction lens voltage -180.0 - -200.0 V, detector (counting) voltage 900.0 - 1000.0 V.

[0034] Further, the parameters of the helium mode are as follows: plasma power 1400.0 - 1550.0 W, sampling depth 0.5 - 0.8 mm, nebulizer gas flow rate 0.9 - 1.0 L / min, makeup gas flow rate 0.7 - 0.9 L / min, helium gas flow rate 4 - 6 mL / min, collision cell focusing lens voltage -7.0 - -10.0 V, extraction lens voltage -180.0 - -200.0 V, detector (counting) voltage 900.0 - 1000.0 V.

[0035] Further, the parameters of the cold flame hydrogen mode are as follows: plasma power 550.0 - 600.0 W, sampling depth 1.0 - 1.5 mm, nebulizer gas flow rate 0.9 - 1.0 L / min, makeup gas flow rate 0.7 - 1.0 L / min, hydrogen gas flow rate 0.4 - 0.7 mL / min, collision cell focusing lens voltage 10.0 - 15.0 V, extraction lens voltage -230.0 - -250.0 V, detector (counting) voltage 900.0 - 950.0 V.

[0036] In the above solution, the relative deviation between the parallel sample test values does not exceed 20%, and the relative deviation between the blank sample test values does not exceed 50%. Otherwise, the sample needs to be prepared again for determination. The calculation formula for the relative deviation is:

[0037]

[0038] where: x1 and x2 are the two test values; RE is the relative deviation between the two test values.

[0039] In the above solution, the content of metal elements in the quartz glass sample is calculated according to the following formula:

[0040]

[0041] where: w is the content of metal elements in the quartz glass sample; c is the average value of the parallel sample test concentration; c0 is the average value of the blank sample test concentration; V is the constant volume of the parallel sample; m is the mass of the quartz glass sample.

[0042] In the above solution, all sample preparation and testing processes are carried out in a clean room with a cleanliness level of 100 or higher, and the heating digestion process is carried out in a fume hood in a clean room with a cleanliness level of 100 or higher.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] 1) The present invention provides a method for determining trace metal impurities in quartz glass. On the one hand, during the sample preparation process, through cleaning with hydrofluoric acid combined with ultrasonic treatment, the surface contamination layer of the quartz glass sample is removed directionally, and the sample is controlled not to be contaminated during the sample preparation process. On the other hand, by preparing parallel samples and blank samples, the relative deviation of the test values is controlled, and the sample is controlled not to be contaminated during the test process, and finally the true metal impurity content is measured.

[0045] 2) The present invention reduces the risk of metal introduction by using high-purity reagents; reduces the risk of metal adsorption by specifying the materials of tools and containers; by controlling the size of the quartz glass sample, the concentration of hydrofluoric acid and the digestion time during digestion, it ensures that the sample is completely digested and quickly evaporated to dryness, avoiding the introduction of environmental pollution due to too long digestion time; by combining helium / hydrogen collision mode detection, it specifically eliminates mass spectrometry interference and improves the signal-to-noise ratio of trace elements; finally, the detection accuracy reaches the ppb level, and the background of metal ions in the blank sample is ≤0.05 ppb. Detailed implementation mode

[0046] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the content of the present invention is not limited to the following embodiments only.

[0047] Embodiment

[0048] 1) Preparation work

[0049] Ultra-high purity hydrofluoric acid: purity ≥99.999%, single metal impurity content <10 ppt, mass fraction is 49%;

[0050] Ultra-high purity nitric acid: purity ≥99.999%, single metal impurity content <10 ppt, volume fraction is 3%;

[0051] Ultra-pure water: single metal element content <10 ppt;

[0052] PFA material digestion tank: Before use, first add 15 mL of ultra-high purity hydrofluoric acid and evaporate to dryness, repeat the operation 4 times, and then soak it with ultra-high purity nitric acid for 36 h;

[0053] Heating device: graphite material heating table;

[0054] Detection equipment: Select an ICP-MS equipment with a detection limit ≤1 ppt;

[0055] Environmental requirements: All sample preparation and testing processes are carried out in a class 100 clean room, and the heating and digestion process is carried out in a fume hood in the class 100 clean room;

[0056] 2) Sample pretreatment

[0057] Put The 8655 quartz glass was placed on a PFA backing plate, and a hammer wrapped with a Class 100 dust-free cloth was used to break the sample to obtain a granular quartz glass sample with a particle size ≤ 1 mm. Using PFA forceps, 0.5 g of the quartz glass sample was taken and placed in a PFA digestion vessel. After adding 5 mL of ultra-high purity hydrofluoric acid, it was heated to 80 °C and dissolved for 10 min. After dissolution, the remaining sample was ultrasonically cleaned, first with ultra-high purity nitric acid for 10 min, and then with ultrapure water for 10 min. This was repeated 2 times. The cleaned sample was dried at 70 °C to obtain the pretreated sample;

[0058] 3) Preparation of parallel samples and blank samples

[0059] Using PFA forceps, two 0.5000 g pretreated samples were taken and placed in PFA digestion vessels labeled a and b. Two clean digestion vessels labeled c and d were taken. 5 mL of ultra-high purity hydrofluoric acid was added to each of the four digestion vessels. Then the digestion vessels were placed on a graphite heating stage to heat and digest the samples. The digestion temperature was 140 °C. Wait until the samples were completely digested until the hydrofluoric acid evaporated completely. Then 5 mL of ultra-high purity nitric acid was added to recover metal ions, obtaining parallel samples a, b and blank samples c, d;

[0060] 4) Testing

[0061] ① Preparation of working curve standard solutions: Standard solutions with gradient concentrations were prepared using the standard stock solutions of the corresponding elements of the components to be measured, with concentrations of 0.1 ng / g, 0.2 ng / g, 0.5 ng / g, and 1.0 ng / g respectively. The standard curve fitting index R 2 = 0.998;

[0062] ② Testing and data processing: Start the inductively coupled plasma mass spectrometry equipment, and tune it to the best state in the hot flame mode, helium mode, and cold flame hydrogen mode respectively. Then introduce the parallel samples and blank samples into the ICP-MS instrument, and perform tests using the cold flame hydrogen mode and helium mode at the same time. The elements detected using the helium mode are: Ti, Ge, Zr, Mo; The elements detected using the cold flame hydrogen mode are: Li, Na, Mg, Al, K, Ca, Cr, Mn, Fe, Co, Ni, Cu.

[0063] Among them, the parameters for helium mode debugging are: plasma power 1550.0 W, sampling depth 0.70 mm, nebulizer gas flow rate 0.97 L / min, compensation gas flow rate 0.80 L / min, helium gas flow rate 4.90 mL / min, collision cell focusing lens voltage -7.8 V, extraction lens voltage -197 V, detector (counting) voltage 950.2 V.

[0064] The parameters for cold flame hydrogen mode debugging are as follows: plasma power 560.0 W, sampling depth 1.2 mm, nebulizer gas flow rate 0.96 L / min, makeup gas flow rate 0.80 L / min, hydrogen gas flow rate 0.50 mL / min, collision cell focusing lens voltage 12.5 V, extraction lens voltage -240.0 V, detector (counting) voltage 930.5 V.

[0065] 5) Test results

[0066] The test values (unit: ppb) of the blank sample and parallel samples are shown in the following table.

[0067]

[0068] The content of metal elements in the quartz glass sample is calculated according to the following formula:

[0069]

[0070] Generally, data where the test value of the parallel sample is not more than 3 to 5 times that of the blank sample is not used for data processing, which can be defined according to the specific experimental environment, and the result is represented as "<0.1", as shown in the following table (the result is retained to 2 decimal places):

[0071]

[0072] The above embodiments are merely examples clearly described and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here, and the obvious changes or modifications thus extended are still within the protection scope of this invention.

Claims

1. A method for determining the content of metal impurities in quartz glass, characterized in that, The following steps are involved: 1) adding ultra-high-purity hydrofluoric acid to a quartz glass sample and then heating to dissolve the surface, ultrasonically cleaning the remaining sample and then drying it to obtain a pre-treated sample; 2) Take at least two pre-treated samples and add ultra-high-purity hydrofluoric acid to each sample and then heat and digest them. The samples are completely digested until the ultra-high-purity hydrofluoric acid is evaporated to dryness. Then, ultra-high-purity nitric acid is added to recover the metal ions to obtain parallel samples. At the same time, prepare at least two blank samples under the same conditions. 3) Prepare a standard solution of the metal element to be measured with a gradient concentration, measure it using an inductively coupled plasma mass spectrometer and draw a standard curve, then measure parallel samples and blank samples to calculate the content of the metal element in the quartz glass sample.

2. The method for determining the content of metallic impurities in fused silica according to claim 1, characterized in that, The quartz glass sample is a block sample with a side length of ≤5 mm and a thickness of ≤1 mm, or a granular sample with a particle size of ≤1 mm.

3. The method for determining the content of metal impurities in fused quartz glass according to claim 1, wherein, The purity of the ultra-high-purity hydrofluoric acid is ≥99.999%, the content of a single metal impurity is <10ppt, and the mass fraction is 40-50%. The purity of the ultra-high-purity nitric acid is ≥99.999%, the content of a single metal impurity is <10ppt, and the volume fraction is 2-5%.

4. The method for determining the content of metal impurities in fused quartz glass according to claim 1, characterized in that, In step 1), the volume ratio of the mass of the quartz glass sample to the ultra-high purity hydrofluoric acid is 1 g: (10-20) mL; the temperature of the heating and dissolving is 70-90° C., and the time is 8-15 min.

5. The method for determining the content of metal impurities in fused quartz glass according to claim 1, wherein In step 1), the remaining sample is ultrasonically cleaned by first cleaning with ultra-high purity nitric acid for 10 to 20 minutes, then cleaning with ultra-pure water for 10 to 20 minutes, and repeating this process 2 to 3 times. The drying temperature is 80 to 100°C.

6. The method for determining the content of metal impurities in fused silica according to claim 1, wherein, In step 2), the pretreated sample is weighed accurately to 0.0001 g, the mass ratio of the pretreated sample to ultra-high-purity hydrofluoric acid is 1 g:(10-15) mL, the heating digestion temperature is 120-140° C., and the volume ratio of the ultra-high-purity nitric acid to the ultra-high-purity hydrofluoric acid is 1:(1-1.5).

7. The method for determining the content of metal impurities in fused quartz glass according to claim 1, characterized in that, The metal element to be measured includes one or more of Li, Na, Mg, Al, K, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Ge, Zr, and Mo; the standard curve contains at least 4 concentration points, and the fitting index R of the standard curve 2 ≥0.995 can be used.

8. The method for determining the content of metal impurities in fused silica according to claim 1, wherein The detection limit of the inductively coupled plasma mass spectrometer is ≤1 ppt. Ti, Ge, Zr, and Mo are detected using helium mode, and Li, Na, Mg, Al, K, Ca, Cr, Mn, Fe, Co, Ni, and Cu are detected using cold flame hydrogen mode.

9. The method for determining the content of metal impurities in fused quartz glass according to claim 1, characterized in that, The tools for taking quartz glass samples are made of PFA or PTFE. The containers for holding quartz glass samples during heating dissolution and heating digestion are made of PFA or PTFE. Before use, 10 to 20 mL of ultra-high-purity hydrofluoric acid is added and evaporated to dryness. The operation is repeated 3 to 5 times, and then soaked in ultra-high-purity nitric acid for 24 to 72 hours. The heating table during heating dissolution and heating digestion is made of graphite or ceramic.

10. The method for determining the content of metal impurities in fused quartz glass according to claim 1, wherein, The relative deviation between the test values of parallel samples is controlled not to exceed 20%, and the relative deviation between the test values of blank samples is controlled not to exceed 50%. All sample preparation and testing processes are carried out in a clean room of Class 100 or higher cleanliness, and the heating digestion process is carried out in a fume hood in a clean room of Class 100 or higher cleanliness.

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