GB/T 13748.9-2026Methods for chemical analysis of magnesium and magnesium alloys - Part 9: Determination of iron and silicon content - Spectrophotometry (English PDF)

6.2.8 Iron Standard Solution A (25 µg/mL). Transfer

50.00 mL of the iron standard stock solution (6.2.7) to a 500 mL volumetric flask and dilute with water. Dilute to the mark and mix well. 1 mL of this solution contains 25 µg of iron.

6.2.9 Iron Standard Solution B (5 µg/mL). Transfer

50.00 mL of iron standard solution A (6.2.8) to a 250 mL volumetric flask and dilute with water. Fill to the mark and mix well. This solution contains 5 µg of iron per mL. Prepare fresh before use.

6.3 Test Procedure

6.3.1 Sample Weigh the sample according to Table 1 (Chapter 5), accurate to 0.0001g, and record it as m0.

6.3.2 Parallel Tests Perform the experiment twice in parallel and take the average value.

6.3.3 Blank Test A blank test was performed along with the sample.

6.3.4 Measurement

6.3.4.1 Place the sample in a 250mL beaker, add 5mL of water, and then add 20mL of hydrochloric acid in portions (6.2.3). Cover the beaker with the top layer of water. After a vigorous reaction, add 2 drops of hydrogen peroxide (6.2.1), heat until completely dissolved, and boil to decompose excess hydrogen peroxide (6.2.1). Continue heating and evaporating until a paste is formed (the volume of the blank test solution accompanying the sample is approximately

0.5 mL). Remove from heat and cool to room temperature. Transfer the test solution to... In a 100mL volumetric flask (filter if turbid). For samples containing zirconium or silicon, if there is insoluble residue, add 1 drop of hydrogen. Fluoroic acid (6.2.2) is used as a solubilizer.

6.3.4.2 Dilute with water to approximately 50 mL and mix well. Add 4 mL of hydroxylamine hydrochloride solution (6.2.4) and 15 mL of acetate-sodium acetate. The buffer solution (6.2.5) and 10 mL of o-phenanthroline solution (6.2.6) were diluted with water to the mark, mixed well, and left to stand for

0.5 h.

6.3.4.3 Transfer a portion of the test solution into the cuvette recommended in Table 1, using the blank test solution accompanying the sample as a reference, and measure the solution at the wavelength of the spectrophotometer. The absorbance was measured at 510 nm, and the corresponding mass of iron (mFe) was obtained from the working curve.

6.4 Drawing the working curve

6.4.1 Based on the mass fraction of iron in the sample, a series of standard solutions were prepared in the following manner.

---When the mass fraction of iron is 0.0010%~0.0050%. transfer 0 mL,

0.50 mL,

2.00 mL, respectively.

6.00 mL of iron standard solution B (6.2.9) were placed in a set of 100 mL volumetric flasks and proceeded according to 6.3.4.2.

---When the iron mass fraction is greater than 0.0050%~0.010%. transfer 0 mL,

0.50 mL,

2.00 mL, respectively.

6.00 mL of iron standard solution A (6.2.8) were placed in a set of 100 mL volumetric flasks and proceeded according to 6.3.4.2.

---When the iron mass fraction is greater than 0.010%~0.100%. transfer 0 mL,

0.50 mL,

3.00 mL, respectively.

9.00 mL of iron standard solution A (6.2.8) were placed in a set of 100 mL volumetric flasks and proceeded according to 6.3.4.2.

6.4.2 Transfer a portion of the test solution into the cuvette recommended in Table 1, using the "zero" concentration solution in the working curve series of standard solutions as a reference, and dilute it at a

6.6 Precision

6.6.1 Repeatability The measured values of two independent test results obtained under repeatability conditions, within the range of the average values given in Table 2, represent the two test results. The absolute difference does not exceed the repeatability limit (r), and the number of cases exceeding the repeatability limit (r) does not exceed 5%. The repeatability limit (r) is calculated using linear data from Table 2. It can be obtained by interpolation or extension.

6.6.2 Reproducibility The measured values of two independent test results obtained under reproducibility conditions, within the range of the average values given in Table 3, represent the two test results. The absolute difference should not exceed the reproducibility limit (R), and the number of cases exceeding the reproducibility limit (R) should not exceed 5%. The reproducibility limit (R) is determined according to the data in Table 3. Obtained by linear interpolation or extrapolation.

7.2.11 Magnesium matrix solution (10 mg/mL). Weigh

5.00 g of magnesium (wMg >= 99.99%, wSi <= 0.0005%) into a 500 mL beaker. Add 50 mL of hydrochloric acid (7.2.4) in portions, cover with a watch glass, and after the vigorous reaction stops, heat slowly until completely dissolved. Then add a few drops of... Add hydrogen peroxide (rho =

1.10 g/mL), continue heating to boiling for 5 minutes, then cool to room temperature. Transfer to a 500 mL volumetric flask and dilute with water to the mark. Mix well and transfer to a plastic bottle.

7.2.12 Silicon standard stock solution (100 µg/mL). Weigh 0.2140 g of silicon dioxide (wSiO2>=99.99%, pre-calcined at 1000°C). (After 1 hour and cooling to room temperature in a desiccator) In a platinum crucible, add 5g of anhydrous sodium carbonate, stir well, then cover with 1g of anhydrous sodium carbonate. Melt at 950°C until transparent, then cool. Extract with hot water, heat until the solution is transparent, and cool to room temperature. Transfer to a 1000mL volumetric flask and add water. Dilute to the mark, mix well, and store in a plastic bottle. 1 mL of this solution contains 100 µg of silicon. Alternatively, use a certified standard solution.

7.2.13 Silicon Standard Solution A (10 µg/mL). Transfer

50.00 mL of silicon standard stock solution (7.2.12) to a 500 mL volumetric flask, and use... Dilute with water to the mark, mix well, and store in a plastic bottle. 1 mL of this solution contains 10 µg of silicon. Prepare fresh before use.

7.2.14 Silicon Standard Solution B (5 µg/mL). Transfer

25.00 mL of silicon standard stock solution (7.2.12) to a 500 mL volumetric flask, and use... Dilute with water to the mark, mix well, and store in a plastic bottle. 1 mL of this solution contains 5 µg of silicon. Prepare fresh before use.

7.2.15 p-Nitrophenol solution (1 g/L).

7.3 Test Procedure

7.3.1 Sample Weigh the sample according to Table 4 (Chapter 5), accurate to 0.0001g, and record it as m1.

7.3.2 Parallel Tests Perform the experiment twice in parallel and take the average value.

7.3.3 Blank Test A blank test was performed along with the sample.

7.3.4 Measurement

7.3.4.1 Place the sample in a.200 mL polytetrafluoroethylene beaker, add 15 mL of bromine water (7.2.1), and slowly add

2.4 mL of sulfuric acid. (7.2.2) Cover the cup. If the orange color of bromine disappears or residue precipitates during the dissolution process, add bromine water (7.2.1). Wait until the sample is completely dissolved. After dissolving, heat to boiling until the orange color disappears. For samples containing silver or calcium, use

3.5 mL of nitric acid (7.2.3) instead of sulfuric acid. (7.2.2).

7.3.4.2 Dilute with water to approximately 30 mL, cool to room temperature, add 1 mL of potassium fluoride solution (7.2.6), and gently shake to combine. Place at 60°C~70°C for 15min~20min, then add 10mL of saturated boric acid solution (7.2.7), mix well, and cool to room temperature.

7.3.4.3 When the mass fraction of silicon is not greater than 0.040%, transfer the test solution to a 100 mL volumetric flask (if turbidity occurs, use a slow quantitative filter). (Filter via paper), dilute with water to approximately 60 mL. When the mass fraction of silicon is greater than 0.040%, transfer the test solution to the corresponding volume according to Table 4. In a volumetric flask (filter using slow-speed quantitative filter paper if turbid), dilute to the mark with water and mix well. Aliquot the corresponding volumes of the test solution according to Table 4. Dilute with water to approximately 60 mL in a 100 mL volumetric flask.

7.3.4.4 Add 1 drop of p-nitrophenol solution (7.2.15) to the test solution, adjust to a bright yellow color with ammonia (7.2.5), and then adjust to a darker color with hydrochloric acid (7.2.4). Colorless and in excess (1 mL). Add 5 mL of ammonium molybdate solution (7.2.8), mix well, and let stand for 10 min. For samples containing silver, use nitric acid... (7.2.3) Replace hydrochloric acid (7.2.4) to adjust to colorless and add

0.8 mL in excess.

7.3.4.5 Add 5 mL of tartaric acid solution (7.2.9), 10 mL of sulfuric acid (7.2.2), and 5 mL of ascorbic acid solution (7.2.10), and dilute with water to the specified concentration. Mark the scale, mix well, and let stand for 15 minutes. For samples containing silver or calcium, use

14.6 mL of nitric acid (7.2.3) instead of sulfuric acid (7.2.2).

7.3.4.6 Transfer a portion of the test solution into the cuvette recommended in Table 4, using the blank test solution accompanying the sample as a reference, and measure the solution at the wavelength of the spectrophotometer. The absorbance was measured at 810 nm, and the corresponding silicon mass (mSi) was obtained from the working curve.

7.4 Drawing the working curve

7.4.1 Based on the mass fraction of silicon in the sample, a series of standard solutions were prepared in the following manner.

---When the mass fraction of silicon is 0.0010%~0.010%. transfer 0 mL,

0.50 mL,

2.00 mL, respectively.

5.00 mL of silicon standard solution B (7.2.14) were added to a series of 100 mL plastic volumetric flasks. Dilute 20 mL of magnesium matrix solution (7.2.11) with water to a volume of approximately 60 mL and mix well. Proceed according to 7.3.4.4~7.3.4.5.

---When the mass fraction of silicon is greater than 0.010%~1.50%. transfer 0 mL,

4.00 mL, respectively.

10.00 mL of silicon standard solution A (7.2.13) were placed in a series of 100 mL plastic volumetric flasks, and the solution was mixed with... A suitable amount of magnesium matrix solution (7.2.11) was diluted with water to approximately 60 mL and mixed thoroughly. Follow the steps in

7.3.4.4 to 7.3.4.5. conduct.

7.4.2 Transfer a portion of the test solution into the cuvette recommended in Table 4, using the "zero" concentration solution in the standard solution series of the working curve as a reference, and dilute it at a

1.1 ratio. The absorbance was measured at a wavelength of 810 nm using a photometer. A working curve was plotted with the mass of silicon on the x-axis and absorbance on the y-axis. The linear correlation coefficient of the curve should not be less than 0.999.

7.6 Precision

7.6.1 Repeatability The measured values of two independent test results obtained under repeatability conditions, within the range of the average values given in Table 5, represent the two test results. The absolute difference should not exceed the repeatability limit (r), and the number of cases exceeding the repeatability limit (r) should not exceed 5%. The repeatability limit (r) is calculated using linear data from Table 5. It can be obtained by interpolation or extension.

7.6.2 Reproducibility The measured values of two independent test results obtained under reproducibility conditions, within the range of the average values given in Table 6, represent the two test results. The absolute difference should not exceed the reproducibility limit (R), and the number of cases exceeding the reproducibility limit (R) should not exceed 5%. The reproducibility limit (R) is determined according to the data in Table 6. Obtained by linear interpolation or extrapolation.