GB/T 13748.8-2026Methods for chemical analysis of magnesium and magnesium alloys - Part 8: Determination of rare earth content (English PDF)

6.2.7 Nitric acid-hydrogen peroxide solution. Add 30 mL of nitric acid (rho=

1.42 g/mL) and 30 mL of hydrogen peroxide (6.2.3) to 150 mL of water. Mix well. Prepare fresh before use.

6.2.8 Saturated oxalic acid solution. Weigh 150g of oxalic acid (H2C2O4·2H2O) into a beaker, add 1000mL of water, and heat to boiling for 1 minute. Then, cool and filter.

6.2.9 Oxalic acid washing solution. Transfer 70 mL of saturated oxalic acid solution (6.2.8) and dilute with water to 500 mL.

6.2.10 Sebacic acid solution (50 g/L). Weigh 50 g of sebacic acid (C10H18O4) and dissolve it in 400 mL of ammonia water (rho =

0.90 g/mL), add... Filter 300 mL of water, dilute with water to 1000 mL, and mix well. Store in a polyethylene bottle.

6.2.11 Bromophenol blue solution (4 g/L). Weigh

0.4 g of bromophenol blue into a mortar, add

8.25 mL of sodium hydroxide solution (5 g/L), and grind. Continue until completely dissolved, then dilute with water to 100 mL and mix well.

6.3 Test Procedure

6.3.1 Sample Weigh the sample according to Table 1, 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 Measurement

6.3.3.1 Place the sample in a 400mL beaker, add 75mL of water, cover with a watch glass, and add hydrochloric acid in portions according to the total integral in Table 1 (6.2.2). After the reaction stops, add an appropriate amount of hydrogen peroxide (6.2.3), heat to boiling for 5 minutes. If there is still residue, filter with medium-speed filter paper and hot water. Wash the beaker and precipitate 4-5 times, discarding the precipitate. Dilute or evaporate the filtrate to approximately 100 mL and cool. If the magnesium alloy contains silver... Before filtering, a small amount of fiber pulp is first spread on the filter paper.

6.3.3.2 Add 3 drops of bromophenol blue solution (6.2.11) to the test solution, adjust the solution to just turn blue-purple with ammonia water (6.2.5), and heat on an electric furnace. Bring to a boil, remove from heat, let stand for 5 minutes, stirring occasionally, filter with high-speed filter paper, and wash the precipitate thoroughly with boiling water to ensure the filtrate volume is no greater than [missing value]. 250 mL of this solution is filtrate A; retain this solution. Dissolve the residue on the filter paper in portions using 20 mL of boiled nitric acid-hydrogen peroxide solution (6.2.7). The precipitate was placed back into the original beaker. The filter paper was washed 5-6 times with hot water. The solution volume was evaporated by heating to approximately 25 mL. This solution is filtrate B. This filtrate should be retained. Solution.

6.3.3.3 Add 10g of ammonium chloride (6.2.1) to filtrate A, first with ammonia water (6.2.4), then with ammonia water (6.2.5), and adjust the solution on the pH meter. The pH of the solution is 8.5, then add an excess of 10 mL of ammonia water (6.2.5). Heat the solution to 90°C, remove it from the heat, and add 20 mL of decane while stirring. The diacid solution (6.2.10) was left to stand for 15 minutes, stirring occasionally, and then filtered through medium-speed quantitative filter paper. The solution was then thoroughly washed with ammonia solution (6.2.6). If zinc is present, wash the precipitate again with 20 mL of ammonia water (6.2.4).

6.3.3.4 The porcelain crucible is ignited at 940°C~960°C and brought to constant weight. The weight is recorded as m

1.Filter paper containing the precipitate is placed into the constant-weight porcelain crucible. After complete ashing at below 500°C (do not allow the filter paper to ignite), calcine in a high-temperature furnace at 750°C~800°C for 30 minutes, then remove and cool.

6.3.3.5 Wash the oxide in the porcelain crucible with water into a beaker containing filtrate B, heat the solution, and add a few drops of hydrogen peroxide (6.2.3) to dilute. Dissolve the oxalic acid oxide, remove the beaker, rinse the beaker walls with water, and dilute to approximately 125 mL. While stirring, slowly add 25 mL of saturated oxalic acid solution. (6.2.8) Place the beaker in a boiling water bath for 30 minutes, then remove it and leave it at room temperature for more than 12 hours (or let it stand overnight).

6.3.3.6 Filter the rare earth oxalate precipitate using slow-speed quantitative filter paper, wash the precipitate thoroughly with oxalic acid washing solution (6.2.9), and then place the precipitate and filter paper in a container. Place the mixture into a porcelain crucible and ashing completely below 500°C (do not allow the filter paper to ignite). Then transfer it to a high-temperature furnace and calcine at 940°C~960°C. 60 min. Remove, place in a desiccator to cool, and weigh. Repeat the ignition process until the difference between two weighings is no greater than 0.0002 g, then weigh and record the result. The value is m2.

6.5 Precision

6.5.1 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 determined by linearity based on the data in Table 2. Obtained by interpolation or extrapolation.

6.5.2 Reproducibility The measured values of two independent test results obtained under reproducibility conditions, within the range of the average values given in Table 3, show that the two test results are absolutely... For differences not exceeding the reproducibility limit (R), the percentage of cases exceeding the reproducibility limit (R) is no more than 5%. The reproducibility limit (R) is determined based on the data in Table 3 using linear regression. Obtained by interpolation or extension.

7.2.4 Tribromoazoarsine solution (

0.85 g/L). Weigh

0.085 g of tribromoazoarsine [2-(2-arsenoylphenylazo)-7-(2,4,6-tribromophenylazo)] [Nitrogen)-1,8-dihydroxynaphthalene-3,6-disulfonic acid] was placed in a beaker, and 50 mL of anhydrous ethanol (rho=

0.79 g/mL) was added to dissolve it before transferring it to... Dilute to the mark with water in a 100mL volumetric flask and shake well.

7.2.5 Cerium Standard Stock Solution (1 mg/mL). Weigh 0.6142 g of cerium dioxide (wCeO2>=99.9%, preheated at 800°C~900°C). Ignite in a furnace for 30 minutes, remove and cool slightly, place in a desiccator for 60 minutes and weigh. Place in a.200 mL beaker and add 5 mL of perchloric acid. (rho=1.67g/mL), 2mL hydrogen peroxide (7.2.1), cover with a watch glass, heat at low temperature until cerium dioxide is completely dissolved, and evaporate to near dryness. Take... After cooling slightly, add 50 mL of hydrochloric acid (7.2.2) and 6 drops of hydrogen peroxide (7.2.1), heat to boiling to completely dissolve the salts and allow the hydrogen peroxide to dissolve. (7.2.1) Once completely decomposed, remove the sample, cool to room temperature, transfer to a 500 mL volumetric flask, add 35 mL of hydrochloric acid (7.2.2), and dilute with water to the mark. Mix thoroughly. This solution contains 1 mg of cerium per mL. Alternatively, use a certified standard solution.

Note. Under the conditions measured in this document, the absorbance of the complexes formed by the light rare earth elements (lanthanum, cerium, praseodymium, and neodymium) with tribromoarsine is basically consistent, therefore it can be used... Cerium working curve.

7.2.6 Cerium Standard Solution (2 µg/mL). Transfer

25.00 mL of cerium standard stock solution (7.2.5) to a 500 mL volumetric flask, add... 75 mL of hydrochloric acid (7.2.2) was diluted to the mark with water and mixed well. Then,

10.00 mL of this solution was transferred to a 250 mL volumetric flask and diluted with water to the mark. Graduate the scale and mix well. 1 mL of this solution contains 2 µg of cerium. Prepare fresh before use.

7.3 Test Procedure

7.3.1 Sample Weigh 0.25g of sample, accurate to 0.0001g, and record it as m3.

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

7.3.3 Blank Test Weigh 0.25g of metallic magnesium (wMg>=99.99%, wRE< 0.001%) and perform a blank test along with the sample.

7.3.4 Measurement

7.3.4.1 Place the sample in a 300mL beaker, cover with a watch glass, and add 20mL of hydrochloric acid (7.2.2) in portions. Heat at low temperature and... Add 2-3 drops of hydrogen peroxide (7.2.1) to completely dissolve the sample. Remove from heat, cool, transfer to a 250 mL volumetric flask, and dilute with water to the specified concentration. Scale, mix well.

7.3.4.2 According to the different rare earth contents in the sample, the test solution was separated according to Table 4, and the second separated test solution was placed in a 50mL volumetric flask. Add

7.0 mL of hydrochloric acid-oxalic acid solution (7.2.3) and shake well. Add

5.00 mL of tribromoazoarsine solution (7.2.4) and dilute with water to the specified concentration. Scale, mix well.

7.3.4.3 Place a portion of the test solution in a 1 cm absorption cell, and measure its absorbance at a wavelength of 632 nm using water as a reference. Subtract the absorbance of the blank test solution accompanying the sample from the absorbance of the test solution, and find the corresponding rare earth mass from the working curve, which is recorded as m4.

7.3.5 Plotting the Working Curve

7.3.5.1 In a set of 50mL volumetric flasks (or colorimetric tubes), add 0mL, 0.25mL, 0.50mL, 1.00mL, 3.00mL, and... Add

7.00 mL of cerium standard solution (7.2.6), then add

7.0 mL of hydrochloric acid-oxalic acid solution (7.2.3) and mix thoroughly. Add

5.00 mL of triglyceride solution. Bromoarsine azo solution (7.2.4), dilute to the mark with water and mix well.

7.3.5.2 Transfer a portion of the series of standard solutions into the absorption cell, using the zero-concentration solution of the standard solution in the working curve as a reference, and analyze it using a spectrophotometer. The absorbance was measured at a wavelength of 632 nm. A working curve was plotted with the mass of cerium on the x-axis and the absorbance on the y-axis. The linearity of the working curve was then determined. The correlation coefficient should be no less than 0.999.

7.5 Precision

7.5.1 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 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 determined by linearity of the data in Table 5. Obtained by interpolation or extrapolation.

7.5.2 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 calculated using linear regression based on the data in Table 6. It can be obtained by interpolation or extension.