GB/T 20975.7-2020Methods for chemical analysis of aluminium and aluminium alloys—Part 7:Determination of manganese content (English PDF)

4.1 Method summary

The sample was dissolved with sodium hydroxide, acidified with sulfuric acid and nitric acid, and oxidized with potassium periodate to develop color in the presence of phosphoric acid. At spectrophotometer wavelength The absorbance was measured at 525.0nm to determine the manganese content.

4.2 Reagents

Unless otherwise stated, only reagents and laboratory secondary water confirmed to be analytically pure are used in the analysis.

4.2.1 Sulfuric acid (rho=1.84g/mL).

4.2.2 Phosphoric acid (rho=1.69g/mL).

4.2.3 Nitric acid (rho=1.42g/mL).

4.2.4 Hydrofluoric acid (rho=1.14g/mL).

4.2.5 Sulfuric acid (1 1).

4.2.6 Sodium hydroxide solution (200g/L).

4.2.7 Fluoroboric mixed acid. Put 800mL of boric acid solution saturated at 20°C and 200mL of hydrofluoric acid (4.2.4) in a plastic bottle Mix well.

4.2.8 Potassium periodate solution (50g/L). Weigh 5g potassium periodate and dissolve in water, add 20mL nitric acid (4.2.3), and dilute with water to 100mL, mix well.

4.2.9 Sodium nitrite solution (20g/L).

4.2.10 Sodium sulfite solution (10g/L). Weigh 1g sodium sulfite, add sulfuric acid (1 20) to dissolve completely, and dilute with sulfuric acid (1 20) to 100mL, mix well.

4.2.11 Water without reducing agent. Add 10mL sulfuric acid (4.2.5) to each liter of water to acidify and boil, add a small amount of potassium periodate, and continue to boil About 10min, set aside after cooling.

4.2.12 Manganese standard storage solution. use a certified standard solution for preparation first. Or weigh 1.000g manganese (wMn>=99.99%) in a beaker, Add 20mL sulfuric acid (4.2.5), about 80mL water, heat to dissolve and boil for 3min, cool, transfer to a 1000mL volumetric flask, Dilute to the mark with water and mix well. This solution 1mL contains 1mg manganese.

4.2.13 Manganese standard solution. Pipette 50.00mL manganese standard stock solution (4.2.12) into a 1000mL volumetric flask and dilute to the mark with water. Mix well. This solution 1mL contains 0.05mg manganese.

4.4 Sample

Process the sample into chips with a thickness of not more than 1mm.

4.5 Analysis steps

4.5.1 Sample

According to Table 1, weigh the sample (4.4) of the corresponding mass (m0) to the nearest 0.0001g.

4.5.2 Parallel test

Do two tests in parallel and take the average value.

4.5.3 Blank test

Do a blank test with the sample. In a 250mL beaker, add 8mL nitric acid (4.2.3), 12mL sulfuric acid (4.2.5), and evaporate to dryness (Be careful not to burn). Dissolve the residue with a small amount of warm water, add 2mL nitric acid (4.2.3), 18mL sulfuric acid (4.2.5), 40mL sodium hydroxide Solution (4.2.6), mix well, heat until the solution is clear, dilute to about 65mL with water, and proceed according to 4.5.4.3. When the aluminum alloy sample contains silicon When the mass fraction is >10.0% and the mass fraction of manganese is < 0.040%, follow the steps below. In a 250mL beaker, add 8mL nitric acid (4.2.3), 12mL sulfuric acid (4.2.5), evaporate to dryness (be careful not to burn), dissolve the residue with a small amount of warm water. Add 2mL nitric acid (4.2.3), 8mL sulfuric acid (4.2.5), dilute with water to about 60mL, add 2mL fluoroboric acid (4.2.7), dilute with water to about 65mL, The following shall be carried out according to 4.5.4.3.

4.5.4 Determination

4.5.4.1 Place the sample (4.5.1) in a platinum (or nickel) dish, add a total of 40 mL of sodium hydroxide solution (4.2.6) in portions, and cover with platinum (or nickel) watch dish, after violent reaction, heat to dissolve and evaporate to a paste, slightly cold. Use as little warm water as possible to wash the cup wall and watch dishes. Dissolve. Carefully transfer the sample solution into a 250mL beaker containing 30mL sulfuric acid (4.2.5) and 10mL nitric acid (4.2.3) in advance; If there is a precipitate of manganese hydroxide adhered to the wall of the platinum (or nickel) cup, dissolve it with a small amount of slightly boiling sodium sulfite solution (4.2.10), and combine the solution with the sample In the solution, wash the platinum (or nickel) dish with warm water, heat the sample solution to clear and cool.

4.5.4.2 When the mass fraction of manganese is 0.0040%~0.040%, add acid according to Table 1, and heat and concentrate the sample solution to about 65mL. When the mass fraction of manganese is >0.040%~2.00%, transfer the sample solution (4.5.4.1) into the corresponding volumetric flask (V0) according to Table 1. Dilute to the mark with water and mix well; pipette the corresponding volume (V1) of the sample solution into a 250mL beaker, add the corresponding amount of acid, and dilute to approximately 65mL.

4.5.4.3 When the mass fraction of silicon in the aluminum alloy sample is> 10% and the mass fraction of manganese is < 0.04%, use the following operations instead of 4.5.4.1 and 4.5.4.2. Place the sample (4.5.1) in a 250mL beaker, add 20mL sulfuric acid (4.2.5), 10mL nitric acid (4.2.3), 2mL fluoroboron Mix the acid (4.2.7), cover with a watch glass, heat slightly until the sample is completely dissolved, and heat to boiling to remove nitrogen oxides. Dilute with warm water to about 50mL, add Pour a small amount of filter paper pulp, heat for several minutes, filter with slow filter paper, wash with warm water, and collect the filtrate in a 250mL beaker. Filter the residue together The paper is placed in a platinum crucible and completely ashed at 500°C~600°C (do not burn the filter paper), and cool. Add a few drops of sulfuric acid (4.2.1), 2mL~ 5mL hydrofluoric acid (4.2.4), add nitric acid (4.2.3) dropwise until the solution is clear, evaporate to dryness, burn at 700°C for several minutes, and cool. Add a few drops Dissolve the residue in a small amount of warm water with sulfuric acid (4.2.5) and heat it until it is completely dissolved (filter if necessary). Incorporate this solution into the sample solution and concentrate to About 65mL.

4.5.4.4 Add 5mL phosphoric acid (4.2.2), heat the sample solution to boiling, add 10mL potassium periodate solution (4.2.8), continue to boil until After the red color appears, continue to add water without reducing agent (4.2.11) to keep the volume of the sample solution unchanged, then boil for another 15 minutes~ 30min, heat preservation for 15min~20min, and cool. Transfer the sample solution into 100 mL rinsed with water without reducing agent (4.2.11) in advance In a volumetric flask, dilute to the mark with water (4.2.11) without reducing agent and mix well.

4.5.4.5 Transfer part of the sample solution (4.5.4.4) and blank test solution (4.5.3) into the corresponding absorption tank, and use water without reducing agent. (4.2.11) is the reference, and the absorbance (A1, A3) is measured at the wavelength of 525.0nm in the spectrophotometer. The remaining solution in the volumetric flask Add 2 drops of sodium nitrite solution (4.2.9) and mix to make the permanganic acid fade, and measure the absorbance (A2, A4). According to the absorption of manganese in the solution Luminosity (A), find the corresponding manganese mass (m1) from the working curve.

4.5.4.6 Calculate the absorbance A of manganese in the solution according to formula (1).

4.5.5 Drawing of working curve

4.5.5.1 Pipette 0mL, 0.80mL, 2.00mL, 4.00mL, 6.00mL, 8.00mL, 10.00mL manganese standard solution (4.2.13) in In a set of 250mL beakers, add 15mL sulfuric acid (4.2.5), 10mL nitric acid (4.2.3), 5mL phosphoric acid (4.2.2), and dilute with water. Release to about 70mL, heat to boiling. Add 10mL potassium periodate solution (4.2.8), continue to boil until red appears, continue to add While keeping the volume of the original water (4.2.11) unchanged, boil it for another 15-30 minutes, keep it warm for 15-20 minutes, and cool. Will melt The liquid is transferred into a set of 100 mL volumetric flasks rinsed with water without reducing agent (4.2.11), and diluted with water without reducing agent (4.2.11) to Scale and mix well.

4.5.5.2 Move part of the series of standard solutions (4.5.5.1) and reagent blank solution (without manganese standard solution) into the corresponding absorption pool to Water without reducing agent (4.2.11) is the reference, and the absorbance (A5, A7) is measured at the wavelength of 525.0nm in the spectrophotometer. Volumetric flask Add 2 drops of sodium nitrite solution (4.2.9) to the remaining test solution and mix to make the permanganic acid fade, and measure the absorbance (A6, A8) respectively. Manganese The amount is the abscissa, the solution absorbance (A) is the ordinate, and the working curve is drawn.

4.5.5.3 Calculate the absorbance A of manganese in the solution according to formula (2).

4.6 Test data processing

4.7 Precision

4.7.1 Repeatability

The measured values of two independent test results obtained under repeatability conditions, within the average range given below, these two test results The absolute difference does not exceed the repeatability limit r, and the case of exceeding the repeatability limit r does not exceed 5%. The repeatability limit r is within the linear range according to the data in Table 2. Obtained by interpolation or extension method.

4.7.2 Reproducibility

The measured values of two independent test results obtained under reproducibility conditions, within the average range given below, the two test results The absolute difference does not exceed the reproducibility limit R, and the case of exceeding the reproducibility limit R does not exceed 5%. Reproducibility limit R According to the data in Table 3, the linear internal Obtained by interpolation or extension method.

5.1 Method summary

In a weakly acidic solution, manganese is complexed with an excess of Na2EDTA standard titration solution. Use xylenol orange as indicator, titrate with zinc standard The solution was titrated with the remaining Na2EDTA standard titration solution to orange-red color to determine the manganese content.

5.2 Reagents

Unless otherwise stated, only reagents and laboratory tertiary water confirmed to be analytically pure are used in the analysis.

5.2.1 Ammonia (rho=0.90g/mL).

5.2.2 Mixed acid. 300mL hydrochloric acid (1 1) and 50mL nitric acid (1 1) mix well.

5.2.3 Hydrochloric acid (1 1).

5.2.4 Hexamethylenetetramine solution (300g/L).

5.2.5 Sodium hydroxide solution (150g/L).

5.2.7 Thiourea solution (100g/L).

5.2.8 Hydroxylamine hydrochloride solution (100g/L).

5.2.9 Sodium hydroxide solution (10g/L).

5.2.10 Zinc standard titration solution (c0=0.025mol/L). Weigh 1.6348g zinc (wZn>=99.99%), add 30mL hydrochloric acid (5.2.3) Heat to dissolve completely, cool, transfer to a 1000mL volumetric flask, dilute to the mark with water, and mix.

5.2.11 Disodium ethylenediaminetetraacetic acid (Na2EDTA) standard titration solution (c1 approx. 0.05mol/L).

---Preparation. Weigh 18.61g disodium ethylenediaminetetraacetic acid (Na2EDTA) in a beaker, add 500mL water, heat to dissolve completely, Cool, filter in a 1000mL volumetric flask, dilute to the mark with water, and mix.

---Calibration. Pipette volume (V2) of 30.00mL zinc standard titration solution (5.2.10) into a 400mL conical beaker, add 50mL Water, 10mL hexamethylenetetramine solution (5.2.4), 2 drops of xylenol orange solution (5.2.12), use Na2EDTA standard titration solution (5.2.11) Titrate until the solution is bright yellow as the end point, record the consumption of Na2EDTA standard titration solution volume (V3).

---Calculation. Calculate the concentration c1 of the Na2EDTA standard titration solution according to formula (4).

5.2.12 Xylenol orange solution (5g/L).

5.2.13 p-nitrophenol solution (2g/L).

5.3 Specimen

Process the sample into chips with a thickness of not more than 1mm.

5.4 Analysis steps

5.4.1 Sample

Weigh the sample (5.3) with a mass (m) of 0.50g to the nearest 0.0001g.

5.4.2 Parallel test

Do two tests in parallel and take the average value.

5.4.3 Determination

5.4.3.1 Place the sample (5.4.1) in a 400mL beaker, slowly add 30mL of sodium hydroxide solution (5.2.5), and heat until the sample is dissolved Complete, dilute with water to about 100mL boil, filter with medium-speed quantitative filter paper. Wash the precipitate 2 times with sodium hydroxide solution (5.2.9)~ 3 times, then wash the precipitate with hot water 5 to 6 times, and discard the filtrate.

5.4.3.2 Add a total of 30 mL of hot mixed acid (5.2.2) to the funnel in batches, dissolve the precipitate in the original beaker, and wash the precipitate with hot water. Filter paper, cool, transfer the filtrate into a 100mL volumetric flask (V4), dilute to the mark with water, and mix.

5.4.3.3 Pipette volume (V5) of 20.00mL sample solution (5.4.3.2) into a conical beaker, add 25mL ammonium fluoride solution (5.2.6), 3mL thiourea solution (5.2.7), 7mL hydroxylamine hydrochloride solution (5.2.8), 2 drops of p-nitrophenol solution (5.2.13), neutralized with ammonia (5.2.1) Yellow, then adjust to colorless with hydrochloric acid (5.2.3) and excess 4 drops. Add 40mL hexamethylenetetramine solution (5.2.4), volume (V6) is 20.00mL Na2EDTA standard titration solution (5.2.11), 2 drops of xylenol orange solution (5.2.12), use zinc standard titration solution (5.2.10) Titrate to orange-red as the end point. Record the volume of the zinc standard titration solution (V7).

Note: When approaching the end point, the titration speed should be slow. After the test solution is orange-red, continue to vibrate for more than 10 seconds until the red color does not fade.

5.5 Test data processing

The manganese content is calculated as the mass fraction wMn of manganese, calculated according to formula (5).

5.6 Precision

5.6.1 Repeatability

The measured values of two independent test results obtained under repeatability conditions, within the average range given below, these two test results The absolute difference does not exceed the repeatability limit r, and the case of exceeding the repeatability limit r does not exceed 5%. The repeatability limit r is within the linear range according to the data in Table 4 Obtained by interpolation or extension method.

5.6.2 Reproducibility

The measured values of two independent test results obtained under reproducibility conditions, within the average range given below, the two test results The absolute difference does not exceed the reproducibility limit R, and the case of exceeding the reproducibility limit R does not exceed 5%. Reproducibility limit R is linear within Obtained by interpolation or extension method.