GB/T 20975.24-2020Methods for chemical analysis of aluminium and aluminium alloys—Part 24: Determination of total rare earth content (English PDF)

4.1 Method summary

The sample is dissolved in hydrochloric acid, and hydrogen peroxide and ethanol are used to eliminate the coexistence of tetravalent titanium ions and trivalent iron ions in a hydrochloric acid-oxalic acid medium. Interference, the rare earth elements of the cerium group and tribromoarsenazo form a stable blue-violet complex, and the absorption is measured at a wavelength of 634.0nm with a spectrophotometer. Photometric, to determine the total content of rare earth elements in the cerium group.

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 Anhydrous ethanol.

4.2.2 Hydrochloric acid (1 1).

4.2.3 Hydrogen peroxide (1 19).

4.2.4 Oxalic acid (H2C2O4·2H2O) solution (80g/L).

4.2.5 Aluminum solution (20mg/mL). Weigh 20.00g pure aluminum (wAl>=99.99%, wRE<=0.0010%) into a 1000mL beaker, cover On the table dish, add 600mL hydrochloric acid (4.2.2) in batches. Slowly heat until the dissolution is complete, remove and cool. Transfer to 1000mL volume In a measuring flask, dilute to the mark with water and mix well.

4.2.6 Tribromoarsenazo [2-(2-arsinoylphenylazo)-7-(2,4,6-tribromophenylazo)-1,8-dihydroxy-3,6-naphthalene Disulfonic acid] solution (0.5g/L).

4.2.7 Cerium standard storage solution. use a certified standard solution to prepare. Or weigh 0.6142g cerium oxide [w(CeO2)>=99.9%, Burn in a high temperature furnace at 800°C~900°C for 30min in advance, take it off a little cold, and place it in a desiccator for 60min before weighing], accurate to 0.0001g, placed in a.200mL beaker, add 5mL perchloric acid (rho=1.67g/mL), 2mL hydrogen peroxide (rho=1.10g/mL), Cover with a watch glass, heat at low temperature until the cerium oxide is completely dissolved, and evaporate to nearly dry. Remove, cool slightly, add 50mL hydrochloric acid (4.2.2), 6 drops Hydrogen oxide (4.2.3), heat and boil to completely dissolve the salts and completely decompose the hydrogen peroxide, remove it, cool to room temperature, and transfer to 500mL capacity In the bottle, add 35mL hydrochloric acid (4.2.2), dilute to the mark with water, and mix. 1mL of this solution contains 1mg of cerium.

Note: Under the measurement conditions of this part, the absorbance of the complex formed by cerium or cerium group rare earth elements and tribromoarsenazo is the same, so cerium can be used instead of cerium group rare earth elements The total amount of vegetarian is the standard.

4.2.8 Cerium standard solution A. Pipette 5.00mL cerium standard stock solution (4.2.7) into a 250mL volumetric flask, add 40mL hydrochloric acid (4.2.2), dilute to the mark with water, and mix well (prepared when used). This solution 1mL contains 20µg cerium.

4.2.9 Cerium standard solution B. Pipette 50.00mL cerium standard solution A (4.2.8) into a 500mL volumetric flask, dilute to the mark with water, and mix well (Now equipped when used). 1mL of this solution contains 2µg of cerium.

4.2.10 Cerium standard solution C. Pipette 1.00mL cerium standard stock solution (4.2.7) into a 100mL volumetric flask, add 40mL hydrochloric acid (4.2.2), dilute to the mark with water, and mix well (prepared when used). 1mL of this solution contains 10µg of cerium.

4.3 Apparatus

Spectrophotometer.

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 the total content of rare earth elements in the cerium group, weigh a sample (4.4) of the corresponding mass (m0) according to Table 1, accurate to 0.0001g.

4.5.2 Parallel test

Do two tests in parallel and take the average value.

4.5.3 Blank test

Pipette 5.0mL aluminum solution (4.2.5) in a 25mL volumetric flask (or colorimetric tube), the following operations are performed according to 4.5.4.3.

4.5.4 Determination

4.5.4.1 Place the sample (4.5.1) in a 300mL beaker, cover with a watch glass, and add 30mL hydrochloric acid (4.2.2) in batches at low temperature.

Heat until the sample is completely dissolved, remove, cool, filter with medium speed filter paper in a volumetric flask corresponding to the volume of the test solution shown in Table 1, and purge the beaker And filter paper 5 to 8 times each, dilute to the mark with water, and mix well.

4.5.4.2 Pipette the test solution (4.5.4.1) into a 25mL volumetric flask (or colorimetric tube) according to Table 1, and add a corresponding volume of aluminum solution (4.2.5).

4.5.4.3 Add 2mL hydrochloric acid (4.2.2), 2mL oxalic acid solution (4.2.4), 2mL absolute ethanol (4.2.1), 3 drops of hydrogen peroxide (4.2.3), Shake well. Add the corresponding volume of tribromoarsenazo solution (4.2.6) in Table 1, dilute to the mark with water, and mix.

4.5.4.4 Place part of the test solution (4.5.4.3) in the corresponding absorption cell, and use the blank test (4.5.3) solution as the reference, and set the wavelength at the spectrophotometer wavelength The absorbance was measured at 634.0nm. Find the total amount of rare earth elements in the cerium group (m1) from the working curve.

4.5.5 Drawing of working curve

4.5.5.1 According to the mass fraction of rare earth elements in the cerium group, the preparation of the working curve series standard solution is divided into the following three types.

a) When the mass fraction of rare earth elements in the cerium group is 0.0010%~0.10%. add each in a set of 25mL volumetric flasks (or colorimetric tubes) 5.0mL aluminum solution (4.2.5), add 0mL, 0.50mL, 1.00mL, 2.50mL, 3.50mL, 5.00mL cerium respectively Standard solution B (4.2.9), the following operations are performed according to 4.5.4.3.

b) When the mass fraction of rare earth elements in the cerium group is >0.10%~0.60%. add each in a set of 25mL volumetric flasks (or colorimetric tubes) 5.0mL aluminum solution (4.2.5), add 0mL, 1.00mL, 2.50mL, 5.00mL, 6.50mL, 7.50mL cerium respectively Standard solution B (4.2.9), the following operations are performed according to 4.5.4.3.

c) When the total mass fraction of rare earth elements in the cerium group is >0.60%~2.50%. add each in a set of 25mL volumetric flasks (or colorimetric tubes) 5.0mL aluminum solution (4.2.5), add 0mL, 0.50mL, 1.00mL, 1.50mL, 2.00mL, 2.50mL cerium standard Solution C (4.2.10), the following operations are performed according to 4.5.4.3.

4.5.5.2 Place part of the series of standard solutions (4.5.5.1) in the corresponding absorption pool, and use the reagent blank solution (without the cerium standard solution) as For reference, the absorbance is measured at a wavelength of 634.0nm with a spectrophotometer, and the mass of cerium is used as the abscissa and the absorbance is the ordinate. curve.

4.6 Test data processing

The total content of rare earth elements in the cerium group is calculated by the mass fraction wRE of the cerium group rare earth elements, calculated according to formula (1).

When the mass fraction of the total rare earth elements of the cerium group is >=1.00%, the calculation result is expressed to two digits after the decimal point; the total amount of the rare earth elements of the cerium group When the quality score of < 1.00%, the calculation result retains two significant digits. The rounding of values shall be implemented in 3.2 and 3.3 of GB/T 8170-2008.

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 of r does not exceed the repeatability limit r, and the repeatability limit r does not exceed 5%. The repeatability limit r is linear according to the data in Table 2. Obtained by interpolation.

4.7.2 Tolerance

The difference between the analysis results between laboratories should not be greater than the allowable difference listed in Table 3.

5.1 Method summary

Dissolve the sample with sodium hydroxide solution to separate interference elements such as Al, Mg, Ca, Zn, Si, etc., and dissolve it with oxalic acid ethanol under pH 2.0 The solution is used as a precipitant to precipitate rare earths, and the formed rare earth oxalate is burned into rare earth oxides at 950°C. According to the proportion of rare earth contained in the sample Calculate the conversion coefficient of rare earth metals and their oxides, and calculate the total content of rare earth elements in the cerium group.

5.2 Reagents

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

5.2.1 Hydrogen peroxide (rho=1.10g/mL).

5.2.2 Ammonia (rho=0.91g/mL).

5.2.3 Hydrochloric acid (1 1).

5.2.4 Sodium hydroxide solution (200g/L).

5.2.5 Oxalic acid ethanol solution (40g/L). Weigh 40g of oxalic acid and dissolve it in 1L of absolute ethanol.

5.2.6 Oxalic acid lotion (2g/L). Dissolve 2g of oxalic acid in 1L of water.

5.2.7 Cresyl red ethanol solution (2g/L). Dissolve 0.2g of cresyl red in 50mL of absolute ethanol, add water to 100mL.

5.3 Apparatus and equipment

High temperature furnace. The temperature can be controlled at 950°C±10°C.

5.4 Sample

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

5.5 Analysis steps

5.5.1 Sample

Weigh the mass (m2) as 1.00g sample (5.4), accurate to 0.0001g.

5.5.2 Parallel test

Do two tests in parallel and take the average value.

5.5.3 Determination

5.5.3.1 Place the sample (5.5.1) in a 300mL beaker, cover with a watch glass, add 40mL sodium hydroxide solution (5.2.4), and wait until the violent reaction stops. After stopping, add 3mL hydrogen peroxide (5.2.1) dropwise, continue to heat and boil until the hydrogen peroxide is completely decomposed, add 100mL hot water, and boil for 1min. Remove it slightly cold, filter with a slow quantitative filter paper, and wash the precipitate with hot water to pH 7~8.

5.5.3.2 Transfer the precipitate and filter paper into the original beaker, add 5 mL of hydrochloric acid (5.2.3), 3 mL of hydrogen peroxide (5.2.1), and heat to precipitate Dissolve, mash the filter paper with a glass rod, and continue to boil until there are no small bubbles. Add 120mL of hot water, boil, remove and cool a little, while it is still hot, keep stirring Add 20mL oxalic acid ethanol solution (5.2.5) under stirring, add 2 to 3 drops of cresol red ethanol solution (5.2.7), use ammonia (5.2.2) and hydrochloric acid (5.2.3) After adjusting the pH to 1.8~2.2 (precision pH test paper), keep it in a water bath at 80°C for 1 hour, and then take it off and leave it for more than 2 hours. Use slow Filter with quantitative filter paper, wash the beaker 3 times with oxalic acid lotion (5.2.6), and wash the precipitate 7 to 8 times. Transfer the filter paper and sediment to a constant weight In an empty platinum crucible or porcelain crucible (m3), ash on an electric furnace.

5.5.3.3 Burn in a high-temperature furnace at 950°C for 1 hour, take it out, and place it in a desiccator to cool for 1 hour before weighing (m4) to constant weight.

5.6 Test data processing

The total amount of rare earth elements in the cerium group is calculated by the mass fraction wRE of the cerium group rare earth elements, calculated according to formula (2).

The calculation result is expressed to two digits after the decimal point. The rounding of values shall be implemented in 3.2 and 3.3 of GB/T 8170-2008.

5.7 Precision

5.7.1 Repeatability

The measured value 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 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.

5.7.2 Reproducibility

The measured values of two independent test results obtained under reproducibility conditions are within the average range given below. These two test results The absolute difference does not exceed the reproducibility limit R, and the reproducibility limit R does not exceed 5%. The reproducibility limit R is linear according to the data in Table 5. Obtained by interpolation or extension.