GB/T 20975.23-2020Methods for chemical analysis of aluminium and aluminium alloys—Part 23:Determination of antimony content (English PDF)

4.1 Method summary

The sample is dissolved in sodium hydroxide, in a sulfuric acid medium, the copper is masked with thiourea, the iron is masked with ascorbic acid, and the color is developed by potassium iodide.

The absorbance was measured at a wavelength of 330.0nm to determine the antimony content.

4.2 Reagents

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

4.2.1 Pure aluminum (wAl>=99.99%, wSb<=0.0010%).

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

4.2.3 Sulfuric acid (12.6, about 5mol/L).

4.2.4 Sulfuric acid (about 2.5mol/L). Dilute sulfuric acid (4.2.3) 1 times.

4.2.5 Potassium iodide solution (550g/L).

4.2.6 Sodium hydroxide solution (200g/L).

4.2.7 Ascorbic acid solution (150g/L, ready when used).

4.2.8 Thiourea solution (100g/L).

4.2.9 Iron solution (0.5mg/mL). Weigh 1.08g ferric ammonium sulfate [Fe(NH4)(SO4)2·12H2O], dissolve it in 100mL water, add 25mL sulfuric acid (4.2.4), transferred to a 250mL volumetric flask, dilute to the mark with water, and mix.

4.2.10 Antimony standard storage solution. use a certified standard solution to prepare. Or weigh 0.1000g antimony powder (wSb>=99.99%) in In a 100mL beaker, add 5mL sulfuric acid (4.2.2), heat to dissolve, after the dissolution is complete, wash with sulfuric acid (4.2.3) into a 1000mL volumetric flask In, dilute to the mark with sulfuric acid (4.2.3) and mix well. 1mL of this solution contains 0.1mg of antimony.

4.2.11 Antimony standard solution. Pipette 50.00mL antimony standard stock solution (4.2.10) into a 250mL volumetric flask, add 25mL water, Sulfuric acid (4.2.4) is diluted to the mark and mixed (the sulfuric acid concentration of the solution is about 2.5mol/L). This solution 1mL contains 0.02mg antimony.

4.3 Apparatus

Spectrophotometer (with UV part), quartz absorption cell.

4.4 Sample

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

4.5 Analysis steps

4.5.1 Sample

Weigh the sample (4.4) with a mass (m0) of 1.00g, accurate to 0.0001g.

4.5.2 Parallel test

Do two tests in parallel and take the average value.

4.5.3 Blank test

Weigh 1.00g pure aluminum (4.2.1), add iron solution (4.2.9) corresponding to the content of the sample, and do a blank test with the sample (4.5.1).

4.5.4 Determination

4.5.4.1 Place the sample (4.5.1) in a 250mL beaker, add 20mL of sodium hydroxide solution (4.2.6), and cover with a watch glass. Be violent After the reaction stops, slowly heat until the sample is completely dissolved.

4.5.4.2 Remove the beaker and let it cool slightly. Carefully add 63mL sulfuric acid (4.2.3), heat to dissolve the salts and evaporate to a volume of about 70mL, remove, Slightly colder.

4.5.4.3 Use medium-speed quantitative filter paper to filter the sample solution in a 100mL volumetric flask (V0), wash the beaker and filter paper with hot water, and cool. To Dilute to the mark with water and mix well.

4.5.4.4 When the mass fraction of antimony is 0.0040%~0.060%, the pipetting volume (V1) is 25.00mL sample solution (4.5.4.3). In a 50mL volumetric flask; when the mass fraction of antimony is >0.060%~0.25%, the pipetting volume (V1) is 5.00mL sample solution (4.5.4.3). In a 50mL volumetric flask, add 22.0mL sulfuric acid (4.2.4).

4.5.4.5 Add 5mL thiourea solution (4.2.8) and 5mL ascorbic acid solution to a 50mL volumetric flask containing sample solution (4.5.4.4) (4.2.7), 10mL potassium iodide solution (4.2.5), dilute to the mark with water, and mix. Leave it for 10 minutes.

4.5.4.6 Put part of the sample solution (4.5.4.5) in a quartz absorption cell, take the blank test (4.5.3) as a reference, and set it at the wavelength of the spectrophotometer. The absorbance was measured at 330.0nm. Find the corresponding antimony mass (m1) from the working curve.

4.5.5 Drawing of working curve

4.5.5.1 Pipette 0mL, 0.50mL, 1.00mL, 3.00mL, 5.00mL, 8.00mL antimony standard solution (4.2.11) into a group In a 50mL volumetric flask, add 28.0mL, 27.5mL, 27.0mL, 25.0mL, 23.0mL, 20.0mL sulfuric acid (4.2.4) sequentially. plus Add 5mL thiourea solution (4.2.8), 5mL ascorbic acid solution (4.2.7), 10mL potassium iodide solution (4.2.5), dilute to the mark with water, mix uniform. Leave it for 10 minutes.

4.5.5.2 Put the standard solution (4.5.5.1) in the quartz absorption cell, and use the reagent blank (without antimony standard solution) as the reference, Measure the absorbance at a wavelength of 330.0nm with a meter (4.3). Using antimony mass as the abscissa and absorbance as the ordinate, the working curve is drawn.

4.6 Test data processing

The antimony content is calculated as the antimony mass fraction wSb, calculated according to formula (1).

The calculation result retains two significant digits. Numerical rounding is 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 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 1. 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, these 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 according to the data in Table 2 Obtained by interpolation or extension.

5.1 Method summary

The sample is dissolved in sulfuric acid. In the acid solution, the antimony (III) is oxidized to antimony (V) by cerium sulfate. Excessive cerium sulfate discolors the methyl orange. Determine the end point of the titration to determine the antimony 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 Hydrochloric acid (rho=1.19g/mL).

5.2.2 Sulfuric acid (1 1).

5.2.3 Standard titration solution of cerium sulfate (c~0.016mol/L). ---Preparation. Weigh 16g cerium sulfate [Ce(SO4)2·4H2O] in a 1000mL beaker, add.200mL sulfuric acid (5.2.2), 600mL of water, heated to dissolve, cooled to room temperature. Transfer to a 2500mL volumetric flask, dilute to the mark with water, and mix. ---Calibration. Weigh 3 parts (m2) of 0.0400g pure antimony (wSb>=99.99%) in a 500mL conical flask and add 20mL concentrated sulfuric acid (rho=1.84g/L), heat to dissolve until it is clear, continue to heat until white smoke is just emitted, remove and cool. Blow with water Wash the bottle mouth, add 80mL water, heat and boil for 5min, remove, add 20mL hydrochloric acid (5.2.1), add 2 drops to 3 drops of methyl Orange solution (5.2.4), immediately titrate with cerium sulfate standard titration solution until the solution turns from red to light yellow, which is the end point. Parallel mark Determine the volume range of the cerium sulfate standard titration solution (5.2.3) consumed should not be more than 0.15mL, whichever is the average value (V4). Along with the calibration blank test, record the volume (V3) of the cerium sulfate standard titration solution (5.2.3) consumed. ---Calculation. Calculate the concentration c of the standard titration solution of cerium sulfate according to formula (2). 60.88---The molar mass of antimony (1/2Sb), in grams per mole (g/mol). The calculation result retains four significant figures. The rounding of values shall be implemented in 3.2 and 3.3 of GB/T 8170-2008.

5.2.4 Methyl orange solution (1g/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 (m3) of 0.20g to the nearest 0.0001g.

5.4.2 Parallel test

Do two tests in parallel and take the average value.

5.4.3 Blank test

Do a blank test with the sample (5.4.1) and record the volume (V5) of the cerium sulfate standard titration solution (5.2.3) consumed.

5.4.4 Determination

Place the sample (5.4.1) in a 500mL Erlenmeyer flask, add 40mL sulfuric acid (5.2.2), heat until the sample is completely dissolved, remove and cool.

Rinse the bottle mouth with water, add about 80mL of water, heat and boil for 5min, remove, add 20mL of hydrochloric acid (5.2.1), add 2 drops to 3 drops of methyl orange Solution (5.2.4), immediately titrate with cerium sulfate standard titration solution (5.2.3) until the solution changes from red to light yellow, which is the end point, and record the consumption of sulfur The volume (V6) of cerium acid standard titration solution (5.2.3).

5.5 Test data processing

The antimony content is calculated as the antimony mass fraction wSb, calculated according to formula (3).

m3 --- the mass of the sample, in grams (g).

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.

5.6 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%. Repeatability limit r is linear within the data in Table 3 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, these two test results The absolute difference of is not greater than the reproducibility limit R, and the case of exceeding the reproducibility limit R does not exceed 5%. Reproducibility limit R is linear according to the data in Table 4 Obtained by interpolation or extension.