GB/T 4698.8-2017Methods for chemical analysis of titanium sponge, titanium and titanium alloys—Part 8: Determination of aluminum content—Separation with sodium hydroxide-EDTA complex-metric titration and inductively coupled plasma atomic emission spectrometry (English PDF)

2.1 Method summary

The test material is dissolved with sulfuric acid. Separate the elements such as titanium, iron, chromium, zirconium, copper, manganese and part of vanadium by sodium hydroxide precipitation. In a weakly acidic medium of pH5, add EDTA complex aluminum. Use zinc acetate standard titration solution to titrate excessive EDTA. Add potassium fluoride to complex aluminum and release quantitative EDTA. Then use zinc acetate standard titration solution to titrate EDTA released, so as to obtain the aluminum content.

For tin interference determination, add potassium iodide to volatilize to remove.

Vanadium affects the judgment of the end point of titration. Add hydroxylamine hydrochloride to eliminate its interference.

2.2 Reagents

Unless otherwise stated, only the confirmed analytically-pure reagents and laboratory grade two water are used in the analysis.

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

2.2.2 Sulfuric acid (1+1).

2.2.3 Hydrochloric acid (1+1).

2.2.4 Potassium iodide solution (200g/L).

2.2.5 Ferric chloride solution (50g/L): Weigh 5g of iron trichloride (FeCl3·6H2O) and dissolve it in 100mL of hydrochloric acid (1+99).

2.2.6 Sodium hydroxide solution (300g/L).

2.2.7 Sodium hydroxide solution (150g/L).

2.2.8 Copper chloride solution (10g/L): Weigh 1g of copper chloride (CuCl2·2H2O) and dissolve it in 100mL of water.

2.2.9 Hydroxylamine hydrochloride solution (100g/L).

2.2.10 Disodium ethylenediaminetetraacetic acid (Na2EDTA) solution

[c(Na2EDTA)]=0.05mol/L]: Weigh 18.6g of Na2EDTA (C10H14N2O8Na2·2H2O) into a 500mL beaker. Add 300mL of water to dissolve. Transfer to a 1000mL volumetric flask. Use water to dilute to the scale mark. Mix well.

2.2.11 Hexamethylenetetramine buffer solution (pH5): Weigh 150g of hexamethylenetetramine in a 1000mL beaker. Add 400mL of water to dissolve. Add about 50mL of hydrochloric acid (rho=1.19g/mL) to adjust the solution to about pH 5 (check with pH test paper). Use water to dilute to 500mL. Mix well.

2.2.12 Potassium fluoride solution (200g/L): Stored in plastic bottles.

2.2.13 Aluminum standard storage solution

Weigh 1.0000g of metallic aluminum (wAl>=99.99%) into a 300mL beaker. Add 20mL of sodium hydroxide solution (2.2.6). After the violent reaction stops, heat to dissolve. Remove it and cool. Add hydrochloric acid (2.2.3) until the precipitated precipitate is dissolved with an excess of 20mL. Cool. Transfer to a 1000mL volumetric flask. Use water to dilute to the scale mark. Mix well. 1mL of this solution contains 1.0mg of aluminum.

2.2.14 Standard titration solution of zinc acetate [c(Zn2+)~0.014mol/L]

2.2.14.1 Preparation: Weigh 3g of zinc acetate [Zn(CH3COO)2·2H2O] into a 200mL beaker. Add 50mL of water to dissolve. Add 2mL of glacial acetic acid (rho=1.05g/mL). Transfer to a 1000mL volumetric flask. Use water to dilute to the scale mark. Mix well.

2.2.14.2 Calibration: Pipette three portions of 5.00mL of aluminum standard

3.2.3 Nitric acid (rho=1.42g/mL)

3.2.4 Titanium (wTi>=99.9%, wAl< 0.005%)

3.2.5 Aluminum standard storage solution: Weigh 1.0000g of metallic aluminum

(wAi>=99.99%) into a 300mL beaker. Add 20mL of sodium hydroxide solution (300g/L). After the violent reaction stops, heat to dissolve. Remove and cool.

Add hydrochloric acid (3.2.1) until the precipitated precipitate is dissolved with an excess of 20mL. Cool. Transfer to a 1000mL volumetric flask. Use water to dilute to the scale mark. Mix well. 1mL of this solution contains 1mg of aluminum.

3.2.6 Aluminum standard solution A: Pipette 10.00mL of aluminum standard

stock solution (3.2.5) into a 100mL volumetric flask. Add 5mL of hydrochloric acid (3.2.1). Use water to dilute to the scale mark. Mix well. 1mL of this solution contains 100µg of aluminum.

3.2.7 Aluminum standard solution B: Pipette 10.00mL of aluminum standard

solution A (3.2.6) into a 100mL volumetric flask. Add 5mL of hydrochloric acid (3.2.1). Use water to dilute to the scale mark. Mix well. 1mL of this solution contains 10µg of aluminum.

3.2.8 Argon (volume fraction>=99.99%)

3.3 Instruments

Inductively coupled plasma atomic emission spectrometer: Equipped with hydrofluoric acid resistant sampling system, of which the resolution is less than 0.006nm (at 200nm).

3.4 Specimen

Follow the promulgated standards for sample preparation of sponge titanium, titanium and titanium alloys.

3.5 Analysis steps

3.5.1 Test material

Weigh 0.10g of specimen (3.4), to the nearest of 0.0001g.

3.5.2 Number of determinations

Conduct two determinations independently. Take the average value.

3.5.3 Blank test

Conduct the blank test with test material.

3.5.4 Preparation of analytical test solution

3.5.4.1 Place the test material (3.5.1) in a 100mL PTFE beaker. Blow in a small amount of water. Add 5mL of hydrochloric acid (3.2.1). Add 1mL of hydrofluoric acid (3.2.2). Heat at low temperature until the sample is completely dissolved.

Then add 0.5mL of nitric acid (3.2.3) dropwise until the solution is clear.

Continue heating to drive off nitrogen oxides. Remove and cool to room temperature.

3.5.4.2 Transfer to a 100mL plastic volumetric flask. Use water to dilute to the scale mark. Mix well.

3.5.5 Preparation of working curve solution

3.5.5.1 Weigh 6 portions of titanium metal (3.2.4) equivalent to the titanium content of the test material (3.5.1) in a series of 100mL PTFE beakers. Operate according to 3.5.4.1 along with the test material.

3.5.5.2 Transfer the solution to six 100mL plastic volumetric flasks. Add 0mL, 1.00mL of aluminum standard solution B (3.2.7), 1.00mL of aluminum standard solution A (3.2.6), 1.00mL, 3.00mL, 6.00mL, 9.00mL of aluminum standard storage solution (3.2.5) in sequence. Use water to dilute to the scale mark. Mix well.

3.5.6 Measurement

In the inductively coupled plasma atomic emission spectrometer, at the selected wavelength (the spectrum line is not specifically specified; the recommended analysis line wavelength of aluminum is 237.312nm, 394.401nm, and the interference of the spectrum line shall be checked when using it), determine the working curve solution (3.5.5.2). When the working curve is linear r>=0.999, conduct the determination of analysis test solution (3.5.4.2). Check the background of the element spectrum and correct it at the appropriate position.

The mass concentration of aluminum element is automatically given by the computer.

3.6 Calculation of analysis results

The amount of aluminum is calculated as the mass fraction of aluminum wAl, calculated according to formula (3):

Where, rho 1 - The mass concentration of aluminum in the measured solution obtained from the working curve, in micrograms per milliliter (µg/mL); […]