GB/T 223.68-1997Methods for chemical analysis of iron, steel and alloy--The potassium iodate titration method after combustion in the pipe furnace for the determination of sulfur content (English PDF)

1 Application Scope

This Standard specifies the potassium iodate titration method after combustion in the pipe furnace for the determination of sulfur content.

This Standard applies to the determination of sulfur content of 0.003 0% (m/m) ~ 0.20% (m/m) in iron, steel, high temperature alloy and precision alloy.

2 Normative References

The provisions in following documents become the provisions of this Standard through reference in this Standard. All editions shown are effective when this Standard is issued. All standards will be revised, however, parties who reach an agreement based on this Standard are encouraged to study if the latest versions of the following standards are applicable.

GB 222-84, Method of Sampling Steel for Determination of Chemical Composition and Permissible Variations for Product Analysis

GB 6379-86, Precision of Test Methods – Determination of Repeatability and

Reproducibility for a Standard Test Method by Interlaboratory Tests

3 Method Summary

Test sample and combustion-supporting agent burn in a pipe furnace at high temperature (1 250°C ~ 1 350°C) by pumping in oxygen; sulfur is fully oxidized into sulfur dioxide; and then use acidic starch solution to absorb and use potassium iodate standard solution for titration. Calculate the content of sulfur in accordance with the volume of potassium iodate consumed.

4 Reagents and Materials

4.1 Oxygen of purity not lower than 99.5% (m/m).

If the content of organic impurities in oxygen is suspected, add one oxidation catalyst

[copper oxide (II) or platinum] pipe heated to the temperature over 450°C for treatment before the purification equipment (5.1).

4.2 Solvents which are applicable to wash the grease or dirt on the surface of samples, such as acetone.

4.3 Anhydrous calcium chloride (solid).

4.4 Potassium iodide (solid).

4.5 Soda asbestos.

4.6 Sulphuric acid (rho 1.84 g/ml).

4.7 Hydrochloric acid (rho 1.19 g/ml).

4.8 Potassium hydroxide (100 g/l).

4.9 Cosolvent.

4.9.1 Iron powder.

4.9.2 Vanadium pentoxide. Place in a furnace of high temperature 600°C to burn for

2 h ~ 3 h in advance, and place in a ground-glass stoppered flask as standby after cooling.

4.9.3 Stannic oxide. Screen out stannic oxide of grain size 0.125 mm to place in a big porcelain boat, pump in oxygen to burn in a pipe furnace for 2 min at 1 300°C, and place in a ground-glass stoppered flask as standby after cooling.

4.10 Starch absorption liquid. Weigh 10 g of soluble starch (sweet potato starch), use a small amount of water to make into it into a paste, add 500 ml of boiling water, stir, heat to boiling before taking down, add 500 ml of water and 2 drops of hydrochloric acid (rho 1.19 g/ml) before stirring up and allowing to stand, take 25 ml of supernatant liquid for use, add 15 ml of hydrochloric acid (rho 1.19 g/ml) and use water to dilute to 1

000 ml before mixing up.

6 Sampling and Sample Preparation

Take or prepare samples in accordance with GB 222 or an applicable national standard for iron.

7 Analytical Procedures

Safety instructions: for combustion analysis, the risks mainly come from the pre- combustion of the porcelain boat and the burns during fusion. The porcelain boat shall only be carried using tweezers and contained in an appropriate container at any time of the analysis. Normal protective measures shall be taken for operating steel cylinders containing oxygen. The existence of high-concentration oxygen in a narrow space may cause fires, so the oxygen existing in the combustion process shall be discharged effectively from the equipment.

7.1 Mount the porcelain tube, switch on the power supply and raise the temperature.

For the samples of iron, carbon steel and low alloy steel, raise the temperature to 1

250°C ~ 1 300°C; and for medium- and high-alloy steel, high-temperature alloy and precision alloy, raise the temperature to over 1 300°C.

7.2 Pump in oxygen, adjust its flow rate to 1 500 ml/min ~ 2 000 ml/min, check whether the pipeline and piston of the whole equipment leaks, regulate and maintain the equipment in the normal working status. After replacing sulphuric acid in the gas- washing bottle and the degreasing cotton in the spherical drying tube and replacing porcelain tube, first burn several non-standard samples and then start analytical operation after saturating the system using sulphur dioxide.