GB/T 4702.14-1988Methods for chemical analysis of chromium metal - The infrared absorption method for the determination of carbon content (English PDF)

Scope

This standard applies to the determination of the carbon content of chromium metal. Measuring range: 0.010% to 0.070%.

This standard complies with GB 1467-78, General rules and general provisions for standards of methods for chemical analysis of metallurgical products.

1 Principle

The sample is burned by heating in a stream of oxygen in a high-frequency induction furnace. The carbon dioxide formed is carried by the oxygen into the measuring cell of the infrared analyzer, where it absorbs infrared energy of a specific wavelength; the absorbed energy is proportional to its concentration, and the carbon content is obtained from the change in the energy received by the detector.

2 Reagents and materials

2.1 Acetone: residue after evaporation with a carbon content below 0.0005%.

2.2 Magnesium perchlorate: anhydrous, granular.

2.3 Soda asbestos: granular.

2.4 Glass wool.

2.5 Tungsten granules: carbon content below 0.002%, particle size 0.8 mm to 1.4 mm.

2.6 Tin granules: carbon content below 0.002%, particle size 0.4 mm to 0.8 mm. Wash with acetone (2.1) when necessary and dry at room temperature.

2.7 Oxygen: purity above 99.95%; oxygen of other grades may be used if a low and consistent blank can be obtained.

2.8 Power gas: nitrogen or compressed air, with impurities (water and oil) below 0.5%.

2.9 Ceramic crucibles: 23 mm x 23 mm or 25 mm x 25 mm (diameter x height), fired for 4 h in a furnace at above 1200 °C, or fired in oxygen, until the blank is lowest.

2.10 Crucible tongs.

4 Sample

4.1 The sample shall pass entirely through a 1.68 mm sieve.

5 Analytical procedure

5.1 Test portion: weigh 0.400 g to 0.500 g of sample.

5.2 Blank test: weigh 0.400 g to 0.500 g of a low-carbon standard sample of the same type as the sample to be tested (carbon below 50 ppm; if no such sample is available, a steel standard of similar composition may be used) into a crucible (2.9) containing tin granules (2.6), cover with 1.500 g +/- 0.005 g of tungsten granules (2.5), and measure on the same range or channel as in 5.5. Repeat until low and consistent readings are obtained. The blank value is the difference between the measured carbon and the known carbon content of the standard sample.