GB/T 223.71-1997Methods for chemical analysis of iron, steel and alloy--The gravimetric method after combustion in the pipe furnace for the determination of carbon content (English PDF)

4.1

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

7.1.2

Pump in oxygen, check whether the pipeline and valve of the whole equipment

leaks, place the porcelain boat loaded with test sample in the porcelain tube, use the silicone rubber stopper to seal the porcelain tube, observe the chromic acid saturated sulphuric acid solution in the quadruple ball and if there is any backflow, it indicates the equipment does not leak.

7.1.3

Connect the water absorption flask and carbon dioxide absorption flask, unwind the valves in succession, pump in oxygen (at the flow rate of 500 mL/min ~ 800 mL/min), conduct gas washing for 3 min ~ 5 min, and close the valves of oxygen and two absorption flasks. Use the long hook to pull back the porcelain boat. After weighing, repeat the operation of pumping in oxygen until the difference between two weighed values is less than 0.3 mg; and analysis may be started after putting the carbon dioxide absorption flask back.

NOTE 1 Pump in oxygen for the newly-loaded carbon dioxide absorption flasks for 20 min ~ 30 min, analyze the test samples of high secondary carbon content and weigh. Pump in oxygen once again for 3 min ~ 5 min, weigh and repeat 1 ~ 2 times, and the difference between two weighed values shall be less than 0.3 mg (when the weight of loss is much more than the value, it indicates that there is water loss, so the value is unusable).

2 When the height of soda asbestos in the carbon dioxide absorption flask becoming white is close to one third of the height of all soda asbestos, the soda asbestos must be replaced. During the mounting of the carbon dioxide absorption flask, operate quickly; or else, the soda asbestos will absorb the carbon dioxide and water in the air soon. The mounting of the carbon dioxide absorption flask can affect the analytical results. If the glass wool is spread uniformly on the bottom, carbon dioxide will rise uniformly during absorption and the absorption is satisfactory, and otherwise, the absorption is unsatisfactory.

7.2 Blank test

Spread fluxing agent (see Table 1) uniformly in the porcelain boat, carry out determination as specified in 7.3.3 and 7.3.4 and determine carefully the increment of the carbon dioxide absorption flask (m1). The blank value is normally not greater than

0.3 mg; and if the blank value is abnormal, find the cause before continuing operation and carry out blank test once again.

7.3.5

Check the porcelain boat and if the slag is uneven and the section of slag has

pores, it indicates the combustion is not complete, so test samples shall be weighed and determined once again.

NOTE 1 The time for preheating high-alloy test samples shall be increased; and oxygen may be pumped in by observing the rise of the liquid level of chromic acid saturated sulphuric acid in the quadruple ball.

2 During the continuous analysis of test samples, the content may be calculated as the difference between the weight measured this time minus the weight measured last time. If the analysis is interrupted for more than 20 min, oxygen shall be pumped in once again for gas washing for 3 min ~ 5 min and the weight of the carbon dioxide absorption flask shall be measured once again.