ISO 4935:1989 pdf download – Steel and iron – Determination of sulfur content – Infrared absorption method after combustion in an induction furnace
5 Apparatus
During the analysis, unless otherwise stated, use only ordinary laboratory apparatus. All volumetric glassware shall be class A, in accordance with IS0 385-1, IS0 648 or IS0 1042 as appropriate. The apparatus required for combustion in a high-frequency induction furnace and the subsequent infrared absorption measurement of the evolved sulfur dioxide may be obtained commercially from a number of manufacturers. Follow the manufacturer’s instructions for the operation of the equipment. Features of commercial instruments are given in annex C.
7 Procedure
SAFE+Y INSTRUCTIONS – The risks related to combus- tion analysis are mainly burns in pre-igniting the ceramic crucibles and in the fusions. Use crucible tongs at all times and suitable containers for the used crucibles. Nor- mal precautions for handling oxygen cylinders shall be taken. Oxygen from the combustion process shall be removed effectively from the apparatus since a high con- centration of oxygen in a confined space can present a fire hazard.
7.1 Apparatus conditioning
Purify the oxygen supply using tubes packed with the inert ceramic (attapulgus clay) impregnated with sodium hydroxide (4.7) and magnesium perchlorate (4.41, and maintain a quies- cent flow rate whilst on standby. Maintain a glass wool filter or a stainless steel net as a dust collector. Clean and change as necessary. The furnace chamber, pedestal post and filter trap shall be cleaned frequently to remove oxide build-up. Allow each item of equipment to stabilize for the time recom- mended by the equipment manufacturers when the main supply is switched on after being out of action for any length of time. After cleaning the furnace chamber and/or changing filters or after the equipment has been inoperative for a period, stabilize the apparatus by burning several samples of similar type to the samples to be analysed prior to setting up for analysis. Flush oxygen through the apparatus and adjust the instrument controls to give a zero reading. If the instrument used provides a direct reading in percentage sulfur, adjust the instrument reading for each calibration range as follows. Select the certified reference material with a sulfur content close to the maximum sulfur content in the calibration series, measure the sulfur content of the certified reference material in the same manner as specified in 7.4. Adjust the reading of the instrument to the certified value. NOTE – This adjustment shall be made before the calibration as specified in 7.5. It cannot replace or correct the calibration.
7.4 Determination
Transfer a tin capsule (5.2) to a ceramic crucible (5.3), press the tin capsule lightly against the bottom of the ceramic crucible, add the test portion (7.2) and cover with I,5 g f 0,l g of the accelerator (4.5). Place the ceramic crucible and contents on the pedestal post, raise to the combustion position and lock the system. Operate the furnace in accordance with the manufacturer’s instruc- tions. At the end of the combustion and measuring cycle, remove and discard the crucible, and record the analyser reading.