BS EN ISO 7526-2020 Ferronickels – Determination of sulfur content – Infrared absorption method after induction furnace com bustion.
8 Procedure
WARNING – The risks related to combustion analysis are mainly burns in pre-igniting the ceramic crucibles and in the fusions. Use crucible tongs at all times and appropriate containers for the used crucibles. Normal precautions for handling oxygen cylinders shall be taken. 0xygen from the combustion process shall be removed effectively from the apparatus since a high concentration of oxygen in a confined space can present a fire hazard.
8.1 Preparing and stabilizing the instrument
8.1.1 Assemble the apparatus and prepare it for operation according to the manufacturer’s instructions.
Test the furnace and analyser to ensure the absence of leaks.
8.1.2 Condition and stabilize the equipment by combusting several samples, similar to those to be analysed, using appropriate fluxes and accelerators, before attempting to calibrate the system or determine the blank
NOTE It is not necessary to use pre-ignited crucibles.
8.1.3 Allow the instrument to cycle several times with oxygen flowing and adjust the zero of the instrument.
8.2 Blank test and zero adjustment
8.2.1 Sulfur contents s 0,05 %
For each instrument range, transfer the selected mass of flux (5.5.2). to the nearest 0,005 g. into a preignited crucible (6.2), add the selected mass of a CRM (5.6) having a very low sulfur content, and then cover it with the selected mass of accelerator (5.5.3).
The type and mass of the flux and accelerator used in the blank test should accord with those used for the determinations (detalls as in 8.4.1]. Record the mass of the CRM. Place the crucible and contents on the furnace pedestal and operate the furnace in accordance with the manufacturer’s instructions.
Repeat the determination three more times. Average the results.
Subtract the sulfur content of the CRM from the average to determine the blank value, If the blank is greater than 0,001 % (mass fraction) and the related standard deviation is greater than 0,000 2 % (mass fraction), find the cause of the problem, fix it and repeat the experiment.
Record the average blank value into the analyser in accordance with the manufacturer’s instructions.
NOTE1 The reading obtained corresponds to the blank due to the crucible, flux and accelerator.
If the analyser does not have automatic blank correction, the blank value should be subtracted from the total result prior to any calculation. .
NOTE 2 An alternative procedure is to record the reading of the blank test and make the correction using a calibration graph.
8.2.2 Sulfur contents > 0,05 %
It is preferable not to carry out a blank correction. However, a check of the blank level shall be done. The value shall remain below 0,000 5 % (mass fraction].
8.3 Calibration
8.3.1 Select a set of steel and/or ferronickel CRMs (5.6] for calibration and verification which, at a minimum, fall at the botom, top, and quartile points of each operational operating range.BS EN ISO 7526 pdf download.