BS EN ISO 7526:2020 pdf – Ferronickels – Determination of sulfur content – Infrared absorption method after induction furnace combustion.
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. Oxygen 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? ≤? 0,05? % For each instrument range, transfer the selected mass of flux (5.5.2), to the nearest 0,005 g, into a pre- ignited 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 (details 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. NOTE 1 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 bottom, top, and quartile points of each operational operating range.
8.3.3 For each detector (see 8.3.2) weigh an appropriate amount (usually 0,50 g) of a CRM having a sulfur content corresponding to the top of each operating range into a pre-ignited crucible (6.2). Add the pre-selected amounts of flux (5.5.2) and accelerator (5.5.3) and combust as described in 8.4.1. Repeat this process twice. If the results are situated in the interval “Certified Value ± 2σ”, adjust the net instrument reading to correspond to the certified content of sulfur in the reference material, according to the manufacturer’s instructions. 8.3.4 Check the linearity of the calibration by analysing at least three times a CRM having a sulfur content in the middle of the range of the detector. The result shall be situated in the interval “Certified Value ± 2σ”. Correct any non-compliant conditions before continuing to the next step. 8.4 Determination 8.4.1 Weigh, to the nearest 0,001 g, 0,5 g to 0,6 g of the test sample, and transfer into a pre-ignited crucible (6.2) containing an appropriate amount of the selected flux (5.5.2), if required. Then cover the test sample with the appropriate quantity of accelerator (5.5.3) and, if necessary, place the lid on the crucible. NOTE The flux and accelerator used will depend on the individual characteristics of the equipment and the type of material being analysed. For ferronickels, 1,0 g to 1,5 g of tungsten plus tin (7 to 9 parts of tungsten + 1 part of tin) can be used. 8.4.2 Place the crucible and contents on the pedestal post of the furnace, raise to the combustion position and lock the system. Operate the furnace in accordance with the manufacturer’s instructions. 8.4.3 Record the analyser reading and repeat the determination at least once. NOTE 1 It is important that a high temperature be maintained after the sample is fused to ensure the complete transfer of the sulfur dioxide from the furnace to the infrared analyser. NOTE 2 Quiescent combustion is necessary to avoid splashing on to the crucible lid.