BS ISO 7524:2020 pdf download – Ferronickels — Determination of carbon content — Infrared absorption method after induction furnace combustion 6.1.3 Maintain a glass-wool filter (5.4) between the furnace chamber and the analyser and change as necessary. The furnace chamber, pedestal post and filter trap should be cleaned frequently to remove oxide residues. 6.1.4 The manufacturer may recommend setting the programming unit to give a pre‑burn period before oxygen enters the furnace chamber. The test portion should be at a red heat during the pre‑burn period. When oxygen is introduced for the combustion stage, the temperature increases substantially. 6.1.5 The temperature reached during combustion depends on the furnace, and the type and quantity of metal in the crucible. A high temperature (>1 700 °C) is maintained after the test portion is fused so that the carbon dioxide can be completely removed from the furnace to the infrared analyser. 6.1.6 The flow rate of oxygen can vary from one instrument to another but is usually about 2,0 l/min during the combustion period. 6.1.7 After the equipment has been idle for a few hours or after cleaning the furnace chamber or filters, the instrument should be stabilized as described in 8.1. NOTE Features of commercial equipment are given in Annex A. 6.2 Ceramic crucibles and lids. Ceramic crucibles, containing the sample and any additions that can be necessary, are required for the combustion. They shall be of precise dimensions for the system and fit the supporting pedestal post so that the test portion in the crucible is positioned correctly within the induction coil for heating. Typical dimensions of combustion crucibles are: a height of 25 mm, an external diameter of 25 mm, an internal diameter of 20 mm, a wall thickness of 2,5 mm and a thickness of base of 8 mm. The dimension of the hole of the lid should be larger than 10 mm. Crucibles and lids shall be as specified by the manufacturer of the instrumentation used and shall be capable of withstanding combustion in an induction furnace without evolving carbon‑containing chemicals so that achieving and maintaining blank values within specification is possible. In order to remove any carbon contamination, for the determination of carbon levels of less than 0,05 % (mass fraction), pre-ignite the crucibles in air or oxygen in a furnace for not less than 1 h at 1 100 °C and store in a desiccator or...
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