ISO 1994:1976 pdf download.Hard coal – Determination of oxygen content.
ISO 1994d follows methods developed by Schütze(ll, Unterzaucherl2l, and Oita and Conwayl3l for the direct determination of the oxygen content of organic compounds. Modifications have been incorporated to avoid errors due to the presence of muisture in Codl. Oxygen is evolved (as water and carbon dioxide) from the mineral matter associated with the coal when the smpIe is pyrolysed and, to reduce errors from this source, coals containing more than 6 % of ash and all samplos of unknown characteristics should be demineralized before analysis (see ISO 602).
1 SCOPE AND FIELD OF APPLICATION
ISO 1994 specifies semi-micro methods for the direct determination of the oxygen content of hard coal.
The nitrogen used for the pyrolysis shall not contain more than 10 ppm of oxygen. If nitrogen of this purity is available commercially, further purifIcation is not necessary if the total “blank” is within the limits specified in clause 7.
4.2 Alternative reagents for converting the volatile pyrolysis products to carbon monoxide
4.2.1 Pure carbon, particle size 0,7 to 2,0 mm1, ash content not exceeding 001 %.
The carbon shall be ignited to dull red heat in an inert atmosphere to remove any oil before being placed in the pyrolysis tube.
Carbon containing up to 0,05 % ash can usually be purified as follows
Break the cake into pieces and insert thorn into a 10 to 12 mm internal diameter silica tube. Pass dry nItrogen (4.1) through the tube and heat the tube slowly to red heat, in stages, using a Bunsen burner. Begin heating the tube at the inlet end and when this is hot, move the burner very slowly along the tube until all the contents have been ignited. Replace the nitrogen with hydrogen and heat again ln a similar manner in a stream of hydrogen. Repeat heating in hydrogen In this way until the effluent gas Is free from hydrogen chloride as shown by Its neutrality to litmus. Replace the hydrogen with nitrogen and allow the contents of the tube to cool to room temperature in a stream of nitrogen.
Remove the platinized carbon, and crush and sieve the product carefully to obtain the maximum yield of 0,7 to 2,0 mm material.
A typical purifying train (see figure 2) consists of the following items:
5.1.1 Pressure regulator, containing heavy (medicinal quality) paraffin; a cylinder 300 mm high and 50 mm in diameter is suitable.
5.1.2 Vertical tube, about 120 mm high and 30 mm internal diameter containing dry magnesium perchiorate
(4.5).
5.1.3 Vertical quartz tube, about 300 mm long and
15 mm internal diameter containing porous copper heated to approximately 500 °C. Porous copper is produced by reducing copper oxide in wire form with hydrogen diluted with nitrogen at the lowest temperature at which reduction occurs, usually between 200 and 250 °C.ISO-1994-1976