ISO 1994-1976 pdf free.Hard coal — Determination of oxygen content.
This international Standard specifies semi-micro methodsfor the direct determination of the oxygen content of hardcoal.
The sample is dried at 105 to 110 c in a stream ofnitrogen and then pyrolysed under conditions in which theorganic matter leaves an oxygen-free char. The volatileproducts，containing the organically bound oxvgen andalso water and carbon dioxide from any mineral matter, aredecomposed with either pure carbon or platinized carbonto convert the oxygen to carbon monoxide.The carbonmonoxide is oxidized to carbon dioxide and determined bya titrimetricl4 ] or a gravimetric procedure.The nitrogen used for the pyrolysis shall not contain morethan 10 ppm of , oxygen. lf nitrogen of this purity isavailable commercially, further purification is not necessaryif the total”blank” is within the limits specified in clause 7.
Alternativereagents for convertingthe volatilepyrolysis products to carbon monoxide
Pure carbon,particle size 0,7 to 2,0 mm1), ashcontent not exceeding 0,01%.
The carbon shall be ignited to dull red heat in an inertatmosphere to remove any oil before being placed in thepyrolysis tube.
Carbon containing up to 0,05 % ash can usually be purifiedas follows :
To remove any residual oil,heat to dull red, in an inertatmosphere,enough carbon to pack the pyrolysis tubeand to provide a sample for the determination of ash.Allow to cool and digest the residue with hydrochloric acid,p 1,18 g/ml, at incipient boiling for 1 h. Allow the carbonto settle and decant the liquid through a hardened filterpaper in a Buchner funnel. Wash the carbon several timesby decantation,then transfer it to the filter and continueuntil the washings are free from chloride. Dry the cake firstby suction, then in an oven at 120°c.
Crush and sieve the dried cake carefully to obtain themaximum yield of 0,7 to 2,0 mm material. Determine theash content of the granules.
Dissolve 5 g of platinum in aqua regia and evaporate thesolution to near dryness. Add 5 ml of hydrochloric acid,p 1,18 g/ml, and again evaporate to near dryness.Continue adding 5 ml portions of hydrochloric acid and evaporatingto near dryness until nitrous fumes are no longer evolvedand then evaporate the solution to dryness. Moisten theresidue with 2 ml of hydrochloric acid and add sufficientwater to dissolve the platinic chloride. Add 5 g of ignitedcarbon that contains not more than 0,01 % of ash (see4.2.1) and more water， if necessary, to form a paste. Mixthoroughly and evaporate to dryness on a water bath,mixing frequently with a glass spatula or rod to ensure ahomogeneous product. Dry the resulting cake at 150°c.
Break the cake into pieces and insert them into a 10 to12 mm internal diameter silica tube.Pass dry nitrogen (4.1) through the tube and heat the tube slowly to red heat, instages, using a Bunsen burner.Begin heating the tube at the inlet end and when this is hot, move the burner very slowiyalong the tube until all the contents have been ignited.
Replace the nitrogen with hydrogen and heat again in asimilar manner in a stream of hydrogen. Repeat heating inhydrogen in this way until the effluent gas is free fromhydrogen chloride as shown by its neutrality to litmus.Replace the hydrogen with nitrogen and allow the contentsof the tube to cool to room temperature in a stream ofnitrogen.
Remove the platinized carbon,and crush and sieve theproduct carefully to obtain the maximum yield of 0,7 to2,0 mm material.ISO 1994 pdf download.