BS EN ISO 439:2020 pdf free.Steel and cast iron – Determination of silicon content – Gravimetric method.
BS EN ISO 439 Heat the uncovered beaker slightly until the attack is complete and then, increase the rate of heating.As soon as the first white perchloric acid fumes appear, cover the beaker with the watch glass and continue fuming for about 20 min. If the alloy contains chromium at contents greater than 1 %, it is recommended to wait for the appearance of the characteristic red colour of the chromic acid. At this stage, chromium can be removed as chromyl chloride: slowly pour down along the sides of the beaker 1 ml to 2 ml of hydrochloric acid (5.1).
Continue heating, until abundant perchloric fumes appear and chromium re-oxidises. Repeat as many times as necessary until the perchloric fumes are no longer orange-coloured, when hydrochloric acid is added again.Allow to cool, carefully moisten with 5 ml of hydrochloric acid (5.1), heat slightly, dilute with 100 ml of water at 70 °C to 80 °C and heat again until the salts are dissolved (taking care not to allow the solution to boil). With a rubber-tipped glass rod, detach any hydrated silicon dioxide or acid-insoluble silicon compounds that may be adhering to the beaker and filter immediately through a filter paper (6.3) containing a little filter-paper pulp of the same quality.Wash the beaker and the filter with hot hydrochloric acid (5.3), transferring the hydrated silicon dioxide and acid-insoluble silicon compounds to the filter, and complete the washing, first with hot hydrochloric acid (5.2) and then with cold water until the iron salts are completely eliminated.NOTE The filter is washed thoroughly in order to avoid popping and loss of residue due to perchloric acid during ignition.Transfer the filtrate and the washings to the beaker previously used for the dissolution, evaporate them by heating until dense white fumes of perchloric acid are evolved, and maintain a steady refluxing
of acid on the walls of the beaker for about 20 min. Moisten with water and dilute according to the procedure specified in 8.3.1, then filter through a second filter paper [6.3) and wash according to the procedure specified in 8.3.2.Then moisten the ignited silicon dioxide with a few drops of sulfuric acid (5.Z), add approximately 5 ml of hydrofluoric acid (5.5), evaporate to dryness and continue heating until the sulfuric acid fumes are completely eliminated. BS EN ISO 439 pdf download.