ISO 439-2020 pdf free download – Steel and cast irons – Determination of silicon content – Gravimetric method (ISO 439:2020)
5.2 Hydrochloric acid solution, 1 + 1.
Add 500 ml of hydrochloric acid (5.1) to 500 ml of water and mix.
5.3 Hydrochloric acid solution, 1 + 19.
Add 10 ml of hydrochloric acid (5.1) to 190 ml of water and mix.
5.4 Nitric acid solution, 3 + 1.
Add 150 ml of nitric acid, ρ approximately 1,40 g/ml, to 50 ml of water and mix.
5.5? Hydrofluoric? acid, ρ approximately 1,14 g/ml.
5.6 Perchloric acid, ρ approximately 1,67 g/ml.
WARNING — Perchloric acid vapour may cause explosions in the presence of ammonia, nitrous fumes or organic material in general.
NOTE Perchloric acid (ρ approximately 1,54 g/ml) can also be used.
5.7 Sulphuric acid solution, 1 + 1.
Cautiously add 50 ml of sulphuric acid, ρ approximately 1,84 g/ml, to 50 ml of water, allow to cool and mix.
6 Apparatus
Ordinary laboratory equipment and the following shall be used:
6.1 Platinum crucibles, of capacity approximately 30 ml.
6.2? Muffle? furnace, adjustable from 800 °C up to 1 100 °C.
6.3 Filter paper, medium-texture, of known low ash content.
7 Sampling
Carry out sampling in accordance with ISO 14284 or appropriate national standards for steels and cast irons.
8 Procedure
8.1 Test portion
Use millings or drillings of a maximum thickness of 0,2 mm.
According to the presumed silicon content, weigh, to the nearest 1 mg, the following mass (m 0 ) of the test portion:
a) for silicon contents between 0,10 % (mass fraction) and 0,50 % (mass fraction): m 0 approximately 5 g;
b) for silicon contents between 0,50 % (mass fraction) and 2,5 % (mass fraction): m 0
approximately 2,5 g;
c) for silicon contents between 2,5 % (mass fraction) and 5,0 % (mass fraction): m 0 approximately 1 g.
8.2Blank test
ln parallel with the determination and following the same procedure, carry out a blank test using thesame quantities of all reagents as used for the determination.
8.3Determination
8.3.1— Acid dissolution of the test portion and formation of hydrated silicon dioxidePlace the test portion (8.1) in a beaker of suitable capacity.
Add 30 ml of hydrochloric acid (5.1), and then gently heat the beaker covered with a watch glass untilthe reaction ceases.Oxidize by careful addition of 15 ml of nitric acid (5.4).When the violent reactionceases, rinse the watch glass with a little portion of hot water and collect the washings in the beaker.Add the volume of perchloric acid (5.6) indicated in Table 1.
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 andcontinue fuming for about 20 min.
lIfthe alloy contains chromium at contents greater than 1 %, it is recommended to wait for the appearanceof the characteristic red colour of the chromic acid.At this stage, chromium can be removed as chromylchloride: 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 manytimes as necessary until the perchloric fumes are no longer orange-coloured, when hydrochloric acid isadded again.
Allow to cool, carefully moisten with 5 ml of hydrochloric acid (5.1), heat slightly, dilute with 100 mlof water at 70 °C to 80 C and heat again until the salts are dissolved (taking care not to allow thesolution to boil).
8.3.2 Filtration and washing
With a rubber-tipped glass rod, detach any hydrated silicon dioxide or acid-insoluble silicon compoundsthat may be adhering to the beaker and filter immediately through a filter paper(6.3)containing a littlefilter-paper pulp of the same quality.
Wash the beaker and the filter with hot hydrochloric acid (5.3),transferring the hydrated silicon dioxideand acid-insoluble silicon compounds to the filter, and complete the washing, first with hot hydrochloricacid (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 acidduring ignition.ISO 439 pdf download.