ISO 3262-19-2021 pdf free download – Extenders — Specifications and methods of test — Part 19: Precipitated silica.
5 Sampling
Take a representative sample of the product to be tested according to ISO 15528.
6Determination of silica content
6.1Principle
A test portion is repeatedly treated with hydrochloric acid and evaporated to dryness. To render thedehydrated silicic acid thus formed as insoluble as possible, it is then heated for 2 h at(140±5) °C.Anychlorides present are removed by extracting the precipitate with hot dilute hydrochloric acid.
The precipitate is ignited at 1 000 °C, giving impure silicon dioxide, which is treated with sulfuric andhydrofluoric acid.The silicon tetrafluoride formed is evaporated off and the silica content is calculatedfrom the resulting loss in mass.
6.2Reagents
WARNING – Hydrofluoric acid is corrosive and toxic. The related operations shall beperformed in fume hood. This document does not point out all possible safety problems. It isthe responsibility of the user to take proper safety and health measures, and to determine theapplicability of regulatory limitations prior to use.
Use only reagents of recognized analytical grade and only water of at least grade 3 purity according tolSO 3696.
6.2.1 Hydrochloric acid (HCI), CAS-No7647-01-01), concentrated,approximately 32 % mass fraction,p ~ 1,16 g/ml.
6.2.2 Hydrochloric acid (HCI), CAS-No 7647-01-0, diluted 1 +1.
Add 1 part by volume of concentrated hydrochloric acid (6.2.1) to 1 part by volume of water.6.2.3 Sulfuric acid (H,so4),CAS-No 7664-93-9, diluted 1 + 1.
Add 1 part by volume of concentrated sulfuric acid, approximately 96 % mass fraction, p ~ 1,84 g/ml,slowly to 1 part by volume of water.
6.2.4 Hydrofluoric acid (HF), CAS-No 7664-39-3, concentrated, approximately 40 % mass fraction,p ~ 1,13 g/ml.
6.3Apparatus
Use ordinary laboratory apparatus and glassware, together with the following.
6.3.1 Dish.
6.3.2  Platinum crucible.
6.3.3  Water bath, capable of being maintained at 100 °C.
6.3.4  Infrared evaporator.
6.3.5  Muffle furnace, capable of being maintained at (1 000 ± 20) °C.
6.3.6  Drying oven, capable of being maintained at (140 ± 5) °C.
6.3.7  Filter paper.
The filter paper used for filtration of the silica shall be of such texture as to retain the smallest particles of precipitate and nevertheless permit rapid filtration 2) .
6.3.8 Desiccator, containing for example magnesium perchlorate as desiccant.
6.4 Procedure
6.4.1 Number of determinationsCarry out the determination in duplicate.6.4.2Test portion
Weigh, to the nearest 0,2 mg, approximately 1 g (mo) of the sample (see Clause 5) into a dish (6.3.1).6.4.3Determination
Slowly add 20 ml of concentrated hydrochloric acid (6.2.1) and evaporate to dryness under the infraredevaporator(6.3.4).Add again 20 ml of concentrated hydrochloric acid and evaporate to dryness.Repeatthis step once more.After the third evaporation, place the dish in the drying oven (6.3.6), maintained at(140 ± 5)oC, and leave for 2 h.
Remove the dish from the oven and allow to cool.Add 50 ml of 1 + 1 hydrochloric acid (6.2.2) to theresidue in the dish and warm it for approximately 20 min on the water bath (6.3.3) at i00 °C.Filterthrough a suitable filter paper (6.3.7) and wash the residue on the filter with hot water until thewashings are neutral.
Pour the filtrate and washings into the original dish and evaporate to dryness. Repeat this evaporationstep another two times, adding each time 10 ml of concentrated hydrochloric acid to the residue.Afterthe third evaporation, heat at (140 ±5) °C for 2 h in the drying oven.
Add 20 ml of 1 + 1 hydrochloric acid to the residue in the dish and warm it for approximately 10 min onthe water bath at 100 C.Filter through a fresh filter paper and wash the residue on the filter with hotwater until the washings are neutral.
lf necessary, check the filtrate for any silicon which may have passed through the filter.
Place the two filter papers with the washed precipitates in the platinum crucible (6.3.2). Dry, char atlow temperature, ignite in the muffle furnace(6.3.5) at (1 000 i 20) C to constant mass (this shouldtake approximately 1 h) and allow to cool in the desiccator (6.3.8).Weigh the ignited precipitate to thenearest 0,2 mg (m1).
Wet the ignited precipitate in the platinum crucible with 2 ml to 3 ml of water, add 1 ml of 1 + 1 sulfuricacid(6.2.3) and 15 ml of hydrofluoric acid (6.2.4) and evaporate to a syrup, taking care to avoid lossby spitting.Allow to cool and wash the sides down with small quantities of water. Then add a further10 ml of hydrofluoric acid and evaporate to dryness.If the evaporation of the silicon tetrafluoride is notcomplete, add a further 10 ml of hydrofluoric acid and evaporate to dryness again.
Heat the residue until white fumes are no longer evolved, then ignite for 30 min in the mufflefurnace at (1 000± 20) °C.Remove from the furnace, allow to cool in the desiccator and weigh to thenearest 0,2 mg (mz).ISO 3262-19 pdf download.