ISO 3262-19-2021 pdf free.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.
6 Determination of silica content
6.1 Principle
A test portion is repeatedly treated with hydrochloric acid and evaporated to dryness. To render the dehydrated silicic acid thus formed as insoluble as possible, it is then heated for 2 h at (140+5) °C. Any chlorides 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 and hydrofluoric acid. The silicon tetrafluoride formed is evaporated off and the silica content is calculated from the resulting loss in mass.
6.2 Reagents
WARNING — Hydrofluoric acid is corrosive and toxic. The related operations shall be performed in fume hood. This document does not point out all possible safety problems. It is the responsibility of the user to take proper safety and health measures, and to determine the applicability of regulatory limitations prior to use.
Use only reagents of recognized analytical grade and only water of at least grade 3 purity according to
ISO 3696.
6.2.1 Hydrochloric acid (HCI), CAS-No 7647-01-0’), concentrated, approximately 32 % mass fraction, p 1,16g/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 (H2S04), CAS-No 7664-93-9, diluted 1 + 1.
Add 1 part by volume of concentrated sulfuric acid, approximately 96 % mass fraction, p 184 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 113 g/ml.
6.3 Apparatus
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 filtration2).ISO 3262-19 pdf download.