ISO 23157:2021 pdf free download – Determination of the silanol group content on the surface of fumed silica – – Reaction gas chromatographic method.
Fumed silica (pyrogenic silicon dioxide) has a relatively high concentration of silanol groups formed during high-temperature flame hydrolysis and the following cooling process. This specified property enables fumed silica to be widely used as a reinforcing filler, thickener, thixotropy-increasing and anti- sagging additive in numerous industries, for example silicone rubber, coating materials, adhesives and sealants.
The determination of the silanol group content on the surface of fumed silica is essential for both manufacturers and users to develop a high-performance, surface modified fumed silica and improve existing products. Further, it also facilitates the communication among interested parties.
In practice, methods of titration, thermogravimetry (TG), infrared spectroscopy (IR) and reaction gas chromatography can be a choice for the determination of the silanol group content on the surface of fumed silica. Among these methods, the method of reaction gas chromatography is preferred by users due to the advantage of higher sensitivity and better reproducibility.
This document provides a detailed procedure for how to conduct the testing of the silanol group content on the surface of fumed silica by means of the reaction gas chromatographic method.
6.5 Sample vials
Glass vials with a septum [e.g. a rubber membrane coated with polytetrafluoroethylene (PTFE)1 and a metallic cap, compatible with the headspace system connected to the gas chromatograph, are used as containers for reactions. It is recommended to use 22 ml glass vials.
6.6 Analytical balance
Capable of weighing to an accuracy of 0,1 mg.
6.7 Gas collecting bag
Gas collecting bags are used to prepare calibration substances. Appropriate volume size (e.g. 500 ml or 1 000 ml) of PTFE bags with a valve is recommended. Purge the gas collecting bags with diluent gas (5.5). Drain the bags before use.
6.8 Syringe
A syringe with a suitable size (e.g. 1 ml, 2,5 ml, 5 ml, 10 ml, 100 ml) is used to measure and transfer the reaction solution, methane gas and calibration substance.
All of the syringe parts that get in contact with the reaction solution shall be made of material (e.g. glass, polypropylene (PP), PTFE, stainless steel) that is inert to the reaction solution and will not affect the reaction solution chemically. The gas syringe for manual sampling shall be provided with a locking valve to avoid gas leakage.
7 Sample pre-treatment and reaction
7.1 Sample pre-treatment
7.1.1 Determination of matter volatile at 105 °C in fumed silica
Heat the weighing bottle (squat form, wide-mouthed), with the ground glass stopper removed, in the oven at 105 °C for 2 h. Allow to cool in the desiccator, insert the stopper and weigh to the nearest 1 mg.
Spread 10 ± 1 g of fumed silica in a uniform layer on the bottom of the weighing bottle, insert the stopper and weigh to the nearest 1 mg.