ISO 20927:2019 pdf download

ISO 20927:2019 pdf download.Rubber compounding ingredients — Precipitated silica — Determination of aggregate size distribution by disc centrifuge
1 Scope
This document specifies a general method for determining the aggregate size distribution (ASD) of silica by using a disc centrifuge according to the principle of sedimentation. As pre-stage the silica is de-agglomerated in water using strong ultrasonic power treatment.
The method is used for precipitated silica.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1 silica aggregate
discrete, rigid colloidal entity that is the smallest dispersible unit in a suspension
Note 1 to entry: In comparison to carbon black [3] the term silica aggregate is less defined and has to be seen always in context with the silica treatment (i.e. ultrasonic power in a silica suspension in water). The references apply to carbon black but are also broadly used by the rubber industry for precipitated silica.
4 Significance and use
A disc centrifuge is used for measuring the aggregate size distribution (ASD) of precipitated silica. As a function of test time and rotational speed, aggregate sizes in the range of approximately 5 nm to 100 µm can be analysed according to the principle of sedimentation. Firstly, the silica sample is dispersed in an aqueous medium by using ultrasonic power treatment. Afterwards, the suspension is transferred to the disc centrifuge and separated according to its aggregate size. The sedimentation is accelerated by centrifugal forces generated by the rotation of the centrifuge. By using a density gradient of sucrose solution the sedimentation can be stabilised. Over the course of the experiment, a separation in different silica aggregate sizes is possible and can be evaluated. For investigations between different laboratories, it is recommended to use the IRM 100 silica standard 1) according to ASTM D5900 (see Clause 7).
7 Calibration of the test equipment
7.1 Calibration of the ultrasonic device Independent from the designated power of the ultrasonic generator under 5.2, the geometry of the ultrasonic probe and the pre-set amplitude, the energy input into the silica suspension can be supposed on a similar level when the documented parameters of the IRM 100 are in line with the detected results. Additionally, the probe is underlying some significant ageing effects depending from the number of tests but also test conditions such as amplitude, time, pulsed/un-pulsed treatment of the suspension. These ageing effects can influence the ultrasonic power input into the sample and manipulate the results. The comparison of results with former data or between different laboratories is impeded or even impossible. By using the IRM 100 as calibration standard, the ageing effects can be detected very early and precautions up to a replacement of the ultrasonic probe can be undertaken timely.