ISO 8130-13-2019 pdf free.Coating powders – Part 13: Particle size analysis by laser diffraction.
4 Pnnciple
A coating powder sample is analysed by dynamic light scattering. The powder particles scatter hght and their intensities are measured at various angles by a multi array detector to yield a scattering pattern. The pattern is then translonned to numerical values, using an appropriate optical model and mathematical prnedurc, to yield the proportion of the total volume of particles for a discrete number at size classes forming a volumetric particle size distribution (PSI)).
5 Apparatus
Ordinary laboratory apparatus, together with the following:
5.1 Laser dllfractlon particle size analyser, as specified in ISO 13320. with a mar range of I im to 300 pm.
The instrument should bc located in a clean drait free environment to avoid particulate contamination and be vibration free such that signal to noise ratio is not compromised. More specific guidance Is provided in ISO 13320.
The apparatus shall have a feeder suitable for coating powders of different particle shape and a dispersing unit ensuring a constant and agglomerate frcc Ilow of the coating powder
For coating powders, compressed air or vacuum is used to disperse the powder particles, and it is essential that thr compressed air Is free from contamination which can influence the measurement.
5.2 Computer to store the optical model br analysis. usually as a model matrix containing light scattering vectors per unit of volume per size class, scaled so the detector’s geometry and sensiuvity and for calculation of the PSI),
5.3 Spatula or spoon, to dispense the coating powder into the feeder unit.
6 Sampling
Take a representative sample of the product under test as specified In ISO 15528. A quantity between 3 g and 5 g is normally sufficient [or each determination and should follow the advice of the instrument supplier,
7 Test conditions
Measurements should be made under standard atmosphere 23/SO class 2 as specilied in ISO 291 or by agreement between the interested parties.
8 Procedure
8.1 General
The operator should be familiar with the procedures specified in ISO 13320 as well as the operating Instructions of the instrument manufacturer.
8.2 Precautions
Follow all the necessary safety Instructions provided by the equipment m.inufactursr. paying particular attention to earthing to prevent Ignition of dust caused by electrostatic discharges.
Allow time for the laser to warm up and ensure alignment of the laser diffraction system components, as per the provided instructions.
Verify that the dispersion unit generates a steady mass flow of powder particles by the obscuration values.
8.3 Testing
8.3.1 Sample preparation
Prepare and disperse a sample according to Clause 6. The sample shall be representative for the batch of product within a stated confidence interval, as specified in ISO 15528. The amount of test sample should correspond to at least the minimum required for precision. The dispersion conditions should lead to complete deagglomeration without comminution.
Using the spatula or spoon (3), add the powder to the powder feeder and adjust the powder flow as recommended by the instrument supplier.
8.3.2 Measurement
Start the test in accordance with the instrument instructions. The level of obscuration should lie between 1 % and 10 %.
8.3.3 Instrument performance
Qualify the instrument performance with respect to both precision and accuracy at regular time intervals by measuring a reference material of known particle size distribution and record the date and results. In the absence of a reference material, use a known sample from a previous run.
Clean the instrument thoroughly after the determination.
8.3.4 Selection of an appropriate optical model
Either the Fraunhofer approximation or the Mie theory is used for calculation of a scattering matrix, which represents the signal at each detector element per unit volume of particles in a given size class.
The choice depends upon the size range of the coating powder particles to be measured, their optical properties and shape.
Inappropriate choice of the optical model or of the values of the refractive index may result In significant bias of the resulting PSD. This bias often manifests itself as inappropriate quantities of material being ascribed to the size classes at the lower end of the size distribution.
Generally, the Fraunhofer approximation is used for coating powders, for which the details on refractive indices are not needed because the model assumes that the material absorbs all light and there is no transmission nor refraction.ISO 8130-13 pdf downlaod.