Static Image Analysis

Introduction

Accurate measurement of particle size and shape is important for real-world product applications as it influences both process performance and product quality. Image analysis has a significant advantage over other methods such as static light scattering, sedimentation, or sieving in that it can quickly analyze each particle image to determine its size and shape. When using the static image analysis method (SIA), particles are placed on a carrier and remain stationary in relation to the camera.

Merits

Since the sample remains static during image taking process, high image quality and richness of detail are assured. With its high accuracy and repeatability, SIA is particularly well suited for characterizing particles with narrow distribution and very small size. The following characteristics apply to SIA:

1. High-resolution and clear images of particles 

2. Undersized particle sensitivity 

3. Small sample volume or weight

Measurement Method

4 steps to determining the particle shape and size by SIA: 

1. Image taking 

To get clear images, special digital cameras are used typically in conjunction with a microscope. The particles are present in a neutral state (e.g., on an objective), and they can be dispersed (separated) both in a dry mode (e.g., by simply conveying and riddling or by using compressed air) and a wet mode in a solvent.

2. Image processing and particles detection

Appropriate software processes lead to enhanced images:  for example, isolated pixels and edging particles are eliminated, and brightness variations and signal noise are retouched.

3. Particles size and shape calculation

Size and shape parameters of every single particle will be calculated with the software.

4. Statistical calculation and classification 

The particles are grouped into classes (e.g., size equivalent classes) based on their attributed features (size and shape parameters).

Application

SIA generates images of the fine particles with high resolution and clarity. Therefore, it is especially well suited for mining and minerals, batteries, electronics and pharmaceutical applications, where statistical calculations of particle shape and size can be made to further differentiate materials in use.

Literature and Norms

[1] ISO 13322-1: Particle size analysis – Image analysis methods – Part 1: Static image analysis methods

[2] ISO 9276-6 Representation of results of particle size analysis – Part 6: Descriptive and quantitative representation of particle shape and morphology