|Both the grain size and distribution of particles making up a raw material can have a major impact on end product performance – and in some cases, productivity.
Not only can any variances in the size of individual minerals affect minerology, but slight changes can also affect rheology, casting rate, drying shrinkage and strength.
Consider every particle in a ceramic casting slip as a sphere (see fig.1). The red spheres represent the hard minerals (flux and filler), while the blue represents kaolin, and the yellow, plastic clay.
Should any part increase or decrease in size even slightly, the gaps between the particles will change, thereby affecting performance, while the makeup of the final product will also change as a result of the changing influence of the individual elements.
Furthermore, while material volume must remain constant to keep the same bulk or slurry density, any drop in particle size will lead to a corresponding increase in surface area.
Screening techniques for optimal ceramics production
As both grain size and the distribution of particles making up a raw material are so critical to performance and product yields, it’s vital to pay attention to the quality and consistency of incoming raw materials.
For coarse raw materials, or residue determination generally greater than 60 µm it is possible to employ wet or dry screening, using ascending mesh sizes set on a vibrating platform. The resultant residues on each sieve can be retained and a percentage distribution calculated. Analysing incoming raw materials batch to batch in this way can allow a profile of supply consistency to be maintained.
With ceramic masses and fine raw materials where the greater sized fractions tend to be less than 2 µm it is often necessary to use more sophisticated screening techniques, enabling the analysis of grain size distribution curves.
This often involves more complex particle sizing techniques involving sedimentation or laser light scattering (LLS), e.g. using a Malvern Mastersizer™.
For more detailed guidance on measurement techniques download our Quick Guide to Measuring Particle Size.