Using the Morphologi G3 for evaluating ceramic granules produced by a spray drying process
Application Note Dec 14, 2015
Malvern Instruments Limited
From the humble cereal bowl to the intricate electronic components in your mobile phone and even body armour, ceramics are found in a diverse range of industries and applications. Despite their wide range of applications they are all are produced in a similar way; by pressing and then firing powders produced using a spray drying technique. Spray drying converts ceramic slurries into freeflowing spherical powders with a narrow particle size distribution.
Fine material is desirable in the manufacture of ceramics as this leads to a high packing density, resulting in low shrinkage when the ceramic part is baked - although fine material is also more cohesive and can give poor flowability. Furthermore, dry blending of the raw ceramic material and additives may lead to segregation of the different components which can be problematic.
To avoid such issues the mixture is usually blended in a slurry to give a homogeneous product before spray drying. In the spray drying process the feed slurry is atomised into tiny droplets by using either a nozzle or rotary atomizer. The atomized spray is then mixed with hot drying gas, which causes droplet evaporation to form the powder. The dried product is then used to manufacture the ceramic components.
Although there has been a lot of research into what makes a good slurry, there has been comparatively little work done on the granular product. While particle size is a critical performance metric governing the mechanical properties of the ‘green body’ and fired ceramic, the proportion of fine material and presence of irregular particles also strongly influence the fluidity and malleability of the final product.
As particles become smaller, the inter-particle forces of attraction between them increase, whilst being simultaneously subjected to lower gravitational forces. Consequently, finer particles flow less freely under gravity than coarser material. Similarly, irregularly shaped particles are subjected to greater frictional forces and so would also be expected to exhibit reduced flowability.
Thus, knowledge of the relationship between the size and shape of the granular material and the properties of the final product can be used to optimize the manufacturing conditions and resultant particle properties. In this application note we explore the use of the Morphologi G3 in evaluating the size and shape of granular particles obtained from a spray drying method.