Abstract

The particle size distribution (PSD) is an essential characteristic of raw materials. This feature is taken into account by nearly all aspects related to the development and optimisation of refractory products. Nevertheless, not only the PSD itself is important but also the shape of the grains. This has long been neglected especially within the field of refractories. For building materials and abrasives e.g. it is common practice to characterise raw materials not only regarding their size distribution but also concerning their shape.

Like the particle size distribution also the grain shape is already determining several important properties of the raw material itself as well as of their mixtures. This might be reflected in the behaviour of a material discharged from a silo, the miscibility of different raw materials, the flowability of a readily mixed composition into a mould, the compactibility etc. Moreover, the properties of refractory products such as porosity, strength, abrasion, corrosion as well as creep resistance might be significantly influenced not only by the size distribution but also by the shape of the raw material particles. Finally it is well known that the reactivity of a particle is determined by its specific surface area and this again is depending on the shape.

Therefore in a first part of this work some general considerations regarding the definition of grain shape, its measurement and the targeted production of raw materials with certain grain shapes will be presented. A second part is then dedicated to the influence of differently shaped raw materials on the properties of refractory castables and bricks. As a result it is shown that raw materials with identical size distribution but with differently shaped grains can influence the physical, mechanical and thermo-mechanical properties of refractories.