Aspect Ratio

Aspect Ratio

Determination of the "length to thickness" ratio of clay minerals

Clay minerals belong to the mineral group of phyllosilicates and form flat plate-shaped minerals due to their structural properties. This external shape can be described by the so-called aspect ratio ("n"), which can be calculated from the edge length "a" in relation to the layer thickness "c" of a clay mineral particle (n = a/c). Our laboratory uses an analytical method with which aspect ratios can be determined by conductivity titrations on mineral suspensions. This method has significant advantages compared to a conventional optical determination of the aspect ratio, for example by scanning electron microscopy (SEM):
  1. With our method, we always consider a representative number of clay mineral particles of a sample
  2. Our procedure is fast and can be carried out in a standardised manner in a short time for a large number of samples
AixMinerals offers the determination of aspect ratios as a stand-alone, but also as a complementary analytical method in addition to a complete characterisation and quantification of the mineral components of a sample.

Figure 1: Schematic graph illustrating the relationship between edge length "a" and layer thickness "c" of clay mineral platelets. There are several processes in clay mineral synthesis and in the preparation of clay raw materials that significantly influence the aspect ratio. (a) reduction of aspect ratio by mechanical destruction, e.g. pulverisation, (b) increase of aspect ratio by decreasing the layer thickness by exfoliation/delamination, (c) increase of aspect ratio by specific growth during synthesis, and (d) further increase of aspect ratio by exfoliation/delamination which gives very high aspect ratios.

Applications

Aspect ratios of clay minerals are an important parameter in the assessment of potential areas of application of the investigated clay raw material. Furthermore, the aspect ratio of a clay raw material is also changed during processing by, for example, drying and grinding processes. By analytically determining the aspect ratios, it is possible to assess optimal processing conditions for clay raw materials. Furthermore, clay minerals are also partly produced synthetically. Measurements of aspect ratios can help to determine the best possible framework conditions for a synthesis.
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