Conclusions: crystal characteristics
Form and specific surface
Form is announced by a more or less equidimensional character of the crystal, that is, when the three main dimensions of an equidimensional crystal are not dissimilar. In the order of increasing non-sphericity, we can distinguish:
- - equidimensional crystals: pyramids, rhombohedra, tetrahedra, hexahedra (cubes), octahedra (cube with truncated corners), dodecahedra;
- - one dimension is slightly lower than the others (tablets);
- - one dimension is significantly lower than the others (plates, scales);
- - one dimension is slightly greater than the others (prisms);
- - one dimension is significantly greater than the others: acicular (rods, needles, fibers).
Specific surface a increases with non-sphericity.
A high specific surface is:
- - detrimental for permeability (filtration);
- - favorable for drying;
- - favorable for chemical reactivity.
Specific surface is acquired directly by filtration.
The intermediate dimension of the crystal is acquired by screening.
The volume is provided by a Coulter counter.
Finally, by microscopic examination of fifteen crystals, we can fix a mean for the ratios:
Knowledge of these two ratios allows us to evaluate the a and в Nyvlt coefficients in order to calculate both volume and surface:
Specific surface a can be estimated easily if the particles can be assimilated to solids of a simple geometrical form. For example: