Thresholding effect
The threshold effect (engl. Threshold effect ) is the property of certain substances (substances threshold), at very low (the so-called sub-stoichiometric ) concentrations, the formation of precipitates to prevent or at least greatly retard. In this way, threshold substances prevent the formation of an insoluble precipitate in a supersaturated solution by blocking the surface of the microcrystals that form first by adsorption , so that no larger crystals can form through attachment. This results, for example, in the stabilization of amorphous and colloidal calcium carbonate in solutions, i.e. the crystalline, insoluble calcite formation is delayed.
Threshold substances can e.g. B. as additives in detergents for the duration of the washing process prevent the formation of laundry encrustations due to poorly soluble compounds (calcium and magnesium carbonate) in the water by delaying precipitation . Suitable additives include compounds from the group of the low molecular weight phosphonates and the higher molecular weight complexing agents (for example polycarboxylates ), which are also used as builders in detergents.
Individual evidence
- ↑ Entry on water softening. In: Römpp Online . Georg Thieme Verlag, accessed on June 14, 2014.