Products for the treatment of drinking water from the Neudos® product family
Neudos® TK and TF
Powdered, specialized phosphates in food grade quality
Neudos® PS und TLS
Silicates and silicate / phosphate solutions
Dispersing agents produced from organic polymers
The effect of phosphates
It has long been known that, even at low levels, phosphates form corrosion protection layers on ferrous materials and also simultaneously stabilize the carbonate hardness of water and suppress the formation of scale. Furthermore, they are part of our natural diet and are, thanks to many years of use in the food industry, one of the most studied chemical compounds.
Corrosion inhibition by phosphate
Phosphates, together with hardness and corrosion products, form compact, firmly-adhering coatings on metallic surfaces, which dramatically slows down the corrosion process. It does not matter whether it is a new or damaged surface. The creation of this coating is an ongoing process which does not affect the quality of the water.
Even a small dosage of less than 5 ppm of phosphate (as P205) results in the rapid disappearance of brown water and the formation of a corrosion protection layer. In order for this layer to form, oxygen is needed to oxidize the iron, generate side-alkalinization and a minimum carbonate hardness in the water of approximately 15 mg/l of calcium carbonate (0.8 °dH).
Under these conditions, a phosphate dosing at the pipe walls separates out a mixture of iron and calcium phosphates and carbonates which, unlike normal iron corrosion products, are largely diffusion-tight and thus combat further metal dissolution. These protective layers have the advantage of not growing ever thicker and thicker. Furthermore, phosphate encourages the formation of the goethite modification of the iron oxide hydrate, whereby the layers are protected against transient corrosion.
Hardness stabilization with polyphosphates
The formation of insoluble calcium carbonate – which is responsible for clogging piping – represents a crystallization process. The crystal nuclei formed in the water grow on the pipe walls in increasingly thick layers.
A prerequisite for this is the creation of regular crystals with uniform surfaces which can grow together to form hard crystal structures. This is where the use of threshold inhibitors such as phosphates is needed.
Polyphosphates prevent further growth of calcite microcrystals through absorption on the crystal surfaces, and promote the formation of distorted crystal structures which stops them from growing together to form compact layers. Stabilizing high carbonate hardness only requires a few mg/l of phosphate.
Use of special phosphates
Practical experience in recent years has shown that specifically-designed mixtures of mono- and polyphosphates are superior to pure phosphates in terms of corrosion inhibition. It is presumed that the transport of diffusion phenomena in the outer layers is responsible for this, but this has not been completely proven yet.
When corrosion and scale formation are present at the same time, phosphate mixtures are again advantageous, as they offer effective protection against both problems. Traces of iron hydroxide are also masked, leading to an immediate reduction in brown water.
Finally, phosphate mixtures, as long as they contain corrosion products and are not pure calcium carbonates, are also able to slowly degrade already formed coatings, without negatively affecting the quality of the water.