Sodium Hexametaphosphate (SHMP) — Frequently Asked Questions

It is scale prevention at doses far below the amount needed to chelate every hardness ion present. A few parts per million of SHMP adsorbs onto the faces of forming calcium carbonate crystals and distorts their growth so they cannot develop into adherent scale. Because it works on the crystal rather than on the calcium in solution, the dose required is a fraction of the stoichiometric amount.

By charging the clay particles so they repel one another. Adsorbed phosphate raises the surface charge on each particle, and mutual repulsion stops them flocculating into a thick paste. The result is a dramatic drop in viscosity, which lets a castable slurry be made at much lower water content, so less water has to be removed in drying and shrinkage is reduced.

Because it is a glassy amorphous solid rather than a crystalline one, formed by fusing and rapidly quenching the melt. Glass dissolves from the surface inward rather than breaking apart along crystal planes. Fine grades dissolve faster than plate; dissolution can be accelerated with warm water and agitation, and pre-dissolving in a make-up tank is normal practice.

Yes. Polyphosphates hydrolyse slowly back to orthophosphate in water, faster at elevated temperature and at extreme pH, and orthophosphate does not sequester or inhibit scale. That means dosing solutions should be made up fresh rather than stored for long periods, and hot systems will consume polyphosphate faster than cold ones.