L’agressivité des eaux dans les chauffe-eau électriques

Agressiveness of water in water-heaters

Ecole Nationale Supérieure de Chimie de Paris

Abstract

Defining a material against which an agressiveness is possible results in distinguishing acid-base processes (towards bases such as (hydroxy-), carbonates, concrete) from electrochemical mechanisms (metals).

The Brönsted concept of acido-basicity emphasizes the ampholyte properties of the hydrogencarbonate species. “Agressive” and “equilibrium CO2” ideas are readily explained by the equilibrium [math] which controls the precipitation of CaC03, protective coating here or thermal barrier there. Heating results in removing gases as well as changing constant values, with the same result: a locally more calcifying water and acidic agressiveness elsewhere. Other types of heterogeneousness are concentration gradients: local pitting is most dangerous, stimulated by Cl^- ions. But the effect of the HCIO/CIO^--CI^- system should not be underestimated. The part of the solvant is shown by filmogen process mechanisms and the importance of the positive colloid yield is underlined for antiscale devices. An annex makes easier practical constant calculuses, gives the instructions of the “DTU” rules for steel pipe waters in buildings and presents a standard analysis bulletin.