Reaction between sodium monofluorophosphate and portlandite and impact on steel reinforcement corrosion inhibition

The chemical products generated in the reaction between sodium monofluorophosphate and cement paste, simulated by a calcium hydroxide solution, were analysed using X-ray diffraction and transmission electron microscopy with energy dispersive X-ray analysis. Portlandite, apatite, fluorite, calcite and amorphous products were identified as the main synthesized phases. Nanoparticles of hydroxyfluoroapatite (Ca5(PO4)3(OH,F)) were also profiled. In a medium of high alkalinity such as the tested experimental conditions, PO3F2-PO3F2- is decomposed into PO43- and F− ions, placing its utility as a corrosion inhibitor for steel reinforcements in doubt.

► Reaction between sodium monofluorophosphate and cement paste. ► Portlandite, apatite, fluorite, calcite and amorphous products. ► Phase identification in XRD quantification. ► Kinetic parameters. ► TEM images at different ages.