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, PO 3 F 2 - is decomposed into PO 4 3 - and F− ions, placing its utility as a corrosion inhibitor for steel reinforcements in doubt.