Preparation and characterization of Mn(H2PO4)2.2H2O crystal inhibitor for ordinary mild steel corrosion in simulated cooling water using FTIR, XRD and electrochemical measurements

Manganese dihydrogen orthophosphate dihydrate Mn(H2PO4)2.2H2O was synthesized by solution co-precipitation method and characterized through single crystal X-ray diffraction, FT-IR and Raman spectroscopy. It crystallizes within monoclinic P21/n space group, with unit cell parameters a = 5.3733(3) Å, b = 10.1700(7) Å, c = 7.3106(5) Å and β = 94.786(7) °: the least–square refinement converged to final agreement factors R1=0.0200 and wR2=0.0548 (I>2σ (Iobs)). The three-dimensional network of the structure is made up by the repetition down (101) plane of layers of Mn octahedra and P tetrahedra joint together via vertex sharing. Strong O-H…O hydrogen bonds interconnect the layers, concurring to fix the network; such interactions were also investigated, as well as the whole structure, by means of infrared and Raman spectroscopy. Last, the corrosion inhibition for ordinary mild steel in simulated cooling water was investigated by this compound using electrochemical measurements. The results showed that it acts as a corrosion inhibitor and their inhibition efficiencies depend to its concentration.