Manganese Phosphatizing Coatings: The Effects of Preparation Conditions on Surface Properties

Abstract

Manganese phosphate coating could be used to protect the surface of steel products. However, it is essential to determine the effects which process parameters, as well as the types of additives used, have on the efficiency of coating deposition. Thus, we present here a process of phosphatization of low-alloy steel (for 15 min at 95 °C) in manganese/nickel baths followed by a passivation process with the use of a silicon and zircon compounds. The microstructure and morphology of the surface were analyzed by SEM EDX and XRD methods. The obtained results showed that the manganese phosphate could be effectively formed at 95 °C in the solution containing nickel and guanidine derivatives. Anodic polarization of manganese coating was investigated in 0.5 M KCl by the analysis of polarization resistance. The effects of the activation process on corrosion properties of the coating have been examined. It was observed that an increased concentration of activating substances in the activation bath results in the enhancement of corrosion resistance.

Modified Manganese Phosphate Conversion Coating on Low-Carbon Steel

“…On the basis of the tests of the cross-section of such coatings, it can be found that there are no two distinct border between the metal and the coating in the standard sample. The coating itself is produced from the substrate [8].…”

“…The methods include the conversion coating of metal with manganese phosphate [1][2][3][4][5][6][7]. During manganese phosphating, the steel product is submerged in a solution containing phosphoric (V) acid, nitric (V) acid and inorganic manganese and nickel compounds as well as organic phosphating accelerators containing NO 2 − nitro groups, e.g., nitro derivatives of benzene or nitro-compounds derived from guanidine [8].…”

Combined Wastewater Treatment from Manganese Phosphate Coating: Coagulation-Ozonation-Fenton Reaction-Sorption

“…Aqueous washing liquids contain the remains of NaOH, KOH, phosphates, surfactants, detergents and emulsifying agent, -after digestion in hydrochloric acid. These washings contain chromium Cr 6+ , nickel Ni 2+ , large amounts of iron Fe 2+ from the etched metal, -after galvanization in a phosphating bath (bath composition: H 3 PO 4 , Mn 2+ compounds, Ni 2+ compounds, nitrates(V), sometimes chlorates and nitro compounds) [33][34].…”

“…wastewater from activation of the metal surface. Depending on the type of activating agent, it contains large amounts of inorganic acids or [33]. Another type of sewage is wastewater and washings from the passivation of metal surfaces.…”

“…These devices operate under extreme conditions, often in a humid environment, and therefore require protection against corrosion. One of the methods for protecting such elements against corrosion is the manganese phosphate coating process, which is the source of wastewater containing orthophosphates, nitrates(V), manganese, nickel, chlorides, sulphates(VI), sodium cations; potassium and even titanium and zirconium compounds, as well as nitrogen compounds such as nitro compounds, including nitroguanidine [33][34]. Due to the high content of these compounds and their chemical diversity, such sewage is particularly burdensome and difficult to treat.…”