Phosphate Coatings: EIS and SEM Applied to Evaluate the Corrosion Behavior of Steel in Fire Extinguishing Solution

Abstract

Phosphate coatings are one of the most important methods in preventing metal corrosion, especially iron alloys. The high interest in this method for industrial applications is mainly due to the low costs associated with the phosphating solution component and technological process. Considering this aspect and the advantages offered to the materials (corrosion resistance, good adhesion, wear resistance), this study evaluates the potential of using the phosphate coating method in health and safety applications. Therefore, the deposition of a layer of zinc phosphate on the steel surface used in the manufacture of components for personal protective equipment was approached. Firefighters, during rescue/evacuation operations, use protective equipment for fall arrest, whose accessories (hooks, carabiners) are made of steel. Due to the low corrosion resistance property of carbon steel, these accessories must be replaced frequently. This paper aims to analyze the possibility of improving the corrosion resistance of carbon steel in a fire extinguishing solution. Accordingly, the electrochemical behavior of two different types of coatings was studied by electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM). In the literature, different corrosion evaluating methods or systems have been considered, and up until now, there has been no previous study to have approached the corrosive behavior of C45, phosphate C45, and painted phosphate C45 immersed in fire extinguishing solution.

Galvanic Corrosion Behaviour of Different Types of Coatings Used in Safety Systems Manufacturing

“…In the case of the painted sample, the increase in the corrosion rate could be explained by the deterioration of the paint layer. These results are expected since, when the C45 sample surface was studied by Energy Dispersive X-Ray Analysis after immersion in FES, a layer with compounds reach in oxygen from the corrosive media (FES) mixed with small quantities of corrosion products was formed [16].…”

“…Although previous studies [14][15][16] have shown that the corrosion resistance, in various corrosive environments, of the carbon steel carabiners has been significantly improved by the deposition of phosphate layers and other subsequent layers. However, knowing that the carabiners or other components of the safety systems contain pieces made of different metals, and the fact that the contact zone between these different metals will act as a galvanic couple when exposed to corrosive media, for a complete evaluation, it is also essential to analyse the galvanic corrosion of the couples which can appear between the metals used in safety systems.…”

“…In the case of the painted sample by coupling with duralumin, its corrosion rate increases even if the corrosion potential is shifted to more negative values. In the EIS results were observed that the PPS sample has a lower corrosion resistance compared with the ZnPS sample, due to the fact that a layer of iron oxide was formed under the paint layer [16].…”

Corrosion Behaviour of Nodular Cast Iron Used for Rotor Manufacturing in Different Wastewaters

“…Better data modelling was achieved by replacing the capacity of the double layer (Cdl) with a constant phase element, respectively CPE (CPE-Constant Phase Element), which expresses the nonideal behaviour of capacities (capacity variation by frequency). The impedance of a constant phase element can be expressed by the relation proposed by Zoltowski [32,33] (1):…”

“…Due to the importance of the cast iron in the pumping system as a material for rotors manufacturing and also for its properties, we consider that it is important to improve the corrosion resistance of the material using advanced coatings like conversion coatings [33], which can improve not only the corrosion behaviour but also the wear resistance.…”