Activation of zinc phosphate coating by silver nitrate pretreatment

Abstract

The effects of a new activation pretreatment based on silver nitrate solution on the formation and protection characteristics of zinc phosphate coating on mild steel surface were studied. The surface morphology of coated samples and microstructural evolution were analysed by the scanning electron microscopy (SEM) and the energy-dispersive spectroscopy. The protection characteristics were evaluated using potentiodynamic polarisation curves and the electrochemical impedance spectroscopy in a 3.5% NaCl solution. Experimental results revealed that the activation pretreatment with silver nitrate solution promotes the nucleation of zinc phosphate coating on steel surface which produced compact coatings with full surface coverage. Introducing the pretreatment with silver nitrate solution prior to the phosphating step strongly influences the surface morphology and corrosion resistance of the phosphate layer. The corrosion resistance of activated phosphate coatings was improved, where the corrosion potential shifted positively, and the corrosion current density was markedly reduced.

Corrosion performance and morphological analysis of activated zinc phosphate coating formed on steel surface

“…Zinc phosphate coatings are used in many surface applications to improve adhesion and protection ability of painted metals (Arthanareeswari et al , 2018; Abdalla and Zuhailawati, 2017). They act as a physical barrier between the metal surface and the aggressive environment and are therefore widely adopted in the automobile and appliance industries (Kellner et al , 2009).…”

Phosphating of Steel in Low-Temperature Solution

“…The use of such temperatures leads to increased energy consumption and sludge formation, also a need to change and clean the heating elements [4]. There are scientific publications in which the possibility of carrying out the process at low temperatures is investigated [5][6][7][8][9][10][11][12][13][14]. However, phosphating compositions contain derivatives of nitric or nitrous acids, which complicate cleaning of the wastewater.…”

Melatonin as an Accelerating Agent for Phosphate Chemical Conversion Coatings on Mild Steel with Enhanced Corrosion Resistance

“…[23][24][25] On the other hand, most of these accelerators are oxidizing compounds and thus in the chemical conversion treatment, Fe 2+ ions dissolved in the processing solution from the ferrous metal material are oxidized to Fe 3+ , thereby preventing the aging of the chemical treatment solution caused by the enrichment of Fe 2+ . [26][27][28][29] The traditional oxidation accelerators for phosphate coatings, such as nitrate, nitrite, chlorate, peroxides, etc., 30,31 have been gradually banned because these accelerators release toxic gases or greenhouse gases. At present, the research of phosphating accelerators is mainly focused on nanoparticles.…”