Electrochemical characterization of chromate free conversion coatings on electrogalvanized steel

Abstract

The chromate conversion treatment is widely used, but it requires highly toxic chromic acid solutions with the consequent effluent disposal and ecological problems. The removal of these toxic chemicals is considered a priority within European Union. The corrosion resistance of three alternative treatments applied on electrogalvanised steel, and immersed in aerated 0.3 M Na 2 SO 4 solution, pH 10, at 25 °C, was investigated using electrochemical techniques. Their performance was compared with the obtained using the traditional Cr 6+ -based treatment in the same conditions. The achieved results show that the alternative coatings exhibited discrete protective properties in the sulphate solution. The nitro-cobalt chemical conversion treatment showed similar protective properties than the traditional Cr 6+ -based treatment, while with the Cr 3+ -based treatment those were very poor. The phosphate treatment initially performed acceptably but as the time elapsed, its protective properties decreased.

Ureasilicate Hybrid Coatings for Corrosion Protection of Galvanized Steel in Chloride-Contaminated Simulated Concrete Pore Solution

“…21,22 The Nyquist plots obtained for samples coated with OIHs synthesized using higher MWs of Jeffamine, namely U(600), U(900) and U(2000) exhibited also two time-constants at high and medium frequency indicating at least two electrochemical processes with similar relaxation time constants, while one inductive loop was observed at the LF end ( Figure 4). This type of impedance spectra have been reported [58][59][60][61][62] for galvanized surfaces due to the surface relaxation processes of adsorbed species (such as corrosion products) on the HDGS surface. Considering the high pH of the chloride-contaminated SCPS and the mechanism proposed by Liebau,8,63 the results suggest that the adsorbed species (such as Zn 2+ , Zn(OH) 2 , Ca(Zn(OH) 3 ) 2 ·2H 2 O) may possibly be the reason for the LF inductive loop found in all HDGS samples coated with U(600), U(900) and U(2000).…”

Preparation and Anti-Corrosive Properties of Cerium Oxide Conversion Coatings on Steel X52

“…Surface treatment is an effective technique to solve the problem, which includes chemical conversion coating, electroplating and electroless plating, physical vapor deposition and so on [10][11][12] . Among these surface treatments, chemical conversion treatment is a simple and cost effective method and has been increasingly used in a wide range of applications.…”

The Effect of Immersion Time and Immersion Temperature on the Corrosion Behavior of Zinc Phosphate Conversion Coatings on Carbon Steel

“…There are different ways to control corrosion including inhibitors, coatings, applying anodic/cathodic protection and proper design 4 . Surface treatment is an effective technique to solve the problem, which includes chemical conversion coating, [5][6][7][8][9] electroplating and electroless plating, 10,11 physical vapor deposition 12,13 and so on. Among these surface treatments, chemical conversion treatment is a simple and cost effective method and has been increasingly used in a wide range of applications.…”