Growth of Anodic Layers on 304L Stainless Steel Using Fluoride Free Electrolytes and Their Electrochemical Behavior in Chloride Solution.

Laura Patricia Domínguez-Jaimes,Ana Conde,Beatriz Escobar-Morales,Juan Manuel Hernández-López,María A Arenas,Anabel Álvarez-Méndez

doi:10.3390/ma15051892

Abstract

Anodic layers have been grown on 304L stainless steel (304L SS) using two kinds of fluoride-free organic electrolytes. The replacement of NH4F for NaAlO2 or Na2SiO3 in the glycerol solution and the influence of the H2O concentration have been examined. The obtained anodic layers were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and potentiodynamic polarization tests. Here, it was found that, although the anodic layers fabricated within the NaAlO2-electrolyte and high H2O concentrations presented limited adherence to the substrate, the anodizing in the Na2SiO3-electrolyte and low H2O concentrations allowed the growth oxide layers, and even a type of ordered morphology was observed. Furthermore, the electrochemical tests in chloride solution determined low chemical stability and active behavior of oxide layers grown in NaAlO2-electrolyte. In contrast, the corrosion resistance was improved approximately one order of magnitude compared to the non-anodized 304L SS substrate for the anodizing treatment in glycerol, 0.05 M Na2SiO3, and 1.7 vol% H2O at 20 mA/cm2 for 6 min. Thus, this anodizing condition offers insight into the sustainable growth of oxide layers with potential anti-corrosion properties.

Highlights

Significant progress has been reached in nanoscience and nanotechnology fields to improve the properties, performance, and durability of materials
The X-ray diffraction (XRD) pattern confirmed that the anodic layer grown in NaAlO2 contained a mixture of Al2O3, AlOOH, and FeOOH but exhibited limited adhesion to the 304L stainless steel (304L Stainless steel (SS)) (Figure 2b)
42.0 ± 2.0 to 243.3 ± 6.5 mV vs. Ag/AgCl (3 M KCl). These findings indicated a better electrochemical response against corrosion for the anodic layer grown with 1.7 vol% H2O

Summary

Introduction

Significant progress has been reached in nanoscience and nanotechnology fields to improve the properties, performance, and durability of materials. Surface and interface engineering has developed surface properties in metallic materials [1]. One of the most common surface modification methods is the anodizing process, which provides a unique combination between functionality and surface morphology, different from bulk material [2]. Due to the applied stimulus, the metal is oxidized. The migration of these ions continues through the oxide developed, enabling the growth of the anodic layer at both the metal/oxide and oxide/electrolyte interface [4]. Their structures and chemical properties depend on several process parameters, such as the electrolyte composition, applied stimulus (potential or current density), and anodizing time [5]

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Conclusion