Enhanced Corrosion Resistance of Layered Double Hydroxide Films on Mg Alloy: The Key Role of Cationic Surfactant.

Qiuxiang Yang,Jingbao Wang,Mohammad Tabish,Jingmao Zhao

doi:10.3390/ma15062028

Abstract

In this study, dense anticorrosion magnesium–aluminum layered double hydroxide (MgAl-LDH) films were prepared for the first time by introducing a cationic surfactant tetradecyltrimethyl ammonium bromide (TTAB) in the process of in situ hydrothermal synthesis of Mg-Al LDH films on an AZ31 magnesium alloy. Results of XRD, FTIR, and SEM confirmed that TTAB forms the MgAl-LDH-TTAB, although TTAB cannot enter into LDH layers, and MgAl-LDH-TTAB powders are much smaller and more homogenous than MgAl-CO32−-LDH powders. Results of SEM, EDS, mapping, and XPS confirmed that TTAB forms the MgAl-LDH-TTAB films and endows LDH films with denser structure, which provides films with better shielding efficiency. Results of potentiodynamic polarization curves (PDP) and electrochemical impedance spectroscopy (EIS) confirmed that MgAl-LDH-TTABx g films have better corrosion resistance than an MgAl-CO32−-LDH film. The corrosion current density (icorr) of the MgAl-LDH-TTAB0.35 g film in 3.5 wt.% NaCl solution was reduced to 1.09 × 10−8 A.cm−2 and the |Z|f = 0.05 Hz value was increased to 4.48 × 105 Ω·cm2. Moreover, the increasing concentration of TTAB in MgAl-LDH-TTABx g (x = 0.025, 0.05, 0.1, 0.2 and 0.35) provided denser outer layer LDH films and thereby increased the corrosion resistance of the AZ31 Mg alloy. Additionally, the |Z|f = 0.05 Hz values of the MgAl-LDH-TTAB0.35 g film still remained at 105 Ω·cm2 after being immersed in 3.5 wt.% NaCl solution for 168 h, implying the good long-term corrosion resistance of MgAl-LDH-TTABx g films. Therefore, introducing cationic surfactant in the process of in situ hydrothermal synthesis can be seen as a novel approach to creating efficient anticorrosion LDH films for Mg alloys.

Highlights

Magnesium and its alloys have gained a lot of interest over the years owing to their many advantages, such as high specific strength, high thermal conductivity, excellent machinability, and ease of recycling
Several anticorrosion approaches for Mg alloys have been established so far, including organic coating [1,2], chemical conversion coating [3,4], surface chemical modification [5,6], micro-arc oxidation (MAO) [7,8], as well as an inhibitor [9,10]
The findings have shown the success of the synthesis of magnesium–aluminum layered double hydroxide (MgAlLDH)-tetradecyltrimethyl ammonium bromide (TTAB), and of the smaller and more homogeneous particles of MgAl-CO3 2− -layered double hydroxide (LDH)

Summary

Introduction

Magnesium and its alloys have gained a lot of interest over the years owing to their many advantages, such as high specific strength, high thermal conductivity, excellent machinability, and ease of recycling. They are, extremely caustic, in corrosive environments containing Cl−. Because of their low corrosion resistance, they are severely limited in their uses in aerospace, biomedical engineering, automotive, and a variety of other areas. In situ generated layered double hydroxide (LDH) coatings on Mg alloys have recently piqued the interest of many researchers owing to its outstanding anticorrosion performance and strong adherence to the substrate [11]. LDH films have high corrosion resistance due to three factors: (i) the LDH film acts as a strong physical barrier to corrosive media such as water molecules and aggressive anions, (ii) LDH can capture aggressive anions, such as

Methods

Results

Conclusion