Effect of Synthesis Conditions on the Controlled Growth of MgAl–LDH Corrosion Resistance Film: Structure and Corrosion Resistance Properties

Abstract

In this study, a series of MgAl–layered double hydroxide (LDH) thin films were synthesized by a single step hydrothermal process at different synthetic conditions on AA6082, and the combined effect of reaction temperatures and crystallization times on in situ growth MgAl–LDH structural geometry, growth rate, and more importantly on the corresponding corrosive resistance properties are briefly discussed. The synthesis of LDH was performed at reaction temperatures of 40, 60, 80, and 100 °C, while the treatment time was varied at 12, 18, and 24 h. The as-prepared synthetic coatings were characterized by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR), while the corresponding corrosion protection efficiency of the developed coating was studied through potentiodynamic polarization studies and electrochemical impedance spectra. The findings demonstrated that extended crystallization time and reaction temperature impart a significant effect on the oriented growth of layered double hydroxide, the surface morphology, and on the film thickness, which had a remarkable influence on the LDH corrosion resistance ability. The LDH coated specimen developed at 100 °C for 18 h reaction time showed a more compact and dense structure compared to the traditional platelet structure obtained at 80 °C for 24 h crystallization time, and interestingly that compact structure exhibited the lowest corrosion current density, up to five orders of magnitude lower than that of bare AA6082.

Chlorides Entrapment Capability of Various In-Situ Grown NiAl-LDHs: Structural and Corrosion Resistance Properties

“…Coatings 2020, 9, Lastpage; doi: FOR PEER REVIEW www.mdpi.com/journal/coatings aggressive media, and this phenomenon is well correlated with the previous works [10][11][12][13] and for NiAl-LDHd a reduction of about 3-orders of magnitude in corrosion current density was observed compared to the substrate. Furthermore, the open circuit potential (OCP) is switched toward nobler values with structural variation from NiAl-LDHa to NiAl-LDHd, whilst a high corrosion potential of −0.18 V vs Ag/AgCl was observed for NiAl-LDHd, probably due to the formation of well-ordered platelet structure.…”

“…All the synthesized NiAl-LDHs films on AA6082 have shown lower corrosion current density along with a shift of the corrosion potential to higher values as compared to bare AA6082, however, NiAl-LDHd has shown the significantly reduced anodic and cathodic current density compared to the substrate and also from other developed NiAl-LDHs. It is also worthy to note that NiAl-LDHd has shown the relatively higher film thickness of around 35 µm, which may provide a comparatively better barrier film against the aggressive media, and this phenomenon is well correlated with the previous works [10][11][12][13] and for NiAl-LDHd a reduction of about 3-orders of magnitude in corrosion current density was observed compared to the substrate. Furthermore, the open circuit potential (OCP) is switched toward nobler values with structural variation from NiAl-LDHa to NiAl-LDHd, whilst a high corrosion potential of −0.18 V vs Ag/AgCl was observed for NiAl-LDHd, probably due to the formation of well-ordered platelet structure.…”

“…Recently, layered double hydroxides (LDHs) have got prominent attention for potential applications in various fields, including, adsorbents [6], drug delivery systems [7], environmental sciences [8], and biomedical science [9]. LDHs have also be found an efficient system to enhance corrosion resistance due to their ion-exchange capabilities, high surface area, a wide range of cationic salts availability, cost-effectiveness and other lucrative characteristics [10][11][12]. LDH is a class of two-dimensional anionic clays, represented by the general formula [M 2+ 1−x M 3+ x (OH) 2 ]…”

“…x+ (A n− ) x/n , and exhibit a brucite like structure that formed when some of the divalent cations (M 2+ ) are substituted by trivalent cations (M 3+ ), while anions (A n ) stabilize the layered positive charge [12,13]. Generally, co-precipitated [14] and in situ growth methods are used to develop LDHs, while in situ growth approach can be an optimum choice due to strong adhesion with the substrate, caused by the chemical bonding between the two phases, and thus can prolong the service life of the LDH based anti-corrosion coatings, moreover simple synthetic approach also made it an attractive approach to investigate [10][11][12][13].…”

Use of Co/Fe-Mixed Oxides as Heterogeneous Catalysts in Obtaining Biodiesel

“…Layered double hydroxides can be prepared by different methods such as coprecipitation, hydrolysis with urea, sol-gel, hydrothermal treatment, combustion and mechanical synthesis, among others, with the most common and economic method being coprecipitation [23][24][25]. Studies have reported that the synthesis method, the conditions of synthesis, the type of cations and structural anions, the metal precursors and the metal ratio M 2+ /M 3+ are determining factors on the properties and applications of LDH [26][27][28][29]. An important element to improve the catalytic activity of LDH is the thermal treatment to form mixed spinel-type oxides, specifically in the production of biodiesel by heterogeneous catalysis [30,31].…”