Ultrasonically assisted macrocyclic ring compound coatings for corrosion protection of copper in 3.5% NaCl solution

ABSTRACT: Macrocyclic ring compounds are potential corrosion inhibitors due to their high planarity, rigidity, and presence of many heteroatoms such as nitrogen, oxygen, phosphorus, and sulfur. However, their application as corrosion inhibitors has been faced with a challenge of insolubility in most organic and aqueous solvents. To overcome this challenge and to harness the untapped hydrophobic property of these compounds, this research, via ultrasonication method dispersed a macrocyclic ring compound known as free-based Phthalocyanine (Pc) to fabricate a corrosion-resistant coating on the Cu surface. The Cu samples were coated through a 24 h immersion by self-assembly method in different systems of sonicated and non-sonicated solutions of the compound in dimethyl sulfoxide (DMSO). The effect of sonication and immersion duration on the coating morphology, compactness, and consequent corrosion inhibition was analyzed. Electrochemical and surface imaging techniques revealed higher corrosion protection in 3.5% NaCl for the Pc coated Cu samples after sonication compared to the non-sonicated systems.

Heat Treatment-Induced Microstructure and Property Evolution of Mg/Al Intermetallic Compound Coatings Prepared by Al Electrodeposition on Mg Alloy from Molten Salt Electrolytes

A method of forming an Mg/Al intermetallic compound coating enriched with Mg17Al12 and Mg2Al3 was developed by heat treatment of electrodeposition Al coatings on Mg alloy at 350 °C. The composition of the Mg/Al intermetallic compounds could be tuned by changing the thickness of the Zn immersion layer. The morphology and composition of the Mg/Al intermetallic compound coatings were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscattered diffraction (EBSD). Nanomechanical properties were investigated via nano-hardness (nHV) and the elastic modulus (EIT), and the corrosion behavior was studied through hydrogen evolution and potentiodynamic (PD) polarization. The compact and uniform Al coating was electrodeposited on the Zn-immersed AZ91D substrate. After heat treatment, Mg2Al3 and Mg17Al12 phases formed, and as the thickness of the Zn layer increased from 0.2 to 1.8 μm, the ratio of Mg2Al3 and Mg17Al12 varied from 1:1 to 4:1. The nano-hardness increased to 2.4 ± 0.5 GPa and further improved to 3.5 ± 0.1 GPa. The Mg/Al intermetallic compound coating exhibited excellent corrosion resistance and had a prominent effect on the protection of the Mg alloy matrix. The control over the ratio of intermetallic compounds by varying the thickness of the Zn immersion layer can be an effective approach to achieve the optimal comprehensive performance. As the Zn immersion time was 4 min, the obtained intermetallic compounds had relatively excellent comprehensive properties.

Studies and Research on the Corrosion Behavior of Ni-Al2O3 Compound Coatings Obtained by Electrochemical Methods

The undertaken research which is described in this paper aims at the corrosion behaviour of composite coatings in nickel matrix using as dispersed phase technical alumina with dimensions of 5 μm and their characterization from a microstructural point of view. The corrosion resistance in the saline fog of the coatings is influenced by the microstructure, the stresses developed in the layer and the roughness.