Electrochemical Impedance Spectroscopy Investigation on the Corrosive Behaviour of Waterborne Silicate Micaceous Iron Oxide Coatings in Seawater

WC-Co and WC-Co-Cr Coatings for the Protection of API Pipeline Steel from Corrosion in 4% NaCl Solution

Two inorganic coatings, namely 88%WC-12%Co (PSC1) and 86%WC-10%Co-4%Cr (PSC2), were deposited on the surface of an API-2H pipeline steel using high velocity oxy-fuel deposition. The corrosion of the uncoated and coated API-2H steel after their immersion in a solution of 4.0% NaCl for 1 h, 24 h, and 48 h has been studied. Various electrochemical measurements such cyclic potentiodynamic polarization, electrochemical impedance spectroscopy, and potentiostatic current versus time were employed. The surface morphology and analysis were carried out via the use of scanning electron microscopy and energy dispersive X-ray examinations. All experiments have revealed that the deposited coatings decreased the cathodic current, anodic current, corrosion current density (jCorr), absolute current versus time, and the corrosion rate (RCorr) compared to the uncoated API-2H steel. The value of jCorr decreased from 47 µA/cm2 for uncoated steel to 38 µA/cm2 for the PSC1-coated steel and 29 µA/cm2 for the PSC2-coated steel. Moreover, prolonging the time of exposure decreases the jCorr and RCorr values. The jCorr values obtained after 48 h recorded 32, 26, and 20 µA/cm2 for the uncoated, PSC1, and PSC2 samples, respectively. Moreover, applying these coatings also led to increasing the corrosion resistance (RP) after all the exposure periods of time. In addition, the PSC2 coating was found to be more protective against corrosion for the surface of the steel than the PSC1 coating.

Ultrasonic Sensors-Assisted Corrosion Studies on Surface Coated AlSi9Cu3 Alloy Die Castings

A novel phenomenon known as Industry X.0 is becoming extremely popular for digitizing and reinventing business organizations through the adaption of rapid and dynamic technological, innovational, and organizational changes for attaining the profitable revenue. This work investigates the die-casted commercially pure aluminum alloyed with 9% silicon and 3% copper (AlSi9Cu3) that is produced through the gravity die casting process. Further, the degradation of surface coating on die-casted AlSi9Cu3 alloy was explored. The acrylic paint electrodeposition (ED) coat, 2-coat polyester without primer and 3-coat polyester with epoxy primer powder coatings were used in this study. Moreover, the 3.5 wt.% of sodium chloride (3.5 wt.% of NaCl) test solution was used for electrochemical and salt spray test and the tools used to assess electrochemical properties were electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and neutral salt spray test (NSS). The microstructure of AlSi9Cu3 after corrosion exposure was investigated; also, the microstructure of coated and uncoated AlSi9Cu3 samples was analyzed by SEM microscopy after corrosion exposure. Besides, the electrochemical studies were also carried out on the Al alloy die casting. It was found that acrylic paint ED coatings exhibited higher corrosion resistance than 2-coat polyester without primer & 3-coat polyester with epoxy primer powder coatings. Acrylic paint ED coating showed higher corrosion resistance in AC and a lower value in DC and 3-coat polyester with epoxy primer powder coating displayed higher corrosion resistance in DC and a lower value in AC.

Influence of Zinc Oxide Nanoparticles and Char Forming Agent Polymer on Flame Retardancy of Intumescent Flame Retardant Coatings

Zinc oxide nanoparticles (ZnO NPs) were synthesized by a precipitation method, and a new charring-foaming agent (CFA) N-ethanolamine triazine-piperazine, melamine polymer (ETPMP) was synthesized via nucleophilic substitution reaction by using cyanuric chloride, ethanolamine, piperazine, and melamine as precursor molecules. FTIR and energy-dispersive X-ray spectroscopy (EDS) studies were employed to characterize and confirm the synthesized ETPMP structure. New intumescent flame retardant epoxy coating compositions were prepared by adding ammonium polyphosphate (APP), ETPMP, and ZnO NPs into an epoxy resin. APP and ETPMP were fixed in a 2:1 w/w ratio and used as an intumescent flame-retardant (IFR) system. ZnO NPs were loaded as a synergistic agent in different amounts into the IFR coating system. The synergistic effects of ZnO NPs on IFR coatings were systematically evaluated by limited oxygen index (LOI) tests, vertical burning tests (UL-94 V), TGA, cone calorimeter tests, and SEM. The obtained results revealed that a small amount of ZnO NPs significantly increased the LOI values of the IFR coating and these coatings had a V-0 ratings in UL-94 V tests. From the TGA data, it is clear that the addition of ZnO NPs could change the thermal degradation behaviors of coatings with increasing char residue percentage at high temperatures. Cone calorimeter data reported that ZnO NPs could decrease the combustion parameters including peak heat release rates (PHRRs), and total heat release (THR) rates. The SEM results showed that ZnO NPs could enhance the strength and the compactness of the intumescent char, which restricted the flow of heat and oxygen.

The Influence of Glass Flake and Micaceous Iron Oxide on Electrochemical Corrosion Performance of Waterborne Silicate Coatings in 3.5% NaCl Solution

Waterborne silicate composite coatings were prepared to replace existing solvent-based coatings for ships. A series of complex coatings were prepared by adding anticorrosive pigments to the silicate resin. Adhesion, pencil hardness, and impact resistance were investigated, and corrosion performance in 3.5% NaCl solution was measured by electrochemical impedance spectroscopy (EIS). The results show that adhesion and impact resistance are high, and that pencil hardness can reach 4H. The curing mechanism for the coatings were investigated by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The mechanism of curing reaction in the studied waterborne silicate paint was found to be different from that reported in the literature. When the coatings were immersed in 3.5% NaCl solution for 8 h, there is only one time constant in the Bode plot, and coating capacitance (Qc) gradually increases while coating resistance (Rc) gradually decreases. Glass flake composite coatings have better corrosion resistance by comprehensive comparison of Qc and Rc.

The Effect of Glass Fiber Powder on the Properties of Waterborne Coatings with Thermochromic Ink on a Chinese Fir Surface

In this study, the effect of glass fiber powder on the properties of waterborne coatings with thermochromic ink was investigated, using Chinese fir board as the base material and temperature-sensitive thermochromic waterborne coatings with thermochromic ink as the paint base. The concentration of glass fiber powder was determined when the microstructure, optical properties, mechanical properties, liquid resistance, and heat preservation effect were the best. The results showed that the paint film with glass fiber powder concentration of 1.0% to 7.0% had better discoloration performance. With an increase of the glass fiber powder concentration, the gloss of the paint film decreased gradually, and when the concentration of glass fiber powder was 0% to 5.0%, the gloss of the paint film was better. The concentration of glass fiber powder had no effect on the adhesion, impact resistance, and liquid resistance. In the first 2.5 min, the temperature value of the waterborne coating with 3.0% glass fiber powder was higher than that without glass fiber powder, which has a certain heat preservation effect. When the glass fiber powder content was 3.0%, the microstructure of paint film was the best. The composition of paint film with different glass fiber powder concentrations was not different and the discoloration performance of paint film with heat preservation effect was not affected by time. The analysis showed that the waterborne coating with 3.0% glass fiber powder had the best comprehensive performance. This work provides a technical reference for the industrialization of heat preservation and thermochromic coating on wood.

Electrochemical Properties of Niobium Coating for Biomedical Application

The preparation of the Nb coating was performed on the bare Ti–6Al–4V alloy using the double glow discharge plasma technique. It was characterized that the Nb coating exhibited a face centered cubic (fcc) crystal structure and a pronounced (200) preferred orientation. The SEM micrograph of the cross section for the coating displayed dense microstructure with a thickness of approximately 18 µm. The critical load (Lc) of the coating was determined to be about 83.5 N by the scratch tests. The electrochemical corrosion resistance of the coating was examined in Ringer’s solution at 37 °C by a series of electrochemical techniques, including open-circuit potential (OCP), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and a Mott–Schottky analysis. As the result of the potentiodynamic polarization, the Nb coating possessed a more positive corrosion potential and lower corrosion current density than the Ti–6Al–4V substrate. EIS fitting date showed that the Nb coating always possessed a higher value of impedance and lower effective capacitance than those of the substrate during the five days of immersion testing. The main component of the passive film developed on the Nb coating was Nb2O5, confirmed by an X-ray photoelectron spectroscopy (XPS) analysis. A Mott–Schottky analysis demonstrated typical n-type semiconductor characteristics of the Nb coating, and both the donor density and flat band potential of the coating were lower than those of the substrate at all the given formation potential. These investigations demonstrate that the Nb coating can significantly improve the corrosion protection of uncoated Ti–6Al–4V and is thus a promising coating for the surface protection of bioimplants.