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Recent Advances in Polymer Nanocomposite Coatings for Corrosion Protection
Published in Mahmood Aliofkhazraei, Advances in Nanostructured Composites, 2019
Subramanyam Kasisomayajula, Niteen Jadhav, Victoria Johnston Gelling
A typical aircraft protective coating system shown in Figure 6 contains 3 layers: (1) surface pretreatment, (2) primer coat, and (3) top-coat. Generally, a chromate conversion coating such as Alodine 1200S with a thickness less than 2 μm is applied as surface pre-treatment on the surface of aluminum alloy to increase adhesion between primer coat and substrate. A primer coat is usually an epoxy-polyamide coating that may contain corrosion inhibitors such as strontium chromate in the form of pigments. In addition to providing corrosion protection to metal substrate, the primer coat is also intended to help to maintain adhesion between the surface pre-treatment and topcoat. Even though the key purpose of a topcoat, generally a polyurethane coating, is to bestow an aesthetic appearance to the overall coating system, it is sometimes designed to add protective functionality as well.
Corrosion
Published in John H. Bickford, An Introduction to the Design and Bchavior of Bolted Joints, 2018
The KISCC value for a fastener can be affected by surface coatings or treatment. Figure 18.15 shows the effect various plating have on low-alloy steel fasteners, for example [34]. A coat of nickel under conventional cadmium led to satisfactory SCC resistance in H-11 bolts heat treated to a UTS of 260 ksi and then loaded to 90% of the proportional limit [40]. The same reference says that nickel and nickel-cadmium coatings in general result in a significant improvement in SCC resistance, as does electroplated cadmium with a chromate conversion coating. Vapor-deposited cadmium and a zinc chromate primer give less but some protection. But plating or surface treatment is not an automatic cure. Gold plating makes little difference [40]. Nor can you eliminate SCC by chrome plating 440 C stainless steel, for example, or by anodizing 2024-T3 aluminum. And carburizing a low-strength carbon steel to a surface hardness corresponding to a UTS of 200 ksi can make that usually-resistant material susceptible [37].
Waste Treatment to Minimize Disposal
Published in E. Higgins Thomas, Hazardous Waste Minimization Handbook, 2018
The EPA lists “wastewater treatment sludges from the chemical conversion coating of aluminum” as hazardous under the classification F019, specifically because they typically contain hexavalent chromium or cyanide (RCRA Appendix VII). In addition to being used in the chromium conversion coating process, hexavalent chromium compounds are used at the facility to deoxidize surfaces (remove oxide surface coating) when preparing parts for chromate conversion coating. Table 8.11 shows the amounts of chromium discharged to the waste treatment plant from the three locations that employ chromate conversion coating at the facility. These data were estimated from composition of the process baths involved and from approximations by company personnel of the production loads on these processes and typical drag-out rates.
Ti/Cr(III) conversion coating on aluminium foil for lithium-ion battery package
Published in Surface Engineering, 2021
Chromate conversion coating has been extensively used in many fields because of its self-healing ability and active corrosion protection, including Al-polymer composite film. However, the hexavalent chromium (Cr(VI)) in wastewater produced during the manufacture of Al-polymer composite film is highly toxic and carcinogenic [7]. For this reason, a number of environment-friendly surface treatments have been developed in response to environmental protection requirements, such as titanium (Ti) conversion coatings [8], zirconium (Zr) conversion coatings [9], phosphate conversion coatings [10], vanadium conversion coatings [11], trivalent chromium (Cr(III)) conversion coatings [12] and rare earth conversion coatings [13]. However, as it is difficult for a single-element conversion coating to achieve excellent overall performance, research interest has been directed towards multiple-elements conversion coatings. Zhu et al. [14] prepared a novel Ti/Zr conversion coating on the Al alloy, which was shown to be more heterogeneous compared with the single Ti or Zr conversion coating. Burattini et al. [15] investigated the effect of titanium as an additive on the corrosion resistance properties of zinc (Zn) coating, and the Zn–Ti composite coating showed good corrosion resistance. Abbasi et al. [16] found that the vanadium additive increased the surface roughness, surface free energy and the adhesion of the conversion coating.
Electrochemical regeneration of hexavalent chromium from aqueous solutions in a gas sparged parallel plate reactor
Published in Environmental Technology, 2022
N. K. Amin, S. A. Nosier, M. H. Abdel-Aziz, M. S. Hassan, G. H. Sedahmed, M. A. El-Naggar
In the metal finishing industry [4,5] hexavalent chromium is used in chromium plating, chromate conversion coating of metals to guarantee subsequent paint adhesion to the metallic substrate and to give extra protection to the metal against corrosion. Hexavalent chromium is also used in printed circuit copper etching [6], plastic etching [7] before the metallization of the plastic surface, production of alloys, leather tanning, pigment making, electroplating, wood preserving, and refractory [8–10]. In all the above applications the waste solution contains Cr3+ in a high concentration and some residual Cr6+, both ions are lethal especially Cr6+ which is carcinogenic.