Synthesis and Characterization of Chromate Conversion Coatings on GALVALUME and Galvanized Steel Substrates
- PDF / 1,323,735 Bytes
- 14 Pages / 593.972 x 792 pts Page_size
- 71 Downloads / 189 Views
ON
CHROMATE conversion coatings (CCCs) have traditionally been employed to prevent the corrosion process in several metallic components and to improve the adhesion of paints, lacquers, and organic components.[1,2] Although these coatings are highly effective, chromium (VI), which is used in the conversion treatment, is a carcinogenic agent.[3,4] Nowadays, as a consequence of the environmental and health risks associated with the use of such coatings, they are being restricted. M.A. DOMI´NGUEZ-CRESPO, Professor, formerly with the Universidad Nacional Auto´noma de Me´xico, Edificio D Facultad de Quı´ mica, Departamento de Metalurgia. Ciudad Universitaria, C.P. 04510 Me´xico D.F., Me´xico, is with the Instituto Polite´cnico Nacional, Grupo de Ingenierı´ a en Procesamiento de Materiales CICATA-IPN, Unidad Altamira. Km 14.5, Carretera Tampico-Puerto Industrial Altamira. C.P. 89600 Altamira, Tamps. Me´xico. Contact e-mail: [email protected] E. ONOFRE-BUSTAMANTE and F.J. RODRI´GUEZ-GO´MEZ, Professors, are with the Universidad Nacional Auto´noma de Me´xico, Edificio D Facultad de Quı´ mica, Departamento de Metalurgia. Ciudad Universitaria. A.M. TORRESHUERTA and A. FLORES-VELA, Professors, are with the Instituto Polite´cnico Nacional, Grupo de Ingenierı´ a en Procesamiento de Materiales CICATA-IPN, Unidad Altamira. Km 14.5, Carretera Tampico-Puerto Industrial Altamira. C.P. 89600. Altamira, Tamps. Me´xico. S.E. RODIL, Professor, is with the Universidad Nacional Auto´noma de Me´xico, Instituto de Investigacio´n en Materiales, Circuito Exterior s/n, Ciudad Universitaria. Del. Coyoaca´n, C.P. 04510 Me´xico D.F., Me´xico. Manuscript submitted February 18, 2008. Article published online June 11, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
Several alternatives have been investigated in recent years, which have led to the development of other nontoxic coating processes with comparable adhesion properties and corrosion protection. For example, zinc, manganese, and iron compounds have been employed together with fluorides,[5] and more recently, new types of conversion pretreatments formed by immersion in solutions containing cerium chloride, phosphates, or other rare earth metal chlorides, such as yttrium and lanthanum, have been studied.[6–9] However, processes with similar performances to that of Cr (VI) have not yet been achieved. Cr (VI) provides an exceptionally good corrosion resistance, which depends upon the base metal, treatment, and film thickness. The protection is due to both the corrosion inhibition effect of the hexavalent chromium contained in the film and the physical barrier by the film itself. Even scratched or abraded films retain a great deal of their protective value, because the hexavalent chromium content is slowly leachable in contact with the moisture, providing a self-healing effect.[10–12] The mechanism by which conventional CCCs inhibit the corrosion of metals is not yet fully understood, although a large number of studies have been performed and some insight has been obtained.[13–15] In order to understand th
Data Loading...
