Thermal and corrosion resistance of metal coatings on optical fiber

• I.V. Petukhov¹, I.S. Semenikhina¹, V.I. Kichigin¹, M.I. Bulatov², N.S. Volokhov¹ and Yu. A. Lapteva¹

¹ Perm State National Research University, st. Bukireva 15, 614068 Perm, Russian Federation
² Perm National Research Polytechnic University, 29, Komsomolsky prosp., 614068 Perm, Russian Federation

Abstract: The thermal and corrosion resistance of Ni coating and double-layer Ni-Au coating applied over protective and strengthening copper layer on the optical fiber has been investigated. This subject was considered because the optical fibers are widely used at high temperatures and in aggressive media. The copper layer was deposited from the melt; Ni and Au were deposited electrolytically. The Cu-Ni and Cu-Ni-Au coatings raise the onset temperature for oxidation in air by 200°C and reduce markedly the rate of coating oxidation. The thermal treatment of the optical fiber with Cu-Ni and Cu-Ni-Au coatings at temperatures of 300 to 400°C brings about small increase in the tensile strength of the fiber. At further rise in the temperature (≥500°C) the tensile strength of the fiber becomes considerably lower, especially for Cu-Ni-Au coatings. The coatings studied pass the humidity chamber test whereas they corrode non-uniformly in the salt spray chamber. After the salt spray test, coating (Ni and Au) delamination was observed in some areas. The corrosion process is probably stimulated by the formation of galvanic couples of copper and nickel or nickel and gold due to the presence of pores and microcracks in the coatings. Nickel coating improves the corrosion resistance in 3% NaCl solution; however, additional Au layer increases the corrosion rate.

Keywords: quartz optical fiber, protective coating, tensile strength, thermal analysis, humidity chamber, salt spray test, 3% NaCl, corrosion resistance, polarization curve

Int. J. Corros. Scale Inhib., 2023, 12, no. 4, 2221-2238
doi: 10.17675/2305-6894-2023-12-4-41

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