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Nonmetallic conducting coatings: Properties and behaviour of iron and iron‐copper phosphate coatings
Author(s) -
Leoni M.,
Randi G.,
Farne G.,
Grimaldi R.
Publication year - 1986
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19860370807
Subject(s) - corrosion , materials science , metallurgy , conversion coating , copper , porosity , welding , phosphate , humidity , sodium hydroxide , composite material , chemical engineering , chemistry , physics , organic chemistry , engineering , thermodynamics
Surface conversion of steel by means of conducting iron phosphate coatings protects mechanical parts blanked from steel sheets, even in a very high‐humidity environment, and also allows their assembly through electrical resistance welding. Corrosion tests carried out by exposing the materials to alternate humid/dry cycles, in a humidostatic chamber at 40°C, indicate that the welding process gives rise to corrosion phenomena. These can be strongly mitigated by using conversion coatings of mixed iron/copper phosphates. Conditions for obtaining optimum corrosion resistance for the final conversion coatings are therefore defined. Measurements of the related corrosion potentials made at 25 °C in a sodium hydroxide solution (pH 12, saturated in oxygen) indicate the existence of threshold values above which corrosion resistance of the phosphatized specimens is acceptable, and suggest a method for performing an industrial control of phosphating efficiency. The performance of converted steel surface has been related to the porosity of phosphate coatings.