Open AccessATMOSPHERIC CORROSION RESISTANCE OF TRIVALENT AND HEXAVALENT CHROME CONVERSION COATING ON ZINC ELECTRODEPOSITS IN HANOI AFTER 5 YEARS NATURAL EXPOSURE
Author(s) -
Nguyễn Thị Thanh Hương,
Lê Bá Thắng,
Bao Liu,
Đào Bich Thủy
Publication year - 2018
Publication title -
vietnam journal of science and technology/science and technology
Language(s) - English
Resource type - Journals
eISSN - 2815-5874
pISSN - 2525-2518
DOI - 10.15625/2525-2518/56/3b/12836
Subject(s) - zinc hydroxide , zinc , corrosion , hydroxide , hexavalent chromium , sulfate , hydrate , calcium hydroxide , metallurgy , materials science , chloride , nuclear chemistry , inorganic chemistry , chromium , chemistry , organic chemistry
In this paper, the corrosion resistances obtained after five year exposure of zinc coatings, trivalent chrome conversion coatings (CCCs) and hexavalent CCCs on zinc electroplatings are compared and discussed. The compositions of corrosion products of sample surfaces after exposure are investigated. The results of analysis by means of X-ray diffraction show that the corrosion products formed on zinc coatings, trivalent CCCs, hexavalent CCCs in atmospheric conditions of Hanoi have the distinctions specialty of the humid tropical climates. Zinc sulfate hydroxide hydrate Zn4SO4(OH)6.H2O; Zinc carbonate hydroxide hydrate Zn4CO3(OH)6.H2O; Simonkolleite Zn5(OH)8Cl2.H2O; Chromium Sulfate Cr2(SO4)3; Zinc chloride sulfate hydroxide hydrat Zn12(OH)15(SO4)3Cl3.H2O; Eskolaite Cr2O3 have been identified. The presence of SO2 results in the formation of Zinc sulfate hydroxide hydrate Zn4SO4(OH)6.H2O. After 5 years of exposure in atmospheric conditions, the hexavalent CCCs on zinc coatings have show the best corrosion resistance and the least corrosion products. The corrosion resistance of the samples decreases in the order: 747 > SP25 ~ TM 3108 > Zn.