Corrosion Products of Zinc-Manganese Coatings: Part Ⅱ―Investigations Using X-Ray Photoelectron Spectroscopy (XPS)

摘要

Our previous investigations (Part Ⅰ, Sept. 2001, pages 56-60) with microprobe analysis and X-ray diffraction (XRD) permitted determination of the composition of the corrosion products formed on galvanic alloys Zn-Mn with different phase composition after treatment in a model neutral-corrosion medium containing Cl ions. An appearance of the compound zinc hydroxide chloride (ZHC) was registered. ZHC leads to a significant increase of the protective ability of these coatings. The amount of this compound strongly depends on the phase composition of the alloy and on the presence (or nonpresence) of chromating film on the sample surface. The intermetallic phase MnZn_7 ensures great ZHC quantities. No chromium compounds on the chromated samples were observed with XRD studies, although this element was registered from the microprobe analysis. The former investigations do not establish all compounds of the elements, which form the passive layer at anodic treatment in 5% NaCl solution. The X-ray photoelectron spectroscopy (XPS) investigations of Zn-Mn galvanic alloy were aimed to complete the results about the compounds of the participating elements throughout the depth of the alloy thickness. Moreover, an additional explanation for the protective mechanism of the manganese and, more exactly, of the intermetallic phase δ_1 in this medium was investigated.