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0-69469 Weinheim, 1995 ou3S-9648/95!o2a2-o180 $5.00+ .25/0 Adc. Muirr. 1995. 7, No. 2 $ ; VCH L+riagsgesellschafi mhH. 0-69469 Weinhrim. 1995 093S-964Xi9S~OZO2-0isl$5.00 + ,2510 Adv. Marer. 1995. 7, No. 2

No abstract

The purpose of this study has been to advance in knowledge of the chemical composition, structure and thickness of the thin native oxide film formed spontaneously in contact with the laboratory atmosphere on the surface of freshly polished commercial AZ31 and AZ61 alloys with a view to furthering the understanding of protection mechanisms. For comparative purposes, and to more fully describe the behaviour of the native oxide film, the external oxide films formed as a result of the manufacturing process (as-received condition) have been characterised. The technique applied in this research to study the thin oxide films (thickness of just a few nanometres) present on the surface of the alloys has basically been XPS (X-ray photoelectron spectroscopy) in combination with ion sputtering. Corrosion properties of the alloys were studied 2 in 0.6M NaCl by measuring charge transfer resistance values, which are deduced from EIS (electrochemical impedance spectroscopy) measurements after 1 hour of exposure. Alloy AZ61 generally showed better corrosion resistance than AZ31, and the freshly polished alloys showed better corrosion resistance than the alloys in as-received condition. This is attributed to a combination of (1) higher thickness of the native oxide film on the AZ61 alloy and (2) greater uniformity of the oxide film in the polished condition. The formation of an additional oxide layer composed by a mixture of spinel (MgAl 2 O 4) and MgO seems to diminish the protective properties of the passive layer on the surface of the alloys in as-received condition.

Ahstrart-This contribution concerns intercalation materials based on the formation of intracrystalline polymer-salt complexes obtained by insertion of poly(ethylene oxide) (PEO) and crown-ether compounds in a layer silicate (montmorillonite), containing Na+ exchangeable cations in their interlayer space. Polyoxyethylene compounds (crown ethers and PEO) are able to associate. interlayer cations modifying dramatically the ionic conductivity of the natural silicate. The new organo-inorganic materials exhibit a two-dimensional structure able to induce an anisotropic character in their electrical properties.