Stock material or miscellaneous articles – Composite – Of metal
Patent
1995-02-27
1998-02-24
Kastler, Scott
Stock material or miscellaneous articles
Composite
Of metal
427333, B05D 304, B32B 1508
Patent
active
057210560
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for the production of corrosion-protected metallic materials by passivation and to the materials obtainable therewith.
The passivation of metals, in particular of aluminium, is known. Aluminium is passivated, albeit to an insufficient extent, by reaction with atmospheric oxygen. On an industrial scale, electrolytic oxidation is used for its passivation (Eloxal process) in which, however, electricity consumption and the use of toxic chemicals are disadvantageous on ecological grounds.
Electrolytic passivation of iron and steel has been hitherto practically impossible or only realisable to an insufficient extent. Steel, as stainless steel, is passive in an acidic medium through the presence of, inter alia, chromium oxides, but very susceptible to pitting since there is no dense homogeneous passive layer. Iron can be temporarily passivated by strong acids against acid attack, but the passive layer is very easily damaged.
The corrosion protection of steel is still an enormous ecological problem and, because of the destruction of supporting structures, machinery and buildings, also a great economic problem. As before, steel has to be protected essentially passively by top coats, i.e. the admission of water and oxygen and salts must be prevented. However, particularly in crevices, at damaged sites of the paints and because of ageing, the traditional paints fail to work and must therefore be replaced at regular intervals. To a certain extent, an "active" protection is achieved through zinc coating, whereby the iron acts as a cathode and is therefore protected cathodically; cathodic protection also takes place through using sacrificial anodes or by applying a suitable voltage.
Observations of a corrosion-protection effect of intrinsically conductive polymers, above all of polyaniline, have been made on several occasions in former years. Thus, A. McDiarmid reported at a conference (ICSM 1986, Kyoto) during a lecture on the electrochemical deposition of polyaniline under anodic potential onto steel and on the observation that the electrochemically coated steel plate was more resistant to corrosion than an uncoated steel plate. This observation was also made by D. DeBerry in the case of stainless steel, onto whose surface polyaniline had been deposited by electrochemical means (J. Elektrochem. Soc. 132, 1022 (1985)). The disadvantages of this procedure are that on a commercial scale, and corrosion-protection effect was.
In WO 89/02155, polyaniline-containing paint dispersions have been proposed for the first time with which a corrosion-protection effect was obtained. The described process for corrosion protection and the proposed formulations have not, however, proved successful in practice since sufficiently reproducible, coatings industry, e.g. as regards coating behaviour, paint adhesion, pore formation, water and oxygen migration values.
Encouraged inter alia by the observations of A. McDiarmid, a working group from the Los Alamos Laboratories, acting on behalf of NASA, likewise carried out corrosion studies with polyaniline-coated steels. This study team coated steel plates with neutral and non-conductive polyaniline from solution, then carried out a "doping" with various "doping" agents and coated this composite structure with corrosion-protection paint. A summary of the results of the studies can be found in Project Report LA-UR-92-360 of the Los Alamos National Laboratories (K. Thompson et al., 1991). Although the Los Alamos Laboratories were able to achieve a certain corrosion-protection effect, they did not achieve the aim of reliably protecting the steel structure against HCl in the corrosive atmosphere of launching boosters during space shuttle launches. In particular, the reproducibility of the corrosion-protection effect left much to be desired; further, there were no details given regarding a possible shift of the corrosion potential. Thus, the authors argue inter alia that the corrosion-protection effect depended on the chemical nature of
REFERENCES:
patent: 5248526 (1993-09-01), Ogawa
patent: 5270417 (1993-12-01), Soga
DeBerry, J. Electro Chemical Society 16 Bd 132, 14 1985 pp. 1022-1026.
Kastler Scott
Zipperling Kessler & Co. (GmbH & Co.)
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