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Les peintures conferent aux subjectiles metalliques des proprietes de resistance et definissent leur aspect esthetique. Proteger un avion ou une voiture en lui appliquant une peinture, c’est proteger sa « duree de vie ». Cette protection doit s’exercer vis‐a‐vis d’une multitude d’agressions : oxygene, eau, variations de temperature, irradiation solaire, pollution atmospherique, degradation et vieillissement acceleres des materiaux a travers leur utilisation repetee, mais aussi operations de maintenance (nettoyage et detection d’usure du support). Il arrive donc un moment ou la protection n’est plus assuree, ce qui necessite un decapage du revetement par l’un des procedes disponibles : mecanique, thermique ou chimique (figure 1 ). Dans le cadre de cet article, apres un bref rappel sur les techniques de decapage thermique et mecanique, on developpera surtout la technique du decapage chimique , de loin la plus utilisee.

Reduction of dioxygen dissolved in water by diethylhydroxylamine (DEHA) in the presence of hydroquinones or quinones as organocatalysts is investigated with regard to reaction rate and catalyst turnover. Eleven p-benzoquinone derivatives bearing various electron-donating, electron-withdrawing and bulky substituents are studied. The catalytic activity of four benzenediols (hydroquinone, resorcinol, catechol and 4-tert-butylcatechol) and of four benzenetriols (hydroxyquinol, phloroglucinol, pyrogallol and 5-tert-butylpyrogallol) is compared. Mechanistic and kinetic studies indicate that the rate-determining step is the regeneration of hydroquinones through the reduction of the corresponding benzoquinones by DEHA. Then, eight natural polyphenols are tested as alternative catalysts to the potential carcinogen hydroquinone. Four of them (purpurin, myricetin, gallic acid and propyl gallate) exhibit some catalytic activity and gallic acid is shown to be even more efficient than hydroquinone itself. A further improvement of the catalytic system is achieved by adding catalase to disproportionate the generated hydrogen peroxide, which is detrimental for the catalyst. Thus, the oxygen scavenging system DEHA–gallic acid–catalase is found to be not only greener but also more efficient than the current system DEHA–hydroquinone since it gives water instead of hydrogen peroxide as the final reduction product of dioxygen.

A supported Mn–porphyrin catalyst was prepared by strong adsorption of the tetracationic Mn[meso-tetra(4-N-methylpyridiniumyl) porphyrin](Cl)4+4Cl– on silica, and was found very efficient for cyclo-octene epoxidation (95% yield, 13 turnovers per min) and for alkane hydroxylation, with alcohol yields and alcohol: ketone ratios remarkably higher than those obtained with corresponding soluble Mn–porphyrins.