Etching a substrate: processes – Nongaseous phase etching of substrate – Etching inorganic substrate
Patent
1994-06-22
1996-07-23
Dang, Thi
Etching a substrate: processes
Nongaseous phase etching of substrate
Etching inorganic substrate
216100, 252 794, 252 791, 134 2, 134 3, 134 41, C09K 1300, C23F 300
Patent
active
055381529
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a composition which has high stabilizing properties, more particularly in the case of inorganic peroxides used in the context of industrial applications.
It more particularly relates to a stabilizing composition for inorganic peroxides used in baths for pickling metal surfaces.
TECHNOLOGY REVIEW
As is known, surface treatment of stainless steels currently provides for the removal of oxides by means of a chemical process.
It sometimes happens that this chemical process is preceded by a mechanical action, such as sandblasting or brushing of the steel, which operation is carried out with a view to obtaining an improvement in the surface of the steels so as to reduce the duration of their chemical treatment.
Pickling baths of the type mentioned generally contain nitric/hydrofluoric mixtures or sulphuric
itric and hydrofluoric acid mixtures, to which have been added process correctors which can be surface-active agents, for improving the wetting characteristics thereof, or inhibitors, for rendering the chemical action uniform.
As the surface treatments for steels currently used are particularly polluting as a result of the presence of nitrogen oxides which are produced during the pickling action or as a result of nitrates present in the waste water, pickling baths have recently been proposed which introduce an alternative solution to the conventional processes.
These baths are usually operated while hot and especially require in the same step an additional mechanical action, the objective of which is to compensate for the absence of disintegrating action due to the absence of nitric acid in these baths.
The additional mechanical action normally provides for the production of turbulence in the pickling solution, whether by stirring the liquid or by blowing air into the baths so as to promote detachment of the oxides from the metal surfaces. The absence of nitric acid in these baths is compensated for by the presence of inorganic peroxides such as hydrogen peroxide.
The presence of inorganic peroxides replaces not only the oxidizing action of nitric acid but it also additionally promotes pickling and passivation of the metal surface.
If the use of these pickling baths which are free of nitric acid makes it possible, on the one hand, to solve the problem of pollution due to the production of nitrogen oxide during the pickling action and the problem brought about by the presence of nitrates in the waste water, it however requires the use of specific equipment which is expensive and which requires periodic maintenance.
Moreover, monitoring of the peroxides present in the baths must normally be carried out using redox measuring instruments which, as is known, are not only very expensive to buy but also have a limited lifetime when they are used for this specific purpose.
Baths containing peroxides additionally have a limited stability, as a result of the presence of metals which catalyze the decomposition of the peroxides.
In order to avoid these disadvantages, and therefore the undesirable decompositions of the peroxides, the dissociation action of the peroxides themselves is currently inhibited, which has the side-effect of reducing the chemical activity of the pickling.
In such a situation, and in order to compensate for the low activity of the pickling baths, it is therefore necessary to operate at temperatures greater than ambient temperatures, while additionally stirring the baths so as to promote detachment of the oxides.
In the light of what has just been explained above, it is clearly understood that if, on the one hand, the baths which are free of nitric acid make it possible for the time being to greatly reduce the degree of pollution, it is necessary, on the other hand, either to operate at temperatures which are generally greater than the usual temperatures or to carry out expensive modifications of the equipment, it being necessary for the latter to be equipped with means for heating and stirring the baths or means for blowing air into the sam
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Dang Thi
Solvay Interox S.p.A.
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