EP0206386A1 - Baths and process for chemically polishing stainless-steel surfaces - Google Patents

Baths and process for chemically polishing stainless-steel surfaces Download PDF

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Publication number
EP0206386A1
EP0206386A1 EP86200920A EP86200920A EP0206386A1 EP 0206386 A1 EP0206386 A1 EP 0206386A1 EP 86200920 A EP86200920 A EP 86200920A EP 86200920 A EP86200920 A EP 86200920A EP 0206386 A1 EP0206386 A1 EP 0206386A1
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per liter
bath
moles
baths
acid
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German (de)
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EP0206386B1 (en
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Daniel Tytgat
Pierre Lefevre
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Solvay SA
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Solvay SA
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    • CCHEMISTRY; METALLURGY
    • C23COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23GCLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G5/00Cleaning or de-greasing metallic material by other methods; Apparatus for cleaning or de-greasing metallic material with organic solvents
    • CCHEMISTRY; METALLURGY
    • C23COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23FNON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F3/00Brightening metals by chemical means
    • C23F3/04Heavy metals
    • C23F3/06Heavy metals with acidic solutions

Definitions

  • the present invention relates to the composition of baths for the chemical polishing of stainless steel surfaces.
  • Chemical polishing of metal surfaces is a well-known technique - (Electrolytic and chemical polishing of metals - W.J. Mc G. TEGART -Dunod -1960 -p. 122 et seq.); it consists of treating the metal surfaces to be polished with baths of mineral acids.
  • baths are generally used comprising a mixture, in aqueous solution, of hydrochloric, phosphoric and nitric acids (patent US-A-2662814).
  • suitable additives such as surfactants, viscosity regulators and brighteners.
  • a composition of a bath for the chemical polishing of stainless steel surfaces comprising, in aqueous solution, a mixture of phosphoric acid, nitric acid and d hydrochloric acid, a viscosity regulator chosen from water-soluble polymers, a surfactant and sulfosalicylic acid as a brightening agent.
  • This known polishing bath has proven to be very effective. However, it has the disadvantage of containing several organic additives, which add to the cost, complicate its implementation and constitute a source of pollution during the rejection of the spent bath.
  • chemical polishing baths comprising a mixture of hydrochloric, nitric and phosphoric acids and a thiourea. It teaches that thiourea has the function of accelerating the speed of chemical polishing.
  • the present invention aims to remedy the aforementioned drawbacks of known polishing baths, by providing bath compositions for the chemical polishing of austenitic stainless steel surfaces, in particular steel alloyed with chromium and nickel, which avoid setting works with multiple additives and produces excellent quality polishes, especially in the case where the surface area to be polished is very high compared to the space available for the bath.
  • the invention therefore relates to baths for the chemical polishing of stainless steel surfaces, comprising, in aqueous solution, a mixture of hydrochloric acid, phosphoric acid and nitric acid; according to the invention, the baths comprise in the aqueous solution, ferricyanide complex ions and an additive capable of breaking down nitrous acid.
  • the ferricyanide complex ions are complex cyanides of general formula Fe III (CN) 6 3- , also called hexacyanoferrates (III) (Encyclopedia of Chemical Technology -Kirk Othmer -John Wiley & Sons, Inc. -1967 -Vol. 12 -pages 25, 26, 31, 32). They can be present in the aqueous solution in the form of all dissolved compounds such as, for example, hexacyanoferric acid (III), ammonium ferricyanide and ferricyanides of alkali and alkaline earth metals. Preferred compounds are the alkali metal ferricyanides, potassium ferricyanide being especially recommended.
  • the additive capable of decomposing nitrous acid has the function of decomposing at least part of the nitrous acid which is formed during the polishing of a steel surface, the nitrous acid being the consequence of an oxidation of ferrous ions released into the bath during polishing.
  • the additive can be chosen from all organic and inorganic substances which are capable of breaking down nitrous acid in an aqueous medium; it should be chosen from among the substances which do not attack the polishing steel and for which the products of the reaction with the acid nitrous do not attack the steel to be polished. Preference is given to substances which are soluble in the aqueous solution containing the mixture of acids.
  • Sulfamic acid, hydroxylamine, hydrazine, hydrogen peroxide, acetone, urea and primary, secondary and tertiary amines are examples of substances which can be used for the bath additive according to the invention .
  • the nitrogen compounds constitute a class of substances which are especially advantageous for the bath additive according to the invention; examples of nitrogen compounds are urea and its derivatives, in particular thiourea and ureines.
  • Urea is a preferred nitrogen compound, according to the invention.
  • the respective contents of phosphoric acid, hydrochloric acid, nitric acid and, in ferricyanide complex ions are chosen according to the nature of the metal treated, the working temperature and the desired time for polishing treatment.
  • the content of additive capable of breaking down nitrous acid depends on various parameters, such as the nature of said additive, the respective contents of hydrochloric acid, phosphoric acid, nitric acid and ferricyanide complex ions, the volume of the bath used. , the configuration of the metal surface to be polished and the nature of the metal. It has been found that, all other things remaining equal, the optimum content of additive in the polishing baths according to the invention is proportional to the depth of attack of the bath in the metal and to the ratio between the area of the metal surface to polish and the volume of the bath used.
  • Preferred baths are those which are essentially free of alkylpyridiniurn chloride, alkylphenol and cellulose ether.
  • a great advantage of the polishing baths according to the invention lies in their ability, after adaptation of the respective concentrations of their constituents, to carry out polishing at moderate speed of action, which can be distributed over several hours, so as to allow uniform polishing.
  • large surfaces or hard to reach surfaces They are especially well suited for polishing metal surfaces with a very large area, compared to the space available for the bath.
  • they find an interesting application for the polishing of metal surfaces whose area (expressed in ml is at least equal to 3 times, preferably greater than 8 times the volume - (expressed in m of the bath polishing which is in contact with it, such as, for example, heat exchangers with a very large exchange surface.
  • the performance of the baths according to the invention is not limited by a maximum value of the ratio between the area of the surface to be polished and the volume of the bath used, this ratio, expressed in m ⁇ 1 , which can for example reach 20 and more.
  • the baths according to the invention are suitable for polishing all austenitic stainless steel surfaces. They find a particularly advantageous application in the polishing of austenitic stainless steels alloyed with chromium and nickel, in particular those containing between 12 and 26% of chromium and between 6 and 22% of nickel, such as steels 18/8 and 18/10 , for example.
  • the invention therefore also relates to a method for polishing a stainless steel surface, according to which the surface is brought into contact with a chemical polishing bath according to the invention.
  • a prefabricated bath can be used, in contact with which the metal surface to be polished is then placed.
  • nitric acid and additive capable of decomposing nitrous acid is carried out after having brought the metal surface into contact with the bath.
  • an additional addition of nitric acid and additive capable of decomposing nitrous acid is carried out.
  • the bath is carried out in situ in contact with the metal surface to be polished.
  • the metal surface is first brought into contact with an aqueous solution containing hydrochloric acid, phosphoric acid, nitric acid and the additive capable of decomposing nitrous acid, then the ions are added. ferricyanide complexes to the solution, while it is in contact with the metal surface.
  • the contact time of the surface to be polished with the bath must be sufficient to achieve effective polishing of the surface; it cannot however exceed a critical value beyond which local corrosions may appear on the surface, unless a complementary addition of nitric acid and an additive capable of breaking down nitrous acid is carried out, in accordance with the particular embodiment of the method, described above.
  • the optimum contact time of the surface to be polished with the bath or the importance of the additional addition of nitric acid and additive capable of breaking down nitrous acid depend on many parameters such as the composition of the steel of the surface to be polished, its initial configuration and roughness, the composition of the bath, the working temperature, the possible turbulence of the bath in contact with the surface, the ratio between the area of the metal surface to be polished and the volume of the bath used; it must be determined in each particular case by routine laboratory work.

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Abstract

Baths for chemical polishing of stainless steel surfaces, comprising, in aqueous solution, a mixture of hydrochloric acid, phosphoric acid and nitric acid, ferricyanide complex ions and an additive capable of decomposing nitrous acid. The baths can be used in particular for chemical polishing of heat exchangers with a very large exchange surface.

Description

La présente invention a pour objet la composition de bains pour le polissage chimique de surfaces en acier inoxydable.The present invention relates to the composition of baths for the chemical polishing of stainless steel surfaces.

Le polissage chimique des surfaces métalliques constitue une technique bien connue - (Polissage électrolytique et chimique des métaux - W.J. Mc G. TEGART -Dunod -1960 -p. 122 et suivantes); elle consiste à traiter les surfaces métalliques à polir avec des bains d'acides minéraux. Pour le polissage chimique des aciers inoxydables austénitiques, on utilise généralement des bains comprenant un mélange, en solution aqueuse, d'acides chlorhydrique, phosphorique et nitrique (brevet US-A-2662814). Pour améliorer la qualité du polissage, il est habituel d'incorporer à ces bains des additifs adéquats tels que des agents tensio-actifs, des régulateurs de viscosité et des agents de brillantage. Ainsi, dans le brevet US-A-3 709 824, on fournit une composition d'un bain pour le polissage chimique de surfaces en acier inoxydable, comprenant, en solution aqueuse, un mélange d'acide phosphorique, d'acide nitrique et d'acide chlorhydrique, un régulateur de viscosité choisi parmi les polymères hydrosolubles, un sur- factant et de l'acide sulfosalicylique à titre d'agent de brillantage. Ce bain de polissage connu s'est révélé très efficace. Il présente toutefois l'inconvénient de contenir plusieurs additifs organiques, qui en grèvent le coût, compliquent sa mise en oeuvre et constituent une source de pollution lors du rejet du bain usé.Chemical polishing of metal surfaces is a well-known technique - (Electrolytic and chemical polishing of metals - W.J. Mc G. TEGART -Dunod -1960 -p. 122 et seq.); it consists of treating the metal surfaces to be polished with baths of mineral acids. For the chemical polishing of austenitic stainless steels, baths are generally used comprising a mixture, in aqueous solution, of hydrochloric, phosphoric and nitric acids (patent US-A-2662814). To improve the quality of the polishing, it is usual to incorporate in these baths suitable additives such as surfactants, viscosity regulators and brighteners. Thus, in US-A-3,709,824, there is provided a composition of a bath for the chemical polishing of stainless steel surfaces, comprising, in aqueous solution, a mixture of phosphoric acid, nitric acid and d hydrochloric acid, a viscosity regulator chosen from water-soluble polymers, a surfactant and sulfosalicylic acid as a brightening agent. This known polishing bath has proven to be very effective. However, it has the disadvantage of containing several organic additives, which add to the cost, complicate its implementation and constitute a source of pollution during the rejection of the spent bath.

Ces bains de polissage connus présentent la particularité d'attaquer le métal à très grande vitesse. Un traitement de polissage d'une surface en acier inoxydable avec de tels bains ne peut généralement pas excéder quelques minutes, sous peine d'engendrer des corrosions locales. Cette grande vitesse d'action des bains de polissage connus est un inconvénient, car elle les rend inutilisables pour certaines applications, notamment pour le polissage de la face interne des parois de cuves de grandes dimensions, telles que des chaudières, des autoclaves ou des cristalliseurs. Le temps nécessité pour le remplissage et la vidange de telles cuves étant en général largement supérieur à la durée du traitement de polissage chimique optimum, il devient en effet impossible d'obtenir un poli uniforme de la paroi, certaines zones de celle-ci étant insuffisamment polies, d'autres étant profondément corrodées. La grande vitesse d'action des bains de polissage chimique connus rend par ailleurs le contrôle du polissage difficile. Ces bains connus sont en outre inopérants pour le polissage de surfaces au contact desquelles le renouvellement du bain est difficile, car il en résulte des modifications brutales des compositions locales du bain. Ils ne sont pas adaptés au polissage d'installations, dans lesquelles l'aire de la surface à polir est très élevée par rapport à l'espace disponible pour le bain, par exemple des échangeurs de chaleur à très grande surface d'échange.These known polishing baths have the particularity of attacking the metal at very high speed. A polishing treatment of a stainless steel surface with such baths can generally not exceed a few minutes, on pain of causing local corrosions. This high speed of action of known polishing baths is a drawback, because it makes them unusable for certain applications, in particular for polishing the internal face of the walls of large tanks, such as boilers, autoclaves or crystallizers . The time required for filling and emptying such tanks being generally much greater than the duration of the optimum chemical polishing treatment, it indeed becomes impossible to obtain a uniform polish of the wall, certain areas of the latter being insufficiently others are deeply corroded. The high speed of action of known chemical polishing baths also makes polishing control difficult. These known baths are also ineffective for polishing surfaces in contact with which the renewal of the bath is difficult, since this results in abrupt modifications to the local compositions of the bath. They are not suitable for polishing installations, in which the surface area to be polished is very high compared to the space available for the bath, for example heat exchangers with very large exchange surface.

Dans le document FR-A-2463820, on divulgue des bains de polissage chimique comprenant un mélange d'acides chlorhydrique, nitrique et phosphorique et une thiourée. On y enseigne que la thiourée a pour fonction d'accélérer la vitesse du polissage chimique.In document FR-A-2463820, chemical polishing baths are disclosed comprising a mixture of hydrochloric, nitric and phosphoric acids and a thiourea. It teaches that thiourea has the function of accelerating the speed of chemical polishing.

La présente invention a pour but de porter remède aux inconvénients précités des bains de polissage connus, en fournissant des compositions de bains pour le polissage chimique de surfaces en acier inoxydable austénitique, notamment en acier allié au chrome et au nickel, qui évitent la mise en oeuvre de multiples additifs et réalisent des polis d'excellente qualité, spécialement dans le cas où l'aire de la surface à polir est très élevée par rapport à l'espace disponible pour le bain.The present invention aims to remedy the aforementioned drawbacks of known polishing baths, by providing bath compositions for the chemical polishing of austenitic stainless steel surfaces, in particular steel alloyed with chromium and nickel, which avoid setting works with multiple additives and produces excellent quality polishes, especially in the case where the surface area to be polished is very high compared to the space available for the bath.

L'invention concerne dès lors des bains pour le polissage chimique de surfaces en acier inoxydable, comprenant, en solution aqueuse, un mélange d'acide chlorhydrique, d'acide phosphorique et d'acide nitrique; selon l'invention, les bains comprennent dans la solution aqueuse, des ions complexes ferricyanure et un additif capable de décomposer l'acide nitreux.The invention therefore relates to baths for the chemical polishing of stainless steel surfaces, comprising, in aqueous solution, a mixture of hydrochloric acid, phosphoric acid and nitric acid; according to the invention, the baths comprise in the aqueous solution, ferricyanide complex ions and an additive capable of breaking down nitrous acid.

Dans les bains selon l'invention, les ions complexes ferricyanure sont des cyanures complexes de formule générale Fe III(CN)6 3-, appelés également hexacyanoferrates (III) (Encyclopedia of Chemical Technology -Kirk Othmer -John Wiley & Sons, Inc. -1967 -Vol. 12 -pages 25, 26, 31, 32). Ils peuvent être présents dans la solution aqueuse à l'état de tous composés dissous tels que, par exemple, l'acide hexacyanoferrique (lll), le ferricyanure d'ammonium et les ferricyanures des métaux alcalins et alcalinoterreux. Des composés préférés sont les ferricyanures des métaux alcalins, le ferricyanure de potassium étant spécialement conseillé.In the baths according to the invention, the ferricyanide complex ions are complex cyanides of general formula Fe III (CN) 6 3- , also called hexacyanoferrates (III) (Encyclopedia of Chemical Technology -Kirk Othmer -John Wiley & Sons, Inc. -1967 -Vol. 12 -pages 25, 26, 31, 32). They can be present in the aqueous solution in the form of all dissolved compounds such as, for example, hexacyanoferric acid (III), ammonium ferricyanide and ferricyanides of alkali and alkaline earth metals. Preferred compounds are the alkali metal ferricyanides, potassium ferricyanide being especially recommended.

L'additif capable de décomposer l'acide nitreux a pour fonction de décomposer une partie au moins de l'acide nitreux qui se forme pendant le polissage d'une surface en acier, l'acide nitreux étant la conséquence d'une oxydation d'ions ferreux libérés dans le bain au cours du polissage. En principe, l'additif peut être choisi parmi toutes les substances organiques et inorganiques qui sont capables de décomposer l'acide nitreux en milieu aqueux; il convient de le choisir parmi les substances qui n'attaquent pas l'acier à polir et pour lesquelles les produits de la réaction avec l'acide nitreux n'attaquent pas l'acier à polir. On donne la préférence aux substances qui sont solubles dans la solution aqueuse contenant le mélange d'acides. L'acide sulfamique, l'hydroxylamine, l'hydrazine, le peroxyde d'hydrogène, l'acétone, l'urée et les amines primaires, secondaires et tertaires sont des exemples de substances utilisables pour l'additif des bains selon l'invention. Les composés azotés constituent une classe de substances spécialement avantageuses pour l'additif des bains selon l'invention; des exemples de composés azotés sont l'urée et ses dérivés, notamment la thiourée et les uréines.The additive capable of decomposing nitrous acid has the function of decomposing at least part of the nitrous acid which is formed during the polishing of a steel surface, the nitrous acid being the consequence of an oxidation of ferrous ions released into the bath during polishing. In principle, the additive can be chosen from all organic and inorganic substances which are capable of breaking down nitrous acid in an aqueous medium; it should be chosen from among the substances which do not attack the polishing steel and for which the products of the reaction with the acid nitrous do not attack the steel to be polished. Preference is given to substances which are soluble in the aqueous solution containing the mixture of acids. Sulfamic acid, hydroxylamine, hydrazine, hydrogen peroxide, acetone, urea and primary, secondary and tertiary amines are examples of substances which can be used for the bath additive according to the invention . The nitrogen compounds constitute a class of substances which are especially advantageous for the bath additive according to the invention; examples of nitrogen compounds are urea and its derivatives, in particular thiourea and ureines.

L'urée est un composé azoté préféré, conformément à l'invention.Urea is a preferred nitrogen compound, according to the invention.

Dans les bains de polissage chimique selon l'invention, les teneurs respectives en acide phosphorique, en acide chlorhydrique, en acide nitrique et, en ions complexes ferricyanure sont choisies en fonction de la nature du métal traité, de la température de travail et de la durée souhaitée pour le traitement de polissage. La teneur en additif capable de décomposer l'acide nitreux dépend de divers paramètres, tels que la nature dudit additif, les teneurs respectives en acide chlorhydrique, en acide phosphorique, en acide nitrique et en ions complexes ferricyanure, le volume du bain mis en oeuvre, la configuration de la surface métallique à polir et la nature du métal. On a trouvé que, toutes autres choses restant égales, la teneur optimum en additif dans les bains de polissage selon l'invention est proportionnelle à la profondeur d'attaque du bain dans le métal et au rapport entre l'aire de la surface métallique à polir et le volume du bain mis en oeuvre.In the chemical polishing baths according to the invention, the respective contents of phosphoric acid, hydrochloric acid, nitric acid and, in ferricyanide complex ions are chosen according to the nature of the metal treated, the working temperature and the desired time for polishing treatment. The content of additive capable of breaking down nitrous acid depends on various parameters, such as the nature of said additive, the respective contents of hydrochloric acid, phosphoric acid, nitric acid and ferricyanide complex ions, the volume of the bath used. , the configuration of the metal surface to be polished and the nature of the metal. It has been found that, all other things remaining equal, the optimum content of additive in the polishing baths according to the invention is proportional to the depth of attack of the bath in the metal and to the ratio between the area of the metal surface to polish and the volume of the bath used.

D'une manière générale, des bains conformes à l'invention qui conviennent bien pour réaliser le polissage chimique de surfaces en aciers austénitiques inoxydables tels que, par exemple, ceux alliés au chrome et/ou au nickel, en un temps compris entre 2 et 24 heures sont ceux contenant

  • -entre 0,5 et 10, de préférence entre 1 et 8, moles d'acide chlorhydrique par litre,
  • -entre 0,01 et 2,5, de préférence entre 0,05 et 1,5 mole d'acide phosphorique par litre,
  • -entre 0,001 et 1,5, de préférence 0,005 et 1, mole d'acide nitrique par litre,
  • -entre 0,3 x 10 -6 et 0,3 x 10.2, de préférence entre 0,3 x 10-5et 0,3 x 10-3 ion-gramme de ferricyanure par litre, et
  • -une quantité d'additif (exprimée en mole par litre du bain) défine par la relation k.
    Figure imgb0001
    .Δe
  • où : S désigne l'aire (exprimée en m2) de la surface métallique à polir;
  • V désigne le volume (exprimé en m3) du bain mis en oeuvre;
  • e désigne la profondeur moyenne (exprimée en microns) d'attaque de la surface métallique à polir par le bain;
  • k est un facteur de proportionnalité (exprimé en
    Figure imgb0002
    ) compris entre 10-8 et 10.2, de préférence entre 10' 7 et 10-3.
In general, baths according to the invention which are very suitable for carrying out the chemical polishing of surfaces made of austenitic stainless steels such as, for example, those alloyed with chromium and / or nickel, in a time of between 2 and 24 hours are those containing
  • between 0.5 and 10, preferably between 1 and 8, moles of hydrochloric acid per liter,
  • between 0.01 and 2.5, preferably between 0.05 and 1.5 moles of phosphoric acid per liter,
  • between 0.001 and 1.5, preferably 0.005 and 1, mole of nitric acid per liter,
  • -between 0.3 x 10 - 6 and 0.3 x 10. 2 , preferably between 0.3 x 10 -5 and 0.3 x 10 -3 gram ion of ferricyanide per liter, and
  • -a quantity of additive (expressed in moles per liter of the bath) defined by the relation k.
    Figure imgb0001
    .Δe
  • where: S denotes the area (expressed in m 2 ) of the metal surface to be polished;
  • V denotes the volume (expressed in m 3 ) of the bath used;
  • e denotes the average depth (expressed in microns) of attack of the metal surface to be polished by the bath;
  • k is a proportionality factor (expressed in
    Figure imgb0002
    ) Of between 10- 8 and 10. 2, preferably between 10 -7 and 10 -3.

Des bains spécialement recommandés sont ceux dans lesquels la molarité globale du mélange d'acides dans la solution aqueuse est comprise entre 1 et 7, de préférence 2 et 6. Les molarités comprises entre 2,5 et 5 sont les plus avantageuses dans la majorité des applications. Des bains préférés sont ceux dans lesquels la solution aqueuse comprend :

  • -de l'acide chlorhydrique à raison de 2,5 à 5 moles par litre,
  • -de l'acide phosphorique à raison de 0,1 à 1 mole par litre,
  • -de l'acide nitrique à raison de 0,01 à 0,5 mole par litre, et
  • -du ferricyanure de potassium, à raison de 0,1 x 10-4 à 0,2 x 10 -3molécule-gramme par litre, et
  • -de l'urée, à titre d'additif capable de décomposer l'acide nitreux, en une quantité, exprimée en moles par litre, définie par la relation précitée dans laquelle k est compris entre 1007 et 10-4.
Specially recommended baths are those in which the overall molarity of the mixture of acids in the aqueous solution is between 1 and 7, preferably 2 and 6. The molarities between 2.5 and 5 are the most advantageous in the majority of applications. Preferred baths are those in which the aqueous solution comprises:
  • -hydrochloric acid at a rate of 2.5 to 5 moles per liter,
  • -phosphoric acid at a rate of 0.1 to 1 mole per liter,
  • -nitric acid at a rate of 0.01 to 0.5 mol per liter, and
  • -potassium ferricyanide, at a rate of 0.1 x 10 -4 to 0.2 x 10 -3 molecule-gram per liter, and
  • -from urea as an additive capable of decomposing nitrous acid, in an amount, expressed in moles per liter as defined by the above equation wherein k is between 7 and 100 10- 4.

Les bains selon l'invention peuvent éventuellement contenir des additifs habituellement présents dans les bains connus pour le polissage chimique des métaux, tels que, par exemple, des agents tensioactifs, des inhibiteurs de corrosion, des régulateurs de viscosités et des agents de brillantage. Le cas échéant on préfère que les bains contiennent ces additifs en des quantités relatives, par rapport au cyanure complexe, qui n'excèdent pas respectivement :

  • -1:3 pondéral, dans le cas d'agents tensioactifs de la classe des chlorures d'alkylpyridinium;
  • -1:1 pondéral, dans le cas d'agents tensioactifs de la classe des alkylphénols;
  • -1:1 molaire, dans le cas d'épaississants choisis parmi les éthers de cellulose.
The baths according to the invention may optionally contain additives usually present in baths known for the chemical polishing of metals, such as, for example, surfactants, corrosion inhibitors, viscosity regulators and brighteners. If necessary we prefer that baths contain these additives in relative amounts, compared to complex cyanide, which do not exceed respectively:
  • -1: 3 by weight, in the case of surfactants of the class of alkylpyridinium chlorides;
  • -1: 1 by weight, in the case of surfactants of the class of alkylphenols;
  • -1: 1 molar, in the case of thickeners chosen from cellulose ethers.

Des bains préférés sont ceux qui sont essentiellement exempts de chlorure d'alkylpyridiniurn, d'alkylphénol et d'éther de cellulose.Preferred baths are those which are essentially free of alkylpyridiniurn chloride, alkylphenol and cellulose ether.

Un grand avantage des bains de polissage selon l'invention réside dans leur aptitude, après adaptation des concentrations respectives en leurs constituants, à réaliser des polissages à vitesse d'action modérée, pouvant être répartis sur plusieurs heures, de façon à permettre le polissage uniforme de surfaces de grandes dimensions ou de surfaces difficilement accessibles. Ils sont spécialement bien adaptés au polissage de surfaces métalliques dont l'aire est très grande, comparée à l'espace disponible pour le bain. A titre d'exemple, ils trouvent une application intéressante pour le polissage de surfaces métalliques dont l'aire (exprimée en ml est au moins égale à 3 fois, de préférence supérieure à 8 fois le volume - (exprimé en m'j du bain de polissage qui est à son contact, telles que, par exemple, des échangeurs de chaleur à très grande surface d'échange. Les performances des bains selon l'invention ne sont pas limitées par une valeur maximum du rapport entre l'aire de la surface à polir et le volume du bain mis en oeuvre, ce rapport, exprimé en m-1, pouvant par exemple atteindre 20 et davantage.A great advantage of the polishing baths according to the invention lies in their ability, after adaptation of the respective concentrations of their constituents, to carry out polishing at moderate speed of action, which can be distributed over several hours, so as to allow uniform polishing. large surfaces or hard to reach surfaces. They are especially well suited for polishing metal surfaces with a very large area, compared to the space available for the bath. For example, they find an interesting application for the polishing of metal surfaces whose area (expressed in ml is at least equal to 3 times, preferably greater than 8 times the volume - (expressed in m of the bath polishing which is in contact with it, such as, for example, heat exchangers with a very large exchange surface. The performance of the baths according to the invention is not limited by a maximum value of the ratio between the area of the surface to be polished and the volume of the bath used, this ratio, expressed in m −1 , which can for example reach 20 and more.

Les bains selon l'invention conviennent pour le polissage de toutes surfaces en acier inoxydable austénitique. Ils trouvent une application spécialement avantageuse dans le polissage des aciers inoxydables austénitiques alliés au chrome et au nickel, notamment ceux contenant entre 12 et 26 % de chrome et entre 6 et 22 % de nickel, tels que les aciers 18/8 et 18/10, par exemple.The baths according to the invention are suitable for polishing all austenitic stainless steel surfaces. They find a particularly advantageous application in the polishing of austenitic stainless steels alloyed with chromium and nickel, in particular those containing between 12 and 26% of chromium and between 6 and 22% of nickel, such as steels 18/8 and 18/10 , for example.

L'invention concerne dès lors aussi un procédé pour le polissage d'une surface en acier inoxydable, selon lequel on met la surface en contact avec un bain de polissage chimique conforme à l'invention.The invention therefore also relates to a method for polishing a stainless steel surface, according to which the surface is brought into contact with a chemical polishing bath according to the invention.

Dans le procédé selon l'invention, on peut mettre en oeuvre un bain préfabriqué, au contact duquel on met ensuite la surface métallique à polir.In the process according to the invention, a prefabricated bath can be used, in contact with which the metal surface to be polished is then placed.

Conformément à une forme d'exécution particulière du procédé selon l'invention, après avoir mis la surface métallique en contact avec le bain, on procède à un ajout additionnel d'acide nitrique et d'additif capable de décomposer l'acide nitreux. En variante, on peut procéder à plusieurs ajouts successifs ou à une addition continue d'acide nitrique et dudit additif, au fur et à mesure de la progression du polissage.In accordance with a particular embodiment of the method according to the invention, after having brought the metal surface into contact with the bath, an additional addition of nitric acid and additive capable of decomposing nitrous acid is carried out. As a variant, it is possible to make several successive additions or to a continuous addition of nitric acid and of said additive, as the polishing progresses.

Dans une forme d'exécution préférée du procédé selon l'invention, le bain est réalisé in situ au contact de la surface métallique à polir. A cet effet, on met d' abord la surface métallique en contact avec une solution aqueuse contenant l'acide chlorhydrique, l'acide phosphorique, l'acide nitrique et l'additif capable de décomposer l'acide nitreux, puis on ajoute les ions complexes ferricyanure à la solution, pendant qu'elle est en contact avec la surface métallique. Dans la mise en oeuvre de cette forme d'exécution du procédé selon l'invention, il est avantageux d'attendre que la surface métallique ait subi une attaque substantielle par la solution d'acides, avant d'y ajouter les ions ferricyanure; en pratique, on peut avantageusement régler l'intervalle de temps entre le moment où on met la surface à polir en contact avec la solution aqueuse et le moment où on ajoute les ions complexes ferricyanure à ladite solution, de manière qu'il y corresponde une attaque de la surface par la solution, d'une profondeur comprise entre 0,1 et 6 microns, de préférence entre 0,5 et 4 microns. En variante, après avoir ajouté les ions complexes ferricyanure à la solution, on peut procéder à des ajouts additionnels d'acide nitrique et d'additif capable de décomposer l'acide nitreux, comme exposé plus haut.In a preferred embodiment of the method according to the invention, the bath is carried out in situ in contact with the metal surface to be polished. For this purpose, the metal surface is first brought into contact with an aqueous solution containing hydrochloric acid, phosphoric acid, nitric acid and the additive capable of decomposing nitrous acid, then the ions are added. ferricyanide complexes to the solution, while it is in contact with the metal surface. In the implementation of this embodiment of the method according to the invention, it is advantageous to wait until the metal surface has undergone a substantial attack by the acid solution, before adding the ferricyanide ions thereto; in practice, it is advantageously possible to adjust the time interval between the moment when the surface to be polished is brought into contact with the aqueous solution and the moment when the ferricyanide complex ions are added to said solution, so that it corresponds to a attack of the surface by the solution, from a depth of between 0.1 and 6 microns, preferably between 0.5 and 4 microns. Alternatively, after adding the ferricyanide complex ions to the solution, additional additions of nitric acid and additive capable of breaking down nitrous acid can be made, as discussed above.

Dans le procédé selon l'invention, le temps de contact de la surface à polir avec le bain doit être suffisant pour réaliser un polissage efficace de la surface; il ne peut toutefois'pas excéder une valeur critique au-delà de laquelle des corrosions locales risquent d'apparaître sur la surface, à moins de procéder à un ajout complémentaire d'acide nitrique et d'additif capable de décomposer l'acide nitreux, conformément à la forme d'exécution particulière du procédé, décrite plus haut. Le temps de contact optimum de la surface à polir avec le bain ou l'importance de l'ajout complémentaire d'acide nitrique et d'additif capable de décomposer l'acide nitreux dépendent de nombreux paramètres tels que la composition de l'acier de la surface à polir, la configuration et la rugosité initiale de celle-ci, la composition du bain, la température de travail, la turbulence éventuelle du bain au contact de la surface, le rapport entre l'aire de la surface métallique à polir et le volume du bain mis en oeuvre; il doit être déterminé dans chaque cas particulier par un travail de routine au laboratoire.In the method according to the invention, the contact time of the surface to be polished with the bath must be sufficient to achieve effective polishing of the surface; it cannot however exceed a critical value beyond which local corrosions may appear on the surface, unless a complementary addition of nitric acid and an additive capable of breaking down nitrous acid is carried out, in accordance with the particular embodiment of the method, described above. The optimum contact time of the surface to be polished with the bath or the importance of the additional addition of nitric acid and additive capable of breaking down nitrous acid depend on many parameters such as the composition of the steel of the surface to be polished, its initial configuration and roughness, the composition of the bath, the working temperature, the possible turbulence of the bath in contact with the surface, the ratio between the area of the metal surface to be polished and the volume of the bath used; it must be determined in each particular case by routine laboratory work.

L'invention va être explicitée par les exemples dont la descripttion va suivre.The invention will be explained by the examples whose description will follow.

Exemple 1Example 1

Une plaque de 20 m2 d'aire, en acier inoxydable de nuance ASTM-316L (acier allié au chrome - (16,0 à 18,0 %), au nickel (10,0 à 14,0 %) et au molybdène (2,0 à 3,0 %)) a été immergée dans 1 m3 d'un bain contenant, par litre :

  • 2,7 moles d'acide chlorhydrique,
  • 0,3 mole d'acide phosphorique,
  • 0,06 mole d'acide nitrique,
  • 30 mg de ferricyanure de potassium.
A 20 m 2 area plate, in ASTM-316L grade stainless steel (chrome alloy steel - (16.0 to 18.0%), nickel (10.0 to 14.0%) and molybdenum (2.0 to 3.0%)) was immersed in 1 m 3 of a bath containing, per liter:
  • 2.7 moles of hydrochloric acid,
  • 0.3 moles of phosphoric acid,
  • 0.06 mole of nitric acid,
  • 30 mg potassium ferricyanide.

Immédiatement après l'immersion de la plaque dans le bain, on a procédé à une addition continue d'une solution aqueuse d'acide nitrique à raison de 0,50 mole d'acide nitrique par heure. On a par ailleurs opéré deux ajouts successifs de 2 kg d'urée, respectivement après 4 heures et 6 heures de traitement. A l'issue de 8 heures de traitement, on a mesuré une profondeur moyenne d'attaque de la plaque par le bain de 108 microns. A ce moment, la plaque a été extraite du bain, lavée à l'eau déminéralisée et séchée. Elle présentait un aspect lisse et brillant.Immediately after immersing the plate in the bath, a continuous addition of an aqueous nitric acid solution was carried out at the rate of 0.50 mole of nitric acid per hour. We also made two successive additions of 2 kg of urea, respectively after 4 hours and 6 hours of treatment. After 8 hours of treatment, an average depth of attack of the plate by the bath of 108 microns was measured. At this time, the plate was removed from the bath, washed with deionized water and dried. It had a smooth and shiny appearance.

Exemple 2Example 2

Une plaque de 427 cm2 d'aire, en acier inoxydable de nuance ASTM-304L (acier allié au chrome (18,0 à 20,0%) et au nickel (8,0 à 12,0 %)) a été immergée dans 935 cm' d'un bain à 55°C, contenant, par litre :

  • 4,5 moles d'acide chlorhydrique,
  • 0,6 mole d'acide phosphorique,
  • 0,03 mole d'acide nitrique,
  • 100 mg de ferricyanure de potassium.
A 427 cm 2 area plate, in stainless steel grade ASTM-304L (steel alloyed with chromium (18.0 to 20.0%) and nickel (8.0 to 12.0%)) was immersed in 935 cm 'of a bath at 55 ° C, containing, per liter:
  • 4.5 moles of hydrochloric acid,
  • 0.6 moles of phosphoric acid,
  • 0.03 mole of nitric acid,
  • 100 mg of potassium ferricyanide.

Toutes les 90 minutes, on a ajouté au bain 0,03 g d'acide nitrique par litre du bain et 1,4 g d'urée par litre du bain. A l'issue de 7 heures de traitement on a mesuré une profondeur moyenne d'attaque du métal par le bain égale à 117 microns. A ce moment, la plaque a été extraite du bain, lavée à l'eau et séchée. Elle présentait un aspect lisse et brillant.Every 90 minutes, 0.03 g of nitric acid per liter of the bath and 1.4 g of urea per liter of the bath were added to the bath. After 7 hours of treatment, an average depth of attack of the metal by the bath equal to 117 microns was measured. At this time, the plate was removed from the bath, washed with water and dried. It had a smooth and shiny appearance.

Claims (10)

1 -Bains pour le polissage chimique de surfaces en acier inoxydable comprenant, en solution aqueuse, un mélange d'acide chlorhydrique, d'acide phosphorique et d'acide nitrique, caractérisés en ce qu'ils comprennent, dans la solution aqueuse, des ions complexes ferricyanure et un additif capable de décomposer l'acide nitreux.1 -Baths for the chemical polishing of stainless steel surfaces comprising, in aqueous solution, a mixture of hydrochloric acid, phosphoric acid and nitric acid, characterized in that they comprise, in the aqueous solution, ions ferricyanide complexes and an additive capable of breaking down nitrous acid. 2 -Bains selon la revendication 1, caractérisés en ce que les ions complexes ferricyanure sont présents à l'état de ferricyanure de potassium et l'additif est sélectionné parmi l'urée et les dérivés de l'urée.2 -Baths according to claim 1, characterized in that the ferricyanide complex ions are present in the state of potassium ferricyanide and the additive is selected from urea and urea derivatives. 3 -Bains selon la revendication 1 ou 2, caractérisés en ce que la solution aqueuse comprend -entre 0,5 et 10 moles d'acide chlorhydrique par litre, -entre 0,01 et 2,5 mole d'acide phosphorique par litre, - entre 0,001 et 1,5 mole d'acide nitrique par litre, -entre 0,3 x 10 -6 et 0,3 x 10. 2 ion-gramme de ferricyanure par litre, et -une quantité d'additif (exprimée en mole par litre du bain) définie par la relation k. v .De
dans laquelle : S désigne l'aire (exprimée en m2) de la surface métallique à polir; V désigne le volume (exprimé en m') du bain mis en oeuvre; e désigne la profondeur moyenne (exprimée en microns) d'attaque de la surface métallique à polir par le bain; k est un facteur de proportionnalité (exprimé en
Figure imgb0003
compris entre 10-8 et 10 -2.
3 -Baths according to claim 1 or 2, characterized in that the aqueous solution comprises -between 0.5 and 10 moles of hydrochloric acid per liter, between 0.01 and 2.5 moles of phosphoric acid per liter, - between 0.001 and 1.5 moles of nitric acid per liter, - between 0.3 x 10 - 6 and 0.3 x 10 . 2 gram ion of ferricyanide per liter, and -a quantity of additive (expressed in moles per liter of the bath) defined by the relation k. v. from
in which : S denotes the area (expressed in m 2 ) of the metal surface to be polished; V denotes the volume (expressed in m ') of the bath used; e denotes the average depth (expressed in microns) of attack of the metal surface to be polished by the bath; k is a proportionality factor (expressed in
Figure imgb0003
between 10 -8 and 10 -2.
4 -Bains selon la revendication 3, caractérisés en ce que la solution aqueuse comprend -entre 1 et 8 moles d'acide chlorhydrique par litre, -entre 0,05 et 1,5 mole d'acide phosphorique par litre, -entre 0,005 et 1 mole d'acide nitrique par litre, -entre 0,3 x 10-5 et 0,3 x 10-3 ion-gramme de ferricyanure par litre, et -une quantité d'additif (exprimée en mole par litre du bain) définie par la relation précitée, dans laquelle k est compris entre 10-7 et 10-3. 4 -Baths according to claim 3, characterized in that the aqueous solution comprises - between 1 and 8 moles of hydrochloric acid per liter, between 0.05 and 1.5 moles of phosphoric acid per liter, -between 0.005 and 1 mole of nitric acid per liter, -between 0.3 x 10 -5 and 0.3 x 10 -3 gram ion of ferricyanide per liter, and a quantity of additive (expressed in moles per liter of the bath) defined by the above-mentioned relation, in which k is between 10 -7 and 10 -3 . 5-Bains selon la revendication 4, caractérisés en ce que la solution aqueuse comprend : entre 2,5 et 5 moles d'acide chlorhydrique par litre, entre 0,1 et 1 mole d'acide phosphorique par litre, entre 0,01 et 0,5 mole d'acide nitrique par litre, entre 0,1 x 10-4 et 0,2 x 10-3 molécule-gramme de ferricyanure de potassium par litre, et
à titre d'additif capable de décomposer l'acide nitreux, de l'urée en une quantité, exprimée en moles par litre, définie par la relation précitée dans laquelle k est compris entre 10 -7 et 10-4.
5-baths according to claim 4, characterized in that the aqueous solution comprises: between 2.5 and 5 moles of hydrochloric acid per liter, between 0.1 and 1 mole of phosphoric acid per liter, between 0.01 and 0.5 mole of nitric acid per liter, between 0.1 x 10 -4 and 0.2 x 10- 3 molecule-gram of potassium ferricyanide per liter, and
as an additive capable of breaking down nitrous acid, urea into an amount, expressed in moles per liter, defined by the above-mentioned relationship in which k is between 10 - 7 and 10 -4 .
6 -Bains selon l'une quelconque des revendications 1 à 5, caractérisés en ce que la molarité globale du mélange d'acides dans la solution aqueuse est comprise entre 2 et 6.6 -Baths according to any one of claims 1 to 5, characterized in that the overall molarity of the mixture of acids in the aqueous solution is between 2 and 6. 7 -Procédé pour le polissage d'une surface en acier inoxydable, selon lequel on met la surface en contact avec un bain de polissage chimique, caractérisé en ce qu'on met en oeuvre un bain conforme à l'une quelconque des revendications 1 à 6.7 -Process for polishing a stainless steel surface, according to which the surface is brought into contact with a chemical polishing bath, characterized in that a bath is used in accordance with any one of claims 1 to 6. 8 -Procédé selon la revendication 7, caractérisé en ce qu'on met d'abord la surface en contact avec une solution aqueuse contenant de l'acide chlorhydrique, de l'acide phosphorique, de l'acide nitrique et un additif capable de décomposer l'acide nitreux, puis on ajoute des ions complexes ferricyanure à la solution.8 -A method according to claim 7, characterized in that first puts the surface in contact with an aqueous solution containing hydrochloric acid, phosphoric acid, nitric acid and an additive capable of breaking down nitrous acid, then complex ferricyanide ions are added to the solution. 9 -Procédé selon la revendication 8, caractérisé en ce que l'intervalle de temps entre le moment où on met la surface en contact avec la solution et le moment où on ajoute les ions complexes ferricyanure à la solution, est réglé de manière qu'il y corresponde une attaque de la surface par la solution, d'une profondeur comprise entre 0,1 et 6 microns.9 - Process according to claim 8, characterized in that the time interval between the moment when the surface is brought into contact with the solution and the moment when the ferricyanide complex ions are added to the solution, is adjusted so that it corresponds to an attack on the surface by the solution, with a depth of between 0.1 and 6 microns. 10 -Procédé selon l'une quelconque des revendications 7 à 9, caractérisé en ce que, pendant que la surface en acier est en contact avec le bain, on ajoute à celui-ci un complément d'acide nitrique et d'additif capable de décomposer l'acide nitreux.10 -A method according to any one of claims 7 to 9, characterized in that, while the steel surface is in contact with the bath, a supplement of nitric acid and additive capable of decompose nitrous acid.
EP86200920A 1985-06-03 1986-05-27 Baths and process for chemically polishing stainless-steel surfaces Expired - Lifetime EP0206386B1 (en)

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EP0425013A1 (en) * 1989-10-26 1991-05-02 SOLVAY (Société Anonyme) Baths and process for chemical polishing of stainless steel surfaces
EP0462646A1 (en) * 1990-06-19 1991-12-27 SOLVAY (Société Anonyme) Baths and process for chemical polishing stainless steel surfaces
FR2717829A1 (en) * 1994-03-28 1995-09-29 Solvay Baths and process for the chemical polishing of stainless steel surfaces.

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US20040140288A1 (en) * 1996-07-25 2004-07-22 Bakul Patel Wet etch of titanium-tungsten film
US20040134873A1 (en) * 1996-07-25 2004-07-15 Li Yao Abrasive-free chemical mechanical polishing composition and polishing process containing same
DE69734868T2 (en) * 1996-07-25 2006-08-03 Dupont Air Products Nanomaterials L.L.C., Tempe COMPOSITION AND METHOD FOR CHEMICAL-MECHANICAL POLISHING

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EP0425013A1 (en) * 1989-10-26 1991-05-02 SOLVAY (Société Anonyme) Baths and process for chemical polishing of stainless steel surfaces
BE1003579A3 (en) * 1989-10-26 1992-04-28 Solvay Baths and method for chemically polishing steel surfaces inxoydable.
EP0462646A1 (en) * 1990-06-19 1991-12-27 SOLVAY (Société Anonyme) Baths and process for chemical polishing stainless steel surfaces
BE1004452A3 (en) * 1990-06-19 1992-11-24 Solvay Baths and method for chemically polishing stainless steel surfaces.
US5209820A (en) * 1990-06-19 1993-05-11 Solvay & Cie (Societe Anonyme) Baths and process for the chemical polishing of stainless steel surfaces
FR2717829A1 (en) * 1994-03-28 1995-09-29 Solvay Baths and process for the chemical polishing of stainless steel surfaces.
WO1995026428A1 (en) * 1994-03-28 1995-10-05 Solvay S.A. Baths and method for chemically polishing stainless steel surfaces
US5762819A (en) * 1994-03-28 1998-06-09 Solvay (Societe Anonyme) Baths and process for chemical polishing of stainless steel surfaces
CN1044264C (en) * 1994-03-28 1999-07-21 索尔维公司 Baths and method for chemically polishing stainless steel surfaces

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KR870000451A (en) 1987-02-18
NO168716C (en) 1992-03-25
NO862175D0 (en) 1986-06-02
JPS6237381A (en) 1987-02-18
FR2582675A1 (en) 1986-12-05
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KR930003606B1 (en) 1993-05-08
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EP0206386B1 (en) 1990-08-08
PT82676B (en) 1988-07-01
ATE55419T1 (en) 1990-08-15
CA1298762C (en) 1992-04-14
FI862361A0 (en) 1986-06-03
ES8704554A1 (en) 1987-04-01
ES555583A0 (en) 1987-04-01
FR2582675B1 (en) 1992-10-02
BR8602514A (en) 1987-01-27
DE3673258D1 (en) 1990-09-13
AU579474B2 (en) 1988-11-24
US4678541A (en) 1987-07-07

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