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EP0892862A1 - Elctrolyte for electropolishing, method of electropolishing a stainless steel or a nickel alloy utilizing the said electrolyte, and its application to decontamination - Google Patents

Elctrolyte for electropolishing, method of electropolishing a stainless steel or a nickel alloy utilizing the said electrolyte, and its application to decontamination

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Publication number
EP0892862A1
EP0892862A1 EP97918208A EP97918208A EP0892862A1 EP 0892862 A1 EP0892862 A1 EP 0892862A1 EP 97918208 A EP97918208 A EP 97918208A EP 97918208 A EP97918208 A EP 97918208A EP 0892862 A1 EP0892862 A1 EP 0892862A1
Authority
EP
European Patent Office
Prior art keywords
electropolishing
electrolyte
acid
stainless steel
nickel alloy
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP97918208A
Other languages
German (de)
French (fr)
Other versions
EP0892862B1 (en
Inventor
Jean-No[L Saas
Jean-Paul Gauchon
Francis Dalard
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Original Assignee
Commissariat a lEnergie Atomique CEA
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Publication of EP0892862A1 publication Critical patent/EP0892862A1/en
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Publication of EP0892862B1 publication Critical patent/EP0892862B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof
    • G21F9/002—Decontamination of the surface of objects with chemical or electrochemical processes
    • G21F9/004—Decontamination of the surface of objects with chemical or electrochemical processes of metallic surfaces
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F3/00—Electrolytic etching or polishing
    • C25F3/16—Polishing
    • C25F3/22—Polishing of heavy metals
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F3/00—Electrolytic etching or polishing
    • C25F3/16—Polishing
    • C25F3/22—Polishing of heavy metals
    • C25F3/24—Polishing of heavy metals of iron or steel

Definitions

  • the present invention relates to an electrolyte for electropolishing, a method of electropolishing a stainless steel or a
  • this process can be used in particular for electropolishing and decontamination of austenitic, ferritic and austeno-ferritic stainless steels and
  • Electropolishing is a process known since 1930 and in particular from document FR-A-707526. This process consists in carrying out an anodic dissolution of the metal part to be treated. This
  • Electropolishing can be used on various metals, but is particularly suitable for stainless steel or for alloys such as
  • 'electropolishing can be used in particular on
  • -osurisee REP
  • these metals for example Inconel 600 and AISI 308L steel
  • such a treatment can be carried out either as a surface preparation method to reduce the susceptibility of the material to be contaminated, or as a method of decontamination by dissolution of the contaminated oxides.
  • polishing electrolytes have a high viscosity - which makes them difficult to use - and contain very little water: namely substantially less than 20% by mass.
  • Electropolishing electrolytes are generally very concentrated acidic media which can be classified into two main categories: - a first category includes electrolytes formed from a mixture based on sulfuric acid, phosphoric acid and water with possible addition of chromic acid or other organic agents. These electrolytes are the most common in the field of electropolishing.
  • compositions of the solutions which give, either on the one hand an anodic passivatjon, or on the other hand a shine are very different; in particular, the brightening and polishing solutions have a zero or very low water concentration, the authors conclude that the brightening conditions are obtained by an anion ratio (such as sulphate, phosphate) on water which is sufficiently high.
  • an anion ratio such as sulphate, phosphate
  • a second category of electrolyte for electropolishing includes electrolytes based on perchloric acid.
  • the solvent is therefore of the organic type: it may for example be acetic acid or acetic anhydride of methanol or alternatively monobutyl ether of ethylene glycol: these electrolytes are gradually being abandoned, because they are very dangerous and have explosive properties as described in the book by WJ TEGART "Electrolytic and chemical polishing of metals". Editions Dunod, Paris, 1960. As a result, during the manufacture and use of many baths must be taken.
  • the electrolyte used for electropolishing austenofer ⁇ mila steels is the same as that used for Inconel 600 and belongs to the first category mentioned above: it is a ternary mixture of sulfuric acid, phosphoric acid and water in very small quantities, to which we can add certain additives such as oxalic acid, chromium or aluminum oxides.
  • the electrolyte must not contain sulfuric acid, since sulfur is prohibited from these primary circuits because it is likely to cause corrosion problems.
  • the third reason is that the phosphoric acid added to this electrolyte has the disadvantage, as well as the phosphates which are derived therefrom, of posing significant problems in terms of the treatment of the effluents charged with these compounds resulting from the electropolishing treatment.
  • nitric acid has the same troublesome properties as perchloric acid already mentioned above, insofar as it is oxidizing.
  • nitric acid like perchloric acid
  • a body or an organic compound capable of being oxidized in particular in the presence of water the oxidation reaction can cause an explosion.
  • the electrolyte must be safe and risk-free to use and inexpensive.
  • the electrolyte must also be free from fluoride, chloride and sulfur ions. Its processing temperature should preferably be less than 60 ° C.
  • This electrolyte must also not contain phosphoric acid and / or phosphates and be completely recyclable or destructible by current effluent treatment techniques.
  • the use of one electrolyte must be compatible with the possibilities of nuclear sites and in particular with the possibilities of treatment of effluents in nuclear power plants.
  • the volume of general solid and liquid waste likely to be stored must be reduced to a minimum.
  • the object of the present invention is therefore to provide an electrolyte for electropolishing which satisfies, inter alia, all the requirements mentioned above.
  • Another subject of the present invention is an electropolishing and / or decontamination process using the above electrolyte which can give satisfactory results on all types of stainless steel, as well as on nickel alloys such as Inconels used in particular in the nuclear industry.
  • nitric acid as the main basic constituent of melanaea, responds to an approach which differs fundamentally steps previously taken in this area of technology.
  • glycolic acid into the mixture while retaining a high water concentration also goes against another prejudice in this field of the technique which is reflected by numerous documents and which wanted that does not mix in an electrolyte for electropolishing an oxidizing acid such as nitric acid with compounds
  • glycolic acid incorporated in the e1 ectrolyte makes it possible in particular to increase the viscosity while maintaining a high water concentration, namely greater than or equal to 28-29% by mass.
  • glycolic acid or hvdroxyacetic acid also denoted by the letters HOAC is part of the series of hydroxycarboxylic acids.
  • Glycolic acid is a relatively strong organic acid, soluble in water in all proportions and combines the acid and alcohol functions.
  • the alcohol function can be used in particular for its solvent power; 1 HOAC also has bactericidal and descaling properties and is commonly used as a base for the formulation of cleaners intended for household and collective use.
  • Glycolic acid is also used, as mentioned in document US-A-4 137 132 in the chromating baths.
  • Document JP-A-55047399 describes an electrolyte for electropolishing Fe-Al-Si alloys which comprises a binary mixture of glycolic acid (40 to 60% by volume) and sulfuric acid. This mixture contains neither water nor nitric acid.
  • the HILL EF document "Development of the glycolic-cit ⁇ c acids (GCA) process for decontamination of LMFBR components", Trans. Am. N ⁇ cl. Soc, 30, 1978 relates to the use of a mixture of glycolic acid (2.5% by weight) and citric acid (2.5% by weight) in aqueous solution, called CGA mixture, a 70 -90 ° C, with a view to chemically decontaminating and without supply of current to the weakly contaminated components in stainless steel 304 and 316 from the LMFBR sector. This document therefore does not describe a electrolyte for electropolishing and further relates to a mixture of two organic acids.
  • GCA glycolic-cit ⁇ c acids
  • the electrolyte according to the invention based on a specific ternary mixture from the point of view of its constituents and their proportions, makes it possible to obtain a shiny surface of the samples of treated metals.
  • austemitic stainless steels such as steels 316L and 304L, as ferritic steels such as steel 430, as austenitic-ferritic steels such as l 308L steel, or Inconels such as the Inconel 600, 690 or 800.
  • the electrolyte according to the invention will be particularly suitable for treating the surfaces of such devices.
  • the electrolyte according to the invention is therefore characterized by great versatility.
  • the electrolyte according to the invention also allows smoothing and polishing of austenitic-ferritic steel samples, for example of the 308L type without a preferential attack on the ferritic network, which constitutes a decisive advantage of the electrolytes according to the invention over the electrolytes of the prior art , in particular the phosphophoric electrolytes.
  • the electrolyte according to the invention also has the obvious advantage over the electrolytes of the prior art of being free of fluoride ions, chlorides and sulphates which are corrosive with respect to stainless steels and nickel alloys.
  • the electrolyte according to the invention has the additional advantage of not containing phosphates and / or phosphoric acid, which reduces the volume of the general waste and makes it easier to alternate.
  • This electrolyte according to the invention does not require heating to be able to be used, it is in fact usable generally at room temperature, that is to say generally from 15 ° C to 45 ° C, preferably from 20 to 30 ° C, more preferably from 20 to 25 ° C and in any case at a temperature below 45 ° C.
  • the elecfrolyte according to the invention has a favorable viscosity, generally between errr ⁇ 1.3 and 3 mm / s.
  • the electrolyte according to the invention also exhibited good conservation properties in the 39168 PCI7FR97 / 00648
  • time at room temperature and it can be stored for a period of for example from one to two months without its essential characteristics being affected.
  • the electrolyte does not contain reagents capable of giving rise to very aggressive, oxidizing or explosive reactions. It can be prepared and used without taking any special precautions and safe for the user.
  • the spent electrolyte can be easily and completely reprocessed by distillation, since the mixture contains a high proportion by mass of nitric acid and water and the glycolic acid is transformed into oxalic acid.
  • It can also be mineralized in a caicinator, which allows this electrolyte to be used to decontaminate components from reprocessing plants.
  • the nitric acid recovered in the distillate can be recycled, which, from an economic point of view is particularly advantageous.
  • the electrolyte generally has the composition expressed in mass fractions mentioned above.
  • a preferred composition will include:
  • Such a preferred electrolyte is more chemically stable, the instability being characterized by the production of nitrous acid, nitrous vapors and the formation of oxalic acid beyond its solubility limit.
  • the invention also relates to a method of electropolishing a stainless steel or a nickel alloy in which said stainless steel or said nickel alloy is brought into contact with
  • This process has all the advantageous characteristics linked to the electrolyte and already mentioned above; this process according to the invention using the specific electrolyte of the invention also makes it possible to achieve high Faradic dissolution yields, generally greater than 80, or even 85%, the dissolution rate being in particular 950 ⁇ m / h .
  • This process can be used for electropolishing all types of stainless steels - both austemetic, for example 316L, 304L, and ferritic, for example 430 or austenoferritic, for example 308L, but also nickel alloys such as Inconels, for example 1 'Inconel 600 or 1' Inconel 640 or 1 'Inconel 800.
  • the invention also relates to a method of electrodecontamination of stainless steels or of nickel alloys contaminated in particular on their surface by radioelements, for example Cobalt 60, in which the contaminated metallic wing is brought into contact with the electrolyte described above.
  • radioelements for example Cobalt 60
  • These stainless steels and / or alloys are, for example, those encountered in the nuclear industry or in another industry.
  • Stainless steels and / or nickel alloys are for example constituent of a component of a nuclear power plant or a reprocessing plant and are encountered in particular in the primary circuit of nuclear power plants such as piping, steam generators. ...
  • the process allows in particular the dissolution of contaminating metallic elements, contained essentially in the oxides of the surface layer, and therefore a significant reduction in contamination to allow intervention by maintenance personnel.
  • the operating conditions of the electropolishing and decontamination process can be easily determined by a person skilled in the art in this field of the technique depending in particular on the material to be treated. They will generally be as follows.
  • composition of the electrolyte for electropolishing and / or decontamination is that already indicated above, namely: - glycolic acid: from 152 to 538 g / kg,
  • the current density is generally greater than or equal to 0.5 A / cm 2 , it is preferably between 0.5 A / cm 2 and 1.5 A / cm 2 , for example lA / cm 2 ; in fact, a certain risk of overheating can cause pitting beyond 1.7 A / cm 2 .
  • the temperature is generally room temperature, preferably at 45 ° C, preferably 20 to 30 ° C, more preferably 20 to 25 ° C and the hydrodynamic regime is preferably a laminar regime.
  • the duration of the process is generally from 60 sec to 80 sec for an erosion, for example of 20 ⁇ m. 5
  • the operating conditions for the electropolishing and electrodecontamination procedures are generally identical.
  • the used electrolysis is thus treated with a view to its elimination, its recycling and / or its rejection.
  • the electrolyte used contains neither phosphoric acid nor phosphate, and the treatment of effluents is thereby greatly facilitated.
  • glycolic acid can oxidize to oxalic acid.
  • reaction between nitric acid and oxalic acid is a slow reaction and that the gases given off: carbon dioxide, carbon dioxide and water do not react with the mixture of acids. .
  • the treatment of the electrolyte used at the end of the electropolishing process with a view to its destruction and / or -> its recycling can therefore comprise:
  • nitric effluent which can be sent to the effluent treatment station; or a distillation of the used electrolyte, followed for example by a calcinator. concentrates sleep the residues can be vitrified, for example, as is the case for certain waste from reprocessing plants.
  • the distillate can optionally be recycled for the reuse of nitric acid in the electropolishing process.
  • FIGS. 4 to 9 represent two- and three-dimensional anamorphic roughness profiles of the surface of the Inconel 600.
  • FIGS. 2 to 9 therefore represent and illustrate the method according to the invention implementing the specific electrolyte according to the invention in the particular case of an electropolishing treatment of an austeno-ferritic steel 308L.
  • FIG. 1 makes it possible to visualize the results obtained with an electrolyte of the prior art (sulfuric and phosphoric acid) and to compare the results obtained with the electrolyte of the invention. The following examples describe and illustrate the invention.
  • Example 1 Results in electropolishing on Inconel 600. This electropolishing treatment is carried out with an electrolyte whose composition is as follows:
  • the treatment is carried out on Inconel 600 samples.
  • Electrolyte flow rate 20 1 / h
  • Treated area 30 cm 2 .
  • the objective of such a treatment is to achieve smoothing and shining of the surface of the samples in Inconel 600.
  • the filter possibly used was 0.8 mm.
  • the starting samples in Inconel 600 are sanded and the values of the starting parameters are therefore the following: 0, 9 ⁇ Ra ⁇ 1, 35 ⁇ m.
  • the bi- and three-dimensional roughness profiles present in FIGS. 4 to 9 show that we observe a disappearance of the micro-roughnesses, a decrease in the arithmetic roughness, as well as a leveling of the sample.
  • the optical haze index is defined by measuring the diffuse light in a geometry at 20 degrees and the brightness index by the reflected intensity / emitted intensity ratio, following a specular reflection. The results are given in the tables
  • Table 2 gives the results when the measurement is made perpendicular to the sanding lines; this is the worst case.
  • Table 3 gives the results carried out parallel to the stripes • this is the most favorable case, since the light is not diffracted by the stripes, but by the surface micro-faults TABLE 2
  • the electropolishing treatment is carried out with an electrolyte according to the invention, the composition of which is as follows:
  • the intensity-potential curves are produced (Fig. 10) using a rotating disk electrode with a surface area of 0.2 mm 2 at 25 ° C and a speed of rotation of 1000 rpm.
  • the intensity-potential curves obtained (where the potential expressed in V on the abscissa is plotted relative to the saturated calomel electrode (DHW) and on the ordinate the current density in mA / cm 2 ) for 304L steel (in dashes) ) for 316L steel (solid line), for 308L steel (dashed line) and for Inconel (dotted line) show that the electrolyte according to the invention makes it possible to polish all types of stainless steels , whether they are austemetic (304L and 316L), fer ⁇ tic or austeno-fer ⁇ tic (308L as in Example 1), and Inconel type alloys. The surface obtained is in all cases polished and shiny.
  • EXAMPLE 3 (COMPARATIVE):
  • An electrolyte according to the invention having the same composition as that of Example 1 is used under the following conditions:
  • the treated surface is a Cobalt 60 contaminated surface forming part of a thermal sleeve in 304L stainless steel taken from the Blayais power station (Jende - France).
  • the electrolyte according to the prior art has also been used under the same conditions and on the same surface.
  • the electrolyte according to the invention allows a significant reduction in activity, greater than the comparison electrolyte, without having the drawbacks thereof.
  • the electrolyte of the invention can be used in particular to decontaminate the components of PWR pressurized water reactors and makes it possible to sufficiently reduce "hot spots” to allow the intervention of operators in maintenance.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Metallurgy (AREA)
  • Food Science & Technology (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • ing And Chemical Polishing (AREA)
  • Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)

Abstract

The invention concerns an electropolishing electrolyte composed of a mixture of glycolic acide, nitric acid and water in the following concentrations: glycolic acid: 152-538 g/kg, nitric acid: 170-568 g/kg, water: 280-678 g/kg. The invention also features a method for the electropolishing of a stainless steel or of a nickel alloy such as an Iconel utilizing this electrolyte, which is particularly useful in the decontamination of surfaces contaminated by radioelements, especially in the nuclear industry.

Description

ELECTROLYTE POUR L'ELECTROPOLISSAGE, PROCEDE ELECTROLYTE FOR ELECTRO-POLISHING, METHOD
D'ELECTROPOLISSAGE D'UN ACIER INOXYDABLE OU D'UNELECTRO-POLISHING OF STAINLESS STEEL OR
ALLIAGE DE NICKEL METTANT EN OEUVRE CET ELECTROLYTE, ETNICKEL ALLOY USING THIS ELECTROLYTE, AND
SON APPLICATION A LA DECONTAMINATIONITS APPLICATION TO DECONTAMINATION
La présente invention concerne un electrolyte pour 1 'électropolissage, un procédé d'électropolissage d'un acier inoxydable ou d'unThe present invention relates to an electrolyte for electropolishing, a method of electropolishing a stainless steel or a
10 alliage de nickel mettant en oeuvre cet electrolyte, et son application à la décontamination, ce procédé peut être utilisé en particulier pour 1 ' électropolissage et la décontamination des aciers inoxydables austénitiques, ferritiques et austéno-ferritiques et10 nickel alloy using this electrolyte, and its application to decontamination, this process can be used in particular for electropolishing and decontamination of austenitic, ferritic and austeno-ferritic stainless steels and
15 des alliages de nickel.15 nickel alloys.
L' électropolissage est un procédé connu depuis 1930 et notamment par le document FR-A-707526. Ce procédé consiste à effectuer une dissolution anodique de la pièce métallique a traiter. CeElectropolishing is a process known since 1930 and in particular from document FR-A-707526. This process consists in carrying out an anodic dissolution of the metal part to be treated. This
20 traitement conduit soit à un nivelage, soit à un orillantage de la surface en l'absence de corrosion cristallographique. La densité de courant de a.ssolution est déterminée à partir de la courbe intensité-potentiel. Ce voltampérogramme présente un20 treatment leads either to leveling or to an orillissement of the surface in the absence of crystallographic corrosion. The current density of a.ssolution is determined from the intensity-potential curve. This voltammogram presents a
2^ oalier de diffusion au cours duquel le polissage est oossible .2 ^ diffusion rider during which polishing is possible.
L'électropolissage peut être mis en oeuvre s.r divers métaux, mais convient particulièrement bien poαr l'acier inoxydable ou pour des alliages tels queElectropolishing can be used on various metals, but is particularly suitable for stainless steel or for alloys such as
"•ιι i ' Inconel . " • ιι i 'Inconel.
De ce fait, le traitementTherefore, the treatment
: ' clectropolissage peut être utilisé en particulier sur: 'electropolishing can be used in particular on
:ι divers constituants des générateurs αe vapeur des: ι various constituents of steam generators
^•"'traies nucléaires du type à réacteur à eau^ • "'nuclear reactor type water reactor
: : -osurisee (REP) ou ces métaux (par exemple l' Inconel 600 et l'acier AISI 308L) sont mis en oeuvre ; un tel traitement peut être réalise soit comme mode de préparation de surface pour diminuer la susceptibilité du matériau à se contaminer, soit comme mode de décontamination par dissolution des oxydes contamines.:: -osurisee (REP) or these metals (for example Inconel 600 and AISI 308L steel) are used; such a treatment can be carried out either as a surface preparation method to reduce the susceptibility of the material to be contaminated, or as a method of decontamination by dissolution of the contaminated oxides.
La grande majorité des électrolytes de polissage connus ont une viscosité élevée - ce qui les rend difficiles a mettre en oeuvre - et contiennent très peu d'eau : à savoir sensiblement moins de 20 % en masse.The vast majority of known polishing electrolytes have a high viscosity - which makes them difficult to use - and contain very little water: namely substantially less than 20% by mass.
Les électrolytes d'électropolissage, en effet, sont généralement des milieux acides très concentres que l'on peut classer en deux grandes catégories : - une première catégorie comprend les électrolytes formés d'un mélange a base d'acide sulfurique, d'acide phosphorique et d'eau avec addition éventuelle d'acide chromique ou d'autres agents organiques. Ces électrolytes sont les plus courants dans le domaine de 1 'électropolissage.Electropolishing electrolytes, in fact, are generally very concentrated acidic media which can be classified into two main categories: - a first category includes electrolytes formed from a mixture based on sulfuric acid, phosphoric acid and water with possible addition of chromic acid or other organic agents. These electrolytes are the most common in the field of electropolishing.
Ainsi, le document de FEDOT'EV "Electropolishing, anodizmg and electroJytic picklinq of metals", Moscou, Robert Draper Ltd. Teddington, 1959 décrit-il un procède d'électropolissage dans lequel il est fait référence à 1 ' électropolissage d'acier allié (Table 9, page 76) par des mélanges ternaires d'acides sulfurique, phosphorique, et d'eau en faible quantité, a savoir inférieure a 20 % en poids. Ces mélanges sont éventuellement additionnes d'acide chromique pour augmenter la brillance de la surface traitée.Thus, the FEDOT'EV document "Electropolishing, anodizmg and electroJytic picklinq of metals", Moscow, Robert Draper Ltd. Does Teddington, 1959 describe an electropolishing process in which reference is made to the electropolishing of alloy steel (Table 9, page 76) with ternary mixtures of sulfuric, phosphoric acids and water in small quantities , namely less than 20% by weight. These mixtures are optionally added with chromic acid to increase the gloss of the treated surface.
CL. FAUST dans "Electropolishing", Métal Fαrushing, Septembre 1992, 9, pp. 89-91 indique cje 1 ' électropolissage est un traitement idéal pour ac_ers inoxydables parmi lesquels sont cites les aciers înoxydaoles de type 302, 410 et 430. Diverses apparences, depuis un aspect satine jusqu'à un aspect brillant "comme un miroir" peuvent être obtenues avec des bains d'acide phosphorique et d'acide sulfurique qui contiennent tous très peu d'eau. Les bains préfères, qui permettent d'obtenir le brillant de type "miroir" sont ceux dans lesquels la proportion d'eau est la plus réduite, c'est-à-dire généralement inférieure à 20 % en poids, comme l'indique la figure 1 de ce document . MAGAINO S., MATLOSZ M., LANDOLT D., dansCL. FAUST in "Electropolishing", Métal Fαrushing, September 1992, 9, pp. 89-91 indicates that electropolishing is an ideal treatment for stainless steels among which are cited oxidoxole steels of type 302, 410 and 430. Various appearances, from a satin appearance to a shiny appearance "like a mirror" can be obtained with baths of phosphoric acid and sulfuric acid which all contain very little water. The preferred baths, which make it possible to obtain the “mirror” type gloss, are those in which the proportion of water is the lowest, that is to say generally less than 20% by weight, as indicated by the figure 1 of this document. MAGAINO S., MATLOSZ M., LANDOLT D., in
"An impédance study of stainless steel electropolishing".- J. Electrochem. Soc, 140, 5, 1993 étudient 1 ' électropolissage de l'acier inoxydable dans des solutions concentrées d'acide phosphorique et d'acide sulfurique. Une faible concentration en eau apparaît comme étant plutôt favorable au brillantage. Par exemple, 1 ' électropolissage d'acier Fe 13Cr par des mélanges contenant 65 % d'acide phosphorique, 20 % d'acide sulfurique et 15 % d'eau est étudie. Dans un article de HOAR T. P., MEARS D.C."An impedance study of stainless steel electropolishing" .- J. Electrochem. Soc, 140, 5, 1993 study the electropolishing of stainless steel in concentrated solutions of phosphoric acid and sulfuric acid. A low concentration of water appears to be rather favorable to brightening. For example, the electropolishing of Fe 13Cr steel with mixtures containing 65% phosphoric acid, 20% sulfuric acid and 15% water is studied. In an article by HOAR T. P., MEARS D.C.
ROTHWELL G. P. "The relationships between anodic passivity, brightening and pitting" - Corrosion Science, 5, 1965, pp. 279-289, il est indique que la passivaticn anodique est produite par la formation sur la surface de l'anode, d'un film d'oxyde très mince de faible conductivité ionique, tandis que le brillant anodique est, quant a lui, produit par le passage de cations dans et a travers des films très minces, solides et compacts, de conductivite amonique élevée, qui ne sont pas composes d'oxyde pur, mais d'oxyαe contamine par des anions étrangers issus de la solution αe brillantage.ROTHWELL G. P. "The relationships between anodic passivity, brightening and pitting" - Corrosion Science, 5, 1965, pp. 279-289, it is indicated that the anodic passivaticn is produced by the formation on the surface of the anode, of a very thin oxide film of low ionic conductivity, while the anodic gloss is produced by the passage of cations in and through very thin, solid and compact films, of high amonic conductivity, which are not composed of pure oxide, but of oxyαe contaminated by foreign anions from the brightening solution.
Les auteurs indiquent, en effet, que les compositions des solutions qui donnent, soit d'une part une passivatjon anodique, soit d'autre part un brillantage, sont très différentes ; en particulier, les solutions de brillantage et de polissage présentent une concentration en eau nulle ou très faible, les auteurs en concluent que les conditions de brillantage sont obtenues par un rapport anion (tel que sulfate, phosphate) sur eau suffisamment élevé.The authors indicate, in fact, that the compositions of the solutions which give, either on the one hand an anodic passivatjon, or on the other hand a shine, are very different; in particular, the brightening and polishing solutions have a zero or very low water concentration, the authors conclude that the brightening conditions are obtained by an anion ratio (such as sulphate, phosphate) on water which is sufficiently high.
Dans un article résumant les connaissances essentielles sur 1 ' électropolissage, D. LANDOLT "Fundamental aspect of electropolishing" dans Electrochem. Acta, 32, 1, 1987 pp. 1-11 indique que de nombreux électrolytes d'électropolissage de cette première catégorie, mis en oeuvre dans la pratique, contiennent une faible quantité d'eau et que les raisons pour cela données dans la littérature semblent quelque peu contradictoires, bien que diverses explications théoriques puissent permettre d'expliquer que de faibles concentrations en eau soient favorables a 1 ' électropolissage .In an article summarizing the essential knowledge on electropolishing, D. LANDOLT "Fundamental aspect of electropolishing" in Electrochem. Acta, 32, 1, 1987 pp. 1-11 indicates that many electropolishing electrolytes of this first category, used in practice, contain a small amount of water and that the reasons for this given in the literature seem somewhat contradictory, although various theoretical explanations may explain that low water concentrations are favorable to electropolishing.
Une deuxième catégorie d' electrolyte pour 1 ' électropolissage, comprend les électrolytes a base d'acide perchlorique.A second category of electrolyte for electropolishing includes electrolytes based on perchloric acid.
Dans ce type d ' electrolyte, contenant un omon très agressif et oxydant, tel que le perchlorate, l'utilisation de l'eau comme solvant est contre indiquée.In this type of electrolyte, containing a very aggressive and oxidizing omon, such as perchlorate, the use of water as a solvent is contraindicated.
Le solvant est donc de type organique : il peut s'agir par exemple d'acide acétique ou d'anhydride acétique de méthanol ou encore d'éther monobutylique de 1 ' ethylene glycol : ces électrolytes sont peu a peu abanαonnes, car ils sont très dangereux et ont des propriétés explosives comme cela est décrit dans l'ouvrage de W.J. TEGART "Polissage electrolytique et chimique des métaux". Editions Dunod, Paris, 1960. De ce fait, lors de la fabrication et de l'utilisation de ces bains, de nombreuses précautions doivent être prises .The solvent is therefore of the organic type: it may for example be acetic acid or acetic anhydride of methanol or alternatively monobutyl ether of ethylene glycol: these electrolytes are gradually being abandoned, because they are very dangerous and have explosive properties as described in the book by WJ TEGART "Electrolytic and chemical polishing of metals". Editions Dunod, Paris, 1960. As a result, during the manufacture and use of many baths must be taken.
Jusqu'à présent, 1 ' electrolyte utilise pour 1 ' électropolissage des aciers austénoferπtiques est le même que celui utilise pour 1 ' Inconel 600 et appartient a la première catégorie mentionnée ci-dessus : il s'agit d'un mélange ternaire acide sulfurique, acide phosphorique et eau en très faible quantité, auquel on peut ajouter certains additifs tels que l'acide oxalique, des oxydes de chrome ou d'aluminium.So far, the electrolyte used for electropolishing austenoferπtiques steels is the same as that used for Inconel 600 and belongs to the first category mentioned above: it is a ternary mixture of sulfuric acid, phosphoric acid and water in very small quantities, to which we can add certain additives such as oxalic acid, chromium or aluminum oxides.
Ce type d' electrolyte doit être remplacé pour trois raisons essentielles :This type of electrolyte must be replaced for three essential reasons:
La première raison est que, si ces électrolytes donnent de bons résultats sur 1 ' Inconel 600 ou sur des aciers inoxydables austenitiques (316L, 30 ... ) cela n'est pas le cas pour les aciers austénoferritiques . La structure biphasée de ces aciers leur confère en effet un comportement original dans la mesure ou il est courant d'observer une dissolution préférentielle de l'une des phases, généralement la ferrite, par rapport a l'autre.The first reason is that, if these electrolytes give good results on the Inconel 600 or on austenitic stainless steels (316L, 30 ...) this is not the case for austenoferritic steels. The two-phase structure of these steels gives them an original behavior effect insofar as it is common to observe a dissolution p r éférentielle of one of the phases, usually ferrite, with respect to the other.
Même si 1 ' électropolissage de telles surfaces permet d'améliorer le Ra ou rugosité arithmétique de 20 % environ après une érosion de 20 ur, l'échantillon est mat et une attaque de la ferrite est observée comme cela est montre sur la figure 1 qui reoresente la visualisation au microscope électronique a oalayage de la surface d'un échantillon d'acier 308L ayant subi un traitement d'électropolissage en milieu acde sulfurique et acide phosphorique avec une érosion -_-_ 40 μm.Even if the electropolishing of such surfaces improves the Ra or arithmetic roughness by about 20% after an erosion of 20 ur, the sample is mat and an attack of the ferrite is observed as shown in FIG. 1 which reoresente the visualization under an electron microscope with scanning of the surface of a 308L steel sample having undergone an electropolishing treatment in sulfuric and phosphoric acid medium with an erosion -_-_ 40 μm.
La deuxième raison conduisant au replacement de ce type d' electrolyte est le fait queThe second reason leading to the replacement of this type of electrolyte is the fact that
.- o certaines applications des électrolytes.- o some applications of electrolytes
J' iectropolissage telle que dans les circuits primaires des réacteurs a eau pressurisée (REP), l ' electrolyte ne doit pas contenir d'acide sulfurique, car le soufre est proscrit de ces circuits primaires du fait qu'il est susceptible d'engendrer des problèmes de corrosion.I electropolishing as in the circuits pressurized water reactors (PWR), the electrolyte must not contain sulfuric acid, since sulfur is prohibited from these primary circuits because it is likely to cause corrosion problems.
La troisième raison est que l'acide phosphorique ajoute dans cet electrolyte présente l'inconvénient, de même que les phosphates qui en sont dérives, de poser des problèmes importants au niveau du traitement des effluents charges en ces composes issus du traitement d'électropolissage.The third reason is that the phosphoric acid added to this electrolyte has the disadvantage, as well as the phosphates which are derived therefrom, of posing significant problems in terms of the treatment of the effluents charged with these compounds resulting from the electropolishing treatment.
Il a ete suggère de mettre en oeuvre l'acide nitrique dans les électrolytes α' électropolissage, mais l'acide nitrique présente les mêmes propriétés gênantes que l'acide perchlorique déjà mentionnées ci-dessus, dans la mesure ou il est oxydant .It has been suggested to use nitric acid in electropolishes with electropolishing, but nitric acid has the same troublesome properties as perchloric acid already mentioned above, insofar as it is oxidizing.
Si l'acide nitrique, a l'instar de l'acide perchlorique est mélange a un corps ou a un compose organique susceptible d'être oxyde en particulier en présence d'eau, la reaction d'oxydation peut provoquer une explosion.If nitric acid, like perchloric acid, is mixed with a body or an organic compound capable of being oxidized in particular in the presence of water, the oxidation reaction can cause an explosion.
Des essais d'électropolissage et de décontamination ont cependant déjà ete réalises sur des aciers inoxydables austenitiques (304L, 316L) dans l'acide nitrique (9 mol/1), par exemple dans les documents de TURNER A D , JUNKISON A R , POTTINGER J S., LAIN M.J. - Nuclear science and technology - "Development of remote electrochemical décontamination for hot cell applications" Commission of the European Communities - Final report - EUR 14192 - 1993 "toutefois, aucun essai n'a ete effectue sur l'acier austeno-ferπtique 308L De plus, cet electrolyte présente des inconvénients, car sa Viscosité est trop raibJe. n ne permet pas d'obtenir un polissage de bonne qualité a cause de défauts d'ondulation lies au régime hydrodynamique.Electropolishing and decontamination tests have however already been carried out on austenitic stainless steels (304L, 316L) in nitric acid (9 mol / 1), for example in the documents of TURNER AD, JUNKISON AR, POTTINGER J S ., LAIN MJ - Nuclear science and technology - "Development of remote electrochemical decontamination for hot cell applications" Commission of the European Communities - Final report - EUR 14192 - 1993 "however, no tests have been carried out on austeno- steel ferπtique 308L In addition, this electrolyte has drawbacks, because its Viscosity is too stiff. good quality due to undulation faults linked to the hydrodynamic regime.
Il existe donc un besoin pour un electrolyte présentant une viscosité réduite sans toutefois être trop faible, afin de permettre une mise en oeuvre facile, pouvant être utilise aussi bien sur les Inconels tels que 1 ' Inconel 600 et les aciers inoxydables austenitiques, ferritiques que sur les aciers austeno-ferπtiques, et donnant d'excellents résultats dans tous les cas : c'est-à-dire essentiellement une surface brillante (et non pas mate) de l'échantillon sans attaque cπstallographique, a savoir pas de piqûres ou d'attaque intergranulaire ou de corrosion sélective d'une phase par rapport aThere is therefore a need for an electrolyte having a reduced viscosity without however being too low, in order to allow an easy implementation, which can be used both on Inconels such as 1 Inconel 600 and austenitic, ferritic stainless steels as on austeno-ferπtic steels, and giving excellent results in all cases: that is to say essentially a shiny (and not mat) surface of the sample without cπstallographic attack, namely no pitting or intergranular attack or selective corrosion of a phase compared to
1 ' autre .The other.
L ' electrolyte doit être d'une utilisation sûre et sans risques, et peu coûteux.The electrolyte must be safe and risk-free to use and inexpensive.
L ' electrolyte doit d'autre part être exempt des ions fluorures, chlorures et soufre. Sa température de mise en oeuvre doit être de préférence inférieure a 60°C.The electrolyte must also be free from fluoride, chloride and sulfur ions. Its processing temperature should preferably be less than 60 ° C.
Il doit également présenter de Donnes conditions de conservation dans le temps a température ambiante.It must also have good storage conditions over time at room temperature.
Cet electrolyte doit en outre, ne pas contenir d'acide phosphorique et/ou phosphates et être totalement recyclable ou destructible par les techniques actuelles de traitement des effluents. Notamment, l'utilisation de 1 ' electrolyte do_t être compatible avec les possibilités des sites nucléaires et en particulier avec les possibilités de traitement des effluents dans les centrales nucléaires. Le volume de déchets solides et liquides génères, susceptibles d'être stockes doit être enfin réduit au minimum.This electrolyte must also not contain phosphoric acid and / or phosphates and be completely recyclable or destructible by current effluent treatment techniques. In particular, the use of one electrolyte must be compatible with the possibilities of nuclear sites and in particular with the possibilities of treatment of effluents in nuclear power plants. Finally, the volume of general solid and liquid waste likely to be stored must be reduced to a minimum.
L'objet de la présente invention est donc de fournir un electrolyte pour 1 ' électropolissage qui satisfasse, entre autres, a toutes les exigences citées ci-dessus .The object of the present invention is therefore to provide an electrolyte for electropolishing which satisfies, inter alia, all the requirements mentioned above.
Un autre objet de la présente invention est un procède d'électropolissage et/ou de décontamination mettant en oeuvre 1 ' electrolyte ci-dessus qui puisse donner des résultats satisfaisants sur tous types d'acier inoxydable, ainsi que sur les alliages de nickel tels que les Inconels utilises en particulier dans l'industrie nucléaire. Ces objets et d'autres encore sont atteints, conformément a l'invention, par un electrolyte constitue d'un mélange ternaire acide glycolique, acide nitrique et eau dans les concentrations suivantes : - acide glycolique • de 152 a 538 g/kgAnother subject of the present invention is an electropolishing and / or decontamination process using the above electrolyte which can give satisfactory results on all types of stainless steel, as well as on nickel alloys such as Inconels used in particular in the nuclear industry. These and other objects are achieved, in accordance with the invention, by an electrolyte consisting of a ternary mixture of glycolic acid, nitric acid and water in the following concentrations: - glycolic acid • from 152 to 538 g / kg
- acide nitrique de 170 a 568 g/kg- nitric acid from 170 to 568 g / kg
- eau de 280 a 678 g/kg- water from 280 to 678 g / kg
La formulation de cet electrolyte va de manière surprenante a l' encontre de tous les préjuges e/istant dans la littérature puisque maigre toutes les contre-indications qui se trouvent dans l'art antérieur et en particulier dans les documents mentionnes ci-dessus ; 1 ' electrolyte selon la présente invention utilise l'eau comme solvant a une concentration élevée, supérieure aux concentrations conseillées dans l'art antérieur (inférieures a 20 o en masse)The formulation of this electrolyte goes surprisingly against all the prejudices e / isting in the literature since thin all the contraindications which are in the prior art and in particular in the documents mentioned above; 1 electrolyte according to the present invention uses water as a solvent at a high concentration, greater than the concentrations recommended in the prior art (less than 20 o by mass)
De même, 1 ' utilisatior d'acide nitrique comme constituant de base princiDal au melanae, ^oTespond a une démarche qui s'écarte fondamentalement des démarches suivies jusqu'alors dans ce domaine de la technique.Likewise, the use of nitric acid as the main basic constituent of melanaea, responds to an approach which differs fundamentally steps previously taken in this area of technology.
Enfin, l'incorporation d'acide glycolique dans le mélange tout en conservant une concentration en 5 eau élevée va également a l' encontre d'un autre préjuge dans ce domaine de la technique qui est reflète par de nombreux documents et qui voulait qu'on ne mélange pas dans un electrolyte pour 1 ' électropolissage un acide oxydant comme l'acide nitrique avec des composesFinally, the incorporation of glycolic acid into the mixture while retaining a high water concentration also goes against another prejudice in this field of the technique which is reflected by numerous documents and which wanted that does not mix in an electrolyte for electropolishing an oxidizing acid such as nitric acid with compounds
10 organiques tels que l'acide glycolique en présence d'eau10 organic such as glycolic acid in the presence of water
Ce sont donc au moins trois préjuges techniques largement répandus dans l'art antérieur, tel qu'il est en particulier reflète par les documentsThese are therefore at least three technical biases widely used in the prior art, as particularly reflected in the documents
!:> cites et discutes ci-dessus, qui ont ete surmontes par les inventeurs de la présente demande, puisqu'il a ete choisi d'une part d'utiliser l'eau comme solvant a une proportion élevée, d'autre part d'utiliser l'acide nitrique comme constituant de base, et enfin 0 d'incorporer de l'acide glycolique dans le mélange.!:> cited and discussed above, which were overcome by the inventors of the present application, since it was chosen on the one hand to use water as a solvent in a high proportion, on the other hand d '' use nitric acid as basic constituent, and finally 0 to incorporate glycolic acid in the mixture.
L'acide glycolique, incorpore dans 1 ' e1 ectrolyte permet notamment d'augmenter la viscosité tout en conservant une concentration en eau élevée, a savoir supérieure ou égale a 28-29 % en masse. -> Rappelons que l 'acide glycolique ou acide hvdroxyacetique encore désigne par îes lettres HOAC fait partie de la série des acides hydroxy- carboxyliques .The glycolic acid incorporated in the e1 ectrolyte makes it possible in particular to increase the viscosity while maintaining a high water concentration, namely greater than or equal to 28-29% by mass. -> Recall that glycolic acid or hvdroxyacetic acid also denoted by the letters HOAC is part of the series of hydroxycarboxylic acids.
Il provient des jus de la canne a sucre, de O i_ oetterave ou de Ja rafle de vigne C'est un produit racilement disponible et de prix peu eleve Sa formule est HO- C •COOHIt comes from the sugarcane, O i_ oetterave or grape juice. It is a product that is highly available and inexpensive. Its formula is HO- C • COOH
HH
L'acide glycolique est un acide organique, relativement fort, soluble dans l'eau en toutes proportions et cumule les fonctions acide et alcool. La fonction alcool peut être utilisée en particulier pour son pouvoir solvant ; 1 ' HOAC possède également des propriétés bactéricides et détartrantes et est couramment utilisé comme base pour la formulation de nettoyants destines aux usages ménagers et collectifs.Glycolic acid is a relatively strong organic acid, soluble in water in all proportions and combines the acid and alcohol functions. The alcohol function can be used in particular for its solvent power; 1 HOAC also has bactericidal and descaling properties and is commonly used as a base for the formulation of cleaners intended for household and collective use.
L'acide glycolique est également utilise, comme le mentionne le document US-A-4 137 132 dans les bains de chromatage.Glycolic acid is also used, as mentioned in document US-A-4 137 132 in the chromating baths.
Le document US-A-4 137 132 décrit des bains pour le dépôt électrolytique d'alliages or-nickel et chrome-nickel qui contiennent de l'acide glycolique.Document US-A-4,137,132 describes baths for the electrolytic deposition of gold-nickel and chromium-nickel alloys which contain glycolic acid.
Le document JP-A-55047399 décrit un electrolyte pour 1 ' électropolissage d'alliages Fe-Al-Si qui comprend un mélange binaire d'acide glycolique (40 a 60 % en volume) et d'acide sulfurique. Ce mélange ne contient ni eau ni acide nitrique.Document JP-A-55047399 describes an electrolyte for electropolishing Fe-Al-Si alloys which comprises a binary mixture of glycolic acid (40 to 60% by volume) and sulfuric acid. This mixture contains neither water nor nitric acid.
Le document de HILL E.F. : "Development of the glycolic-citπc acides (GCA) process for décontamination of LMFBR components", Trans. Am. Nαcl. Soc, 30, 1978 est relatif à l'utilisation d'un mélange d'acide glycolique (2,5 % en poids) et d'acide citrique (2,5 % en poids) en solution aqueuse, appelé mélange CGA, a 70-90°C, en vue de decontammer chimiquement et sans apport de courant αes composants faiblement contamines en acier inoxydable 304 et 316 provenant de la filière LMFBR. Ce document ne décrit donc pas un electrolyte pour 1 ' électropolissage et de plus concerne un mélange de deux acides organiques.The HILL EF document: "Development of the glycolic-citπc acids (GCA) process for decontamination of LMFBR components", Trans. Am. Nαcl. Soc, 30, 1978 relates to the use of a mixture of glycolic acid (2.5% by weight) and citric acid (2.5% by weight) in aqueous solution, called CGA mixture, a 70 -90 ° C, with a view to chemically decontaminating and without supply of current to the weakly contaminated components in stainless steel 304 and 316 from the LMFBR sector. This document therefore does not describe a electrolyte for electropolishing and further relates to a mixture of two organic acids.
La formulation des électrolytes est un domaine complètement imprévisible, et les propriétés d'un mélange donné ne peuvent absolument pas être déduites des propriétés des mélanges connus qui en diffèrent par un de leurs constituants ou des propriétés de chacun des constituants du mélange donne pris individuellement. Rien ne pouvait donc laisser supposer que l'incorporation d'acide glycolique dans un electrolyte pour 1 'électropolissage allait conduire a l'ensemble des propriétés surprenantes et avantageuses, caractéristiques de 1 'electrolyte selon l'invention. De plus, le choix de l'acide glycolique, parmi les nombreux acides organiques existants, afin de l'incorporer dans un tel mélange, n'était absolument pas évident et est en lui-même surprenant et inattendu.The formulation of electrolytes is a completely unpredictable field, and the properties of a given mixture can absolutely not be deduced from the properties of known mixtures which differ by one of their constituents or from the properties of each of the constituents of the given mixture taken individually. Nothing could therefore suggest that the incorporation of glycolic acid in an electrolyte for electropolishing would lead to all of the surprising and advantageous properties characteristic of the electrolyte according to the invention. In addition, the choice of glycolic acid, among the many existing organic acids, to incorporate it into such a mixture, was absolutely not obvious and is in itself surprising and unexpected.
L' electrolyte selon l'invention base sur un mélange ternaire spécifique du point de vue de ses constituants et de leurs proportions, permet d'obtenir une surface brillante des échantillons de métaux traités .The electrolyte according to the invention based on a specific ternary mixture from the point of view of its constituents and their proportions, makes it possible to obtain a shiny surface of the samples of treated metals.
On aboutit en effet a un lissage et a un brillantage de la surface aussi bien par exemple des aciers inoxydables austémtiques tels que les aciers 316L et 304L, que des aciers ferritiques tels que l'acier 430, que des aciers austéno-ferritiques tels que l'acier 308L, ou encore des Inconels tels que 1' Inconel 600, 690 ou 800.This results in a smoothing and a surface gloss as well, for example austemitic stainless steels such as steels 316L and 304L, as ferritic steels such as steel 430, as austenitic-ferritic steels such as l 308L steel, or Inconels such as the Inconel 600, 690 or 800.
Du fait que l 'acier 308L et 1 ' Inconel sont les constituants essentiels des générateurs de vapeur, 1 ' electrolyte selon l'inventior conviendra αonc particulièrement pour traiter les surfaces de tels appareils. L ' electrolyte selon l'invention se caractérise donc par une grande polyvalence. En effet, au contraire des électrolytes de l'art antérieur qui ne donnaient de bons résultats d'électropolissage que pour 1 ' Inconel 600 ou les aciers inoxydables austémtiques (316, 304, etc.), 1 ' electrolyte selon l'invention permet également le lissage et le brillantage des échantillons en acier austéno-ferritique, par exemple de type 308L sans que ne se produise une attaque préférentielle du réseau ferritique, ce qui constitue un avantage décisif des électrolytes selon l'invention sur les électrolytes de l'art antérieur, en particulier les électrolytes suifophosphoriques .Due to the fact that 308L steel and Inconel are the essential constituents of steam generators, the electrolyte according to the invention will be particularly suitable for treating the surfaces of such devices. The electrolyte according to the invention is therefore characterized by great versatility. In fact, unlike the electrolytes of the prior art which only gave good electropolishing results for the Inconel 600 or the austemic stainless steels (316, 304, etc.), the electrolyte according to the invention also allows smoothing and polishing of austenitic-ferritic steel samples, for example of the 308L type without a preferential attack on the ferritic network, which constitutes a decisive advantage of the electrolytes according to the invention over the electrolytes of the prior art , in particular the phosphophoric electrolytes.
L' electrolyte selon l'invention présente également l'avantage évident sur les électrolytes de l'art antérieur d'être exempt des ions fluorures, chlorures et sulfates qui sont corrosifs vis-à-vis des aciers inoxydables et des alliages de nickel.The electrolyte according to the invention also has the obvious advantage over the electrolytes of the prior art of being free of fluoride ions, chlorides and sulphates which are corrosive with respect to stainless steels and nickel alloys.
L'electrolyte selon l'invention présente l 'avantage supplémentaire de ne pas contenir de phosphates et/ou d'acide phosphorique, ce qui redu±t le volume des déchets génères et en facilite le ti alternent .The electrolyte according to the invention has the additional advantage of not containing phosphates and / or phosphoric acid, which reduces the volume of the general waste and makes it easier to alternate.
Cet electrolyte selon l'invention ne nécessite pas de chauffage pour pouvoir être mis en oeuvre, il est en effet utilisable généralement a température ambiante, c'est-a-dire généralement de 15°C a 45°C, de préférence de 20 a 30°C, de préférence encore de 20 a 25°C et en tous les cas a une température inférieure a 45°C.This electrolyte according to the invention does not require heating to be able to be used, it is in fact usable generally at room temperature, that is to say generally from 15 ° C to 45 ° C, preferably from 20 to 30 ° C, more preferably from 20 to 25 ° C and in any case at a temperature below 45 ° C.
L ' elecfrolyte selon l'invention présente une viscosité favorable, généralement comprise errr^ 1,3 et 3 mm /s .The elecfrolyte according to the invention has a favorable viscosity, generally between errr ^ 1.3 and 3 mm / s.
L' electrolyte selon l'invention présenta également de bonnes propriétés de conservation dans le 39168 PCI7FR97/00648The electrolyte according to the invention also exhibited good conservation properties in the 39168 PCI7FR97 / 00648
1313
temps à température amoiante, et il peut être stocké sur une durée par exemple de un à deux mois sans que ses caractéristiques essentielles ne soient affectées.time at room temperature, and it can be stored for a period of for example from one to two months without its essential characteristics being affected.
L' electrolyte ne contient pas de réactifs susceptibles de donner lieu à des réactions très agressives, oxydantes, ou explosives. Il peut être préparé et utilisé sans prendre de précautions particulières et sans danger pour l'utilisateur.The electrolyte does not contain reagents capable of giving rise to very aggressive, oxidizing or explosive reactions. It can be prepared and used without taking any special precautions and safe for the user.
L'electrolyte usé peut être facilement et totalement retraité par distillation, puisque le mélange contient une forte proportion en masse d'acide nitrique et d'eau et que l'acide glycolique se transforme en acide oxalique.The spent electrolyte can be easily and completely reprocessed by distillation, since the mixture contains a high proportion by mass of nitric acid and water and the glycolic acid is transformed into oxalic acid.
Il peut également être minéralisé dans un caicinateur, ce qui permet d'utiliser cet electrolyte pour décontaminer des composants des usines de retraitement .It can also be mineralized in a caicinator, which allows this electrolyte to be used to decontaminate components from reprocessing plants.
L'acide nitrique récupéré dans le distillât peut être recyclé, ce qui, d'un point de vue économique est particulièrement avantageux.The nitric acid recovered in the distillate can be recycled, which, from an economic point of view is particularly advantageous.
Enfin, l'utilisation de 1 ' electrolyte selon l'invention, du fait de la présence d'acide nitrique, est compatible avec les possibilités de retraitement des effluents des centrales électriques, nucléaires, ainsi que des autres sites nucléaires, qui constituent un des domaines d'application préféré de 1 'electrolyte selon la présente invention.Finally, the use of one electrolyte according to the invention, due to the presence of nitric acid, is compatible with the possibilities of reprocessing the effluents of nuclear power plants, as well as of other nuclear sites, which constitute one of the preferred fields of application of the electrolyte according to the present invention.
L'electrolyte a généralement la composition exprimée en fractions massiques mentionnée ci-dessus. Une composition préférée comprendra :The electrolyte generally has the composition expressed in mass fractions mentioned above. A preferred composition will include:
- acide glycolique : de 152 à 538 g/kg- glycolic acid: from 152 to 538 g / kg
- acide nitrique : de 170 à 240 g/kg- nitric acid: from 170 to 240 g / kg
- eau : de 292 à 678 g/kg.- water: from 292 to 678 g / kg.
Un tel electrolyte préféré est plus stable chimiquement, l'instabilité se caractérisant par la production d'acide nitreux, de vapeurs nitreuses et la formation d'acide oxalique au-delà de sa limite de solubilité .Such a preferred electrolyte is more chemically stable, the instability being characterized by the production of nitrous acid, nitrous vapors and the formation of oxalic acid beyond its solubility limit.
L'invention concerne également un procédé d'électropolissage d'un acier inoxydable ou d'un alliage de nickel dans lequel ledit acier inoxydable ou ledit alliage de nickel est mis en contact avecThe invention also relates to a method of electropolishing a stainless steel or a nickel alloy in which said stainless steel or said nickel alloy is brought into contact with
1 ' electrolyte décrit ci-dessus.1 electrolyte described above.
Ce procédé présente l'ensemble des caractéristiques avantageuses liées à 1 ' electrolyte et déjà mentionnées ci-dessus ; ce procédé selon l'invention mettant en oeuvre 1 ' electrolyte spécifique de l'invention, permet également d'atteindre des rendements faradiques de dissolution élevés, généralement supérieurs à 80, voire 85 %, la vitesse de dissolution étant notamment de 950 μm/h.This process has all the advantageous characteristics linked to the electrolyte and already mentioned above; this process according to the invention using the specific electrolyte of the invention also makes it possible to achieve high Faradic dissolution yields, generally greater than 80, or even 85%, the dissolution rate being in particular 950 μm / h .
Ce procédé peut servir a 1 ' électropolissage de tous types d'aciers inoxydables - aussi bien austémtiques, par exemple 316L, 304L, que ferritiques, par exemple 430 ou austénoferritiques, par exemple 308L mais aussi d'alliages de nickel tels que les Inconels, par exemple 1 ' Inconel 600 ou 1 ' Inconel 640 ou encore 1 ' Inconel 800.This process can be used for electropolishing all types of stainless steels - both austemetic, for example 316L, 304L, and ferritic, for example 430 or austenoferritic, for example 308L, but also nickel alloys such as Inconels, for example 1 'Inconel 600 or 1' Inconel 640 or 1 'Inconel 800.
On constate donc que ce procède peut être employé pour traiter les divers alliages utilises notamment dans l'industrie nucléaire. Il est bien évident que ce procède conviendra également pour le traitement des aciers inoxydables et alliages de nickel rencontres dans tous types d'industries. L'invention concerne également un procédé d ' electrodecontaminati on d'aciers inoxydables ou d'alliages de nickel contamines notamment a leur surface par des radioéléments, par exemple le Cobalt 60, dans lequel l'ailiaqe métallique contamine est mis en contact avec l ' electrolyte décrit ci-dessus. Ces aciers inoxydables et/ou alliages sont par exemple ceux rencontrés dans l'industrie nucléaire ou dans une autre industrie.It is therefore found that this process can be used to treat the various alloys used in particular in the nuclear industry. It is obvious that this process will also be suitable for the treatment of stainless steels and nickel alloys encountered in all types of industries. The invention also relates to a method of electrodecontamination of stainless steels or of nickel alloys contaminated in particular on their surface by radioelements, for example Cobalt 60, in which the contaminated metallic wing is brought into contact with the electrolyte described above. These stainless steels and / or alloys are, for example, those encountered in the nuclear industry or in another industry.
Les aciers inoxydables et/ou alliages de nickel sont par exemple constitutifs d'un composant d'une centrale nucléaire ou d'une usine de retraitement et se rencontrent notamment dans le circuit primaire des centrales nucléaires telles que les tuyauteries, les générateurs de vapeur .... Le procédé permet notamment une dissolution des éléments métalliques contaminants, contenus essentiellement dans les oxydes de la couche superficielle, et donc une réduction notable de la contamination pour permettre une intervention du personnel de maintenance.Stainless steels and / or nickel alloys are for example constituent of a component of a nuclear power plant or a reprocessing plant and are encountered in particular in the primary circuit of nuclear power plants such as piping, steam generators. ... The process allows in particular the dissolution of contaminating metallic elements, contained essentially in the oxides of the surface layer, and therefore a significant reduction in contamination to allow intervention by maintenance personnel.
Les conditions opératoires du procédé d'électropolissage et de décontamination peuvent être facilement déterminées par l'homme du métier dans ce domaine de la technique en fonction notamment du matériau à traiter. Elles seront généralement les suivantes .The operating conditions of the electropolishing and decontamination process can be easily determined by a person skilled in the art in this field of the technique depending in particular on the material to be treated. They will generally be as follows.
La composition de 1 ' electrolyte pour 1 ' électropolissage et/ou la décontamination est celle déjà indiquée ci-dessus, à savoir : - acide glycolique : de 152 à 538 g/kg,The composition of the electrolyte for electropolishing and / or decontamination is that already indicated above, namely: - glycolic acid: from 152 to 538 g / kg,
- acide nitrique : de 170 à 568 g/kg- nitric acid: from 170 to 568 g / kg
- eau : de 280 à 678 g/kg.- water: from 280 to 678 g / kg.
La densité de courant est généralement supérieure ou égale à 0,5 A/cm2, elle est de préférence comprise entre 0,5 A/cm2 et 1,5 A/cm2, par exemple lA/cm2 ; en effet, un certain risque d ' échauffement peut provoquer une piqûration au-delà de 1,7 A/cm2.The current density is generally greater than or equal to 0.5 A / cm 2 , it is preferably between 0.5 A / cm 2 and 1.5 A / cm 2 , for example lA / cm 2 ; in fact, a certain risk of overheating can cause pitting beyond 1.7 A / cm 2 .
La température est généralement la température ambiante, à savoi- lt α 45°C, de préférence 20 a 30°C, de préférence encore 20 a 25°C et le régime hydrodynamique est de préférence un régime laminaire.The temperature is generally room temperature, preferably at 45 ° C, preferably 20 to 30 ° C, more preferably 20 to 25 ° C and the hydrodynamic regime is preferably a laminar regime.
La durée du procède est généralement de 60 sec à 80 sec pour une érosion par exemple de 20 μm. 5 Les conditions opératoires des procèdes d'électropolissage et d'électrodecontamination sont généralement identiques.The duration of the process is generally from 60 sec to 80 sec for an erosion, for example of 20 μm. 5 The operating conditions for the electropolishing and electrodecontamination procedures are generally identical.
L' electrolyse use est ainsi traité en vue de son élimination, de son recyclage et/ou de son 0 rejet.The used electrolysis is thus treated with a view to its elimination, its recycling and / or its rejection.
Selon une caractéristique particulièrement intéressante de la présente invention, 1 'electrolyte utilise ne contient ni acide phosphorique ni phosphate, et le traitement des effluents s'en trouve de ce fait 5 grandement facilité.According to a particularly advantageous characteristic of the present invention, the electrolyte used contains neither phosphoric acid nor phosphate, and the treatment of effluents is thereby greatly facilitated.
En effet, l'acide glycolique peut s'oxyder en acide oxalique. D'autre part, il a été démontre que la reaction entre l'acide nitrique et l'acide oxalique est une reaction lente et que les gaz dégages : oxyde 0 αe carbone, anhydride carbonique et eau ne reagissent pas avec le mélange d'acides.Indeed, glycolic acid can oxidize to oxalic acid. On the other hand, it has been demonstrated that the reaction between nitric acid and oxalic acid is a slow reaction and that the gases given off: carbon dioxide, carbon dioxide and water do not react with the mixture of acids. .
Selon l'invention, le traitement de 1 ' electrolyte use a l'issue du procède d'électropolissage en vue de sa destruction et/ou de -> son recyclage peut donc comprendre :According to the invention, the treatment of the electrolyte used at the end of the electropolishing process with a view to its destruction and / or -> its recycling can therefore comprise:
- une oxydation en voie humide de l'acide glycolique en acide oxalique, puis en C02, terme final de l'oxydation. Dans ce cas, on obtient un effluent nitrique qui peut être envoyé a la station du 0 traitement des effluents ; ou une distillation de 1 ' electrolyte use, suivie par exemple d'une calcinatior. des concentrât s dort les résidus peuvent être par exemple vitrifies, comme c'est le cas pour certains déchets des usines de ι retraitement. Le distillât peut éventuellement être recycle en vue de la réutilisation de l'acide nitrique dans le procède d'électropolissage.- wet oxidation of glycolic acid to oxalic acid, then to C0 2 , the final oxidation term. In this case, a nitric effluent is obtained which can be sent to the effluent treatment station; or a distillation of the used electrolyte, followed for example by a calcinator. concentrates sleep the residues can be vitrified, for example, as is the case for certain waste from reprocessing plants. The distillate can optionally be recycled for the reuse of nitric acid in the electropolishing process.
L'invention sera mieux comprise a la lecture de la description suivante d'un mode de réalisation préférentiel donné a titre d'exemple îllustratif et non limitatif, cette description étant faite en référence aux dessins joints dans lesquels :The invention will be better understood on reading the following description of a preferred embodiment given by way of illustrative and nonlimiting example, this description being made with reference to the accompanying drawings in which:
- la figure 1 représente une visualisation au MEB (microscope électronique à balayage) de la surface d'un échantillon d'acier inoxydable 308L ayant subi un traitement d'électropolissage en milieu acide sulfurique et acide phosphorique (érosion de 40 μm) , les figures 2 et 3 représentent une visualisation au MEB de la surface d'un échantillon d' Inconel 600 ayant subi un traitement d'électropolissage en milieu acide nitrique et acide glycolique, c'est-à-dire avec un electrolyte conforme à l'invention (érosion de 30,7 μm) , les figures 4 à 9 représentent des profils de rugosité anamorphoses bi et tridimensionnels de la surface de 1 ' Inconel 600.- Figure 1 shows a SEM display (scanning electron microscope) of the surface of a 308L stainless steel sample having undergone an electropolishing treatment in sulfuric acid and phosphoric acid medium (erosion of 40 μm), the figures 2 and 3 represent a SEM display of the surface of a sample of Inconel 600 having undergone an electropolishing treatment in a nitric acid and glycolic acid medium, that is to say with an electrolyte according to the invention ( erosion of 30.7 μm), FIGS. 4 to 9 represent two- and three-dimensional anamorphic roughness profiles of the surface of the Inconel 600.
Les différents profils bi et tridimensionnels présentés sont respectivement : la surface initiale de l'acier (figures 4, 6 et 8), puis cette même surface après une érosion de 30 μm (figures 5, 7 et 9) .The different two and three-dimensional profiles presented are respectively: the initial surface of the steel (Figures 4, 6 and 8), then this same surface after an erosion of 30 μm (Figures 5, 7 and 9).
- les figures 6 et 7 montrent tous les pics de la microrugosite, alors que sur les figures 8 et 9 a r/ec lissage filtre de 0,8 mm), ces pics ont disparu pour faire apparaître un planage (macrorugosité) .- Figures 6 and 7 show all the peaks of the microroughness, while in Figures 8 and 9 at r / ec filtering of 0.8 mm), these peaks disappeared to reveal a leveling (macrorugosity).
- la figure 10 représente les couroes . ". msitcs (ordonnée : densité de courant en mA/cm2) - (abscisse : potentiel en volt/électrode au Cdlomel sature : ECS) pour des aciers inoxydables austémtiques 316L (courbe en trait plein) et 304L- Figure 10 shows the couroes. ". msitcs (ordinate: current density in mA / cm 2 ) - (abscissa: potential in volts / saturated Cdlomel electrode: DHW) for stainless steels austemetic 316L (solid line curve) and 304L
(courbe en tirets) , pour un acier austeno-ferπtique(dashed curve), for an austeno-ferπtique steel
308L (courbe en trait mixte) , et pour de 1 ' Inconel308L (curve in phantom), and for Inconel
(courbe en pointillés) . Les figures 2 à 9 représentent et illustrent donc le procédé selon l'invention mettant en oeuvre 1 ' electrolyte spécifique selon l'invention dans le cas particulier d'un traitement d'électropolissage d'un acier austéno-ferritique 308L. La figure 1 permet de visualiser les résultats obtenus avec un electrolyte de l'art antérieur (acide sulfurique et phosphorique) et de comparer les résultats obtenus avec 1 ' electrolyte de 1 ' invention . Les exemples suivants décrivent et illustrent l'invention.(dotted curve). FIGS. 2 to 9 therefore represent and illustrate the method according to the invention implementing the specific electrolyte according to the invention in the particular case of an electropolishing treatment of an austeno-ferritic steel 308L. FIG. 1 makes it possible to visualize the results obtained with an electrolyte of the prior art (sulfuric and phosphoric acid) and to compare the results obtained with the electrolyte of the invention. The following examples describe and illustrate the invention.
Exemple 1 : Résultats en électropolissage sur de 1 ' Inconel 600. Ce traitement d'électropolissage est effectue avec un electrolyte dont la composition est la suivante :Example 1: Results in electropolishing on Inconel 600. This electropolishing treatment is carried out with an electrolyte whose composition is as follows:
- acide glycolique : 213 g/kg- glycolic acid: 213 g / kg
- acide nitrique : 239 g/kg - eau : 548 g/kg.- nitric acid: 239 g / kg - water: 548 g / kg.
Le traitement est effectué sur des échantillons en Inconel 600.The treatment is carried out on Inconel 600 samples.
Les conditions opératoires sont les suivantes : Débit d'electrolyte : 20 1/hThe operating conditions are as follows: Electrolyte flow rate: 20 1 / h
Température 20°CTemperature 20 ° C
Densité de courant 1 A/cm2 Current density 1 A / cm 2
Distance Anode-Cathode : 2 cmAnode-Cathode distance: 2 cm
Surface traitée : 30 cm2. L'objectif d'un tel traitement est d'aboutir au lissage et au brillantage de la surface des échantillons en Inconel 600.Treated area: 30 cm 2 . The objective of such a treatment is to achieve smoothing and shining of the surface of the samples in Inconel 600.
Pour mesurer l'état de la surface, on utilise deux types de mesures :To measure the surface condition, two types of measurements are used:
1° ) Mesures de profil de rugosité1 °) Roughness profile measurements
Ces mesures sont reflétées essentiellement par deux paramètres : d'une part, la rugosité arithmétique (Ra) et d'autre part la rugosité maximale (Rmax) toutes deux exprimées en micromètres.These measurements are mainly reflected by two parameters: on the one hand, the arithmetic roughness (Ra) and on the other hand the maximum roughness (Rmax) both expressed in micrometers.
Ces mesures de rugosité ont été effectuées avec un appareil "SURFASCAN" de la Société SOMICRONIC. La longueur d'évaluation est de 20 mm ; et les mesures sont effectuées selon les normes NF-E05-015 et NF-E05-052.These roughness measurements were carried out with a "SURFASCAN" device from the company SOMICRONIC. The evaluation length is 20 mm; and the measurements are carried out according to standards NF-E05-015 and NF-E05-052.
Le filtre éventuellement utilise était de 0, 8 mm.The filter possibly used was 0.8 mm.
Les échantillons de départ en Inconel 600 sont poncés et les valeurs des paramètres de départ sont donc les suivantes : 0, 9 < Ra < 1, 35 μm .The starting samples in Inconel 600 are sanded and the values of the starting parameters are therefore the following: 0, 9 <Ra <1, 35 μm.
Les résultats obtenus sont les suivants et sont présentés dans le Tableau 1.The results obtained are as follows and are presented in Table 1.
TABLEAU 1TABLE 1
Les profils de rugosité bi et tridimensionnels présentes sur les figures 4 a 9 montrent que l'on observe une disparition des micro-rugosites, une diminution de la rugosité arithmétique, ainsi qu'un planage de l'échantillon The bi- and three-dimensional roughness profiles present in FIGS. 4 to 9 show that we observe a disappearance of the micro-roughnesses, a decrease in the arithmetic roughness, as well as a leveling of the sample.
2 ° ) Mesures d'indices de brillance et d'indices de voile optique2) Measurements of gloss indices and of optical haze indices
Des mesures d'indices de brillance et des mesures d'indices de voile optique ont ete effectuées sur les échantillons.Gloss index measurements and optical haze index measurements were carried out on the samples.
Ces mesures ont ete effectuées selon les normes suivantes : DIN 67530 ; ISO 2813 ; ASTM D523 en mettant en oeuvre un brillancemetre "HAZEGLOSS" de la Société BYK GARDNER. L'indice de voile optique est défini par la mesure de la lumière diffuse dans une géométrie a 20 degrés et 1 ' indice de brillance par le rapport intensité reflechie/mtensite émise, suite a une reflexion speculaire. Les résultats sont donnes dans les tableauxThese measurements were carried out according to the following standards: DIN 67530; ISO 2813; ASTM D523 by using a "HAZEGLOSS" glossmeter from the BYK GARDNER Company. The optical haze index is defined by measuring the diffuse light in a geometry at 20 degrees and the brightness index by the reflected intensity / emitted intensity ratio, following a specular reflection. The results are given in the tables
2 et 3 suivants.2 and 3 following.
Le tableau 2 donne les résultats lorsque la mesure est effectuée perpendiculairement aux raies de ponçage ; il s'agit du cas le plus défavorable. Le tableau 3 donne les résultats effectues parallèlement aux rayures • il s'agit du cas le plus favorable, puisque la lumière n'est pas diffractee par les rayures, mais par les microdefauts de surface TABLEAU 2Table 2 gives the results when the measurement is made perpendicular to the sanding lines; this is the worst case. Table 3 gives the results carried out parallel to the stripes • this is the most favorable case, since the light is not diffracted by the stripes, but by the surface micro-faults TABLE 2
TABLEAU 3TABLE 3
ee
Des observations optiques complètent les Ό mesures effectuées ci-dessus :Optical observations complete the Ό measurements made above:
- les échantillons d'Inconel 600 obtenus par ce traitement d'électropolissage présentent à l'oeil nu un aspect brillant,- the Inconel 600 samples obtained by this electropolishing treatment present a shiny appearance to the naked eye,
- αes observation au microscope électronique a balayage !•> (MEB) (conditions d'observation : grandissements X 500) d-> la surface de l'échantillon d'Inconel 600 ayant subi - - traitement d'électropolissage (érosion de 30 μm) ~"r tient clairement une surface nette, lisse et propre, SαP.a attaque cristallographique (voir figures 2 et 3) . >) z.<~ effet dans le cas contraire, la surface aurait un -socet mat . EXEMPLE 2 RESULTATS EN ELECTROPOLISSAGE sur des aciers inoxydables austénitiques (316L et 304L) , austénoferritiques 308 L, et sur l' Inconel .- observation by scanning electron microscope! • > (SEM) (observation conditions: magnifications X 500) d-> the surface of the sample of Inconel 600 having undergone - - electropolishing treatment (erosion of 30 μm) ~ " r clearly maintains a clean surface , smooth and clean, SαP.a crystallographic attack (see Figures 2 and 3).>) z. < ~ effect otherwise, the surface would have a matt -socet. EXAMPLE 2 RESULTS IN ELECTRO-POLISHING on austenitic stainless steels (316L and 304L), austenoferritic 308 L, and on Inconel.
Le traitement d'électropolissage est effectué avec un electrolyte selon l'invention dont la composition est la suivante :The electropolishing treatment is carried out with an electrolyte according to the invention, the composition of which is as follows:
- acide glycolique : 272 g/kg- glycolic acid: 272 g / kg
- acide nitrique : 305 g/kg- nitric acid: 305 g / kg
- eau : 423 g/kg. On réalise les courbes intensités-potentiels (Fig. 10) a l'aide d'une électrode a disque tournant de surface 0,2 mm2 à 25°C et à une vitesse de rotation de 1000 tr/mm.- water: 423 g / kg. The intensity-potential curves are produced (Fig. 10) using a rotating disk electrode with a surface area of 0.2 mm 2 at 25 ° C and a speed of rotation of 1000 rpm.
Les courbes intensités-potentiels obtenues (où sont portés en abscisse le potentiel exprimé en V par rapport à l'électrode au calomel saturé (ECS) et en ordonnée la densité de courant en mA/cm2) pour l'acier 304L (en tirets) pour l'acier 316L (en trait plein), pour l'acier 308L (en trait mixte) et pour 1 ' Inconel (en pointillés) montrent que 1 ' electrolyte selon l'invention permet de polir tous les types d'aciers inoxydables, qu'ils soient austémtiques (304L et 316L), ferπtiques ou austéno-ferπtiques (308L comme dans l'Exemple 1), et les alliages de type Inconel. La surface obtenue est dans tous les cas polie et brillante. EXEMPLE 3 (COMPARATIF) :The intensity-potential curves obtained (where the potential expressed in V on the abscissa is plotted relative to the saturated calomel electrode (DHW) and on the ordinate the current density in mA / cm 2 ) for 304L steel (in dashes) ) for 316L steel (solid line), for 308L steel (dashed line) and for Inconel (dotted line) show that the electrolyte according to the invention makes it possible to polish all types of stainless steels , whether they are austemetic (304L and 316L), ferπtic or austeno-ferπtic (308L as in Example 1), and Inconel type alloys. The surface obtained is in all cases polished and shiny. EXAMPLE 3 (COMPARATIVE):
On effectue un traitement d'électropolissage dans les mêmes conditions que l'exemple 2 sur des échantillons analogues d'acier 308L, mais en utilisant un electrolyte classique d'électropolissage ayant la composition suivante :An electropolishing treatment is carried out under the same conditions as Example 2 on similar samples of 308L steel, but using a conventional electropolishing electrolyte having the following composition:
- acide sulfurique : 440 g/kg,- sulfuric acid: 440 g / kg,
- acide phosphorique : 440 g/kg, - eau : 120 g/kg. Les échantillons d'acier 308L obtenus par ce traitement d'électropolissage présentent ur aspect mat .- phosphoric acid: 440 g / kg, - water: 120 g / kg. The 308L steel samples obtained by this electropolishing treatment have a matt appearance.
Une observation au microscope électronique à balayage MEB de la surface de l'échantillon d'acier 308L, réalisée dans les mêmes conditions que pour l'exemple 2, ayant subi le traitement d'électropolissage (érosion de 40 μm) montre clairement qu'une attaque de la ferrite s'est produite, ce qui confirme l'aspect mat observé (Fig. 1) .Observation with a SEM scanning electron microscope of the surface of the 308L steel sample, carried out under the same conditions as for Example 2, having undergone the electropolishing treatment (erosion of 40 μm) clearly shows that a Ferrite attack has occurred, which confirms the dull appearance observed (Fig. 1).
On obtient donc, grâce au procédé selon l'invention, mettant en oeuvre un electrolyte spécifique, un brillantage de la surface en acier austeno-ferritique sans attaque préférentielle du reseau ferπtique, alors que 1 ' electrolyte de l'art antérieur donne une surface mate et une attaque de la ferrite . EXEMPLE 4 : RESULTATS EN DECONTAMINATIONWe therefore obtain, thanks to the method according to the invention, using a specific electrolyte, a brightening of the austeno-ferritic steel surface without preferential attack of the ferπtique network, while the electrolyte of the prior art gives a matt surface and a ferrite attack. EXAMPLE 4: RESULTS IN DECONTAMINATION
Un electrolyte selon l'invention ayant la même composition que celui de l'exemple 1 est mis en oeuvre dans les conditions suivantes :An electrolyte according to the invention having the same composition as that of Example 1 is used under the following conditions:
- Régime laminaire- Laminar regime
- Température : 25°C- Temperature: 25 ° C
- Densité de courant : 1,5 A/cm2 - Surface traitée : 28 a 30 cm2 (selon- Current density: 1.5 A / cm 2 - Surface treated: 28 to 30 cm 2 (depending on
1 ' échantillon) .1 sample).
La surface traitée est une surface contaminée en Cobalt 60 faisant partie d'une manchette thermique en acier inox 304L prélevée sur la centrale du Blayais (Gironde - France) .The treated surface is a Cobalt 60 contaminated surface forming part of a thermal sleeve in 304L stainless steel taken from the Blayais power station (Gironde - France).
A des fins de comparaison, on a également mis en oeuvre dans les mêmes conditions et sur la même surface, 1 ' electrolyte suivant αe l'art antérieur.For comparison purposes, the electrolyte according to the prior art has also been used under the same conditions and on the same surface.
Il s'agit d'un electrolyte suifo-phosphorique ayant la composition qui suit : - acide sulfurique : 440 g/kgIt is a sulfophosphoric electrolyte having the following composition: - sulfuric acid: 440 g / kg
- acide phosphorique : 220 g/kg- phosphoric acid: 220 g / kg
- eau : 340 g/kg.- water: 340 g / kg.
Les résultats sont rassemblés dans le tableau 4 ci-dessous.The results are collated in Table 4 below.
TABLEAU 4TABLE 4
On note que 1 'electrolyte selon l'invention permet une réduction de l'activité significative, supérieure à 1 ' electrolyte de comparaison, sans en présenter les inconvénients.It should be noted that the electrolyte according to the invention allows a significant reduction in activity, greater than the comparison electrolyte, without having the drawbacks thereof.
L' electrolyte de l'invention est utilisable en particulier pour décontaminer les composants des réacteurs à eau pressurisée REP et permet de réduire suffisamment les "points chauds" pour permettre l'intervention des opérateurs en maintenance. The electrolyte of the invention can be used in particular to decontaminate the components of PWR pressurized water reactors and makes it possible to sufficiently reduce "hot spots" to allow the intervention of operators in maintenance.

Claims

REVENDICATIONS
1. Electrolyte d'électropolissage caractérisé en ce qu'il est constitué d'un mélange d'acide glycolique, d'acide nitrique et d'eau dans les concentrations suivantes :1. Electropolishing electrolyte characterized in that it consists of a mixture of glycolic acid, nitric acid and water in the following concentrations:
- acide glycolique de 152 à 538 g/kg,- glycolic acid from 152 to 538 g / kg,
- acide nitrique de 170 à 568 g/kg,- nitric acid from 170 to 568 g / kg,
- eau de 280 à 678 g/kg.- water from 280 to 678 g / kg.
2. Procédé d'électropolissage d'un acier inoxydable ou d'un alliage de nickel caractérisé en ce que ledit acier inoxydable ou alliage de nickel est mis en contact avec 1 ' electrolyte selon la revendication 1.2. A method of electropolishing a stainless steel or a nickel alloy characterized in that said stainless steel or nickel alloy is brought into contact with one electrolyte according to claim 1.
3. Procédé selon la revendication 2, caractérisé en ce que l'acier inoxydable est choisi parmi les aciers inoxydables ferritiques, austémtiques et austénoferritiques .3. Method according to claim 2, characterized in that the stainless steel is chosen from ferritic, austemic and austenoferritic stainless steels.
4. Procédé selon la revendication 2, caractérisé en ce que l'alliage de nickel est choisi parmi 1 ' Inconel 600, 1 ' Inconel 690 et 1 ' Inconel 800. 5. Procédé selon la revendication 2, caractérisé en ce que la densité de courant est comprise entre 0,5 et 1,4. Method according to claim 2, characterized in that the nickel alloy is chosen from 1 'Inconel 600, 1' Inconel 690 and 1 'Inconel 800. 5. Method according to claim 2, characterized in that the density of current is between 0.5 and 1,
5 A/cm2.5 A / cm 2 .
6. Procédé selon la revendication 2, caractérisé en ce que 1 ' électropolissage est effectué à température ambiante.6. Method according to claim 2, characterized in that one electropolishing is carried out at room temperature.
7. Procédé selon la revendication 2, caractérisé en ce que le traitement de 1 ' electrolyte usé comprend une oxydation en voie humide de l'acide glycolique en gaz carbonique, moyennant quoi on obtient un effluent nitrique qui peut être envoyé à la station de traitement des effluents.7. Method according to claim 2, characterized in that the treatment of the spent electrolyte comprises a wet oxidation of glycolic acid to carbon dioxide, whereby a nitric effluent is obtained which can be sent to the treatment station effluents.
8. Procédé selon la revendication 2, caractérisé en ce que le traitement de 1 ' electrolyte usé comprend une distillation dudit electrolyte, suivie d'une calcination des concentrats. 8. Method according to claim 2, characterized in that the treatment of the spent electrolyte comprises a distillation of said electrolyte, followed by a calcination of the concentrates.
9. Procédé selon la revendication 8, caractérisé en ce que les résidus de la calcination des concentrats issus de ladite distillation sont vitrifiés. 9. Method according to claim 8, characterized in that the residues from the calcination of the concentrates from said distillation are vitrified.
10. Procédé selon la revendication 8, caractérisé en ce que le distillât issu de ladite distillation est recyclé en vue de la réutilisation de l'acide nitrique dans le procédé d'électropolissage.10. The method of claim 8, characterized in that the distillate from said distillation is recycled for the reuse of nitric acid in the electropolishing process.
11. Procédé selon la revendication 2, caractérisé en ce que 1 'electrolyte est mis en contact avec la surface contaminée en radioéléments d'un acier inoxydable ou d'un alliage au nickel.11. Method according to claim 2, characterized in that the electrolyte is brought into contact with the surface contaminated with radioelements of a stainless steel or a nickel alloy.
12. Procédé selon la revendication 2, caractérisé en ce que l'acier inoxydable ou l'alliage de nickel sont constitutifs d'un composant d'une centrale nucléaire ou d'une usine de retraitement. 12. Method according to claim 2, characterized in that the stainless steel or the nickel alloy constitute a component of a nuclear power plant or a reprocessing plant.
EP97918208A 1996-04-12 1997-04-11 Elctrolyte for electropolishing, method of electropolishing a stainless steel or a nickel alloy utilizing the said electrolyte, and its application to decontamination Expired - Lifetime EP0892862B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FR9604586A FR2747399B1 (en) 1996-04-12 1996-04-12 ELECTROLYTE FOR ELECTRO-POLISHING, METHOD FOR ELECTRO-POLISHING A STAINLESS STEEL OR A NICKEL ALLOY USING THE SAME, AND ITS APPLICATION TO DECONTAMINATION
FR9604586 1996-04-12
PCT/FR1997/000648 WO1997039168A1 (en) 1996-04-12 1997-04-11 Elctrolyte for electropolishing, method of electropolishing a stainless steel or a nickel alloy utilizing the said electrolyte, and its application to decontamination

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EP0892862A1 true EP0892862A1 (en) 1999-01-27
EP0892862B1 EP0892862B1 (en) 2000-01-12

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EP (1) EP0892862B1 (en)
DE (1) DE69701135T2 (en)
FR (1) FR2747399B1 (en)
WO (1) WO1997039168A1 (en)

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US11578016B1 (en) 2021-08-12 2023-02-14 Saudi Arabian Oil Company Olefin production via dry reforming and olefin synthesis in a vessel
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US11617981B1 (en) 2022-01-03 2023-04-04 Saudi Arabian Oil Company Method for capturing CO2 with assisted vapor compression

Also Published As

Publication number Publication date
DE69701135T2 (en) 2000-08-31
FR2747399B1 (en) 1998-05-07
WO1997039168A1 (en) 1997-10-23
EP0892862B1 (en) 2000-01-12
DE69701135D1 (en) 2000-02-17
FR2747399A1 (en) 1997-10-17

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