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
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
  • C23G1/025—Cleaning or pickling metallic material with solutions or molten salts with acid solutions acidic pickling pastes
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/14—Cleaning or pickling metallic material with solutions or molten salts with alkaline solutions

Definitions

• the present invention relates to an organic decontamination gel usable for radioactive decontamination of surfaces, in particular of metallic surfaces.
• organic gel is meant, according to the invention, a gel in which the viscosifying agents are essentially organic, that is to say free of any inorganic or mineral material.
• the decontamination of parts soiled by radioactive elements can be carried out either by mechanical treatments or by chemical treatments.
• the methods using mechanical treatments have the disadvantage of causing a more or less significant modification of the surface of the part and of being, moreover, difficult to implement on parts of complicated shape.
• the methods of treatment by dipping which essentially consist in entraining the radioactive elements fixed on the surface of the part by means of solutions of active decontamination agents, in particular of Ce (IV) stabilized in strong concentrated acid medium such as acid. nitric or sulfuric, have the disadvantage of leading to the production of large volumes of effluents whose subsequent treatment in particular by concentration is very expensive.
• the dipping methods using solutions pose certain problems for the treatment of large parts which it is difficult to immerse and to fully immerse in the reagent solution.
• Decontamination solutions in fact only allow treatment by soaking of removable metal parts of limited sizes, that is to say that these solutions can in practice be used only in the context of the dismantling of radioactive installations.
• Decontamination gels can therefore be described as colloidal solutions comprising a generally mineral viscous agent such as alumina or silica and an active decontamination agent, for example an acid, a base, an oxidizing agent, a reducing agent or a mixture of these, which is chosen in particular according to the nature of the contamination and the surface.
• An oxidizing gel for stainless steels will allow the elimination of fixed contamination hot and cold.
• a reducing gel will preferably be used in addition to the oxidizing gel and alternately for the dissolution of the hot-formed oxides, for example in the primary circuit of pressurized water reactors (PWR).
• a decontaminating gel consisting of a colloidal solution of an organic or inorganic compound is used, to which a decontaminating product such as hydrochloric acid, stannous chloride, oxine and / or sodium fluoride is optionally added.
• a decontaminating product such as hydrochloric acid, stannous chloride, oxine and / or sodium fluoride is optionally added.
• these gels give satisfactory results, they nevertheless have the drawback of being able to eliminate the encrusted radioactivity only over a small thickness of the surface of the part, for example over a thickness of approximately 1 ⁇ m.
• Document FR-A-2 656 949 describes an oxidizing decontaminating gel which makes it possible to remove the radioactive elements deposited on the part as well as the radioactive elements encrusted on its surface.
• This decontaminating gel consists of a colloidal solution comprising: a) 8 to 25% by weight of a mineral gelling agent, preferably based on silica, preferably fumed silica or alumina, b) 3 to 10 mol / 1 of a mineral base or of a mineral acid, and c) 0.1 to 1 mol / 1 of an oxidizing agent such as
• Ce, Co or Ag having a normal Eo redox potential greater than 1400 mV / ENH (normal hydrogen electrode) in a strong acid medium (pH ⁇ 1) or in the reduced form of this oxidizing agent.
• the gel also comprises 0.1 to 1 mol / l of a compound d) capable of oxidizing the reduced form of this oxidizing agent.
• a compound d) capable of oxidizing the reduced form of this oxidizing agent.
• This oxidizing gel does not, however, have sufficient effectiveness with respect to the adherent metal oxide layers deposited on the surface of alloys such as austenitic steels, the Inconel 600 and the Incoloy.
• Document FR-A-2 695 839 therefore describes a reducing decontaminating gel which makes it possible to remove these adherent metal oxide layers and which comprises: a) 20 to 30% by weight of a mineral gelling agent, preferably based on alumina, b) 0.1 to 14 mol / l of a mineral base, such as NaOH or KOH, and c) 0, 1 to 4.5 mol / 1 of a reducing agent having an oxidoreduction potential Eo of less than -600 mV / ENH in a strong base medium (pH> 13) chosen from borohydrides, sulfites, hydrosulfites, sulfides, hypophosphites, zinc and hydrazine.
• a strong base medium chosen from borohydrides, sulfites, hydrosulfites, sulfides, hypophosphites, zinc and hydrazine.
• the application of gels to the surface, for example the metal surface, to be decontaminated is preferably carried out by spraying with a spray gun, for example under a pressure which can range from 50 to 160 bars and even beyond, the gel being stirred before spraying to make the gel homogeneous. After an adequate duration of action, the gel is rinsed by spraying water, then the effluents generated are treated for example by neutralization, decantation and filtration. All the gels described above, whether alkaline, acidic, reducing or oxidizing, have, in addition to the advantages already mentioned above, such as the possibility of treating parts of complex shape, the advantages in particular of easy implementation.
• control of this thixotropy is fundamental to allow a projection and an optimal adhesion of the gel on the surface to be treated.
• the speed of resumption of gels, or partial or total restructuring, constitutes the essential concept for their projection.
• the restructuring means a return to gelation, therefore an adhesion to the surface, and a short recovery time characterizes a gel quickly recovering sufficient viscosity after spraying to avoid any sagging.
• the incorporation into the viscosifier of the decontamination gel, in addition to the mineral viscosifier, of an organic viscosifier (called coviscosant) makes it possible to greatly improve the rheological properties of the gels, and to decrease significantly their mineral load and the solid waste produced without the corrosive properties and other decontamination qualities of these gels being affected.
• the gels described in this document are perfectly sprayable, are easily removed by rinsing after application, filtration during the treatment of effluents is facilitated and the volume of ultimate solid waste is reduced accordingly.
• the organic co-viscous polymer or surfactant is easily degraded during the treatment of the effluents.
• the mineral load of the gels described in document FR-A-2 746 328 is still significant, since it is generally close to 5%, which implies in particular the need for a complex filtration system.
• the intervening personnel are exposed to a certain dose of radiation.
• the object of the present invention is to provide a decontamination gel which meets, among other things, all of the needs mentioned above.
• the object of the present invention is also to provide a decontamination gel which does not have the drawbacks, defects, limitations and disadvantages of the methods of the prior art and which solves the problems of the prior art.
• a decontamination gel consisting of a solution comprising: a) a viscosity agent; b) an active decontamination agent; in which the viscosity agent a) is an exclusively organic viscosity agent chosen from water-soluble organic polymers.
• the gels according to the invention therefore do not contain any mineral viscosants, such as silica or alumina. Consequently, since their mineral load, linked to the viscosant is substantially zero, all the disadvantages due to the solid waste created by this mineral load are eliminated, in particular a complex and costly filtration and recovery system for this waste. is no longer necessary.
• the only waste produced in small quantities contains only easily degradable organic products, preferably exclusively composed of carbon, nitrogen, oxygen and hydrogen without elements prohibited in nuclear power, such as sulfur or halogens.
• the gels according to the invention surprisingly retain their characteristic structure much longer than gels comprising a viscous mineral, and dry much less quickly, while also retaining their corrosion properties. Their elimination by rinsing is thus facilitated and the volume of rinsing effluents reduced.
• the gels according to the invention exhibit excellent temperature resistance - for example, up to 80 ° C. - or, in other words, excellent heat resistance, that is to say that the recycling and the extended corrosion properties of these gels are, among other things, preserved at these high temperatures. This property is particularly important in certain specific uses, where the surfaces to be treated are permanently at a high temperature, for example, greater than or equal to 40 ° C.
• the preparation of the gels according to the invention is easy and rapid and uses only readily available reagents, of low cost; the gels according to the invention can therefore be implemented on a large scale and on an industrial level.
• the gels according to the invention come under a completely surprising approach and going against what could have been expected. Indeed, nothing could have suggested that the total elimination of the mineral viscosant in the gels of the prior art, represented in particular by FR-A-2 746 328, would lead to gels having all the required properties, in particular for regarding their rheology.
• the viscosity agent a) is an exclusively organic viscosity agent which is chosen from water-soluble polymers.
• polymers can be used in the gel at a content, generally from 1 to 11%, preferably 2 to 8% by weight, more preferably from 4 to 6% by weight; at these contents, they allow in particular a significant improvement in the rheological properties of the gels and a total elimination of the mineral filler, for example, of alumina and / or silica.
• the polymer generally has a molar mass defined by the average molar mass by weight of 200,000 to 5,000,000 g / mol.
• the term “polymer according to the invention” means both the opolymers and the block or block copolymers.
• this polymer must fulfill a certain number of conditions linked in particular to its use in nuclear installations.
• the polyacrylic acid polymer consists of the repetition of the following monomer unit (I): -CH 2 CH (C0 2 H) -.
• the average molar mass by weight of polyacrylic acid polymers is generally from 450,000 to 4,000,000. Preferably, the average molar mass by weight is 4,000,000. Indeed, it has been demonstrated that the formation of 'a gel requires increasing percentages of polymer with the decrease of the macromolecular chain. This is due to the fact that an average molar mass by significant weight corresponding to a longer chain length must promote better crosslinking and therefore the formation of a more viscous gel for a smaller quantity of polymer.
• Copolymers of acrylic acid with acrlamide generally have an average molar mass by weight from 200,000 to 5,000,000; preferably from 200,000 to 4,000,000.
• the percentage of each of monomers in the copolymer of acrylic acid and acrylamide is variable; the copolymer will generally comprise from 95 to 60% by weight of acrylic acid and from 5 to 40% by weight of acrylamide.
• a preferred copolymer is a copolymer with an average molar mass by weight of 200,000 and whose percentage by weight of acrylamide is 10%.
• copolymers can be block or random.
• the random copolymer of formula (I):
• Suitable acrylic acid-acrylamide copolymers are marketed by the SCOTT BADER Company ®, as the TEXIPOL ® such as TEXIPOL ® 63 - 510.
• This product comes in the form of an aqueous solution at 25 % of a polyacrylic acid-acrylamide copolymer (molar mass: 10 6 ; percentage of acrylamide: 20 - 30%) dispersed in an organic phase composed of toluene hite spirit or 20% isopar in the form of an ulsion with 5% surfactant.
• the gels according to the invention can also comprise an organic surfactant which is included in the organic viscosity agent.
• n defines the length of the aliphatic chain and is an integer which can vary from 6 to 18, preferably from 6 to 12
• m controls the size of the pole head and is an integer which can vary from 1 to 23, preferably 2 to 6.
• the compounds C 6 E 2 are examples of surfactants.
• Such compounds C n E m are available from ALDRICH Company ® ® and SEPPIC.
• the nature of the surfactant depends on the type of decontamination gel used, that is to say on the nature and content of the active decontamination agent b) and on the nature and content of the agent. organic polymeric viscosant.
• the compounds C n E m are particularly suitable for use in gels comprising polyacrylic acid, in particular particularly in acid oxidizing gels comprising polyacrylic acid.
• the surfactant content depends on the nature of the decontamination gel as well as on the concentration and the nature of the organic viscosity agent.
• This surfactant content will generally be between 0.1 and 5% by weight, preferably between 0.2 and 2% by weight, more preferably between 0.5 and 1% by weight.
• the viscosity agent a) according to the invention can be used in any decontamination gel regardless of the type thereof, that is to say whatever the active decontamination agent b) used in decontamination gel.
• the decontamination gel according to the invention may contain as active decontamination agent b) an acid, preferably a mineral acid preferably chosen from acid hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid and their mixtures.
• the acid is generally present at a concentration of 1 to 10 mol / 1, preferably from 3 to 10 mol / 1.
• Such a gel is particularly suitable for eliminating cold-fixed contamination on ferritic steels.
• the viscosity agent is preferably a polyacrylic acid, more preferably of average molar mass in high weight, that is to say greater than or equal to 450,000, for example, close to 4,000 000.
• the viscosity agent is in this type of gel generally present at a concentration of 3 to 12% by weight.
• the decontamination gel according to the invention can also contain, as active decontamination agent b), a base, preferably an inorganic base, preferably chosen from soda, potash and their mixtures.
• a base preferably an inorganic base, preferably chosen from soda, potash and their mixtures.
• the base is generally present at a concentration of 0.1 to 14 mol / l.
• alkaline gel has interesting degreasing properties and is particularly suitable for eliminating contamination which is not fixed on stainless and ferritic acids.
• the viscosity agent is preferably an acrylic acid-acrylamide copolymer, for example of the TEXIPOL type, 63-510.
• a typical example of a basic or alkaline decontamination gel according to the invention consists of a solution comprising:
• Such a basic thixotropic gel according to the invention without any viscous mineral filler has the following properties: a lifetime of the order of a week;
• this gel does not require any heating during its synthesis.
• the decontamination gel according to the invention may also contain as active decontamination agent b) a reducing agent
• this reducing agent may for example be a reducing agent such as that described in document FR-A-2 695 839 in which the reducing agent used is a reducing agent having a normal redox potential E 0 less than -600 V / ENH (normal hydrogen electrode) in a strong base medium (pH> 13).
• a reducing agent such as that described in document FR-A-2 695 839 in which the reducing agent used is a reducing agent having a normal redox potential E 0 less than -600 V / ENH (normal hydrogen electrode) in a strong base medium (pH> 13).
• borohydrides, sulfites, hydrosulfites, sulfides, hypophosphites zinc, hydrazine and their mixtures.
• metal salts for example salts of alkali metals such as sodium.
• the pH of the colloidal solution is preferably greater than or equal to 14 so that the borohydride remains stable.
• the reducing agents as described in document FR-A-2 695 839 are generally associated with an inorganic base such as NaOH or KOH at a concentration generally between 0.1 and 14 mol / 1, the concentration of reducing agent being , meanwhile, generally between 0.1 and 4.5 mol / 1.
• the viscosifying agent is rather an acrylic acid-acrylamide copolymer, for example of the TEXIPOL type, 63-510.
• reducing gel is generally used in addition to and alternating with an oxidizing gel as described below.
• a typical example of a reducing decontamination gel according to the invention consists of a solution comprising: - from 9 to 11% by weight of acrylic acid-acrylamide copolymer of average molar mass by weight of 200,000, and containing 20% by weight of acrylamide;
• Such a reducing gel according to the invention has the following characteristics: - gel life around one week;
• This gel does not require any other heating during its synthesis.
• the decontamination gel according to the invention may also contain, as active decontamination agent b), an oxidizing agent.
• This oxidizing agent may for example be an oxidizing agent such as that described in document FR-A-2 659 949 in which the oxidizing agent used is an oxidizing agent which must have a normal redox potential greater than 1400 mV / ENH in a strong acid medium (pH ⁇ 1), that is to say an oxidizing power greater than that of permanganate.
• oxidizing agents are particularly suitable when the surface to be decontaminated is a metallic surface, for example of a noble alloy, such as stainless steels 304 and
• these oxidizing agents can also oxidize certain very insoluble colloidal oxides such as Pu0 2 to transform them into a soluble form such as Pu0 2 + .
• the oxidizing agent in its reduced form, for example one can use Ce, Co 11 , Ag 1 , on condition of adding to the gel a compound capable of oxidizing this form reduced, or on condition that the gel is combined with another gel or with another colloidal solution containing a compound capable of oxidizing this reduced form of the oxidizing agent.
• the compound capable of oxidizing the reduced form of the oxidizing agent can consist, for example, of an alkali metal persulfate.
• Oxidizing agents of which Cerium (IV) is preferred, are generally combined, with a mineral base, or for stabilization purposes, with a mineral acid such as HCl, H 3 P0 4 , H 2 S0 4 and preferably HN0 3 at a concentration generally between 1 and 10 mol / 1, preferably from 2 to 10 mol / 1, more preferably from 2 to 3 mol / 1, for example 2.88 mol / 1, the concentration of oxidizing agent being, for its part, generally between 0.1 and 2 mol / 1, preferably between 0.6 and 1.5 mol / 1, more preferably this concentration is 1 mol / 1.
• an oxidizing cation such as Ce, Ag or Co ⁇
• Ce, Ag or Co ⁇ When an oxidizing cation such as Ce, Ag or Co ⁇ is used as the oxidizing agent, it can be introduced in the form of one of its salts such as nitrate, sulphate or the like, but it can also be electrogenerated.
• the preferred oxidizing gels contain cerium (IV) in the form of electrified cerium (IV) nitrate Ce (N0 3 ) 4 or hexanitrato diammonium cerate (NH 4 ) 2 Ce (N0 3 ) 6 , the latter being preferred due to the relative instability of cerium (IV) nitrate in concentrated nitric medium.
• Nitric acid stabilizes cerium at the IV oxidation level, participates in corrosion and ensures, among other things, the maintenance in solution of corroded species, namely complex oxo-nitrato of the transition metals constituting the metal alloy.
• Such gels contain the organic viscosity agent, preferably polyacrylic acid at a concentration generally of 2 to 12% by weight.
• the viscosifier is a polyacrylic acid, more preferably a polyacrylic acid, of relatively high weight average molar mass, for example of 4,000,000, but it is also possible to use TEXIPOL, for example TEXIPOL 63-510, already described above.
• This type of gel can also comprise, in addition to said viscosant, a surfactant or surfactant as defined above, preferably C 6 E 2 or C ⁇ 2 E 4 , at a concentration of 0.1 to 1.5%. in weight .
• a surfactant or surfactant as defined above, preferably C 6 E 2 or C ⁇ 2 E 4 , at a concentration of 0.1 to 1.5%. in weight .
• a first typical example of an oxidizing decontamination gel according to the invention consists of a solution comprising:
• Such an oxidizing gel has the following properties
• a second typical example of an oxidizing decontamination gel according to the invention consists of a solution comprising: - from 7 to 8% by weight of polyacrylic acid with an average molar mass by weight of 450,000;
• surfactants preferably C 6 E 2 or C_ 2 E 4 .
• Such an oxidizing gel containing polyacrylic acid as viscosity agent has the following properties:
• a third typical example of an oxidizing decontamination gel according to the invention consists of a solution comprising:
• the decontaminating gels described above can be used in particular for the decontamination of metal surfaces and this, both in the context of the periodic maintenance of existing installations, as well as the dismantling of nuclear installations.
• the gels according to the invention can be used for example to decontaminate tanks, fuel storage pools, glove boxes etc.
• the subject of the invention is also a method for decontaminating a metal surface, which comprises applying to the surface to be decontaminated a decontaminating gel according to the invention, maintaining this gel on the surface for a period of time sufficient to carry out the decontamination, this duration ranging for example from 10 min. at 24 h, preferably from 30 min to 10 h, and more preferably from 2 to 5 hours, and the elimination of this gel from the metal surface thus treated, for example by rinsing or by mechanical action.
• the surface to be decontaminated can be a surface whose temperature is, even permanently, greater than or equal to 40 ° C., by example, from 40 ° C to 80 ° C.
• the amounts of gel deposited on the surface to be decontaminated are generally from 100 to
• 2000 g / m 2 preferably from 100 to 1000 g / m 2 , more preferably from 200 to 800 g / m 2 . It is obvious that the treatment can be repeated several times each time using the same gel or gels of different natures during the different successive stages, each of these stages comprising the application of a gel, the maintenance of the gel on the surface and removing the gel from the surface, for example by rinsing or mechanical action.
• the treatment can be repeated on the entire surface to be treated or on only part of it having for example a complex shape, or depending on the activity of the surface.
• the decontamination process may include the following successive steps as described in document FR-A-2 695 839: 1) apply to the surface to be decontaminated a reducing decontaminating gel according to the invention, maintain this gel on the surface for a period ranging from 10 min to 5 h and rinse the metal surface to remove this reducing gel, and 2) apply to the surface thus treated, an oxidizing gel in an acid medium, maintain this gel on the surface for a period ranging from 30 min to 5 h and rinse the metal surface thus treated to remove this oxidizing gel.
• the decontamination process may include the following steps:
• the contact time can vary between wide limits and also depends on the nature of the active decontamination agent and on the nature of the organic viscosity agent.
• the contact time is preferably from 30 min to 5 hours, more preferably from 2 to 5 hours.
• the contact time will preferably be 10 minutes to 5 hours.
• the application of the gel to the metal surface to be decontaminated can be carried out by conventional methods, for example by spraying with a spray gun, by soaking and draining, by packaging or even by means of a brush.
• we applies the gel by spraying / spraying for example under a pressure (Airless compressor) at the level of the injector ranging from 10 to 200 kg / cm 2 for example, from 10 to 160 kg / cm 2 , for example again from 50 to 100 kg / cm 2 .
• the gel can be removed, preferably by rinsing, from the treated surface, it can also be removed by other means, for example mechanical, or by a jet of gas, for example of compressed air.
• demineralized water or an aqueous solution is usually used in which the gel used can be dissolved or in which it can form a detachable and water-entrainable film.
• the rinsing can be carried out under pressure, that is to say at a pressure for example from 10 to 160 kg / cm 2 .
• the gels according to the invention comprising a viscous agent which is only organic, retain over a prolonged period, which can range up to 48 hours and more, their gel texture, the rinsing the surface is much easier, can be done at low pressure for example 15 kg / cm 2 , or even without pressure and requires a reduced amount of demineralized or other water, for example less than 10 liters / m.
• the number of rinsing treatments (or passes) during a decontamination operation is reduced, since the gel according to the invention does not contain any mineral filler.
• the quantity of effluents generated defined in particular by the volume of the rinsing effluents is greatly reduced.
• the gels of the prior art the viscosifying agent of which is mineral, in part or in whole, and which only comprise, for example, silica, become after application, and in a relatively short time, dry and cracked, rinsing is very difficult and requires a large amount of water under high pressure. As a result, large quantities of liquid effluents are generated.
• the rinsing effluents are then treated adequately, for example they can be neutralized, for example by soda in the case where an acid gel has been used.
• the effluents are then generally subjected to a solid-liquid separation, for example by filtration with a cartridge filter to give on the one hand liquid effluents, and on the other hand solid waste, the quantity of which is extremely reduced, or even zero, due to the very low mineral load of the gels according to the invention which in fact comes only from the active decontamination agent.
• the amount of mineral filler in the gel according to the invention is even so small, that it makes it possible to transfer the rinsing effluents to an evaporator without any prior treatment.
• Decontaminating the gels of the invention can be prepared in a simple manner, for example by a j outant to an aqueous solution of component b), that is to say the active decontamination agent, the thickening agent a) exclusively organic.
• the active agent b) comprises, in addition, the oxidizing agent, a mineral acid chosen, for example, from HN0 3 , HC1, H 3 P0 4 H 2 S0 4 and their mixtures, preferably HN0 3
• the following preparation process was particularly advantageous, in particular in terms of preparation time: first of all, the viscosifying agent a) is mixed with a solution of mineral acid with stirring and , optionally, heating, to dissolve the polymer and obtain a viscous and homogeneous acid gel, and then the oxidizing agent, such as
• the gels according to the invention generally have a very long storage period, however the chemical inertness of certain surfactants, although good, is limited in time, for example in the presence of an oxidant such as Ce (IV).
• Acid oxidizing gels were prepared, the active agent of which is (NH 4 ) 2 Ce (N0 3 ) e in nitric acid and which comprise an acrylic acid-acrylamide copolymer, namely TEXIPOL 63 510, as organic viscosifier.
• the gels prepared include silica (CaS 0 Sil M5) and are based on the gels described in document FR-A-2,746,328.
• These gels are prepared in the following manner: the nitric acid solution and the “TEXIPOL” are moderately heated to a temperature of approximately 50 ° C. with stirring, the time to obtain a homogeneous mixture, this time can range from about 24 hours to about 48 hours.
• Oxidizing gels without any inorganic filler (in the thickening agent) were prepared as follows: the TEXIPOL ®, whose concentration is higher than 5% by weight, is added with heating to the nitric acid solution, and forms a homogeneous solution. It then suffices to directly add (NH 4 ) 2 Ce (N0 3 ) 6 .
• Demixing occurs during mixing. It takes some time maintaining moderate stirring (3-10 days) depending on the composition of the gel TEXIPOL ® and (NH 4) 2 Ce (N0 3) 6 before obtaining the gel.
• the gels with a low cerium concentration (nos. 7, 8 and 9) have a less viscous appearance than their counterparts whose concentration is higher. Their coloring is also paler.
• the most significant corrosion power reaches 0.3 ⁇ m for gel No. 1, after a single treatment of two hours and an amount of gel equal to lkg / m.
• the corrosive power seems to be limited to a value close to 0.4 ⁇ m. it is indeed the maximum thickness eroded during the experiment over an application period of 14 hours (n ° 2). The gel became colorless, translucent and did not dry; it is easily cleaned with water under low pressure.
• the gels which have the strongest corroding powers are tgll .1 and tgll .2 which paradoxically have the lowest initial titles in Ce (IV). Furthermore, it is observed that the faster the gel setting time, the better the corrosion. Indeed the oxidation of the polymer decreases the concentration of Ce (IV) in the gel. The higher the initial titer in cerium, the longer the gel setting time.
• An optimal formulation is a balance between a percentage by weight of Texipol and an ideal concentration of Ce (IV), which must be neither too low, which gives a weak corrosion; neither too strong, which gives a long setting time and therefore low corrosion.
• the optimal percentage of Texipol must be both sufficient to impart a value of the viscosity necessary for the adhesion of the gel, and minimum in order to allow good corrosion.
• the following procedure was used for the preparation of the oxidizing gels comprising nitric acid and (NH 4 ) 2 Ce (NO 3 ) 6 , with the exception of those in which the gels comprise silica.
• the polymer and the nitric acid solution are mixed.
• the polymer dissolves quickly with manual stirring for about a quarter of an hour.
• a very viscous and homogeneous gel, of whitish appearance, is thus obtained.
• This acid gel has a fairly long shelf life and can therefore be prepared several days in advance.
• (NH 4 ) 2 Ce (N0 3 ) 6 is added , ensuring that the mixture is always homogeneous.
• the formation of lumps of (NH 4 ) 2 Ce (N0 3 ) 6 is avoided.
• the addition of diammonium hexanitrotocetate leads to a fluidification of the mixture. Resting the mixture for about an hour is necessary in order to obtain a sprayable gel.
• gels according to the invention illustrate the general corrosion-erosion power of the gels according to the invention, as well as gels comprising, in addition to the organic viscosant polymer, silica as an inorganic viscosant.
• the gels studied in these examples are acid oxidizing gels containing nitric acid and cerium hexanitrotocetate.
• the viscous polymer is a polyacrylic acid.
• the 2.88M HN0 3 gel corrodes better than the 2M gel.
• the mass loss is 26 mg higher, which corresponds to an additional erosion of 32%.
• the role played by the title in nitric acid is determinant in erosion for a constant concentration of (NH 4 ) Ce (N0 3 ) 6 .
• An effective formulation D (see below) has thus been developed.
• Gels A and B were prepared to reduce the titer in (NH 4 ) 2 Ce (N0 3 ) 6 in order to further lower the mineral load while retaining good corrosion power.
• Gel C was prepared to optimize viscosity.
• gel B did not flow after 4 hours of application. It rinses very easily. The erosion is 102 mg or 1.22 ⁇ m.
• Table VII groups together the data relating to the change in the corrosion power of gel B. Table VII
• the values of eroded thickness are spread over a narrow range of between 0.66 and 0.77 ⁇ m for a duration of application of two hours. No change in the corrosion power of the gel is noted in the period of time considered from t 0 to t 0 + 6 h.
• gel C is applied to a vertical wall (wall) or to a horizontal wall upside down (ceiling) for at least four hours to check the good adhesion of the frost during the erosion process.
• the thickness eroded as a function of the duration of application of the gel was measured. In any case, rinsing the gel is very easy.
• the erosion limit for gel C in the first pass is 120 mg (1.44 ⁇ m) for an application period of 12 hours.
• the duration of application influences the corrosion which is significant during the first four hours of contact.
• the amount of gel applied influences corrosion.
• the mass losses were 94 mg at a rate of 1 kg / m 2 and 56 mg at a rate of 0.5 kg.
• An increase in the temperature of the plate causes the gel to dry.
• the gel dries in one hour and at 80 ° C in half an hour. Eroded thicknesses of 1.07 ⁇ m and 0.95 ⁇ m are respectively obtained.
• the increase in temperature leads to greater hourly erosion. Rinsing is very easy for the plate at 40 ° C and a little less easy for the one at 80 ° C.
• the corrosion power does not decrease during the first hours of use of the gel (more than 24 hours).
• corrosion experiments carried out on gels which have been prepared for 24 hours have shown that corrosion decreases slightly. Indeed, we go from a limit corrosion of 1.44 ⁇ m for a gel applied immediately after it has been prepared, and this, for 12 hours, to a limit corrosion of 1.04 ⁇ m for a liquid gel applied 24 hours after its preparation.
• a second gel pass always increases the corrosion power when the passes are made from a gel taken at the same "age" (in the first six hours the corrosion power of the gel does not decrease). For example, we go from corrosion to first class of 1.28 ⁇ m at an erosion of 1.45 ⁇ m in the second pass for two successive passes of 4 hours each of a gel C.
• a characteristic common to all gels is a 24 hour shelf life beyond which the gel gradually loses its viscous structure.
• This example illustrates the influence of the polymer concentration on corrosion.
• the polymer concentration being increasing from PI to P4, it is thus noted that the increase in the percentage of polymers in the medium (for a constant titer in Ce (IV)) leads to a reduction in the corrosion power.
• the viscosity of the gels increases with the polymer concentration from PI to P4.
• too high a viscosity of the gels leads to inhomogeneous spreading over the surface. These lumps of gels remain red during the time of application and therefore do not allow participation in the corrosion of the entire amount of gel initially applied.
• Table IX collects the data on PI, P2, P3 and P4. The duration of the gel application is three hours and the amount applied is 1 kg / m 2 .
• This example illustrates the influence of the cerium concentration on corrosion.
• the 1.25 million polymer gives the medium a lower viscosity but it offers a more homogeneous structure (without lumps) and more flexible which allows good spreading of the gel.
• the corrosion limit of an A8 gel is 1.54 ⁇ m for an application time of 18 hours.
• Table XII collates the data relating to the corrosion experiments of viscose gels with a polyacrylic acid polymer (4,000,000 and / or 1,250,000), and coviscosed with 0.5% silica. Table XII
• gels were prepared incorporating a polyacrylic acid and a polyoxyethylene type surfactant.
• Table XIII gives the compositions of each of these gels.
• ceric solution (NH 4 ) 2 Ce (N0 3 ) 6 (1, 2M) + HN0 3 (2M) is mixed directly with the polymer and the surfactant. The mixture is homogenized by stirring.
• Table XIV summarizes the data on the corrosive power of these gels.
• the organic thickening agent is an acrylic acid-acrylamide copolymer (Texipol ®). These gels include soda, or sodium borohydride in soda as active agents. Gels containing alumina have also been prepared for comparison.
• the gels are prepared in the following manner:

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