Classifications

• • 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
• • 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
  • C23G1/10—Other heavy metals
  • C23G1/106—Other heavy metals refractory metals

Definitions

• the present invention relates to a method for carrying out the pickling, in an acid bath, of metallic products containing titanium or at least one element of the chemical family of titanium.
• the pickling operation consists of immersing the finished products in pickling baths composed of nitric acid HNO3 and hydrofluoric acid HF in a proportion of 6 to 16% of HNO3 per liter and from 1 to 5 % of HF per liter, the temperature of use of the baths being between 40 ° C to 60 ° C.
• nitric acid an acid which leads to the creation of particularly toxic NO2 vapor, and of nitrates in the effluents (nitrites and nitrates). If the maximum authorized nitrate content limit is relatively high, that relating to nitrites is much lower because nitrites lead to the formation of harmful substances nitrosamines.
• titanium transforms into TiCl3 which sublimates at 80 ° C. Before sublimation, TiCl3 decomposes into TiCl4 + TiCl2 according to the equation: 2 TiCl3 TiCl4 + TiCl2 (I)
• TiCl4 is particularly volatile, its vapor pressure at 50 ° C being equal to 42 mm of Hg.
• the subject of the invention is a process for pickling in an acid medium metallurgical products containing titanium or at least one element of the chemical family of titanium, process by which an oxidizing agent is introduced into the acid bath, avoiding the drawbacks of pickling processes described above, characterized in that, to increase the pickling kinetics, at least one peroxygen compound of titanium or at least one element of the titanium family included in the product to be stripped is formed, the metal being ionized to a higher valence, the formation of the peroxygen compound is monitored by a measurement of the redox potential, and - The amount of oxidizing agent is limited so as to maintain a redox potential below the passivation potential of the metal product.
• Such a method is based on the fact that the oxygenated compounds of the metal, when they are ionized at a higher valence, are aggressive with respect to the metal itself and its oxides ionized at a lower valence.
• the term “ionization” to a higher valency is understood in particular to mean ions such as titanate, vanadate; zirconate, niobate, tantalate and uranate.
• the acid pickling bath is a bath containing essentially an acid chosen from hydrofluoric acid, sulfuric acid, hydrochloric acid, phosphoric acid, and formic acid, but another acid can be used.
• an acid chosen from hydrofluoric acid, sulfuric acid, hydrochloric acid, phosphoric acid, and formic acid, but another acid can be used.
• an agent with a strong oxidizing power is introduced into the acid bath, which results in the formation of at least one peroxygen compound of the metal.
• titanium and the elements of the titanium family form with the oxidants oxygenated compounds.
• compounds of the type are obtained M being Ti or one of the elements of the chemical family of Ti. These compounds constitute persalts, particularly oxidizing substances.
• the oxidizing agent is chosen from hydrogen peroxide, urea peroxide or a gas such as ozone or oxygen.
• the hydrogen peroxide is introduced directly into the acid bath in an amount of less than 0.50% by weight; it can also be introduced in the form of a persalt or a peracid, a body which by decomposition in an acid medium gives hydrogen peroxide.
• Urea peroxide can be used in an amount less than 1.2% by weight.
• the method according to the invention relates to a pickling process in an acid bath of metallic products or metallic alloys containing titanium or at least one element of the chemical family of titanium, in particular vanadium, zirconium, niobium, tantalum and uranium.
• the pickling reaction mechanism will be similar for the different metals mentioned and for the alloys.
• the basic acid bath is preferably a hydrofluoric acid bath, the concentration of which is in the range 0.2-10% by weight.
• Other acids can be used such as for example sulfuric acid, provided that they contain a peroxygenated form of the metallic element of the titanium family included in the product to be stripped.
• Titanium trifluoride transforms into TiF4 tetrafluoride in the presence of an excess of HF.
• the method according to the invention consists in forming at least one oxygenated compound of the metal ionized to its higher valency and in the case of titanium stripping a peroxygenated titanium compound, pertitanate, which is particularly aggressive towards with respect to titanium and its oxides.
• pertitanate is obtained for example by the action of hydrogen peroxide on titanium fluoride, according to the reactions: Ti4+ + H2O2 + 2H2O ⁇ TiO42 ⁇ + 6H+ (III) 2TiO42 ⁇ + Ti + 16 H+ ⁇ 3Ti4+ + 8H2O (IV)
• reaction (IV) there is no longer an excess of H2 but the formation of H2O, which reduces the effect of the introduction of H+ into the meshes of the crystal lattice of the metal or of the alloy to be stripped and thereby reduces the embrittlement of the pickled product.
• Pertitanate can also be obtained by the action of urea peroxide which, by decomposition, gives hydrogen peroxide. This compound is solid, therefore more easily transportable.
• pertitanate can be achieved by injecting ozone into the bath.
• the pertitanate formation reactions are then: Ti4+ + O3 + H2O ⁇ Ti42 ⁇ + H2+ (V) 2TiO42 ⁇ + Ti + 16 H+ ⁇ 3Ti4+ + 8H2O (VI)
• Ozone can be replaced by oxygen.
• persalts that can be used are in particular: permanganates, persulfates, pertitanates, pervanadates, perborates ...
• Peracids also breaking down into H2O2 in an acid medium can be used.
• perboric acid pertitanic acid, peracetic acid, persulfuric acid which are mainly acids used in other fields of industry.
• REDOX potential is the potential difference measured between a non-corrodable electrode (for example platinum) and a reference electrode (for example Ag / AgCl or saturated calomel), these two electrodes being immersed in the bath to be studied.
• the measured value makes it possible, on the one hand, to characterize the oxidizing power of the pickling bath and on the other hand, to readjust the bath by introducing chemical compounds in order to maintain a determined oxidizing power of the bath.
• the redox potential is notably included in the interval: (+ 150, - 350) mV / Ag / Agcl.
• the method according to the invention improves the pickling efficiency of titanium and its alloys, elements of the chemical family of titanium and their alloys, and this by using a base bath preferably containing only one acid, oxidizing bath the main oxidizing agent of which is a peroxygen compound of titanium or of an element of the titanium family.
• the loss in weight of flat products is 40 to 80 g / m2.
• the surface condition obtained is comparable to that obtained using the hydrofluoric nitro process. There is no over-stripping effect.
• the use of hydrogen peroxide gives a treated, bleached surface with appreciable aesthetic appearance.
• the advantage of the process according to the invention lies in particular in the fact that the oxidant is created "in situ" without the addition of toxic or polluting substances.
• the pickling reaction being carried out mainly by pertitanate and / or a peroxide of the elements of the titanium family, the consumption to hydrofluoric acid is reduced.
• peroxygenated compounds pertitanates, perzirconates, pertantalates, perniobates, peruranates, pervanadates
• H2O2 a substance which is particularly interesting from an ecological point of view because it breaks down into H2O and O2, an element favorable to biogenesis.
• the method according to the invention therefore leads to the reduction, or even the elimination, of toxic substances in the atmosphere and in the effluents.
• the treatment is in accordance with ministerial instructions from industrialized countries.
• a treatment with lime milk leads to precipitation of metallic hydroxides without rejection of toxic anionic forms, which is not the case with nitrates, all of which are soluble in water.
• the process according to the invention is a clean and ecological process.

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• Chemical & Material Sciences (AREA)
• Metallurgy (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Organic Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• Transition And Organic Metals Composition Catalysts For Addition Polymerization (AREA)
• Materials For Medical Uses (AREA)
• Chemical Treatment Of Metals (AREA)
• Cosmetics (AREA)
• Manufacture And Refinement Of Metals (AREA)

Applications Claiming Priority (2)

Publications (3)

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ID=9384174

Family Applications (1)

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Cited By (4)

Families Citing this family (4)

Family Cites Families (10)

• 1989
  • 1989-07-26 FR FR8910093A patent/FR2650303B1/fr not_active Expired - Fee Related
• 1990
  • 1990-07-25 CA CA002037893A patent/CA2037893C/en not_active Expired - Fee Related
  • 1990-07-25 DE DE69013447T patent/DE69013447T2/de not_active Expired - Fee Related
  • 1990-07-25 EP EP90402144A patent/EP0415807B1/de not_active Expired - Lifetime
  • 1990-07-25 RU SU4895068/12A patent/RU2168560C2/ru not_active IP Right Cessation
  • 1990-07-25 ES ES90402144T patent/ES2064686T3/es not_active Expired - Lifetime
  • 1990-07-25 JP JP2511471A patent/JP2945136B2/ja not_active Expired - Fee Related
  • 1990-07-25 AT AT90402144T patent/ATE113080T1/de not_active IP Right Cessation
  • 1990-07-25 WO PCT/FR1990/000564 patent/WO1991002109A1/fr not_active Ceased
  • 1990-07-25 KR KR1019910700229A patent/KR100191864B1/ko not_active Expired - Fee Related
  • 1990-07-25 AU AU61684/90A patent/AU634277B2/en not_active Ceased
• 1991
  • 1991-03-22 FI FI911398A patent/FI93371C/fi active

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