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
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F15/00—Other methods of preventing corrosion or incrustation
• • 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
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/80—After-treatment
• • 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
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
  • C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
  • C23F13/04—Controlling or regulating desired parameters
• • 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
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
  • C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
  • C23F13/06—Constructional parts, or assemblies of cathodic-protection apparatus

Definitions

• the present invention relates to the protection of metals against corrosion at high temperatures, more particularly, to a process of protecting metals against such corrosion wherein a potential difference is applied between the metal to be protected and a substantially continuous layer of corrosion product formed on the external surface of this metal.
• the positive electrode is made of -a material having a higher conductivity than that of said corrosion product and is non-fusible and substantially non-corrodible at the high temperature of use.
• metal or alloy to be protected will be referred to as metal for sake of brevity.
• the electric current between the electrodes must have a well-defined direction, which prohibits the use of an alternating current. Only a direct cunrent, a pulsed unidirectional current or a rectified current can thus be used for the purpose of this invention.
• the current density may then be reduced to very low values without any new increase of the corrosion to be observed.
• the current may even be completely interrupted during relatively large periods without any new increase of the corro-v sion to be observed.
• Such a result is of considerable industrial interest since it provides means for manufacturing metal pieces pretreated so as to protect them against corrosion during a subsequent use in the presence of corrosive gases at high temperatures, whereas the application of the general process according to the invention with low current densities requires the concomitant supply of current during the period of use of the metal under corrosive conditions.
• the corrosion product formed in a first stage after the current is supplied has a particular structure which prevents a new penetration of the gas toward-s the metal or at least a normal development of the corrosion process.
• the presence of a layer of corrosion product of the metal between the latter and the positive electrode is. an essential feature for the practice of this invention.
• This layer will be preferably chosen as thin as possible but, nevertheless, sufficient to avoid any direct contact between the positive electrode and the metal to be protected.
• the corrosion product consists of a derivative of the metal to be protected, stable at high temperatures and formed by attack of the latter by means of a corrosive material or compound. This attack will be advantageously carried out at a high temperature and, for instance, at that temperature at which said metal will be subjected during its intended use.
• the corrosion product may be of a mineral nature such as, for instance, a salt, a sulfide or an oxide of the metal. It may be either of the same nature as that which would be normally formed on the metal due to the action of the corrosive medium if said metal was not protected against corrosion according to the process of this invention, or of a different nature.
• the corrosion product will be preferably selected to have the lowest possible permeability with respect to the corrosive materials, such as gases, so as to obtain the above mentioned permanent'protection.
• the layer of the corrosion product for instance, is easily obtained by contacting at high temperature the metal to be protected with a corrosive agent, preferably in the gaseous form and preferably in quiet atmosphere.
• a simple corrosion agent would be air.
• a direct contact of the positive electrode with the corrosion product layer is strictly necessary for obtaining the protection of the metal against corrosion according to this invention since such a protection is not achieved satisfactorily when this condition is not fulfilled and as long as this electrode is entirely isolated from the corrosion product by a continuous coating of corrosive gas as thin as it may be.
• connection of the negative terminal of a current generator to the metal to be protected and of the positive terminal of said generator to an auxiliary electrode positioned in the corrosive gas in front of said metal provides a negligible, if any, protection of the latter.
• the positive electrode may be made of any material having a conductivity higher than that of the oxidation product and which is resistant to high temperatures. It
• an electrode of a non-corrodible metal, infusible at the temperature of use and particularly of a noble metal which may have any shape including that of a grate, a spiral or a metal deposit even of the porous form.
• the positive electrode consists of a deposit of an oxide or another compound substantially more conductive than the corrosion product and not susceptible of being attacked itself by the corrosive gases.
• the positive electrode consists of a metal deposit on the corrosion product
• the corrosion is stopped as soon as a sufliciently high current density passes therethrough. This tends to confirm that when using other types of electrodes the relative inefliciency of the process during the starting period is due to an insufficient contact with the electrode.
• the present process may be advantageously used in numerous cases and where a metal or alloy is in contact with corrosive gases at high temperature, at which it is normally corrodible, for instance at temperatures higher than 500 C. and more generally higher than 800 C.
• gases there may be mentioned oxygen, air, carbon dioxide, steam, sulfur dioxide, hydrogen sulfide, the combustion gases as a general rule, the vapors of metalloids or acids, etc.
• gases are either normally in the gaseous state or are produced in situ by decomposition or vaporization of solids or liquids such as, for instance, nitrates, chlorates, perchlorates, hydrogen peroxide or even liquid oxygen.
• metals as iron, nickel, cobalt, chromium, molybdenum, tungsten, vanadium, zirconium, titanium, tantalum, aluminum, magnesium, manganese, copper and zinc either as such or admixed together or in the form of alloys with other elements including certain metalloids such as carbon or silicium may be efficiently protected by use of the process or treatment according to this invention.
• the present process may be used for reducing the corrosion in furnaces, heat exchangers, nuclear reactors particularly those using carbon dioxide as cooling medium, gasor vapor-turbines, rockets, jets and turbo-jets and numerous other applications.
• Example 1 A cylinder of tungsten is subjected to a preliminary oxidation by means of oxygen under atmospheric pressure at a temperature of 950 C. for 20 minutes so as to form on the external surface thereof an oxide layer about 0.4 mm. thick. The cylinder is then rapidly cooled and on its surface is wound a spiral of a platinum wire of a 0.1 mm. diameter, said spiral having a pitch of about 1 mm. By connecting the spiral to the positive pole and the cylinder to the negative pole of a direct current source while raising again the temperature of the cylinder to 950 C. in oxygen atmosphere, a flow of electric current through the oxide is observed.
• the oxidation degree is expressed by the weight increase of the sample, which increase corresponds to the combination of oxygen with the metal.
• the weight in crease thus amounts to 11 rng/cm. during the 20 minutes of the preliminary oxidation phase.
• After 40 minutes from the moment of the current supply with a density of 255 ma./cm. a further weight increase amounting to 18 Ing./om. is observed.
• the weight of the cylinder remains unchanged.
• the density of the current is then lowered to 30 ma./cm. and then to 0.05 ma./cm. and kept at said first value for 2 hours and said second value for 20 minutes without any change to be observed in the weight of the sample.
• the current supply is then interrupted and the weight of the sample starts increasing again at a rate of 10 mg./cm. in 20 minutes.
• This experiment shows the efiiciency of the process according to this invention as well as the absence of effect when using a platinum wire alone without any current supply.
• Example 2 is repeated with a sample consisting of a cylinder of tungsten having a 2% thorium content and at a temperature of 1000 C.
• the corrosion degree amounts to 15 mg./cm.
• the current density applied is chosen equal to 20 ma./cm.
• the corrosion degree is nullified.
• the current supply is interrupted and the corrosion starts again at a rate of 15 mg./om. in 3 hours.
• Example 3 mg/cm. for the 6 following hours and is thereafter A complete protection of the metal may also be obtained with lower current densities of respectively 50 and 12 ma./cm.
• the current supply may be interrupted and said complete protection is still maintained for several tens of hours.
• Example 4 Example 1 is repeated with a sample consisting of a cylinder of brass having a 70% copper content and a 30% zinc content, and at a temperature of 850 C.
• the corrosion degree attains 4rng./cm. and after a density of current of 200 ma./cm. has been supplied it still amounts to 1 rug/cm. during the next twenty minutes. The corrosion degree is thereafter completely nullified. After 4 days the current supply is interrupted and the corrosion starts again at a rate of 4 mg./cm in two hours.
• Example 5 Example 1 is repeated but with the use of an auxiliary electrode consisting of a very thin porous platinum deposit obtained ⁇ by coating the surface of the pre oxidized tungsten with a solution of platinum in aqua regia having added thereto hydroxylamine chlorhydrate, and heating the sample to a temperature of 500 C. up to the formation of a metallic platinum deposit of about 3 mg./cm.
• the corrosion degree in minutes, in the absence of current attains 6 mg./cm.
• the corrosion is immediate-1y stopped and no change in the weight of the sample has been observed in the following 54 hours during which the experiment was continued.
• Example 6 With a current density of 12 rn a./cm. the weight increase of the bar is zero after 54 hours.
• Example 7 The experiment according to Example 3 is repeated in a carbon dioxide atmosphere, under atmospheric pressure, with two identical cylindrical samples of the same stainless steel, each sample having a weight of 2.3 g., a height of mrn., and a diameter of 4 mm., said samples having both been preliminary subjected to the same preoxidation treatment by oxygen, and covered with a spiral of platinum wire.
• Example 8 Steel samples having a carbon content of 0.1% and a 17% chromium content have been electrolytically polished in a 10% perchloric acid solution in acetic acid.
• the other parts of the samples were first subjected to the same test for 5 hours. Their weight also increased by 3.3 mg./cm. Then the metal of the resulting samples was connected to the negative terminal of a generator, Whereas the positive terminal thereof was connected to a platinum wire spiral laid over the surface of the samples, on the preliminarily formed oxide layer. The samples were then brought again in an oxygen atmosphere to a temperature of 950 C., while causing a density of current of 1.5 amp/cm. .to pass Itherethrough. The weight of the spiral (unchanged throughout the experiment) being not taken into account, it has been observed that 60 hours after the beginning of the current supply (i.e. hours after the beginning of the test) the total weight increase of the samples amounted to 6.4 mg./crn. and remained unchanged at this level.
• said corrosion product is a member of the group consisting of the oxides, sulfides, and mineral salts of the metal to be protected.
• said positive electrode is 'made of a material which, at the temperature of use, is infusible and substantially non-corrodible.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Prevention Of Electric Corrosion (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Secondary Cells (AREA)

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Publications (1)

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Citations (13)

Family Cites Families (6)

• 0
  • NL NL278929D patent/NL278929A/xx unknown
• 1961
  • 1961-05-26 FR FR863129A patent/FR1416303A/fr not_active Expired
• 1962
  • 1962-05-25 US US197614A patent/US3265601A/en not_active Expired - Lifetime
  • 1962-05-25 DK DK235862AA patent/DK103428C/da active
  • 1962-05-25 DE DEJ21819A patent/DE1301190B/de active Pending
  • 1962-05-25 GB GB20282/62A patent/GB956915A/en not_active Expired
  • 1962-05-25 SE SE5946/62A patent/SE303914B/xx unknown
  • 1962-05-26 ES ES277725A patent/ES277725A1/es not_active Expired

Patent Citations (13)

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