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
  • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
  • C23F13/005—Anodic protection

Definitions

• titanium has taken a prominent place as a structural metal because of its outstanding corrosion resistance to many electrolytes. There remain however some important electrolytes in which the corrosion rates of titanium and its alloys prohibit their use for handling such media, e.g. as storage tanks and other equipment.
• carbon When carbon is the cathodic material, it may take the form of discrete particles embedded in the surface, each particle being capable of protecting a surrounding area many times its size.
• the protection given appears to be of a permanent nature and any scratches or damage of a similar character to the surface of the metal become sealed over by a protective film. This is opposite to the effect normally produced by coating a metal with a more noble or cathodic metal.
• the current passing to the titanium to reduce its rate of corrosion may be produced by the galvanic couple formed between the titanium and more noble material when contact is made therebetween.
• the contact between the two parts may be direct, i.e. by the attachment of the more noble material to the titanium surface, or indirect, i.e. by means of a wire or other lead external to the electrolyte.
• Electrical contact between the titanium and the more noble element may with advantage be effected by in corporating the element in the surface of the metal and for this purpose a number of methods are available.
• 'For metals such as platinum, functioning as a cathode, attachment may be achieved by plating'or spot-welding or vacuum deposition or spraying techniques.
• non-metallic materials such as carbon
• deposition by decomposition of carbon monoxide orcarbon dioxide vapours, or coating with oil and subsequently carbonising may be carried out. Bonding the metal to pieces of graphite is also suitable.
• a method which can be used for both metals and non-metals is to introduce the cathodic material as a small quantity of powder during the last with potential, there is a more or less rapid drop towards a condition in which the titanium is substantially completely passive. --In cases therefore in which the poto give the requisite protection will vary with the cir- 45 cumstanoes. Many cases, a potential of 1.0 volt positive to the standard calomel electrode will give virtually complete protection and, for most electrolytes, it will rarely be necessary to raise the potential to more than about 3 volts. The power costs of operating the present invention are small in relation to the saving of plant and materials that is effected thereby.
• the invention has special application to the improvement of the corrosion resistance of titanium in nonoxidizing acids.
• EXAMPLE 1 A titanium strip 5 ems. long x 1 cm. wide is electrically connected to a graphite cathode and immersed in 40% w./w. sulphuric acid at 60 C., the graphite being partly immersed therein.
• the electrical connection is by way of an external wire spot-welded to the titanium at one end and secured 2Jl'.”ll'.S other end as a push fit in a small hole drilled in the graphite.
• the corrosion of the titanium expressed in inches penetration per year is 0.0035 as compared with the value of 1.12. inches for an unprotected control sample immersed in the solution.
• EXAMPLE 2 The procedure of the previous example is repeated employing in place of the graphite a smooth platinum electrode coated with platinum black. The corrosion rate of the titanium as compared with that of an uncoupled control sample is reduced by a factor of approximately one-third.
• EXAMPLE 3 A large tank constructed from titanium sheet and maintained at a positive potential of 3.0 volts with respect to a graphite cathode is protected from corrosion by 40% W./w. sulphuric acid contained within the tank at a temperature of 60 C.
• the arrangement employs a graphite cathode partly immersed in the sulphuric acid in the tank, the electrical cell so formed being connected with a continuously trickle-charged battery.
• the power consumption is approximately 3 watts per thousand square feet of immersed titanium surface. Comparative tests carried out for a period of the order of 700 hours indicate that the corrosion rate of the titanium is 7x 10 inches per year as compared with 1 inch per year for an unprotected specimen of titanium.
• the accompanying table shows the degree of protection afforded to titanium in other electrolytes.
• a method of reducing corrosion as set forth in claim 1 including increasing the potential difference between said structure and said non-ferrous material sufficiently to maintain said protective film by means of a source of direct current electricity electrically connected between said structure and said non-ferrous material, the positive connection being to said structure.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Testing Resistance To Weather, Investigating Materials By Mechanical Methods (AREA)
• Coating By Spraying Or Casting (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Prevention Of Electric Corrosion (AREA)

Applications Claiming Priority (3)

Publications (1)

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Family Applications (1)

Country Status (6)

Cited By (15)

Families Citing this family (3)

Citations (7)

• 0
  • BE BE569804D patent/BE569804A/xx unknown
  • DE DENDAT1250234D patent/DE1250234B/de active Pending
• 1957
  • 1957-07-26 GB GB23726/57A patent/GB860968A/en not_active Expired
• 1958
  • 1958-07-17 US US749052A patent/US3102086A/en not_active Expired - Lifetime
  • 1958-07-23 CH CH6213058A patent/CH375583A/de unknown
  • 1958-07-26 FR FR771211A patent/FR1239322A/fr not_active Expired

Patent Citations (7)

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