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					 The Corrosion of Titanium and
its Alloys at High Temperatures
          and Pressures

              James Vaughan
              Peter Reid
              Akram Alfantazi
              David Dreisinger
              Desmond Tromans
              Mimoune Elboudjaini
                        Outline

        Introduction
        Results
        Conclusions




Introduction
                Titanium Information
       Abundant on Earth
       Very reactive
       Alloyed for mechanical properties
               (Mo, Ni, Al, V)
       Alloyed for corrosion resistance
               (Pd, Ru, Mo, Ni)
Introduction
                    Motivation
 Ti and Ti-alloys are used as the liner and internal
      components of autoclaves


 Corrosion repairs
    require expensive
          process downtime

 Knowledge of corrosion at these conditions is limited
Introduction
                      HPAL Conditions
                                200 – 270 °C
        Temperature
                              473 – 543 Kelvin
                                Up to 725 psi
           Pressure
                                      5 Mpa
               H2SO4             30-100 gpL
                Cl-          500 - 100,000 ppm
          Slurry
                          Ni, Co, Fe, Cu, Al, Mg, Mn
        Constituents

Introduction
                 Materials Tested

     ASTM           Alloy Additions             Uses
     Grade
    Ti-1, Ti-2        Unalloyed             Liner, parts
      Ti-7              0.15 Pd           Corrosion repairs
      Ti-12         0.3 Mo – 0.8 Ni       Nozzles, valves
      Ti-18      3 Al – 2.5 V – 0.05 Pd    Agitator blades


Introduction
                   Objectives

 Explore the electrochemical behaviour of Titanium
    and its alloys at high temperatures and pressures
          in H2SO4
 Characterize the corrosion products




Introduction
                     Approach
           Develop E-pH stability diagrams
           Polarization techniques
           XPS and AES




Introduction
                        Results
     E-pH Stability Diagrams
           298, 498 Kelvin
           Ti ion activity = 1X10-6
           Potential vs. SHE (298 Kelvin)



Results
          E-pH Diagram, 298 Kelvin




Results
          E-pH Diagram, 498 Kelvin




Results
                          Results
Electrochemical Tests (< 373 K)
      SR = 0.5 mV / s
      Reference: Hg / Hg2SO4
      Corrected for LJP




Results
                                 Open Circuit Potential
                                Ti-1, 100 gpL H2SO4, 298 Kelvin

                 0.1
                 0.0                        Thinning of the oxide
E (mV) vs. NHE




                 -0.1
                 -0.2                    Spontaneous activation
                 -0.3
                 -0.4                     Formation of TiH2
                 -0.5
                 -0.6
                        0   2        4          6         8         10   12

Results                                    Time (Hours)
                                     Potentiodynamic Scan
                                   Ti-1, 100 gpL H2SO4, 298 Kelvin
                0.5


                                                                   Passive current
E (V) vs. NHE




                                                                   Ti(III) to Ti(IV)

                0.0
                              Hydrogen evolution


                                                              Active dissolution of Ti
                -0.5
                       -15   -10    -5     0          5       10       15      20
                                                          2
                                          Current (uA/cm )
Results
                                            Anodic Scans
                   0                                   Ti-1

                -100                                                     H2SO4 / Temperature
                                                                              (gpL / K)
                -200
E (mV) vs NHE




                -300            Increased Temperature
                                                                               100 / 323
                -400        Increased Acidity                                  30 / 343
                -500                                                           100 / 343
                -600

                -700
                   1.E-05                1.E-04                     1.E-03             1.E-02
                                                  Current (A/cm2)
Results
                       Results
Electrochemical Tests (> 423 K)
CANMET MTL
      30 gpL H2SO4
      463, 498 and 523 K




Results
                            Open Circuit Potential, High Temperature
                 200                  During the autoclave warm-up

                                                            Ti-18, 403-498 K
                 100                                        Ti-12, 405-498 K
E (mV) vs. NHE




                                                            Ti-7, 466-498 K
                   0
                                                            Ti-2, 483-498 K



  -100
-110 mV
-150 mV
                 -200
                    -5000         -2500          0             2500            5000

Results                                    Time (Seconds)
            E-pH Diagram, 498 Kelvin

-0.11
-0.15




          0.6
Results
                Potentiodynamic Scan, Ti-7, High Temperature
              1.5
                     Temperature/ Pressure
                           elvin a)
                         (K / kP
              1.0
                          473/ 1930
              0.5
E(V vs. N E
         H




              0.0
   )




              -0.5


              -1.0
                 1.E-08                1.E-07                   1.E-06   1.E-05

Results                                         Current (A 2)
                                                          /cm
                 Potentiodynamic Scan, Ti-12, High Temperature
                1.5
                       Temperature / Pressure
                             (K / kPa)
                1.0
                            473 / 1930
E (V) vs. NHE




                0.5         498 / 2760

                0.0


                -0.5


                -1.0
                   1.E-08                 1.E-07                     1.E-06   1.E-05

                                                   Current (A/cm2)
Results
                 Potentiodynamic Scan, Ti-18, High Temperature
                1.5
                    Temperature / Pressure
                          (K / kPa)
                1.0
                       498 / 2760
E (V) vs. NHE




                0.5         523 / 4240


                0.0


                -0.5


                -1.0
                   1.E-08                1.E-07                     1.E-06   1.E-05
                                                               2
Results                                           Current (A/cm )
          Oxide Film Characterization
              XPS and AES
Immersion Sample Conditions:
      30 gpL H2SO4
      498 K
      3 Hours




Results
          XPS Chemical Analysis, Ti-12

                                   Oxygen




                                    Titanium




Results
          AES Chemical Depth-Profile, Ti-12



               Titanium     Scan Rate = 300 A/min




              Oxygen


                           Depth of 4500 Angstroms
     Carbon

Results
             AES Chemical Depth-Profile, Ti-18



           Titanium                Scan Rate = 300 A/min




          Oxygen


                      Depth of 2200 Angstroms
          Carbon

Results
                   Conclusions
    There was no rapid general corrosion or localized
     corrosion of the samples at the conditions tested


     Increased stability of the oxide with temperature

          Inhibitor ions from the autoclave walls


Conclusions
                  Conclusions
    The alloyed samples exhibited a higher open
   circuit potential than the unalloyed samples
    The oxide thickness of the Ti-12 immersion test
   sample was greater than for the Ti-18




Conclusions
              Acknowledgements
 CANMET Materials Technology Laboratories
 TIMET (Titanium Metals Corporation)
 NSERC




Conclusions

				
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