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UBC Theses and Dissertations
Corrosion of titanium and titanium alloys in aqueous acid electrolyte Reid, Peter W. A.
Abstract
The corrosion characteristics of three dilute Ti alloys (ASTM 1, 2, and 7) in aqueous sulphuric acid electrolytes were studied using open circuit potential measurements, potentiodynamic techniques, and long term immersion testing. The effects of acid concentration, alloying addition, temperature, and the iron and chloride content of the electrolyte were examined. The open circuit potential measurements resulted in Ti grade 7 coming to a higher open circuit potential with the electrolyte at approximately 0.07 V[sub SHE], while the rest potentials for Ti grades 1 and 2 were approximately -0.50 V[sub SHE]- The difference is believed to be the result of Pd alloying additions, which act as a catalyst for reduction reactions on the surface of the active Ti alloys during crevice corrosion. By decreasing the required over voltage for the reduction of species such as H⁺ to occur, a more oxidizing overall mixed potential of the system is achieved. Potentiodynamic scanning around the corrosion potential of titanium alloys in sulphuric acid (H₂SO₄) yielded maximum corrosion rates of 4.9 x 10 ⁻⁵ mm/yr (0.002 mpy). In all cases corrosion rates increased with lower pH and higher Cl⁻ content. Potentiodynamic testing of the [Fe³⁺]/[Fe²⁺] redox couple shows limiting currents to be controlled by concentration polarization, and the kinetics of the overall reactions were faster on the surface of the more noble Pt electrode. Slopes were on the order of 150-300 mV/decade, with exchange current densities of 10 ⁻⁷ and 10 ⁻⁷ for Ti and Pt respectively. All corrosion potentials were in the range of 0.5 to 0.7 V[sub SHE]. During the long-term immersion testing, Ti grade 7 proved to be more corrosion resistant than the commercially pure alloys due to the formation of a visibly thicker oxide layer. Preferential attack, when visible, was initiated on metallic iron and iron oxide impurities in the alloys and was observed on all immersion coupons.
Item Metadata
Title |
Corrosion of titanium and titanium alloys in aqueous acid electrolyte
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2003
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Description |
The corrosion characteristics of three dilute Ti alloys (ASTM 1, 2, and 7) in aqueous
sulphuric acid electrolytes were studied using open circuit potential measurements,
potentiodynamic techniques, and long term immersion testing. The effects of acid
concentration, alloying addition, temperature, and the iron and chloride content of the
electrolyte were examined.
The open circuit potential measurements resulted in Ti grade 7 coming to a higher open
circuit potential with the electrolyte at approximately 0.07 V[sub SHE], while the rest potentials for Ti
grades 1 and 2 were approximately -0.50 V[sub SHE]- The difference is believed to be the result of
Pd alloying additions, which act as a catalyst for reduction reactions on the surface of the
active Ti alloys during crevice corrosion. By decreasing the required over voltage for the
reduction of species such as H⁺ to occur, a more oxidizing overall mixed potential of the
system is achieved.
Potentiodynamic scanning around the corrosion potential of titanium alloys in sulphuric
acid (H₂SO₄) yielded maximum corrosion rates of 4.9 x 10 ⁻⁵ mm/yr (0.002 mpy). In all cases
corrosion rates increased with lower pH and higher Cl⁻ content.
Potentiodynamic testing of the [Fe³⁺]/[Fe²⁺] redox couple shows limiting currents to be
controlled by concentration polarization, and the kinetics of the overall reactions were faster on
the surface of the more noble Pt electrode. Slopes were on the order of 150-300 mV/decade,
with exchange current densities of 10 ⁻⁷ and 10 ⁻⁷ for Ti and Pt respectively. All corrosion
potentials were in the range of 0.5 to 0.7 V[sub SHE].
During
the long-term immersion testing, Ti grade 7 proved to be more corrosion resistant
than the commercially pure alloys due to the formation of a visibly thicker oxide layer.
Preferential attack, when visible, was initiated on metallic iron and iron oxide impurities in the
alloys and was observed on all immersion coupons.
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Extent |
5368119 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-10-29
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0079151
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2003-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
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Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.