Introduction Atmospheric Corrosion Prevention Methods What are Mg alloys? Mixture of metals to form...
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Introduction Magnesium Alloy Corrosion By Group 15: Nathan Lam, Graham Tait, Zhanyi Zhou, Muhammad Ibrahim Atmospheric Corrosion Prevention Methods What are Mg alloys? • Mixture of metals to form a stronger and more corrosion resistant metal • Mainly magnesium mixed with aluminum, zinc, manganese, silicon, copper, rare earth metals or zirconium Why use Mg alloys? • High strength • Light weight • Environmentally friendly • Cost effective What is it used in? • Aerospace technologies • Medical applications • Automobile parts Galvanic Corrosion Conversion coating • Chromate conversion • Phosphate-permanganate conversion Important considerations • oxidants • promoters • corrosion inhibitors • wetting agents • pH buffer regulators Electrophoretic coating (E- COATING) • Core idea: colloidal particles are suspended in a liquid medium, mitigated under the influence of an electric field and then are deposited onto an electrode. • Advantages: 1. low porosity providing corrosion protection. 2. Coating of complicated shaped surfaces 3. Inexpensive for mass production Potential corrosion pollutants • Sulfur Dioxide (SO 2 ) • Nitrogen Dioxide (NO 2 ) • Ozone (O 3 ) • Carbon Dioxide (CO 2 ) • Nitric Acid (HNO 3 ) • Sea salt (NaCl) • Ammonium sulfate ((NH 4 ) 2 SO 4 ) Formation of electrolyte layer • Occurs by adsorption on the hydroxylated oxide • Conductivity increases when NaCl or (NH 4 ) 2 SO 4 dissolve in the layer Observations • Deposition of SO 2 increased with addition of NO 2 and O 3 • Dissolution of CO 2 causes formation of carbonates, eventually becomes supersaturated and precipitates. Stress Corrosion Cracking Hydrogen Embrittlement • H atoms diffuse into metal • Slow physical cracks form • Can cause failures of the alloy even under safe loading. Reference Anodization Passivation layer • Formation of a oxide layer that prevents, and slows down further oxidation • Layer formed by anodization includes: magnesium oxide, magnesium hydroxide, and magnesium silicate Quality and thickness • Pilling-Bedworth Ratio • Voltage, current density, concentration • Surface treatment ato m “Crysta l” radius (Å)[2] % size differen ce from Mg Electrone gativity[ 3] Mg 0.86 - 1.31 Fe 0.69 19.7 1.83 As 0.72 16.3 2.18 Element of interest: reduction reaction Electrochemical potential E 0 (V) [1] Magnesium (Mg): Mg 2+ + 2e - Mg (s) -2.372 Iron (Fe): Fe 2+ + 2e - Fe (s) -0.44 Electrochemical process Corrosion at anode uses Electrochemical potential differences Uneven distribution of atoms • Alloy = solid solution o Mg solvent & Fe solute • Solubility is key o Depends on Hume-Rothery Rules 1. Atom size 2. Electronegativity 1 - Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press . ISBN 0-8493-0487-3 . 2 - Shannon, R.D., Prewitt, C.T., Effective Ionic Radii in Oxides and Fluorides. (1969). Acta Crystallographica, B25:925-946. 3 - Elect neg : J.E. Huheey, E.A. Keiter, and R.L. Keiter in Inorganic Chemistry : Principles of Structure and Reactivity, 4th edition, HarperCollins, New York, USA, 1993 4 - Birbilis, N., Williams, G., Gusieva, K., Samaniego, A., Gibson, M.A., McMurray, H.N. Poisoning the Corrosion of Magnesium. (2013). Electrochemical communications. 34: 295-298. 5 - Blawert C., dietzel W., ghali E., Song G. (2006), Advanced engineering Materials 8(7): 511-533 Arsenic protection •Reduction in loss of metal & evolution of H 2 •Sterics block hydrogen from recombining and poisons the reaction (www.mgalloycorrosion.wikispaces. com) [4 ] [4 ] [4 ] [5 ]
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Transcript of Introduction Atmospheric Corrosion Prevention Methods What are Mg alloys? Mixture of metals to form...
Introduction
Magnesium Alloy CorrosionBy Group 15: Nathan Lam, Graham Tait, Zhanyi Zhou, Muhammad Ibrahim
Magnesium Alloy CorrosionBy Group 15: Nathan Lam, Graham Tait, Zhanyi Zhou, Muhammad Ibrahim
Atmospheric CorrosionPrevention Methods
What are Mg alloys?• Mixture of metals to form a stronger and
more corrosion resistant metal• Mainly magnesium mixed with aluminum,
zinc, manganese, silicon, copper, rare earth metals or zirconium
Why use Mg alloys?• High strength • Light weight• Environmentally friendly• Cost effective
What is it used in?• Aerospace technologies• Medical applications• Automobile parts
Galvanic Corrosion
Conversion coating• Chromate conversion• Phosphate-permanganate conversion
Important considerations• oxidants • promoters • corrosion inhibitors• wetting agents • pH buffer regulators
Electrophoretic coating (E- COATING)• Core idea: colloidal particles are
suspended in a liquid medium, mitigated under the influence of an electric field and then are deposited onto an electrode.
• Advantages:1. low porosity providing corrosion
protection. 2. Coating of complicated shaped
surfaces 3. Inexpensive for mass production
Potential corrosion pollutants• Sulfur Dioxide (SO2)• Nitrogen Dioxide (NO2)• Ozone (O3)• Carbon Dioxide (CO2)• Nitric Acid (HNO3)• Sea salt (NaCl)• Ammonium sulfate ((NH4)2SO4)
Formation of electrolyte layer• Occurs by adsorption on the
hydroxylated oxide
• Conductivity increases when NaCl or (NH4)2SO4 dissolve in the layer
Observations • Deposition of SO2 increased with addition
of NO2 and O3
• Dissolution of CO2 causes formation of carbonates, eventually becomes supersaturated and precipitates.
Stress Corrosion CrackingHydrogen Embrittlement• H atoms diffuse into metal • Slow physical cracks form• Can cause failures of the alloy even
under safe loading.
Reference
Anodization Passivation layer• Formation of a oxide layer that prevents,
and slows down further oxidation• Layer formed by anodization includes:
magnesium oxide, magnesium hydroxide, and magnesium silicate
Quality and thickness• Pilling-Bedworth Ratio• Voltage, current density, concentration• Surface treatment
atom “Crystal” radius(Å)[2]
% size difference from Mg
Electronegativity[3]
Mg 0.86 - 1.31Fe 0.69 19.7 1.83As 0.72 16.3 2.18
Element of interest: reduction reaction
Electrochemical potential E0 (V) [1]
Magnesium (Mg): Mg2+ + 2e- Mg(s)
-2.372
Iron (Fe): Fe2+ + 2e- Fe(s)
-0.44
• Electrochemical processo Corrosion at anode
Causes• Electrochemical potential differences• Uneven distribution of atoms• Alloy = solid solutiono Mg solvent & Fe solute
• Solubility is keyo Depends on Hume-Rothery Rules
1. Atom size2. Electronegativity
1 - Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0487-3. 2 - Shannon, R.D., Prewitt, C.T., Effective Ionic Radii in Oxides and Fluorides. (1969). Acta Crystallographica, B25:925-946. 3 - Elect neg : J.E. Huheey, E.A. Keiter, and R.L. Keiter in Inorganic Chemistry : Principles of Structure and Reactivity, 4th edition, HarperCollins, New York, USA, 1993 4 - Birbilis, N., Williams, G., Gusieva, K., Samaniego, A., Gibson, M.A., McMurray, H.N. Poisoning the Corrosion of Magnesium. (2013). Electrochemical communications. 34: 295-298.5 - Blawert C., dietzel W., ghali E., Song G. (2006), Advanced engineering Materials8(7): 511-533
Arsenic protection• Reduction in loss of
metal & evolution of H2 • Sterics block hydrogen
from recombining and poisons the reaction
(www.mgalloycorrosion.wikispaces.com)
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