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Anodizing Aluminum and Microstucture of a Steel Sprocket

Anodizing Aluminum and Microstucture of a Steel Sprocket. Ian Buchanan & Kris Magri Santa Rosa Junior College ENGR 45, Younes Ataiiyan Dec 07, 2009. Ian Buchanan is a Civil Engineering major, hoping to work in construction.

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Anodizing Aluminum and Microstucture of a Steel Sprocket

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  1. AnodizingAluminum and Microstucture of a Steel Sprocket Ian Buchanan & Kris Magri Santa Rosa Junior College ENGR 45, Younes Ataiiyan Dec 07, 2009

  2. Ian Buchanan is a Civil Engineering major, hoping to work in construction Kris Magri is a Mechanical Engineering major who plans to work in robotics Authors

  3. Purpose of Anodizing Photo by Ron Newman, http://www.focuser.com/anodize.html Grow an aluminum oxide layer on the aluminum so it can be dyed Corrosion and wear resistance Hardening (Type III) Color – cosmetic

  4. Overview • Aluminum part immersed in acid electrolyte • Apply electrical current, DC, ~12V • The part is the anode (+) (thus the name) • Electrolysis and chemical reaction occurs • Porous aluminum oxide layer grows on the aluminum • Up to 3000 times thicker than naturally occuring Al2O3 layer • Dye goes into pores, results in bright colors • Place in boiling water to seal pores

  5. Electrochemistry • Electrolyte in Solution: Free ions ,conductive • Sulfuric, oxalic, or phosphoric acid typically used • 15% solution of sulfuric acid (H2SO4) our procedure • Electrolysis: Extracts constituent elements from solution • Anode • Evolution of oxygen • 2Al + 3H20  Al203 + 6H+ + 6e- • Cathode • Evolution of hydrogen • 6H20 + 6e-  3H2 (g) + 6OH-

  6. Pore growth • Acid electrolyte acts as solvent for oxide • Dissolves portions of barrier oxide layer • Oxide grows at metal/oxide interface • Rate of growth dependent on current, concentration, temperature, voltage • Hexagonal shape Photo from Artists Anodizing Aluminum, D. LaPlantz, 1988, p. 17

  7. Anodizing Setup Materials Aluminum item (anode) Aluminum wire Aluminum sheet (cathode) Sulfuric Acid 15% Non-metal container Power supply Distilled/de-ionized water Dye (RIT clothes dye) Baking soda Photo by Kris Magri

  8. Process Diagram by Kris Magri

  9. Anodizing Tank Photo by Ed Troxell Photo by Kris Magri

  10. Cathode design • Cathode at least 1/3 the area of the part • Experimental 1st cathode very large and very far away, poor results • Radial cathode worked best

  11. Sealing • Aluminum oxide converted to hydrated form • Al2O33H2O has more volume than Al2O3 • Clogs the pores • Hot water seal: Boiling de-ionized water or steam • Other sealing: nickel acetate, cobalt acetate (cold), sodium or potassium dichromate (hot)

  12. Results Photo by Kris Magri

  13. Current Density • 10-15 ASF (Amp•hr/ft2) desired rate • 4A for 20 min, part is 4.42 in2 43.4 ASF • 1A for 20 min, part is 4.42 in2 10.8 ASF • Poor results at 4A but good results at 1A • Rate of oxide thickening proportional to current density up to some point • Dissolution point – barrier layer being removed faster than new oxide layer being formed

  14. More about Anodizing • Type II • This is the procedure we used • .00007" to .001" oxide layer thickness • Type III • Low temp (50 degree) at higher current (24 ASF) • Over .001"

  15. Anodizing in General • Other metals that can be anodized • Titanium, magnesium, niobium, tantalum, tungsten, zirconium • Ti utilizes interference property of oxide film instead of dye for color • History • Anodizing developed around 1917 with first US patent in 1925 (*AAA)

  16. Resources • Aluminum: Properties and Physical Metallurgy, Edited by John E. Hatch, American Society for Metals, 1984 • Materials Science and Metallurgy, Herman W. Pollack, 3rd Edition, Reston Publishing, 1981 • Artists anodizing aluminum: The sulfuric acid process, David LaPlantz, Press de LaPlantz, 1988 • Wikipediahttp://en.wikipedia.org/wiki/Electrolyte • Mr. Titaniumhttp://mrtitanium.com/interference.html • Anodizing Aluminum, by Ron Newmanhttp://www.focuser.com/anodize.html

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