170 likes | 470 Views
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.
E N D
AnodizingAluminum 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 Kris Magri is a Mechanical Engineering major who plans to work in robotics Authors
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
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
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-
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
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
Process Diagram by Kris Magri
Anodizing Tank Photo by Ed Troxell Photo by Kris Magri
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
Sealing • Aluminum oxide converted to hydrated form • Al2O33H2O 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)
Results Photo by Kris Magri
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
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"
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)
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