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Aluminum Anodize

Aluminum Anodize. By: Randall Marks. Aluminum Oxide. Amorphous aluminum oxide (alumina, Al 2 O 3 ) forms in a layer 2-3 nm thick when bare aluminum is exposed to oxygen Protects from further oxidation Stress causes fractures in the surface, but not peeling

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Aluminum Anodize

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  1. Aluminum Anodize By: Randall Marks

  2. Aluminum Oxide • Amorphous aluminum oxide (alumina, Al2O3) forms in a layer 2-3 nm thick when bare aluminum is exposed to oxygen • Protects from further oxidation • Stress causes fractures in the surface, but not peeling • How can this natural coating be improved upon?

  3. Anodize Process

  4. Types of Anodize • Barrier Anodize • Near neutral electrolyte solution • Max 1um thick • Porous Anodize • Acidic electrolyte solution • Can be several hundred um thick

  5. Barrier Anodize • Forms oxide on both sides • Dielectric, which supports up to 1 V/nm • Too thin for most mechanical applications

  6. Porous Anodize Formation

  7. Porous Anodize Sealing • Hot water forms hydrous oxide crystals, sealing the pores. • Dyes or electroplated metals can be sealed inside the pores for various colorations

  8. Hard Anodize • Hard Anodize Formation • Low temperature • Low acidity • Applications • Durable protective layer • Bearings • Not sealed to hold lubricants in the pores • Surface is second hardest material known

  9. Optics Applications • Reduction of stray light/spectral reflections • Bead blasted black anodize • No outgassing • Black anodize not good for bearing type surfaces • Adhesive preparation • Phosphoric acid preparation • Left unsealed • Corrosion resistance

  10. Important Application Considerations • AMS governing specs: • AMS 2469-AMS 2474 • Part grows by approximately half the oxide thickness • Surface Young’s Modulus around 300 MPa. • Does not protect against all chemicals • Highly susceptible to strong acids and bases

  11. References • Case Western Reserve University Electrochemistry Encyclopedia • http://electrochem.cwru.edu/ed/encycl/art-a02-anodizing.htm • AACOA Inc. Anodizing Presentation • http://www.aacoa.com/presentations/anodizing_presentation-c.pdf

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