Chapter 13: Chemical Degradation

3/13 (No Quiz)

Material Type

  1. Ceramic

  2. Metal

  3. Polymer

  4. Composite (all 3)

Types of Degradation → depends on material + environment

  1. Chemical

  2. Mechanical

  3. Electrical

Materials degrade (different types) → degradation effects ↔ organism/bio response

Chemical Degradation: oxidation + reduction

  • usually oxidation of metals

  • Oxidation is LOSS of electrons

  • Reduction is GAIN of electrons

You should know top reactive elements on reactivity series*

Approaches of Chem Degradation:

  1. Reactivity Series

  2. Pourbaix Diagram

  3. Corrosion + Electrochemistry Studies

Interesting Values: slide 9 **

  • FOR BIO STUFF USE STAINLESS STEEL (mostly iron, some carbon + other stuff)

    • Fe2+ + 2e- → Fe -0.44 V

    • We expect if we put any of this stuff into the human body, it will corrode

    • negative values react**

    • positive values means it requires energy to react

  • regular bridge use regular steel

  • Cobalt Chromium Alloys (be careful about circulation in human body bc anemia)

  • Titanium Alloys (most bio compatible)

If you put a metal in an acidic ==> more likely to react

Pourbaix Diagram:

  • what is this - see when something corrodes dependent on pH and EM (volts)

    • Immunity - does not react (does not corrode)

    • Passivation - surface of metal has something else (prevents degradation)

      • most metals can’t use unless passivated***IMPORTANT owo

    • Corrosion

  • how do I read it

    • SHE: hydrogen equivalent (not important)

  • tells you if you can use a certain metal like reactivity series (useful but has limitations)

Types of Corrosion: real world corrosion is kind of a mess

  1. Uniform Attack: losing electrons into the surroundings (same everywhere, ALWAYS HAPPENING)

  2. Galvanic Corrosion: two different activities (avoid at all cost)

  3. Crevice Corrosion: two different metals in contact, holes

  4. Pitting Corrosion: at a point due to heterogeneity?

  5. Intergranular Corrosion: in grain structure, when stuff is rotated and still next to each other you get leftover things that don’t have the same number of bonds which will be weaker than the other atoms there

  6. Leaching: lose one but not the other?

  7. Erosion: everything above with FLOW (fluid movement over it)

  8. Stress and Fatigue Corrosion:

    1. Fatigue is repetitive actions: generating and removing stress which creates damage

Have all these, which is the worst (weighted)

Guessing Corrosion (pt1):

  1. Pitting

  2. Uniform Corrosion

  3. Crevice

  4. Crevice Corrosion

  5. Intergranular

  6. Pitting

Guessing Corrosion (pt2):

  1. Galvanic

  2. Erosion

  3. Leaching

  4. Intergranular

  5. Stress + Fatigue

What types of corrosion should you worry about in these start from 11 clockwise:

  1. hip implant: uniform attack, crevice, mechanical stress, fatigue

  2. screw thing: crevice, mechanical stress, uniform attack

  3. knee replacement: mechanical, uniform, fatigue

  4. wheelchair: uniform, crevice, fatigue + mechanical, erosion, pretty much everything

    1. what you don’t wanna see: galvanic

  5. artificial heart: erosion, uniform attack, mechanical stress + fatigue

Mechanical/chem stress → bio response therefore put pacemaker in good location

Quiz 14: What type of corrosion is it?

  1. Pitting: each little dot is a corrosion pit on the saucepan

  2. Crevice

  3. Intergranular

  4. Pitting

  5. Galvanic

  6. Erosion

  7. Leaching (preferencial leaching + grain structure)

  8. Intergranular

Top Left: Crevice