Metallic Corrosion Study Guide

Question 1

in an electrochemical redox reaction, loss of electrons___ and gain of electrons is_____

Answer 1

oxidation is loss

reduction is gain

Question 2

describe the mechanism of metallic corrosion

Answer 2

corroded state is preferred since lowest energy state

metal atoms ionize, go into solution and combine with oxygen

metal flakes off

Question 3

define galvanic corrosion

Answer 3

two different metals/alloys that are in close proximity in a electrolytic enviorment….. this is the type of corrosion that occurs

Question 4

what is corrosion

Answer 4

is the degration of metals to oxide, hydroxide or other compounds through chemical reactions

Question 5

what are two primary factors that drive metallic corrosion

Answer 5

thermodynamic forces-they cause oxidation and reduction

surface barrier- such as surface oxide layer

Question 6

what substance is oxidized and which substance is reduced in the formation of rust?

Answer 6

oxidized-iron FE

reduced- oxygen

Question 7

what is the main function of the oxide layer on the surface of a metal

Answer 7

to reduce corrosion

Question 8

state and describe 3 types of corrosion

Answer 8

galvanic corrosion- two different metals/alloys are close proximity in electrolytic enviornment….. extinct tendencies towards oxidation. this causes corrosion

crevice corrosion- found in crevices or deep, narrow flaws.. this can arise from localized oxygen depletion and metal ion concentration gradients

pitting corrosion- formation of pits

intergranular corrosion- preferential attack along grain boundries.

fretting- wear process due to relative motions in highly loaded devices exaggerated by corrosive enviorment

Question 9

name a describe two basic reactions associated with corrosion

Answer 9

ionization- formation fo metallic cations under acidic or reducing (oxygen poor) conditions

oxidation- reduction of metal with oxygen

hydroxylation- reaction of water under alkaline or oxidizing conditions

Question 10

how does galvanic corrosion occur?

Answer 10

two metals/alloys are close in proxmit in an electrolytic environment. distinct tendencies towards oxidation

Question 11

in galvanic series, is gold magnesium , tiantim considered one of the most active metals in sea water?

Answer 11

Magnesium more active

then Titatnium, then gold

Question 12

which type of corroision occurs when two different metals/alloys are in close proximity in an electrolytic enviornment?

Answer 12

galvanic corrosion

Question 13

what is fretting corrosion?

Answer 13

Wear process due to relative motions in highly loaded devices exaggerated by corrosive environment – contacting surface – Device micromotions

Question 14

what can one do to protect against corrosion?

Answer 14

Use appropriate metals • Avoid implantation of dissimilar metals • Minimize pits and crevices • Avoid transfer of metal from tools to the implant during surgery • A metal that does not corrode in one part of the body may corrode somewhere else

Question 15

describe uniform attack corrosion

Answer 15

General corrosion that is evenly distributed over entire corrosion region

–Rusting of iron, tarnishing of silverware • Most readily detectable (visual) and preventable (alloying, surface coatings)

Question 16

explain deposit corrosion

Answer 16

Foreign substances with moisture which come from the environment, adhering to a surface of a metal cause the deposit corrosion because of the lack of oxygen under the deposit. Once a while, the dirt should be removed to reduce deposit corrosion.

Question 17

what is the difference between galvanic corrosion and fretting corrosion

Answer 17

Fretting
• Wear process due to relative motions in highly loaded devices exaggerated by corrosive environment – contacting surface – Device micromotion

Galvanic Corrosion • Two different metals/alloys that are in close proximity in an electrolytic environment – Distinct tendencies toward oxidation

Question 18

describe the possible affects of corrosion of medical devices

Answer 18

a loss of mechanical properties- not as strong

may become less biocompatible and be rejected from host