Ceramics

Question 1

1. Define ceramic materials

Answer 1

a compound of metallic and non‐metallic elements. (ex: oxides, nitrides)

Question 2

3. Compare and contrast ceramics and metals in terms of their general mechanical properties

Answer 2

CERAMICS:
CONS: lack toughness, too brittle/more stiff, too liable to fracture.
PROS: chemically stable - they are already‐oxidized compounds, and they do not corrode and release ions to the surroundings. more biocompatible, better aesthetics than metals. stronger, higher mod of elasticity

METALS: more durable, tougher. absorb more strain and have higher plasticity.

Question 3

4. Critique ceramic materials in terms of their general mechanical properties

Answer 3

opaque or transparent. low toughness (yet high strength)

PROS: strong, dense, insulators of electricity like metals, retain strength at high temps
CONS: brittle, stiff, liability to fracture

Question 4

5. List the 3 general methods of reinforcement of ceramics

Answer 4

1. bond ceramic to another material
2. incorporate a component that can hinder the propagation of cracks through the material
3. use “transformation toughening” ZIRCONIA - puts crack under compression which is OK, remember tension is bad.

Question 5

Bond type in ceramic structure

Answer 5

Ionic bonds. - very strong bond. difficult to stretch (high mod) and difficult to break (high strength)

Question 6

True or false: Ceramics can be crystalline and amorphous/glasses

Answer 6

True

Question 7

Ionized atoms - not possible to form dislocations which means ___ plasticisy

Answer 7

no plasticity aka brittle. once the bonds are broken, a crack appears and grows

Question 8

Under tension ceramics are ___, under compression ceramics are ____

Answer 8

under tension - brittle
under compression - strong

because to break, you need a crack and cracks can only grow in tension (arrows pull away)
to prevent: hinder propagation of crack and prevent tension, compression is ok

Question 9

REVIEW “Methods to difficult/hinder the propagation of cracks in ceramics”

Answer 9

26 min into ceramics lecture. or page 2 of summary

Question 10

to hinder propagation, sometimes we add ____ and ____ into the ceramic material

Answer 10

alimina and feldspar - helps make ceramic less brittle and these are an obstacle for the crack

Question 11

ZIrconia ONLY (ZrO2 - zirconium oxide) (transformation toughening).

Answer 11

tetragonal structure. enough external stress results in tetragonal structure transform to monoclinic. happens right at tip of cracks where sharpness is highest and stress is highest. remember high stress leads to tetra –> mono. change in volume occurs locally where there is an expansion and compresses tip of crack. compression prevents propagation of crack.

Question 12

zirconia has high ___ and ____

Answer 12

toughness and flexural strength. best of all ceramics

Question 13

ceramics in dentistry

Answer 13

** inert ceramics - porcelain