Ceramics Flashcards
Ceramics definition
a compopund of metallic and non metallic elements
Oxides, nitrides, silicates, carbides…
Properties of ceramics
Strong, stiff Brittle Dense Insulators of electricity Refractory (retain strength at high temp; poor heat conductors) Most are opaque Chemically stable (don't corrode)
Compared to metals, ceramics have a higher…
Modulus of elasticity - more rigid
Higher strength - higher max stress
Compared to ceramics, metals have a higher…
Plasticity
Toughness
What bonds form ceramic structure?
ionic bonds
The structure of ceramics can be ____ or _____
Crystalline
Amorphous/glasses
The ionic bonds in ceramics are very strong bonds - what does this mean in terms of its mechanical properties?
Very difficult to stretch = high modulus of elasticity
Very difficult to break = high strength
In the ionic bonds of ceramics, ionized atoms share only specific electrons. What implications does this have on its mechanical properties?
Not possible to form dislocations
- No plasticity
- Brittle - once bonds are broken, crack appears
Metals are inherently unstable, thus they tend to…
oxidize
Why are ceramics chemically stable?
already in an oxidized state
Ceramics are chemically stable, and thus DO NOT…
Corrode
Release ions, etc. into surroundings
Metals are able to form dislocations because…
metallic bonds have electrons that are free to be shared with any atom in the structure
Under tension stresses, what is the mechanism for fracture in ceramics?
Easy propagation of cracks
Why are ceramics NOT brittle under compression stresses?
Cracks do not propagate
do metals or ceramics have better mechanical properties
metals
Ceramics are more brittle
are metals or ceramics more chemically durable
ceramics
ceramics are brittle under ____, and strong under _____
tension
compression
Mechanism of failure in tension
propagation of cracks
Cracks in ceramics can only grow in ____
tension
What are 3 techniques for the reinforcement of ceramics?
- Bond ceramic to another material
- Incorporate a component that hinders the propagation of cracks through the material
- Transformation toughening - hinders crack propagation
How can you hinder the propagation of cracks in porcelain crowns?
Aluminous porcelain Leucite reinforced porcelain Infiltrated Cracks are stopped by ceramic particlees of a different nature Acts as an obstacle to the crack
Alumina incorporation into a feldspar/aluminosilicate matrix is the most common example of ____ in dentistry
Incorporating a component to hinder the propagation of cracks
Transformation toughening of ceramics
Method of reinforcing ceramics
Materials transform under high stress to give a different structure
Only used in zirconia-based ceramics
transformation toughening is exclusively used with
zirconia based ceramics
