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Biomaterials Exam 1 > Ceramics > Flashcards

Ceramics Flashcards

1
Q

Ceramics definition

A

a compopund of metallic and non metallic elements

Oxides, nitrides, silicates, carbides…

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2
Q

Properties of ceramics

A 
Strong, stiff
Brittle
Dense
Insulators of electricity
Refractory (retain strength at high temp; poor heat conductors)
Most are opaque
Chemically stable (don't corrode)
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3
Q

Compared to metals, ceramics have a higher…

A

Modulus of elasticity - more rigid

Higher strength - higher max stress

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4
Q

Compared to ceramics, metals have a higher…

A

Plasticity

Toughness

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5
Q

What bonds form ceramic structure?

A

ionic bonds

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6
Q

The structure of ceramics can be ____ or _____

A

Crystalline

Amorphous/glasses

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7
Q

The ionic bonds in ceramics are very strong bonds - what does this mean in terms of its mechanical properties?

A

Very difficult to stretch = high modulus of elasticity

Very difficult to break = high strength

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8
Q

In the ionic bonds of ceramics, ionized atoms share only specific electrons. What implications does this have on its mechanical properties?

A

Not possible to form dislocations

  • No plasticity
  • Brittle - once bonds are broken, crack appears
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9
Q

Metals are inherently unstable, thus they tend to…

A

oxidize

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10
Q

Why are ceramics chemically stable?

A

already in an oxidized state

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11
Q

Ceramics are chemically stable, and thus DO NOT…

A

Corrode

Release ions, etc. into surroundings

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12
Q

Metals are able to form dislocations because…

A

metallic bonds have electrons that are free to be shared with any atom in the structure

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13
Q

Under tension stresses, what is the mechanism for fracture in ceramics?

A

Easy propagation of cracks

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14
Q

Why are ceramics NOT brittle under compression stresses?

A

Cracks do not propagate

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15
Q

do metals or ceramics have better mechanical properties

A

metals

Ceramics are more brittle

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16
Q

are metals or ceramics more chemically durable

A

ceramics

17
Q

ceramics are brittle under ____, and strong under _____

A

tension

compression

18
Q

Mechanism of failure in tension

A

propagation of cracks

19
Q

Cracks in ceramics can only grow in ____

A

tension

20
Q

What are 3 techniques for the reinforcement of ceramics?

A
  1. Bond ceramic to another material
  2. Incorporate a component that hinders the propagation of cracks through the material
  3. Transformation toughening - hinders crack propagation
21
Q

How can you hinder the propagation of cracks in porcelain crowns?

A 
Aluminous porcelain
Leucite reinforced porcelain
Infiltrated
Cracks are stopped by ceramic particlees of a different nature
Acts as an obstacle to the crack
22
Q

Alumina incorporation into a feldspar/aluminosilicate matrix is the most common example of ____ in dentistry

A

Incorporating a component to hinder the propagation of cracks

23
Q

Transformation toughening of ceramics

A

Method of reinforcing ceramics
Materials transform under high stress to give a different structure
Only used in zirconia-based ceramics

24
Q

transformation toughening is exclusively used with

A

zirconia based ceramics

25
Q

Transformation toughening of zirconia (zirconium oxide)

A

If zirconia contains 3% mol yttria = stable in tetragonal form = can handle transformation
WHEN A CRACK FORMS, the stress transforms the zirconia around the crack from tetragonal to monoclinic
When it transforms around a crack - volume expands = puts crack under compression = no propagation
The transformation at the tip of the crack has a stress concentration effect = no propagation can happen under COMPRESSION stress
= less brittle = TOUGHER

26
Q

Zirconia based ceramics have the highest ____, ____, and _____ of all dental ceramics

A

strength
toughness
flexural strength

27
Q

What are the general applications of ceramics in dentistry?

A

inert ceramics - porcelain
reactive ceramics - ZnO, glass ionomer, CaSO4-gypsum
refractory
ceramics as abrasives

28
Q

What are the major constituents of inert ceramics?

A

Feldspar (aluminosilicate)
Alumina
Zirconia

29
Q

Porcelain is an inert ceramic and is used in dentistry for…

A

Crowns
Bridges
Veneers
Metal-ceramic restorations (PFM)

Biomaterials Exam 1 (7 decks)

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