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BCS > Transitions in materials > Flashcards

Transitions in materials Flashcards

1
Q

What are the 5 classes of materials?

A

Metals, ceramics, glasses, polymers, composites

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2
Q

Give examples of primary and secondary bonds

A

Primary: covalent (share), ionic (donate), metallic (weaker, sea of e-s)
Secondary: Van der Walls, H bonds

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3
Q

Which metals are used in dentistry?

A

Amalgam for fillings
Stainless steel (iron and chronium) for braces
Gold for fillings
Titanium for implants

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4
Q

What property helps implants to bond with bone?

A

Titanium oxide on surface

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5
Q

Properties of metals

A

Hard, opaque, lustrous
Good conductors of heat and electriity
Generally malleable
Can be cast and amalgamated

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6
Q

Define the metallic bond

A

Consists of a lattice of bonded metal cations with a sea of electrons

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7
Q

Why are metals lustrous?

A

Photons are absorbed by free e-s, which move up to a higher energy level. When they fall back down the energy is reemited as light

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8
Q

Why are metals ductile?

A

Cations are able to align while being shielded by their fluid like sea of e-s

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9
Q

Why do metals not shatter?

A

They just dent. The mobile e’s sheild cations from each other, preventing violent repulsion and allowing metal to change shape.

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10
Q

How are metal cations organised?

A

7 different crystal lattices

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11
Q

What is a transition in dental materials?

A

Reorganisation of distribution of atoms in a material. Occurs at transition temp

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12
Q

What are the common transitions for metals?

A

Solid > liquid > solid
Solid + liquid > solid
Solid > solid

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13
Q

Which ceramics and glasses are used in dentistry?

A

PerioGlas, zirconia, lithium disilicate, porcelain, HA

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14
Q

What are ceramics?

A

Inorganic, non-metallic compounds
Usually crystalline
Compounds of metal ions but not metallic themselves
Occasionally term ceramic is used to encompass glasses (inorganic amorphous materials)

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15
Q

Properties of ceramics

A

Brittle, hard
high melting points
weak in tension, high compression strength
ordered 3D structure of covalently and ionically bonded compounds of a metal with a non-metal e.g. Al2O3

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16
Q

How are ceramics produced?

A
  1. Powder synthesis
  2. Preconsolidation processing (milling/ grading/ additives)
  3. Compaction/ shape forming (produce ‘green body’
  4. Drying
  5. Densification (sintering)
    MIX SIEVE SQUASH DRY HEAT
17
Q

Methods for producing a ‘green body’ ready for drying

A 
Dry pressing
Isostatic pressing
Slip casting
Tape casting
Extrusion
Injection moulding
18
Q

Common transitions in ceramics

A

Powder > sinter (shrinkage) > solid
Solid > hot press > solid
Slid + liquid > solid (setting reaction)

19
Q

What are glasses?

A

Brittle, hard materials
Non-crystalline solids
No long range (atomic) order
Supercooled liquid where nucleation has been avoiding

20
Q

How are glasses formed?

A

By melting, sol-gel techniques or vapour deposition

21
Q

What does supercooled mean?

A

Cooled below melting point without solidification (usually very past), then chucked in water

22
Q

Common transitions in glass

A

Normal cooling –> Crystallisation –> No glass formation

Supercooling –> no time to organise molecules –> amorphous –> forms a glass

23
Q

What is a classic glass former?

A

Basic building block for silica (ceramic or glass) is silica tetrahedron with identical bond lengths and bond angles. Tetrahedra bonded to neighbouring tetrahedra via bridging oxygens

24
Q

What changes the melting point of a glass?

A

Putting ions in the way, disrupting structure

25
Q

What are glass-ceramics formed by?

A

Formed by controlled crystallisation of glass

2 stage heat treatment: nucleation & growth

26
Q

What is the structure of glass-ceramics?

A

Typically pore free, little measurable decrease in volume on ceramming

27
Q

Name 3 polymers used in dentistry?

A

Acrylic resin
Polyether
Alginate

28
Q

What is the glass transition temperature?

A

The T at which the polymer chains begin to flow past each other. No immediate point of melting

29
Q

Common transitions in polymers

A

Solid > liquid > solid
Monomer > solid
polymer liquid > polymer solid
-polymers melt slowly with heat and solidify when being cooled

30
Q

What are composites?

A

2 materials mixed together

31
Q

3 composites used in dentistry

A

GIC
IPS e.max lithium disilicate
Dental composite (-resin)

32
Q

Common transitions in composites

A

Depend on exact constituents on composites

Cannot make generalisations

33
Q

LOOK AT WORD DOC AND LEARN GRAPHS

A

LOOK AT WORD DOC AND LEARN GRAPHS

BCS (35 decks)

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