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Materials 121 > Chapter 6 - Ceramics and Glasses > Flashcards

Chapter 6 - Ceramics and Glasses Flashcards

1
Q

What is an example of a traditional ceramic?

A

Clay, Porcelain, Whiteware, Crockery etc…

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2
Q

What is an example of an advanced ceramic?

A

Alumina (for spark plugs, silicon carbide (for grinding/polishing), etc…

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3
Q

What is an example of a natural ceramic?

A

Teeth, bones, seashells etc…

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4
Q

Define “Ceramics”?

A

The term ceramics defines a type of solid material that is made of a structure including both metallic and non-metallic components.

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5
Q

True/False: Ceramics are extremely Strong.

A

True, but only in compression.

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6
Q

True/False: Ceramics are ductile.

A

False, ceramics are extremely brittle.

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7
Q

True/False: Ceramics are Hard.

A

True, ceramics are hard materials.

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8
Q

True/False: Ceramics work well as conductors of both heat and electricity.

A

False, ceramics are great electrical and thermal insulators.

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9
Q

True/False: Ceramics have low chemical stablility.

A

False, ceramics are very chemically stable.

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10
Q

True/False: Ceramics have a high melting point.

A

True, ceramics are hard to melt.

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11
Q

Why are covalent bonds so directional?

A

Because the nature of their bonding system causes the bonded atoms to always be a similar distance away from each other (same bond angle).

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12
Q

In an Ionically bonded ceramic which is the cation and which is the anion?

  • Metal
  • Non-Metal
A

The cations are the metallic atoms, and the anions are non-metallic atoms.

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13
Q

True/False: Ionically bonded molecules must always be electrically neutral.

A

True.

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14
Q

Why is the relative size of the atoms in the ionic molecule important with regards to whether a molecule is viable.

A

Because the cations must not touch each other and the anions must not touch each other. While having as many cations in contact with anions as possible and vice versa. If the difference in size of the two atoms is too great it becomes difficult for them to bond.

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15
Q

True/False: Cations are usually smaller than anions.

A

True.

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16
Q

How are ceramic structures named?

A

Ceramic structures are usually named after the most common material that has that structure.
Eg: Rock Salt or Sodium Chloride structure.

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17
Q

Why are ceramics typically brittle?

A

Bonds only form in specific patterns. So they cannot reform after slip. Causing fractures.

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18
Q

Why are ceramics typically stiff?

A

Because the covalent and ionic bonds are significantly stronger than the metallic bonds.

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19
Q

Why do ceramics never reach their true theoretical strength?

A

Because the object can never be truly free of all imperfections.

20
Q

What are the two reasons for how porosity affects strength?

A
  1. Reduces cross-sectional area. (Stress = Force/Area)

2. Pores act as stress concentrators. Stress has to move around the pores.

21
Q

Why are fibres typically stronger than bulk materials?

A

Because the fibres tend to have much smaller pores.

22
Q

Why are metals so much more tough than ceramics?

A
  1. No plastic deformation.
  2. Even a tiny pore (or crack/hole/scratch) has a large effect on the fracture toughness.
  3. Highly likely that ceramics contain porosity.
23
Q

Which is the limiting factor for ceramics? Toughness or Strength?

A

Toughness.

24
Q

What are the main toughening mechanism for ceramics?

A
  1. Densifying (reducing porosity)
  2. Reinforce it with something else (usually something with high tensile strength.
  3. Transformation toughening.
25
Q

What is transformation toughening?

A

Transformation toughening describes a metastable phase of both tetragonal and cubic structured ceramics. As it is a solid and the stable form (monoclinic and cubic) has a larger volume it is unable to reach its true stable form, however when a crack forms the new space gives room for the change to monoclinic structures.

26
Q

In order to cast a ceramic you must first add ____ to the clay to form either a ____ or _____.

A

Water to the clay to form a slip or slurry.

27
Q

When _____ is added to clay it becomes very plastic.

A

Water.

28
Q

When a clay body is slip cast or hydroplastically formed it needs?

A

Drying and Firing.

29
Q

What can be a side effect of the proces of firing?

A

Vitrification.

30
Q

What is vitrification?

A

Vitrification describes a process by which some of the components of a ceramic melt during the firing process and then solidify as glass.

31
Q

What is the cause of the relatively low density limit of green compact?

A

The density limit is so low because powders are not good at transmitting the pressure.

32
Q

What is uniaxial pressing?

A

The process by which a powdered ceramic is placed into some kind of form and then pressed into shape from one direction.

33
Q

What is double-action pressing?

A

The process by which a powdered ceramic is placed into some kind of form and then pressed from two directions simultaneously.

34
Q

What is isostatic pressing?

A

The process by which a powdered ceramic is formed by being pressed from every direction simultaneously. This is the best but also the most expensive process.

35
Q

How can the green compact be turned into a useful ceramic?

A

Through densifying (making more dense) usually through the process of sintering.

36
Q

What is sintering?

A

Sintering is a process of heat treating a green compact (not melting it) in order to cause the grains of the structure to shrink together. This occurs through diffusion.

37
Q

True/False: Sintering is necessary for creating advanced ceramics.

A

True.

38
Q

True/False: Sintering reduces the surface area of the ceramic particles.

A

True. As the particles shrink into each other they no longer have large gaps between the particles, reducing the surface area.

39
Q

True/False: Sintering reduces the total volume of the object being sintered.

A

True.

40
Q

How can you increase the speed at which you can sinter a ceramic?

A
  1. Increase the temperature.

2. Decrease the particle size.

41
Q

True/False: Glass has a crystalline structure.

A

False, glass has an amorphous structure (non-crystalline).

42
Q

Define glass.

A

A type of ceramic with no long range order.

43
Q

What are “Network Modifiers”?

A

Network modifiers are chemicals that are added to a glass in order to disrupt the network of connections in the glass structure in order to provide certain properties.

44
Q

Define Viscosity?

A

Viscosity is the resistance of a material to flow.

45
Q

What are the properties of glass?

A
  1. Excellent Optical Properties
  2. High Chemical Stability
  3. Electrical Insulator
  4. Thermal Properties (expansion) can be altered by varying composition
  5. Extremely Brittle (low fracture toughness)
46
Q

When tempering glass the outer surface is put into ______ while the inside is put into _______.

A

The outer surface is in residual compression while the inside is in residual tension.

Materials 121 (8 decks)

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