Lecture 3 - Ceramics

Question 1

What type of bonding is predominantly found in ceramics?

Answer 1

Ionic bonding

Ionic bonding involves the transfer of electrons from metals to non-metals, creating cations and anions.

Question 2

What is the coordination number in ceramics?

Answer 2

The number of anion nearest neighbors for a cation (and vice versa)

This indicates how many oppositely charged ions surround a given ion in a lattice.

Question 3

Define polymorphism in the context of ceramics.

Answer 3

When a single material can exist in more than one crystal structure

Different atomic arrangements of the same substance lead to different properties.

Question 4

What is allotropy?

Answer 4

Polymorphism that occurs in elemental solids

Example: Carbon exists as both graphite and diamond.

Question 5

What characterizes ionic bonding?

Answer 5

Electrons are transferred, forming cations and anions that create a tight electrostatic lattice

This results in strong, non-directional bonds with high melting points but brittleness.

Question 6

Explain covalent bonding in ceramics.

Answer 6

Atoms share valence electrons in a directional manner, forming networks

Covalent bonds are very strong, as seen in diamond or SiC.

Question 7

What is the purpose of the transverse bending test?

Answer 7

To test brittle materials by bending them until they fracture

Unlike tensile tests, bending tests are used because ceramics are too brittle.

Question 8

Describe brittleness in ceramics.

Answer 8

Ceramics tend to fracture under tensile load without plastic deformation at room temperature

This is a key characteristic of both crystalline and amorphous ceramics.

Question 9

What is the definition of flexural strength?

Answer 9

The stress at which a ceramic fractures during bending

It is measured using a transverse bending test.

Question 10

What is viscous flow in amorphous ceramics?

Answer 10

A deformation process where atoms slide past each other under stress

This occurs without dislocations, similar to thick syrup.

Question 11

What is the glass transition temperature (Tg)?

Answer 11

The temperature at which a glassy ceramic transitions from brittle to rubbery

Below Tg, the material is stiff glass; above Tg, it starts to flow.

Question 12

What is sintering?

Answer 12

Heating a compacted ceramic powder below its melting point to fuse particles

This process is used to strengthen and densify ceramics.

Question 13

What is the equation for flexural strength?

Answer 13

Flexural strength = 3FL/2bd

Variables: F = load at fracture, L = distance between support points, b = width, d = height.

Question 14

How does porosity affect ceramics?

Answer 14

Porosity reduces flexural strength by acting as stress concentrators

This makes it easier for cracks to initiate and propagate.

Question 15

What are typical crack configurations in ceramics?

Answer 15

Impact or point loading, bending, torsion, internal pressure

These configurations indicate how ceramics may fail under different stresses.

Question 16

What are slip systems in ceramics?

Answer 16

Specific crystallographic planes and directions where dislocations can move

Motion of dislocations is the main mechanism for plastic deformation.

Question 17

What is heat capacity (C)?

Answer 17

The amount of heat required to produce a unit rise in temperature for 1 mole of a substance

It indicates the material’s ability to absorb heat.

Question 18

What does the linear coefficient of thermal expansion (αl) indicate?

Answer 18

The extent to which a material expands upon heating

It is a material property relevant to thermal behavior.

Question 19

What is electrical conductivity in ceramics?

Answer 19

Often low due to the unavailability of free electrons for conduction

This is a typical characteristic of traditional ceramics.

Question 20

What characterizes corrosion in ceramics?

Answer 20

A process involving oxidation and reduction reactions in an aqueous environment

Ceramics can be resistant to corrosion but some can dissolve in water.

Question 21

List the properties of ceramics.

Answer 21

• High melting temperatures
• Low thermal and electrical conductivity
• High flexural strength
• Brittle
• Chemically resistant

These properties make ceramics suitable for various applications.

Question 22

What are glasses in ceramics?

Answer 22

Non-crystalline, often silicate-based materials containing other oxides

Soda-lime glass is a common example, consisting of SiO2 and other oxides.

Question 23

What are the properties of glass-ceramics?

Answer 23

Fine-grained, polycrystalline materials made by crystallization of glass

They undergo high-temperature heat treatment to form crystals.

Question 24

What are clays?

Answer 24

Naturally found, often silicate-based layered materials

Clays are inexpensive and easy to fabricate.

Question 25

What are refractories?

Answer 25

Substances resistant to heat, remaining unreactive in severe environments ## Footnote They provide thermal insulation and are classified based on composition.

Question 26

What defines abrasives?

Answer 26

Hard, wear-resistant materials used for grinding ## Footnote Examples include diamonds and aluminum oxide.

Question 27

What is Portland cement?

Answer 27

A hydraulic cement formed by grinding and mixing raw materials, then heating ## Footnote It sets and hardens through cementation bonds at room temperature.

Question 28

What is the significance of orbital hybridization in carbon?

Answer 28

It results in various allotropes of carbon with different structures and properties ## Footnote This is key to understanding carbon's diverse material forms.

Question 29

List properties of diamond.

Answer 29

* Chemically inert * Extremely hard * Very low sliding coefficient of friction * High thermal conductivity * Transparent with high index of refraction ## Footnote These properties make diamond suitable for various applications.

Question 30

What are the properties of graphite?

Answer 30

* Anisotropic properties * Soft with lower modulus of elasticity than diamond * Chemically stable at high temperatures * High resistance to thermal shock * Optically opaque ## Footnote Graphite has unique properties that differentiate it from diamond.

Question 31

What characterizes carbon nanotubes?

Answer 31

A single-atomic-layer of graphite rolled into a tube with unique properties ## Footnote They are strong, stiff, and have anisotropic electrical properties.

Question 32

What are advanced ceramics?

Answer 32

Materials with engineered mechanical, electrical, magnetic, optical, or biological properties ## Footnote They are designed for advanced technologies.

Question 33

What are bioceramics?

Answer 33

Ceramic-based biomaterials used in regenerative medicine ## Footnote Examples include bioinert ceramics like alumina and zirconia.

Question 34

What challenges are faced in the fabrication and processing of ceramics?

Answer 34

High melting temperatures and brittleness ## Footnote These challenges affect the production and application of ceramic materials.