Materials Science-Sci Oly

Characteristics of ceramics

Hard, brittle, and electrically and thermally insulative

Ceramic bonding

mostly ionic, some covalent

Ionic bonding energy range

600kJ/mol to 1500kJ/mol

Metallic bonding energy range

62 kJ/mol to 850 kJ/mol

Face Centered Cubic

Crystal structure where atoms are located at 8 corners and centered at each of the 6 faces.

FCC atomic packing factor

0.74

FCC side length

A=4R√2

Body Centered Cubic

Crystal structure where atoms are located at each of the 8 corners as well as in the center of the cubic cell

BCC atomic packing factor

0.68

BCC side length

A = 4R√3

BCC Coordination number

8

Hexagonal Close Packing

Crystal structure composed of two hexagons of 6 atoms each, an additional atom in the center of each hexagon, and a triangle between the two hexagons.

HCP atomic packing factor

0.74

HCP coordination number

12

Simple cubic

Crystal structure where there are atoms at each corner of the unit cell

SC packing factor

0.52

SC side length

A=2R

SC coordination number

6

Crystallinity

The degree of structural order in a solid

Crystalline

Items arranged in an ordered pattern extending in all spacial dimensions

Polycrystalline

Contain true crystal portions with mixed sizes and orientations.

Amorphous

Short range order but have significantly less linkage compared to crystalline structures.

Amorphous examples

Gels, thin films, and glass

Polycrystalline examples

Metals and many ceramics.

X-Ray Diffraction

X-rays change direction on contact with matter, resulting in changes in radiation intensity, that is used to determine the three-dimensional arrangement of atoms.

Bragg's Law

When the X-ray is incident onto a crystal surface, its angle of incidence will reflect with the same angle of scattering.

Bragg's Law Formula

nλ = 2dsinθ

Light microscopy

Any kind of microscope that uses visible light to observe specimens

Pros of Light microscopy

- No risk of radiation leakage

- Inexpensive with low maintenance cost

Electron microscope

Use a beam of electrons to scan or pass through the specimen.

Pros of electron microscope

- Higher magnification (up to 16000x directly, and up to 1000000x photographically).

- High-resolution images provide detailed structural information.

- Widely used in scientific research for in-depth analysis of materials.

Cons of electron microscope

- Risk of radiation leakage.

- Expensive with high maintenance costs.

Ceramic

non-metallic, inorganic materials that are shaped and hardened by heating to high temperatures.

Time Temperature Transformation Diagram (TTT Diagram)

Shows what happens to a material at different temperatures and times

X-axis of TTT Diagram

Time (often on a logarithmic scale), which shows how long the material is held at a certain temperature.

Y-axis of TTT Diagram

Temperature, which indicates the temperature at which the material is processed.

Transformation Lines

These lines represent different phase transformations (e.g., austenite to martensite for steels, crystallization for ceramics).

Nose Curve

The curve where transformation starts and completes, indicating the optimal time and temperature for achieving specific microstructures.

Start Line

Marks the beginning of a phase transformation (e.g., the start of crystallization).

Finish Line

Marks the end of the transformation, indicating when the phase change is complete.

Isothermal Transformation Region

Area within the diagram where a material is held at a constant temperature to allow specific transformations to occur.

No-Transformation Region

Areas where no significant phase changes occur during the given time and temperature conditions.

Interpreting Phase Changes

The TTT diagram provides insight into what happens to the material's structure when subjected to different heating and cooling schedules.

Interpreting Timing and Temperature

The diagram shows the optimal time and temperature needed to achieve desired transformations.

Phase Keeping Diagram

Illustrate the relationship between temperature, pressure, and the phases of a substance at equilibrium.

Unary phase change diagram

Illustrate the phase behavior of a single substance as temperature and pressure change.

Binary phase change diagram

Depicts the phase behavior of two components at various temperatures and compositions.

X-Axis of binary phase diagram

Represents the percent composition of the two materials

Y-Axis of binary phase diagram

Represents temperature, indicating how temperature affects the phase behavior of the mixture

Single phase regions

Areas where only one phase exists

Two-Phase Regions

Areas where two phases coexist, represented by lines or curves on the diagram.

Liquidus Line

Upper boundary of the two-phase region.

Solidus Line

Lower boundary of the two-phase region.

Eutectic Point

lowest temperature at which existence of a liquid phase is possible

Eutectoid point

Point on a phase diagram where a solid phase transforms into 2 different solid phases

Peritectic Point

A point where a solid and a liquid phase transform into a second solid phase upon cooling.

materials characterization

Measuring and determining physical, chemical, mechanical, and microstructural properties of materials.

Microscopy

Probing and mapping a material's surface and subsurface structure by using photons, electrons, ions, or physical cantilever probes

Spectroscopy

The study of the properties of light that depend on wavelength.

Contributors to heat capacity in metals

free electrons

Contributors to heat capacity in insulators

atomic vibration

Heat capacity

the number of heat units needed to raise the temperature of a body by one degree.

Thermal expansion

Atoms vibrate more vigorously with temperature increases

Thermal conductivity

Ability of a material to transfer heat through a structure

Thermal shock

Stress and potential cracking or failure resulting from rapid temperature changes

Insulation

A material's ability to resist the flow of heat or electrcity

Piezoelectricity

Conversion of pressure to electric voltage

Ceramics

nonmetal, inorganic substances that are hardened by heat