Materials Science Chapters 1-6, 17

If the carbon content in common steel increases, the hardness then…

Increases

Increasing the temperature generally _________ electrical resistance.

Increases

Deformation in a material typically ________ electrical resistance.

Increases

The efficacy of heat conduction __________ as porosity increases.

Decreases

When in this structure, electron position is described in terms of proprietary density, and the aspects of this are determined by quantum numbers.

Wave

T or F: Most elements have unstable configurations.

True

1 - e(-0.25 * ΔEN²)

Percent Ionic Character

Atomic arrangement of a material that has periodic, 3D arrays of molecules.

Crystalline

Atomic arrangement of a material that has any non-periodic arrangement

Noncrystalline, Amorphous

Metals have dense atomic packing because…

Bonds are nondirectional, low bond energy, high shielding

The coordination number (C#) is the number of…

Nearest neighbors

SCC Coordination Number

6

SCS Radius (where a is edge length)

0.5a

SCS Atoms per unit cell

1

SCS Atomic Packing Factor

0.52

BCC Coordination Number

8

BCC atoms per unit cell

2

BCC Atomic Packing Factor

0.68

BCC Radius (where a is edge length)

sqrt(3) * a * 0.25

FCC Coordination Number

12

FCC Atoms per unit cell

4

FCC Radius

sqrt(2) * a * 0.25

HCP atoms per unit cell

6

Ideal ratio for c:a in HCP material structure.

1.633

HCP Radius is actually dependent on the how many factors?

Think: there are different molecules in this structure

2 (edge length a and edge length c)

What atomic facters determine crystal structure in ceramics?

Relative sizes, charge neutrality

When the ratio of cation:anion increases, the coordination number….

Increases

Bond hypridization is possible where there is significant ___________ bonding.

Covalent

The Percent Ionic Character is what percent of atoms becomes…

Hybridization

The most common elements on earth are…

Silicon, Oxygen

A polymorphic form of quartz, a type of ceramic. Known as (SiO₂)

Silica

When SiO₄ is bound to other stuff, we get….

Silicates

Bonds within silicates do what two things?

Maintain charge neutrality, ionically bond silicates

Structure of glass.

Amorphous

Fused silica (SiO₂) with no impurities; noncrystalline stucture.

Glass

Tetrahedrally structured carbon.

Diamond

Layered parallel-hexagonal arrayed carbon

Graphite

Describe the structure of graphite

• Weak van der Waal’s between layers, so the planes slide easily

• Layered hexagonal arrays make the planes

When property values depend on direction; observed in single crystals.

Ansiotropy

Polycrystals where properties have random orientation.

Isotropic

Polycrystals where properties are textured.

Ansiotropic

When there are 2+ structures for the same material.

Polymorphism; allotropy

Carbon has multiple forms, such as diamond and graphite. This is an example of the trait…

Allotropy

A hydrocarbon where each carbon is singly bonded to four other atoms.

Saturated

A hydrocarbon where some carbon is doubly/triply bonded to four other atoms.

Unsaturated

The property describing that two compounds with the same chemical formula may have multiple different structures.

Isomerism

The average number of repeat monomers per chain.

Degree of Polymerization

Grains that are roughly the same dimension in all directions after solidification.

Equiaxed

Grains that are elongated in one direction after solidification.

Columnar

Something added to a substance during solidification to make smaller, more uniform, equiaxed grains.

Grain Refiner

Heat treating polymers causes % crystallinity to…

Increase

Polymers are usually a mix of straight regions (crystalline) and squiggly regions called _____ regions.

Amorphous

A type of crystals that, in polymers, are only for slow and carefully controlled growth rates.

Single Crystals

Polymer semi-crystalline structure that alternates chain-folded crystallites and amorphous regions.

Spherulite

Polymer spherulite structures have relatively ______ growth rates.

Fast

Each spherulite in polyethylene can look like what shape?

Maltese Cross

Two steps of solidification in solids.

• Nuclei form

  • Crystals grow until their boundaries meet one another

The slight atomic disorder in grain boundaries leads to what two attributes?

• High atomic mobility

• High chemical reactivity

Dimension of Defect:

Vacancies

0

Dimension of Defect:

• 0 (point)

• 1 (linear)

• 2 (interfacial)

Interstitial atoms

0

Dimension of Defect:

• 0 (point)

• 1 (linear)

• 2 (interfacial)

Substitutions

0

Dimension of Defect:

• 0 (point)

• 1 (linear)

• 2 (interfacial)

Dislocations

1

Dimension of Defect:

• 0 (point)

• 1 (linear)

• 2 (interfacial)

Grain boundaries

2

What point defect of a metal does the picture describe?

Vacancy

What point defect of a metal does the picture describe?

Self-interstitial

In metals, each ____________ is a potential vacancy

Lattice site

In ceramics, vacancy point defects can happen with _________.

• Cations

• Anions

• Cations and anions

Cations and anions

In ceramics, interstitial point defects can happen with _________.

• Cations

• Anions

• Cations and anions

Note: one option is observed more normally, because the other is usually too large

Cations

Conditions for substitutions in metals (Hume-Rothery Rules)

• Difference in atomic radius < 15%

• Proximity in periodic table (e.g. similar electronegativities)

• Same crystal structure (pure metals)

• Valences (higher valences dissolve easier)

A polymer linear dislocation where part of the polymer extends from the base in a twisting manner

Screw

A polymer point defect where the chain drops off the boundary and ends.

Dangling chain

A polymer point defect where the typically straight chain starts warping and wiggling.

Noncrystalline region

A polymer point defect where the chain trails off of the base and eventually returns.

Loose chain

A polymer point defect where the chain stops before it should.

Vacancy

A polymer point defect where two loops of the chain connect horizontally

Branch

In a screw dislocation, the measure of lattice distortion (Burger’s vector) is ________ to the dislocation line.

Parallel

A plane dislocation that occurs when an extra half-plane of atoms is inserted into the base structure, perpendicular to the dislocation line.

Edge

Dislocations _____ when stresses are applied and results in ________ deformation

Permanent (plasic)

Mirror reflections of atom positions of one side is a twin to the other; an interfacial defect

Twin boundaries

These interfacial faults occur when there is an error in the planar stacking sequence. For example, ABABC instead of ABCABC

Stacking faults

Catalytic reactions normally occur at….

Surface defect sites

Grain boundaries are (more/less) susceptible to etching.

More

Number of Grains Per Inch² at 100x magnification.

2^{ASTM # - 1}

Metallographic scopes often use this type of light to increase contrast.

Polarized

The best resolution for an optical microscope is….

100nm

The best resolution for an electron microscope is…

0.003nm

The best possible magnification for an electron microscope is…

1,000,000X

The best possible magnification for an optical microscope is…

1,000X

Electron beams in an electron microscope are focused by what type of lenses?

Magnetic?

Type of microscopy where surface atoms are imaged using a tiny probe that tapers to a single atom; atoms can be rearranged by pushing them with a tip.

STM (scanning tunneling microscopy)

Three types of dislocation imperfections.

Edge, screw, mixed

Gases and liquids have this diffusion mechanism.

Random (Brownian)

Diffusion of atoms of one material into another.

Interdiffusion

Atomic migration in a pure metal

Self-diffusion

The rate of vacancy diffusion depends on…

Number of vacancies, activation energy

Interstitial diffusion is (faster, slower) than vacancy.

Faster

A type of interstitial diffusion where the outer surface is selectively hardened by diffusing carbon atoms into the surface.

Case hardening

Case hardening diffuses what atoms into the surface of the material?

Carbon

Diffusion of very small concentrations of atoms of impurity (e.g. phosphorous) into the semiconductor silicon.

Doping

The target of diffusion in doping is what material?

Silicon