Materials Final

What property related to bonding is affected by bond length?

Melting Temperature (Tm)

What is the relationship between bond energy (Eo) and melting temperature (Tm)?

The larger the bond energy (Eo), the higher the melting temperature(Tm) of the material. This is because stronger bonds require more energy to break, resulting in higher melting points.

What is the formula for the coefficient of thermal expansion (αl)?

$αl = ΔL / (Lo * (T2 - T1))$

How does bond energy (Eo) affect the coefficient of thermal expansion (αl)?

The smaller the bond energy (Eo), the larger the coefficient of friction(αl), meaning materials expand more easily with heat. This is because weaker bonds allow for greater atomic displacement with temperature increases.

What are the properties of ceramics regarding bond energy and melting temperature?

Ceramics have large bond energy, high melting temperature, and small coefficient of thermal expansion

What type of bonding is found in metals?

Metallic bonding

What are the properties of metals regarding bond energy and melting temperature?

Metals have variable bond energy, moderate melting temperature, and moderate coefficient of thermal expansion.

What type of bonding is characteristic of polymers?

Covalent and secondary bonding

What are the properties of polymers regarding bond energy and melting temperature?

Polymers have weak bond energy, low melting temperature, and large coefficient of thermal expansion.

What is the significance of the Strength to Stiffness Ratio?

It is a key factor in the material selection process

What does the term 'Forever Materials' imply?

It suggests that while engineered materials can last a long time

What are the components of the Materials Life Cycle Diagram?

Usable products, energy, water, effluents, air emissions, raw materials, solid waste, and other impacts.

What types of impacts are classified in modern life cycle assessments?

Environmental and social impacts

Name three environmental impacts considered in materials life cycle assessments?

Greenhouse gas emissions, ecotoxicity, and eutrophication.

What are some social impacts considered in materials life cycle assessments?

Employment, wages, workplace conditions, community, and education.

What costs are associated with materials selection?

Monetary cost, energy cost, environmental cost, ethical cost, social cost, and political cost.

Polycrystalline materials

Most engineering materials are polycrystalline

Unit cell types

Triclinic, monoclinic, orthorhombic, tetragonal, hexagonal, rhombohedral, and cubic are defined by their unit cell axis lengths and angles.

Periodic lattice structures

Describe all possible periodic lattice structures in 3D

Point indices

Point indices q r s fall in the range of 0 to 1

Point lattice coordinates

Point lattice coordinates Px Py Pz include dimension

What are the four tenets of materials science and engineering?

structure, processing, properties, performance

The units cells of crystal structures explain structure at what length scale?

atomic scale

Name three different classes of material properties?

thermal, mechanical, electrical

Write a 4-step procedure for evaluating materials selection for an industrial application.

1. In service conditions 2. Trade-off material properties 3. Deterioration of material properties 4. economical material and fabrication

Generic Life-Cycle of Materials

Synthesis and processing - engineered materials - product design, manufacture, assembly - applications - waste/recycle - raw materials

Give three examples of material life cycle impacts

environmental impacts, acidification, eutrophication, greenhouse gas emissions

volume of cubic unit cell

a^3

What are the three main classes of materials that we will discuss in this course?

metals, ceramics, polymers

What type(s) of bonding would be expected for brass

metallic

What type(s) of bonding would be expected for epoxy

covalent

What type(s) of bonding would be expected for BaS (barium sulfide)

ionic

What type(s) of bonding would be expected for solid xenon

van der Waals

What type(s) of bonding would be expected for bonze

metallic

What type(s) of bonding would be expected for nylon

covalent with some van der Waals

What type(s) of bonding would be expected for AlP (aluminum phosphide)

covalent

subatomic level (

electrons and nuclei of individual atoms

microscopic level (10^-8 - 10^-4m)

arrangement of small grains (groups of atoms)

macroscopic level

viewable with the unaided eye

Mechanical properties

relate deformation to an applied load or force

thermal properties

related to a change in temperature gradients (ex: heat capacity)

electrical properties

stimulus is an applied electric field (ex: electrical conductivity)

magnetic properties

response of material to a magnetic field (ex: magnetization)

optical properties

stimulus is electromagnetic or light radiation (ex: refraction)

examples of mechanical properties

stress, strain, ductility

features of metals and alloys

conductive, strong, malleable, ductile, tough, high density, opaque, reflective

features of ceramics

brittle, hard, strong, insulative, compounds of metals and nonmetals

features of polymers

soft, ductile, low density, mostly insulators, optically transparent or translucent

principle quantum # (n)

describes the principle energy level of the atom

orbital quantum # (l)

describes the subshells (0 - n-1)(s, p, d, f)

magnetic quantum # (ml)

defines the number of energy states for each subshell (-l to +l)

spin quantum # (ms)

defines the spin orientation of electrons (+.5 or -.5)

electronegativity

measure of how willing atoms are to accept electrons

physical properties of ionic bonds

high melting and boiling points

physical properties of covalent bonds

high melting point, hard, transparent, brittle or cleave, good insulators

physical properties of metallic bonds

conductive, opaque, ductile

crystalline

atoms are packed in an ordered arrangement

amorphous

no pattern to the atomic arrangement

unit cell

smallest structural unit that can describe the crystal

lattice

the 3D array of points corresponding to atom positions

close packed direction in an SC crystal

edges

cube edge length in SC crystal

2R

of atoms in a SC unit cell

1

coordination # of SC unit cell

6

close packed direction of BCC crystal

long diagonals

of atoms in a BCC unit cell

2

coordination number of BCC unit cell

8

close packed direction of FCC crystal

planar diagonals

edge length of BCC unit cell

(4R)/(3)^.5

edge length of FCC unit cell

2R(2^.5)

of atoms in a FCC unit cell

4

coordination # of FCC unit cell

12

order of densities of materials

metals>ceramics>polymers

single crystals

perfectly periodic arrangement of atoms

polycrystals

a collection of many small crystals or grains

polymorphism

materials exist in more than one crystal structure

allotropy

the material is an elemental solid

point coordinates (q, r, s)

fall between 0 and 1, do not get commas or parenthesis

point lattice coordinates

px, py, and pz include dimension

equivalent directions

directions that have the same spacing of atoms are equivalent

boltzmann's constant

8.617x10^-5ev/K

tempered martensite

formed by heat treating martensite

reduces brittleness

reduces internal stress caused by quenching

bonding in ceramics

can be ionic, covalent, or mixed

relationship between ionic character and electronegativity

% ionic character increases with difference in electronegativity

factors that determine crystal structure of ceramics

maintaining electrical neutrality

relative size of ions (stable structures require anions and cations to touch)

coordination number

of anions nearest neighbors for a cation

relationship between coordination number and the ratio of radii

coordination number increases with the ratio of the radii: (rcation/ranion)

vacancies in ceramics

exist for both cations and anions

interstitials in ceramics

Exist for cations

Not normally observed for anions because anions are large relative to the interstitial sites

Shottky Defect

a paired set of cation and anion vacancies

Why are ceramics more brittle than metals?

reduced slip

resistance to motion of ions of like charge past one another

Flexural Stress

3 point bend test

the fracture stress determined is known as the flexural strength of the modulus of rapture

Cause of Layered Silicates

Negative charge balanced by an adjacent plane rich in positively charged cations

Bonding within layered silicates

strong and intermediate ionic-covalent

Bonding between sheets of layered silicates

weak, van der Waal’s forces

Structure of silicates

polymorphic forms

ring and chain structure

laminar structures

3D crystalline structures

Bonding in crystalline silicates

3-D crystalline network: every oxygen atom is shared by adjacent tetrahedra

electrical neutrality is maintained

3 main ceramic forming techniques

cementation, particular forming, glass forming

Hydroplasticity of clay

• water molecules fit in between layered sheets

• reduces degree of van der Waals bonding

• when external forces applied - clay particles free to move past one another - becomes hydroplastic

Drying

As water is removed, interparticle spacings decrease (shrinkage)