materials science final exam

metals

composed of one or more metallic elements, strong, ductile, high thermal and electrical conductivities, opaque, reflective, can be shaped or cast, some are very hard, chemically reactive (corrosion)

polymers

organic - carbon as the main building block, composed of molecular chains or networks, usually synthetic (man made), soft, ductile, low strengths, low densities, low thermal & electrical conductivities, opaque, translucent or transparent, can be formed into different shapes, plastics and elastomers

ceramics

compounds of metallic and non-metallic elements (oxides, carbides, nitrides, sulfides), hard, brittle, low thermal & electrical conductivities, opaque, translucent, or transparent, highly wear resistant, high melting temperature

composites

two or more materials coming from the three categories: metals, polymers, ceramics, usually reinforcing filler material and a binding material, the constituents keep their original properties, combination of properties not present in single material

semi

conductors / electronic materials - electrical properties intermediate between conductors and insulators, extremely sensitive to concentrations of impurity atoms

biomaterials

used in devices implanted into the human body

smart materials

sense and respond to changes in their environment

nanomaterials

distinguished on the basis of their size - the dimensions of their structural entities are on the order of a nanometer

mechanical properties

factors that affect hardness

electrical properties

factors that affect electrical resistivity

thermal conductivity

measure of a material's ability to conduct heat

ionic bonding

in compounds composed of metallic and nonmetallic elements, metallic elements give up valence electrons to nonmetal elements, predominant in ceramics

covalent bonding

similar electronegativities share electrons to achieve stable configurations

metallic bonding

primary bonding type found in metals and their alloys, valence electrons not bound to any particular atom - "electron cloud"

crystalline materials

atoms are situated in a repeating or periodic 3D array over large atomic distances

noncrystalline materials

don't have the long-range atomic order - "amorphous"

non

directional - bonds between metal atoms - no preference for direction in which neighboring atom should lie for bonding strength to be maximized

unit cell

small group of atoms in a specific crystal arrangement from which the entire structure can be built by repetition in 3D

coordination number

number of nearest-neighbor or touching atoms

atomic packing factor

number of atoms in a unit cell

ceramic bonding

can be ionic and/or covalent

factors that determine crystal structure

relative size of atoms, maintenance of charge neutrality

relative size of ions

formation of stable structures - maximize number of oppositely charged ion neighbors

maintenance of charge neutrality

net charge in ceramic should be zero

coordinaton number

ratio of cation radius to anion radius

silicates

materials composed primarily of silicon and oxygen

characterized based on the various arrangements of the silicon

oxygen tetrahedron

point coordinate

lattice position in a unit cell - _ _ _

crystallographic direction

line directed between two points in the unit cell - [ _ _ _ ] - head(arrow)-tail, convert to integer

linear density

number of atoms per length that are centered on the direction vector for a specific crystallographic direction

planar density

number of atoms per unit area that lie in a particular crystallographic area

single crystals

occur when the periodic arrangement of atoms (crystal structure) extends without interruption throughout the entire specimen

polycrystalline

crystalline material composed of more than one crystal or grain

anisotropy

property value depends on crystallographic direction of measurement, observed in single crystals

isotropy

properties are independent of the direction of measurement

polycrystals

properties may/may not vary with direction, if grains are randomly oriented: isotropic, if grains are textured: anisotropic

x

ray diffraction - determine crystal structure and interplanar spacing

saturated hydrocarbons

each carbon singly bonded to four other atoms

polymer

many repeated units, most are hydrocarbons

unsaturated hydrocarbons

double and triple bonds somewhat unstable - can form new bonds

isomerism

compounds with same chemical formula can have quite different structures, different physical properties based on state

molecular weight

mass of a mole of chains

degree of polymerization

average number of repeat units per chain

molecular shape / conformation

chain bending and twisting are possible by rotation of carbon atoms around their chain bonds

head

to-tail configuration - predominates in most polymers

head

to-head configuration - polar repulsion between R groups

configurations

must break bonds to change

stereoisomers

compounds that differ in their spatial arrangements of their atoms

tacticity

stereoregularity or spatial arrangement of R groups along chain

isotactic

all R groups on same side of chain

syndiotactic

R groups alternate sides

atactic

R groups randomly positioned

cis

isoprene - H atom and CH3 group on same side of chain

trans

isoprene - H atom and CH3 group on opposite sides of chain

thermoplastics

soften when heated and harden when cooled, most linear polymers, branched polymers with flexible chains

thermosetting polymers

network polymers, do not soften upon heating, harder and stronger than thermoplastics

copolymers

two or more monomers polymerized together

random copolymer

A and B randomly positioned along chain

alternating copolymer

A and B alternate in polymer chain

block copolymer

large blocks of A units alternate with large blocks of B units

graft copolymer

chains of B units grafted onto A backbone

crystalline regions

thin platelets with chain folds at faces, chain folded structure

semicrystalline polymers

alternating chain-folded crystallites and amorphous regions

solidification

result of casting of molten material

grain boundaries

regions between grains (crystals), crystallographic misalignment across a grain boundary, slight atomic disorder: high atomic mobility, high chemical reactivity

point defects (0

dimensional) - vacancies, interstitial atoms, substitutional impurity atoms

linear defects (1

dimensional) - dislocations

interfacial defects (2

dimensional) - grain boundaries

vacancies

vacant atomic sites

self

interstitials - host atoms positioned in interstitial positions between atoms

interstitial site

a small void space that under usual circumstances is not occupied

point defects in ceramics

vacancies, interstitials

vacancies in ceramics

both cations and anions

interstitials in ceramics

cations

frenkel defect

cation vacancy-cation interstitial pair

shottky defect

paired set of cation and anion vacancies

alloys

created when impurity atoms are added to a metal, often to achieve some specific characteristic

solvent (host)

component/element present in larger amounts

solute

compound present in smaller amounts

solid solution

formed when solute atoms are added to the solvent and the crystal structure is maintained/no new structures are formed

point defects in polymers

defects due in part to chain packing errors and impurities such as chain ends and side chains

dislocations

one-dimensional defects around which atoms are misaligned, most when stresses are applied, permanent (plastic) deformation results from motion

edge dislocation

extra half plane of atoms inserted in a crystal structure, b perpendicular to dislocation line

screw dislocation

spiral planar ramp resulting from shear deformation, b parallel to dislocation line

b

direction of lattice distortion, represents magnitude and direction of lattice distortion resulting from dislocation in a crystal lattice

twin boundaries (or planes)

mirror reflections of atom positions of one side of twin plane to the other side

stacking faults

occur when there is an error in the planar stacking sequence

catalyst

increases the reaction rate by lowering the activation energy needed, reactions normally occur at surface defect sites

diffusion

mass transport by atomic motion

diffusion mechanisms

gases and liquids - random (brownian) motion, solids - vacancy diffusion or interstitial diffusion

interdiffusion (impurity diffusion)

diffusion of atoms of one metal into another metal, atoms diffuse from high to low concentration regions

self

diffusion - atomic migration in pure metals (atoms changing positions)

vacancy diffusion

atoms and vacancies change positions, applied to host and substitutional impurity atoms, rate depends on: number of vacancies, activation energy to exchange

interstitial diffusion

small, interstitial atoms move from one interstitial position to an adjacent one

fick's first law

steady-state diffusion

fick's second law

nonsteady-state diffusion

doping

diffusion of very small concentrations of atoms of an impurity into the semiconductor silicon

elastic deformation

non-permanent and reversible, time-independent

poisson's ratio

ratio of axial and lateral deformation

plastic deformation

permanent and nonrecoverable