MSE-

What are ceramics? How do they differ from metals?

What are ceramics? How do they differ from metals?

ceramics are materials and nonmetallic compounds for which interatomic bonds are ionic or predominantly ionic with covalent bonds.

ceramics differ from metals in their properties in that they have a more complex crystal structure, have higher melting points, and aren’t electrical conductors

Name a few distinctive characteristics of typical ceramics

-high melting point

-hard & brittle as a result of ionic and covalent compounds

Name 4 different crystal structures of ceramics

-AX (rock salt)

-AX2 (fluorite)

-ABX3 (perovskite)

-AB2X4 (spinel)

whats an anion and a cation?

an anion is a negatively charged ion, a cation is a positively charged ion

whats a coordination # in a ceramic?

a coordination # is the number of anion nearest neighbors to cation

two defects in ceramics

• frenkel (cation-vacancy x cation interstital)

• schottky (cation vacancy x anion vacancy)

Sketch unit cell for:

what is silica & silicate

• silica is the simplest material made up of silicon and oxygen

• silicate is salts containing both silicon and oxygen

3 examples of ceramic materials

• sand

• clay

• zirconia

show indicated plane w anions and cations

4 characteristics of a polymer that impact both melting point and glass transition

chain double bonds
(ii) bulky side groups
(iii) polar groups.
(iv) molecular weights

cite 1 reason why ceramics are generally harder yet more brittle than metals

ceramics are made up of ionic and covalent bonds which are highly directional & do not easily slip. these bond types have limited slip systems and reduce dislocation making ceramica harder to deform and cause brittleness.

metals on the other hand, are made up of metallic bonds and which have significantly more slip systems and are therefore easier to deform

distinction between glass transition temp and melting temp

glass transition temp is where upon cooling, a noncrystalline ceramic or polymer transforms from a supercooled liquid to rigid glass

melting point on the other hand is where upon heating a material phase transforms into a liquid

SAMPLE PROBLEM

describe a typical polymer

a polymer is a chain like structure made up of repeating unit monomers. these monomers form a repeating long macromolecular chain, during polymerization reactive monomer sites, extend the chain

Name and briefly describe the 4 types of polymer molecular structures (pg 562)

• linear: repeat units are joined together end to end in single chains

• branched: structure w/ side-branched chains extending from primary chains

• cross-linked: adjacent linear chains joined together by covalent bonds

• network: multifunctional monomers w/ 3+ active covalent bonds; creates 3D networks

cite the differences in behavior between thermoplastic and thermosetting polymers

thermoplastics soften when heated and harden when cooled while thermosetting polymers are permanently hard and do not soften with heating

SCHEMATIC PLOTS OF THE 3 CHARACTERISTICS STRESS STRAIN BEHAVIORS FOR POLYMERIC

describe the mechanism for which elastomeric polymers deform elastically

Large elastic extensions are possible for elastomeric materials that are amorphous and lightly
crosslinked. Deformation corresponds to the unkinking and uncoiling of chains in response to an
applied tensile stress. Crosslinking is often achieved during a vulcanization process; increased
crosslinking enhances the modulus of elasticity and the tensile strength of the elastomer. Many
elastomers are copolymers, whereas silicone elastomers are really inorganic materials

discuss how the factors listed as bullet points, affect the polymer tensile modulus and/strength

• molecular weight = increases as tensile strength increases

• degree crystallinity = tensile modulus increases significantly as crystallinity increases

• pre deformation= Stiffness and strength are enhanced by permanently deforming the polymer in tension

• heat treatment = tensile modulus increases as annealing temp increases

what is Ohm’s Law and how is electrical resistivity related to electrical resistance

• the ease with which a material transmits an electric current

• electrical resistivity = (measure of material’s resistance to the passage of electric current) is related to resistance (how much the material used to make wire/component resists current) bc resistivity depends on resistance (the amount of current passing through a wire or lack thereof is inherently related to what the wire was made with)

list 4 characteristics that affect a polymers melting and glass transition temp

• molecular weight

• chemical bonds

• degree crystallinity

• chain stiffness

cite polymer application types and general characteristics of each

SEE TXTBOOK

How are materials classified as electrical conductors, semiconductors, or insulators

• Metals are good conductors, typically having conductivities on the order of 107 (Ω·m)−1. electrical insulators are materials with very low conductivities, ranging between 10−10 and 10−20 (Ω·m)−1;. Materials with intermediate conductivities, generally from 10−6 to
  104 (Ω·m)−1, are termed semiconductors.

In the electron energy band structure, what is an "energy gap"

In the band structure of electrons, one band is completely filled with electrons. If an empty conduction band exits separated from the valence band, an energy gap lies
between them

Schematically illustrate the temperature-dependence of electrical conductivity in a pure metal and
a pure semiconductor.

Distinguish between intrinsic and extrinsic semiconducting materials.

• For intrinsic behavior, the electrical properties are inherent in the pure material, and electron
  and hole concentrations are equal.

• extrinsic = Electrical behavior is dictated by impurities for extrinsic semiconductors. Extrinsic
  semiconductors may be either n- or p-type depending on whether electrons or holes,
  respectively, are the predominant charge carriers

For a p–n junction, explain the rectification process in terms of electron and hole motions.

…

Briefly describe the phenomena of ferroelectricity and piezoelectricity.

• Ferroelectric materials exhibit spontaneous polarization

• electric field is generated when mechanical stresses are applied to a piezoelectric material.

optical #2 briefly explain why metals are opaque to electromagnetic radiation having photon energies within the visible region of the spectrum.

optical #4 : Briefly explain what determines the characteristic color of (a) a metal and (b) a transparent nonmetal

Briefly explain why metallic materials are opaque to visible light.