Materials Final

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Glass Ceramics

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An inorganic glass that is transformed from noncrystalline to one that is crystalline through heat treatment. They have been designed to have relatively high mechanical strengths, low coefficients of thermal expansion, relatively hih temperature capabilities, good dielectric properties and good biological compatibility. Very easily formed. Applications include ovenware, tableware, oven windows and rangetops.

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Clay

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Inexpensive and found naturally in great abundance. Products are very easily formed with proper mixing conditions by a process of forming, drying and firing. Products fall in to the catagories of strutural and whiteware. Applications include building bricks, tiles, porcelain and pottery.

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Refractories

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Often used in large amounts and have the notable properties of the capacity to withstand high temperatures without melting or decomposing and the capacity to remain inreactive and inert when exposed to severe environments. Performance is generally based on its composition and there are several classifications - fireclay, silica, basic and special. Typical applications are furnace linings for metal refining, glass manufacturing, metallurgical heat treatment and power generation.

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Cements

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Very commonly used and produced in extremely large amounts. When mixed with water they form a paste that eventually sets and hardens. Therefore it is easily formed, can form to many shapes and has good structural properties. The most common variety is the portland kind.

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Crystalline solids DO or DO NOT experience a change in slope of their specific volume at the glass transition temperature?

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DO NOT

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The _____________ represents the temperature at which the viscosity is 103 Pa s (104 P viscosity); the glass is easily deformed at this viscosity.

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working point

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The process during uniaxial and isostatic powder pressing, that is characterized by the formed piece shrinking and experiencing a reduction in porosity and thus, improving in mechanical integrity.

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sintering

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Frenkel defect is...

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In an ionic solid, a cation–vacancy and cation– interstitial pair.

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Flexural Strength Equation

(from quiz)

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(sigma)fs = (sigma)0 exp(-nP)

P=porosity percent

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To predict the crystal structure, for ex: of MgO, you...

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divide the radius of Mg by the radius of O.

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To calculate the theoretical density you use the equation...

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density =Weight of ions per unit cell / Unit cell volume

(row) =(na*Ma+nc*Mc) / (NA*Vuc)

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Number-average molecular weight= Mn=

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=(sum)xM

x=number of a given element(Atom) in the repeat unit

M=that atoms molecular weight

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degree of polymerization=DP=

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=Mn/m

m=rereat unit

Mn=Number-average molecular weight

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An isomer is a polymer with ____________ composition as another but has ________ atomic arrangment.

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the same

a different

Front 15

Which type of molecular structure is characterized by adjacent linear chains joined at various positions by covalent bonds?

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Crosslinked

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A graft copolymer is characterized by:

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Side branches of a homopolymer are attatched to the main chain of another homopolymer.

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Which type of polymer is considered recyclable?

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Thermoplastics

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Many composite materials are composed of just two phases. One is termed the _________ which surrounds the other phase called the _________.

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Matrix,

dispersed phase

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For Reinforced Concrete, the steel rebar is the matrix or dispersed phase of this composite?

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dispersed phase!

the concrete is the matrix

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the stress decays over time and follows the equation ...

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σ(t)=σ(0)exp(-t/τ), (equation 15.10)

σ(0) =initial stress

τ =relaxation time(constant)

t=a given time in seconds

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the relaxation modulus is...

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Er(t)= σ(t) / (initial strain)

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maybe look at

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transition temperature in book ch 15.

ex: glass transition temp

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Equations for upper and lower bound of modulous of elasticity with a matrix phase and particle phase.

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Front 24

Which of the following fiber reinforced composites will be isotropic?

-continuous, aligned

-discontinuous, randomly oriented

-discontinuous, aligned

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discontinuous, randomly oriented!

isotropic=same strength in all directions

discontinuous=different fiber pieces, not long strands

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Equation for critical fiber length,

lc=...

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=(fiber tensile strength)(fiber diameter) / (2*fiber to matrix bond strength)

eq. 16.3 in book

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For a discontinuous and aligned-fiber composite having a uniform distribution of fibers and in which l > l c , the longitudinal strength (sigma*cd ) is given by the relationship=....

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eq. 16.18 in book

σcd = σ f* Vf (1-lc/2l) + σm' (1 − Vf )

σ f =fracture strength(tensile) of fiber

σm ' =stress in matrix at failure

Vf=volume percent of fiber as decimal

lc=critical length

l=actual length

Front 27

Which are the primary carriers of electricity in semiconducting materisl?

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Holes and electrons

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A standard p-n junction light emitting diode (LED) can emit which of the following?

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a single color of light

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Superconductivity is the phenomenon in which a material's resistivity...

This material can then be manipulated to create...

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...essentially drops to zero when cooled below a critical temperature.

...powerful magnetic fields because there are minimal electrical losses associated with the electrical fields that create the magnetic fields.

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one equation for SPECIFIC LONGITUDINAL STRENGTH=...

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....=longitudinal tensile strength/specific gravity

or...

...=sigma/density

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one equation for longitudinal specific modulus=...

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...=longitudinal tensile modulus/specific gravity

or...

...=E/density

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for longitudinal loading, that the ratio of the load carried by the fibers to that carried by the matrix is

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Front 33

longitudinal strength of the composite=

with continuous fibers

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Front 34

the efficiency reinforcement, n, is dependant on fiber length l.

and x represents the length of the fiber at each end.

and the equation is...

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Front 35

What is the distinction between cement and concrete?

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Concrete consists of an aggregate of particles that are bonded together by a cement.

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(b)the use of concrete as a structural material.

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(1) it is a relatively weak and brittle material;

(2) it experiencesrelatively large thermal expansions (contractions) with changes in temperature;

(3) it may crackwhen exposed to freeze-thaw cycles.

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Briefly explain three techniques that are utilized to strengthen concrete by reinforcement.

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(1) reinforcement with steel wires, rods, etc.;

(2)reinforcement with fine fibers of a high modulus material;

(3) introduction of residual compressivestresses by prestressing or posttensioning

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The two characteristics of component ions that determine the crystal structure of a ceramic compoundare:

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1) the magnitude of the electrical charge on each ion

2) the relative sizes of the cations and anions.

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A Frenkel defect involes a cation vacancy and an anion vacancy, true or false?

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False

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The “degree of polymerization”refers to

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The number of repeat units in an averagemolecule

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Thermoplastics facts

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-- little crosslinking-- ductile-- soften w/heating-- polyethylenepolypropylenepolycarbonatePMMApolystyrene

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thermosets facts

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-- large crosslinking(10 to 50% of mers)-- hard and brittle-- do NOT soften w/heating-- vulcanized rubber, epoxies,polyester resin, phenolic resin

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Isomerism

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two compounds with same chemical formula canhave quite different structures

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Stereoisomers are

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mirror images – can ’t superimpose without breaking a bond

Configurations – to change must break bonds

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More Polar means...

Not Polar means....

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More intermolecular bonding

Weaker intermolecular bonding

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Some semicrystallinepolymers formspherulite structures, which are...

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Alternating chain-foldedcrystallites andamorphous regions• Spherulite structure forrelatively rapid growthrates

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Vacancies-- vacancies exist in ceramics for both cations and anions•

Interstitials-- interstitials exist for cations-- interstitials are not normally observed for anions because

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anions are large relative to the interstitial sites

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Shottky Defect

Frenkel Defect

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Missing the big one

Missing the small one

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Firing:--

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heat treatment between 900-1400ºC -- vitrification: liquid glass forms from clay and flux – flows between SiO2 particles. (Flux lowers melting temperature).

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Tempering:-- puts

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surface of glass part into compression -- suppresses growth of cracks from surface scratches.

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Defects–

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Interstitials (Cation) – Vacancy (Cation/anion) – Frenkel (vacancy/interstitial) – Shottky (Vacancy only)

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an Epoxy is a

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thermoset

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The temperature at which the polymer experiences the transition from rubbery into rigid states is termed the

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glass transition temperature, Tg .

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When warmed above roomtemperature a typical polymer firststarts to soften at..

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its glass transition temperature

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How does deformation by drawingof a semicrystalline polymer affectits tensile strength?

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Increases

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types of polymers

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coatings

adhesives

films

foams

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Limitations of polymers:

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-- E, sy, Kc, Tapplication are generally small.

-- Deformation is often time and temperature dependent.

-- UV degradation

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Lowering the temperature of a polymer results in:

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Behavior that mimics increasing the strain rate(hotter=softer, faster=harder,cooler=harder)

Freezing the motion of the side chains

An increase in elastic modulus