exam 3 hw Flashcards
comparison of thermoplastic and thermosetting polymers on basis of mechanical characteristics upon heating
thermosplastics: soften
thermosetting: do not
comparison of thermoplastic and thermosetting polymers according to possible molecular structures
Thermoplastics are typically linear molecular chains
thermosets are network polymers or extensive crosslinked polymers
Briefly describe the phenomenon of viscoelasticity.
Viscoelasticity is a phenomena in which a material exhibits a combination of mechanical properties of anelastic solid and a viscous liquid
Explain how each of the following influences the tensile or yield strength of a semi crystalline polymer and why
(Molecular Weight)
(Degree of crystallinity)
(Deformation by drawing)
(Annealing of an under deformed material)
Molecular Weight- higher -> increase TS + YS as a result of increased chain entanglement
Degree of crystallinity- higher-> increased TS + YS as a result of more secondary bonding
Deformation by drawing -> increased TS + YS as a result of higher Chain alignment
Annealing of an under deformed material-> increased TS + YS due to higher degree of crystallinity
(a) Briefly explain the difference between oxidation and reduction electrochemical reactions (b) which reaction occurs at the anode and which at the cathode?
Oxidation is the process in which a metal atom gives up electrons.
Reduction is the process in which a metal ion accepts and electron
The Anode goes through oxidation
the cathode goes through reduction
Briefly explain why cold-worked metals are more susceptible to corrosion than non-cold-worked metals.
In general increased strength ( like Prim cold-working) is a result of a high dislocation density. Dislocations, like grain boundaries, are more susceptible to corrosion. Therefore the cold-worked metal is also.
(a) What are inhibitors? (b) What possible mechanisms account for their effectiveness?
(a) Inhibitors decrease corrosiveness when added to an environment
(b) Reaction w/ The corrosive species making it inert or react w/ the corrosive material producing a protective coating.
What is the distinction between electronic and ionic conduction?
Electronic conduction is due to the moment of free electrons through the material.
Ionic conduction is due to the movement of ions through the material.
How does the electron structure of an isolated atom differ from that of a solid material?
Electrons exist at somewhat discrete levels in an isolated atom.
In a solid, the electron energy levels (orbitals) interact to form allowable and non allowable ranges
Briefly state what is meant by the drift velocity and mobility of a free electron.
The drift velocity of a free electron is the average electron velocity in the direction of the force imposed by and electric field.
The mobility is the proportionality constant between the drift velocity and the electric field. It is also a measure of the frequency of scattering events (and is inversely proportional to the frequency of scattering).
Will boron act as a donor or as an acceptor when added to silicon? Why?
Boron will act as an acceptor in silicon because it has one fewer valence electron than silicon does.
Briefly explain why metals are typically better thermal conductors than ceramic materials.
Metals get the electron contribution to thermal conductivity and have a very large number of carrice. Ceramics do not get an electron contribution.
Briefly explain the manner in which information is stored magnetically
Magnetic field induced alignment of magnetic domains.
Distinguish among materials that are opaque translucent, and transparent in terms of their appearance and light transmittance
Opaque: no light transmittance, can not see through!
Translucent: some light transmittance, appear cloudy
Transparent: light transmittance, appear clear
Briefly explain why some transparent materials appear colored while others are colorless
Transparent materials may only allow certain spectral ranges to transmit, resulting in filling of some light -> this results in the removal of some color and the transmission of non-white light.
