Materials Final Flashcards
Even though Silicon is an intrinsic semiconductor, how can it be made into an extrinsic semiconductor?
By intentionally adding a small number of impurities (doping)
-Doping an element of different valance into the Si
If a material is amorphous, it can be characterized as having:
An atomic structure without long-range order
A thermoplastic polymer is best described as being compromised of:
Covalently bonded, long-chain molecules held together by van der Waal’s forces with or without long range order
What is the most important physical characteristic that influences the elastic properties of a material?
Bond strength
As it refers to polymers, the term cross linking means:
The formation of covalent bonds between polymer chains
Although the density can vary widely within any class of materials, the density of a metal is generally greater than the density of a ceramic because:
-atoms are more closely packed in metals than in ceramics
-ceramics are usually a mixture of metal atoms and lighter, non-metallic elements
The bulk modulus of a material is used to characterize:
The resistance of a material to volume change during hydrostatic loading
As it refers to the atomic structure of a crystalline material, what is a “line” defect?
An edge dislocation
The Burgers vector of a dislocation:
Has a magnitude equal to the shear displacement caused by the motion of the dislocation
Plastic deformation increases the yield strength of a metal because:
The number of entangled dislocations increases
Brass (a Cu-Zn alloy) is stronger than pure copper. This is because:
The zinc atoms distort the copper lattice
Is the following statement true? The structure of a thermoset is a 3-D network of covalently bonded molecules
True
Is the following statement true? The Young’s modulus of a thermostat is generally higher than a thermoplastic polymer
True
Crystalline ceramics do not experience significant plastic deformation because:
-the stress required to move dislocations is greater than the fracture stress
-the ionic bonds are too strong
-Small flaws in the material act as stress concentrators, causing fracture before plastic deformation can occur
The vulcanizing process is used to:
Create cross-links in elastomers
The specific heat Cp of a material is equal to:
The energy required to raise the temperature of a unit mass of the material by one degree
Metals typically have a higher value of fracture toughness than ceramics because:
Metals plastically deform
The basic result obtained from a creep test is a plot with which two parameters:
Strain and time
Creep deformation becomes an important consideration at which homologous temperature?
0.4
How many atoms are in a simple cubic?
1 atom
How many atoms are in a face centred cubic unit cell?
4 atoms
How many atoms are in a body-centred cubic unit cell?
2 atoms
The number of independent close-packed directions in a close-packed plane of atoms is:
3
What is the definition of a nanoparticle?
A structure with at least 1 dimension less than 1 micrometer
