Materials Science Exam #3

What is a composite?

A combination of 2 or more distinct materials that are artificially made

Constituent phases must be __________ dissimilar and separated by distinct phase

chemically

What are the three classifications of composites?

particle-reinforced

fiber-reinforced

structural

What is an example of a particle-reinforced composite? How is it produced?

Concrete

Aggregate bound together with cement

What is reinforced concrete?

When steel rods are within the concrete and has similar properties to those of concrete

Concrete is much stronger under ________ than _________. This is known as prestressed concrete

compression, tension

What is the goal of a fiber reinforced material?

have a high strength per weight

_____>>_____ for continuous. What are the fibers like during this?

l, lc; the fibers are aligned

_____>>_____ for discontinuous. What are the fibers like during this?

lc,l; the fibers are either aligned or random

What is a laminar composite?

2D sheets or panels that have high strength direction. Layers are stretched to orientation of high strength varies

What are sandwich panels? What is their goal? what are they usually used in?

2 strong outer sheets separated by core of lower strength and stiffness. to have a high specific strength. aircrafts- light

Below Tg, a polymer is _______, while above, the polymer is _________.

brittle and rigid-like; flexible and leathery

Factors that influence Tg (increase) in polymers

bulky side groups, polar side atoms, chain double bonds,

Drift velocity is proportional to _________

electrical field.

Resistance is influenced by ______, _______, and _______ of the material

shape, size, properties

What is the Band Theory?

A material conducting in a partially filled energy band

What are the two ways conduction occurs?

1. empty conduction band

2. overlap

Categories in overlap conduction

- insulators due to energy barrier being too large (large gap)

- semi-conductor(small gap)

What is a intrinsic semiconductor?

pure semiconducting material that will conduct electricity if energy provided to cross the gap

Intrinsic semiconductors have _____ bonds. Why?

covalent; holes left by previous electrons are carriers

What is an extrinsic semiconductor (Doping).

Very ductile substitutional solid solution, solute atoms have different valence than solvent atoms:

What is n-type semi conductivity?

(negative) instrinsic material doped with impurity that has donor electrons wth energy close to conduction band

What is p-type semi conductivity?

(positive) when an electron moves into a hole, it elevated its energy level to just above the valence band

What is dielectric?

materials that are electrically insulating

What is the dielectric (breakdown) strength

the ability of hold energy at a high voltage OR the max electrical field dielectric can maintain without electrical breakdown

What is piezoelectricity?

mechanical force can produce an electrical response. Example: speakers

What is Barium Titanate?

BaTiO3 (piezoelectric material)

What is a soft magnet?

easily magnetized and disorganized

What is a hard magnet?

magnets that don't easily disorganize

What are the elements that when magnetized at T room can produce strong magnetic field around themselves. What is the term that describes this?

Fe, Co, Ni; ferromagnetic

Magnation is _______in nature

dipolar

What does dipolar mean?

2 poles; lines leave one pole and travel to the other. This makes a torque and can produce a magnetic field by a current- carrying conductive

What is a solenoid?

A cylindrical coil that consists of N turns, length, l, and current (I).

How is the solenoid affected with a bar and applied current?

If a demagnetizing bar is placed inside a solenoid and current applied, magnetic field is stronger than without the bar

Ferromagnetic characteristics

strong magnetic field, magnetization is greater than the field generated by the solenoid

Magnetic properties of materials ultimately come from magnetic _______ moment. How is this caused?

dipole; electrons and their motions

What are the types of motions for electrons

1. orbiting

2. spin

What is the significance of the motions of electrons?

Orbiting and spin cancel each other out

Why are some materials very magnetic?

the electrons are not paired in outer shells

Magnetization is proportional to the applied ______.

field

What are the types of magnetism?

Diamagnetism, Paramagnetism

What is diamagnetism?

a very weak form of magnetism non-permanent, lasts only while the field is applied (negative).

What materials do diamagnetism occur in?

All materials, but can only be recognized if other forms of magnetization are not there

What is Paramagnetism?

materials which exhibit small, positive magnetic susceptibility in presence of magnetic field that disappears when the field is absent (positive).

What is the Bohr magneton?

electron spinning on its axis has a dipole moment

Curie Temperature

As your increase T to a point where ferromagnetic materials lose magnetization and become paramagnetic- When it is cooled, it returns back to the original magnetization (ferromagnetic)

Annealing

heat treatment where material is heated for a long time and slowly cooled

What does annealing do to a material?

relieves stress from cold working and uneven cooling. This increases toughness and ductility.

What is the purpose of annealing?

to produce a specific microstructure.

What are the viscosity refrence points for glass?

1. Working points

2. Softening points

3. Annealing point

4. Strain point

What is the working point?

point at which glass fabrication can be done (10^4p)

What is the softening point?

glass will flow appreciably under its own weight (10^8p)

What is the annealing point?

internal stresses are relieved (10^13p)

The higher the ______, the more ______.

viscosity, rigid

Viscosity is related to _____. The higher the _____, the lower the ______.

temperature, temperature, viscosity

What is vitrification?

some ceramics contain a glass phase which serves as a reaction medium by which diffusion can take place at lower T than rest of the material

What is vitrification affected by?

Compression

What is sintering?

A process by which small particles are bonded together by solid state diffusion- at a very high pressure.

What is the strain point?

point at which (above/below?) is a rigid solid

Fiber reinforced- longitudinal

along direction of fibers

Fiber reinforced-transverse

perpendicular to direction of fibers

What is the dielectric breakdown strength?

ability to hold energy at a high voltage or the max electrical field a dielectric can maintain without electrical breakdown

An increase in temperature results in an increase in _______

conductivity

Magnetic Susceptibility

magnetization is proportional to the applied field, H

F

T/F: with an increase in temperature, there is an increase in paramagnetism

Ferromagnetism

Large fields where magnetic susceptibility is up to 10^6: iron, Nickel, Co