Module 3.1 - Physical Behavior

Question 1

What is the heat of fusion ∆Hf and why is it almost always positive?

Answer 1

amount of heat needed to go from solid to liquid state, and it’s positive because the solid needs to ABSORB heat to change state

Question 2

Why is ∆Sf almost always positive?

Answer 2

Because going from solid to liquid always increases disorder.

Question 3

For ceramics, metals, and polymers, arrange them in terms of Tm?

Answer 3

Ceramics > metals > polymers

Question 4

What are the two factors affecting the melting points of ionic ceramics?

Answer 4

1. Ionic Charge
2. Covalent Character of Ionic Bond

Question 5

If the ionic charges on the two elements are greater, what happens to the material’s bond energy?

Answer 5

Increase in material’s bond energy

Question 6

When the covalent character of the bond is increased, what happens to ∆Hf and why?

Answer 6

It is decreased because having more covalent bonds means that less ionic bonds need to be broken. Since ionic bonds are harder to break, less energy is needed to break these, since covalent bonds are broken instead.

Question 7

There are very strong PRIMARY bonds between Si, C, N, and O. True or false?

Answer 7

True.

Question 8

Some ceramics can decompose rather than melting. Give an example?

Answer 8

Si3N4

Question 9

For the coefficient of thermal expansion, it is dependent on a change in what factors? What other factor remains constant?

Answer 9

Change in length and temperature while pressure remains constant.

Question 10

Thermal expansion can be traced from the anharmonicity or asymmetry of the curve. Once there is an increase in the energy well, what happens?

Answer 10

There is asymmetry.

Question 11

Thermal expansion can be traced from the anharmonicity or asymmetry of the curve. Based on this, is it easier to pull atoms apart or push them together?

Answer 11

Pull them apart since the energy curve is less steep.

Question 12

Which has a lower α (CTE) value, metals or ceramics?

Answer 12

Ceramics (notice how they will expand less at high temperatures)

Question 13

When the temperature increases, what happens to the α value?

Answer 13

It also increases

Question 14

Which has a lower alpha (CTE) value, covalently bonded ceramics or close-spacked structures? Why?

Answer 14

Covalently bonded structures, because of the covalent bonding, the structures are more open to vibration and changes in configuration without expansion.

Question 15

Isotropic structures tend to be cubic and polycrystalline. True or false?

Answer 15

True

Question 16

With the force vs distance curve, the net force between ions at equilibrium is?

Answer 16

0

Question 17

What atoms are pulled apart, according to the force-distance curve, what happens?

Answer 17

There’s a restoring force that tends to pull them back together.

Question 18

According to the force-distance curve, what will cause breaking and plastic deformation in the macro material?

Answer 18

When the atoms are beyond the separation of r-fail.

Question 19

What is the theoretical strength of a solid?

Answer 19

Stress required to simultaneous break all the bonds across a fracture plane?

Question 20

Typically bonds will fail when they’re stretched up to what percentage?

Answer 20

25%

Question 21

Why is the maximum actual strength much less than the maximum theoretical strength?

Answer 21

Because of the presence of defects (i.e. slip, twinning, dislocations, etc.) in real materials.

Question 22

What is surface energy?

Answer 22

Amount of energy needed to create unit area of new surface.