Term
| Define thermal behaviors of materials |
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Definition
-Heat capacity
-specific heat |
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Term
| When a material is heated, what happens |
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Definition
-thermal expansion
-heat flow |
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Term
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Definition
| indicates the heat flow rate of certain material |
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Term
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Definition
| Defines the amount of heat required to raise temperature by 1k (=1 Celsius) |
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Term
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Definition
| heat capacity per unit mass |
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Term
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Definition
Increase the thermal vibration of atoms
Leads to increase in distance between atoms |
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Term
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Definition
Thermal gradient between different heat zone causes heat flow
Free electrons transfer heat rapidly (metal)
Randomized electron spins in ferromagnetic materials |
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Term
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Definition
| Steeper slope at F=0 higher elastic modulus |
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Term
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Definition
| Deeper well higher bonding energy |
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Term
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Definition
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Term
| Highest to lowest for thermal expansion and why |
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Definition
polymer>metals>ceramics and glasses
b/c ceramics and glasses have deeper wells than other materials (higher bonding energy)higher melting point
-less change in anatomic distance with increasing temp
-higher elastic modulus |
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Term
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Definition
-low melting point
-low elastic modulus
-high thermal expansion coefficient |
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Term
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Definition
-high melting point
-high elastic modulus
-low thermal expansion coefficient |
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Term
| thermal expansion coefficient |
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Definition
-function of temperature
-higher coefficient at higher temperature in general
-some glass-ceramics has a negative coefficient, good for thermal shock |
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Term
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Definition
K: thermal conductivity
dQ/dt: the rate of heat transfer
A: cross sectional area
dT/dx: teperature gradient
Different material has their own thermal conductivity
thermal conductivity is a function of temperature |
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Term
| Two primary mechanisms of conduction |
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Definition
Atomic vibrations
Conduction of free electrons |
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Term
| What material is a good conductor and why? |
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Definition
| Metal: better conduction by kinetic energy of conduction electrons |
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Term
| What material is a poor conductor and why? |
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Definition
electrons
Poor conductor (ceramic, polymer): only by atomic vibration |
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Term
| Structural disorder by chemical impurities results |
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Definition
| in a similar decrease in thermal conductivity |
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Term
| Structural disorder interferes |
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Definition
| with the movement of the waveform |
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Term
True of false:
Metal alloys tend to have lower thermal conductivities than pure metals |
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Definition
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Term
| The thermal conductivity of ceramics and polymers can be further reduced by |
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Definition
| the presence of porosity. (air pocket has very low conductivity) |
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Term
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Definition
-Fracture of the material as a result of a temperature change (usually a sudden cooling from high temperature)
-common for brittle materials (ceramics, glasses |
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Term
| The mechanism of thermal shock |
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Definition
1. Thermal expansion
2. Residual stress |
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Term
| Thermal Shock by Thermal expansion |
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Definition
| A failure stress can be built up by constraint of thermal expansion |
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Term
| Thermal Shock by residual stress |
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Definition
Rapid temperature changes produce temporary temperature gradients resulting in surface tensile stresses
Surface tensile stress compress the interior and the interior pull the surface
This causes internal residual stress
Residual stress – temperature gradients by finite thermal conductivity(thick shape) |
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