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BSEE
KB3UON
EIEIO

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Thermal Conductivity & Coefficient of Expansion
Thermal conductivity is the propensity for any material to transfer heat from one point to another. Of course for heat to "flow," it is necessary for a difference of temperature to exist within a continuous section of the material. Thermal conductivity is analogous to electrical conductivity. Similarly, thermal resistance is the inverse of thermal conductivity as electrical resistance is the inverse of electrical conductivity.

Coefficient of expansion is the rate at which a material will grow in length with an increase in temperature. Most material grow in a fairly linear fashion, particularly within a defined range of temperatures. A positive coefficient of expansion indicates that the material gets longer as its temperature increases. Most metals are like that. Ice is a well-known example of a negative coefficient of expansion, since it contracts in length with increasing temperature (in other words, ice expands as it gets colder).


Substance Thermal Conductivity
(W/cm·°C)
Coefficient of
Thermal Expansion
(ppm/°C)
Density
(g/cm3)
Specific Thermal Conductivityb
(W/cm·°C)
Air (still) 0.0003      
Alumina 0.276      
Alumina (85%) 0.118      
Aluminum 2.165 0.23 2.7 0.81
Beryllia (99.5%) 1.969      
Beryllia (97%) 1.575      
Beryllia (95%) 1.161      
Beryllium 1.772      
Beryllium-Copper 1.063      
Boron Nitride 0.394      
Brass (70/30) 1.220      
Copper 3.937 0.17 8.9 0.45
Copper/Invc/Copper 1.64 0.084 8.4 .020
Copper/Mod/Copper 1.82 0.060 9.9 0.18
Copper/Mod-Cu/Copper 2.45-2.80 0.60-0.10 9.4 0.26-0.30
Diamond (room temp) 6.299      
Epoxy 0.002      
Epoxy (thermally conductive) 0.008      
FR-4  (G-10) 0.003      
GaAs 0.591      
Glass 0.008      
Gold 2.913      
Heatsink Compound 0.004      
Helium (liquid) 0.000307      
Invar 0.11 0.013 8.1 0.014
Iron 0.669      
Kovar 0.17 0.59 8.3 0.020
Lead 0.343      
Magnesium 1.575      
Mica 0.007      
Molybdenum 1.299      
Monel 0.197      
Mylar 0.002      
Nickel 0.906      
Nitrogen (liquid) 0.001411      
Phenolic 0.002      
Platinum 0.734      
Sapphire (a-axis) 0.32      
Sapphire (c-axis) 0.35      
Silicon (pure) 1.457      
Silicon (0.0025 Ω-cm) 1.457      
Silicon Carbide 0.90      
Silicon Dioxide (amorphous) 0.014      
Silicon Dioxide (quartz, a-axis) 0.059      
Silicon Dioxide (quartz, c-axis) 0.11      
Silicone Grease 0.002      
Silicone Rubber 0.002      
Silicon Nitride 0.16 - 0.33      
Silver 4.173      
Stainless Steel (321) 0.146      
Stainless Steel (410) 0.240      
Steel (low carbon) 0.669      
Teflon 0.002      
Tin 0.630      
Titanium 0.219 0.086 4.4 0.016
Tungsten 1.969      
Water 0.0055      
Zinc 1.024      
 

a: Approximate values from 0 °C to 100 °C
b: Thermal conductivity divided by specific gravity
    (introduced by Dr. Carl Zweben & K.A. Schmidt)
c: Invar
d: Molybdenum


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