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BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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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 Conductivity^b (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/Inv^c/Copper	1.64	0.084	8.4	.020
Copper/Mo^d/Copper	1.82	0.060	9.9	0.18
Copper/Mo^d-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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