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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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Copyright: 1996 - 2026 |
About RF Cafe 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 tying up your telephone line, and a lady's voice announced "You've Got Mail" when a new message arrived... |
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