Heat Conduction

Flow of internal energy (heat) from a region of higher temperature to one of lower temperature by the interaction of the adjacent particles (atoms, molecules, ions, electrons, etc.) in the intervening space. The factors that affect the rate of heat transfer by conductionTransfer of heat as a result of collisions between molecules; when one end of an object is heated or excited, the molecules vibrate faster and their energy is transferred sequentially to their neighbors. are the temperature difference (ΔT), length (l), cross-sectional area (A), and thermal conductivity of the material (k):

Conductivities are usually given in units of W/m·K. They are highest in metallic solids, lower in nonmetallic solids, very low in liquids, and extremely low in gases. The best ordinary metallic conductors are silver (429 W/m·K), copper (401), gold (317), aluminum (237), and tungsten (174). Among nonmetallic solids, diamondOne of the naturally occurring forms of carbon found in meteorites. Each C atom is bonded through covalent sp3 hydrid orbitals to four others. The strength of the C-C bonds makes diamond the hardest naturally occurring substance (according to the Mohs scale) in terms of resistance to scratching. There are is best (895); most silicateThe most abundant group of minerals in Earth's crust, the structure of silicates are dominated by the silica tetrahedron, SiO44-, with metal ions occurring between tetrahedra). The mesodesmic bonds of the silicon tetrahedron allow extensive polymerization and silicates are classified according to the amount of linking that occurs between the minerals have low values (forsteritePure* magnesium end-member (Mg2SiO4) of the olivine solid solution series and an important mineral in meteorites. When magnesium (Mg) is completely substituted by iron, it yields the the pure Fe-olivine end member, fayalite (Fe2SiO4). The various Fe and Mg substitutions between these two end-members are described based on their forsteritic (Fo), 4.6; almandine, 3.6; diopside, 4.2; hornblende, 2.0; feldsparAn alumino-silicate mineral containing a solid solution of calcium, sodium and potassium. Over half the Earth’s crust is composed of feldspars and due to their abundance, feldspars are used in the classification of igneous rocks. A more complete explanation can be found on the feldspar group page., 2.3–2.7; calcite, ~3). Some minerals show strong dependence of conductivity with crystal axes. For example, the conductivity of quartzComposed of SiO2, quartz is one of the silica group minerals most common in Earth's crust, but never found in meteorites as inclusions visible to the naked eye. Quartz in meteorites has been found in very small quantities in eucrites, other calcium-rich achondrites, and in the highly reduced E chondrites. is 6.2 ⊥c and 10.2 ||c at 30 °C. The material with the greatest thermal conductivity (105) is the super fluid heliumHelium (He) Second lightest and second most abundant element (after Hydrogen) in the universe. The most abundant isotope is He (99.9998%), He is very rare. Helium comprises ~8% of the atoms (25% of the mass) of all directly observed matter in the universe. Helium is produced by hydrogen burning inside II, which only exists at temperatures below 2.17 K.