Thermal expansion

About: Thermal expansion is a research topic. Over the lifetime, 21040 publications have been published within this topic receiving 349407 citations. The topic is also known as: heat expansion.

Is the inner core of the Earth pure iron

Abstract: The properties of the inner core (1C) of the Earth are widely assumed to be consistent with those of pure, solid iron in the hexagonal close-packed (e) phase. This hypothesis is re-examined here using a density model of the Earth's core generated from extrapolated, static high-pressure data for e iron and pyrite. Densities of constant-composition mixtures at room temperature and core pressures are compared with corresponding Earth-model densities. An effective volume thermal expansivity, αeff, is calculated for a range of expected core temperatures that brings the room-temperature density into agreement with the Earth-model density at the pressure of the inner-core boundary (ICB). It seems that αeff would have to be significantly larger than previous estimates of the thermal expansion at core conditions. A qualitatively similar conclusion is obtained if an isotherm reduced from shock-wave data is used for e iron instead of the static data. We argue that, of several explanations for this difference (errors in Earth-model densities, a high-volume thermal expansivity at megabar pressures, a high-temperature core (>7,000 K), and the presence of a light component), the last alternative is the most probable and that the IC is not, therefore, pure iron.

Design of materials with extreme thermal expansion using a three-phase topology optimization method

Abstract: We show how composites with extremal or unusual thermal expansion coefficients can be designed using a numerical topology optimization method. The composites are composed of two different material phases and void. The optimization method is illustrated by designing materials having maximum thermal expansion, zero thermal expansion, and negative thermal expansion. Assuming linear elasticity, it is shown that materials with effective negative thermal expansion coefficients can be obtained by mixing two phases with positive thermal expansion coefficients and void. We also show that there is no mechanistic relationship between negative thermal expansion and negative Poisson's ratio.

Crystallographic Observation of Dynamic Gas Adsorption Sites and Thermal Expansion in a Breathable Fluorous Metal–Organic Framework†

Abstract: Playing accordion: Cooling a single crystal of a microporous fluorous metal-organic framework under ambient atmosphere leads to very large breathing upon gas adsorption, during which multiple N(2) molecules are filled into channels and cages (see picture). While the framework exhibits remarkable positive thermal expansion under vacuum, a gigantic apparent negative thermal expansion takes place when the crystal is exposed to N(2) at ambient pressure.

Thermal expansion coefficient of polycrystalline silicon and silicon dioxide thin films at high temperatures

Abstract: The rapid growth of microelectromechanical systems (MEMS) industry has introduced a need for the characterization of thin film properties at all temperatures encountered during fabrication and application of the devices. A technique was developed to use MEMS test structures for the determination of the difference in thermal expansion coefficients (α) between poly-Si and SiO2 thin films at high temperatures. The test structure consists of multilayered cantilever beams, fabricated using standard photolithography techniques. An apparatus was developed to measure the thermally induced curvature of beams at high temperatures using imaging techniques. The curvatures measured were compared to the numerical model for multilayered beam curvature. The model accounts for the variation in thermomechanical properties with temperature. The beams were designed so that the values of Young’s moduli had negligible effect on beam curvature; therefore, values from literature were used for ESi and ESiO2 without introducing si...