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.

Two Decades of Negative Thermal Expansion Research: Where Do We Stand?

Abstract: Negative thermal expansion (NTE) materials have become a rapidly growing area of research over the past two decades. The initial discovery of materials displaying NTE over a large temperature range, combined with elucidation of the mechanism behind this unusual property, was followed by predictions that these materials will find use in various applications through controlled thermal expansion composites. While some patents have been filed and devices built, a number of obstacles have prevented the widespread implementation of NTE materials to date. This paper reviews NTE materials that contract due to transverse atomic vibrations, their potential for use in controlled thermal expansion composites, and known problems that could interfere with such applications.

The thermal expansion of graphite from 15?c. to 800?c.: part I. Experimental

Abstract: The variation with temperature of the a and c unti-cell dimensions of hexagonal Ceylon graphite has been measured over the temperature range 15°-800°c. by the X-ray powder method. At 14°6c., a=2.4562±0.0001 kx. c=6.6943±0.0007 kx. The carbon-carbon bond length, C-C=1.4210±0.0001a. The a dimension shows a slight contraction up to about 400°c., a small expansion occurring above this temperature. The thermal expansion in the c direction is large; the average value for a over the temperature range is 28.3 × 10-6. The complex nature of the expansion in both directions is discussed qualitatively.

High‐temperature elastic constant data on minerals relevant to geophysics

Abstract: The high-temperature measurements of elastic constants and related temperature derivatives of nine minerals of interest to geophysical and geochemical theories of the Earth's interior are reviewed and discussed. A number of correlations between these parameters, which have application to geophysical problems, are also presented. Of especial interest is α, the volume coefficient of thermal expansion, and a section is devoted to this physical property. Here we show how α can be estimated at very high temperatures and how it varies with density. An estimate of α for Mg-perovskite at deep-mantle conditions is made. The formula for the Gruneisen ratio γ as a function of V and T is presented, including plots of the numerical values of γ over a wide T and V range. An example calculation of γ for MgO is made. The high-T-high-P values of γ calculated here agree well with results from the ab initio method of calculation for MgO. The use of the thermoelastic parameters is reviewed, showing application to the understanding of thermal pressure, thermal expansivity, enthalpy, and entropy. We review an extrapolation formula to determine Ks, the adiabatic bulk modulus, at very high T. We show that the thermal pressure is quite linear with T up to high temperatures (∼1800 K), and, as a consequence, the anharmonic contribution to the Helmholtz free energy is sufficiently small, so that it can and should be ignored in thermodynamic calculations for mantle conditions.

Physical Properties of Mixed Conductor Solid Oxide Fuel Cell Anodes of Doped CeO2

Abstract: Samples of CeO2 doped with oxides such as CaO and Gd203 were prepared. Their conductivities and expansions on reduction were measured at 1000~ and the thermal expansion coefficients in the range 50 to 1000~ were determined. The ionic and electronic conductivity were derived from curves of total conductivity vs. oxygen partial pressure. For both types of conductivity a dependence on dopant valency was observed. The electronic conductivity was independent of dopant radius in contrast to the ionic which was highly dependent. These measured physical properties are compared with the ideal requirements for solid oxide fuel cell anodes. Not all requirements are fulfilled. Measures to compensate for this are discussed.