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.

Zero Thermal Expansion in ZrMgMo3O12: NMR Crystallography Reveals Origins of Thermoelastic Properties

Abstract: The coefficient of thermal expansion of ZrMgMo3O12 has been measured and was found to be extremely close to zero over a wide temperature range including room temperature (αl = (1.6 ± 0.2) × 10–7 K–1 from 25 to 450 °C by X-ray diffraction (XRD)). ZrMgMo3O12 belongs to the family of AMgM3O12 materials, for which coefficients of thermal expansion have previously been reported to range from low-positive to low-negative. However, the low thermal expansion property had not previously been explained because atomic position information was not available for any members of this family of materials. We determined the structure of ZrMgMo3O12 by nuclear magnetic resonance (NMR) crystallography, using 91Zr, 25Mg, 95Mo, and 17O magic angle spinning (MAS) and 17O multiple quantum MAS (MQMAS) NMR in conjunction with XRD and density functional theory calculations. The resulting structure was of sufficient detail that the observed zero thermal expansion could be explained using quantitative measures of the properties of th...

Moment-Induced Magnetic Scattering and Magnetovolume Effect in Fe65(Ni1-xMnx)35 Alloys

Abstract: The temperature dependences of electrical resistivity and thermal expansion were measured for face-centered cubic Fe 65 (Ni 1- x Mn x ) 35 ternary alloys. The electrical resistivity of ferromagnetic alloys ( x 0.3) increases below the Neel temperature and shows a resistance minimum. These behaviors are explained in terms of the magnetic scattering by induced moments below the magnetic ordering temperature. The expansion of volume due to the magnetic ordering was observed in both ferro- and antiferromagnetic alloys. To explain the volume expansion by the magnetic ordering, a new mechanism of magnetovolume effect based on the change of cohesive energy due to the spin polarization in 3 d band is proposed.

Evolution of mechanical properties of granite at high temperature and high pressure

Abstract: Rock engineering works, such as geothermal and deep hydrocarbon resource development and deep underground geological disposal of nuclear waste, are closely related to the mechanical properties of rocks at high temperature and high pressure. This study reports on the use of the micro-CT technique, acoustic emission (AE) technique and the 600 °C 20MN servo-controlled trixial compression system for rock testing under high temperature and high pressure to study the evolution of mesostructure, AE characteristics and the evolution of macro-mechanical properties of granite under high temperature and high pressure. The results obtained from the experiments show that: (1) Very few micro-cracks occur when granite is at 200 °C, while mylonitic crystal granular structures appear at 500 °C. (2) AE characteristics indicate that the thermal cracking of granite is intermittent and multi-stage. Under the influence of thermal cracking, the permeability of granite also presents several peaks. (3) Under the stress state equivalent to 1000 m buried depth, the thermal deformation and the thermal expansion coefficient both have different stages from room temperature to 600 °C. The thermal expansion coefficient under triaxial pressure is approximately 20 times less than the coefficient without confinement, showing that this parameter is profoundly affected by the confining pressure. The failure mode of granite under high temperature is shear failure, just as under room temperature. The stress–strain curve, however, presents different characteristics compared to those under room temperature. (4) When subjected to confining pressure, the elastic modulus of granite has different periods. Overall, it decreases with the increase of temperature.