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.

Thermal expansion coefficient of single-crystal silicon from 7 K to 293 K

Abstract: We measured the absolute lengths of three single-crystal silicon samples by means of an imaging Twyman-Green interferometer in the temperature range from 7 K to 293 K with uncertainties of about 1 nm. From these measurements we extracted the coefficient of thermal expansion with uncertainties on the order of $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}/\mathrm{K}$. To access the functional dependence of the length on the temperature, usually polynomials are fitted to the data. Instead we used a physically motivated model equation with seven fit parameters for the whole temperature range. The coefficient of thermal expansion is obtained from the derivative of the best fit. The measurements conducted in 2012 and 2014 demonstrate a high reproducibility, and the agreement of two independently produced samples supports single-crystal silicon as a reference material for thermal expansion. Although the results for all three samples agree with each other and with measurements performed at other institutes, they significantly differ from the currently recommended values for the thermal expansion of crystalline silicon.

Chapter 3 Invar: Moment-volume instabilities in transition metals and alloys

Abstract: Publisher Summary The term “invar” stands for alloys showing minimum thermal expansion coefficients (maximum spontaneous volume magnetostriction) in certain ranges of composition and temperatures. Invar effect originates from investigations by Ch.E. Guillaume who found that ferromagnetic fcc FeNi alloys at concentrations around Fe 65 Ni 35 show almost constant thermal expansion as a function of temperature in a wide range around room temperature. According to his results, the linear thermal expansion coefficient α = (1/ l )/(d l /d T ) of Fe 65 Ni 35 Invar at 300 K is about 1.2 × 10 -6 K -1 , thus an order of magnitude smaller than in the pure components Fe and Ni and even smaller than in a Pt–10% Ir alloy, the material used for the prototype meter. The chapter summarizes the magnetic phase diagrams of the most important binary and ternary alloy systems showing moment–volume instabilities in general and Invar or Elinvar behavior in special composition ranges. Besides the magnetic-transition temperatures, Curie temperatures T C for ferromagnetic (FM) transitions, Neel temperatures T N for antiferromagnetic (AF) transitions, and T f for spin glass (SG) or re-entrant spin glass (RSG) like transitions, the diagrams contain information about the structural phases occurring in the systems.

Thermophysical properties of Yb2O3 doped Gd2Zr2O7 and thermal cycling durability of (Gd0.9Yb0.1)2Zr2O7/YSZ thermal barrier coatings

Abstract: (Gd1−xYbx)2Zr2O7 compounds were synthesized by solid reaction. Yb2O3 doped Gd2Zr2O7 exhibited lower thermal conductivities and higher thermal expansion coefficients (TECs) than Gd2Zr2O7. The TECs of (Gd1−xYbx)2Zr2O7 ceramics increased with increasing Yb2O3 contents. (Gd0.9Yb0.1)2Zr2O7 (GYbZ) ceramic exhibited the lowest thermal conductivity among all the ceramics studied, within the range of 0.8–1.1 W/mK (20–1600 °C). The Young's modulus of GYbZ bulk is 265.6 ± 11 GPa. GYbZ/YSZ double-ceramic-layer thermal barrier coatings (TBCs) were prepared by electron beam physical vapor deposition (EB-PVD). The coatings had an average life of more than 3700 cycles during flame shock test with a coating surface temperature of ∼1350 °C. Spallation failure of the TBC occurred by delamination cracking within GYbZ layer, which was a result of high temperature gradient in the GYbZ layer and low fracture toughness of GYbZ material.

Micro/Nanoscale Spatial Resolution Temperature Probing for the Interfacial Thermal Characterization of Epitaxial Graphene on 4H‐SiC

Abstract: Limited internal phonon coupling and transfer within graphene in the out-of-plane direction significantly affects graphene-substrate interfacial phonon coupling and scattering, and leads to unique interfacial thermal transport phenomena. Through the simultaneous characterization of graphene and SiC Raman peaks, it is possible, for the first time, to distinguish the temperature of a graphene layer and its adjacent 4H-SiC substrate. The thermal probing resolution reaches the nanometer scale with the graphene (≈1.12 nm) and is on the micrometer scale (≈12 μm) within SiC next to the interface. A very high thermal resistance at the interface of 5.30 (-0.46) (+0.46) x 10(-5) Km2 W(-1) is observed by using a Raman frequency method under surface Joule heating. This value is much higher than those from molecular dynamics predictions of 7.01(-1.05) (+1.05) x 10(-1) and 8.47(-0.75) (+0.75) x 10(-10) Km2 w(-1) for surface heat fluxes of 3 × 10(9) and 1 × 10(9) and 1 x 10(10) W m(-2) , respectively. This analysis shows that the measured anomalous thermal contact resistance stems from the thermal expansion mismatch between graphene and SiC under Joule heating. This mismatch leads to interface delamination/separation and significantly enhances local phonon scattering. An independent laser-heating experiment conducted under the same conditions yielded a higher interfacial thermal resistance of 1.01(-0.59) (+1.23) x 10(-4) Km2 W(-1). Furthermore, the peak width method of Raman thermometry is also employed to evaluate the interfacial thermal resistance. The results are 3.52 × 10(-5) and 8.57 × 10(-5) K m2 W(-1) for Joule-heating and laser-heating experiments, respectively, confirming the anomalous thermal resistance between graphene and SiC. The difference in the results from the frequency and peak-width methods is caused by the thermal stress generated in the heating processes.