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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.


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Journal ArticleDOI
TL;DR: In this paper, the authors show that all three cell edges of orthorhombic Y2W3O12 decrease with increasing temperature, giving an average linear thermal expansion coefficient of −7.0×10−6 K−1.

122 citations

Journal ArticleDOI
TL;DR: In this article, a relatively large sample of gallium nitride (GaN) was grown as a single crystal using the hydride vapor phase epitaxy (HVPE) process and the thermal diffusivity of the single crystal has been measured using a vertical-type laser flash method.
Abstract: A relatively large sample of gallium nitride (GaN) was grown as a single crystal using the hydride vapor phase epitaxy (HVPE) process. The thermal diffusivity of the single crystal has been measured using a vertical-type laser flash method. The thermal expansion was measured using a dilatometer in order to estimate the thermal diffusivity with sufficient reliability. The effect of sample thickness and temperature on thermal diffusivity was evaluated. The specific heat capacity of GaN was also measured by using a differential scanning calorimeter. The thermal properties of single-crystal GaN have been compared with the measured thermal properties of single-crystal silicon carbide (SiC). The thermal conductivity of single-crystal GaN at room temperature is found to be 253 � 8:8% W/mK, which is approximately 60% of the value obtained for SiC. The excellent thermal property that is obtained in this study clearly indicates that GaN crystals are one of the promising materials for use in high-power-switching devices. [doi:10.2320/matertrans.MRP2007109]

122 citations

Journal ArticleDOI
TL;DR: The origin of the negative thermal expansion in Si is examined, and it is found that the different thermal-expansion behaviors between Si and C can be explained by the different relative strengths of bond-bending and bond-stretching forces.
Abstract: Phonon-dispersion curves, lattice mode Gr\"uneisen parameters, and the coefficients of thermal expansion are calculated for Si and C within a tight-binding model. The results are in good agreement with experimental data. The origin of the negative thermal expansion in Si is examined, and we find that the different thermal-expansion behaviors between Si and C can be explained by the different relative strengths of bond-bending and bond-stretching forces.

122 citations

Journal ArticleDOI
TL;DR: A ceramic thermal-barrier coating needs to be refractory and chemically inert, and it also needs to possess a high thermal expansion coefficient of ~11 × 10−6 K−1, to match the nickel-base superalloy substrate as discussed by the authors.
Abstract: Thermal-barrier coatings are finding increasing use in engineering applications, particularly in gas turbines. Such coatings, consisting of ceramic insulating layers bonded to the superalloy substrate by oxidation-resistant alloy coatings, are deposited onto components to reduce heat flow through the cooled substrate and to limit operating temperature. They have been used effectively on static components such as combustor cans, flare heads, hot gas seal segments, fuel evaporators, and deflector plates, giving considerable improvements in component life. They have been used successfully on vane platforms. In recent years, the emphasis has shifted toward the development of coatings for high-risk areas, such as turbine blades.A ceramic thermal-barrier coating needs to be refractory and chemically inert, and to have low thermal conductivity. However, it also needs to possess a high thermal expansion coefficient of ~11 × 10−6 K−1, to match the nickel-base superalloy substrate. The latter specification has focused attention on ZrO2. However, ZrO2 is polymorphic and undergoes two phase changes, cubic to tetragonal at 2350°C and tetragonal to monoclinic at 1170°C. The latter transformation is accompanied by a 5% volume increase which means that ZrO2 has to be alloyed to stabilize one of the high-temperature phases. Early systems in the 1970s consisted of ZrO2 stabilized with MgO, but this has been shown to be a metastable system. Present-day commercial thermal-barrier coatings consist of a plasma-sprayed yttria- or magnesiastabilized zirconia layer on top of an M-Cr-Al-Y bond coat. The latter plays a very important role by helping to key the ceramic to the alloy substrate and to accommodate the mechanical strains arising because of differences in thermal expansion coefficients and elastic moduli between the ceramic and the substrate.

122 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023603
20221,249
2021683
2020742
2019759
2018767