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.

Dimensional Instability of Doped Lanthanum Chromite

Abstract: Lattice expansion phase stability, and dimensional stability of doped lanthanum chromites have been examined over a wide range of temperatures and oxygen partial pressures. Reduction of doped lanthanum chromite resulted in a linear expansion of the sample that was dependent on the acceptor (Sr, Ca) concentration, temperature, oxygen partial pressure, and oxygen content within the sample. Additional doping with aliovalent B-site additives significantly reduced lattice expansion in reducing environments. The lattice expansion in reducing environments was directly related to the loss of lattice oxygen and the simultaneous reduction of Cr{sup 4+} to Cr{sup 3+} to maintain electroneutrality.

Energetic materials: variable-temperature crystal structures of γ- and ∊-HNIW polymorphs

Abstract: Crystals of γ- and ∊-hexanitrohexaazaisowurtzitane (γ- and ∊-HNIW, space group P21/n for both crystals) have been investigated in the 100–298 K temperature range using single-crystal X-ray diffraction techniques. Temperature-dependent changes of their crystal lattices have been evaluated from the second-rank thermal expansion tensors. Both lattices undergo anisotropic thermal expansion, that of γ-HNIW being more anisotropic than that of the ∊ phase. Comparison with previously reported predictions from molecular dynamics calculations indicates significant differences. Although there are many short (less than van der Waals) intermolecular interactions in both polymorphs, there is no obvious relationship between the short distances and the difference in thermal expansion behavior. Non-linear temperature dependence of the atomic displacement parameters is indicative of anharmon­icity of the crystal mean field potential.

Thermal Expansion and Second‐Order Transition Effects in High Polymers: Part I. Experimental Results

Abstract: Experimental values of second‐order transition temperatures Tm and of cubical expansion coefficients below and above this temperature are presented for several new materials, notably saran. The thermal expansion behavior of two‐component systems of incompatible materials (polystyrene plus polyolefins) has been studied. For relatively coarse dispersions (1000A), Tm is 82°C, independent of composition, while the difference Δβ in cubical expansion coefficient above and below Tm is directly proportional to the volume fraction of polystyrene in the mixture. Unplasticized saran behaves similarly in that Tm is constant while Δβ decreases linearly with increasing crystallinity. For molecular dispersions of incompatible materials both Tm and Δβ are functions of composition. It is shown that for most high polymers Tm increases with increasing intermolecular force constants, while the product of Tm and cubical coefficient of expansion above Tm is roughly constant (0.1 to 0.2).