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.

The partial molar volume, thermal expansivity, and compressibility of H2O in NaAlSi3O8 liquid: new measurements and an internally consistent model

Abstract: The molar volumes of 19 hydrous albitic liquids (1.9 to 6.1 wt% H2Ototal) were determined at one bar and 505–765 K. These volume data were derived from density measurements on hydrous glasses at 298 K, followed by measurements of the thermal expansion of each glass from 298 K to its respective glass transition temperature. The technique exploits the fact that the volume of a glass is equal to that of the corresponding liquid at the limiting fictive temperature (Tf′), and that Tf′ can be approximated as the temperature near the onset of the rapid increase in thermal expansion that occurs in the glass transition interval. The volume data of this study were combined with available volume data for anhydrous, Na2O-Al2O3-SiO2 liquids to derive the partial molar volume (±1) of the H2O component \(\) in an albitic melt at ∼565 K and one bar. To extend the determination of \(\) to higher temperatures and pressures, the molar volumes of the hydrous albitic liquids determined in this study were combined with those measured by previous authors at 1023–1223 K and 480–840 MPa, leading to the following fitted values (±1) at 1673 K and one bar: \(\) (±0.46)×10−3 cm−3/mol-K, and dV¯H2Ototal/dP=−3.82 (±0.36)×10−4 cm3/mol-bar. The measured molar volumes of this study and those of previous authors can be recovered with a standard deviation of 0.5%, which is within the respective experimental errors. There is a significant difference between the values for \(\) derived in this study as a function of temperature and pressure and those obtained from an existing polynomial, primarily caused by the previous absence of accurate density measurements on anhydrous silicate liquids. The coefficients of thermal expansion (=4.72×10−4/K) and isothermal compressibility (T=1.66×10−5/bar) for the H2O component at 1273 K and 100 MPa, indicate that H2Ototal is the single most expansive and compressible component in silicate liquids. For example, at 1473 K and 70 MPa (conditions of a mid-ocean ridge crustal magma chamber), the presence of just 0.4 wt% H2O will decrease the density of a basaltic liquid by more than one percent. An equivalent decrease in melt density could be achieved by increasing the temperature by 175 degrees or the decreasing pressure by 230 MPa. Therefore, even minor quantities of dissolved water will have a marked effect on the dynamic properties of silicate liquids in the crustal environment.

Growth of 1,3,5‐Triamino‐2,4,6‐trinitrobenzene (TATB) I. Anisotropic thermal expansion

Abstract: Expansion of TATB is studied on a molecular level by means of x-ray crystallography. Continuous monitoring of the cell constants of TATB between 214 K and 377 K allows calculation of a volume change of +5.1% for this molecular system. Expansion of the pure material is almost exclusively a function of a 4% linear increase in the c axis (the perpendicular distance between sheets of hydrogen-bonded TATB). Calculated from these data, the volume coefficient of thermal expansion for crystalline TATB is 30.4 × 10−5 K−1. The structural features of crystalline TATB and its anisotropic thermal-expansion behaviour are compared with those of graphite and boron nitride. Two other crystalline products in the bulk TATB are either actual polymorphs of TATB or impurities.

Mechanical and thermal properties of nanocarbon-reinforced aluminum matrix composites at elevated temperatures

Abstract: This study evaluated the mechanical and thermal properties of aluminum alloy 2024 (Al2024) matrix composites reinforced with multi-walled carbon nanotube (MWCNT) or few-layered graphene (FLG) in the temperature range of 250–430 °C. The Al2024/MWCNT and Al2024/FLG composites were fabricated using powder metallurgy, and the associated microstructures were observed. At 350 °C, both composites maintain high yield stress about 110 MPa, since uniform dispersion of the nano-scale reinforcements has a strong interface, hinders the dislocation movement and eutectic phase coarsening and severe softening of the matrix. The composites also show a low thermal expansion coefficient of ∼18×10−6/K. The results are respectively over ∼2.5 times higher strength and ∼20% lower CTE than those of commercial Al alloy used as piston material (AlSi12CuMgNi).

The properties and microstructure of Al-based composites reinforced with ceramic particles

Abstract: Aluminum (Al)-based composite materials which were produced using both powder metallurgical and vacuum plasma spraying (VPS) techniques are presented. The objective was to produce materials with low coefficients of thermal expansion, tailored to approach those of steel (≃13×10 −6 K −1 ), and to improve the mechanical properties of the matrix. Composite materials based on Al are used in different fields where weight and thermal stability are key requirements. Typical applications include aerospace components, electronic packaging, high precision instrumentation, and automobile engine components. The nature, size and the relative quantities of the different reinforcing phases were considered in calculations involving the optimization of the main characteristics of the composites. Fine dispersed powders of Si 3 N 4 , AlN, TiB 2 , B 4 C (5–10 μm) and 3Al 2 O 3 ·2SiO 2 (20–75 μm) were used as the strengthening phases, while pure Al, 6061 and Al–27Si–6Ni alloys were used as the matrix. The dimensional and relaxation stability was investigated for several of the extruded composites. The mechanical properties of the extruded composites and the VPS produced composites were tested. Through a combination of plastic deformation and heat treatment (annealing or quenching with ageing) major improvements in the mechanical properties of the VPS composites were obtained. Varying levels of improvement were seen in the ductility of the VPS composite materials (elongation values ranging from two to ten times greater than the as-sprayed values). The ultimate tensile strengths were also improved by 30–75% compared to the as-sprayed values.