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.

Electrical and thermophysical properties of ZrB2 and HfB2 based composites

Abstract: Electrical resistivities, thermal conductivities and thermal expansion coefficients of hot-pressed ZrB2–SiC, ZrB2–SiC–Si3N4, ZrB2–ZrC–SiC–Si3N4 and HfB2–SiC composites have been evaluated. Effects of Si3N4 and ZrC additions on electrical and thermophysical properties of ZrB2–SiC composite have been investigated. Further, properties of ZrB2–SiC and HfB2–SiC composites have been compared. Electrical resistivities (at 25 °C), thermal conductivities (between 25 and 1300 °C) and thermal expansion coefficients (over 25–1000 °C) have been determined by four-probe method, laser flash method and thermo-mechanical analyzer, respectively. Experimental results have shown reasonable agreement with theoretical predictions. Electrical resistivities of ZrB2-based composites are lower than that of HfB2–SiC composite. Thermal conductivity of ZrB2 increases with addition of SiC, while it decreases on ZrC addition, which is explained considering relative contributions of electrons and phonons to thermal transport. As expected, thermal expansion coefficient of each composite is reduced by SiC additions in 25–200 °C range, while it exceeds theoretical values at higher temperatures.

Transparent, high strain point spinel glass-ceramics

Abstract: Transparent, refractory glass-ceramics based on 10 nm crystals of spinel solid solution in a highly siliceous residual glass can be produced from compositions in the SiO 2 –Al 2 O 3 –ZnO–MgO–TiO 2 –ZrO 2 system. The glass-ceramics possess excellent chemical durability as well as thermal expansion coefficients of 35–40 × 10 −7 /°C and strain point temperatures of over 900°C. Titania serves as both an extremely effective nucleating agent in these glasses and as an integral component of the spinel crystals. The materials are designed such that fluxes in the glass partition into the spinel crystals during the crystallization process, leaving a continuous residual glass very high in silica. The strain points of the resultant glass-ceramics approach those of vitreous silica and quartz materials which require significantly more expensive manufacturing processes. These glass-ceramics are excellent substrate candidates for high temperature, high quality polysilicon thin films. Potential products include solar cells and active matrix liquid crystal displays.

The thermal expansion behaviour of the framework silicates

Abstract: This paper gives a revision and expansion of an earlier interpretation of the thermal expansion behaviour of the framework silicates. The partially-collapsed and ideal fully-expanded structures of quartz, cristobalite, and sodalite are characterized by the geometric relationship between the angle of rotation of their tetrahedra from the ideal fully-expanded state, their cell parameters, and the length of the tetrahedron edge. Their thermal expansion behaviour is interpreted as due mainly to the effect of the rotation of the tetrahedra towards the fully-expanded state modified by anisotropic thermal motion of the framework oxygens and distortion of the tetrahedra from a regular form. With the leucite and sodalite groups the significance of the interframework cations is discussed.

Properties of Yttrium Oxide Ceramics

Abstract: The cubic structure of yttrium oxide is stable to 1800°C. in air as indicated by petrographic, X-ray, and differential thermal analyses. A change in lattice parameter of less than ±0.007 a.u. was observed on heating the oxide to 1800°C. The mean specific heat of Y2O3 to 1600°C. was 0.13 cal. per gm. per °C. The coefficient of linear expansion to 1400°C. was 9.3 × 10−6 in. per in. per °C. Compacts of Y2O3 required a temperature of 1800°C. for vitrification. In equimolecular binary mixtures heated in the powdered state at 1500°C., Y2O3 formed compounds with Al2O3 and Fe2O3 and solid solutions with ZrO2 and HfO2. Y2O3 did not react with CaO, MgO, or ThO2. Crystal types and unit-cell sizes of the reaction products are included.

Bulk crystal growth and characterization of a new polar polymorph of BaTeMo2O9: α-BaTeMo2O9

Abstract: Bulk single crystals of α-BaTeMo2O9 with dimensions up to 51 × 30 × 20 mm3 were grown successfully by a top-seeded solution growth (TSSG) method using TeO2-MoO3 mixture as a flux. High-resolution X-ray diffraction measurement on the (400)-faced plate indicates that the full-width at half-maximum (FWHM) of the rocking curve is 16.55′′. The as-grown crystal exhibits {010}, {002}, {110}, {111} and {201} facets, which are in good accordance with the predicted growth morphology based upon the Bravais-Friedel and Donnay-Harker (BFDH) method. In addition, thermal properties including thermal expansion, specific heat, thermal diffusivity and thermal conductivity were investigated as a function of temperature. The average linear thermal expansion coefficients along the a-, b-, and c-axis from 30 °C to 500 °C were measured to be αa = 9.10 × 10−6 K−1, αb = 19.58 × 10−6 K−1 and αc = 11.94 × 10−6 K−1, respectively. The specific heat was measured to be 0.433–0.566 J (g K)−1 over the temperature range of 30–540 °C. The thermal conductivity along the a-axis is larger than those along other directions (κa>κb> κc). The transmission spectra and refractive indices were also measured. The α-BaTeMo2O9 crystal exhibits a wide transmission window ranging from 380 nm to 5530 nm. The large birefringence of α-BaTeMo2O9 (Δn = 0.305 for light at 404.7 nm) indicates that it is not only Type I and II phase-matchable, but also a very promising candidate for optical devices.