Papers by Keyword: Thermal Expansion Coefficient

Abstract: A prospective fuel cell sealing material using silica sand from Bancar, Tuban, East Java has been investigated. The investigation was aimed to enhance the value of such natural sand and was started by a treatment using magnetic separation and immersion with HCl to produce pure silica powder. Ceramic composites were then synthesized by a solid state reaction method by mixing the silica powder, magnesia (MgO), and 5-20wt% of boria (B₂O₃), pressing the mixture into pellets and finally sintering them at 1150 °C for 4 hours. By Archimedes method, it was found that the addition of B₂O₃ is favorable to reduce the porosity of composites with a maximum value reaching 0.68(0)% for the composite with 20% B₂O₃. An X-ray diffraction technique revealed that a liquid phase sintering had occurred, indicated by the appearance of quartz (SiO₂), forsterite (Mg₂SiO₄) and protoenstatite (MgSiO₃) in the sample without B₂O₃ and quartz and protoenstatite in the composites with 5 and 10 wt% of B₂O₃. Meanwhile, the composite SMB15h, in addition to quartz and protoenstatit, also contains a new phase, namely suanite (Mg₂B₂O₅). In SMB204h, there are quartz and suanite.The phase compositions were determined using the Rietveld method from which thermal expansion coefficient values of 9.5-12 ppm °C^-1 had been predicted. These results showed that natural-sand-based composites could fairly satisfy the required conditions of fuel-cell sealing materials.

Abstract: (Sm_1-xNd_x)₂Ce₂O₇ ceramics was synthesized by solid reaction method at 1873K for 10h in the present investigation. The density, phase structure, thermal conductivity and thermal expansion coefficient of (Sm_1-xNd_x)₂Ce₂O₇ ceramics were studied by the Archimedes method, X-ray diffraction (XRD), laser-flash and pushing rod. The (Sm_1-xNd_x)₂Ce₂O₇ ceramics have pure fluorite-structure. The thermal conductivity of (Sm_1-xNd_x)₂Ce₂O₇ ceramics decreased with an increase of Nd₂O₃ content at identical temperature conditions, and the thermal expansion coefficient increased with increasing Nd-doping content. The synthesized (Sm_1-xNd_x)₂Ce₂O₇ ceramics can be explored as an ideal candidate material for future thermal barrier coatings.

Abstract: A representative volume element is chosen to act as the research object to analyze the thermal expansion coefficient of the dispersion fuel elements. The thermal analysis is carried out for the thermal behaviors using FEM. The results are compared with several theoretical models.

Abstract: Thermodynamic equilibrium of Fe-36Ni-base Invar alloy containing C contents from 0.25 to 0.38 weight per cent during solidification has been investigated in this study. From the thermodynamic simulation using ThermoCalc®, it has been revealed that equilibrium phases which can be formed are two kinds of MC-type precipitates, i.e. (Nb, Mo, V)C and MoC, and M₂C carbides. The MoC carbide was expected to be formed at relatively lower temperature below 770^oC. Microstructure observation revealed the coarse precipitates in the as-cast ingots, which was Mo-rich non-equilibrium phase and could be resolved by the successive heat treatment. With increasing C contents from 0.25 to 0.38 wt.%, tensile strength of Invar alloy increased from 950 to 1100MPa after hot rolling and thermal expansion coefficient showed a trivial increase. Hot-rolled Invar alloy was successfully drawn at room temperature from 6 to 4 mm in diameter, which dramatically decreased thermal expansion coefficient.

Abstract: This paper focused on the epoxy resin/inorganic filler composites. The electrical and thermal properties of the composites were tested and analyzed at room temperature. The influence of temperature on the thermal conductivity and thermal expansion coefficient was studied. Based on the electrical and thermal properties of the composites, the simulation model of the fully enclosed epoxy resin casting bus bar (FEERCB) was built, and the temperature field distribution of the FEERCB was calculated. T The study results showed that the volume resistivity, dielectric constant, dielectric loss factor and breakdown strength of the epoxy resin/inorganic filler composites were 1.74×10¹⁴Ω·cm, 3.44, 3.75 and 22.31 kV/mm respectively at room temperature. The thermal conductivity and thermal expansion coefficient of the composites were 2.55 W/m·K and 21.73×10^-6 /°C, achieved the insulation requirements for FEERCB. In the temperature range of the test, with increasing temperature, the thermal conductivity reduced gradually, while the thermal expansion coefficient increased gradually. The simulation results showed that the FEERCB has remarkable performance on the heat dissipation and current carrying capability.

Abstract: Asphalt mixture was considered as a two-phase composite, in which coarse aggregates are embedded into asphalt mastic matrix, namely a mix of fine aggregates and asphalt, so that a theoretical framework was proposed to correlate its effective thermal expansion coefficient with its components and microstructures based on the Eshelby equivalent inclusion theory. A four-parameter model with the experimentally determined parameters was used to characterize the viscoelastic constitutive behavior of asphalt mastic. The thermal expansion coefficient prediction of asphalt mixture was conducted and compared with the predictions by the sparse method and the self-consistent method. It was revealed that the prediction from the proposed theoretical framework is reasonable.

Abstract: The paper introduces the measuring principle of glass thermal expansion coefficient. It expresses the features and advantages of the linear variable differential transformer measuring principle by comparing the thermal expansion coefficient measurement methods analysis. Meanwhile, the paper introduces DIL402PC dilatometer measuring devices and measurement procedures. It use standard samples to execute thermal expansion instrument system check from the accuracy and repeatability. The result shows thermal expansion coefficient of linear expansion instrument bias of DIL402PC dilatometer is within the error range of the theoretical value. The process proves it has a wide range of applications.

Abstract: Two types of mullite-Al₂O₃ composites were designed and sintered in situ from different composition containing Al composites e.g. kaolin, alumina hydroxide and calcined bauxite etc, and auxiliary additives. The phase composition and microstructure were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. Bulk density, apparent porosity, thermal expansion coefficient and bending strength were also measured. The two samples exhibited XRD reflections characteristic of alumina and mullite phases. The amount of these phases depended on starting batch compositions, and reaction of starting and auxiliary materials together to form mullite. Because of in-situ formation of mullite fiber, the bulk density and bending strength were improved and apparent porosity was decreased for the composites with uniform microstructure. The presence of high mullite phase was found to decrease the thermal expansion coefficient. The potential effect of these morphologies and phase on properties was discussed. These mullite-Al₂O₃ composite was expected to have major applications in the areas of refractory material.

Abstract: The low-thermal expansion coefficient (CTE) of cement paste and concrete are designed and prepared with fly ash in this study. The thermal expansion property and pore structure of cement/concrete are tested by Thermal Dilatometer, MIP, and SEM. The test results show that the addition of fly ash lowers the thermal expansion rate and coefficient of hardened paste. The increase of addition level is accompanied by the decrease of the thermal expansion coefficient. The introduction of fly ash could improve the pore structure of concrete, thus improve the thermal expansion property of cement concrete.

Abstract: Mo-Cu alloy with high density can be fabricated at lower sintering temperature by high-energy ball-milling mechanical-alloying method and adding activation element. The rule of change of microstructure and its effect on the thermal expansion coefficient are studied. It is found that the holes in the Mo-Cu alloy sintered at lower temperature disappear, and Mo and Cu distribute uniformly. The Mo particles are fine-grained, and distribute uniformly in the Cu particles using the mechanical-alloying method. The change of thermal expansion coefficient with temperature is in accordance with the effect of adding activation element. There is a minor inflexion in the thermal expansion coefficient curve at 500°C. The change of thermal expansion coefficient with temperature is the same as 95% Al₂O₃ sealing material. Thus, the thermal property between Mo-Cu alloy and 95% Al₂O₃ match well.