Papers by Keyword: Thermal Property

Abstract: The basic properties of PuO_2−x were reviewed, and the equilibrium defects in PuO_2−x were evaluated from the experimental data of the oxygen potential and electrical conductivity as well as the Ab-initio calculation results. Consistency among various properties was confirmed, and the mechanistic models for thermal property representations were derived.

Abstract: The microdefects, the thermal expansion coefficients and the magnetization -temperature curves of the Fe₆₄Ni_36-xCo_x (x=1~10) were characterized by means of positron lifetime, X-ray diffraction, Michelson's interferometer and VSM modular on PPMS, respectively. The Fe₆₄Ni₃₀Co₆ alloy is a mixture of BCC and FCC structures. With the Co content increasing in Fe₆₄Ni_36-xCo_x alloys, the BCC phase increases, while the FCC phase decreases. In comparison with other Fe₆₄Ni_36-xCo_x alloys, the Fe₆₄Ni₃₁Co₅ alloy has a rather high magnetization at temperature lower than T_c, a relatively large change of the magnetization with the temperature near T_c, and a rather low thermal expansion coefficient.

Abstract: In this study, thermal properties of plain-woven laminates are analyzed micro-, meso-and macroscopically based on a multiscale approach. For this, the effects of thermal expansion of constituents are incorporated into the micro/meso/macro homogenization method for plain-woven laminates developed by our research group. This method enables us to analyze thermal properties of not only fiber bundles in laminates but also fibers and matrix materials in fiber bundles, in addition to their macroscopic thermal properties. The present method is then applied to the thermal property analysis of plain-woven carbon fiber/epoxy laminates subjected to a macroscopic temperature change from 180°C to 20°C. Two types of carbon fibers, i.e. HTA and P75, are considered in the analysis. It is shown that quite high thermal residual stress can occur in fiber bundles, fibers and a matrix. It is also shown that the present method can predict the change of thermal properties of the laminates depending on the difference of fibers.

Abstract: LaMgAl₁₁O₁₉ was synthesized at 1550 °C using La₂O₃, MgO and Al₂O₃ as raw materials. The samples were characterization by XRD and SEM. The tablet shaped crystals free of impurity phase formed under this condition. The thermal diffusivities were measured by laser flash method and the determined intrinsic thermal conductivities decreased as temperature increases from 25 °C to 1000 °C. As comparison, intrinsic thermal conductivities of LaMgAl₁₁O₁₉ are lower than that of 7YSZ. The synthesized LaMgAl₁₁O₁₉ was heat treated at higher temperature from 1600 °C to 1700 °C and no change in the phase indicates that the LaMgAl₁₁O₁₉ phase is stable under 1700 °C, which is very important for thermal barrier coatings (TBCs) serving at elevated temperature.

Abstract: In this paper, high temperature multilayer thermal insulations were to investigate in thermal protection systems for hypersonic vehicles. The thermal response and thermal property of the multilayer insulations were simulated and analyzed by using Ansys software. The calculation results were analyzed and the effects of parameters such as layer thermal conductivity, layer thickness, layer density, and numbers of layer are clarified. Thermal property of multilayer insulations was optimized. The results are helpful to the optimum design of the multilayer insulation system.

Abstract: To improve the heat absorbed and scattered properties of quartz fiber tile, porous phenolic resin impregnated quartz fiber tile composite for ablator and thermal insulator was prepared by impregnating the quartz fiber tile with ethanol solution of phenolic resin, and then drying and cured. The phenolic resin impregnated quartz fiber tile ablative composite is a new heat protection composite material with lower density, lower heat conductivity and low mass ablation. It can be used as the widespread thermal protection system of the aero craft in the high heat flux, high temperature and extreme condition. The thermal property and ablation property of the composites were studied respectively. The ablation property of PICA was evaluated by the oxyacetylene ablation experiment. The microstructure morphology of specimen before and after ablation was viewed by SEM. The thermogravimetric analysis of the ablator was taken from room temperature to 800°C.

Abstract: A series of addition-type imide oligomer (degree of polymerization: n=1-9) derived from 2,3,3',4'-diphenyl ether tetracarboxylic acid dianhydride (a-ODPA), 3,4'-oxydianiline (3,4'-ODA) and 4-phenylethynylphthalic anhydride (PEPA) was synthesized by thermal imidization. The resultant oligomers were characterized for their chemical architecture, thermal property, and processability. The experimental results showed that oligomers PI-1 and PI-2 had somewhat crystalline phase. PI-4, PI-6 and PI-9 exihibited high solubility in solvents. These imide oligomers have a very low melt viscosity, and thus provide wide processing window by the rheological behaviors. Furthermore, the cured polyimides exhibited excellent thermal stability under N₂ atmosphere. The temperatures of 5% weight loss in N₂ atmosphere were all above 524°C.

Abstract: A fluorine-containing benzoxazine monomer (BAF-4fa) from 4-(trifluoromethyl) aniline, 4,4′-(Hexafluoroisopropylidene) diphenol or bisphenol-AF and paraformaldehyde was synthesized using solventless method at temperature of 110°C without any catalyst. Chemical structure and thermal properties of as-synthesized benzoxazine resin were investigated and compared with fluorine-containing benzoxazine resin as well as with traditional bisphenol-A aniline based benzoxazine (BA-a) system. From Fourier transform infrared spectrum of BAF-4fa monomer, absorption band at 1243 cm^-1 which were assigned to C-O-C stretching mode of oxazine ring and band around 1505 cm^-1 and 951 cm^-1 which were attributed to tri-substitutued benzene ring from the oxazine ring moieties were observed. The result is in good agreement with the BA-a monomer, indicating successful preparation of BAF-4fa via solventless technology. The obtained BAF-4fa also exhibits thermal curing ability which is a signature of benzoxazine resin. The exothermic heat of reaction of BAF-4fa was found to be less than that of BA-a as observed by a differential scanning calorimeter. The BAF-4fa monomer was step-cured at 200°C for 2 hours, 250°C for 3 hours followed by 270°C for 2 hours to achieve its fully cured stage. Glass transition temperature of PBAF-4fa from tanδ of dynamic mechanical analysis was found to be much higher than that of PBA-a i.e. 288°C vs 189°C. From thermogravimetric analysis, thermal degradation at 10% weight loss of PBAF-4fa was found to be 453°C compared to the value of 341°C of PBA-a while the char yield was 53% vs 28% of the BA-a polymer. As a consequence, the incorporation of fluorine atoms into polybenzoxazine is able to improve various thermal stability of the polymer which allows such application as high temperature resistance materials including electronic packaging, thermal resistance coating.

Abstract: SMC composites consist of chopped glass fiber as a reinforcements, polyester and mineral fillers. Among them, filler is one of the important factors for improving mechanical and thermal properties of composites, but it has not drawn much attention for SMC composites. In this study, the size effect of calcium carbonate as mineral filler on mechanical properties of SMC composites was discussed using five different sizes of commercial calcium carbonates without chopped fiber reinforcement, to focus on the size effect itself. The SMC process was modified to be suitable for a laboratory scale composed of three steps. The mean sizes of the calcium carbonates were 3 – 20 μm, and the specific surface areas were calculated to be 1 – 5 m²/g by BET. Small size of calcium carbonate having high surface area up to 4 m²/g showed high thermal resistance, and showed higher strength comparing to the large fillers because it affected to form a dense packed microstructure.

Abstract: The thermal property of new composition of eutectic molten salt was investigated to obtain low melting point and better stability at temperature of 500°C as heat transfer fluid in solar thermal energy system. The NaCl used was purified from seawater. The eutectic molten salts were prepared in ten different weight ratios and experiments were carried out using nitrogen as inert gas with heating of 10°C/min to the temperature from 25°C to 500°C. Experimental results indicated that all mixtures exhibited low melting point (<163°C) and high stability. The thermal degradation of LiNO₃, NaNO₃, KNO₃ and NaCl exhibit in the DTG profiles respectively. From the present study it can be concluded that major weight loss of the system is due to the dissociation of lithium nitrate to lithium oxides.