Papers by Keyword: Solid Reaction

Abstract: The MgTiO₃ and CaTiO₃ powders were synthesized by solid reaction method, and MgTiO₃-CaTiO₃ ceramic was prepared using pressureless sintering method. The experiment prepared MgTiO₃-CaTiO₃ ceramics with high compactness and stable permittivity by the way of changing the mole ratio of MgTiO₃ and CaTiO₃ to investigate the effect of CaTiO₃ on the performances of MgTiO₃-CaTiO₃ ceramics. The results show that Mg₂TiO₄ formed as second phase during sintering. Volume density and dielectric constant of MgTiO₃-CaTiO₃ ceramics with 10%mol CaTiO₃ reach maximum of 3.612g/cm³ and 17.8, respectively, under 1460°C sintering temperature. And for the MgTiO₃-CaTiO₃ ceramics with 5%mol CaTiO₃ the maximum values which are 3.5g/cm³ and 16.6, respectively, appear under 1510°C sintering temperature.

Abstract: The forming mechanism of Dy2Ce2O7 prepared by solid reaction using CeO2 and Dy2O3 as reactants was analyzed by X-ray diffraction method. It is indicated that there is almost no solid solution reaction between Dy2O3 and CeO2 before 1300°C, the Dy3+ cations enter the crystal lattice of CeO2 and substitute sites of Ce4+ cations in the range between 1300°C and 1400°C which resulted in the formation of Dy2O3-CeO2 solid solution. The Dy2O3-CeO2 solid solution transformed gradually into Dy2Ce2O7 after 1400°C and pure Dy2Ce2O7 can be obtained at 1500°C. No other intermediate phases were found in the whole process.

Abstract: The SiC/Cu composite was prepared by the method, which is patented in China, casting the metal into the SiC skeleton in a special furnace at 1160°C by pressure, caused by pressure difference between pressured gas and vacuum. During the preparation, the SiC decomposed. The carbon precipitated and the silicon, which has well affinity with the metal, formed silicon-copper compounds as Cu4Si, gathering in the silicon-copper interface area, identified by means of EDS and XRD. The mechanism of the solid reaction was discussed and the microstructure and morphology was studied by means of optical devices, SEM, EDS and XRD as well. And the diffusion coefficient was calculated.

Abstract: The specimens of O-phase Ti-22Al-25Nb (at%) intermetallics coated with silica-based enamel received mass gains of about 1 mg/cm2, after 300 h of oxidation or hot corrosion at 800 °C. These rates were much faster than the growth rates of silica films at the same temperature. To understand this phenomena, the specimens were analyzed using SEM, XRD, EPMA and TEM. An oxide layer with thickness of several μm was observed at the enamel/substrate interface of the coated specimens after either oxidation or hot corrosion. XRD and TEM analysis revealed the newly formed oxide layer was composed of α-Al2O3, Al2SiO5, Al2TiO5, rutile-TiO2 and NbO2. It was shown by EPMA profiling that an Al-depleted zone was located just beneath the oxides. It was proposed that the solid reactions between the enamel coating and the O-phase Ti-Al-Nb played important roles for the oxidation and hot corrosion behavior of the coated specimens.

Abstract: A differential thermal analyzer (DTA) and a X-ray diffractometer (XRD) were used to study the solid transformations in binary SnO2-CeO2 oxide system. For 100wt% Sn and 100wt%Ce, the transformations from amorphous xerogels to rutile and fluorite start from about 310 and 250°C, respectively. The crystallizations to two-phase mixtures of rutile and fluorite take place at higher temperatures. The two-phase mixtures appear in the region whose composition is between about Sn-10wt%Ce and Sn-75wt%Ce. Sintered at 450°C for one hour, rutile phase dissolves about 10wt% fluorite, and fluorite dissolves about 25wt% rutile. Precipitation reactions take place when the sintering temperature is raised. The phenomenon that precipitation reactions are observed for rutile and fluorite solid solutions means that lower temperature sintering produces solid solutions with high supersaturation. In the as-sintered samples, the grain sizes are fine nano-crystals and the complicated microstructures help the other cations to locate at discontinuous regions.