Tetsushi Matsuda

Thermophysical properties of BaZrO3 and BaCeO3

Abstract Polycrystalline perovskite type oxides, BaZrO 3 and BaCeO 3 , have been prepared by mixing the appropriate amounts of ZrO 2 , CeO 2 , and BaCO 3 followed by reacting at 1273 K and sintering at 1773 K. The thermophysical properties, viz. the thermal expansion coefficient, melting point, elastic moduli, Debye temperature, and Vickers hardness, of BaZrO 3 and BaCeO 3 have been measured. The harmonic and dilatational terms of the heat capacity have been evaluated by using the values of the thermal expansion coefficient, compressibility, and Debye temperature measured in the present study, The relationships between several properties of BaZrO 3 and BaCeO 3 show the typical characteristics of the perovskite type oxides.

Thermal and mechanical properties of zirconium hydride

The physico–chemical properties of zirconium hydride such as mechanical and thermal properties have been studied in the present study. The zirconium hydride specimens in the form of pellets (6 mm φ×10 mm l) had the hydrogen contents with 1.5–1.7 H/Zr, which were fabricated directly from zirconium metal in a modified UHV Sieverts apparatus. All the zirconium hydrides prepared in the present study showed CaF2 type δ ZrH2−x. The lattice parameter slightly increased with the hydrogen content. The thermal expansion coefficients of the zirconium hydrides evaluated from high-temperature X-ray diffraction data were larger than that of zirconium metal and increased with the hydrogen content. The longitudinal and shear sound velocities of the zirconium hydride were slightly different from those of zirconium metal, which enabled us to estimate the elastic properties. The zirconium hydride had higher elastic moduli than zirconium metal and the elastic moduli slightly depended on the hydrogen content. The microhardness of the zirconium hydride was much higher than that of zirconium metal and decreased with increasing hydrogen content. The Debye temperature of the zirconium hydride estimated from the sound velocities was larger than that of pure zirconium metal. The heat capacity was also estimated from the sound velocities and the thermal expansion data.

Heat capacities and thermal conductivities of perovskite type BaZrO3 and BaCeO3

Abstract Polycrystalline perovskite type oxides, BaZrO3 and BaCeO3, have been prepared by mixing the appropriate amounts of ZrO2, CeO2, and BaCO3 followed by reacting at 1273 K and sintering at 1773 K. The thermal conductivities of BaZrO3 and BaCeO3 have been evaluated from the heat capacity, thermal diffusivity, and density. The heat capacity has been measured by using a differential scanning calorimeter (DSC) in a high purity argon atmosphere. In the temperature range from room temperature to about 1400 K, the thermal diffusivity has been measured by a laser flash method in vacuum. The thermal conductivities of both BaZrO3 and BaCeO3 decrease with increasing temperature, showing phonon conduction characteristics. The thermal conductivity at room temperature of BaZrO3 is 5.2 Wm−1K−1, which is about 3 times larger than that of BaCeO3.

Thermal properties of zirconium hydride

Abstract Zirconium hydride specimens with hydrogen contents of 1.45–1.70 H/Zr were fabricated directly from zirconium metal in a modified UHV Sieverts apparatus. All the zirconium hydride fabricated in the present study were found from X-ray diffraction analysis to be CaF2-type δ-ZrH2−x. At temperatures of 350–700 K, the heat capacity of the zirconium hydride was measured using an enthalpy method by means of a differential scanning calorimeter (DSC), and the experimental results were consistent with the values estimated from the sound velocities and the thermal expansion coefficient. In the temperature range of 300–700 K, the thermal diffusivity of the zirconium hydride was examined by a laser flash method. The thermal diffusivity decreased with increasing temperature and was not markedly influenced by the hydrogen content. The thermal conductivity of the zirconium hydride was calculated from thermal diffusivity and heat capacity and found to have slightly lower thermal conductivity than pure zirconium metal.

High temperature phase transitions of SrZrO3

The thermal properties of SrZrO3 were evaluated from room temperature to 1400 K. SrZrO3 was prepared by the solid state reaction of SrCO3 and ZrO2 powders. X-ray diffraction measurements showed that the sample has a perovskite structure. The sample for the measurements of the thermal properties was prepared from a sintered body. The heat capacities of SrZrO3 were measured using a differential scanning calorimeter (DSC) in a high purity argon atmosphere. The phase transitions of SrZrO3 were confirmed at higher temperature. The linear thermal expansion of SrZrO3 was measured using a dilatometer. The thermal expansion data exhibited an excess volume increment that was related to one of the phase transitions confirmed by DSC.

Characteristics of zirconium hydride and deuteride

The electrical and thermal properties of zirconium hydride and deuteride have been measured. The lattice parameter of δZrD2−x was smaller than that of δZrH2−x, and the deuteride had higher elastic moduli than the hydride. The electrical and thermal conductivities of δZrH2−x were slightly different from pure Zr metal. The electronic structure of the zirconium hydride was found from XPS measurements to differ from those in the pure Zr metal, and there was a peak due to the Zr–H bond at 6.4 eV below Fermi energy in the XPS spectra. The density of states was estimated by a molecular orbital calculation, and the agreement between the XPS valence band measurements and the calculations was quite satisfactory. Some of the mechanical and thermal properties of zirconium hydride and deuteride were interpreted in terms of the results of the molecular orbital calculation.

Thermophysical properties of rock-like oxide fuel with spinel-yttria stabilized zirconia system

Abstract Thermal expansion, thermal diffusivity, melting temperature, Vickers hardness and creep rate of the rock-like oxide (ROX) fuel were measured with the MgAl 2 O 4 (spinel)–ZrO 2 (Y,Gd) (YSZ: stabilized zirconia) system and the MgAl 2 O 4 –YSZ–UO 2 system in the temperature range between room temperature and 1800 K in order to evaluate thermophysical properties. Thermal expansion coefficients of MgAl 2 O 4 –YSZ composites increased with increasing YSZ content and the values were well represented by the Turners equation. Addition of UO 2 to MgAl 2 O 4 –YSZ composite resulted in an increase of thermal expansion. Thermal conductivity values of the MgAl 2 O 4 –YSZ composites decreased with increasing YSZ content and agreed with predictions of the Maxwell–Eucken equation. The eutectic temperature of MgAl 2 O 4 –YSZ and MgAl 2 O 4 –YSZ–UO 2 systems was found to be 2200 K. High temperature hardness of the composites was higher than that of YSZ or MgAl 2 O 4 . The hardness of ROX fuel was considerably higher than that of UO 2 . The creep rate of MgAl 2 O 4 –YSZ composite was controlled by the lattice diffusion of YSZ.

Thermoelectric properties of BaUO3

The thermoelectric properties of BaUO3 were evaluated in the temperature range from room temperature to about 1000 K. In order to clarify the phonon glass property of BaUO3, the heat conduction mechanism were also studied. The electrical resistivity was higher by approximately four orders of magnitude than that of the state-of-the-art thermoelectric materials. The Seebeck coefficient was negative in the whole temperature range, and the maximum absolute value bore comparison with the currently used thermoelectric materials. The thermal conductivity was extremely low and like glasses in spite of its simple crystal structure, indicating that BaUO3 has a phonon glass property. The heat conduction of BaUO3 was mainly composed by the phonon contribution at low temperatures and the excitonic contribution at high temperatures. The dimensionless figure of merit ZT was extremely lower than that of the state-of-the-art thermoelectric materials. In order to utilize BaUO3 as an actual thermoelectric module, optimization of the electrical properties are required.

Thermophysical properties of BaUO3

Thermophysical properties of BaUO 3 , specifically melting point, thermal expansion coefficient, elastic moduli, Debye temperature, and thermal conductivity, have been studied. The longitudinal and shear sound velocities of BaUO 3 were measured by an ultrasonic pulse-echo method at room temperature, which enabled us to calculate the elastic properties and the Debye temperature. Microhardness measurements were made for BaUO 3 at room temperature using a micro-Vickers hardness tester. These mechanical properties of BaUO 3 differed from those of UO 2 . The thermal conductivity was calculated from the measured density and thermal diffusivity and literature values of heat capacity. The thermal conductivity of BaUO 3 was about one-tenth that of UO 2 . The thermophysical properties of BaUO 3 were found to be glass-like rather than like those of typical ceramics.

Thermal properties of SrCeO3

Abstract The thermal properties of SrCeO 3 were evaluated from room temperature to 1400 K. SrCeO 3 was prepared by the solid state reaction of SrCO 3 and CeO 2 powders. X-ray diffraction measurements showed that the sample has an orthorhombic perovskite-type structure at room temperature. The sample for the measurements was prepared from a sintered body. The heat capacities of SrCeO 3 were measured using a differential scanning calorimeter. The thermal expansion of SrCeO 3 was measured using a dilatometer and thermal expansion coefficients were evaluated. No phase transitions were observed in this study.