Electrical Conductivity of Mullite Ceramics

The electrical conductivity of a lab-produced homogeneous mullite ceramic sintered at 1625 degrees C for 10h with low porosity was measured by impedance spectroscopy in the 0.01Hz to 1MHz frequency range at temperatures between 300 degrees C and 1400 degrees C in air. The electrical conductivity of the mullite ceramic is low at 300 degrees C (approximate to 0.5x10-9Scm-1), typical for a ceramic insulator. Up to approximate to 800 degrees C, the conductivity only slightly increases (approximate to 0.5x10-6Scm-1 at 800 degrees C) corresponding to a relatively low activation energy (0.68eV) of the process. Above approximate to 800 degrees C, the temperature-dependent increase in the electrical conductivity is higher (approximate to 10-5Scm-1 at 1400 degrees C), which goes along with a higher activation energy (1.14eV). The electrical conductivity of the mullite ceramic and its temperature-dependence are compared with prior studies. The conductivity of polycrystalline mullite is found to lie in-between those of the strong insulator -alumina and the excellent ion conductor Y-doped zirconia. The electrical conductivity of the mullite ceramic in the low-temperature field (< approximate to 800 degrees C) is approximately one order of magnitude higher than that of the mullite single crystals. This difference is essentially attributed to electronic grain-boundary conductivity in the polycrystalline ceramic material. The electronic grain-boundary conductivity may be triggered by defects at grain boundaries. At high temperatures, above approximate to 800 degrees C, and up to 1400 degrees C gradually increasing ionic oxygen conductivity dominates

Radiation Damage of LaMgAl11O19 and CeMgAl11O19 Magnetoplumbite

Studies of radiation damage in magnetoplumbite-type LaMgAl11O19 and CeMgAl11O19 are reported. Ion irradiation was conducted on ceramic composites containing a LaMgAl11O19 phase at 500 degrees C with 10MeV Au+ ions and on ceramic composites containing CeMgAl11O19 phase at 800 degrees C with 92MeV Xe+ ions. The radiation response of these similar LnMgAl(11)O(19) (Ln=La and Ce) hexaaluminate magnetoplumbite phases was evaluated using transmission electron microscopy (TEM) and X-ray diffraction (XRD). LaMgAl11O19 was amorphized by 10MeV Au ions with swelling of the structure within an approximate 2m radiation depth from the irradiation surface. CeMgAl11O19 did not amorphize after 92MeV Xe-ion irradiation, but ion track damage contrast is seen in approximately 5m of the irradiated depth. SRIM Monte-Carlo simulations of nuclear displacements correlate with the experimental results

Radiation damage in multiphase ceramics

Four-phase ceramic composites containing 3 mol% Y2O3 stabilized ZrO2 (3Y-TZP), Al2O3, MgAl2O4, and LaPO4 were synthesized as model materials representing inert matrix fuel with enhanced thermal conductivity and decreased radiation-induced microstructural damage with respect to single-phase UO2. This multi-phase concept, if successful, could be applied to design advanced nuclear fuels which could then be irradiated to higher burn-ups. 3Y-TZP in the composite represents a host (fuel) phase with the lowest thermal conductivity and Al2O3 is the high thermal conductivity phase. The role of MgAl2O4 and LaPO4 was to stabilize the structure under irradiation. The radiation response was evaluated by ion irradiation at 500 degrees C with 10 MeV Au ions and at 800 degrees C with 92 MeV Xe ions, to simulate damage due to primary knock-on atoms and fission fragments, respectively. Radiation damage and microstructural changes were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy and computational modeling. Al2O3. Y2O3 stabilized ZrO2 and MgAl2O4 phases exhibit high amorphization resistance and remain stable when irradiated with both Au and Xe ions. A monoclinic-to-tetragonal phase transformation, however, is promoted by Xe and Au ion irradiation in 3Y-TZP. The LaPO4 monazite phase appears to melt, dewet the other phases, and recrystallize under Au irradiation, but does not change under Xe irradiation. (C) 2013 Elsevier B.V. All rights reserved