Physical properties of 8 mol% Ceria doped yttria stabilised zirconia powder and ceramic and their behaviour during annealing and sintering

The thermal behaviour of 8 mol% Ceria doped 16 mol% yttria stabilised zirconia (Ce-YSZ) powder, synthesised by the wet co-precipitation method, has been investigated in details. The lattice parameter, mean crystallite size and lattice distortions have been determined as a function of calcination temperature. After grinding by attrition followed by fractionating in acetone, the powders were compacted and sintered at 1600 degrees C in air for 5 h. The sintering behaviour of pellets was studied by dilatometry. revealing different sintering behaviour depending on (he calcination temperature of the powders and the type of agglomerates. The influence of these latter parameters on the microstructure of pellets has been investigated. The pellets produced from powders calcined at low-temperature, front 110 to 600 degrees C, present the highest densities and the best morphological structure. (c) 2005 Elsevier Ltd. All rights reserved

Thermal and Crystallization Behaviour of ThO2-CeO2 system

The effect of the addition of ceria on the thermal behaviour and crystallization of thoria powders prepared by a "soft" co-precipitation method was investigated in detail using TG-DSC and XRD. It was shown that the synthesized powders consist of a mixture of pure thoria and cera and (ThCe)O-2 solid solution with ceria content different from the initial. All powders were crystallized after drying. and a solid solution with homogeneous composition of (ThCe)O-2 was formed during heating from 700 to 1100 degrees C. At temperatures above 1100 degrees C. all investigated powders form homogeneous (ThCe)O-2 solid solutions with face-centred cubic. fluorite-type structures, without any apparent segregation of ceria or thoria. The (ThCe)O-2 lattice parameter was found to be a function of the ceria content according to Vegard's law. (C) 2009 Elsevier B.V. All rights reserved

Compressibility and sinterability of CeO2-8YSZ powders synthesized by a wet chemical method

The compressibility and sinterability of CeO2-8YSZ powders prepared by co-precipitation were investigated in detail. It was shown that the compressibility curves are characterized by three linear parts at low, middle and high pressures. The middle and high regions of the applied pressure, as least investigated, were studied in detail. The specific values of the compaction pressure (P-Y2) and density (rho(Y2)) at the intersection point of the compressibility curves were determined for all investigated powders. It was shown that the compressibility curves for all investigated powders can be described by two straight lines by using special coordinates rho(G)/rho(Y2) and log(P/P-Y2).The sinterability curves of powders after drying and after calcination at 350 degrees C have a pronounced maximum. The optimum compaction pressures (P*) corresponding to the pressure at the maximal value of sintered density were determined for all investigated powders. It was shown that the region of optimal pressures is in the upper part of the middle-pressure region, whereas the P*/P-Y2 ratio varies between 0.7 and 0.9. The influence of the powder fractionation on the sinterability of the powders was also studied in detail as a function of the compaction pressure and calcination temperature. (C) 2008 Elsevier Ltd. All rights reserved

Thermal and Crystallization Behaviour of 8YSZ-CeO2 system

The effect of the addition of ceria (0-100%) on the thermal behaviour and crystallization of yttria cubic-stabilised zirconia powders prepared by a "soft" co-precipitation method was investigated in detail using thermogravimetry coupled with differential scanning calorimetry (TG-DSC) and X-ray diffraction (XRD). It was shown that the synthesized powders after drying constitute a mixture of pure ceria and (ZrYCe)Ox solid solution with a reduced ceria content. The synthesized powders after drying with ceria contents up to 20 mol.% are amorphous. Their crystallization in the temperature range of 623-873 K is accompanied by two exothermal effects, which can be explained by the crystallization of (ZrYCe)Ox solid solution with a reduced ceria content and the incorporation of ceria into this matrix, respectively. The powders with a ceria content above 20 mol.% are already crystallized after drying, and a solid solution with equilibrium composition of (ZrYCe)Ox is formed during heating to 873 K. At temperatures above 873 K, all investigated powders form homogeneous (ZrYCe)Ox solid solutions with face-centred cubic, fluorite type structure, without any apparent segregation of ceria. The (ZrYCe)Ox lattice parameter was found to be a function of ceria content according to Vegard's law. (C) 2008 Elsevier B.V. All rights reserved

Ion distribution models for defect fluorite ZrO2 - AO1.5 (A = Ln, Y) solid solutions : II: Thermodynamics of mixing and ordering

Thermodynamic mixing properties of AxB1-xO2-0.5xV0.5x, fluorite-type solid solutions (B = Zr, A = {Nd-Yb, Y}, V = oxygen vacancy) are modelled as functions of four parameters, ΔH1, ΔH2, ΔH3 and ΔH4, which correspond to the enthalpy effects of the reactions 6A + 8B = 7A + 7B (1), 6A + 8B = 8A + 6B (2), 6B + 8B = 7B + 7B (3) and 6A + 8A = 7A + 7A (4), involving six cation species, 6A, 7A, 8A, 6B, 7B and 8B. The model predicts that the disordered configuration containing all cation species evolves with the decreasing temperature such that 6-fold coordinated cations tend to vanish within 0 ≤ x ≤ 1/2 domain, while 8-fold coordinated cations become extinct within 1/2 ≤ x ≤ 1 domain. The further evolution within the intervals of 0 ≤ x ≤ 1/3, 1/3 ≤ x ≤ 1/2, 1/2 ≤ x ≤ 2/3 and 2/3 ≤ x ≤ 1 favours the extinction of 7A, 8B, 7B and 6A cation species, respectively. With the further decrease in the temperature 6-fold B and 8-fold A cations reappear within the domains of 1/3 ≤ x ≤ 1/2 and 1/2 ≤ x ≤ 2/3 via the reaction 7A + 7B = 8A + 6B. The configurational entropy reduces along with these transformations. The model fits structural and calorimetric data on Zr-based AxB1-xO2-0.5xV0.5x systems and provides hints to understanding of ionic conductivity and radiation susceptibility data

Physical properties and leaching behaviour of spent fuel BISO coated particles

The safe disposal in a geological repository is proposed for the spent fuel elements obtained from operation of High Temperature Reactors. The behavior of the fuel particles under disposal conditions is a key question for the long-term nuclear waste disposal. In the present work, the spent fuel BISO coated particles, which have been irradiated to a burn-up of 10% FIMA, were studied. The size and morphological characteristics of the coated particles were investigated by the using of optical and SEM microscopy. The distribution of the Cs-137 amount in the coated particle was studied in detail. It was shown the activity was concentrated mainly inside the kernels and in the carbon buffer layer, while the outside carbon layer contained 0.1% of the total Cs-137 only. Further, the thoria-based (Th0.834U0.166)O-2 kernels were mechanically isolated from the coated particles, and their solution behavior was studied using the flow through experiments. In all experiments the average flow rate was similar to 7-8 ml/day. Dissolution of irradiated and unirradiated kernels in HCl solution with the different value of pH (from 0 to 5) was investigated at the temperatures 90,55 and 20 degrees C. The amounts of the radionuclide leached in solutions were determined by ACP-MS, gamma- und alpha-spectrometry. On the basis of the obtained results the important leaching characteristics such as the normalized leaching rate, the activation energy value for the release of the different radionuclides were calculated. (C) 2011 Elsevier Ltd. All rights reserved