Solid perovskite process

O2 species formed over LaFeo SCU0.2O3 after O2 adsorption were investigated via O2-TPD experiments as described in Table 9, showing a-02 peaks at 253 and 671 °C and P-O2 peak at 793 °C. In the presence of 20 ppm SO2 in the adsorption gas, a diminution of adsorbed O2 species (especially ai-02) formed over LaFeo 8CU0 2O3 was found (see Table 9), indicating a competitive adsorption between gaseous SO2 and O2 at the same site. Acidic SO2 was believed preferentially adsorbed on the surface of perovskite compared to O2 due to the basicity of this solid. A process similar to a-02 adsorption upon anion vacancies is involved ... 

Double Substitution In such processes, two substitutions take place simultaneously. For example, in perovskite oxides, La may be replaced by Sr at the same time as Co is replaced by Fe to give solid solutions Lai Sr Coi yFey03 5. These materials exhibit mixed ionic and electronic conduction at high temperatures and have been used in a number of applications, including solid oxide fuel cells and oxygen separation. 

Zhong H-H, Zhou X-L, Liu X-Q, and Meng G-Y. Synthesis and electrical conductivity of perovskite Gd1 ICaICr03 (0Sx 0.3) by auto-ignition process. Solid State Ionics 2005 176 1057—1061. 

The hosts for ACT and REE immobilization are phases with a fluorite-derived structure (cubic zirconia-based solid solutions, pyrochlore, zirco-nolite, murataite), and zircon. The REEs and minor ACTs may be incorporated in perovskite, monazite, apatite-britholite, and titanite. Perovskite and titanite are also hosts for Sr, whereas hollandite is a host phase for Cs and corrosion products. None of these ceramics is truly a single-phase material, and other phases such as silicates (pyroxene, nepheliiie, plagioclase), oxides (spinel, hibonite/loveringite, crichtonite), or phosphates may be present and incorporate some radionuclides and process contaminants. A brief description of the most important phases suitable for immobilization of ACTs and REEs is given below. 

Smith, K. L. Lumpkin, G. R. 1993. Structural features of zirconolite, hollandite and perovskite, the major waste-bearing phases in Synroc. In Boland, J. N. Fitz Gerald, J. D. (eds) Defects and Processes in the Solid State Geoscience Applications. The McLaren Volume. Elsevier Science Publishers, B.V., 401-422. 

Barium titanate is one example of a ferroelectric material. Other oxides with the perovskite structure are also ferroelectric (e.g., lead titanate and lithium niobate). One important set of such compounds, used in many transducer applications, is the mixed oxides PZT (PbZri-Ji/Ds). These, like barium titanate, have small ions in Oe cages which are easily displaced. Other ferroelectric solids include hydrogen-bonded solids, such as KH2PO4 and Rochelle salt (NaKC4H406.4H20), salts with anions which possess dipole moments, such as NaNOz, and copolymers of poly vinylidene fluoride. It has even been proposed that ferroelectric mechanisms are involved in some biological processes such as brain memory and voltagedependent ion channels concerned with impulse conduction in nerve and muscle cells. 

Ozaki [1245] in his review classified perovskites prepared from metal alkoxides according to conditions of their crystallization. He described the following three possibilities of crystallization of perovskites (1) direct crystallization in the course of hydrolysis, (2) one-step process of thermal treatment of the amorphous hydrolysis products, and (3) crystallization as a result of the solid-state reactions between the first crystallized oxides. At present, it has become evident that the careful choice of processing conditions (which includes pre-hydrolysis and hydrolysis stages) allows most of the perovskites enumerated by Ozaki to be obtained without thermal treatment after hydrolysis. If the thermal treatment is, nevertheless, necessary, it is important to choose the appropriate atmosphere (air, oxygen, or oxygen-water vapor flow). 

Li et al. developed a solid-state reaction process to synthesize perov-skite-type LaCoOs NCs with grain diameters of 15 0 run (Li et al., 2002). In the first step of the preparation, 5 run composite hydroxide NPs were s)mthesized by grinding metal nitrates liquid paste and mixing with KOH. Then the composite powders were calcined at 800 °C, yielding a single-phase oxide. Tien-Thao et al. prepared LaCo Cui J.O3 x < 0.3) by mechano-synthesis (Tien-Thao et al., 2008). The sample has various distinct Co " " ions in the perovskite lattice, which are more reducible. The reduced catalyst surface comprising cobalt and copper atoms is very selective for the hydrogenation of CO. 

For the solid oxide fuel cells (SOFCs), a number of environmentally critical items have been identified (Zapp, 1996). The carrier sheet electrolyte may be produced from yttrium-stabilised zirconium oxide with added electrodes made of, e.g., LaSrMn-perovskite and NiO-cermet. Nitrates of these substances are used in manufacturing, and metal contamination of wastewater is a concern. The high temperature of operation makes the assembly very difficult to disassemble for decommissioning, and no process for recovering yttrium from the YSZ electrolyte material is currently known. 

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