MgO matrix

The fluorescence spectra of Sm3+, Eu3+, Tb3+ and Dy3+ in a MgO matrix has also received attention [624]. In thorium oxide matrices, samples with low Eu3+ concentration (Tho.se Euo.i4 O1.93) show [579] strong fluorescence whereas concentration quenching is observed in the sample Tho.5 Euo.5 O1.75. 

Impurity atoms ( 3.7). The presence of substitutional atoms can lead to modified chemical centers on the surface. The replacement of Mg ions by Ni ions, as in MgO-NiO solid solutions, introduces transition metal atoms in a MgO matrix and can alter the local properties of the material. Even more effective is the replacement of a divalent Mg cation by a monovalent dopant like Li. In order to compensate the charge, some O anions at the surface become O, a paramagnetic species. 

Let us consider first isovalent cations. MgO can dilute ions of similar size, as for instance Ni or Co forming NiO-MgO and CoO-MgO solid solutions with an infinite range of composition. The effect of progressively replacing Mg by Ni or similar cations (Co ", Cu ) on the surface properites has been investigated both experimentally [83,177,178] and theoretically [179,180]. The presence of Ni cations diluted in the MgO matrix results in an efficient catalyst for nitrous oxide, N2O, decomposition this has been attributed to the different bond strength of the Ni-0 and Mg-0 bonds at the surface [177]. Plane wave calculations on Ni-doped MgO have shown that the presence of Ni atoms on the... 

The mobile ions are C026 ions which move from the cathode to the anode through the molten Li, K, and Na carbonates immobilized in a MgO matrix the water is produced at the anode. Water is removed together with C02, possible traces of CO react at the anode with H20, forming C02 and H2. Therefore, it is very convenient to use MCFC with fuels such as natural gas or other hydrocarbons. 

Bauer (1921) developed the first high-temperature MCFC based on a molten (Na/K)2C03 electrolyte, immobilized in a MgO matrix.The MCFC in its present form was developed by G. H. J. Broers in 1951. Small laboratory cells were constructed using a non-sintered MgO + molten carbonate paste electrolyte. The durability of these cells was tested up to 6 mo. Common features of today s cells and the early Broers cells are the nickel-based electrodes with planar and bipolar construction and the alkali carbonate electrolyte in inert matrix filler. The basic operating principles are still the same and the cell is represented below. 

For characterization we used IR and ESR spectroscopy. ESR spectra were recorded on a JE0L-FE-3X type spectrometer in the X-band using Mn in MgO matrix for field calibration. For IR studies KBr pellet and self-supporting wafer techniques were utilized. Adsorption of N2 and solid-gas (O2, H2) interactionE were investigated in a high vacuum equipment supplemented with MS gas analysis. 

This experimental run used a membrane manufactured by wicking an equilibrium composition electrolyte into a partially sintered MgO matrix. The cathode in this cell was carbon and the anode was CoSg. The process gas supplied to the cathode had an HjS concentration of 1.33% and a CO, concentration of 19.3%. H,S concentrations were driven as low as 2000 ppm as shown in Figure 5 (corresponding to 84.9% removal), but CO, removal was also observed as shown in Figure 6. Condensed sulfur was recovered from the anode sweep lines, but poor cell seals on the anode side made complete sulfur recovery impossible. 

Typical SEM images of the BaTiOy-MgO composites are shown in Fig. 3. The white BaTiOy particles homogenously dispersed within the MgO matrix grains and at grain boundaries. The average grain size of MgO matrix varied from 5.65 jxm for the monolithic MgO to less than 5 jjtm for the 10 vol% BaTiOy added MgO, as shown... 

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