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Grinding effects on the synthesis and sintering of cordierite were investigated. The grinding of a precursor gel derived from colloidal processing promoted the homogeneous distribution of elements in the gel, resulting in improved reactivity for the formation of cordiertie. Grinding the calcined powder enhanced the homogeneity of the resulting powder and caused the accumulation of internal energy as crystal strain; consequently, the densities of the sintered bodies increased and the optimum temperature range for sintering widened.

One-chamber solid oxide fuel cells (SOFCs) working in mixtures of methane and air have been studied extensively, 1-6 because of the advantages of the direct use of hydrocarbons such as methane as fuel gas without a reformer and the simpler cell structure compared to that of a conventional fuel cell. For instance, this cell can easily be stacked using staggered anodes and cathodes on one side of the electrolyte, 3,7-9 thus the ohmic resistance of the cell can be decreased by reducing the distance between anode and cathode rather than by using thin electrolytes as done in conventional SOFCs. The working principle of this cell is based on the difference in catalytic activity between Pt and Au electrodes for the partial oxidation of CH 4 to form H 2 and CO at high temperatures, as shown in Eq. 1which is active for the Pt electrode and relatively inactive for the Au electrode, thus resulting in the formation of electromotive force (emf) between the two electrodes. Presently, the electrolyte materials investigated in the one-chamber cell include mixed ionic (H ϩ and O 2Ϫ ) conductors such as BaCeO 3 -based ceramics 3,4 and an oxygen ion conductor such as yttria-stabilized zirconia (YSZ), as widely used in conventional SOFCs. It was reported that a power density of up to 0.17 W cm Ϫ2 was generated at 950ЊC for a one-chamber cell using BaCe 0.8 Y 0.2 O 3Ϫ␣ as electrolyte. 4 However, it was found that the BaCeO 3 -based ceramic electrolyte would react with CO 2 , a product of the cell, to form BaCO 3 at the surface of the electrolyte and consequently degrade cell performances. 10 The emf of a one-chamber cell using YSZ as electrolyte will decrease with time. Moreover, the power density is very low due to the large polarization characteristics of both Au and Pt electrodes. 5,6 It was suggested by comparison with the good performance of Au and Pt electrodes on BaCeO 3 -based electrolyte, which exhibits partial electronic conduction, 2,4 that electronic conduction at the electrolyte surface may play a role by increasing the length of the threephase boundaries where electrode reactions take place, leading to a decrease in electrode polarization. As a result, investigations have sought to improve the polarization characteristics of Au and Pt electrodes by using TiO 2 -doped or Pr 6 O 11 -coated YSZ electrolytes 5,6 in which electronic conduction (n-type or p-type) was expected to be present.In this work, Au and Pt electrodes were modified by incorporating oxides with cations of different valence. The valence change or electron hopping mechanism in the oxide additives was expected to provide some electrocatalysis of the electrode reactions. Experimental results showing improved discharge characteristics of electrodes and electrolyte with added MnO 2 and the corresponding microstructures of the electrolyte/electrodes interfaces are reported, and the possible effects of MnO 2 in the electrodes and the electrolyte are discussed in this paper. ExperimentalThe structure of the one-chamber fuel cell is illustrated in Fig. 1a. The dis...

Electrochemical removal of NO and CH, from a gas stream containing excess 0, , H,O and CO, has been carried out between 400 and 800 "C using a single-compartment reactor, which is constructed from Ce0,-based solid electrolyte with two palladium electrodes. At all temperatures studied, both NO and CH, were decomposed by applying a direct current to the reactor. NO was decomposed to N, in two different ways depending on the applied current. At low currents, NO was electrolysed together with 0, at the palladium cathode; and, at high currents, NO was catalytically reduced over the palladium surface free from adsorbed oxygen. By investigating the influences of the concentration of NO, H,O, CO,, CH, or C,H, contained in the reactant gas to these two decompositions, their mechanisms are discussed in detail.The exhaust gases from diesel and lean-burn engines contain several hundred ppm of NO, and several % of O,, H,O and CO, . Three-way automotive catalysts unfortunately cannot reduce NO, under such oxidizing conditions. We have proposed a new method for removing NO electrochemically from a gas stream in the presence of excess O,, H,O and CO, above 700 "C.' An electrochemical cell, Pd I yttria-stabilized Paper 6/03058K;