Electrochemical filters for oxygen sensors with improved surface properties

Oxygen sensors based on YSZ (yttria stabilized zirconia) are best known for high temperature measurements. The protection of such oxygen sensors with dense electrochemical filters is an effective way to increase their life time in aggressive industrial atmospheres. This work reports on the performance of sensors protected by composite or single phase mixed conducting filters. The first group includes materials based on GCO (Gd₂O₃ doped CeO₂)+LC (LaCoO₃), and on YSZ+LCM (La(Mn,Co)O₃). Sensors protected with GCO+LC composites showed the best performance amongst the composite filters already evaluated. Electroded single phase GCO filters were also tested to check on the role of surface reaction kinetics on the overall oxygen transport process across the filter. The fastest sensor responses to a sudden decrease in oxygen partial pressure were obtained with deposited electrodes either on both surfaces of the filter or on the filter cathode side. These preliminary results suggest that the cathodic process is more relevant than the anodic one in determining the filter permeability (and protected sensor performance), which fulfils the logical requirement of electrode free surfaces in contact with the furnace atmosphere. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

HNbO3 and HTaO3: New cubic perovskites prepared from LiNbO3 and LiTaO3 via ion exchange

The synthesis of HNbO₃ and HTaO₃ from LiNbO₃ and LiTaO₃ via ion exchange in hot aqueous acid solutions is reported. This reaction is accompanied by a topotactic structural transformation from the rhombohedral LiNbO₃ structure to the cubic perovskite structure; cell constants are a = 3.822(1) Å for HNbO₃ and 3.810(2) Å for HTaO₃. These new compounds have been characterized by powder X-ray diffraction, thermogravimetric analysis, and solid-state NMR. They are electronic insulators and have low ionic conductivity. Evidence of partially proton-exchanged phases Li_1?xH_xMO₃ was also seen. The possible significance of this ion exchange reaction for devices using LiNbO₃ or LiTaO₃ is discussed.     

A theoretical study of the structure of the liquid Ga-diamond (111) interface

We present the results of a computer simulation study of the structure of the interface between liquid Ga and the (111) face of diamond, with which we reinterpret the findings from an x-ray reflectivity study of that interface [W. J. Huisman, J. F. Peters, M. J. Zwanenburg, S. A. de Vries, T. E. Derry, D. Abernathy, and J. F. van der Veen, Nature (London) 390, 379 (1997); Surf. Sci. 402-404, 866 (1998)]. That experimental study has been interpreted to show that the contact of Ga with the (111) face of diamond induces the formation of Ga(2) molecules for several layers into the bulk liquid, with the axes of the Ga(2) molecules in successive layers oriented perpendicular to the diamond surface. No driving force for the proposed formation of Ga(2) molecules is identified. The simulations reported in this paper are based on a model that permits chemical binding of Ga, as a dimer, to the C=C double bonds in the reconstructed (111) face of diamond, thereby identifying the driving force for dimerization. We show that an isolated pi complex with the Ga(2) axis perpendicular to the C=C double bond is stable. We then modify the pseudopotential-based self-consistent Monte Carlo simulation scheme for describing inhomogeneous liquid metals, using the calculated potential-energy surface of Ga(2)(C=C) in the region close to the diamond surface. In this model only the Ga adjacent to the diamond is composed of dimers. The interfacial density distribution obtained from the simulations predicts an x-ray reflectivity that is in good agreement with that observed.     

Spirans XXII. Synthesis of 4,4-dialkyl-4-germacyclohexanone and 8,8-dialkyl-8-germaazaspiro [4.5] decanes

4,4-Dialkyl-4-germacyclohexanones have been synthesized and their reactions studied. The diethyl ketone has been converted into N-(-dimethylaminopropyl)-2 aza-8,8-diethyl-8-germaspiro[4.5]decane ( 16 ). The biological properties of 16 have been examined in some detail. The reactions of this new ketone with some other reagents are reported.     

Quenching of electronically-excited UF6 emission by selected organics

Rate constants at 25°C have been evaluated for the quenching of electronically excited UF6 by selected organic molecules. Values for the rate constants at 25°C (units of 10¹¹ ρ/mole s) for CH₄, C₂H₆, C₂F₆, CHF₂CHF₂, C₂H₂, and C₂H₄ are 0.061, 3.8, 0.022, 0.072, 6.0, and 5, respectively.