Lead oxide , pyrochlor

Lead-Ruthenate Pyrochlore Modified Nafion Membrane for Tunable Heterogeneous Catalytic Oxidation... 

S. Venkatesan, A. S. Kumar, J.-M. Zen, A Rugged Lead-ruthenate pyrochlore Membrane Catalyst for Highly Selective Oxidation of Alcohols, J. Mol. Catal. A Chem. 250 (2006) 87-93. 

PbO , Lead oxide solid solns. with ruthenium oxide (RujOj), pyrochlore, 22 69... 

RU2O3, Ruthenium oxide, solid solns. with lead oxide Pb02, pyrochlore, 22 69 RU2O3C14H12, Ruthenium, p-carbonyl-p.-methylene-bis[carbonyl(it -cyclopen-tadienyl)-, 25 182... 

Zen, J.M., Kumar, A.S., and Chen, J.C., Electrochemical behavior of lead-ruthenium oxide pyrochlore catalyst Redox characteristics in comparison with that of ruthenium dioxide, J. Mol. Catal. A, 165, 177, 2001. 

It should be noted that the exact cation stoichiometry of the product is highly sensitive to the exact metal concentration of the ruthenium source solution and temperature and pH of the reaction medium (inadvertent increases in both of these parameters lead to increased solubility of lead in the alkaline reaction medium and consequently yield solid products of lower lead ruthenium ratios). While synthesis of a pure lead ruthenium oxide pyrochlore is relatively easy, the precise cation stoichiometry of the product is a property that is not always easy to control. A relatively quick check on the cation stoichiometry of the lead ruthenium oxide product can be obtained, however, by using the correlation between lattice parameter and composition that is displayed in Fig. 1. When lattice parameter and cation stoichiometry are independently determined, the relationship shown in Fig. 1 also provides an assessment of product purity since data points that show significant departures from the displayed linear correlation indicate the presence of impurity phases. The thermal stability of the lead ruthenium oxides decreases with increasing occupancy of tetravalent lead on the octahedrally coordinated site, but all of the ruthenium oxide pyro-chlores described are stable to at least 350° in oxygen. 

Enzyme-like behavior was observed for electrocatalyt-ic oxidation on Nafion/lead-ruthenium oxide pyrochlore chemically modified electrodes.Nafion is loaded with lead(II) and ruthenium(III) cations by ion exchange, and then their oxides are prepared by in situ precipitation in such a way that the catalytically active sites remain... 

The polycrystalline film consists of the tetragonal phase of PZT with peaks arising at approximately 20 = 22 , 31°, 39°, 45°, and 55°. Tliese peaks correspond to the (100), (110), (111), (200), and (211) orientations, respectively. A bro peak centered around 26 = 30° was also evident. This may correspond to the metastable pyrochlore phase. The pyrochlore phase is lead deficient, such that Pb, labeled x, in Pbx(Zro.4gTio.s2)03, is less than one, consistent with the loss of lead oxide during the anneal at 650°C. Lead oxide is known to evaporate from films during the thermal annealing conditions described here (17,18). 

Microelectronic technologies have also been used in nitrite biosensors and electrochemical sensors (Suzuki and Taura, 2001 Adhikari and Majumdar, 2004). Ameida et al. (2013) have also developed a method of electrochemical nitrite measurement by means of a gold working electrode covered with 1,2-diaminobenzene (DAB) integrated in a FIA system. This sensor helps improve selectivity, repeatability, stability, and sensitivity. A Nafion/lead-ruthenate pyrochlore electrode chemically modified for determination of NO2 oxidation and NO reduction based on AC-impedance spectroscopy and FIA has also been tested (Zen et al., 2000). Quan and Shin (2010) also tested an electrochemical nitrite biosensor based on co-immobilization of copper-containing nitrite reductase and viologen-modified chitosan (CHIT-V) on a glassy carbon electrode (GCE). 

Direct attack by hot 70—80 wt % hydrofluoric acid, sometimes with nitric acid (qv), is effective for processiag columbites and tantalo-columbites. Yields are >90 wt%. This method, used in the first commercial separation of tantalum and niobium, is used commercially as a lead-in to solvent extraction procedures. The method is not suited to direct processiag of pyrochlores because of the large alkaU and alkaline-earth oxide content therein, ie, ca 30 wt %, and the corresponding high consumption of acid. 

---