Urea adsorbs on the ruthenium titanium oxide electrode, depressing the observed current. For artificial kidney dialysate concentrations of urea and NaCl (0.50 kg/m3 and 100 mol/m3, respectively), the major electrolysis products are N, , CO,, 0,, and H, , and the reaction mechanism is solution oxidation of urea by anodically generated active chlorine. A nitrogen-yielding direct electrode reaction is observed at high urea concentration (30 kg/m3) and low NaCl concentration (10-100 m o~ / m3). J. C. Wright, A. S. Michaels SCOPEUrea is the major nitrogenous waste metabolite produced by the body. Bioengineering applications of urea oxidation by electrochemical means include water reclamation from urine for extended space flight (Lockheed, 1977), implantable bioelectrochemical sensors (Marincic et al., 1979), and dialysate regeneration for the artificial kidney (Yao et al., 1974;Bizot and Sausse, 1975; Fels, 1978). Previous investigations of urea electrooxidation have almost exclusively involved the use of platinum electrodes. Most investigators have claimed that the chloride in physiological solutions is first oxidized to active chlorine, and that urea is oxidized by the active chlorine in a bulk solution reaction (Bizot and Sausse, 1975;Lockheed, 1977; Fels, 1978;Quellhorst et al., 1978). However, urea adsorption on platinum electrodes has been confirmed by radiotracer experiments (Gromyko et al., 1979;Horanyi et al., 1979), and direct electrode reaction of urea has been reported (Gromyko et al., 1973(Gromyko et al., , 1974Keller et al., 1980). High surface area ruthenium titanium oxide electrodes (Beer, 1966(Beer, , 1967) provide a potential alternative to platinum electrodes. In the present study the electrochemistry of urea at the ruthenium titanium oxide electrode primarily was investigated for aqueous solution concentrations of urea and chloride found in artificial kidney dialysate; more concentrated solutions also were studied. CONCLUSIONS AND SIGNIFICANCEUrea (0.50-30.0 kg /m3) depressed the observed anodic current, thus indicating urea adsorption on the ruthenium titanium oxide electrode. In the absence of a cell separator, electrolysis of solutions representative of artificial kidney dialysate (pH 7.5, 100 mol/m3 NaCl + 0.5 kg/m3 urea) above the chloride discharge potential yielded N, and CO, (from urea oxidation) and 0, (from water oxidation) at the anode; H, is produced at the cathode. The N, evolved matched the urea con- 1450September 1986 sumed within experimental error (+ 15%). Coulombic efficiencies for urea oxidation of 18 to 54% were observed. For these solutions, the mechanism for urea electrooxidation at the ruthenium titanium oxide electrode involves solution oxidation of the urea by anodically generated active chlorine in a series of reaction steps. The rate of the last overall step, which converts chlorinated nitrogen compounds to molecular nitrogen, increases with pH. At high urea concentrations (30 kg/ rn3) and low NaCl concentrations (10-100 mol/m3), a direct electrode reaction is observed...

The crystal structure of Th­(BH4)4 is described. Two of the four BH4 – ions are terminal and tridentate (κ3), whereas the other two bridge between neighboring ThIV centers in a κ2,κ2 (i.e., bis-bidentate) fashion. Thus, each thorium center is bound to six BH4 – groups by 14 Th–H bonds. The six boron atoms describe a distorted octahedron in which the κ3-BH4 – ions are mutually cis; the 14 ligating hydrogen atoms define a highly distorted bicapped hexagonal antiprism. The thorium centers are linked into a polymer consisting of interconnected helical chains wound about 4-fold screw axes. The structures of An­(BH4)4 (An = Th, U) were also investigated by DFT. The geometries of [An­(BH4)6]2–, [An3(BH4)16]4–, and [An5(BH4)26]6– fragments of the polymeric structures were optimized at the B3LYP and/or PBE levels. Most calculated geometries are 14-coordinate and agree with the experimental structures, but isolated [Th­(BH4)6]2– units are predicted to feature 16-coordinate ThIV centers.

The batch materials used in glass production are often too coarse to allow phase evolution measurements by in situ high‐temperature x‐ray diffraction (HTXRD). Reducing the particle sizes to accommodate these measurements changes the reaction kinetics and can alter the reaction pathway. Unlike conventional laboratory XRD, which operates in reflection mode and analyzes the surface region of finely ground powder, neutron diffraction can be used to characterize as‐received batch materials by means of an intense beam which penetrates through a bulk sample. In this study, the phase evolution in a glass‐forming batch made with fine batch materials was probed in situ by both HTXRD and time‐of‐flight neutron diffraction to determine the similarities and differences between measurements by the two techniques. Then, the same composition, prepared using the coarser, as‐received size distributions of the same batch materials, was studied by both techniques, demonstrating the unique capability of neutron diffraction to analyze material which is too coarse for the HTXRD, and to reveal the effect of the particle size distribution on the reaction kinetics.

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