Solutions of N2O4 and N2O5 in anhydrous and aqueous nitric acid were examined by Raman spectroscopy to gain a more detailed knowledge of the species present in these solutions and to assess the applicability of Raman spectroscopy as an analytical measurement technique. Solutions of N2O4 in HNO3 show evidence of the presence of the associated species, 3NO(+). NO3-(N4O62+), which had been identified previously in a solid compound. The effects of water on the spectra of these solutions were also examined. The nitronium cation, NO2+, is the dominant species in solutions of N2O5 in anhydrous HNO,, and the spectra of concentrated solutions of N2O5 exhibit a band that has not been reported previously. This weak band, which may be the same as a band found in the spectra of solids containing the nitronium cation, has been attributed to a second vibrational mode of the molecule. This indicates a nonlinear conformation of the NO, + ion, and suggests that it is strongly associated with other species in solution. The Raman data indicate that N2O5 in HNO3 is completely ionized at concentrations to at least 3.0 mol l(-1) (21 wt%). (C) 1997 John Wiley & Sons, Ltd.

The method for the electrosynthesis of N2O5 in nitric acid hy anodic oxidation of N2O4 has been scaled up to produce quantities of 15 to 50 kg of solution containing 20 to 30 weight percent N2O5. A two- or three-cell, divided, plate-and- frame electrolyzer operated in the bipolar mode was employed to test various combinations of candidate electrode coatings and separators, and to study the electrochemical characteristics of the process. Two sizes of electrolyzers were used, each having single-electrode areas of 0.096 and 0.25 m(2). The best performing anode/substrate materials were either Pt-Lr on niobium, or IrO2 on aluminum; the best cathode materials were Pt or Pt-Ir on niobium. The preferred cell separator is a hydrophilic, porous polytetrafluorene-ethylene diaphragm, but an FEP-polymer anion-exchange membrane is also satisfactory. Production of N2O5 was achieved with chemical yields of 80 to 90% and current efficiencies of 50 to 70%. Maximum current densities were in the range of 0.1 to 0.2 A cm(-2); Cell voltages were 3 to 5 V and specific energies were 1.6 to 1.8 kWh kg(-1). In the electrolyzer catholyte, N2O4 is generated at nearly theoretical yield, and could be recovered and recycled as an anolyte feedstock. The E-0' of the N2O5/N2O4 couple in anhydrous nitric acid was estimated to be + 1.66 +/- 0.02 V vs. SHE.

Advances in the technique and scope of controlled-potential coulometry during the past 30 years have made it ideally suited to the analysis of materials when high accuracy is desired. Its advantages include an inherent, routine measurement precision of better than 0.1% with 1–10 mg of analyte, minimal use of chemical calibrants, stable instrument calibrations, and excellent selectivity for elements such as the actinides and precious metals.

AbstractMethods have been developed for the precise assay of the explosive l,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) using procedures that quantitatively measure total nitro and/or total amino functional groups. The method for the determination of total nitro groups is based on the dissolution of TATB in DMSO‐NaOH, electrolytic reduction of ‐NO2 to ‐NH2, and measurement by controlled‐potential coulometry. The reduction is carried out at a mercury pool electrode at −0.60 V versus standard calomel electrode (SCE) in a supporting electrolyte 1 M in H3PO4 and 3 M in HClO4. Background corrections are low, and samples containing 0.1 mg to 2 mg of TATB per ml can be analyzed with a precision and accuracy of 0.25% to 0.5%.The method for determining total amino groups is based on the conversion of ‐NH2 to NH3 in a Kjeldahl‐type apparatus. The sample does not require an acid digestion step. The ‐ NH2 groups are readily converted to NH3 and distilled from a solution of NaOH and dimethylsulfoxide (DMSO). Individual samples of 120 mg‐170 mg of TATB can be conveniently assayed for amino groups with an accuracy and precision of about 0.25%.

Abstract A pilot-size brine handling system was operated from Magmamax Well 1 in southern California to study the characteristics of siliceous scale deposition and to evaluate the possibility of treating the brine with chemical additives to control scaling. The rates of formation, chemical constitution, and morphology of the scales were examined as functions of temperature, brine salinity, substrate material, and antiscalant additive activity. Potential antiscalant compounds were screened using a silica-precipitation inhibition test at 90°C. The most active classes of compounds were those containing polymeric chains of oxyethylene and polymeric nitrogen compounds that are cationic in character. The best single compound was Corcat P-18™ (Cordova Chemical Co. polyethylene imine; molecular weight ~1,800). This compound had no effect on the scale formed at 220°C but it reduced the rates of scaling at 125 and 90°C by factors of 4 and 18, respectively, and it also functioned as a corrosion inhibitor. The best additive formulation for the brines of the Salton Sea Geothermal field (SSGF) appears to be a mixture of an organic silica-precipitation inhibitor, a small amount of hydrochloric acid, and a phosphonate crystalline deposit inhibitor.

Abstract. An apparatus has been designed for collection of ground‐water samples in locations of limited water flow when atmospheric contamination must be avoided. The system consists of a packer outfitted with valves, a flow cell, and probes for measurement of dissolved oxygen, pH, and Eh, and is designed for installation in a 3‐inch (7.6‐cm) diameter borehole. The oxygen probe, which is a commercially available electrochemical device, functions accurately without water flow or oxygen consumption. The borehole collector system has been used to characterize the ground water in the Climax granite stock at the Nevada Test Site of the U.S. Department of Energy.

Pulsed laser excitation sources provide a convenient means of initiating and probing photophysical and photochemical processes at the semiconductor electrode-electrolyte interface. Both time-resolved optical and electrochemical measurements are used to characterize the dynamics of intra-electrode charge separation and interfacial charge transfer as a function of applied bias, solution composition, and electrode physical properties. The philosophy behind this approach to transient measurements will be illustrated with recent experimental results involving single crystal and polycrystalline electrodes.

Pulsed laser excitation sources provide a convenient means of initiating and probing photophysical and photochemical processes at the semiconductor electrode-electrolyte interface. Both time-resolved optical and electrochemical measurements are used to characterize the dynamics of intra-electrode charge separation and interfacial charge transfer as a function of applied bias, solution composition, and electrode physical properties. The philosophy behind this approach to transient measurements will be illustrated with recent experimental results involving single crystal and polycrystalline electrodes.

A mobile, field test system has been developed for on-line evaluation of geopressured brine injectability at elevated pressures and temperatures. The apparatus consists of a flow system that is connected directly to the well-site brine-handling equipment. The system permits injectability assessment on the basis of standard membrane filtration tests and an examination of the effects of brine aging by means of incubation tests. Auxiliary instrumentation is used to characterize the brine suspended solids. The test system is being used to diagnose water quality at the design wells.

A nitrogen laser and a nitrogen pumped dye laser have been used in a coulostatic electrochemistry experiment to characterize photoemission phenomena at a dropping mercury electrode. Time-resolved, transient voltage excursions following irradiation of a dropping mercury electrode by a single laser pulse were examined. Scavenging of the photoemitted electrons by N2O was studied in aqueous and DMF solutions as a function of laser intensity, wavelength and electrode potential. The pH dependence of the NO3− scavenging reaction was determined and compared to results obtained by other techniques. The complicated photoemission scavenging behavior of methyl viologen was studied. Earlier results with cw laser irradiation were confirmed and the importance of adsorption in the results of the laser coulostatic photoemission experiments was demonstrated. Preliminary results are reported for the effect of surfactants on photoemission.

i o n w e l l s .F i e l d measurements were made a t 13OoC and l i n e pressures up t o 3800 p s i g .Scale i n h i b i t e d (phosphonate-polyacrylate threshold-type, carbonate scale i n h i b i t o r ) , prefiltered-scale-inhibited, and

Photoemission current at a mercury electrode has been characterized electrochemically for aqueous solutions of methyl viologen, the disodium salt of anthraquinone-1,5-disulfonic acid, hydroquinone, p-benzoquinone, and chlorophyllin, and in DMF solutions of N2O and anthraquinone. The scavenging species could be determined by comparing photoemission current-voltage curves with polarographic and cyclic voltammetric data.

The Lawrence Livermore Laboratory Brine Treatment Test System at Niland, Imperial Valley, California, has been used to evaluate a number of cationic polymers and surfactants as scale control agents. An initial group of compounds was narrowed to four on the basis of their activity as silica precipitation inhibitors. Three of these and certain combinations of compounds were then given a 40-h test to determine their effectiveness in retarding scales formed at 220, 125, and 90/sup 0/C. The best single compound was Corcat P-18 (Cordova Chemical Co. polyethylene imine, M.W. approx. = 1800). It had no effect on the scale at 220/sup 0/C, but it reduced the scales at 125 and 90/sup 0/C by factors of 4 and 18, respectively, and it also has activity as a corrosion inhibitor. Other promising compounds are PAE HCl (Dynapol poly(aminoethylene, HCl salt)), which also somewhat reduces the 220/sup 0/C scale; Ethoquad 18/25 (Armak methyl polyoxyethylene(15) octadecylammonium chloride); and Mirapol A-15 (a Miranol Chemical polydiquaternary compound). The best additive formulation for the brines of the Salton Sea Geothermal Field appears to be a mixture of one of these silica precipitation inhibitors with a small amount of hydrochloric acid and a phosphonate crystalline deposit inhibitor. Speculations are presented as to the mechanism of inhibition of silica precipitation and recommendations for further testing of these additives.

Several new classes of organic compounds have been screened as potential geothermal scale control agents by examining their effect on the precipitation of silica from Magmamax No. 1 brine. The substances were tested using the Lawrence Livermore Laboratory Brine Treatment Test System at the Niland, California, Test Site. Solutions of the test substances were injected into flowing brine at 210{sup 0}C, the brine was flashed to 125{sup 0}C, and then the kinetics of solids and silica precipitation from effluent brine held at 90{sup 0}C were measured. Three new types of compounds were shown to have activity as precipitation inhibitors: polyethylene imines, polyethyloxazalines, and quaternary ammonium compounds containing polyoxyethylene. Among the latter, Ethoquad 18/25, which is methyl-polyoxyethylene(15) octadecylammonium chloride, is the leading candidate antiscalant. It is a more powerful inhibitor of silica precipitation than the pure polyoxyethylene polymers, and it apparently has no high temperature solubility limitations. Measurements were made of the concentrations of monomeric silica and the effect of addition of inhibitor at various points in the Brine Treatment Test System. Five different silane compounds showed no activity toward silica.