Solutions Of Mixed Oxides Research Articles

Determination of uranium and plutonium in mixed oxide samples by X-ray methods and their comparison with potentiometry

Uranium and plutonium in nuclear fuels are generally determined by conventional potentiometric methods which generates large quantities of radioactive waste. In the present study, K-edge densitometry (KED) and Energy dispersive X-ray fluorescence (EDXRF) have been examined for the determination of uranium and plutonium in solutions as an alternative to potentiometric methods. In the present study, uranium plutonium mixed oxide (MOX) pellets were dissolved in nitric acid medium containing small quantities of HF. Uranium and plutonium in MOX solutions were determined by KED and EDXRF methods and the results are compared with the one obtained by conventional potentiometric methods. The relative standard deviation (RSD) of the analytical results for U and Pu using KED were found to be better than ±1% and ± 0.9% respectively. Similarly, RSD for U and Pu by EDXRF were found to be better than ±1.6% and ± 0.8%, respectively. The absolute difference between KED and EDXRF with respect to potentiometric data for uranium and plutonium were calculated and it was found to be marginal indicating that KED and EDXRF methods can be employed for the routine analysis of U and Pu in solutions. X-ray methods employed in the present study are non-consumptive, direct and offer precise determination of U and Pu and generate no waste.

Passivation properties of HfO2-SiO2 mixed metal oxide thin films with low reflectivity on silicon substrates for semiconductor devices

HfO2-SiO2 mixed oxide-based thin films were introduced in this work, and their passivation and anti-reflection properties were examined by using carrier lifetime, x-ray diffraction, scanning electron microscope, energy dispersive x-ray analysis, reflectance, and Fourier transform infrared measurements. The HfO2-SiO2 mixed oxide solutions were prepared with different composition ratios, and the thin films were formed on p-type CZ-Si substrates using the spin-coating technique. Annealing of the samples was carried out in ambient air at different temperatures after optimizing the solution ratio. When annealed at 600 and 700°C, the average reflectance of the samples was observed to be around 15% in the spectral range of 300-1000 nm, with a minimum reflectance point lying in the visible range. The effective carrier lifetimes increased up to 32 μs after annealing at 600°C compared to the initial lifetime of around 2 μs. Annealing at higher temperatures significantly decreased the carrier lifetimes (4.5 and 0.6 μs for 700 and 800°C, respectively). The results of this study revealed that the HfO2-SiO2 mixed oxide films can provide a good passivation effect in addition to an effective anti-reflection property depending on the annealing temperature.

In Situ Persulfate Oxidation of 1,2,3-Trichloropropane in Groundwater of North China Plain.

In situ injection of Fe(II)-activated persulfate was carried out to oxidize chlorinated hydrocarbons and benzene, toluene, ethylbenzene, and xylene (BTEX) in groundwater in a contaminated site in North China Plain. To confirm the degradation of contaminants, an oxidant mixture of persulfate, ferrous sulfate, and citric acid was mixed with the main contaminants including 1,2,3-trichloropropane (TCP) and benzene before field demonstration. Then the mixed oxidant solution of 6 m3 was injected into an aquifer with two different depths of 8 and 15 m to oxidize a high concentration of TCP, other kinds of chlorinated hydrocarbons, and BTEX. In laboratory tests, the removal efficiency of TCP reached 61.4% in 24 h without other contaminants but the removal rate was decreased by the presence of benzene. Organic matter also reduced the TCP degradation rate and the removal efficiency was only 8.3% in 24 h. In the field test, as the solution was injected, the oxidation reaction occurred immediately, accompanied by a sharp increase of oxidation–reduction potential (ORP) and a decrease in pH. Though the concentration of pollutants increased due to the dissolution of non-aqueous phase liquid (NAPL) at the initial stage, BTEX could still be effectively degraded in subsequent time by persulfate in both aquifers, and their removal efficiency approached 100%. However, chlorinated hydrocarbon was relatively difficult to degrade, especially TCP, which had a relatively higher initial concentration, only had a removal efficiency of 30%–45% at different aquifers and monitoring wells. These finding are important for the development of injection technology for chlorinated hydrocarbon and BTEX contaminated site remediation.

The effectiveness of disinfection and flushing procedures to prevent coliform persistence in aircraft water systems.

A full-scale reproduction of an aircraft drinking water system was conditioned using municipal tap water with a mixture of free chlorine and chloramines, and subsequently contaminated with coliforms. Disinfection was undertaken using chlorine dioxide, ozone and a mixed oxidant solution followed by flushing until no disinfectant residual remained. Results showed that coliforms were not persistent on the aircraft plumbing surfaces, and coliforms were not detected after disinfection and flushing with any disinfectant. The one exception was the aerator installed in the lavatory faucet, which was coliform positive after disinfection with ozone and mixed oxidants. These data suggest that the faucet aerators could be a source of coliform contamination that may result in coliform positive samples. Further experiments conducted on disinfection of aerators with glycolic acid and quaternary ammonia (both commonly used by the airlines) showed no detectable coliforms on coliform contaminated aerators after 30 minutes of soaking in the disinfectants.

Evaluating Efficacy of Field-Generated Electrochemical Oxidants on Disinfection of Fomites Using Bacteriophage MS2 and Mouse Norovirus MNV-1 as Pathogenic Virus Surrogates

Surface disinfection, as part of environmental hygiene practices, is an efficient barrier to gastroenteritis transmission. However, surface disinfectants may be difficult to obtain in remote, resource-limited, or disaster relief settings. Electrochemical oxidants (ECO) are chlorine-based disinfectants that can be generated using battery power to electrolyze brine (NaCl) solutions. Electrolysis generates a mixed-oxidant solution that contains both chlorine (HOCl, OCl(-)) and reactive oxygen species (e.g., ·OH, O3, H2O2, and ·O2-) capable of inactivating pathogens. One onsite generator of ECO is the Smart Electrochlorinator 200 (SE-200, Cascade Designs, Inc.). In a laboratory study, we assessed ECO surface disinfection efficacy for two gastrointestinal virus surrogates: bacteriophage MS2 and murine norovirus MNV-1. We quantified both infectivity and nucleic acid inactivation using culture-dependent and independent assays. At free available chlorine concentrations of 2,500ppm and a contact time of 30s, ECO inactivation of infective MS2 bacteriophage exceeded 7 log10 compared to MNV-1 disinfection of approximately 2 log10. Genomic RNA inactivation was less than infective virus inactivation: MS2 RNA inactivation was approximately 5 log10 compared to MNV-1 RNA inactivation of approximately 1.5 log10. The results are similar to inactivation efficacy of household bleach when used at similar free available chlorine concentrations. Our work demonstrates the potential of ECO solutions, generated onsite, to be used for surface disinfection.

Effect of HF and Plasma Treated Glass Surface on Vapor Phase-Polymerized Poly(3,4-ethylenedioxythiophene) Thin Film : Part II

In this study, in order to investigate how consecutive treatments of glass surface with HF acid and water vapor/Ar plasma affect the quality of 3-aminopropyltriethoxysilane self-assembled monolayer (APS-SAM), poly(3,4-ethylenedioxythiophene) (PEDOT) thin films were vapor phase-polymerized immediately after spin coating of FeCl3 and poly-urethane diol-mixed oxidant solution on the monolayer surfaces prepared at various treatment conditions. For the film characterization, various poweful tools were used, e.g., FE-SEM, an optical microscope, four point probe, and a contact angle analyzer. The characterization revealed that a well prepared APS-SAM on a glass surface treated with water vapor/Ar plasma is very useful for uniform coating of FeCl3 and DUDO mixed oxidant solution, regardless of HF treatment. On the other hand, a bare glass surface without APS-SAM but treated with HF and water vapor/Ar plasma generally led to a very poor oxidant film. As a result, PEDOT films vapor phase-polymerized on APS-SAM surfaces are far superior to those on bare glass surfaces in the quality and electrical characteristics aspects.

Investigation of the use of Chlorine Based Advanced Oxidation in Surface Water: Oxidation of Natural Organic Matter and Formation of Disinfection Byproducts

AbstractDisinfection byproduct (DBP) formation during the treatment of raw Colorado River Water (CRW) using aqueous chlorine and ultraviolet (UV) light advanced oxidation processes (AOPs) was investigated. Here, CRW was combined with aqueous chlorine from two distinct sources (electrochemically-generated Mixed Oxidant Solution (MOS) and commercial sodium hypochlorite) and then exposed to ultraviolet C (UV-C) and ultraviolet A (UV-A) light. The impact of the treatment process on the structure of (NOM) in the CRW was examined, as well as the resulting production of various halogenated organic Disinfection By-Products (DBPs). Both AOP conditions tested resulted in destruction of chromophoric components of the NOM, while formation of total amounts of haloacetic acids and trihalomethanes was far below the US EPA regulated maximum contaminant level values for these contaminants, even though the UV and chlorine doses used in these studies were much higher than the typical doses used in an actual treatment process.

Microstructure and Dielectric Properties of PZS-PLZT Ceramics System

Piezoelectric ceramics are an important class of solid-state materials as they exhibit a wide range of applications. This article investigates the sintering temperature effect on microstructure and dielectric properties of a new ceramics material Pb (Zn, Sb) O3-PbLa (Zr, Ti) O3 (PZS-PLZT), which was prepared by a solid mixed-oxide solution method. Scanning electron micrograph (SEM) and X-ray diffraction (XRD) techniques was employed to examine the crystallization of the ceramics. The results of XRD show that the phase structure of the samples is tetragonal. The lattice parameters and the density increased with increase of the sintering temperature. The dielectric constant and the dielectric loss of the investigated samples decreased with increase in the frequency.

Heat capacity measurements and XPS studies on uranium–lanthanum mixed oxides

Heat capacity measurements were carried out on (U 1− y La y )O 2± x ( y = 0.2, 0.4, 0.6, and 0.8) using differential scanning calorimeter (DSC) in the temperature range 298–800 K. Enthalpy increment measurements were carried out on the above solid solutions using high temperature drop calorimetry in the temperature range 800–1800 K. Chemical states of U and La in the solid solutions of mixed oxides were determined using X-ray photoelectron spectroscopy (XPS). Oxygen to metal ratios of (U 1− y La y )O 2± x were estimated from the ratios of different chemical states of U present in the sample. Anomalous increase in the heat capacity is observed for (U 1− y La y )O 2± x ( y = 0.4, 0.6 and 0.8) with onset temperatures in the range of 1000–1200 K. The anomalous increase in the heat capacity is attributed to certain thermal excitation process, namely, Frenkel pair defect of oxygen. The heat capacity value of (U 1− y La y )O 2± x ( y = 0.2, 0.4, 0.6, and 0.8) at 298 K are 65.3, 64.1, 57.7, 51.9 J K −1 mol −1, respectively. From the XPS investigations, it was observed that the O/M ratios at the surface are higher than that in the bulk. In uranium rich mixed oxide samples, the surface O/M ratios are greater than 2 whereas that in La rich mixed oxides, they are less than 2, though the bulk O/M in all the samples are less than 2.

Stress-Induced Hsp70 Gene Expression and Inactivation of Cryptosporidium parvum Oocysts by Chlorine-Based Oxidants

Our research on the mechanisms of action of chlorine-based oxidants on Cryptosporidium parvum oocysts in water revealed a dual-phase effect: (i) response to oxidative stress, which was demonstrated by induced expression of the Hsp70 heat shock gene, and (ii) oocyst inactivation as a result of long-term exposure to oxidants. The relative biocidal effects of sodium hypochlorite (bleach) and electrolytically generated mixed oxidant solution (MOS) on C. parvum oocysts were compared at identical free chlorine concentrations. Oocyst inactivation was determined by quantitative reverse transcription-PCR (qRT-PCR) amplification of the heat-induced Hsp70 mRNA and compared with tissue culture infectivity. According to both assays, within the range between 25 and 250 mg/liter free chlorine and with 4 h contact time, MOS exhibits a higher efficacy in oocyst inactivation than hypochlorite. Other RNA-based viability assays, aimed at monitoring the levels of beta-tubulin mRNA and 18S rRNA, showed relatively slow decay rates of these molecules following disinfection by chlorine-based oxidants, rendering these molecular diagnostic viability markers inappropriate for disinfection efficacy assessment.

Oxidative steam reforming of methanol for hydrogen production over Cu/CeO2-ZrO2catalysts

Abstract Hydrogen production from oxidative steam reforming of methanol (OSRM) was studied over copper supported on mixed ZrO2-CeO2 oxides. Experimental X-ray diffraction (XRD) results showed the formation of mixed oxide solutions on the sample with 50 wt.-% of zirconia in the support, this finding was associated with low surface area present on this sample. Amongst all the samples studied, the Cu/CeO2-rich catalysts exhibited, at 300°C, nearly a 100% conversion, 60% in selectivity to H2 and nearly 40% to CO2, compared to samples with > 50 wt.-% of ZrO2 in the catalytic support. Temperature-programmed reduction (TPR) analysis from the copper supported on ceria-rich oxides showed reversible reduction-oxidation behaviour, in consequence, the combination of copper states Cu0/Cu2+ on the surface of the catalysts responsible for the reaction can be regenerated. In addition, these catalysts in the region of low temperatures in which they showed high catalytic activity had the lowest reduction temperature peaks....

Steam reforming of ethanol for production of hydrogen over Ni/CeO [formula omitted]–ZrO [formula omitted] catalyst: Effect of support and metal loading

Steam reforming (SR) of ethanol for hydrogen production was investigated over Ni/Ce 1 - x Zr x O 2 ( x = 0 , 0.26, 0.59, 0.84 and 1) catalyst prepared by co-precipitation and incipient wetness impregnation technique. The effect of support composition as well as metal loading on SR reaction was studied in a downflow tubular fixed bed reactor at atmospheric pressure with an ethanol/water molar ratio of 1:8, over a temperature range of 400 to 650 ∘ C. The catalysts were characterized by various techniques, such as surface area, temperature-programmed reduction (TPR), X-ray diffraction (XRD) and H 2 chemisorption. The XRD results confirmed the formation of mixed oxide solution. TPR results revealed that, compared to pure oxide support, strong interaction exists between the mixed oxide support and metal. Among the catalyst examined, Ce 0.41 Zr 0.59 O 2 and Ce 0.16 Zr 0.84 O 2 supports were the least active and Ni/Ce 0.74 Zr 0.26 O 2 catalyst with 30 wt% metal loading exhibited high catalytic activity and hydrogen selectivity (5.8 mol/mol of ethanol reacted) at a temperature of 600 ∘ C. At this temperature, the ethanol conversion was 100% and the selectivities of CO, CH 4 , CO 2 were 0.47, 0.33, 1.15 mol/mol of ethanol reacted, respectively. For nickel supported on Ce 0.74 Zr 0.26 O 2 , the activity was found to correlate with the hydrogen consumed during TPR. Another reason for the high activity of 30 wt% Ni/Ce 0.74 Zr 0.26 O 2 could be due to the high oxygen storage capacity of cubic Ce 0.74 Zr 0.26 O 2 . This helps to increase the availability of surface oxygen.

Effect of the mixed-oxidant solution on infectivity of Cryptosporidium parvum oocysts in a neonatal mouse model

Cryptosporidium parvum oocysts were exposed to the mixed-oxidant solution, which was electrochemically generated by Miox Water Disinfection Unit, and sodium hypochlorite in phosphate buffered saline (PBS, pH 7.2) or biologically treated wastewater at 25 degrees by using concentrations of residual chlorine of up to 5 mg/l and contact times of up to 8 h. The effect of two disinfectants on infectivity of the oocysts in a neonatal murine model was comparatively evaluated by determining the total number of oocysts recovered from the intestine. Exposure to the mixed-oxidant solution at 2 and 5 mg/l (residual chlorine) yielded a significant inactivation of infectivity in the dose- and exposure time-dependent manner, while exposure to 5 mg/l (residual chlorine) of sodium hypochlorite for contact times of up to 4 h produced no measurable inactivation of infectivity. Morphological examination also revealed a picture of degenerating oocysts after exposure to 5 mg/l (residual chlorine) of the mixed-oxidant solution, but not with sodium hypochlorite. When the oocysts were exposed to either biologically treated wastewater--or PBS-diluted the mixed-oxidant solution at 5 mg/l (residual chlorine) for 4 h, the disinfectants produced a significant inactivation of infectious oocysts. The decrease number of the oocysts was 0.8 log 10 in the former and 2.1 log 10 in the latter. These results demonstrate that the mixed-oxidant solution may be a useful disinfectant against Cryptosporidium oocysts, but appropriate applications need to be validated.

Treatment of waste containing EDTA by chemical oxidation

Ethylenediaminetetraacetic acid (EDTA) is a chelating agent that has been extensively used to enhance the solubilization of heavy metal cations and release of EDTA contributes to environmental problems. EDTA is recalcitrant to microbial metabolism and chemical oxidation is considered a possible method of remedial treatment. The use of the commercially available process of MIOX Corporation generates mixed oxidants on site and this solution is markedly effective in the destruction of the chelating characteristic and the decarboxylation of EDTA. When measuring the release of C-14 from carboxyl labeled EDTA, the mixed oxidant solution was comparable to the Fenton's reaction over a broad pH range. The presence of Mn 2+, Cr 3+, or Fe 3+ at levels equal to that of EDTA stimulated the rate of EDTA decomposition; however, the rate of EDTA breakdown was inhibited when the concentration of Cr 3+ or Mn 2+ exceeded the concentration of EDTA. The treatment of Co 2+–EDTA or Cu 2+–EDTA with mixed oxidants in the presence of ultra violet light resulted in the loss of chelation ability of EDTA. In the absence of chelated metals, over 75% of the chelation property of a 70 mM EDTA solution was destroyed in 45 min. The reaction products resulting from the use of mixed oxidants added to EDTA were non-toxic to bacteria and should not contribute to additional environmental problems.

Analysis of Minor Actinides in Mixed Oxide Fuel Irradiated in Fast Reactor, (I)

The MOX (mixed oxide) fuels, 29.97wt% (analytical value is 28.08 wt%) plutonium in 8.3 or 12.1 wt% enriched uranium were irradiated up to 120 GWd/t in the MARK-II core of JOYO. The irradiated MOX fuels were dissolved in 8 M nitric acid solution. Anion exchange chromatographic procedures were developed for the isolation of neptunium contained in these MOX solutions. Neptunium-237 was separated from the other actinides by using the developed chromatographic technique and the content of 237Np was determined by a spectrometry.It was found that the content of 237Np slightly increased with increasing burnup. The content did not exceed 0.08 wt% in the 30 wt% MOX fuels irradiated up to about 120 GWd/t. Model calculation by ORIGEN-2 reproduces well the observed content of 237Np.

Analysis of Minor Actinides in Mixed Oxide Fuel Irradiated in Fast Reactor, (I). Determination of Neptunium-237.

The MOX (mixed oxide) fuels, 29.97wt% (analytical value is 28.08 wt%) plutonium in 8.3 or 12.1 wt% enriched uranium were irradiated up to 120 GWd/t in the MARK-II core of JOYO. The irradiated MOX fuels were dissolved in 8 M nitric acid solution. Anion exchange chromatographic procedures were developed for the isolation of neptunium contained in these MOX solutions. Neptunium-237 was separated from the other actinides by using the developed chromatographic technique and the content of 237Np was determined by a spectrometry. It was found that the content of 237Np slightly increased with increasing burnup. The content did not exceed 0.08 wt% in the 30 wt% MOX fuels irradiated up to about 120 GWd/t. Model calculation by ORIGEN-2 reproduces well the observed content of 237Np.

Thermal and X-ray studies on mixed metal oxalates - (NH 4)Ln IIIU IV(C 2O 4) 4·8H 2O (Ln = La, Ce, Pr, Nd Tb)

Five mixed metal oxalates of lanthanides and uranium of the formula (NH 4)Ln IIIU IV(C 2O 4) 4·8H 2O were prepared and characterised by chemical, infrared spectroscopy, X-ray diffraction and thermal methods. The X-ray powder diffraction data of all the compounds were indexed on an orthorhombic unit cell. Thermal decomposition of the compounds proceeded with the loss of water molecules below 475 K followed by decomposition in the temperature range of 625 to 655 K to give Ln 2O 2CO 3 and UO 2+ x as intermediate products. The intermediate products reacted above 975 K to form solid solutions of mixed oxides having a fluorite structure. Activation energy values were derived for the dehydration of lanthanum and terbium compounds. Lattice parameters of the fluorite phases of the mixed oxides formed by heating the compounds in air, argon and N 2 H 2 have been determined.

Inactivation of Cryptosporidium parvum oocysts and Clostridium perfringens spores by a mixed-oxidant disinfectant and by free chlorine.

Cryptosporidium parvum oocysts and Clostridium perfringens spores are very resistant to chlorine and other drinking-water disinfectants. Clostridium perfringens spores have been suggested as a surrogate indicator of disinfectant activity against Cryptosporidium parvum and other hardy pathogens in water. In this study, an alternative disinfectant system consisting of an electrochemically produced mixed-oxidant solution (MIOX; LATA Inc.) was evaluated for inactivation of both Cryptosporidium parvum oocysts and Clostridium perfringens spores. The disinfection efficacy of the mixed-oxidant solution was compared to that of free chlorine on the basis of equal weight per volume concentrations of total oxidants. Batch inactivation experiments were done on purified oocysts and spores in buffered, oxidant demand-free water at pH 7 an 25 degrees C by using a disinfectant dose of 5 mg/liter and contact times of up to 24 h. The mixed-oxidant solution was considerably more effective than free chlorine in activating both microorganisms. A 5-mg/liter dose of mixed oxidants produced a > 3-log10-unit (> 99.9%) inactivation of Cryptosporidium parvum oocysts and Clostridium perfringens spores in 4 h. Free chlorine produce no measurable inactivation of Cryptosporidium parvum oocysts by 4 or 24 h, although Clostridium perfringens spores were inactivated by 1.4 log10 units after 4 h. The on-site generation of mixed oxidants may be a practical and cost-effective system of drinking water disinfection protecting against even the most resistant pathogens, including Cryptosporidium oocysts.

Comment on the Interpretation and Application of Limiting Critical Concentrations of Fissile Nuclides in Water

Calculations of the infinite multiplication factor for aqueous homogeneous mixtures of mixed oxides of plutonium and natural uranium at low fissile concentrations (7 g Pu/ℓ) disclose a maximum to occur in the value of k∞ at a weight fraction, Pu/(Pu + U), of ∼0.0035. With mixed oxide solutions containing 7 g Pu/ℓ, the value of k∞ is estimated to be nearly 1.04, whereas in the absence of the natural uranium, the maximum value of k∞ at 7 g Pu/ℓ in water is ∼4% less or near unity. The occurrence of this peak in value of k∞ is due to the 235U content in the natural uranium. Thus, in the presence of natural uranium, it should be borne in mind that the limiting subcritical concentration of plutonium (given as 7.0 g Pu/ℓ) in water must be reduced to values <7.0 g Pu/ℓ to ensure sub criticality of the mixture.

Etude a haute température des systèmes formés par les sesquioxydes de lanthane avec les sesquioxydes de lanthanides II. Influence de la trempe sur la nature des phases obtenues à la température ambiante

Splat cooling from the solar-furnace melt of mixed-oxide solutions of lanthanide oxides in La 2 O 3 changes the range of solid solution or produces phases of crystal structure not observed for the individual oxides in the pure state. Significant inertness to hydration has been obtained for type A hexagonal solutions enriched in Yb 2 O 3 by the effect of quenching.