Soft X-ray spectromicroscopy studies of pitting corrosion of reinforcing steel bar

Pitting corrosion of reinforcing steel bar (rebar) imbedded in concrete by chloride ions can cause concrete degradation. It is thus necessary to develop methods to mitigate concrete corrosion which could include using a protective polymer rebar coating. Corrosion studies of polyvinyl butyral-carbon black polymer-coated rebar using soft X-ray fluorescence (XRF) microprobe and micro-X-ray absorption near edge spectroscopy (μ-XANES) are reported in this study. After removal of the polyvinyl butyral-carbon black polymer coating, Fe Lα₁, Mn Lα₁, and O Kα₁ XRF maps were collected as well as Fe and Mn L₃-edge μ-XANES spectra from different regions across the whole rebar surface by collection of total electron yield (TEY) and partial XRF yield (PFY) spectra. The distribution of metallic Fe and Fe corrosion products was determined by analysis of the Fe XRF map. The μ-XANES spectra indicated a higher fraction of Fe (III) phases on the corroded rebar surface, while Fe (II/III) phases were the major corrosion products beneath the surface region. In addition, Mn (II) and Mn (III) were determined as the valence states of the manganese corrosion products.     

Leaching effect on phosphate rock

The uranium content in ground phosphate rock was leached out with alkaline solution, however, a poor yield was obtained. XRD, TGA and -spectrometric analyses in the solid fraction showed that francolite is the main mineral in which uranium is present in different oxidation states (+4 and +6). It was found that considerable amounts of uranium and carbonate were extracted from francolite, which suggests the presence of different uranium compounds in the bulk.     

Localization and chemical forms of cadmium in plant samples by combining analytical electron microscopy and X-ray spectromicroscopy

Cadmium (Cd) is a metal of high toxicity for plants. Resolving its distribution and speciation in plants is essential for understanding the mechanisms involved in Cd tolerance, trafficking and accumulation. The model plant Arabidopsis thaliana was exposed to cadmium under controlled conditions. Elemental distributions in the roots and in the leaves were determined using scanning electron microscopy coupled with energy dispersive X-ray microanalysis (SEM-EDX), and synchrotron-based micro X-ray fluorescence (μ-XRF), which offers a better sensitivity. The chemical form(s) of cadmium was investigated using Cd L_III-edge (3538 eV) micro X-ray absorption near edge structure (μ-XANES) spectroscopy. Plant μ-XANES spectra were fitted by linear combination of Cd reference spectra. Biological sample preparation and conditioning is a critical point because of possible artifacts. In this work we compared freeze-dried samples analyzed at ambient temperature and frozen hydrated samples analyzed at −170 °C. Our results suggest that in the roots Cd is localized in vascular bundles, and coordinated to S ligands. In the leaves, trichomes (epidermal hairs) represent the main compartment of Cd accumulation. In these specialized cells, μ-XANES results show that the majority of Cd is bound to O/N ligands likely provided by the cell wall, and a minor fraction could be bound to S-containing ligands. No significant difference in Cd speciation was observed between freeze-dried and frozen hydrated samples. This work illustrates the interest and the sensitivity of Cd L_III-edge XANES spectroscopy, which is applied here for the first time to plant samples. Combining μ-XRF and Cd L_III-edge μ-XANES spectroscopy offers promising tools to study Cd storage and trafficking mechanisms in plants and other biological samples.     

Template‐Free Synthesis and Mechanistic Study of Porous Three‐Dimensional Hierarchical Uranium‐Containing and Uranium Oxide Microspheres

A novel type of uranium‐containing microspheres with an urchin‐like hierarchical nano/microstructure has been successfully synthesized by a facile template‐free hydrothermal method with uranyl nitrate hexahydrate, urea, and glycerol as the uranium source, precipitating agent, and shape‐controlling agent, respectively. The as‐synthesized microspheres were usually a few micrometers in size and porous inside, and their shells were composed of nanoscale rod‐shaped crystals. The growth mechanism of the hydrothermal reaction was studied, revealing that temperature, ratios of reactants, solution pH, and reaction time were all critical for the growth. The mechanism study also revealed that an intermediate compound of 3 UO₃?NH₃?5 H₂O was first formed and then gradually converted into the final hydrothermal product. These uranium‐containing microspheres were excellent precursors to synthesize porous uranium oxide microspheres. With a suitable calcination temperature, very uniform microspheres of uranium oxides (UO_2+x, U₃O₈, and UO₃) were successfully synthesized.     

Direct determination of uranium in sintered deeply depleted uranium oxide pellets by wavelength dispersive X-ray fluorescence spectrometry

This paper presents studies on direct non-destructive determination of uranium in sintered deeply depleted (DD) uranium oxide (UO₂) pellets by wavelength dispersive X-ray fluorescence (WDXRF) spectrometry. A special collet was designed and fabricated for holding the sintered DDUO₂ pellets for direct analysis, thus avoiding the sample preparation steps. The samples were analyzed using a calibration plot obtained from WDXRF spectra of matrix matched calibration standards. The WDXRF determined uranium values were found to be in very close agreement with titrimetric values and has reproducibility better than 0.05% (RSD, 1 s, n = 10) for the sintered DDUO₂ pellets having U: 86.81–88.04 wt%.

     

Photoluminescence of Uranium(VI): Quenching Mechanism and Role of Uranium(V)

The photoluminescence of uranium(VI) is observed typically in the wavelength range 400–650 nm with the lifetime of several hundreds μs and is known to be quenched in the presence of various halide ions (case A) or alcohols (case B). Here, we show by density functional theory (DFT) calculations that the quenching involves an intermediate triplet excited state that exhibits uranium(V) character. The DFT results are consistent with previous experimental findings suggesting the presence of photoexcited uranium(V) radical pair during the quenching process. In the ground state of uranyl(VI) halides, the ligand contributions to the highest occupied molecular orbitals increase with the atomic number (Z) of halide ion allowing larger ligand‐to‐metal charge transfer (LMCT) between uranium and the halide ion. Consequently, a larger quenching effect is expected as Z increases. The quenching mechanism is essentially the same in cases A and B, and is driven by an electron transfer from the quencher to the UO₂²⁺ entity. The relative energetic stabilities of the triplet excited state define the “fate” of uranium, so that in case A uranium(V) is oxidized back to uranium(VI), while in case B uranium remains as pentavalent.     

聚电解质膜PDAC/PSS诱导CaCO3结晶的研究

以模拟软体动物珍珠层的周期性基质控制形成过程制备仿生层状复合材料. 将聚苯乙烯磺酸钠(PSS)与聚二烯二甲基氯化铵(PDAC)用逐层浸渍的方法使其组装成多层膜, 用于诱导过饱和溶液中CaCO₃的结晶, 详细研究了膜紫外吸收随组装层数增加的线性变化. 扫描电镜和X射线衍射表征了晶体的形貌和结构. (PDAC/PSS)₁₅PDAC膜诱导获得的CaCO₃晶体为六面体结构, 晶体尺寸为30～40 μm; (PDAC/PSS)₁₅膜诱导CaCO₃结晶, 可以在膜表面获得形貌与珍珠层非常相似的CaCO₃晶体, 结晶10 h获得的晶片结构呈规则的六边形, 片尺寸约为10～20 μm. X射线衍射结果表明两种晶体的晶格结构与天然珍珠层差异明显, 说明静电作用为晶体形貌的主控因素之一, 但不是晶格结构的决定因素. 复合材料断面电镜照片表明其为层状结构.     

Analytical techniques for the separation and determination of transuranium element ultratraces in depleted uranium ammunitions

It is well known that ammunition containing depleted uranium (DU) was used by NATO during the Balkan conflict. To evaluate the DU origin (natural uranium enrichment or spent nuclear fuel reprocessing) it is necessary to check the presence of activation products (²³⁶U, ^239+240Pu, ²⁴¹Am, ²³⁷Np, etc.) in the ammunition.

Every transuranium element (TRU) was separated from the uranium matrix by extraction chromatography with microporous polyethylene (Icorene) supporting suitable stationary phases. Plutonium was separated by tri-n-octylamine (TNOA). ²⁴¹Am was separated by TNOA and di(2ethylhexylphosphoric) acid (HDEHP). Neptunium also was separated by tri-n-octylamine using different conditions. After elution, the TRU elements were electroplated and counted by alpha spectrometry. The TRU decontamination factors from uranium were higher than 10⁶.

The final chemical yields ranged from 50 to 70%. The detection limit was 1?Bq?kg^?1 for 0.10?g ammunition; ^{239 + 240}Pu and ²⁴¹Am concentrations in two penetrators were 26 and 70?Bq?kg^?1 and <1 and 3.4?Bq?kg^?1, respectively; the ²³⁷Np concentration in one penetrator was 30.1?Bq?kg^?1.

The presence of these anthropogenic radionuclides in the penetrators indicates that at least part of the uranium originated from the reprocessing of nuclear fuel, although because of their very low concentrations, the radiotoxicological effect is negligible.     

Preparation of poly(p‐oxybenzoyl) crystals using direct polymerization of p‐hydroxybenzoic acid in the presence of boronic anhydrides

Poly(p‐oxybenzoyl) (POB) crystals were prepared by reaction‐induced crystallization during direct polymerization of p‐hydroxybenzoic acid in the presence of boronic anhydrides. Polymerizations were carried out at 300 °C in dibenzyltoluene at a concentration of 1% with three kinds of anhydrides of boronic acid such as 3,4,5‐trifluorophenylboronic acid (TFB), 4‐methoxyphenylboronic acid (MPB) and 4‐biphenylboronic acid (BPB). The POB crystals were formed as precipitates in the solution and the morphology was considerably influenced by both the structure of the boronic anhydride and its concentration (c_B). Needle‐like crystals were firmed in the presence of TFB anhydride (TFBA) at c_Bs of 5 and 10 mol % by the spiral growth of lamellae. Spherical aggregates of slab‐like crystals were formed at c_Bs from 50 to 100 mol %. The polymerization with MPB anhydride and BPB anhydride (BPBA) also yielded the needle‐like crystals at c_Bs of 50 and 5 mol %, respectively. The polymerization with TFBA at lower c_B was favorable to prepare the needle‐like crystal. Molecular weight was also influenced by the structure of the boronic anhydride and c_B. M_n increased generally with c_B and BPBA gave the highest M_n of 14.7 × 10³ at c_B of 100 mol %. The loose packing of the molecules in the crystal caused by the bulkiness of the end‐groups made the polymerization in the crystals more efficiently. Morphology and molecular weight of the POB crystals could be controlled by the chemical structure and the content of boronic anhydride. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Binding of uranyl ion by 2,2′-dihydroxyazobenzene attached to crosslinked polystyrenes covered with highly populated quaternary ammonium cations

2,2′-Dihydroxyazobenzene (DHAB) derivatives were attached to poly(chloromethylstyrene-co-divinylbenzene) (PCD) because of the high affinity of DHAB for uranyl ion. Chloromethyl groups of PCD were converted to quaternary ammonium ions by treating them with tertiary amines. Two strategies were adopted to improve the uranyl-binding ability of the immobilized DHAB: (1) the creation of a highly cationic microenvironment around the DHAB moieties and (2) the introduction of electron-withdrawing groups to DHAB. Capacity of the resins for uranyl uptake was measured, revealing that about 10 to 46 mg of uranium could be complexed to 1 g of the resins. Formation constants (K_f) for the uranyl complexes of the resins were determined. In the presence of ≥0.02 M bicarbonate ion at pH 8.02, log K_f values of 14.3 to 15.8 were obtained. Uranium extraction from seawater with two kinds of resins prepared in this study was carried out on the east coast of the Korean peninsula. The amount of uranium extracted from seawater was up to 150 μg/g resin. Thus, the uranium-extracting capability of the DHAB-containing polystyrene resins was improved significantly by the structural modifications. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4117–4125, 1999     

Uranium sorption from aqueous solutions on sodium-form of HEU-type zeolite crystals

The uranium sorption from aqueous solutions (concentration range 50–20.000 mg/l) by the sodium-form (Na-form) of HEU-type zeolite crystals (particle-size <20 m) has been investigated by means of a batch-type method. The INAA, RI-XRF, powder-XRF, SEM-EDS and FT-IR techniques were used for the study of the experimental products. The absolute uranium uptake by the material reached the value of 11.68 mg/g in the case of initial concentraton 20,000 mg/l. On the other hand theK _d -values indicated that the relative uranium uptake, and consequently the percentage of removal, is higher for concentrations below 100 mg/l. The uranium uptake by the zeolite is attributed to different sorption processes such as ion-exchange, adsorption and surface precipitation, taking place both to the interior and the surface of the crystals and strongly depending on the pH of the solutions. The investigated zeolitic material was sufficiently resistant at the low initial pH of the solutions with dealumination phaenomena only observed in the case of the most acidic solution used.     

Facile Syntheses of pure Uranium(III) Halides: UF3, UCl3, UBr3, and UI3

Herein we describe a convenient lab scale synthesis for pure and solvent‐free binary uranium(III) halides UCl₃, UBr₃, and UI₃. This is achieved by the reduction of the respective uranium(IV) halides with elemental silicon in borosilicate ampoules at moderate temperature. The silicon tetrahalides SiX₄ formed as a side product are utilized for the removal of excess starting material via a chemical vapor transport reaction. The syntheses introduced herein avoid the need for pure metallic uranium and are based on uranium(IV) halides synthesized from UO₂ and the respective aluminum halides and purified by chemical vapor transport. These uranium(III) halides are obtained in single crystalline form. A similar reaction yields UF₃ as a microcrystalline powder. However, no beneficial transport reaction occurs with this halide. Also, a higher temperature has to be applied and steel ampoules have to be used. The identities and purity of the products were checked by powder X‐ray diffraction as well as IR spectroscopy. The synthesis of UI₃ enabled its crystal structure determination on single crystals for the first time. UI₃ crystallizes in the PuBr₃ structure type with space group type Cmcm and a = 4.3208(9), b = 13.923(3), c = 9.923(2) Å, V = 596.9(2) ų, and Z = 4 at T = 100 K.     

Comparative extraction efficiencies of tri-<Emphasis Type="Italic">n</Emphasis>-butyl phosphate and <Emphasis Type="Italic">N,N</Emphasis>-dihexyloctanamide for uranium recovery using supercritical CO<Subscript>2</Subscript>

Extraction of uranium from tissue paper, synthetic soil, and from its oxides (UO₂, UO₃ and U₃O₈) was carried out using supercritical carbon dioxide modified with methanol solutions of extractants such as tri-n-butyl phosphate (TBP) or N,N-dihexyl octanamide (DHOA). The effects of temperature, pressure, extractant/nitric acid (nitrate) concentration, and of hydrogen peroxide on uranium extraction were investigated. The dissolution and extraction of uranium in supercritical CO₂ modified with TBP, from oxide samples followed the order: UO₃ ≫ UO₂ > U₃O₈. Addition of hydrogen peroxide in the modifier solution enhanced the dissolution/extraction of uranium in dynamic mode. DHOA appeared better than TBP for recovery of uranium from different oxide samples. Similar enhancement in uranium extraction was observed in static mode experiments in the presence of hydrogen peroxide. Uranium estimation in the extracted fraction was carried out by spectrophotometry employing 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP) as the chromophore.     

Optimization of molar content of amidoxime and acrylic acid in UHMWPE fibers for improvement of seawater uranium adsorption capacity

Ultra-high molecular weight polyethylene (UHMWPE) fibrous adsorbents with different molar content of amidoxime (M _AO) and acrylic acid (M _AA) were prepared by graft polymerization of acrylonitrile (AN) and acrylic acid (AA), followed by amidoximation. Uranium adsorption experiments in both artificial and natural seawater were carried out to investigate the effect of M _AO and M _AA on the uranium adsorption capacity of UHMWPE fibrous adsorbents. Adsorption results showed that the UHMWPE fibrous adsorbent with M _AO = 4.27 and M _AA = 4.64 mmol/g-ads exhibited better uranium adsorption capacity in both artificial (7.01 mg-U/g-ads) and natural (0.77 mg-U/g-ads) seawater.

     

Solvent extraction, speciation, separation and recovery of uranium(VI) from nuclear fuel, phosphate rocks and monazite sand with N-phenylbenzo-18-crown-6-hydroxamic acid

Summary A method for solvent extraction, separation and recovery of uranium was developed using a new reagent, N-phenylbenzo-18-crown-6-hydroxamic (PBCHA) in the presence of cerium, thorium and lanthanides. Uranium was extracted with a dichloromethane solution of PBCHA producing an orange coloured complex at l_max = 400 nm with a molar absorptivity of 5.0 ^. 10⁴ l ^. mol^{-1 .} cm^-1 and which obeyed Beer's Law in the range of 0.48-5.76 ppm. For ICP-AES the extract was directly introduced into the plasma to enhance the sensitivity several folds with a detection limit of 0.5 ppb. The extraction constants of uranium crown hydroxamic acid complexes were also determined. The selectivity factors K_uranyl(b₂K/K or b₂K'_e/K) for uranium crown hydroxamate were evaluated by comparing the K_uranyl with the stability constants of competing metal cations (K) and anions (K) and were found remarkably large. Uranium was recovered in 99.95% purity from monazite sand and phosphate rocks. It could be also preconcentrated and determined in environmental samples.     

A Polarographic Study of ϵ-Caprolactam Complexes of Uranium and Tellurium

The polarographic behaviour of uranium and tellurium has been studied in the presence of increasing concentration of complex forming agent viz. ?-caprolactam at pH 4.4 for U(VI) and at pH 10.0 for Te(IV) at μ=0.1 M KNO₃. In both cases the waves have been found to be diffusion controlled and irreversible. The values of kinetic parameters (σπ_a and K°_f,h) have been calculated as a function of the ligand concentration. Method is suitable for the quantitative determination of these metals individually and simultaneously with the effect of diverse ions.     

Die Isolierung und Charakterisierung von Komplexen des Uran (IV) mit Di-(2-äthylhexyl)-orthophosphorsäure aus Perchlor-, Schwefel- und Salpetersäurelösungen

Zusammenfassung Die Herstellung und Charakterisierung von Komplexen des Uran (IV) durch Extraktion des U(IV) aus schwefel-, perchlor-, phosphor- und salpetersauren Lösungen mit unverdünnter Di-(2-äthylhexyl)-orthophosphorsäure (HDEHP) wird beschrieben. Die Zusammensetzung der in Kontakt mit Schwefelund Perchlorsäure erhaltenen Komplexe entspricht der Formel [U(DEHP)₄] _n , die in Kontakt mit Salpetersäure erhaltenen Komplexe besitzen die Formel [U(NO₃)(DEHP)₃] _n . Durch Aufnahme von Absorptionsspektren im infraroten Bereich (4000 bis 625 cm^–1) konnten Anhaltspunkte über die Struktur der Komplexe-insbesondere über die Anwesenheit des Nitrats-erhalten werden. Die charakteristischen Banden werden diskutiert und mögliche Bindungsarten des Nitrats und Urans besprochen.

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The isolation and characterization of complexes of uranium (IV) with di-(2-ethylhexyl)-orthophosphoric acid from perchloric, sulphuric and nitric acid solutions

The preparation and characterization of complexes of uranium(IV) by extraction of U(IV) from sulfuric, perchloric, phosphoric and nitric acid solutions with undiluted di-(2-ethylhexyl)-orthophosphoric acid (HDEHP) is described. The composition of the complexes in contact with sulfuric and perchloric acid follows the formula [U(DEHP)₄] _n ; complexes in contact with nitric acid correspond to [U(NO₃)(DEHP)₃] _n . Absorption spectroscopy in the infrared region (4000–625 cm^–1) yielded structural information about these complexes, especially about the presence of nitrate. The characteristic absorption bands are discussed as well as possible types of bonding of the nitrate ion and of uranium.

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Herrn Univ.-Prof. Dr.H. Nowotny gewidmet.     

Die kinetische polarographische Stufe des Urans in Gegenwart von Chlorat-Ionen

An increase of the 2nd polarographic uranium(VI) wave has been observed in the presence of chlorate ions in HClO₄–NaClO₄, or HClO₄–NaClO₄–NaCl supporting electrolyte, resp. The polarographic measurements at different temperatures and at various perchloric acid concentrations show that this increase is due to a kinetic U(III)-U(IV) current. The activation parameters of the U(III)-U(IV) oxidation reaction with ClO₃ ^– have been calculated usingKautecky's method.The approximately 5fold increase of the 2nd polarographic wave allows the determination of small amounts of uranium (10^–5–10^–6 mole/l).

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Novel network morphology of poly(p‐oxybenzoyl)

Polymerization of 4‐acetoxybenzoic acid (ABA) with 3,5‐diacetoxybenzoic acid (DABA) was examined to control the morphology of poly(p‐oxybenzoyl) (POB). Polymerizations were carried out at a concentration of 1.0% in an aromatic solvent Therm S‐1000® (mixture of dibenzyltoluene) at 320 °C. Polymerization of ABA yielded the POB fibrillar crystals, but the polymerization with DABA at a concentration in the feed (χ_f) of 0.10–0.15 afforded novel network structures comprised of spheres connected by fibrillar crystals. The diameter of the spheres prepared at χ_f of 0.15, which were 0.7 and 5.0 μm, showed bimodality. The network distance, fibril length, and fibril width were 6.1, 2.6, and 0.1 μm, respectively. They possessed high crystallinity. The network structure was formed as follows. Co‐oligomers were first precipitated in the beginning of the polymerization by liquid–liquid phase separation to form the microdroplets. The fibrillar crystals were formed in the coalesced spheres by the crystallization of oligomers induced by the increase of molecular weight. The fibrillar crystals connecting the spheres gradually appeared owing to the shrinkage of the spheres. The fibrillar crystals grew from the surface of the spheres with the crystallization of homo‐oligomers of 4‐oxybenzoyl units, and finally the network structure was completed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1624–1634, 2005     

Extraction of uranium by amine, amide and benzamide grafted covalently on silica gel

Organic complexing moieties such as amine, 2°-amide and benzamide functional groups were covalently linked to silica gel by performing organomodification on commercially available silica gel. The extraction of uranium as a function of pH, time, concentration of uranium and the effect of ions such as Fe²⁺, Co²⁺, Ni²⁺ and CO₃ ^2- on the distribution coefficient of uranium by sorbent was studied. The data was fitted into Langmuir adsorption isotherm. The selectivity of the sorbents towards uranium were found to decrease in the order gel-amine >> gel-benzamide ≅ gel-2°-amide at all pHs. The presence of metal ions such as Fe²⁺, Co²⁺, Ni²⁺ and CO₃ ^2- were found to decrease the distribution coefficients (K _d, ml/g) of uranium and the decrease was very high when Fe²⁺ was present. The performance of the sorbent, gel-amine, under a given column condition was tested by following the breakthrough curve of uranium up to C/C ₀ = 0.025. The sorbent was found to be good for the quantitative pre-concentration of uranium from a large amount of sodium. This revised version was published online in July 2006 with corrections to the Cover Date.