Sol-Gel Microsphere Pelletisation Process for Fabrication of (U,Pu)O2, (U,Pu)C and (U,Pu)N Fuel Pellets for the Prototype Fast Breeder Reactor in India

A “dust-free” sol-gel microsphere pelletisation (SGMP) process has been developed for fabrication of (U,Pu)O₂, (U,Pu)C and (U,Pu)N fuel pellets containing around 15% plutonium for the forthcoming prototype fast breeder reactor (PFBR) in India. The objective was to produce homogeneous sintered pellets of ∼85% T.D. with a predominantly open-pore structure. Hydrated gel-microspheres of UO₃+PuO₂ and UO₃+PuO₂+C have been prepared from nitrate solutions of uranium and plutonium by the “ammonia internal gelation” process, using hexamethylene tetramine (HMTA) as an ammonia generator and silicone oil at 90±1°C as gelation bath. For oxide fuel pellets, the hydrated UO₃+PuO₂ gel-microspheres were calcined at around 700°C in Ar+8% H₂ atmosphere to produce “non-porous”, “free-flowing” and coarse (around 400 micron) microspheres which could be directly pelletised at 550 MPa to green pellets. The mixed oxide pellets were subjected either to low temperature (∼1100°C) oxidative sintering (LTS) in N₂+air containing ∼1500 ppm O₂ or to high temperature (1650°C) sintering, (HTS) in Ar+8% H₂. For monocarbide and mononitride pellets, hydrated gel-microspheres of UO₃+PuO₂+C were subjected to carbothermic synthesis in vacuum (∼1 Pa) and flowing nitrogen (flow rate: 1.2 m³/h) in the temperature range of 1450–1550°C respectively. The monocarbide and mononitride microspheres thus produced were relatively hard and required higher compaction pressure (∼1200 MPa) for making reen pellets which could be sintered to 85% T.D. in Ar+8% H₂ at 1700°C. The sintered oxide, monocarbide and mononitride pellets had a “blackberry” “open” pore microstructure with fine grain size. The microspheres retained their individual identity in the sintered pellets because during sintering densification took place mainly within and not between the microspheres.     

H/D exchange kinetics: Experimental evidence for formation of different b fragment ion conformers/isomers during the gas-phase peptide sequencing

Electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) combined with H/D exchange reactions was utilized to explore the existence of different b₅⁺ and b₄⁺ fragment ion conformers/isomers of hexapeptide WHWLQL in the gas phase. Distinct H/D exchange trends for protonated WHWLQL ([M + H]⁺) and its b₅⁺ and b₄⁺ fragment ions (with ND₃) were observed. Isolated ¹²C_all isotopomers of both b₅⁺ and b₄⁺ fragment ions yielded bimodal distributions of H/D exchanged product ions. The H/D exchange reaction kinetics also confirmed that b₅⁺ and b₄⁺ fragment ions exist as combination of slow-exchanging (“s”) and fast-exchanging (“f”) species. The calculated rate constant for the first labile hydrogen exchange of [M + H]⁺ (k_{[M + H]} ⁺ = 3.80 ± 0.7 × 10⁻¹⁰ cm³ mol⁻¹ s⁻¹) was ∼30 and ∼5 times greater than those for the “s” and “f” species of b₅⁺, respectively. Data from H/D exchange of isolated “s” species at longer ND₃ reaction times confirmed the existence of different conformers or isomers for b₅⁺ fragment ions. The sustained off-resonance irradiation collision-activated dissociation (SORI-CAD) of WHWLQL combined with the H/D exchange reactions indicate that “s” and “f” species of b₅⁺ and b₄⁺ fragment ions can be produced in the ICR cell as well as the ESI source. The significance of these observations for detailed understanding of protein sequencing and ion fragmentation pathways is discussed.     

Fabrication of SiO2 hollow microsphere with urchin-like structure based on template from directed assembly of block copolymer

We report here a novel strategy for fabrication of SiO₂ hollow microspheres with urchin-like structure based on templates from directed assembly of block copolymer, poly(2-cinnamoyloxyethyl acrylate)-block-poly(acrylic acid-co-styrene) (PCEA-b-P(AA-co-Sty)). The structures of template from directed assembly of copolymers as well as that of as-obtained hollow SiO₂ microspheres were observed by a combination technique of optical microscope, scanning electron microscope, and transmission electron microscopy. It is shown that the hollow microspheres consist of aligned SiO₂ “spines” radially growing from the core which are induced a favorable growth by the structures of the template from directed assembly of PCEA-b-P(AA-co-Sty). The “spine” density of the hollow SiO₂ sphere can be tuned by controlling the structure of the copolymer with different hydrolysis degree of poly(tert-butyl-acrylate) to PAA, and the ultimate size of the resultant SiO₂ hollow sphere can be adjusted by solvent and temperature in the sol–gel process, etc.     

Phase Evolution of Cu?S System in Ethylene Glycol Solution: the Effect of Anion and PVP on the Transformation of Thiourea

The transformation mechanisms of thiourea in ethylene glycol solution was systematically investigated in this report, which shows the transformation process is influenced by the anion (NO^3?, Cl^?, Br^?) and polyvinylpyrrolidone (PVP). Thiourea (tu) isomerizes into ammonium thiocyanate when NO^3? is present, regardless of the existence of PVP. For Cl^?, thiourea coordinates with copper anion to form [Cu(tu)]Cl·1/2H₂O complex whether PVP is present. When it comes to Br^?, thiourea hydrolyzes in the cooperation of PVP or coordinates with copper anion to form [Cu(tu)Br]·1/2H₂O complex without PVP. The different transformation routes will lead to different phase evolution of the Cu? S system. This work may provide a new understanding of the transformation of thiourea in ethylene glycol solution. The optical properties of the as‐prepared copper sulfides exhibit signi?cant stoichiometry‐dependent features which may have potential applications in semiconductor photovoltaic devices.     

SIMS depth profiling of vertical p-channel Si-MOS transistor structures

SIMS depth profiling during O₂ ⁺ bombardment has been performed to analyse epitaxially grown Si p-n-p layers, which define the p-channel region in vertical Si-p MOS transistors, as well as to establish “on-chip” depth profiling of the functional vertical device. The SIMS detection limit of ³¹P in Si, phosphorus used as n-type dopant in the transistor, has been optimised as a function of the residual gas pressure in the SIMS analysis chamber and of the sputter erosion rate. We demonstrate that good vacuum during SIMS analysis combined with high erosion rates allows the simultaneous quantitative SIMS depth profiling of n- and p-type dopant concentrations in the vertical transistor. Small area “on-chip” SIMS depth profiling through the layered structure of Al-contact/TiSi₂/Si(p-n-p)/Si-substrate has been performed. Factors influencing the depth resolution during “on-chip” analysis of the transistor are discussed especially in terms of sputtering induced ripple formation at the erosion crater bottom, which has been imaged with atomic force microscopy. Received: 15 August 1996 / Revised: 17 January 1997 / Accepted: 21 January 1997     

Experimental estimation of possibilities of suspension technology of polypropylene production with application of different generations of ziegler-natta catalysts

On the basis of R&D results on laboratory and pilot levels the possibility of production and expansion of “Tomskneftekhim” Ltd. brand assortment of polyolefin plastics with the use of contemporary titaniummagnesium catalysts (TMC) is analyzed. The production results of “Tomskneftekhim” Ltd. polypropylene output, reached due to the use of catalyst systems of I (aluminothermal TiCl₃) and II (MSK-TiCl₃) generations, and forecasting results for system of IV generation (TMC) are presented in the report. The experimental testing of propylene polymerization kinetic features, raw material quality, and influence of catalyst system composition and conditions of formation on exploitation characteristics of TMC was carried out by the example of two trade marks of TMC. The conclusion was drawn that the realization by “Tomskneftekhim” Ltd. of a complex program of R&D activities for implementation of the IV generation catalyst system in the suspension technology of the polypropylene production will increase the competitiveness of the process.     

Gas dynamics in an arc discharge chamber as a factor governing the isolation of C60 and other “magic” fullerenes

A joint analysis of fullerene assembly kinetics and gas flow dynamics in an arc chamber for the production of fullerenes showed that the effective annealing of fullerenes and the evident dominance of “magic” fullerenes C₆₀ and C₇₀ were mainly explained by the difference between the thermal dissociation rates of these and less stable C₆₂ and C₆₈ fullerenes. The percent of “nonmagic” fullerenes was also shown to depend on the structure of the gas flows formed in the arc discharge chamber. The majority of newly formed fullerenes were not immediately removed from the chamber, bur were trapped by closed gas flows. Back in the hot region of the chamber, fullerenes were simultaneously annealed and dissociated under the action of high temperature and, partially, UV radiation. The “nonmagic” fullerenes were most actively suppressed in a non-pumpable discharge chamber.     

Revisiting the problem of correcting retention parameters for pressure and temperature in gas chromatography

Summary It has been shown [1, 2] that the compressibility correction factor equals the ratio of gas pressure at the column outlet to the average pressure in the column,j=p _o /p _c , and, therefore, by multiplying by this factor, all experimentally measured retention volumes and flow rates are converted from ambient pressure to the average pressure in the column. This makes retention volumes corrected in this way independent of pressure. In contrast, correcting retention times for gas compressibility has no physical meaning and terms such as “corrected retention time” and “net retention time” should not be used. Similarly, recalculating corrected retention volumes to a standard temperature of 273 K appears to provide a thermodynamically sound basis for comparison of data obtained at different temperatures. In reality, it distorts actual relationships and should not be used. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997.     

An electrochemical investigation on (MoO<Subscript>3</Subscript>+PVP+PVA) nanobelts for lithium batteries

Molybdenum trioxide (MoO₃) xerogel films modified with poly(vinyl alcohol)+poly(vinyl pyrrolidone) (PVP+PVA) polyblends were obtained by ion-exchange method with sol-gel technique. Investigations were conducted using X-ray “diffractometry”, Fourier transform infrared spectroscopy, and cyclic voltammetry. The results show that the H atoms in polyblend are H-bonded with the O atoms in the Mo=O bonds of MoO₃ xerogel, which effectively shield the electrostatic interaction between MoO₃ interlayer and Li⁺ ions when MoO₃ xerogel is modified by the intercalation of (PVP+PVA). The reversibility of the insertion/extraction of Li⁺ ions is greatly improved by the modification with polyblend of MoO₃ nanocomposite films. MoO₃ and (PVP+PVA) _x MoO₃ (x = 0, 0.5) nanobelts were obtained by a simple hydrothermal process from MoO₃ sol. The electrochemical cells with configuration Li/(LiPF₆+EC+DMC)/MoO₃ modified by (PVP+PVA) were fabricated and their discharge profiles studied.     

Reversible chemisorption of carbon dioxide: simultaneous production of fuel-cell grade H2 and compressed CO2 from synthesis gas

One vision of clean energy for the future is to produce hydrogen from coal in an ultra-clean plant. The conventional route consists of reacting the coal gasification product (after removal of trace impurities) with steam in a water gas shift (WGS) reactor to convert CO to CO₂ and H₂, followed by purification of the effluent gas in a pressure swing adsorption (PSA) unit to produce a high purity hydrogen product. PSA processes can also be designed to produce a CO₂ by-product at ambient pressure. This work proposes a novel concept called “Thermal Swing Sorption Enhanced Reaction (TSSER)” which simultaneously carries out the WGS reaction and the removal of CO₂ from the reaction zone by using a CO₂ chemisorbent in a single unit operation. The concept directly produces a fuel-cell grade H₂ and compressed CO₂ as a by-product gas. Removal of CO₂ from the reaction zone circumvents the equilibrium limitations of the reversible WGS reaction and enhances its forward rate of reaction. Recently measured sorption-desorption characteristics of two novel, reversible CO₂ chemisorbents (K₂CO₃ promoted hydrotalcite and Na₂O promoted alumina) are reviewed and the simulated performance of the proposed TSSER concept using the promoted hydrotalcite as the chemisorbent is reported.     

Adsorption and electrophysical properties of semiconductors of the InSb-CdS system

Adsorption and the electrophysical properties (changes in electrical conductivity) of thin film solid solutions and binary components of the new InSb-CdS system are studied by means of piezoquartz microweighing, IR spectroscopy and probe compensation in the temperature range of 273–353 K and a range of adsorbate gas (NH₃, NO₂) pressures of 0.2–9.8 Pa. The areas of physical and chemical adsorption accompanied by the charging of the (mostly positive) surface are determined. The mechanisms and regularities of adsorption as a function of external conditions and composition of the system are established, and certain similarities and patterns of changes in the adsorption and electroconductivity, and parallelisms of the “acidbase characteristic-composition,” “adsorption characteristic-composition,” and “electrophysical characteristics-composition” dependences are described. These prove to be useful in studying the adsorption mechanism and in identifying the most active components of the system relative to NH₃ and NO₂, proposed as materials for respective sensors/detectors.     

The SML pump of carbon cycles in oceans

1 Introduction Recently the concepts and models of “pump” are used frequently in studying global cycles and varieties of elements in marine chemistry and marine biogeo-chemistry. For example, there are many “pump” con-cepts including the concepts of s…     

Surface functionalization via in situ interaction of plasma-generated free radicals with stable precursor-molecules on cellulose

The surface functionalization process was accomplished in a consecutive 3 step process including: (1) Argon- and oxygen-plasma enhanced generation of free radical sites on cellophane surfaces; (2) “In situ” gas phase derivatization in the absence of plasma using hydrazine, ethylene diamine, or propylene diamine; (3) Second “in situ”, gas phase derivatization in the absence of plasma using oxallyl chloride or “ex situ” derivatization in the presence of glutaraldehyde. The presence of free radical sites on the plasma exposed cellophane surfaces was demonstrated using “in situ” sulfur dioxide and nitric oxide labeling techniques. It was shown that the free radical sites readily react under “in situ” conditions with the stable chain-precursor components and generate the desired spacer-chain molecules. ESCA, ATR-FTIR analysis and dying techniques were used to monitor the cellophane surface changes. A factorial design was used for selecting the optimal plasma parameters. Functionalized cellophane substrates were used for immobilization of α-chymotrypsin in the presence of spacer-chain molecules. The activity of the immobilized α-chymotrypsin was found to be lower in comparison to the activity of the free enzyme and the presence of virgin cellophane in the free enzyme solution also reduced significantly the activity of the enzyme. It is suggested that the swollen state of the cellophane plays a significant role in the decrease of the immobilized enzyme activity.     

Mechanism of the formation of 2-aminothiazole in the reaction of chloroacetaldehyde with thiourea

The kinetics of the reaction of chloroacetaldehyde with thiourea in water at the C=O and C-Cl bonds were studied. The first step of the formation of the 2-aminothiazole is the reaction of the NH₂ group of thiourea with the C=O group of chloroacetaldehyde. Hydrogen chloride evolution and the formation of a thiazole ring are secondary processes that occur simultaneously.Communication X of the series Studies of Chlorinated Aldehydes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 927–929, July, 1971.     

Clustering of pentacene and functionalized pentacene ions in a matrix-assisted laser desorption/ionization orthogonal TOF mass spectrometer

A high-performance orthogonal time-of flight (TOF) mass spectrometer, in combination with the matrix assisted laser desorption/ionization (MALDI) source operating at elevated pressure (∼1 torr in N₂), was used to perform MALDI-TOF analyses of pentacene and some of its derivatives with and without an added matrix. These molecules are among the most interesting semiconductor materials for organic thin film transistor applications (OTFT). The observation of ion-molecule reactions between “cold” analyte ions and neutral analyte molecules in the gas phase has provided some insight into the mechanism of pentacene cluster formation and its functionalized derivatives. Furthermore, some of the matrices employed to assist the desorption/ionization process of these compounds were observed to influence the outcome via ion-molecule reactions of analyte ions and matrix molecules in the gas phase. The stability and reactivity of the compounds and their clusters in the MALDI plume during gas-phase expansion were evaluated; possible structures of the resulting clusters are discussed. The MALDI-TOF technique was also helpful in distinguishing between two isomeric forms of bis-[(triisopropylsilyl)-ethynyl]-pentacene.     

A flow analysis system with an amperometric detector for the determination of hydrogen sulphide in waters

 A flow analysis system with an amperometric H₂S detector and a gas extraction unit as well as an integrated coulometric calibration unit is described, which allows an on-line determination of hydrogen sulphide in aquatic samples. By variation of different parameters (e.g. flow rate, gas injection volume, pH of solution) a wide dynamic working range of concentrations from 1 μmol/l H₂S to 750 μmol/l is accessible. The sampling rate is about 36 samples h⁻¹ using an average flow rate of 1.78 ml/min and a gas injection volume of 28 μl. The measuring system is designed as a portable device. In combination with the polyethylene-tube of a PTFE-underwater pump field-measurements on board are possible. Received: 16 February 1995/Revised: 5 April 1995/Accepted: 11 April 1995 Acknowledgements. This work was supported by the Bundesminister für Forschung und Technologie under the project “DYSMON II” (03F0123D) and by the Fonds der Chemischen Industrie zur F?rderung von Chemie und Biologischer Chemie. Correspondence to: P. Jeroschewski     

Calcium phosphate colloids with hierarchical structure controlled by polyaspartates

 Precipitation of calcium phosphate in a double-jet experiment in the presence of sodium polyaspartic acid results in a structural evolution of stable colloidal objects with a variety of unconventional morphologies. This structural evolution is characterized by a combination of techniques, namely static and dynamic light scattering, small-angle and wide-angle X-ray scattering, and transmission electron microscopy. It is shown that after immediate formation of amorphous precursor nanoparticles with a “parachute architecture”, the system transfers into a hollow sphere morphology in the 500-nm region and is composed of plateletlike nanocrystals, and again is transferred into a final, “snowball-like” morphology of high structural definition and monodispersity. The kinetics depends on the amount and the molecular weight of the polymer, but similar structural elements are found in all the cases examined. When repeated in a triple-jet experiment, which also ensures a constant polymer concentration, it was possible to intercept a postulated intermediate structure in practically complete yield, namely crystalline hydroxyapatite nanofibres with extremely high axial ratios which form an interwoven gel. Received: 11 May 2001 Accepted: 14 September 2001     

Characterization of a covalent triazine-humic acid conjugate by gas chromatography

The aim of the described method was the characterization of a “atrazine-mercaptopropionic acid” humic acid conjugate, which was required for the calibration of immunoassays to determine bound residues. In order to estimate the amount of bound triazine, an oxidative nucleophilic substitution reaction of the covalently linked “atrazine-mercaptopropionic acid” to a new triazine derivative “atrazine-methoxyethanol” was performed. This cleavage product was quantified by gas chromatography. The conditions for this cleavage procedure were optimized and applied to the “atrazine-mercaptopropionic acid” humic acid conjugate and to a humic acid blank. The amount of bound “atrazine-mercaptopropionic acid” was calculated to 16.6 ± 2.5 μmol triazine per gram humic acid, which is equivalent to 0.39 ± 0.07% atrazine. Received: 7 August 1997 / Accepted: 12 September 1997     

Probe—detektor-anordnungen zur Kernstrahlungsmessung für Analytische Zwecke

The “analytical power” of detection systems is investigated, considering typical arrangements in analytical terms. From N atoms of interest in a sample Z counts are drawn: Z=R N (R registration yield). Crude data ZM contain also background U generated by interferences: ZM=Z+U. Identification and separation of Z is accompanied by errors ~σ_MU^1/2 due to imperfect distinguishability and to statistical error (σ_M model inherent factor). With “selectivity”=σ_M ^- (R/R_interference)^1/2 the figure of merit is G=selectivity efficiency/interference)^1/2. Sample background dominating, “interference” or both “interference” and “efficiency” have to be cancelled. Present semiconductor spectrometry of low energy γ-quanta and of large rates is not very far from its limits. Further progress will be obtained by enhancement of high energy efficiency and reduction of natural background.      

Multivariate analysis of HT/GC-(IT)MS chromatographic profiles of triacylglycerol for classification of olive oil varieties

The ability of multivariate analysis methods such as hierarchical cluster analysis, principal component analysis and partial least squares-discriminant analysis (PLS-DA) to achieve olive oil classification based on the olive fruit varieties from their triacylglycerols profile, have been investigated. The variations in the raw chromatographic data sets of 56 olive oil samples were studied by high-temperature gas chromatography with (ion trap) mass spectrometry detection. The olive oil samples were of four different categories (“extra-virgin olive oil”, “virgin olive oil”, “olive oil” and “olive-pomace” oil), and for the “extra-virgin” category, six different well-identified olive oil varieties (“hojiblanca”, “manzanilla”, “picual”, “cornicabra”, “arbequina” and “frantoio”) and some blends of unidentified varieties. Moreover, by pre-processing methods of chemometric (to linearise the response of the variables) such as peak-shifting, baseline (weighted least squares) and mean centering, it was possible to improve the model and grouping between different varieties of olive oils. By using the first three principal components, it was possible to account for 79.50% of the information on the original data. The fitted PLS-DA model succeeded in classifying the samples. Correct classification rates were assessed by cross-validation.