Kinetics of thermal decomposition of gelled UO3 microspheres

The kinetics of decomposition of gelled UO₃ microspheres has been studied by thermal analysis (DTA and TG) and by X-ray examination. UO₃ microspheres prepared via a hydrolysis process were used in the study. The DTA and TG curves were obtained in various atmospheres at different heating rates. The activation energies for the various stages of decomposition were calculated using the Carrol and Manche method.

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Zusammenfassung Die Kinetik der Zersetzung von Gel UO₃ Mikrokügelchen wurde mittels Thermoanalyse (DTA und TG) und Röntgenstrukturanalyse untersucht. Die in dieser Abhandlung benutzten UO₃ Mikrokügelchen wurden unter Zuhilfenahme von Hydrolyseprozessen hergestellt. Die DTA- und TG-Kurven wurden in verschiedenen Atmosphären und bei verschiedenen Aufheizgeschwindikeiten aufgenommen. Mit der Methode von Carrol und Manche wurden die Aktivierungsenergien für die einzelnen Schritte der Zersetzung berechnet.

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, UO₃, . . .

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The authors wish to express their thanks to Professor F. H. Hammad for his guidance and encouragement throughout this work.     

Effects of washing conditions on the thermal decomposition behaviour of gelled UO3 microspheres

DTA, TG and DTG curves obtained in various atmospheres using different heating rates were used together with X-ray examinations to study the thermal decomposition mechanisms of two types of gelled UO₃ microspheres: ammonia-washed (UN) and hot water-washed (UH) microspheres. The kinetics of the thermal decompositions were studied. The specific reaction rate constantk _r for the decomposition of UO₃ to U₃O₈ could be expressed in terms of the activation energy and the pre-exponential factor by the expressions: $$\begin{gathered} K_r (s^{ - 1} ) = 1.277 \times 10^{18} \exp \frac{{ - 295.4}}{{RT}}for the UN spheres, \hfill \\ K_r (s^{ - 1} ) = 8.406 \times 10^{19} \exp \frac{{ - 263.2}}{{RT}}for the UH spheres. \hfill \\ \end{gathered} $$      

Thermal and X-ray analysis studies of UO3 gel microspheres

The thermal decomposition behaviour of UO₃ gel microspheres has been studied. Thermal analysis involved DTA, TG, DTG and X-ray examination. The effects of washing the UO₃ gel microspheres with hot water and with ammonia solution were investigated, as were the effects of soaking the microspheres in ammonia solution before or after washing on the crystallite size. The results indicate that the thermal decomposition of UO₃ gel microspheres includes five steps: the first two for dehydration, the third for ammonia removal, the fourth for ammonia oxidation and the last step for UO₃ recrystallization.

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Zusammenfassung Die thermische Zersetzung von UO₃-Gelmikrokugeln wurde mittels DTA, TG, DTG und Röntgendiffraktometrie untersucht. Die Auswirkungen des Waschens der UO₃-Gelmikrokugeln mit heißem Wasser und mit Ammoniaklösungen sowie der Einfluß des Wässerns der Mikrokugeln vor und nach dem Waschen mit Ammoniaklösungen auf die Kristallitgröße wurden untersucht. Die thermische Zersetzung der UO₃-Gelmikrokugeln verläuft in 5 Schritten: in den ersten beiden erfolgt die Dehydratisierung, im dritten die Abgabe und im vierten die Oxydation von Ammoniak und schließlich im letzten Schritt die Rekristallisation von UO₃.

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, , ₃. , . , ₃ , , — , — , ₃.

     

Effects of drying conditions on thermal decomposition behaviour of UO3 gel microspheres

The effects of the drying conditions on the thermal behaviour of UO₃ gel microspheres were studied by TG, DTA and X-ray examination. The effects of drying with air, steam or alcohol on the crystal structure and crystallite size were also studied. The results indicate that the thermal decomposition of UO₃ gel microspheres involves five steps: the first two for dehydration, the third for ammonia release, the fourth for ammonia oxidation, and the last one for UO₃ recrystallization. It was also found that the crystal growth varied from 110 Å after air drying to 512 Å and 496 Å after steam and alcohol treatment, respectively.

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Zusammenfassung Die Effekte der Trocknungsbedingungen auf das thermische Verhalten von UO₃-Gelmikrokugeln wurden mittels TG, DTA und Röntgenanalyse untersucht. Ebenfalls wurden die Auswirkungen der Trocknung mit Luft, Dampf und Alkohol auf die Kristallstruktur und die Kristallitgröße untersucht. Die Ergebnisse deuten darauf hin, daß die thermische Zersetzung der UO₃-Gelmikrokugeln in 5 Schritten verläuft: die ersten zwei sind Dehydratisierungsprozessen, der dritte der Freisetzung und der vierte der Oxydation von Ammoniak und der letzte der Rekristallisation des UO₃ zuzuschreiben. Die Kristallitgröße variiert zwischen 110 Å nach Lufttrocknung und 512 bzw. 496 Å nach Trocknung mit Dampf bzw. Alkohol.

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, UO₃ . , UO₃. , UO₃ : — , — , — — UO₃. , 110 Å 512 496 Å , , .

     

Spray dried calcium gelled arabinoxylan microspheres: A novel carrier for extended drug delivery

Arabinoxylan (AX) microspheres were formulated by ionotropic gelation for extended drug delivery. AX from Plantago ovata was tested for gelation with aluminium, barium, calcium, magnesium, and iron(III) chloride. Only calcium was found to lead to weak gelation with AX. The conventional needle extrusion produced fragile AX beads with calcium and hence the spray drying process was adopted for the preparation of metronidazole hydrochloride (MH) loaded AX microspheres. MH loading in AX microspheres was 30.8 mass %, 31.9 mass %, and 29.3 mass % in formulations gelled with 0.05 g, 0.1 g, and 0.15 g of calcium chloride per 100 mL of solution, respectively. Scanning electron microscopy revealed the crystallinity reduction of MH in microspheres. The surface of drug loaded calcium gelled AX microsphere was rougher than that of an ungelled one. Interactions of calcium with AX and the amorphous nature of the drug in the microspheres were evidenced by infrared spectroscopy and X-ray diffraction studies. Calcium-induced gelation can extend the drug release to over 90 min in 0.1 M HCl despite the hydrophilic nature of AX and the high solubility of metronidazole.     

Recycling of uranium containing alkaline waste solution generated in the preparation of UO3 microspheres by the internal gelation process

Summary A recent study has indicated the feasibility of recycling of chemicals from alkaline waste generated in the preparation of UO₃ microspheres by the internal gelation process. Present paper investigates the recycle process, the volume of the secondary uranium waste. Result shows that prior to start the recycle process, the waste solution should be freed from uranium by ion-exchange. Optimized experimental condition to achieve maximum reduction in the volume of uranium based waste is discussed.     

Characterization of UO 2 2+ exchanged Y zeolite

The present study discusses the incorporation of uranyl ion into Y-zeolite framework. The UO ₂ ²⁺ sorption was measured by neutron activation analyses. The Y-zeolite framework distorts in response to the cations present in the structure. Hence, depending on the amount and the location of the exchanged cations, the features of the X-ray diffraction pattern may vary. From the Rietveld analysis of these patterns, the positions occupied by the UO ₂ ²⁺ cations in the zeolite network were determined.     

Characterization and chemistry of polyaldehyde microspheres

The chemical composition of polyacrolein (PA) microspheres of various types as well as polyglutaraldehyde (PGL) microspheres was elucidated. Nephelometric measurements were used for studying the stability properties of the polyaldehyde microspheres in different pH and salt concentrations. The stability of the aldehyde groups themselves at various pH and temperature was also determined. The polyaldehyde microspheres covalently bind amino ligands, e.g., proteins, antibodies, enzymes, and drugs in a single step. The effect of temperature and the influence of thiol compounds on the reaction between the polyaldehyde microspheres and amino ligands was examined. The reaction of the polyaldehyde microspheres with sodium hydrogen sulfite is also described.     

On the lattice of Ba3UO6

Electron diffraction has allowed the determination of the superlattice of Ba₃UO₆. The structure is a commensurate one-dimensional long-period superstructure of the perovskite structure, the long period being oriented along the [351]_c direction.     

The determination of UO2 and UO3 in different layers of a single crystal of uraninite

Summary The authors have performed analyses on different layers of a single uraninite crystal, a cleveite from Auselmyren, Aust-Agder, Norway. The separation of the layers having been made by mechanical means, it was possible to determine the amount of uranous oxide in them.About 0,05 g. of mineral is brought into solution by heating with sulfuric acid and the UO₂ content determined by titration with 1/100 n. permanganate-solution. The liquid is then reduced in aJones reductor and another titration gives the entire amount of uranium. The ratio UO₂/UO₃ can then be deducted.It is highest in the core, diminishing gradually towards the outside. The same is found also for the UO₂ content, while the amount per cent. of UO₃ is highest in the outside layer and lowest in the core.

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Zusammenfassung Die beiden Autoren haben Analysen in den verschiedenen Schichten eines einzelnen Uraninitkristalles — Cleveit aus Auselmyren, Aust-Agder, Norwegen — durchgeführt. Nach Trennung der Schichten auf mechanischem Wege war es möglich, die Mengen von Urano-Oxyd in jeder gesondert zu bestimmen.Ungefähr 0,05 g Mineral werden durch Erhitzen mit Schwefelsäure in Lösung gebracht und der Urandioxydgehalt wird durch Titration mit 1/100 n-Permanganatlösung bestimmt. Die Lösung wird dann im Reduktor nachJones reduziert und eine neuerliche Titration ergibt die Gesamtmenge des Urans. Daraus läßt sich das Verhältnis UO₂:UO₃ ableiten.Dieser Quotient ist am höchsten im Innern des Minerals und nimmt gegen die äußeren Schichten stetig ab. Dasselbe Verhalten zeigte der Urandioxydgehalt, während der perzentuelle Gehalt an Urani-Oxyd am größten in den äußeren Schichten und am kleinsten in den inneren ist.

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Résumé Les auteurs ont effectué l'analyse des différentes souches d'u d'un seul cristal d'uraninite — une clévéïte d'Auselmyren, Aust-Agder, Norvège. Les souches ayant été séparées mécaniquement, on parvint à doser leur teneur en oxyde uraneux.0,05 g. près, du minéral ont été dissous, à chaud, dans de l'acide sulfurique et la teneur en dioxyde d'uranium fut dosée par titrage avec de la solution 0,01 n de permanganate.Enfin, la solution est réduite dans un réducteurJones et un nouveau titrage donne la quantité totale d'uranium. On trouve, de cette façon, la proportion de UO₂:UO₃.Ce quotient est le plus élevé au centre du cristal et va décroissant continuellement vers la surface. Il en est de même quant à la teneur du dioxyde d'uranium, tandis que le pourcentage de UO₃ est le plus élevé dans la souche superficielle et le plus bas dans le centre du cristal.

     

新化合物五氧化铀的电喷雾串联质谱法制备与表征

采用醋酸铀酰为原料在气相中制备了HOUO2OH负离子, 在一定条件下再与O2反应, 从而制备了UO5负离子, 并采用串联质谱法对UO5进行了表征, 考察了生成条件对制备UO5负离子的影响. 初步实验表明在不同能量作用下UO5负离子能释放出O2. 探讨了气相中负离子与分子反应生成UO5负离子的可能机理, 指出通过调控分子与离子的碰撞时间和碰撞能量可以控制离子的电子活动半径, 合适的能量可使电子云的半径落在rinert≤rReactiverreactive≤rdecomposition之间, 从而促进某些化学反应的进行, 以合成某些通常状况下难以生成的物质.     

Quasi-isothermal dilatometric studies of the influence of oxygen pressure on the initial sintering stage of UO2 powder compacts

Quasi-isothermal dilatometry (QID) is a useful technique for sintering studies of powder compacts. In the present work the principle of this technique and the method of calculating activation energies from the QID curves is first described? then, using this method, the sintering mechanism and the influence of oxygen pressure on the initial sintering stage of UO₂ compacts are evaluated. The controlling mechanism was found to be grain boundary diffusion of uranium vacancies with an activation energy of 234 kJ/mole in accordance with literature data.     

Relativistic bond lengthening of UO 2 2+ and UO2

Summary Relativistic calculations on UO₂ [1] have shown that relativity leads to substantial bondlengthening in this compound, in contrast to the bond contraction found almost exclusively for other compounds. The bond lengthening isnot caused by the relativistic expansion of the 5f valence AO of U, which is the primary bond forming orbital on U in UO₂. The origin of the bond lengthening can be traced back to the semi-core resp. subvalence character of the U 6p AO. The valence character of 6p shows up in an increasing depopulation of the 6p upon bond shortening, and hence loss of mass-velocity stabilization. The core character of 6p shows up in large off-diagonal mass-velocity matrix elements 5p|h _MV|6p which are shown to have an overall bond lengthening effect. The larger expansion in UO₂ than in UO ₂ ²⁺ is due to destabilization of U levels in UO₂, caused by repulsion of the two additional 5f electrons.The present analysis corroborates the picture of relativistic bond length effects of Ref. [2].     

A study of gelled enzyme ultrafiltration reactors

Experiments were carried out in UF reactors with dynamically formed gelled enzyme artificial membranes. Unstirred batch systems and UF reactors with continuous recirculation of the substrate on the membrane were investigated. A significant increase in enzyme stability was tested in both systems. The enzymes used were acid phosphatase, urease, and β-glucosidase. The agreement between the experimental results and the predictions of a simple analytical model for the two classes of UF heterogeneous enzymatic reactors is generally satisfactory.     

Die IR-Spektren von NH4UO2AsO4·3H2O und NH4UO2PO4·3H2O

The infrared spectra of the title compounds, as well as that of the structurally related mineral meta-autunite, [Ca(UO₂)₂(PO₄)₂·n H₂O], are reported and discussed using the available crystallographic data. The results can be considered as representative for the full group of the so-called torbernite-minerals.     

Characterization of surface NH3+Cl- groups on poly(styrene-co-Boc-aminostyrene) microspheres obtained by controlled acidic treatment

Different samples of aminated latex of poly(styrene-co-Boc-aminostyrene) microspheres with mean diameters varying from 0.7 to 1.0 microm were prepared by dispersion copolymerization of styrene (ST) and Boc-aminostyrene (Boc-AMST). The copolymer compositions determined by nuclear magnetic resonance (1H NMR) were Boc-AMST/ST 6.9/93.1 mol/mol % (BOC7 sample) and Boc-AMST/ST 31.3/68.7 mol/mol % (BOC30 sample). The average molecular weights determined by gel permeation chromatography were 126 kDa (BOC7 sample) and 51 kDa (BOC30 sample). The latex containing NH-carbo-tert-butoxy groups (NH-Boc) were treated with 2 M HCl in isopropyl alcohol/water (1:1 vol/vol), at 50 degrees C for 3, 6, 9, 24, and 30 h, in order to control the extent of deprotection reaction of the NH-Boc. The deprotection reaction resulted in the formation of NH3+Cl- groups on the particle surfaces. The kinetic of the deprotection reaction was investigated by 1H NMR analyses and the yield varied from 20 to 40%. The resulting -NH3+Cl- groups on the microsphere surfaces were examined, in particular, by electron spectroscopy imaging (ESI) using an energy-filtered transmission electron microscope (EFTEM) that clearly demonstrated the presence of Cl on the particle surfaces. Scanning electron photomicrographs recorded for the above samples showed that the particle morphology was maintained after the acidic treatment.     

Interaction in Systems Ln2O3-CsPO3 and Ln2O3- UO3-CPO3

Abstract

The systems Ln₂O₃-CsPO₃ and Ln₂O₃-UO₃-CsPO₃ were investigated and three sets of compounds A, B, C were isolated.