Different Pathways of Secondary Phase Formation Induced by Colloidal and Dissolved Silica During the Dissolution of UO2 Nuclear Fuel in Leaching Tests

2003 ◽  
Author(s):  
M. Amme ◽  
H. Lang ◽  
M. Sto¨ckl
Keyword(s):  
Nuclear Fuel ◽  
Electrostatic Interactions ◽  
Elevated Temperatures ◽  
Secondary Phase ◽  
Sodium Metasilicate ◽  
Batch Reactors ◽  
Secondary Phases ◽  
Surface Charges ◽  
Solid Materials ◽  
Si Content

We investigated the different dissolution behaviour of UO2 nuclear fuel material in waters containing silica in two different physical and chemical forms (dissolved ions and as SiO2 colloids, respectively) at elevated temperatures (95 °C in autoclaves). It was investigated if SiO2 colloids can act as carrier material for U ions during a interface geochemical dissolution process, a process that might possibly enhance the mobilization of uranium. Herefore, leaching / dissolution tests were conducted in batch reactors, using both dissolved Si (sodium metasilicate solution), as well as synthetic SiO2 colloids (100 nm diameter). Solid materials were examined with scanning electron microscopy (SEM-EDX) after the tests and ICP-OES was used for analysis of concentrations of U and Si in solutions. Thermodynamic calculations were applied for modelling the surface charges of the solid materials. Results show that a treatment with colloidal SiO2 has different effects on the surfaces than a leaching in dissolved silicate solutions. In the presence of colloids, well-crystallized secondary phases containing U and Si (most obviously uranyl silicates) were found on the surfaces, which were attacked by the treatment. This was not the case when dissolved Si was used. SiO2 colloids were partly found to remain on the surfaces after 1000 h at 95 °C. Dissolved U concentrations decreased with increasing Si content in the systems, especially so when colloidal Si was used. Ultrafiltration showed that the greatest part of the dissolved U was associated with Si colloids. A surface charge model suggests that the different effects are due to the development of electrostatic interactions between the UO2 and SiO2 surfaces.

Calcium Vanadinite: An Alternative Apatite Host for Cl-rich Wastes

2014 ◽  
Vol 1665 ◽  
pp. 319-324 ◽  
Author(s):  
M. R. Gilbert
Keyword(s):  
Elevated Temperatures ◽  
Secondary Phase ◽  
Phase System ◽  
Secondary Phases ◽  
Waste Forms ◽  
Good Potential ◽  
Multi Phase

ABSTRACTApatites are often seen as good potential candidates for the immobilization of halide-rich wastes and, in particular, chlorapatite (Ca5(PO4)3Cl) has received much attention in recent years. However, synthesis of chlorapatite waste-forms can produce a complicated multi-phase system, with a number of secondary phases forming, including β-TCP (Ca3(PO4)2), spodiosite (Ca2(PO4)Cl) and pyrophosphate (Ca2P2O7), many of which require elevated temperatures and extended calcinations times to reduce. Calcium vanadinite (Ca5(VO4)3Cl) demonstrates a much simpler phase system, with calcination at 750 °C yielding Ca5(VO4)3Cl together a small quantity of a Ca2V2O7secondary phase, the formation of which can be retarded by the addition of excess CaCl2. Characterization of compositions doped with SmCl3as an inactive analogue for AnCl3show the Cl to be immobilized in the vanadinite whilst the Sm forms a wakefieldite (SmVO4) phase.

High Temperature Corrosion Behavior of Si-Containing Alloys in the Gas Phase of Air-(Na2SO4+25.7mass%NaCl)

2011 ◽  
Vol 696 ◽  
pp. 272-277 ◽  
Author(s):  
Toto Sudiro ◽  
Tomonori Sano ◽  
Akira Yamauchi ◽  
Shoji Kyo ◽  
Osamu Ishibashi ◽  
...  
Keyword(s):  
High Temperature ◽  
Gas Phase ◽  
Corrosion Behavior ◽  
Elevated Temperatures ◽  
High Temperature Corrosion ◽  
Ni Content ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Corrosion Resistant Alloy ◽  
Si Content

The objective of this study is to develop an excellent corrosion resistant alloy for high temperature coating applications. The Si-containing alloys consisting of CoNiCrAlY and CrSi2 alloys with varying Si and Ni content respectively were prepared by spark plasma sintering (SPS) technique. The corrosion behavior of these alloys was investigated in the gas phase of air-(Na2SO4+25.7mass%NaCl) at elevated temperatures of 923, 1073 and 1273K. The results showed that CoNiCrAlY alloy with 30mass% Si content and CrSi2 alloy with 10mass% Ni content were the most effective materials for application in the gas phase of air-(Na2SO4+25.7mass%NaCl) due to the formation of protective Al2O3/SiO2 and SiO2 scale, respectively. Therefore, it is realized that CoNiCrAlY-30mass% Si and CrSi2-10mass% Si coating are very effective for improving of high temperature corrosion resistance of STBA21 steel.

Mechanical Property and Oxidation Behavior of LPS-SiC Materials

2006 ◽  
Vol 321-323 ◽  
pp. 913-916
Author(s):  
Sang Ll Lee ◽  
Yun Seok Shin ◽  
Jin Kyung Lee ◽  
Jong Baek Lee ◽  
Jun Young Park
Keyword(s):  
Mechanical Property ◽  
Fracture Toughness ◽  
Oxidation Behavior ◽  
Elevated Temperatures ◽  
Indentation Test ◽  
Bending Test ◽  
Secondary Phases ◽  
Three Point Bending ◽  
Different Temperatures

The microstructure and the mechanical property of liquid phase sintered (LPS) SiC materials with oxide secondary phases have been investigated. The strength variation of LPS-SiC materials exposed at the elevated temperatures has been also examined. LPS-SiC materials were sintered at the different temperatures using two types of Al2O3/Y2O3 compositional ratio. The characterization of LPS-SiC materials was investigated by means of SEM with EDS, three point bending test and indentation test. The LPS-SiC material with a density of about 3.2 Mg/m3 represented a flexural strength of about 800 MPa and a fracture toughness of about 9.0 MPa⋅√m.

Rational Design of Organic Electro-Optic Materials

2001 ◽  
Vol 708 ◽  
Author(s):  
Alex Jen ◽  
Robert Neilsen ◽  
Bruce Robinson ◽  
William H. Steier ◽  
Larry Dalton
Keyword(s):  
Wavelength Division Multiplexing ◽  
Material Properties ◽  
Electrostatic Interactions ◽  
Rational Design ◽  
Elevated Temperatures ◽  
Optical Loss ◽  
Quality Factors ◽  
Electro Optic ◽  
Lattice Hardening

ABSTRACTA number of material properties must be optimized before organic electro-optic materials can be used for practical device applications. These include electro-optic activity, optical transparency, and stability including both thermal and photochemical stability. Exploiting an improved understanding of the structure/function relationships, we have recently prepared materials exhibiting electro-optic coefficients of greater than 50 pm/V and optical loss values of less than 0.7 dB/cm at the telecommunication wavelengths of 1.3 and 1.55 microns. When oxygen is excluded to a reasonable extent, long-term photostability to optical power levels of 20 mW has been observed. Photostability is further improved by addition of scavengers and by lattice hardening. Long-term (greater than 1000 hours) thermal stability of poling-induced electro-optic activity is also observed at elevated temperatures (greater than 80°C) when appropriate lattice hardening is used. The successful improvement of organic electro-optic materials rests upon (1) attention to the design of chromophore structure including design to inhibit unwanted intermolecular electrostatic interactions and to improve chromophore instability and (2) attention to processing conditions including those involved in spin casting, electric field poling, and lattice hardening. A particularly attractive new direction has been the exploitation of dendrimer structures and particularly of multi-chromophore containing dendrimer structures. This approach has permitted the simultaneous improvement of all material properties. Development of new materials has facilitated the fabrication of a number of prototype devices and most recently has permitted investigation of the incorporation of electro-optic materials into photonic bandgap and microresonator structures. The latter are relevant to active wavelength division multiplexing (WDM). Significant quality factors (greater than 10,000) have been realized for such devices permitting wavelength discrimination at telecommunication wavelengths of 0.01 nm.

scholarly journals Crowding within synaptic junctions influence the degradation of adenoside nucleotides by CD39 and CD73 ectonucleotidases

2021 ◽  
Author(s):  
Hadi Rahmaninejad ◽  
Tom Pace ◽  
Peter Kekenes-Huskey
Keyword(s):  
Electrostatic Interactions ◽  
Configurational Entropy ◽  
Reaction Diffusion ◽  
Adenosine Monophosphate ◽  
Adenosine Diphosphate ◽  
Surprising Result ◽  
Surface Charges ◽  
Association Rate ◽  
Synaptic Junction ◽  
Reaction Diffusion Model

Synapsed cells can communicate using exocytosed nucleotides like adenosine triphosphate (ATP). Ectonucleotidases localized to a synaptic junction degradesuch nucleotides into metabolites like adenosine monophosphate (AMP) or adenosine, oftentimes in a sequential manner. CD39 and CD73 are a representativeset of coupled ectonucleotidases, where CD39 first converts ATP and adenosine diphosphate (ADP) into AMP, after which the AMP product is dephosphorylated into adenosine by CD73. Hence, CD39/CD73 help shape cellular responses to extracellular ATP. In a previous study [1] we demonstrated that the rates of coupled CD39/CD73 activity within synapse-like junctions are strongly controlled by the enzymes' co-localization, their surface charge densities, and the electrostatic potential of the surrounding cell membranes. In this study, we demonstrate that crowders within a synaptic junction, which can include globular proteins like cytokines and membrane-bound proteins, impact coupled CD39/CD73 electronucleotidase activity and in turn, the availability of intrasynapse ATP. Specifically, we simulated a spatially-explicit, reaction-diffusion model for the coupled conversion of ATP -> AMP and AMP -> adenosine in a model synaptic junction with crowders via the finite element method. Our modeling results suggest that the association rate for ATP to CD39 is strongly influenced by the density of intrasynaptic protein crowders, as increasing crowder density suppressed ATP association kinetics. Much of this suppression can be rationalized based on a loss of configurational entropy. The surface charges of crowders can further influence the association rate, with the surprising result that favorable crowder/nucleotide electrostatic interactions can yield CD39 association rates that are faster than crowder-free configurations. However, attractive crowder/nucleotide interactions decrease the rate and efficiency of adenosine production, which in turn increases the availability of ATP and AMP within the synapse relative to crowder-free configurations. These findings highlight how CD39/CD73 ectonucleotidase activity, electrostatics and crowding within synapses influence the availability of nucleotides for intercellular communication.

scholarly journals Bone Morphogenetic Protein 2 (BMP-2) Aggregates Can be Solubilized by Albumin—Investigation of BMP-2 Aggregation by Light Scattering and Electrophoresis

Pharmaceutics ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 1143
Author(s):  
Julius Sundermann ◽  
Holger Zagst ◽  
Judith Kuntsche ◽  
Hermann Wätzig ◽  
Heike Bunjes
Keyword(s):  
Light Scattering ◽  
Bone Morphogenetic Protein ◽  
Electrostatic Interactions ◽  
Hydrophobic Interactions ◽  
Pharmaceutical Research ◽  
Bone Morphogenetic Protein 2 ◽  
Growth Factor Delivery ◽  
Surface Charges ◽  
High Tendency ◽  
Morphogenetic Protein

Bone morphogenetic protein 2 (BMP-2) has a high tendency to aggregate at physiological pH and physiological ionic strength, which can complicate the development of growth factor delivery systems. The aggregation behavior in differently concentrated BMP-2 solutions was investigated using dynamic and static light scattering. It was found that at higher concentrations larger aggregates are formed, whose size decreases again with increasing dilution. A solubilizing effect and therefore less aggregation was observed upon the addition of albumin. Imaged capillary isoelectric focusing and the simulation of the surface charges of BMP-2 were used to find a possible explanation for the unusually low solubility of BMP-2 at physiological pH. In addition to hydrophobic interactions, attractive electrostatic interactions might be decisive in the aggregation of BMP-2 due to the particular distribution of surface charges. These results help to better understand the solubility behavior of BMP-2 and thus support future pharmaceutical research and the development of new strategies for the augmentation of bone healing.

scholarly journals In situ nuclear-glass corrosion under geological repository conditions

2019 ◽  
Vol 3 (1) ◽  
Author(s):  
Mathieu Debure ◽  
Yannick Linard ◽  
Christelle Martin ◽  
Francis Claret
Keyword(s):  
Pure Water ◽  
Secondary Phase ◽  
Predictive Modelling ◽  
Diffusion Experiment ◽  
Secondary Phases ◽  
Glass Corrosion ◽  
Geological Repository ◽  
High Level ◽  
Rock Supports

Abstract Silicate glasses are durable materials but laboratory experiments reveal that elements that derive from their environment may induce high corrosion rates and reduce their capacity to confine high-level radioactive waste. This study investigates nuclear-glass corrosion in geological media using an in situ diffusion experiment and multi-component diffusion modelling. The model highlights that the pH imposed by the Callovo–Oxfordian (COx) claystone host rock supports secondary-phase precipitation and increases glass corrosion compared with pure water. Elements from the COx rock (mainly Mg and Fe) form secondary phases with Si provided by the glass, which delay the establishment of a passivating interface. The presence of elements (Mg and Fe) that sustain glass alteration does not prevent a significant decrease in the glass-alteration rate, mainly due to the limited species transport that drives system reactivity. These improvements in the understanding of glass corrosion in its environment provide further insights for predictive modelling over larger timescales and space.

Simulation of Poly-Disperse Multiphase Systems via Computational Fluid Dynamics

2006 ◽  
Author(s):  
Daniele L. Marchisio ◽  
Marco Vanni ◽  
Antonello A. Barresi ◽  
Giancarlo Baldi
Keyword(s):  
Method Of Moments ◽  
Fluid Model ◽  
Secondary Phase ◽  
Primary Phase ◽  
Momentum Balance ◽  
Multiphase Model ◽  
Secondary Phases ◽  
Discrete Events ◽  
Multiphase Systems ◽  
Two Phases

Multiphase systems, such as sprays and aerosols, are characterized by the existence of a continuous primary phase and a disperse secondary phase. The interaction between the two phases and/or the chemical reactions can affect both composition and characteristic velocity of the primary and secondary phases, as well as the size distribution of the secondary phase. In order to describe these systems, the continuity, mass balance and momentum balance equations as well as additional equations for turbulence, must be solved. Nevertheless if there is the need to account for the evolution of the secondary phase because of continuous and discrete events the population balance equation must be solved. In this work two very efficient ways to cope with these issues will be presented. In particular the use of the quadrature method of moments coupled with the mixture multiphase model, and the multi-fluid model will be presented and discussed.

PH3 Effects on the Electrochemical Degradation of SOFC Anode

2011 ◽  
Author(s):  
Huang Guo ◽  
Gulfam Iqbal ◽  
Bruce S. Kang
Keyword(s):  
Electrochemical Performance ◽  
Secondary Phase ◽  
Anode Surface ◽  
Electrochemical Degradation ◽  
Secondary Phases ◽  
Nickel Phosphate ◽  
Secondary Phase Formation ◽  
Cell Anode ◽  
Fuel Cell Anode ◽  
Ppm Level

Solid Oxide Fuel Cell anode is readily degraded by trace amount of Phosphine (PH3) contaminant that is found in coal-derived syngas. PH3 interacts with the anode material and affects its electrochemical performance by forming secondary phases. In this paper, the influence of the ppm level of PH3 with moisture is investigated on the formation of secondary phases and hence on anode electrochemical performance degradation. Nickel yttria-stabilized zirconia (Ni-YSZ) anode shows immediate and severe electrochemical degradation due to PH3 in moist hydrogen condition attributed to the nickel-phosphate secondary phase formation. Whereas in dry hydrogen condition, nickel-phosphide is preferred to form on the anode surface that shows less deleterious effects on SOFC performance as compared to nickel-phosphate.

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