Dissolution of Synthetic Brannerite at 90°C

2000 ◽  
Vol 663 ◽  
Author(s):  
Y. Zhang ◽  
K.P. Hart ◽  
B.S. Thomas ◽  
Z. Aly ◽  
H. Li ◽  
...  
Keyword(s):  
Surface Layer ◽  
Deionized Water ◽  
Minor Phase ◽  
Release Rates ◽  
Static Tests ◽  
Surface Alteration ◽  
Order Of Magnitude ◽  
Synthetic Groundwater ◽  
A Minor ◽  
Titanate Ceramic

ABSTRACTBrannerite, as a minor phase, exists in the pyrochlore-rich titanate ceramic formulations designed for immobilization of surplus weapons Pu. The dissolution of synthetic brannerite was studied at 90°C using static tests in pH 4 solution, deionized water and Finnsjön synthetic groundwater.After 140 days the normalized U release rates into a pH 4 solution and deionized water reach similar values, ~10−2 g m−2 d−1, and are about 2 orders of magnitude higher than those in Finnsjön synthetic groundwater. The normalized Ti release rate into Finnsjön synthetic groundwater is about an order of magnitude higher than those in pH 4 solution and deionized water. The dissolution of brannerite is incongruent in the pH 4 solution and deionized water (preferential release of U over Ti), and nearly congruent in Finnsjön synthetic groundwater. SEM observations of the samples after 140 days in pH 4 solution and deionized water revealed minor surface alteration, in the form of a thin surface layer, probably TiO2, as a result of preferential releases of U in both cases.

Aqueous Dissolution and Surface Alteration Studies of Nd-bearing Zirconolite in 0.001M Citric Acid at 90°C

2003 ◽  
Vol 807 ◽  
Author(s):  
Peter J. McGlinn ◽  
Terry McLeod ◽  
Gilles Leturcq ◽  
Zaynab Aly ◽  
Mark G. Blackford ◽  
...  
Keyword(s):  
Citric Acid ◽  
Secondary Phase ◽  
Citric Acid Solution ◽  
Release Rates ◽  
Water Release ◽  
Phase Development ◽  
Surface Alteration ◽  
Order Of Magnitude ◽  
Parallel Tests ◽  
Influence Of Ph

ABSTRACTNd-bearing zirconolite was leached at 90°C for 6 months in 0.001M citric acid, and also in deionised water, to determine the effect of organic-bearing solutions on durability. The pH of the citric acid solution was adjusted to 5 using KOH, approximating that of the water in the parallel tests, to avoid the influence of pH on chemical durability of the zirconolite.Releases were incongruent in the tests carried out in water. Release rates of Ti, Zr and Nd were comparatively very low (commonly too low to be measured) over the first 80 days of leaching. Rates for Ca and Al were 2 to 4 orders of magnitude higher than Ti, Zr and Nd over this same period. At about 80 days, there was an anomalous decrease in pH from 6 to 4 which enhanced release rates of Ti and Nd in particular. There was development of titania crystals, and the suggestion of hydrolysed titania, on the surface after 6 months. Thermodynamic equilibrium between the leachates and hydrolysed species on the surface of the zirconolite may be the key to apparent cessation of alteration, at least during thefirst 80 days of leaching.By contrast, zirconolite leached in 0.001M citric acid maintained release rates of Ti, Zr and Nd 2 to 4 orders of magnitude greater than those in water for the first 80 days, values sustained, within an order of magnitude, for the remainder of the leach tests. Releases were congruent. The surface of the zirconolite showed no signs of secondary phase development. This suggests complexation by citrate ions prevented control by hydrolysed species on zirconolite solubility.

Durability of Pu-doped Titanate and Zirconate Ceramics Designed for Pu Immobilisation

2002 ◽  
Vol 713 ◽  
Author(s):  
Y. Zhang ◽  
K.P. Hart ◽  
B.D. Begg ◽  
E.A. Keegan ◽  
A.R. Day ◽  
...  
Keyword(s):  
Secondary Phase ◽  
Processing Temperature ◽  
Processing Conditions ◽  
Release Rates ◽  
Rich Phase ◽  
Glass Forming ◽  
Order Of Magnitude ◽  
Ceramic Sintering ◽  
Impurity Elements ◽  
Titanate Ceramic

ABSTRACTCeramics rich in pyrochlore-structured titanate and fluorite-structured zirconate phases designed for surplus Pu immobilisation, with and without process impurities, have been leach tested at 90°C in deionised water. The zirconates consist mainly of a defect-fluorite with secondary impurity-containing phase-powellite/scheelite (when sintered in Ar but not when sintered in air), a spinel or magnetoplumbite type phase, a glass forming silicate and a secondary U-rich phase (when sintered in air with added impurities). The pyrochlore-rich baseline titanate ceramic consists of pyrochlore, brannerite and Hf-rutile. When impurities are added zirconolite and a silicate glass are also present. The pyrochlore-rich titanate with 5 wt% of impurities sintered at 1300°C is highly durable. A well-densified zirconate version without impurities has comparable elemental releases to those of the titanate ceramic but a zirconate with 5 wt% of impurities sintered at 1400°C in air or Ar shows much higher U and Ca releases than the titanate ceramic. Sintering atmospheres, changing from Ar to air, can influence Pu and U release rates up to an order of magnitude. High Ga releases from zirconates with impurities show that the secondary phase containing Ga is not durable. The higher processing temperature and the apparent inability to incorporate many impurity elements suggest that zirconates are not as flexible as titanates in respect of processing conditions and aqueous durability.

Waste Glass Leaching: Chemistry and Kinetics

1986 ◽  
Vol 84 ◽  
Author(s):  
Bruce C. Bunker
Keyword(s):  
Release Kinetics ◽  
Glass Structure ◽  
Waste Glass ◽  
Release Rates ◽  
Glass Dissolution ◽  
Surface Alteration ◽  
Order Of Magnitude ◽  
Level Of Understanding ◽  
Radionuclide Release ◽  
Glass Leaching

AbstractNuclear waste glass leaching has been studied extensively during the past ten years. Although much has been learned concerning the kinetics and mechanisms of glass dissolution, it does not appear that accurate predictions can yet be made concerning the release kinetics for specific elements from a given glass as a function of environmental conditions. In order to reliably predict elemental release rates, one needs to know: 1) how a given element is incorporated into the glass structure, 2) how specific sites in the glass react with water, 3) how the composition and reactivity of the leachate influence glass reactivity, 4) how the structure and reactivity of the glass changes in surface alteration layers, and 5) how glass dissolution modifies the chemistry of the leachate. At our current level of understanding, we are only able to make qualitative predictions concerning each of the above factors which allow us to make “order of magnitude” or “upper limit” predictions for radionuclide release rates.

scholarly journals Discharge of debris from ice at the margin of the Greenland ice sheet

2002 ◽  
Vol 48 (161) ◽  
pp. 192-198 ◽  
Author(s):  
Peter G. Knight ◽  
Richard I. Waller ◽  
Carrie J. Patterson ◽  
Alison P. Jones ◽  
Zoe P. Robinson
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
High Rate ◽  
Outlet Glacier ◽  
Tidewater Glaciers ◽  
Sediment Production ◽  
Basal Ice ◽  
Order Of Magnitude ◽  
Sediment Transfer ◽  
A Minor

AbstractSediment production at a terrestrial section of the ice-sheet margin in West Greenland is dominated by debris released through the basal ice layer. The debris flux through the basal ice at the margin is estimated to be 12–45 m3 m−1 a−1. This is three orders of magnitude higher than that previously reported for East Antarctica, an order of magnitude higher than sites reported from in Norway, Iceland and Switzerland, but an order of magnitude lower than values previously reported from tidewater glaciers in Alaska and other high-rate environments such as surging glaciers. At our site, only negligible amounts of debris are released through englacial, supraglacial or subglacial sediment transfer. Glaciofluvial sediment production is highly localized, and long sections of the ice-sheet margin receive no sediment from glaciofluvial sources. These findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a minor percentage of the debris released at the margin. These data on debris flux through the terrestrial margin of an outlet glacier contribute to our limited knowledge of debris production from the Greenland ice sheet.

The stress generated in a non-dilute suspension of elongated particles by pure straining motion

1971 ◽  
Vol 46 (4) ◽  
pp. 813-829 ◽  
Author(s):  
G. K. Batchelor
Keyword(s):  
Theoretical Formula ◽  
Rigid Sphere ◽  
Cross Sectional ◽  
Outer Flow ◽  
Rigid Particles ◽  
Bulk Stress ◽  
Order Of Magnitude ◽  
Sectional Plane ◽  
Dilute Suspension ◽  
A Minor

In a pure straining motion, elongated rigid particles in suspension are aligned parallel to the direction of the greatest principal rate of extension, provided the effect of Brownian motion is weak. If the suspension is dilute, in the sense that the particles are hydrodynamically independent, each particle of length 2l makes a contribution to the bulk deviatoric stress which is of roughly the same order of magnitude as that due to a rigid sphere of radius l. The fractional increase in the bulk stress due to the presence of the particles is thus equal to the concentration by volume multiplied by a factor of order l2/b2, where 2b is a measure of the linear dimensions of the particle cross-section. This suggests that the stress due to the particles might be relatively large, for volume fractions which are still small, with interesting implications for the behaviour of polymer solutions. However, dilute-suspension theory is not applicable in these circumstances, and so an investigation is made of the effect of interactions between particles. It is assumed that, when the average lateral spacing of particles (h) satisfies the conditions b [Lt ] h [Lt ] l, the disturbance velocity vector is parallel to the particles and varies only in the cross-sectional plane. The velocity near a particle is found to have the same functional form as for an isolated particle, and the modification to the outer flow field for one particle is determined by replacing the randomly placed neighbouring particles by an equivalent cylindrical boundary. The resulting expression for the contribution to the bulk stress due to the particles differs from that for a dilute suspension only in a minor way, viz. by the replacement of log 2l/b by log h/b, and the above suggestion is confirmed. The relative error in the expression for the stress is expected to be of order (log h/b)−1. Some recent observations by Weinberger of the stress in a suspension of glass-fibre particles for which 2l/h = 7·4 and h/2b = 7·8 do show a particle stress which is much larger than the ambient-fluid stress, although the theoretical formula is not accurate under these conditions.

scholarly journals Does Fully Radioactive Glass Behave Differently than Simulated Waste Glass?

1992 ◽  
Vol 294 ◽  
Author(s):  
X. Feng ◽  
J. K. Bates ◽  
C. R. Bradley ◽  
E. C. Buck
Keyword(s):  
Radiation Field ◽  
Nuclear Waste ◽  
Potassium Feldspar ◽  
Waste Glass ◽  
Solution Ph ◽  
Static Tests ◽  
Leach Rate ◽  
Nuclear Waste Glass ◽  
Surface Alteration ◽  
Leach Behavior

ABSTRACTStatic tests at SA/V (ratio of surface area of glass to solution volume) 20,000 m−1 on SRL 200 glass compositions show that, at long test periods, the simulated nuclear waste glass (nonradioactive) leaches faster than the corresponding radioactive glass by a factor of about 40, although comparative tests, done through 560 days, at lower SA/V, 2000 m−1, indicate little difference in the leach behavior of the two types of glasses. The similarity in leach behavior between radioactive and simulated glasses at SAN of 2000 m−1 or lower is also observed for SRL 165/42 and 131/11 compositions. The accelerated glass reaction with the simulated glass 200S is associated with the formation of crystalline phases such as clinoptilolite (or potassium feldspar), and a pH excursion. The radiation field generated by the fully radioactive glass reduces the solution pH. This lower pH, in turn, may retard the onset of increased reaction rate. The radiation field generated by the radioactive glasses does not directly affect the stability of the glass surface alteration layer under those conditions where the radioactive and simulated glasses react at the same rate. These results suggest that the fully radioactive nuclear waste glass 200R may maintain a much lower leach rate than the simulated 200S, if the lower pH in the 200R leachate can be sustained. Meaningful comparison tests between radioactive and simulated nuclear waste glasses should include long-term and high SA/V tests.

scholarly journals Nanosilver in Biomedicine: Advantages and Restrictions

2021 ◽  
Author(s):  
Olga V. Morozova ◽  
Dmitry V. Klinov
Keyword(s):  
Gene Expression ◽  
Immune Response ◽  
Surface Layer ◽  
Drug Efficacy ◽  
Multidrug Resistant ◽  
Deionized Water ◽  
Sensitivity Threshold ◽  
Specific Interactions ◽  
Anti Cancer ◽  
Potential Formation

Nanosilver (in a range 1–100 nm) binds with thyol-, amino- and carboxy-groups of aminoacid residues of proteins and nucleic acids, thus providing inactivation of pathogenic multidrug-resistant microorganisms. Besides antibacterial, antiviral, antifungal and anti-cancer properties Ag-based nanomaterials possess anti-inflammatory, anti-angiogenesis and antiplatelet features. Drug efficacy depends on their stability, toxicity and host immune response. Citrate coated Ag nanoparticles (NPs) remain stable colloid solutions in deionized water but not in the presence of ions due to replacement of Ag+ by electrolyte ions, potential formation of insoluble AgCl, subsequent catalyzed oxidative corrosion of Ag and further dissolution of surface layer of Ag2O. Protein shells protect core of AgNPs from oxidation, dissolution, aggregation and provide specific interactions with ligands. These nanoconjugates can be used for immunoassays and diagnostics but the sensitivity threshold does not exceed 10 pg Cytotoxicity of AgNPs conjugated with proteins is associated with the rate of intracellular Ag+ release, a ‘Trojan horse’ effect, and exceeds one of Ag+ because of endocytosis uptake of NPs but not ions. Relatively toxic nanosilver causes immunosuppression of the majority of cytokines with a few exceptions (IL-1β, G-CSF, MCP-1) whereas AgNO3 additionally activate TNFα and IL8 gene expression.

scholarly journals Hardening of Nickel Alloys by Ion Implantation of Titanium and Carbon

1996 ◽  
Vol 444 ◽  
Author(s):  
S. M. Myers ◽  
D. M. Follstaedt ◽  
J. A. Knapp ◽  
T. R. Christenson
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Surface Layer ◽  
Ion Implantation ◽  
Finite Element Modeling ◽  
Yield Stress ◽  
Nickel Alloys ◽  
Element Modeling ◽  
Order Of Magnitude ◽  
Amorphous Surface

AbstractDual ion implantation of titanium and carbon was shown to produce an amorphous surface layer in annealed bulk nickel, in electroformed Ni, and in electroformed Ni7 5Fe 2 5. Diamond-tip nanoindentation coupled with finite-element modeling quantified the elastic and plastic mechanical properties of the implanted region. The amorphized matrix, with a thickness of about 100 nm, has a yield stress of approximately 6 GP and an intrinsic hardness near 16 GPa, exceeding by an order of magnitude the corresponding values for annealed bulk Ni. Implications for micro-electromechanical systems are discussed.

scholarly journals Cerebrospinal fluid ceftazidime kinetics in patients with external ventriculostomies.

1996 ◽  
Vol 40 (3) ◽  
pp. 763-766 ◽  
Author(s):  
R Nau ◽  
H W Prange ◽  
M Kinzig ◽  
A Frank ◽  
A Dressel ◽  
...  
Keyword(s):  
Central Nervous System ◽  
Cerebrospinal Fluid ◽  
Nervous System ◽  
High Performance ◽  
Elimination Half ◽  
Daily Dose ◽  
Order Of Magnitude ◽  
The Central Nervous System ◽  
Occlusive Hydrocephalus ◽  
A Minor

Ceftazidime has proven to be effective for the treatment of bacterial meningitis caused by multiresistant gram-negative bacteria. Since nosocomial central nervous system infections are often accompanied by only a minor dysfunction of the blood-cerebrospinal fluid (CSF) barrier, patients with noninflammatory occlusive hydrocephalus who had undergone external ventriculostomy were studied (n = 8). Serum and CSF were drawn repeatedly after the administration of the first dose of ceftazidime (3 g over 30 min intravenously), and concentrations were determined by high-performance liquid chromatography by using UV detection. The concentrations of ceftazidime in CSF were maximal at 1 to 13 h (median, 5.5 h) after the end of the infusion and ranged from 0.73 to 2.80 mg/liter (median, 1.56 mg/liter). The elimination half-lives were 3.13 to 18.1 h (median, 10.7 h) in CSF compared with 2.02 to 5.24 h (median, 3.74 h) in serum. The ratios of the areas under the concentration-time curves in CSF and serum (AUCCSF/AUCS) ranged from 0.027 to 0.123 (median, 0.054). After the administration of a single dose of 3 g, the maximum concentrations of ceftazidime in CSF were approximately four times higher than those after the administration of 2-g intravenous doses of cefotaxime (median, 0.44 mg/liter) and ceftriaxone (median, 0.43 mg/liter) (R. Nau, H. W. Prange, P. Muth, G. Mahr, S. Menck, H. Kolenda, and F. Sörgel, Antimicrob. Agents Chemother. 37:1518-1524, 1993). The median AUCCSF/AUCS ratio of ceftazidime was slightly below that of cefotaxime (0.12), but it was 1 order of magnitude above the median AUCCSF/AUCS of ceftriaxone (0.007) (Nau et al., Antimicrob. Agents Chemother. 37:1518-1524, 1993). The concentrations of ceftazidime observed in CSF were above the MICs for most Pseudomonas aeruginosa strains. However, they are probably not high enough to be rapidly bactericidal. For this reason, the daily dose should be increased to 12 g in cases of P. aeruginosa infections of the central nervous system when the blood-CSF barrier is minimally impaired.

Alpha-Spectroscopy and Leach Testing of Synroc Doped With Actinide Elements

1999 ◽  
Vol 556 ◽  
Author(s):  
K. P. Hart ◽  
E. R. Vance ◽  
R. Stanojevic ◽  
R. A. Day
Keyword(s):  
Surface Layer ◽  
Surface Area ◽  
Release Rate ◽  
Daily Basis ◽  
Alpha Spectroscopy ◽  
Release Rates ◽  
Monthly Basis ◽  
Surface Examination ◽  
Actinide Elements

AbstractSynroc specimens doped individually with ˜ 1 wt% of Np or Pu have been studied, after leaching for >2,500 days, using α-spectroscopy and SEM. In the last leaching period, the leachant was replaced on either a daily or monthly basis. When the leachant was replaced on a daily basis the release rate of Np was similar to that measured when the samples were first leached, whereas for the monthly replacement the release rates of Np or Pu were about a factor of 20 to 30 lower than that for daily replacement. These findings agree generally with the results obtained from surface examination of the samples which showed that the thickness of actinidedepleted surface layer of anatase was 0.3 μm for monthly replacement but only 0.1 μm when the leachant was replaced frequently. Overall, the results suggest that release of actinides from Synroc are controlled by solubility limiting effects at the surface area to volume ratios employed in MCC-1 tests.

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