Kinetic study of uranium residue dissolution in ammonium carbonate media

The purpose of this study was to determine the kinetics of the dissolution of a uranium residue in ammonium carbonate media. The residue is generated in the production of medical isotopes. The effects of parameters, such as varying peroxide and carbonate concentrations, dissolution time as well as temperature on the extraction rate have been separately studied. Results indicate complete dissolution of the residue at 60 °C, after 30 min, in ammonium carbonate solution enriched with hydrogen peroxide. The yield and rate of uranium extraction were found to increase as a function of both temperature, in the range of 25–60 °C, and hydrogen peroxide concentration. The extraction process was governed by chemical reaction as the activation energy was found to be 45.5 kJ/mol. The order of reaction with respect to uranium concentration was found to be approximately first order.     

Preparation and evaluation of oral dosage form using acylglycerols. II. Effect of food ingestion on dissolution and absorption of aspirin from the granules prepared by acylglycerols in human subjects.

The dissolution behavior of the aspirin enteric granule prepared using acylglycerols, glyceryl monostearate (GMS) and glyceryl trilaurate (GTL), was investigated in vitro and in human subjects in a fasting or non-fasting state. Aspirin was slowly released from the granule in vitro at pH 1.2. No acceleration of the aspirin dissolution rate in the medium without lipase and cholic acid was observed when the pH level of the medium increased to a neutral region (pH 6.4). However, the dissolution of aspirin was significantly increased by increasing the concentrations of lipase and cholic acid in the medium. Lipase appears to play an essential role in the dissolution process of aspirin granules. In human subjects, the average levels of the cumulative amount of total salicylate excreted in a urine-time curve, and the mean residence time (MRT) obtained after oral administration of a granule in the fasting state were markedly delayed in comparison with the results observed using an aqueous solution and a crystalline form of aspirin. In comparing the fasting condition with the non-fasting condition (after food ingestion), no significant difference was recognized in the total amount of salicylate excreted in urine to an infinite time (Ae(infinity)), whether the MRT was obtained by granule, crystalline form or aqueous solution. It can be concluded that aspirin granule prepared by GMS and GTL has a property of pancreatic lipase-sensitive dissolution, and its bioavailability is unaffected by food intake.     

过硫酸铵水溶液对聚乙烯表面作用的研究

本文利用X光电子能谱(XPS)及其它技术对过硫酸铵水溶液处理聚乙烯表面改进粘合性的作用机理进行了研究。结果表明,过硫酸铵的氧化作用使聚乙烯表面引入酮、醛、羧基等含氧基团,使其粘合强度显著提高。高密度聚乙烯表面的氧化深度小于40,低密度聚乙烯的均匀氧化深度在40—90之间。处理后的聚乙烯表面未发现明显的交联产物。     

Dissolution Behavior of Irradiated Mixed-oxide Fuels with Different Plutonium Contents

The effects of Pu content on the dissolution rate and the mass of the insoluble residue of irradiated mixed oxide fuel were studied. On the basis of the kinetic analysis assuming the surface-area model, the dissolution rate was found to decrease exponentially with an increase of the Pu content, but those were estimated to be up to 10³ times larger than non-irradiated fuels. The mass of the insoluble residue tended to increase with an increase of the Pu content, possibly due to the promotion of fission product formation and an increase of refractory Pu enriched zone.     

Mussel adhesive protein mimetic polymers for the preparation of nonfouling surfaces

A new biomimetic strategy for modification of biomaterial surfaces with poly(ethylene glycol) (PEG) was developed. The strategy exploits the adhesive characteristics of 3,4-dihydroxyphenylalanine (DOPA), an important component of mussel adhesive proteins, to anchor PEG onto surfaces, rendering the surfaces resistant to cell attachment. Linear monomethoxy-terminated PEGs were conjugated either to a single DOPA residue (mPEG-DOPA) or to the N-terminus of Ala-Lys-Pro-Ser-Tyr-Hyp-Hyp-Thr-DOPA-Lys (mPEG-MAPD), a decapeptide analogue of a protein found in Mytilus edulis adhesive plaques. Gold and titanium surfaces were modified by adsorption of mPEG-DOPA and mPEG-MAPD from solution, after which surface analysis by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy confirmed the presence of immobilized PEG on the surface. The ability of modified surfaces to resist cell attachment was examined by culturing 3T3 fibroblasts on the surfaces for up to 14 days. Quantitative image analysis revealed that cell adhesion to mPEG-DOPA and mPEG-MAPD modified surfaces decreased by as much as 98% compared to control surfaces. Modified Ti surfaces exhibited low cell adhesion for up to 2 weeks in culture, indicating that the nonfouling properties of mPEG-DOPA and mPEG-MAPD treated surfaces persist for extended periods of time. This strategy paradoxically exploits the strong fouling characteristics of MAP analogues for antifouling purposes and may be broadly applied to medical implants and diagnostics, as well as numerous nonmedical applications in which the minimization of surface fouling is desired.     

Uranium ore processing: Kinetics of the growth and dissolution of a potential host solid from a model surface

As part of an investigation concerning the fate of²²⁶Ra during uranium ore milling and long-term tailings storage, we have investigated the growth of potential host solids-barium sulfate and lead sulfate-on mica, a model surface. The kinetics of dissolution of barium sulfate-and of a barium sulfate solid containing²²⁸Ra as a trace component into 10^–3M sulfuric acid were subsequently investigated using a flow-cell and radiotracer techniques. It was found that ther dissolution of both the barium sulfate host and the²²⁸Ra trace component was congruent. The dissolution reaction appears to be surface controlled.     

神府次烟煤在不同温度下的热溶产物表征

利用FT-IR、热重、GPC以及同步荧光分析等对神府次烟煤在不同温度条件下的1-甲基萘热溶物和热溶残煤进行了表征。结果表明,热溶物中含有较多的脂肪结构,灰分几乎全部转移至残煤中;热溶残煤与神府原煤的热失重特性存在明显差别;在300~360 ℃,随着温度升高,热溶物数均分子量呈增加趋势,进一步提高温度,分子量减小;热溶物缩合芳环数随着温度升高而增加。据此表明,在低于煤初始热解温度下神府次烟煤的热溶主要以溶剂化作用破坏煤中的非共价键为主,其中,酮、酯等轻质组分易于脱除;而高于煤初始热解温度的热溶过程则伴有侧链和桥键等弱共价键断裂的热解反应和自由基缩聚反应,热溶物中三环等稠环芳香结构增加。     

Evaluation of some dry ashing methods for anodic stripping voltammetric determination of cadmium and lead in biological materials

Several dry-ashing methods were evaluated for the accurate determination of cadmium and lead in biological materials by anodic stripping voltammetry. The method utilizing sulphuric acid as the ashing aid at 500°C was found to be most suitable for the determination of both elements. However, a carbonaceous residue still required that substantial sample dilution be made after dissolution of the sample ash to avoid interferences to the stripping electrode process(es). The dissolution of the sample ash with hydrochloric acid as preferred to the use of nitric acid in obtaining more reproducible results.     

形状记忆聚合物表面水下油黏附性的可逆调控

采用模板法在形状记忆聚合物表面获得一种具有形状记忆特征的表面微结构, 在氧等离子作用下, 表面呈现低黏附的水下超疏油特性. 在外压作用下, 表面微结构发生坍塌, 失去水下超疏油性, 同时表面对油滴呈高黏附特征. 在120 ℃热处理后, 表面微结构恢复到了原始状态, 在等离子进一步作用下, 表面即可恢复到最初的低黏附水下超疏油状态. 因此通过外压、 热处理及等离子作用即可实现对表面微结构及其水下油黏附性能的可逆调控. 研究表明, 表面不同的微结构状态赋予表面不同的黏附性能, 在原始表面液滴处于低黏附的Cassie态, 而在坍塌结构表面水滴处于高黏附的Wenzel态.     

Reaction rates and dissolution mechanisms of quartz as a function of pH

In this computational study, we present the dissolution rates for quartz as a function of pH at 298 K. At any given pH, the dissolution of the quartz surface depends on the distribution of protonated, deprotonated, or neutral species. The dissolution mechanism for each of these three species was investigated by ab initio electronic structure calculations to obtain the reaction profile. Using the barrier height along with the partition functions for the transition state and the reactants in the rate-limiting steps, we calculated the TST rate constants for the reactions for the temperature range of 200-500 K. At 298 K the rate constant (s-1) for the dissolution of neutral species was found to be several orders of magnitude smaller than the rate-limiting steps for the protonated and deprotonated species. The values of the rate constants were used in the rate law expression to calculate the overall dissolution rate (mol m-2 s-1) at a given pH. The calculated rates were compared to previously reported experimental and theoretical rates and were found to be in good agreement over 2-12 pH range.     

Dissolution of ZnO nanoparticles at circumneutral pH: a study of size effects in the presence and absence of citric acid

Understanding size-dependent processes, including dissolution, of engineered nanoparticles is essential in addressing the potential environmental and health impacts of these materials as well as their long-term stability. In this study, experimental measurements of size-dependent dissolution of well-characterized zinc oxide (ZnO) nanoparticles with particle diameters in the range of 4 to 130 nm have been measured at circumneutral pH (pH 7.5) and compared. Dissolution was found to be enhanced with smaller ZnO nanoparticles compared to larger-sized particles, even though the nanoparticles were present in solution as aggregates with hydrodynamic diameters on the order of 1-3 μm in size. The presence of citric acid significantly enhanced the extent of ZnO dissolution for all sizes, and the greatest enhancement was observed for the 4 nm particles. Although these results are found to be in qualitative agreement with theoretical predictions, a linearized form of the Kelvin equation to calculate a surface free energy yielded quantities inconsistent with expected values from the literature. Reasons for this inconsistency are discussed and include potential deviations of solubility behavior from classical thermodynamics as a result of a lack of detailed knowledge of surface structure and surface properties, including the presence of different surface crystal facets, and the aggregation state.     

Rheological analysis and quantitative evaluation of wet kneaded wax matrix

The properties of the wet kneaded wax matrix were evaluated using a compression tester, whereby a newly proposed sigma index for the plastic deformation was assessed in the pressure transmission diagram. The sigma index was indicative of a characteristic of the plastic yield point in the rheological behavior, and presented an initial and abrupt deformation of wet kneaded mass when the wet kneaded mass was subjected to the pressure. The value of sigma index was confirmed to decrease along with an increase in the plasticity of wet kneaded mass. The wet mass of wax matrix was prepared under various kneading time, and then extruded. The properties of the extruded granules such as pore volume, strength and dissolution were investigated. As a result, it was found that the sigma index decreased with an increase in kneading time. The granules with small value of sigma index showed few porosities, large strength and slow dissolution. It was demonstrated that the sigma index linked the characteristics of wet kneaded mass to the dissolution and the other granule properties. Existence of this link was revealed by sigma index evaluation relevant to the plasticity. The sigma index could be a decisive criterion to permit an in-process evaluation of the kneading progress quantitatively, and also useful for anticipating the dissolution of the final granules roughly.     

Preparation of a novel magnetic powder resin for the rapid removal of tetracycline in the aquatic environment

Magnetic powder resin Q150 with high specific surface area of 1074 m~2/e was prepared by the membrane emulsificationsuspension polymerization technique.Adsoption of tetracycline on the obtained sorbent Q150 was evaluted by using the granule resin(GR) XAD-4,the powder activated carbon(PAC) 1240AC and the granule activated carbon(GAC) HD4000 for comparison.It was found that Q150 had a larger adsorption capacity,faster kinetic and easier regeneration under alkaline condition.The results suggested that the powder resin(PR) Q150 would be a promising sorbent for removing antibiotics and even other organic micropollutants from the aquatic environment.     

An improved meniscus surface model for contacting rough surfaces

Based on the Extended-Maugis-Dugdale (EMD) elastic theory, a single asperity capillary meniscus model considering asperity deformation due to both contact and adhesive forces was developed. Specifically included in the single asperity meniscus model was the solid surface interaction inside the contact area. Subsequently, the single asperity model was coupled with a statistical roughness surface model to develop an improved meniscus surface model applicable to a wide-range of humidity levels and adhesion parameter values. Simulations were performed using typical surfaces found in microelectromechanical systems (MEMS) and magnetic storage hard disk drives to examine the effects of surface roughness and relative humidity. It was found that smoother surfaces give rise to higher adhesive and pull-off forces, and at higher relative humidity levels, the capillary force governs the adhesive behavior. As the humidity decreases, the solid surface interaction increases and needs to be included in the total meniscus adhesion. By integrating the adhesive force-displacement curves, the adhesion energy per unit area was calculated for MEMS surfaces and favorably compared with reported experimental data.     

On the dissolution of cellulose in tetrabutylammonium acetate/dimethyl sulfoxide: a frustrated solvent

We have found that the dissolution of cellulose in the binary mixed solvent tetrabutylammonium acetate/dimethyl sulfoxide follows a previously overlooked near-stoichiometric relationship such that one dissolved acetate ion is able to dissolve an amount of cellulose corresponding to about one glucose residue. The structure and dynamics of the resulting cellulose solutions were investigated using small-angle X-ray scattering (SAXS) and nuclear magnetic resonance techniques as well as molecular dynamics simulation. This yielded a detailed picture of the dissolution mechanism in which acetate ions form hydrogen bonds to cellulose and causes a diffuse solvation sheath of bulky tetrabutylammonium counterions to form. In turn, this leads to a steric repulsion that helps to keep the cellulose chains apart. Structural similarities to previously investigated cellulose solutions in aqueous tetrabutylammonium hydroxide were revealed by SAXS measurement. To what extent this corresponds to similarities in dissolution mechanism is discussed.     

MSINDO study of acid promoted dissolution of planar MgO and NiO surfaces

Despite the structural similarity, MgO is fast dissolving in low pH solution, whereas NiO is slow dissolving under the same conditions. In addition, the planar MgO (100) surface immediately reconstructs to form pits and protrusions, whereas this behavior has not been observed with NiO (100). Our previous study, using the semiempirical self-consistent field molecular orbital (SCFMO) method MSINDO showed that it was possible for MgO dissolution but not NiO dissolution to occur via the migration of a metal-oxygen pair to an ex situ position. However, we have now found a more energetically favorable and realistic dissolution mechanism involving the dissociation of a water molecule (adsorbed on a metal site) prior to migration. Products from this dissociation (H and OH) weaken adjacent metal-oxygen bonds. Dissociation of a second adsorbed water molecule is required to complete the process. For both oxides, the energy barrier determined from the energy profile of the metal-oxygen pair migration was found to be lower than the activation energy of water dissociation at the planar surface as reported in previous study. This would suggest that the dissociation of water molecules at the planar surface is rate-determining in the surface restructuring step of dissolution. It was demonstrated that surface restructuring and dissolution of MgO is possible whereas highly improbable for NiO, in agreement with experimental observations.     

Microstructure and composition of annealed Al/Ti-metallization layers

Al/Ti multilayers with columnar grains were deposited by electron-beam evaporation on piezoelectric LiNbO₃ substrates. After annealing in air and under vacuum conditions dissolution of the Ti interlayer was observed for all samples. The original Ti interlayer dissolved completely and globular Al₃Ti grains were formed within an Al matrix. All samples had an oxidized adhesive Ti bottom layer and a 10 nm thin Al layer below this adhesive Ti bottom layer, which remains intact after the applied heat treatment. This resistance against dissolution by interdiffusion could be caused by the oxidation. These changes in the microstructure and in the chemical composition were investigated by conventional and analytical TEM.     

Trace element analysis of sediments by HR-ICP-MS using low and medium resolution and different acid digestions

For the multielement analysis of sediments (Li, Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Mo, Cd, Sn, Sb, Cs, Ba, lanthanides, Hf, Tl, Pb, Bi, Th, U) a dissolution with a hydrofluoric - sulfuric - nitric acid mixture, subsequent evaporation of the acids, dissolution of the residue by HCl, evaporation of the acid and redissolution of the residue by HNO₃ is a useful procedure which allows the dissolution of a wide range of mineral mixtures. An ICP-MS was used for the determination of the elements. For Cr, Ni, Cu and Zn the analysis may be complicated by the interferences of sulfur or chlorine species, which remain in the solution during dissolution. The best analytical results for these elements can be achieved in the medium resolution mode of a HR-ICP-MS. In the low resolution mode (quadrupole instrument characteristics) the determination of these elements should be performed by the isotopes of ⁵²Cr, ⁶²Ni, ⁶³Cu, ⁶⁸Zn as it was found that interferences from remaining acids are of minor importance. Received: 2 January 1997 / Revised: 17 March 1997 / Accepted: 25 March 1997     

Structural Characteristics and Permeability of Ethyl Cellulose Films Containing Different Plasticizers

The effect of different type of plasticizers was investigated in ethyl cellulose as coating polymer for manufacturing coated pellets of modified release containing a water soluble model drug. Scanning electron microscopic image analysis (SEM), differential scanning calorimetry (DSC), X-ray photoelectron spectroscopic chemical surface analysis (XPS) were used to study the films, and the dissolution profiles of coated pellets were evaluated. The effect of the different plasticizers and coating levels on the first order dissolution rate constant is determined by statistical experimental design. Correlation was found between the dissolution rate constant and the structural characteristics of the coating layer containing different plasticizers. Partial segregation of the plasticizers was detected especially on the surface of the films, which is in correlation with the differences in the glass transition temperatures. PEG 400 is found to be compatible enough to form continuous, durable EC coating at 5% concentration level, which gave the slowest dissolution.     

Competition-based transfer of carbohydrate expression information from a cell-adhered surface to a secondary surface

An information transfer strategy was developed for the visualization of carbohydrate expression by the competition of a primary cell-adhered solid surface with a carbohydrate assembled surface as an artificial secondary surface for one species. The strategy could be effectively utilized for in situ monitoring of dynamic carbohydrate expression on an adhesive cell surface.