Dissolution kinetics of fluorapatite in the hydrochloric acid solution

A thermochemical study of hydrochloric acid attack of synthetic fluorapatite was performed by a DRC. The calculated thermogenesis curves show one peak. The plot of the heat quantity as a function of the dissolved mass undergoes only one straight segment, and the thermogenesis curves present a single peak, suggesting the occurrence of a one-step dissolution process. The dissolution kinetics was examined according to the heterogeneous reaction models and showed that the dissolution is controlled by the product layer diffusion process with a reaction rate expressed by the following semiempirical equation; \(\left[ {1 + 2(1 - X) - 3(1 - X)^{{\frac{2}{3}}} } \right] = 3195 \times 10^{ - 2} C^{0.145} \left( {\frac{S}{L}} \right)^{ - 0.628} e^{{ - \frac{2600}{\text T}}} t\). The activation energy was determined as 21.6 ± 1.5 kJ mol^?1     

Resonant photoadsorption of uranyl ions in solution

Experimental evidence is given for the photoadsorption of uranyl ions in solutions, under the selective action of laser radiation. The effect was studied in two different systems involving uranyl solutions in contact with the surfaces of a ZnSe plate or a silicon wafer, respectively. Infrared spectrophotometrical methods as well as the measured value of the dielectric breakdown field showed in both cases an accumulation of resonant ions on the irradiated sites.     

Squarete complexes of uranyl ions in aqueous solution

The stability constants of UO ₂ ²⁺ -squarate complexes are measured at ionic strengths of 0.05M, 0.06M, 0.075M, 0.09M, 0.1M (squaric acid-perchloric acid) using a solvent extraction method at a pH of 1.1 and a temperature of 25 °C. The extractant used is dinonylnaphthalenesulfonic acid in n-heptane. The aqueous phase was made of a mixture of squaric and perchloric acid and²³³U radio tracer. The stability constants of squarate complexes of UO ₂ ²⁺ is seen to decrease linearly with the square root of the ionic strength.     

Surface modification of EPDM rubber by plasma treatment

The effect of argon, oxygen, and nitrogen plasma treatment of solvent cast EPDM rubber films has been investigated by means of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and surface energy measurements. Plasma treatment leads to changes in the surface energy from 25 to 70 mN/m. Treatment conditions influenced both the changes in surface energy and the stability, and it became more difficult to obtain good contact angle measurements after longer (> ca. 4 min) treatment times, probably because of an increasingly uneven surface structure. XPS analyses revealed that up to 20 at. % oxygen can be easily incorporated and that variations of approximately 5% can be controlled by the plasma conditions. Oxygen was mainly found in hydroxyl groups, but also as carbonyl and carboxyl. XPS analyses showed more stable surfaces than expected from contact angles, probably because XPS analysis is less surface sensitive than contact angle measurements. AFM measurements revealed different surface structures with the three gases. The surface roughness increased generally with treatment time, and dramatic changes could be observed at longer times. At short times, surface energy changes were much faster than the changes in surface structure, showing that plasma treatment conditions can be utilized to tailor both surface energies and surface structure of EPDM rubber.     

Surface modification of natural cellulose substances:toward functional materials and applications

Combining various synthetic chemical processes and biological assemblies provides a promising strategy for the design and fabrication of functional materials with tailored structures and properties.The unique multilevel structures and morphologies of natural cellulose substances such as ordinary commercial laboratory filter paper make them ideal platforms for the self-assemblies of various functional guest molecules that are to be deposited on the surfaces of their fine structures,and the resulting composite matters show significant potentials for various applications.The surface sol-gel process was employed to deposit ultrathin metal-oxide(e.g.,titania and zirconia)gel films to coat the cellulose nanofibers in bulk filter papers;thereafter,monolayers of specific guest substrates were immobilized onto the surfaces of the metal-oxide gel films.Highly selective,sensitive,and reversible chemosensors based on the surface modification of filter paper were obtained toward the fluorescence and colorimetric detection of various analytes such as heavy-metal ions,inorganic anions,amino acids,and gases.Cellulosebased composite materials with superhydrophobic,antibacterial,or luminescent properties were fabricated by self-assembly approaches toward practical applications.     

Surface modification of synthetic and natural fibres by fixation of cyclodextrin derivatives

It is demonstrated that cyclodextrin derivatives can be fixed permanently onto polymer surfaces by functional groups using conventional technologies of textile processing. As a result of the modification process some properties of the fibres are directly influenced. But also special effects may be obtained by complexing specific chemical substances, because the fixed cyclodextrin cavities do not loose their complexing power. Conceivable fields of application are medical or technical textiles and textiles for clothing.     

Surface modification of quarry stone by hexamethyldisiloxane plasma treatment

The surface of quarry stone was modified by continuous plasma polymerization of hexamethyldisiloxane. The hydrophilic surface of the quarry stone was made hydrophobic and impermeable to water. Three different reaction times were analyzed. All of them resulted in the formation of a homogenous layer on the quarry stone surface. Contact angle and FT‐IR analyses show that the hydrophobic character of the surface is due to methyl groups on the surface. The change in the contact angle with temperature and the wetting temperature (T_w) are also discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Surface modification of natural rubber film by polymerisation of methyl methacrylate in water-based system

Polymerisation of methyl methacrylate (MMA) on the surface of natural rubber (NR) film was studied in order to increase the surface hardness, roughness and, hence, to decrease the friction coefficient of rubber. We used the two-step process: (i) swelling of MMA and tert-butyl hydroperoxide, emulsified in an aqueous solution of sodium dodecyl sulphate, onto the NR film surface, and (ii) subsequently immersing the swollen rubber strip into an alkaline aqueous solution of ferrous ion/fructose for redox initiation. The presence of PMMA on the NR surface was examined by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). Increasing the concentration of ferrous ion caused an increase in MMA conversion. The surface morphology observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) in tapping mode revealed the aggregation of micronmetre-scale nodules on the modified surface. The surface hardness and roughness increased with increasing PMMA content.     

Determination of free acidity in uranyl solution by pH measurement

In this paper the modification of Ahrland's method for the determination of free acidity of uranyl solutions has been studied. The modified method gave satisfactory results because the free acidity of original saturated ammonium sulphate solution was considered. Relative error of the determination was less than 5%. Moreover this modification method is suitable for uranyl solutions containing relatively high concentrations of uranium and ratio of uranium to acid.     

The polarographic electroreduction of uranyl ion in arsenic acid solution

The electroreduction of uranyl ion in arsenic acid studied by d.c. polarography shows one reduction wave at all the used arsenic acid concentrations corresponding to one electron reduction mechanism. At low arsenic acid concentration (0.1–0.3M) UO₂(ClO₄)₂ is reduced to HUO₂AsO₄. At higher acid concentration (0.6M) the HUO₂AsO₄ molecules are reduced to UO ₂ ⁺ (pentavalent uranium). It is also reliable to study polarographic behaviour of uranyl ions in arsenic acid solutions up topH 3.01. It is also possible to apply this method for the analytical determination of uranyl ion concentrations up to 2mM.

---

Die Polarographische Elektroreduktion von Uranyl-Ion in Arsensäurelösungen

Zusammenfassung Die Elektroreduktion von Uranyl-Ion in Arsensäurelösung zeigte bei allen untersuchten Arsensäurekonzentrationen eine polarographische Reduktionswelle, die einem Einelektronenreduktionsmechanismus entspricht. Bei niederen Arsensäurekonzentrationen (0.1–0.3M) wird UO₂(ClO₄)₂ zu HUO₂AsO₄ reduziert. Bei höheren Säurekonzentrationen (0.6M) werden die HUO₂AsO₄-Moleküle zu UO ₂ ⁺ (fünfwertiges Uran) reduziert. Das polarographische Verhalten der Uranyl-Ionen konnte bis zu einempH von 3.01 untersucht werden. Es ist möglich, diese Methode zur analytischen Bestimmung von Uranyl-Ionen bis zu einer Konzentration von 2 mM einzusetzen.

     

Surface reactions kinetics between nanocrystalline magnetite and uranyl

Magnetite is the most important end member of iron corrosion products under reducing environment, which is the condition expected in a deep geological high level radioactive waste disposal. Nanocrystalline magnetite was synthesized in the laboratory and its physicochemical properties were analyzed in detail. The kinetics of the adsorption of U(VI) and the kinetics of the actinide reduction to a lower oxidation state, in presence of the oxide, were studied by means of batch sorption techniques and X-ray photoelectron spectroscopy (XPS) analysis. The results showed that the uranium sorption and reduction processes on the magnetite surface have very fast kinetics (hours), the reduction process being triggered by sorption. XPS measurements showed that the speciation of uranium at the surface does not show significant changes with time (from 1 day to 3 months), as well as the quantity of uranium detected at the surface. The surface speciation depended on the initial pH of the contact solution. Considering that the Eh of equilibrium between magnetite and the solution, under our experimental conditions, is slightly positive (50-100 mV), the uranium reduction would also be thermodynamically possible within the liquid phase. However, the kinetics of reduction in the liquid occur at a much slower rate which, in turn, has to depend on the attainment of the magnetite/solution equilibrium. The decrease of uranium in solution, observed after the uranyl adsorption stage, and particularly at acidic pH, is most probably due to the precipitation of U(IV) formed in the solution.     

Surface modification of oxidized cellulose haemostat by argon plasma treatment

In this paper we focused on cold plasma treatment of oxidized cellulose haemostat. Oxidized cellulose was modified in inert argon plasma. The changes of surface composition were examined by XPS and FTIR. Surface morphology of fibres was studied by SEM. Gravimetry was used to study ablation and water absorption. Antibacterial effect of pristine and plasma treated samples was examined by growth of Escherichia coli and Staphylococcus epidermidis. Behaviour of pristine and plasma treated samples in water, physiological saline solution and phosphate buffered saline was observed by changes in the pH of their solutions. Modification of oxidized cellulose by inert argon plasma caused significant changes in the chemical composition of its surface layers as well as changes in morphology of those layers while maintaining or improving the antibacterial properties. We found out that modification by inert argon plasma improves the properties necessary for haemostatic function of oxidized cellulose.     

Surface modification in microchip electrophoresis

Different approaches and techniques for surface modification of microfluidic devices applied for microchip electrophoresis are reviewed. The main focus is on the improved electrophoretic separation by reducing analyte-wall interactions and manipulation of electroosmosis. Approaches and methods for permanent and dynamic surface modification of microfluidic devices, manufactured from glass, quartz and also different polymeric substrates, are described.     

Redox energetics and kinetics of uranyl coordination complexes in aqueous solution

Detailed voltammetric results for five uranyl coordination complexes are presented and analyzed using digital simulations of the voltammetric data to extract thermodynamic (E(1/2)) and heterogeneous electron-transfer kinetic (k(0) and alpha) parameters for the one-electron reduction of UO(2)(2+) to UO(2)(+). The complexes and their corresponding electrochemical parameters are the following: [UO(2)(OH(2))(5)](2+) (E(1/2) = -0.169 V vs Ag/AgCl, k(0) = 9.0 x 10(-3) cm/s, and alpha = 0.50); [UO(2)(OH)(5)](3-) (-0.927 V, 2.8 x 10(-3) cm/s, 0.46); [UO(2)(C(2)H(3)O(2))(3)](-) (-0.396 V, approximately 0.1 cm/s, approximately 0.5); [UO(2)(CO(3))(3)](4-) (-0.820 V, 2.6 x 10(-5) cm/s, 0.41); [UO(2)Cl(4)](2-) (-0.065 V, 9.2 x 10(-3) cm/s, 0.30). Differences in the E(1/2) values are attributable principally to differences in the basicity of the equatorial ligands. Differences in rate constants are considered within the context of Marcus theory of electron transfer, but no specific structural change(s) in the complexes between the two oxidation states can be uniquely identified with the underlying variability in the heterogeneous rate constants and electron-transfer coefficients.     

高氯酸溶液中激发态铀酰离子的发光衰减研究

本文以氮分子激光器为激发光源,研究了激发铀酰离子在高氯酸溶液中的发光衰减和时间分辨发光光谱.铀酰离子的发光衰减与铀浓度以及溶液的pH有关,当铀浓度Cu<10^-^3mol.dn^-^3时,溶液pH为1.5-4.0范围内,发光呈单一指数衰减;当Cu≥10^3^-mol.dm^-^3时,发现发光呈双指数衰减,即除了上述发光组份外,还观察到另一发光寿命较长的组份.用时间分辨方法测得的铀酰溶液的发光光谱表明,上述现象与激发态水合铀酰离子及其水解产物形成的发光体有关.     

Surface modification and adhesion characteristics of polycarbonate films after graft copolymerization

The surfaces of ozone-pretreated polycarbonate films were subjected to further modification by thermally induced graft copolymerization with acrylic acid (AAc), sodium salt of styrene sulfonic acid (NaSS), N,N-dimethylacrylamide (DMAA), N,N-(dimethylamino)ethyl methacrylate (DMAEMA) and 3-dimethyl(methacryloyl ethyl)-ammonium propanesulfonate (DMAPS) monomers. The structure and composition at the copolymer interface were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). For polycarbonate films with a substantial amount of grafted polymer, the hydrophilic graft penetrates or becomes partially submerged beneath a thin surface layer of dense substrate chains. This microstructure was further supported by the water contact angle measurements. Adhesive-free adhesion studies revealed that the AAc, DMAA or DMAPS graft copolymerized polycarbonate film surface adhered strongly to another similarly modified surface (homo-interface) when brought into direct contact in the presence of water and subsequently dried. The development of the lap shear strength is dependent on the concentration of the surface graft, the microstructure of the grafted surface, the adhesion (drying) time, and the nature of the interfacial interaction. The simultaneous presence of chain entanglement and electrostatic interaction readily results in substantially enhanced adhesion strengths between two DMAPS graft copolymerized surfaces or between an AAc and a DMAA graft copolymerized surface (hetero-interface). XPS analyses of the delaminated surfaces suggest that failure occurred cohesively below the graft-substrate interface. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 357–366, 1998     

Theoretical study of electron transfer in uranyl(VI)–uranyl(V) complexes in solution

The rates of the electron self‐exchange between uranyl(VI) and uranyl(V) complexes in solution have been investigated in detail with quantum chemical methods. The calculations have shown that the bond length of U? Oyl is elongated by 0.1 Å when the extra electron is localized on the sites. The diabatic potential surfaces are obtained. The inner reorganization energies are 212.6 and 226.8 kJ mol^?1 for hydroxide and fluoride bridge systems, respectively. The solvent reorganization energies are 28.12 and 31.60 kJ mol^?1 for hydroxide and fluoride bridge systems, respectively. The nuclear frequency factors are 3.17 × 10¹³ and 3.12 × 10¹³ s^?1 for hydroxide and fluoride bridge systems, respectively. The electronic coupling matrix elements are 1.89 and 4.06 kJ mol^?1 for hydroxide and fluoride bridge systems, respectively. The electron‐transfer rates of our calculations are 12.95 and 0.819 M^?1 s^?1 for hydroxide and fluoride bridge systems, respectively. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Surface modification of vinylidene fluoride-hexafluoropropylene copolymer films by direct-current discharge treatment

Changes in the contact properties of the surface of a vinylidene fluoride-hexafluoropropylene copolymer film by dc discharge treatment were studied. It was found that the modification considerably improved the contact properties of the films because of the appearance of oxygen-containing polar groups on the polymer surface. The formation of these groups was detected by X-ray photoelectron spectroscopy and Fourier-transform IR spectroscopy.