Kinetics of fluoride ion release from dental restorative glass ionomer cements: the influence of ultrasound,radiant heat and glass composition

To compare the effect of ultrasonic setting with self curing on fluoride release from conventional and experimental dental glass ionomer cements. To compare hand mixed and capsule mixing and the effect of replacing some of the reactive glass with zirconia. In a novel material which advocated using radiant heat to cure it, to compare the effect of this with ultrasound. To evaluate the effect of ultrasound on a glass ionomer with fluoride in the water but not in the glass. 10 samples of each cement were ultrasonically set for 55 s; 10 controls self cured for 6 min. Each was placed in 10 ml of deionised water which was changed at 1, 3, 7, 14, 21, 28 days. The solution fluoride content was measured using a selective ion electrode. All ultrasound samples released more fluoride than the controls. Release patterns were similar; after a few days, cumulative fluoride was linear with respect to t^1/2. Slope and intercept of linear regression plots increased with ultrasound. With radiant heat the cement released less fluoride than controls. The effect of ultrasound on cement with F in water increased only slope not intercept. Zirconia addition enhances fluoride release although the cement fluorine content is reduced. Comparison of capsule and hand mixing showed no consistent effect on fluoride release. Ultrasound enhances fluoride release from GICs. As heat has an opposite effect the heat from ultrasound is not its only action. The lesser effect on cement with fluoride only in the water indicates that of ultrasound enhances fluoride release from glass.     

含AlF3和ZrF4氟化物玻璃的分相与析晶

以摩尔组成为8．7MgF2-17．4CaF2-8．7SrF2-13．3BaF2-13．0YF3-31．6．AlF3-7．3ZrF4的氟化物玻璃为对象，研究了玻璃的分相和析晶．研究表明，玻璃中同时含有AlF3和ZrF4时，玻璃产生明显的分相，玻璃在高温下对水比较敏感，容易产生表面析晶．玻璃内部的析晶主要来自稳定性较差的富Al相，受空气中水分的影响，玻璃表面的析晶首先产生于富Zr相．依据玻璃的分相和析晶表现，讨论了含AlF3和ZrF4氟化物玻璃的表面析晶机理．     

Characteristics of equilibrium, kinetics studies for adsorption of fluoride on magnetic-chitosan particle

The magnetic-chitosan particle was prepared and characterized by the SEM, XRD, FT-IR and employed as an adsorbent for removal fluoride from the water solution in the batch system. The Langmuir isotherms, Bradley's isotherm, Freundlich isotherm and Dubinin-Kaganer-Radushkevich (DKR) isotherm were used to describe adsorption equilibrium. The kinetic process was investigated using the pseudo-first-order model, pseudo-second-order model and intra-particle diffusion model, respectively. The results show that the magnetic-chitosan particle is amorphous of irregular clumps in the surface with groups of RNH(2), RNH(3), Fe-O, etc. Bradley's equation and two-sites Langmuir isotherms were fitted well with the adsorption equilibrium data; the maximal amount of adsorption of 20.96-23.98 mg/l and free energy of 2.48 kJ/mol were obtained from the Bradley's equation, two-sites Langmuir isotherm and DKR modeling, respectively. The pseudo-second-order with the initial adsorption rate 2.08 mg/g min was suitable to describe the kinetic process of fluoride adsorption onto the adsorbent. In overall, the major mechanism of fluoride adsorption onto the heterogeneous surface of magnetic-chitosan particle was proposed in the study.     

Interaction of InAs and InSb with aqueous solutions of nitric acid

InSb dissolution in 7.8–15.6 N HNO₃ is controlled by the oxidizer diffusion to the surface. InAs dissolution in 15.6 N HNO₃ is controlled by diffusion in solution; at low acid concentrations, the dissolution rate is limited by diffusion through the loose oxide layer forming on the sample surface. The different dissolution kinetics of InAs and InSb in HNO₃ can be explained by the different properties of the surface layers of hydrous arsenic and antimony oxides.     

氢化锆在高温水蒸气中的氧化行为

通过恒温恒压氧化实验研究了氢化锆在300~700℃高温水蒸气中的氧化行为。结果表明,氢化锆的质量增重随着氧化温度的升高而增大。在氧化过程进行15h以后,OH-/O在氧化膜中的内扩散成为氧化反应的控速步骤。水蒸气中的H抑制了氢化锆在高温氧化条件下的氢损失。氧化膜主要由单斜相M-ZrO2组成,氧化膜的最外层由四方相T-ZrO2和立方相C-ZrO2组成。     

Effect of distilled water on the optical properties and surface degradation of Zr-Ba based glass

Work has been performed to investigate the effect of distilled water on the optical properties and surface degradation of the glass known as ZBLAN, that could be employed as an optical fiber. Employing spectral techniques through the use of optical spectra, exposure of this material to an aqueous environment was found to cause weakening of the glass structure and a loss in signal transmission of the material. Also using methods normally applied in the corrosion of metals and alloys, like weight loss, our data has revealed that fluoride glass containing significant levels of Zr and Ba were highly unstable in the presence of water, produced a corrosion potential, and may possibly under go electrochemical rather than chemical dissolution, which in turn allowed formation of enriched Zr and Ba surface films. Presently the exact mechanism of degradation is unclear. This instability and degradation, showed an important deterioration in the optical properties of the glass, and brings into question the selection of Zr-Ba glass as optical fiber material or its use in electronic circuits where humidity may exist.     

Deposition of biomimetic biocompatible oxides on metallic glass surface by electro-discharge coating process

Bulk metallic glass demonstrates superior mechanical properties and excellent bio-mechanical stability compared to routinely used biomaterials like titanium, cobalt-chromium, stainless steel, et cetera. However, the metallic glass surface do not easily adhere to the leaving tissues due to native bio-inert oxide layer, which have poor wear resistance and low hardness. In this current study an innovative method for surface coating of bulk metallic glass by mixing hydroxyapatite powder during electro-discharge machining has been employed. A biomimetic nano-porous bio-ceramic layer of oxides and carbides was deposited on metallic glass surface. The modified surface integrity and composition were investigated by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction characterization techniques. The characterization results confirmed the formation of a natural bone-like nano-porous surface topography on the metallic glass surface using a novel hydroxyapatite-mixed electro-discharge coating process. In addition, a favourable surface chemistry in the form of bioceramic carbides (zirconium carbide, titanium carbide) and zirconium oxide layers, was achieved.     

Surface tension and density of copper–Zirconium alloys in contact with fluoride refractories

The surface tension and density of copper–zirconium alloys were measured over a wide range of zirconium concentration (from 7.182 to 74.0 at.%) at temperatures between 1000 and 1250^°C by the “large drop” method in cups made on calcium fluoride. The surface tension and density polytherms are straight lines with negative temperature coefficients. The excess volume of mixing is negative, the maximum decrease in volume, observed for a 47.0 at.% Zr alloy, being 3.4%     

Kinetics of barium molybdate crystallization from lithium chloride melts

The kinetics of crystal growth of barium molybdate from unstirred supersaturated solutions of molten lithium chloride has been studied at 700 and 800° C. The growth is shown to be controlled by the rate of diffusion up to an extent of 35% and 56% at the two temperatures. At first the growth occurs characteristically by slow diffusion transport of the solute through the solution on to the crystal surface and later by a surface-reaction controlled mechanism.     

Kinetics of fly ash leaching in strongly alkaline solutions

We have leached fly ash samples from six power stations in potassium hydroxide solutions at a water-to-solid mass ratio of 40 g/g. A wet chemical method was developed which provides for a detailed characterization of the reactivity of fly ash. The leaching process could be divided into three stages. In stage one, reaction progress measured by the relative mass of fly ash reacted (α) was controlled by the rate of glass network dissolution while very little gel formed (α < 0.1). In stage two, more gel (mainly oxides of Fe, Ca, Mg, and Ti) formed on the glass surface, and the rate of glass dissolution was limited by diffusion (0.1 < α < 0.45). In stage three, zeolite crystallized on top of the gel layer, and an aluminosilicate gel formed in situ, while diffusion continued to control reaction progress (α > 0.45). The data were modeled using a modified Jander equation and rate constants were calculated for each process. The rate constants for stage one reflect an intrinsic glass property, chemical durability, which increased linearly with increasing concentration of network formers in the glass phase of a fly ash.     

Aqueous Sol-Gel Coating of Pitch-Based Graphite Fibers for Inclusion in Aluminum Matrix Composites

A coating on graphite is required to provide a wettable surface and prevent reaction between the graphite and the molten metal during the fabrication of high thermal conductivity metal matrix composites. An aqueous sol-gel procedure using zirconium acetate precursors to form continuous, crack-free, bridge-free zirconia coatings approximately 0.1 µm thick on graphite fibers 10 µm in diameter is described. Parameters were determined for dip-coating the fibers as a tow in an aqueous zirconium acetate solution and developing the coating structure by thermal desiccation, pyrolysis, and crystallization in a controlled environment.     

Photoinduced recovery of gamma-irradiated fluoride glasses

Radiation-induced changes in the optical properties of fluoride glasses (FGs) were studied on samples of zirconium fluoride and aluminum fluoride based compositions gamma-irradiated to a total dose of 1.2 MGy. Upon exposure, the fundamental absorption edge smears and shifts toward longer wavelengths. The FGs studied exhibit self-recovery of the optical properties, whereby the radiation-induced absorption decreases in the course of storage without action of any external factors. Photostimulated recovery of the optical properties of the gamma-irradiated FGs was studied in the range of light wavelengths from 400 to 1200 nm at a light intensity of 1–3 mW/cm². The maximum rate of recovery for both zirconium and aluminum fluoride based glasses was observed for the photoannealing at 600 nm.     

Doping of glass with lithium ion

Doping of glass with lithium ion can be accomplished by exposing the glass to a solution of organic solvent containing a soluble lithium ion salt, such as LiBr and a small amount of water. Under such conditions, the activity of solvated Li+ is very high causing it to partition into the hydrated glass surface. Laser-induced breakdown spectroscopy and atomic absorption spectroscopy have been used to monitor the partitioning between glass and organic phase, respectively.     

Manufacturing‐induced surface contaminations

In the course of classical optics manufacturing glass components are in permanent direct contact with aqueous operating materials. Such contact leads to a certain absorption of water and hydrogenous compounds that may induce severe glass defects. In this contribution, absorption of hydrogen and other contaminants during grinding of glass was observed and qualitatively detected via laser‐induced breakdown spectroscopy. It is shown that hydrogen, calcium, magnesium, and carbon are implanted into the glass surface where the contaminant concentration increases over grinding time or contact time of the glass surface with water and the grinding tool, respectively. The contaminants hydrogen, calcium, and magnesium can be attributed to the water used as lubricant. In contrast, carbon most likely originates from wear debris of the used silicon carbide grinding pads. Several possible mechanisms that lead to such surface contamination of glasses during grinding – diffusion, accumulation in micro cracks as well as the formation of hydrated silica – are finally introduced.     

Triplet-state photoexcitation dipole-jump relaxation method to observe adsorption/desorption kinetics at a reversed-phase silica/solution interface

Electronic excitation of a probe chromophore can lead to a change in dipole moment that influences its activity or solubility in solution and changes its relative affinity for partitioning between two phases. Photoexcitation of a probe molecule can, therefore, perturb a sorption equilibrium, and the relaxation kinetics of the probe to the new equilibrium conditions can be monitored in a time-resolved luminescence experiment. The adsorption/desorption kinetics of rose bengal, distributed between a C-18 derivatized porous-silica surface and a liquid mobile-phase solution, were investigated. These kinetics were determined by observing their effect on the phosphorescence decay of the triplet state of rose bengal and its quenching by ferricyanide. The methanol/water solvent compositions were varied to alter the fraction of adsorbed rose bengal. The adsorption rate constant for the triplet state was determined from the dependence of the phosphorescence relaxation rate on dye concentration in solution. The results indicate that the adsorption kinetics are diffusion controlled and that the relaxation is influenced by efficient triplet-energy transfer between excited- and ground-state rose bengal at the C-18 silica/solution interface.     

Separation of fluoride from fluoroelastomers by diffusion in test tubes.

The conventional procedure for separation of fluoride as trimethylfluorosilane in Conway diffusion cells involves the use of grease for sealing the cell and also for closing the hole in the lid drilled for introduction of hexamethyldisiloxane. We have developed a simpler procedure in which diffusion is carried out in 5-mL test tubes without the use of grease. Results of analysis of fluoride following diffusion from water, urine, and bone samples are in excellent agreement with those obtained by other procedures not involving diffusion. Separation of fluoride from partly and fully cured fluoroelastomers is achieved by first grinding the samples in a liquid nitrogen mill and then using methyl ethyl ketone as an adjuvant to perchloric acid employed in the diffusion procedure.     

The fabrication and properties of Zr-O-F ceramics for the immobilization of Zircaloy nuclear waste

The hot-pressing behaviour of hydrated zirconium oxide (with fluoride) derived from Zircaloy nuclear waste is described. The material densifies at relatively low temperatures to give a crystalline ceramic with monoclinic ZrO₂ and an oxyfluoride (Zr₁₀O₁₃F₁₄) as major phases. Doping with the inactive radwaste ions U⁴⁺, Sr²⁺ and Cs⁺ has shown that these should be taken into solid solution in the ceramic at the levels at which they are likely to be present in actual waste. Dissolution tests are described which establish that the ceramics are resistant to attack by water and hence should provide suitable leachresistant hosts for the immobilization of the radwaste ions.     

Properties of Sm 3 + ions in fluorozirconate fiber

The spectroscopic properties of Sm3 + ions in fluorozirconate fiber are presented. We found that our results were not in full agreement with previous research on Sm3 +doped silica. We observed that the visible emission bands have a relative strength closer to unity, and we measured a fluorescence lifetime that is three times longer than previously reported. The implications of these findings on the role of Sm3 + in zirconium barium fluoride glass and on the operation of Sm3 + doped fiber devices are discussed.     

Oxidation kinetics of zirconium in water vapour between 750 and 1250°C

The zirconium oxidation has been followed in H₂/H₂0 gas mixtures by microgravimetry and morphological observations between 750 and 1250°C. The reaction rate is governed by a mixed regime of oxygen diffusion through multiplex oxide layers of zirconia and an oxygen solid solution. After the metal core has disappeared the reaction proceeds by direct oxidation of the solid solution. Different kinetic behaviours have been shown according to the phase couples present.