Showing papers on "Dissolution published in 2005"
TL;DR: The results from DSC and (13)C NMR indicated that LiOH/urea and NaOH/UREa aqueous solutions as non-derivatizing solvents broke the intra- and inter-molecular hydrogen bonding of cellulose and prevented the approach toward each other of the cellulose molecules, leading to the good dispersion of cellulOSE to form an actual solution.
Abstract: Rapid dissolution of cellulose in LiOH/urea and NaOH/urea aqueous solutions was studied systematically. The dissolution behavior and solubility of cellulose were evaluated by using (13)C NMR, optical microscopy, wide-angle X-ray diffraction (WAXD), FT-IR spectroscopy, DSC, and viscometry. The experiment results revealed that cellulose having viscosity-average molecular weight ((overline) M eta) of 11.4 x 104 and 37.2 x 104 could be dissolved, respectively, in 7% NaOH/12% urea and 4.2% LiOH/12% urea aqueous solutions pre-cooled to -10 degrees C within 2 min, whereas all of them could not be dissolved in KOH/urea aqueous solution. The dissolution power of the solvent systems was in the order of LiOH/urea > NaOH/urea >> KOH/urea aqueous solution. The results from DSC and (13)C NMR indicated that LiOH/urea and NaOH/urea aqueous solutions as non-derivatizing solvents broke the intra- and inter-molecular hydrogen bonding of cellulose and prevented the approach toward each other of the cellulose molecules, leading to the good dispersion of cellulose to form an actual solution.
808 citations
TL;DR: In this article, the corrosion inhibition of mild steel in 1-M hydrochloric acid solution by some 2,5-bis n -thienyl)-1,3,4-thiadiazoles (n -TTH) has been studied in relation to the concentration of the inhibitors as well as the temperature using chemical (weight loss) and electrochemical (ac impedance and dc polarisation) techniques.
794 citations
TL;DR: The solvent properties of ionic liquids, their effects on enzyme performance such as activity, stability and selectivity, and their applications in biocatalysis are discussed.
629 citations
TL;DR: Spectroscopic evidence indicates that tricarbonylamide and carbonyl functional groups of tetracycline could be responsible for sorption to mineral surfaces, which will increase understanding of the environmental occurrence, fate, and transport characteristics of antibiotics, which are considered as emerging organic contaminants.
Abstract: The effect of solution chemistry (pH, sorbate-to-sorbent ratio, ionic strength (I)) and reaction time on the sorption of tetracycline to the hydrous oxides of Al (HAO) and Fe (HFO) was examined. Sorption to HAO increased with increasing pH up to pH 7 (no such trend for HFO) above which it decreased at higher pH values for both the hydrous oxides. Experimental results indicate that ligand-promoted dissolution is occurring during tetracycline sorption to these hydrous oxides. Ligand-promoted dissolution was more significant for HAO than HFO attributable to the difference in labile surface sites between these two sorbents. The ability of tetracycline to form strong complexes with Al and Fe will increase the solubility of these minerals. Sorption of tetracycline was quite rapid and equilibrium was achieved after 8 h. However, soluble metal (Me: Al or Fe) concentrations attained equilibrium only after 24 h. Ligand-promoted dissolution appears to be a two-step process; initially, 1:1 Me-tetracycline soluble co...
432 citations
TL;DR: The products of forsterite dissolution and the conditions favorable for magnesite precipitation have been investigated in experiments conducted at temperature and pressure conditions relevant to geologic carbon sequestration in deep saline aquifers as discussed by the authors.
374 citations
TL;DR: Pokrovsky et al. as mentioned in this paper measured dissolution rates of calcite, dolomite and magnesite powders at 25 °C and pH from 3 to 4 as a function of salinity and partial pressure of CO2.
368 citations
TL;DR: In this paper, a 1-Butyl-3-methylimidazolium chloride ionic liquid has been developed for the dissolution and regeneration of wool keratin fibers, which can be used to prepare Wool keratin/cellulose blended materials directly.
348 citations
TL;DR: The immobilization of the metals during pH increase and the subsequent remobilization caused by re-acidification can be well described by a geochemical equilibrium speciation model that accounts for metal complexation at hydrous ferric oxides, for ion exchange on the zeolite surfaces, as well as for dissolution and precipitation processes.
Abstract: In this study, we investigated the removal of Fe, Pb, Cd, and Zn from synthetic mine waters by a natural zeolite. The emphasis was given to the zeolite's behavior toward a few cations in competition with each other. Pb was removed efficiently from neutral as well as from acidic solutions, whereas the uptake of Zn and Cd decreased with low pH and high iron concentrations. With increasing Ca concentrations in solution, elimination of Zn and Cd became poorer while removal of Pb remained virtually unchanged. The zeolite was stable in acidic solutions. Disintegration was only observed below pH 2.0. Forward- and back-titration of synthetic acidic mine water were carried out in the presence and absence of zeolite to simulate the effects of a pH increase by addition of neutralizing agents and a re-acidification which can be caused by subsequent mixing with acidic water. The pH increase during neutralization causes precipitation of hydrous ferric oxides and decreased dissolved metal concentrations. Zeolite addition further diminished Pb concentrations but did not have an effect on Zn and Cd concentrations in solution. During re-acidification of the solution, remobilization of Pb was weaker in the presence than in the absence of zeolite. No substantial differences were observed for Fe, Cd, and Zn immobilization. The immobilization of the metals during pH increase and the subsequent remobilization caused by re-acidification can be well described by a geochemical equilibrium speciation model that accounts for metal complexation at hydrous ferric oxides, for ion exchange on the zeolite surfaces, as well as for dissolution and precipitation processes.
346 citations
TL;DR: It has been shown that initial crystalline state is maintained following particle size reduction and that the dissolution characteristics of nifedipine nanoparticles were significantly increased in regards to the commercial product.
337 citations
TL;DR: In this paper, the performance of Fe-ZSM-5 catalysts was investigated for selective catalytic reduction (SCR) of NO by isobutane (2000 ppm NO, 1000 ppm NH3, 1% O2, 750,000 h−1).
288 citations
TL;DR: Study of the early steps of reaction of 2-microm sized particles of Bioglass, in solutions buffered with TRIS at different pH, by means of ICP-ES and FTIR spectroscopy showed that the process of silica formation is not separable from cation leaching from the glass, as well as the formation of the calcium phosphate rich layer.
TL;DR: This work shows that mineral dissolution can be understood through the same mechanistic theory of nucleation developed for mineral growth, and reveals that the “salt effect,” recognized almost 100 years ago, arises from a crossover in dominant nucleation mechanism to greatly increase step density.
Abstract: The central control of mineral weathering rates on biogeochemical systems has motivated studies of dissolution for more than 50 years. A complete physical picture that explains widely observed variations in dissolution behavior is lacking, and some data show apparent serious inconsistencies that cannot be explained by the largely empirical kinetic “laws.” Here, we show that mineral dissolution can, in fact, be understood through the same mechanistic theory of nucleation developed for mineral growth. In principle, this theory should describe dissolution but has never been tested. By generalizing nucleation rate equations to include dissolution, we arrive at a model that predicts how quartz dissolution processes change with undersaturation from step retreat, to defect-driven and homogeneous etch pit formation. This finding reveals that the “salt effect,” recognized almost 100 years ago, arises from a crossover in dominant nucleation mechanism to greatly increase step density. The theory also explains the dissolution kinetics of major weathering aluminosilicates, kaolinite and K-feldspar. In doing so, it provides a sensible origin of discrepancies reported for the dependence of kaolinite dissolution and growth rates on saturation state by invoking a temperature-activated transition in the nucleation process. Although dissolution by nucleation processes was previously unknown for oxides or silicates, our mechanism-based findings are consistent with recent observations of dissolution (i.e., demineralization) in biological minerals. Nucleation theory may be the missing link to unifying mineral growth and dissolution into a mechanistic and quantitative framework across the continuum of driving force.
TL;DR: Upon reduction with alkali metals, single-wall carbon nanotubes (SWNTS) are shown to form polyelectrolyte salts that are soluble in polar organic solvents without any sonication, use of surfactants, or functionalization whatsoever, thus forming true thermodynamically stable solutions of naked SWNTs.
Abstract: Upon reduction with alkali metals, single-wall carbon nanotubes (SWNTS) are shown to form polyelectrolyte salts that are soluble in polar organic solvents without any sonication, use of surfactants, or functionalization whatsoever, thus forming true thermodynamically stable solutions of naked SWNTs.
TL;DR: In this article, a disc-type electrode was introduced to reduce the taper of the machining depth and 3D micro structures including a hemisphere with 60 µm diameter were fabricated by electrochemical milling.
Abstract: In this paper, electrochemical machining (ECM) for fabricating micro structures is presented. By applying ultra short pulses, dissolution of a workpiece can be restricted to the region very close to an electrode. Using this method, 3D micro structures were machined on stainless steel. Good surface quality of the structures was obtained in the low concentration electrolyte, 0.1 M H2SO4. In ECM, when the machining depth increases, structures taper. To reduce the taper, a disc-type electrode is introduced. By electrochemical milling, various 3D micro structures including a hemisphere with 60 µm diameter were fabricated.
TL;DR: The results emphasise that the metals contained in the carbonaceous aerosols are easier dissolved than in the alumino-silicated particles, and the effects of trace metals on the atmospheric aqueous chemistry and as atmospheric wet input to the marine biota are maximal for "aged" droplets.
TL;DR: The physical state of felodipine changed from crystalline to amorphous during the CSE and SAS processes, confirmed by DSC/XRD data and solubility increased with decreasing drug/polymer ratio or increasing HCO-60 content.
TL;DR: Experimental results confirm that dissolution rates do not only depend on the surface area and particle size of the processed powder, but are greatly affected by other physico-chemical characteristics such as crystal morphology and wettability that may reduce the benefit of micronization.
TL;DR: In this paper, the authors used oxygen K-edge absorption and emission spectra to determine the electronic structures of iron(III) (hydr)oxides (hematite, goethite, lepidocrocite, akaganeite and schwertmannite) and manganese(IV) oxides (pyrolusite, birnessite, cryptomelane).
TL;DR: In this article, the electrodissolution of aluminum electrodes in aqueous solutions containing sulfate or chloride ions is studied in order to obtain a better understanding of the electrocoagulation process.
Abstract: The electrodissolution of aluminum electrodes in aqueous solutions containing sulfate or chloride ions is studied in this work. The results obtained are important in order to obtain a better understanding of the electrocoagulation process, as the electrodissolution of the anode surface is its first step. It has been determined that both chemical and electrochemical dissolution play an important role in the aluminum generation. The chemical dissolution of aluminum is strongly influenced by the pH. Alkaline pHs increase the dissolution rate by orders of magnitude. Within the experimental conditions used, the supporting media does not seem to influence greatly the chemical dissolution process. The electrochemical dissolution process depends mainly on the specific electrical charge passed. Salinity does not significantly affect the electrodissolution rate. Good fittings between experimental and modeled data are obtained by modeling the system with a simple model based on two assumptions: a highly segregated ...
TL;DR: Powder X-ray diffraction analysis showed that IMC in solid dispersion particles is in amorphous state irrespective of the type of silica formulated, and dissolution property of IMC was remarkably improved by formulating the silica particles to the solid Dispersion particles.
TL;DR: In this article, the authors evaluated the effects of porosity in hardened cement paste on dissolution phenomena, and found that the larger the pore volume of the sample, the more rapidly portlandite is dissolved.
TL;DR: In this article, the authors present rate expressions that systematically describe the initial oligomerization of silica in terms of concentration of initial silica, ionic strength, and pH for a natural brine solution.
TL;DR: The catalytic deactivation of R-NiSn catalysts was explored during hydrogen production by aqueous-phase reforming (APR) of ethylene glycol.
TL;DR: In this paper, the authors measured dissolution rates of diopside, forsterite (Fo100 and Fo92), wollastonite, and hornblende in NaCl solutions as a function of pH (1≤pH≤12), pCO2 (0 and 1 atm) and activity of HCO3− and CO32− (10−5≤∑CO2≤0.1 M).
TL;DR: In this paper, the pseudomorphism is initiated by epitaxial growth at the fluid-mineral interface, when the dissolution of the parent phase results in an interfacial fluid layer that is supersaturated with respect to a different solid composition.
Abstract: Solid-fluid interactions often involve the replacement of one phase by another while retaining the morphology and structural details of the parent phase, i.e, pseudomorphism. We present in situ observations of the evolution of both the solid and fluid compositions at the interface during such a replacement reaction in the model system KBr-KCl-H 2 O, in which a single crystal of KBr is replaced by a single crystal of KCl. The pseudomorphism is initiated by epitaxial growth at the fluid-mineral interface, when the dissolution of the parent phase results in an interfacial fluid layer that is supersaturated with respect to a different solid composition. The subsequent evolution of the coupled dissolution and growth can be related to local equilibrium defined by a Lippmann diagram. The reaction features, including the development of porosity in the new solid phase, share many characteristics of replacement reactions in nature as well as in technical applications.
TL;DR: In this paper, a hybrid series gas-liquid electrical discharge reactor was used to study the effect of electrophilic attack on phenol degradation in water by pulsed electrical discharges generated simultaneously in the gas phase and directly in the liquid.
Abstract: Oxidation processes induced in water by pulsed electrical discharges generated simultaneously in the gas phase in close proximity to the water surface and directly in the liquid were investigated in a hybrid series gas?liquid electrical discharge reactor. The mechanism of phenol degradation was studied through its dependence on the gas phase and liquid phase compositions using pure argon and oxygen atmospheres above the liquid and different initial pH values in the aqueous solution. Phenol degradation was significantly enhanced in the hybrid-series reactor compared with the phenol removal by the single-liquid phase discharge reactor. Under an argon atmosphere the mechanism of phenol degradation was mainly caused by the electrophilic attack of OH? radicals produced by the liquid phase discharge directly in water and OH? radicals produced by the gas phase discharge at the gas?liquid interface. Under an oxygen atmosphere the formation of gaseous ozone dominated over the formation of OH? radicals, and the contribution of the gas phase discharge in this case was determined mainly by the dissolution of gaseous ozone into the water and its subsequent interaction with phenol. At high pH phenol was degraded, in addition to the direct attack by ozone, also through indirect reactions of OH? radicals formed via a peroxone process by the decomposition of dissolved ozone by hydrogen peroxide produced by the liquid phase discharge. Such a mechanism was proved by the detection of cis,cis-muconic acid and pH-dependent degradation of phenol, which resulted in significantly higher removal of phenol from alkaline solution observed under oxygen atmosphere than in argon.
TL;DR: The solubility and dissolution rates of AMP were significantly increased by solid dispersions and cyclodextrin complexes as well as their physical mixtures.
TL;DR: In this paper, a laboratory incubation study of the effects of biotic Fe(III) (hydr)oxide reduction on P solubilization in a humid tropical forest soil (Ultisol) under a wet moisture regime (3000-4000 mm annual rainfall).
TL;DR: In this paper, the authors measured the dissolution rates of 12 natural dissolved organic matter (DOM) isolates including humic, fulvic, and hydrophobic acid fractions, and found that dissolution was controlled by the interaction of DOM with the cinnabar surface.
TL;DR: In this article, the adsorption of oxalate and malonate at the water-goethite interface was studied as a function of pH and total ligand concentrations by means of quantitative adaption measurements and attenuated total reflectance Fourier transform infrared spectroscopy.