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131.
Raffaella Ruffini Alessandro Borghi Roberto Cossio Filippo Olmi Gloria Vaggelli 《Mikrochimica acta》2002,139(1-4):151-158
Quartz is a common phenocryst in acidic volcanic rocks but rarely contributes to the understanding of the magmatic or eruptive
processes due to its apparent chemical homogeneity. Cathodoluminescence studies indicate that volcanic quartz is strongly
zoned with respect to the trace elements. The determination of this zoning can help to elucidate the crystallisation history
of the magmatic rock. Polished thin sections from rhyolitic and dacitic volcanic rocks were examined by cathodoluminescence
mounted on an optical microscope and analysed by electron probe microanalysis. X-ray mapping of the trace elements incorporated
in the zoned quartz was also performed. The interpretation of the data obtained from these different analytical methods provides
useful information on the chemical zoning of single crystals and therefore on the chemico-physical conditions of the melt
from which the quartz crystallised. Quartz from dacitic rock shows a complex cathodoluminescence oscillatory zoning, consisting
of large red-brown and blue bands concentric to a resorbed core. Quartz from rhyolite shows simpler cathodoluminescence zoning,
consisting of dark to bright blue luminescent bands. The EMPA analyses and the X-ray maps combined with the cathodoluminescence
images suggest a clear correlation between the concentrations of some trace element (mainly Al and Ti, acting as activators
of luminescence) and the cathodoluminescence colours pattern zoning. The incorporation of these trace elements during the
growth of the crystals is linked to small variations in the thermo-chemical properties of the magma such as temperature and
chemical composition. 相似文献
132.
Reactivity and swelling of nanometer films of alternating maleic anhydride copolymers were investigated in dependence on the kind of comonomer and molar mass of copolymer in aqueous solution at pH 7.4 and pH 3.0 in order to reveal their characteristics under physiological conditions. Fully hydrolyzed (maleic acid) chains of the copolymers with styrene, propene, and ethylene comonomers covalently bound to SiO2 substrates showed a "mushroom" swelling behavior at pH 7.4 with a layer thickness scaling of N3/5. Decreasing the environmental pH was found to induce a comonomer-dependent shrinking or collapse of the immobilized polymers due to the change in ionization. From the swelling kinetics of non-hydrolyzed chains, the time constants and characteristics of swelling and anhydride hydrolysis were determined and found to depend on the type of comonomer. The short- and long-term swelling kinetics [l approximately t and approximately ln(t)1/2] were found to be in agreement with theoretical models of polymer swelling, while at intermediate time scales enhanced swelling was observed due to hydrolysis reaction of maleic anhydride groups. The findings elucidate the variety of properties of maleic anhydride copolymer films under physiological conditions, which can advantageously be applied for biofunctionalization of different templates. 相似文献
133.
The piezoelectric quartz crystal(PQC)impedance analyzer was used to monitor in situ the generation of monodisperse silica particles during the hydrolysis of tetraethyl orthosilicate (TEOS) and their adsorption onto and Au electrode in alcohol solutions containing water(6-15mol/L)and ammonia(0.2-2.0 mol/L).The equivalent circuit parameters,the resonance frequencies and the half-peak width values of the conductance spectra of the PQC resonance were obtained.The resonant frequency decreased notably while the motional resistance changed very slightly(within 1Ω during the hydrolysis reaction,suggesting that the mass effect dominated the adsorption of generated monodisperse silica particles on the gold electrode in this system.Changes in f0 indicated that the ammonia concentration affected the hydrolytic reaction obviously,and the influence of water concentration on the reaction was small while the water was significantly excessive.Kinetics of monodisperse silica particle adsorption occurring at the electrode i solution interface was analyzed using a first-order reaction scheme.In addition,the electrolyte-induced precipitation of the monodisperse silica of adsorbed particles per area and the converge of monodisperse silica particles were obtained from scanning electron nicroscope(SEM)observations. 相似文献
134.
Many metal ions are spontaneously adsorbed onto a piezoelectric quartz crystal and change the oscillation frequency. The pH ranges in which the metal ions adsorbed were just below that of precipitate formation as the ‘hydroxides’; frequency changes caused by adsorption were not observed in these pH ranges where the ‘hydroxides’ formed. Cationic organic reagents, such as crystal violet and methylene blue, were also adsorbed on the piezoelectric quartz crystal but non-ionic and anionic organic compounds were not. These results showed that the crystal was negatively charged on the surface. 相似文献
135.
136.
137.
Cyclic voltammetric investigation of the interaction of methylene blue (MB) with heparin (hep) at a gold electrode is presented. The combination of MB with heparin formed a nonelectroactive complex MB-hep, which resulted in the peak current decrease of MB. The anodic peak current difference of MB was found to be proportional to the concentration of heparin in the range of 0.666-64.5 μg mL−1 with a detection limit of 270 ng mL−1 and a satisfactory result was obtained for the determination of heparin in injection samples. The equilibrium constant for MB-hep complex was calculated to be 7.32 × 105. The dynamic process of competition of Ba2+ with methylene blue for binding heparin was monitored using quartz crystal microbalance (QCM) technique. The reaction rate constant between Ba2+ and MB-hep was estimated to be 0.0022 s−1. 相似文献
138.
The adsorption behaviors of two organic molecules, benzoic acid (BA) and 2-butyne-1,4-diol (BD), on metal electrodes have been studied using an electrochemical quartz crystal microbalance (EQCM) combined with the cyclic voltammetry technique. In the range of potentials studied, BA molecules were adsorbed onto an electrodeposited gold electrode with a saturation concentration of 5.0 × 1014 molecules/cm2. It was found that the Frumkin isotherm model was most suitable to depict the electrosorption behavior. The isotherm parameters by nonlinear fitting, which agreed with the literature values, implied BA was chemisorbed on the gold surface. For BD on an electrodeposited nickel electrode, the equivalent molar mass of the reaction species was calculated on the basis of the voltammetry curve and mass curve, which were obtained simultaneously during the potential scan. The analysis of EQCM data for the electrosorption of BD on gold and nickel electrodes showed an irreversible characteristic; the latter effectively inhibited the hydrogen evolution reaction. 相似文献
139.
长缝石英管氢化物-火焰原子吸收光谱法测定化探样品及铅锭中微量锡 总被引:1,自引:0,他引:1
长缝石英管氢化物原子吸收法测定锡,具有较低的检出限,是一个方便、快速、灵敏的分析方法,特别适用于地质化探样品及铅锭的测定.通过对锡氢化物发生的酸度等条件进行了研究并提出克服干扰元素的办法.地质样品测定下限为0.5×10~(-6)g,铅锭样品测定下限为0.075×10~(-6)g.完全满足地质化探及铅锭测定的技术要求. 相似文献
140.
Contamination of the structural materials of nuclear reactors is a crucial question in view of radiation protection, especially,
if due to some leakage, uranium and its fission products appear in the cooling water. Since it is rather difficult to obtain
in situ experimental data on the actual amount of adsorbed radioactive species, the surface contamination may be quantified
by measuring bulk activity concentrations of the cooling water and by calculating the amount of adsorbed material on the surfaces
by using a partition coefficient. To do this, the knowledge of an appropriate adsorption isotherm is needed. Thus, our paper
presents results, based on electrochemical measurements, about the extent and effect of the adsorption of certain fission
products—caesium and iodide—in their ionic forms on the surface of some alloys used in the nuclear industry. Our findings
allow the conclusion that the adsorption of these ions can be described by a Langmuir-type isotherm, where the saturation
values correspond to surface monolayers. 相似文献