Summary High-resolution 1H NMR spectra (1H HR-NMR) of solutions of isotactic (i) and syndiotactic (s) poly(methyl methacrylate) (PMMA) in toluene-d8 were measured in the concentration range 0.2 to 10% w/v; for solutions of s-PMMA (10% w/v), 1H NMR spectra with magic angle rotation (MAR-NMR) at various temperatures and 13C NMR spectra with strong proton decoupling were also measured. It was found that even in very dilute solutions of s-PMMA in toluene-d8 a considerable portion (76%) of polymer segments are associated: association is of intramolecular origin and is due to interaction of long syndiotactic sequences. Prom NMR spectra the motion of associated segments appears as isotropic with and effective correlation frequency 106 – 107 Hz. A globular structure of the associates of s-PMMA is proposed. 相似文献
The removal of cadmium by anion exchange from 55 w% H3PO4 (black acid from a Nissan H process) at 90°C in the presence of small amounts of halides (Cl-, Br-, I-) was investigated. Cadmium distribution coefficients, [CD]resin/[CD]acid (concentrations in mol/1), larger than 250 were obtained with HBr equilibrium concentrations of more than 0.10 w% in the phosphoric acid solution or with HI concentrations of more than 150 ppm. The regeneration of the Cd loaded resin was performed with a very dilute phosphoric acid solution (< 1 w% H3PO4). The excess of iodide in the phosphoric acid solution could also be- removed by anion exchange. A value of about 90 was obtained for the iodide distribution coefficient of a weakly basic resin. This resin could be regenerated with an 1 M NH3 solution at 50°C. The rate of adsorption and desorption of both cadmium and iodide were mainly determined by the diffusion in the resin|particle. Effective diffusivities of about 3*10-13 mZ/s and 1.3*10-11mZ/s were obtained for the adsorption of cadmium in the presence of HI and for the adsorption of iodide respectively. 相似文献
The thermal decomposition of cyclopentadiene has been studied in the temperature range 1260–1530 K behind reflected shocks. The total pressure ranged from 1.5 to 2.3 bar. Resonance absorption was used to record the temporal concentration profiles of H atoms. This sensitive technique allowed the study of the reaction systems under favorable conditions by applying very low initial concentrations (0.5–8 ppm). For cyclopentadiene decomposition R1, C5H6 → C5H3-c + H, a rate expression of k1 = 1.1 × 1015 exp(–38760/T) s−1 was deduced. In a separate series of experiments the consumption by cyclopentadiene of H atoms, which had been generated by the thermal decay of ethyl iodide, was investigated. A preliminary value of k2 = 1.4 × 1014 exp(–2739/T) cm3 mol−1 s−1 was deduced for the total rate of H-atom consumption by cyclopentadiene R2, C5H6 + H → products. 相似文献
From chronovoltammetric and cyclovoltammetric polarization curves three mechanisms of iodide ions have been established: 3I? = I?3 + 2e,2I?3 = 3I2 + 2e and 2I? = I2 + 2e under certain conditions of scan rate, concentration of iodide ions and area of electrode in the aqueous solutions KI (background solution 1 N Na2SO4) with half-wave potentials of 0.428, 0.489 and 0.507 V by silver/silver chloride electrode. 相似文献
Thermodynamic predictions are reported for platinum and palladium in aqueous ammonia and iodide solutions, to define less
aggressive conditions than used hitherto for leaching palladium and platinum from secondary materials. Cyclic voltammetry
and amperometry of thin films of palladium, electrodeposited onto rotating vitreous carbon disc electrodes, indicated that
partially oxidised adsorbed species passivated dissolution in aqueous ammonium sulfate. By contrast, dissolution rates in
aqueous potassium iodide solutions were a significant fraction of that corresponding to the mass transport controlled rate
of reduction of tri-iodide, which was demonstrated to be a suitable oxidant for the envisaged metal recovery process. However,
iodide concentrations > 1 m were required to achieve adequate solubility of the oxidation products, assumed to be PdI42− ions, thereby avoiding inhibition by PdI2. The reduction of tri-iodide on palladium was very facile, with large exchange current densities and Tafel coefficients;
two alternative mechanisms are proposed that fitted experimental results well. In addition, a kinetic model to predict dissolution
rates of Pd in tri-iodide solutions gave good agreement with experimental data, provided an equilibrium constant of 10−4.5 was used for the PdI2/PdI42− reaction, rather than the value of 10−2.8 derived from thermodynamic data. 相似文献
The potentiodynamic formation of AgI films by reaction (1) on an Ag rotating disc electrode was studied and the results were compared to previous work regarding the formation of anodic AgBr and Ag2S films, In dilute iodide solutions, a very porous AgI film is formed at a rate controlled by the diffusion of I? to the electrode surface. At higher iodide concentrations, and particularly in high conductivity supporting electrolytes, a porous AgI film forms at a rate initially limited by ionic migration in solution followed by diffusion of I? in the pores of the AgI film.In 1 M NaI solutions, when AgI becomes rather soluble, thick granular AgI films form at a rate limited by the solid-state migration of ions in the bulk of the film. On the basis of the low-field model of film growth, the ionic conductivity of these AgI films has been determined to be 8.7 × 10?5 Scm?1相似文献
When a nonionic surfactant, such as hexaoxyethylene glycol dodecyl ethers (6ED) is added to an aqueous iodine solution in the presence of potassium iodide, some spectral changes corresponding to the interaction of iodine-potassium iodide mixture with 6ED are found above the critical micelle concentration (CMC) of 6ED. The absorption maximum bands of complexes formed between 6ED and iodine are significantly different from those formed between 6ED and iodine-potassium iodide mixture in aqueous solution. The complexes of iodic compounds (such as iodine, triiodide ion and polyiodide ion) with 6ED show absorption bands at 390 nm, 370 nm and 385 nm which are assigned to an interaction between iodine-6ED, triiodide ion-6ED and polyiodide ion-6ED, respectively. When the concentration of polyethylene glycol (PEG, MW=200–600) becomes high in aqueous triiodide ion solution, the maximum absorption wavelength of triiodide ion solution also shifts toward 370 nm, similar to that of the triiodide ion-6ED complex. If it is assumed that the absorbance between I3? and the EO chain in 6ED is the same as that between I3? and the EO chain of PEG, the concept of effective EO number can be applied to explain the behavior in the absorption spectra among I3?, 6ED and PEG. Here, the effective EO number is defined as the product of EO chain length and concentration of each 6ED and PEG in the complexes. The effective EO number and concentration of PEG decrease in the triiodide ion-PEG complex as the molecular weight of PEG becomes large. Moreover, the effective EO number and concentration of 6ED are lower than those of PEG at all maximum absorption wavelengths. 相似文献
The Faradaic rectification studies of the two electron charge transfer processes, cationic and anionic redox couples, have been carried out. The mechanism of the iodide—iodine reaction through single charge transfer comprises the following steps, of which reaction (b) is the slowest and controls the rate of overall reactions. The values of the transfer coefficient and rate constant are obtained for the second step, which is rate determining in both the directions. The values of the parameters obtained when the concentration of the electrochemical species (I2) is much less in comparison to that of iodide, are αc = αa = 0·5 and kOa of the order of 5 × 10?5 cm/s. The parameters for the iodide—iodine reaction, using 1·0 M KNO3 as supporting electrolyte, are αc = 0·49, αa = 0·51 and kOa of the order of 5 × 10?3 cm/s. For the stannous-stannic reaction either of the two steps appears to be rate determining in both directions and the values of the parameters obtained are αc = 0·48, αa = 0·52 and k0a = 2·1 × 10?3 cm/s. 相似文献
Reduction of metal ions in dilute solutions is of great interest for purification of waste waters and process liquids. Hydrogen gas is a very attractive reductant, since its use gives no additional pollution. In this paper the reduction of chromate in a sulphuric acid medium has been studied. A new electrochemical cell, a GBC-cell, which is a combination of a gas-diffusion electrode in direct contact with a packed bed of carbon particles, is introduced. Hydrogen gas flows along the hydrophobic side of the gas-diffusion electrode and a chromate solution is pumped upwards through the bed. Experiments were carried out with H2SO4 solutions initially containing 70 mol m–3 chromate at various temperatures, solution flow rates, H2SO4 concentrations and bed thicknesses. Experimental results for the chromate reduction are described by an empirical relation. It has been found that the reduction of chromate is a first-order reaction in chromate and the apparent rate constant for the chromate reduction increases with decreasing chromate concentration and increasing temperature, H2SO4 concentration and bed thicknesses and is practically independent of the flow rate of the solution. It is concluded that the new GBC-cell is very attractive for the reduction of chromate in dilute solutions and for industrial abnlication on a large scale. 相似文献
An attempt to relate the different values of the ion-exchange selectivity coefficient in different media is made by considering the two phases as ionic solutions where the activity coefficients of species can be evaluated by means of Mikulin's equation.The selectivity coefficients of the NH4+/H+, Na+/H+, and Li+/H+ exchanges in a sulfonated cation exchanger and of the NO3−/Cl− exchange in a quaternary ammonium anion exchanger have been measured under different conditions characterized by the degree of crosslinking of the ion exchanger, the water activity of the solution, the concentration ratio of two counterions, and the concentration ratio of a third possible counterion.The water activity of the solution is an essential parameter to be controlled, particularly in dilute or moderately concentrated solutions. A representation of the experimental results on the ion-exchange selectivity coefficient is given in terms of two parameters allowing the selectivity coefficient to be predicted even in very concentrated ionic media. 相似文献
Argillaceous rocks are considered potential host rocks for radioactive waste repositories. The concrete matrix that could be used as a barrier could react with the groundwater of the geological site, inducing a drastic change in its chemical composition and its pH (10–13). Consequently, the physicochemical properties of the rock in contact with this alkaline solution may be modified and, in turn, may induce modification on the behaviour of radioelements. This study, applied to the argillite of Tournemire, involves characterizing I− sorption to an argillaceous rock in alkaline media in batch experiments under N2-controlled conditions. I− was added as a 125I radiotracer and measured by γ spectrometry.Preliminary experiments were conducted with different solution/solid ratios (v/m=2.5, 5 and 20 ml g−1) and contact times (1–14 days) in order to determine the optimal experimental conditions. The chosen v/m ratio was 5 ml g−1 as the best compromise between a high Kd value and a low error of the measure. The chosen experiment duration was 1 day because I− sorption was highest and to limit the effects of pyrite oxidation. One of the experiments, performed with a radio-sterilized sample to test possible effects from microorganisms, showed that they could enhance iodide retention, particularly during the first 2 contact days.The influence of pH on I− sorption was tested using solutions between values of 8.3 and 12.8. The Kd values were independent of pH and very low (0.3 ml g−1).Finally, the influence of the chemical composition of concrete fluids was also tested. Three solution compositions corresponding to different steps in the evolution of fluids in contact with altering concrete were used: fluid in contact with fresh concrete (pH 13.2), with moderately degraded concrete (pH 12.1) and with strongly degraded concrete (pH 11.5). Each solution contained variable amounts of sodium, potassium, calcium, silica and sulphate. I− sorption was also very low (Kd0.2 ml g−1). Additional experiments were conducted with alkaline solutions containing different amounts of SO42− ions (10−3–10−2 M) to test sulphate–iodide sorption competition. I− retention was independent of the sulphate concentration. 相似文献
Electrode reaction of ammoniated electrons was investigated with voltammetry, potentiometry and chronoamperometry. Experiments were conducted on Pt, Au and W electrodes in 0.5 M LiI, NaI, KI, CsI and KBr solutions of liq. NH3. The results in dilute solutions (< 10<−4 M) do not reflect the differences in alkali metal, electrode metal and supporting electrolyte and are explained by a simple one-electron transfer process whose transferring species is a free solvated electron and its ion-pair with a metal cation in a rapid equilibrium. The formal standard potential is −2.155 ± 0.005 V vs. Pb/Pb(NO3)2 (0.05 M) at −40°C in liq. NH3 involving 0.5 M alkali metal iodide. The lower limit of the averaged diffusion coefficient is 0.7 × 10−4 cm2 s−1. At higher metal concentrations (> 10−2 M), a two-electron transfer process tends to prevail, which is explained by considering the dimer of ion-pairs as the diffusing species. 相似文献
Growth of lucerne was inhibited by sodium iodide even more than that of ryegrass above a concentration equivalent to 1µg cm–3 of iodine in an applied solution. In sand-culture the extent to which the iodide depressed yield of dry matter depended on the type of nutrient-solution used to stimulate and maintain vigorous growth. In contrast, where the plants were grown in soil the depression was independent of the nutrient-solution used. This difference between solutions is a reflection of the extent to which growing plants can modify pH in the root-zone of a sandy unbuffered substrate and leads to a conclusion that acidity greatly enhances the toxic effect of the iodine. There are reasons for believing that in sunlight iodine may be lost by volatilization even from living plant-tissue. The implication of these findings is discussed in relation to using either iodized fertilizers or iodized salt-blocks in order to maintain iodine in pastoral systems at levels satisfactory for animal-health. 相似文献
The corrosion behaviour of tin in stagnant mono-, di- and trichloroacetic acids solutions in the pH range 1–6 and at concentrations 4.0 to 5 × 10?4 M was investigated. The results indicate behaviour that is generally the same but there is some dependence on the acid concentration and the pH value. In 4.0 to 10?2 M solutions, the corrosion rate (W) increased with increasing acid concentration and decreasing pH value from 1 to 4 as follows: log W=a+b log C, where b=0.70, 0.42 and 0.35 for tri-, di- and mono-chloroacetic acids respectively. At high concentrations 4.0 to 10?2 M and in the pH range 1–6, the steady state corrosion potential shifted in the negative direction with increase of acid concentration accompanied by an increase in the corrosion rate, indicating that the corrosion process becomes anodically controlled by the complexing of Sn2+ ions with organic acid anions and that the order of aggressiveness is mono-<di-<trichloroacetic acids. In dilute solutions (10?2 to 5.10?4 M) in the pH range 1–6 the steady state potential shifted in the noble direction with increase of acid concentration (accompanied by a remarkable decrease in the corrosion rate). Corrosion inhibition in dilute solutions was attributed to film formation on the surface of tin which may result from the hydrolysis of tin species. 相似文献
Summary Kinetic analysis of the cationic polymerization of 5-methyl-2-oxazoline (5-MeOZO) was performed with methyl tosylate(MeOTs) and methyl iodide(MeI) initiators by using 1H NMR spectroscopy. With MeOTs the polymerization of 5-MeOZO proceeded through oxazolinium tosylate species 3 and 4 and the rate constant of propagation (kp) was determined. With MeI, on the other hand, the propagating ends are present in equilibrium between alkyl iodide (covalent) species 7, 9 and 11 and oxazolinium(ionic) species 6, 8 and 10. Two model reactions enabled to determine the equilibrium constant (K) of 6/7 and to evaluate the reactivity of covalent species 9 (reflected by kp(c)) and of ionic species 8 (reflected by kp(i)). Both species 8 and 9 propagate concurrently and contribute to the whole propagation at comparative extents. 相似文献