The initial rate of persulphate (I) decomposition at 50°C in the presence of nitrogen and methacrylonitrile (MAN) in an unbuffered aqueous solution (pH 4–7) may be written as: in the concentration ranges of persulphate (I) (0.25–2.50) × 10?2 (m/dm3) and of (MAN) 0.18–0.36 (m/dm3). During the reaction, a white substance (polymethacrylonitrile) separates out in the colloidal state or in the precipitate form from the medium depending on the ionic strength of the medium. The pH of the medium was found to decrease rapidly and continuously with time in the absence of methacrylonitrile, but it decreased slowly and continuously with time in the presence of the monomer, MAN. If an additional quantity of MAN is injected late in a run, the rate of persulphate decomposition is further accelerated in a given run. However, the rate of persulphate decomposition is found to decrease continuously in the presence of MAN with time, i.e., as the monomer is converted to polymer. It is suggested that MAN accelerates the decomposition of persulphate ions, due to the following reactions in the aqueous phase: and where (Mj˙)w is a-water soluble oligomeric or polymeric (j = 1–10) free radical. The estimated values of k5 and k10 are 1.05 × 10?5 and 1.14 × 103 (in dm3/m/s), respectively. 相似文献
The AC conductivity of fluorite‐structured La2Ce2O7 ceramic was measured under air and argon with different humidity between 250 and 550 °C. It was observed that the total conductivity in wet air and argon was higher than that under dry atmospheres. The effect of water vapor partial pressure ( ) on the conductivity of La2Ce2O7 in air was investigated in detail. The total conductivity increased remarkably with the water vapor partial pressure, and this phenomenon became more notable at lower temperatures. The enhancement of the conductivity was attributed to the proton conduction behavior of La2Ce2O7 in wet atmospheres, and the proton conductivity reached 6.68 × 10–5 S cm–1 in wet air (3% H2O) at 550 °C. The relationship between the proton conductivity (σH) and in wet air could be fitted to . The estimated proton transport number increased with increasing water vapor partial pressure and decreasing temperature, and varied between 0.05 and 0.89 in this study. 相似文献
This study focuses on a high-temperature operation in electrodialysis of salt solutions and studies the effect of temperature on limiting current density and mass transfer. Experiments were conducted under various conditions of temperature (T), varying from 15 to 90°C; of dialysate concentration (Cd), varying from 5 × 10?3 to 3 × 10?2M ; and of dialysate velocity (ud), varying from 0.206 to 2.44 cm s?1. A least squares fitting of the experimental data on limiting current density (Ilim) yields an Arrhenius equation as follows: The molar flux N? (mol cm?2 s?1), initial concentration (C0; M ) and temperature (T; °C) were found to have the following relationship: N?/C0 is slightly increased with increasing temperature ranging from 25 to 70°C. 相似文献
The reaction of sulphur dioxide-oxygen mixtures with methyl radicals, generated by the photolysis of azomethane at Λ 3400 Å, has been studied in the temperature range 50–150° in an attempt to evaluate some of the basic reactions involved in the sulphoxidation of free radicals and hydrocarbons. Addition of sulphur dioxide to a mixture of methyl radicals and oxygen leads, unexpectedly, to an initially increased consumption of oxygen. A rate constant has been determined for the reaction: a value of 1·7 × 1016 mole?2 cm6 sec?1 being obtained. Using this value, the rate constant for the reaction: has been estimated to be ~ 7·8 × 107 mole?1 cm3 sec?1. Comparison of the reactions of acetyl and methylsulphonyl radicals with oxygen and with radicals in dicates that in both cases acetyl radicals are much more reactive by ~ 103 times. 相似文献
The rate of thermal decomposition of persulfate in aqueous solution in the presence of acrylonitrile (AN) monomer (M) and of nitrogen, may be written as: in the concentration range of persulfate (1.8 to 18.0) ×10-3, and of monomer (M), 0.30 to 1.20, mol dm-3. It was observed that the pH of the solution containing persulfate and monomer did not alter during polymerization if the monomer concentrations were close to its solubility under the experimental conditions. Conductance of the aqueous solutions of persulfate and monomer was found to decrease during the reactions. In an unbuffered aqueous solution containing only persulfate, however, the pH was found to decrease continuously at 50°C with time, while the conductance of the solution was found to increase. The monomer (AN) had no effect on the glass electrodes of the pH meter in aqueous solutions, and also on the electrodes of the conductivity cell. It has been suggested that the secondary or induced decompositions of persulfate were due to the following elementary reactions: where (Mj· radicals (j = 1 to 10) are water-soluble oligomeric or polymeric free radicals. kx and ky at 50°C have been estimated as 1.70 X 10-5 and 5.08 × 103 dm3 mol-1 s-1, respectively. By measuring pH of freshly prepared persulfate solutions at 25°C, it is suggested that 0.05–0.30% of persulfate reacts molecularly with water (i.e., hydrolysis), as soon as it (10-3 to 10-2 mol dm-3) is added to distilled water (pH 7.0). This hydrolysis was found to be stopped in dilute sulfuric acid solution (pH 3–4). 相似文献
A dual-calibration method for the determination of molecular weights and molecular weight distribution of styrene–maleic anhydride copolymers (S/MA) by gel permeation chromatography (GPC) is introduced. It might be applicable to copolymers of other type. A linear relationship of intrinsic viscosity [η] and weight-average molecular weight (M?w) for unfractionated S/MA in tetrahydrofuran (THF) at 25°C can be expressed by the equation The maleic anhydride content of the copolymers ranges from 5 to 50 mole-%, and the M?w range is from 2 × 104 to 7 × 106. The plot of log [η] M?w versus GPC elution volume of the S/MA copolymers falls on the same curve as that of the polystyrene standards in THF. 相似文献
A powder mixture of ZrO2-30 mol% Ti was sintered at 1500 °C/h under various controlled partial pressures of oxygen (PaO2). The microstructure of each sintered sample was characterized using x-ray diffractometry and analytical transmission electron microscopy/energy-dispersive spectroscopy. TiO and highly oxygen-deficient zirconia were found after sintering at PaO2 ~2.1×10−4 atm, which implies that the oxidation–reduction reaction is a controlling mechanism when there is a trace of residual oxygen. When the PaO2 was increased to 1.05×10−1 atm, the dissolution of residual oxygen and nitrogen in the chamber into the titanium led to the formation of TiO(N) with nitrogen in solid solution. It was inferred that the oxygen in TiO(N) was also supplied by zirconia since the zirconia became oxygen-deficient in the sintered composites. After sintering in air (PaO2 ~2.1×10−1 atm), TiO2 and TiN were formed along with nearly stoichiometric zirconia, indicating that oxygen and nitrogen in air played a major role in the oxidation and nitridization reaction of titanium. The degree of oxygen deficiency x in ZrO2−x decreased with increasing oxygen partial pressure, which led to an increased volume fraction of the monoclinic phase. 相似文献
The rate of the thermal decomposition of potassium persulfate has been studied in an unbuffered aqueous solution at 50°C in nitrogen atmosphere in the presence of vinyl acetate (VA) monomer (M). It has been found that the initial rate of persulfate decomposition may be written as in the concentration range of persulfate (1.85 × 10?2–1.85 × 10?3 m/dm3) and VA (0.054–0.27 m/dm3). The pH of the aqueous solution of persulfate was found to decrease continuously at 50°C, but there was no measurable change of pH of the aqueous solution containing persulfate and VA at 50°C in the presence of nitrogen at the early stages of the reaction. VA, methyl acetate, and ethyl acetate have been found to undergo very slow hydrolysis in aqueous solution at 50°C. The partition coefficient (β) of the monomer between the polymer phase and the aqueous phase was found to be 21 ± 2 in the presence and absence of electrolytes (K2SO4, 10?4–10?3 m/dm3) by the bromometric estimation of the monomer present in the aqueous phase containing known amounts of monomer [1.80–2.20%, w/v] and freshly prepared polymer (0.3–0.5 g/100 mL). Above 10?2 (m/dm3) persulfate, the polymer obtained was found to be insoluble in common solvents, viz., acetone, benzene, etc. Highly purified sodium dodecyl sulfate (0.5–5.0 × 10?3 m/dm3) had no measurable effect on the rate of persulfate decomposition. 相似文献
Potassium persulfate modes of thermal decomposition and reactions with ethyl acrylate in aqueous solution at 50°C in nitrogen atmosphere have been investigated. It has been found that the rate of persulfate decomposition may be expressed as ?d(S2O)/dt ∝ (S2O)1.00 ± 0.06 × (M)0.92±0.05 while the steady state rate of polymerization (Rp) is given by Rp ∝ (S2O)0.50 ± 0.50 × (M)1.00 ± 0.06 in the concentration ranges of the persulfate, 10?3?10?2 (m/L), and monomer (M), 4.62?23.10 × 10?2 (m/L), i.e., within its solubility range. In the absence of monomer, the rate of persulfate decomposition was slow and first order in persulfate at the early stages of the reaction when the pH of the solution was above 3.0. The separating polymer phase was a stable colloid at low electrolyte concentrations even in the absence of micelle generators. It has been shown that the oxidation of water soluble monomeric and oligomeric radicals by the S2O ions in the aqueous phase, viz., \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm M}_j^ \cdot + {\rm S}_2 {\rm O}_8^{2 - } \to {\rm M}_j - {\rm O} - {\rm SO}_3^ - + {\rm SO}_4^{ \cdot - } $\end{document} is not kinetically significant in this system. It has been found that the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm M} + {\rm S}_2 {\rm O}_8^{2 - } \rightarrow{k}{\rm M} - {\rm O} - {\rm SO}_3^ - + {\rm SO}_4^{ \cdot - } $\end{document} would also lead to chain initiation at the outset of the polymerization reaction. k has been estimated as 5.41 × 10?5 (L/m/s) at 50°C. Taking kp as 103 (L/m/s), kt has been estimated as 0.168 × 106 (L/m/s). The partition confficient (β) of the monomer between the polymer phase and the aqueous phase was found to be 16 ± 2, at 50°C. The rate constant for persulfate ion dissociation has been found as 1.40 × 10?6 s?1 at 50°C. 相似文献
A series of soft to tough copolymers have been prepared by the cationic copolymerization of the modified linseed oils Dilulin or ML189 with DCPD. Soxhlet extraction and solid‐state 13C NMR spectra indicate that the bulk copolymers consist of a cross‐linked oil/DCPD network interpenetrated with certain amounts of soluble components. The Tgs of the resulting Dil/DCPD and ML189/DCPD copolymers are in the range 15–83 and 8–77 °C, respectively, and increase linearly with the increase of the DCPD amount. The room‐temperature storage moduli range from 4.43 × 106 to 1.52 × 109 Pa for the Dil/DCPD copolymers and from 3.72 × 106 to 1.44 × 109 Pa for the ML189/DCPD copolymers.
The Differential Scanning Calorimetry (DSC) trace for a commercial phenolic resole resin shows two distinct peaks. Assuming that these represent two independent cure reactions results in a kinetic model of the form: with κi = κio exp(-Bi/T). The Arrhenius parameters were estimated from a plot of ln(β/T) versus 1/Tp. The parameters, p, n1, and n2 were obtained by writing the DSC response predicted by the equation above in terms of a function which contains temperature as the only variable. with $ \theta _i = \left({1/\beta} \right)\int_{T_0}^T {\kappa _i dT \le r_i} $ dT ? ri and ri = 1/(1-ni). Fitting this equation to the DSC response measured at a scan rate of 4°C/min obtains p ≈ 0.66; n1 ≈ 0.55; n2 ≈ 2.2; B1 ≈ 8285; B2 ≈ 7480; κ1 ≈ 1. 12 × 108 s?1; κ2 ≈ 0.99 × 106 S?1. 相似文献
Au nanoparticles supported on Vulcan XC‐72R carbon were prepared by a modified NaBH4 method in aqueous solution and employed as electrocatalyst of oxidation for the direct borohydride fuel cell (DBFC). The morphology and structure of as‐prepared particles were examined by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). It was found that Au nanoparticles were mainly about 3.0 ± 0.5 nm in size and uniformly distributed on the surface of Vulcan XC‐72R carbon. The electrooxidation behaviors of and fuel cell performances using carbon‐supported Au nanoparticles as catalysts were investigated. Compared with Au/C prepared by conventional reduction method, the kinetics of oxidation on as‐prepared carbon supported 3.0 ± 0.5 nm Au nanoparticles were significantly improved. The DBFC employing carbon supported 3.0 ± 0.5 nm Au nanoparticles showed a maximum power density of 85.3 mW cm–2 at 60 °C. 相似文献
The zero‐length column (ZLC) technique has been developed to measure the intracrystalline diffusivity of strongly adsorbed species in large zeolite crystals above 50 μm in the Henry's law range of sorption equilibrium. The ZLC is a macroscopic technique, and there is a need of large crystallites or pellets to measure the intracrystalline diffusivity Dc of fast diffusion species or the macropore diffusivity DP of weakly adsorbed species, respectively. Another limitation is that ZLC desorption curves produce similar concentration profiles (linear isotherms) in bidisperse adsorbents (pellets) under macropore or micropore diffusion control. Moreover, the forms of the response curves are very similar in both diffusion‐ and nonlinear equilibrium‐controlled processes, leading to some misinterpretations of ZLC experiments. In this work, two criteria are developed showing that, in order to macroscopically measure the micropore diffusion time constant or the macropore diffusion time constant , the time of the ZLC experiments t should be higher than 7.0 × 10?2 or 7.0 × 10?2 , respectively. The interpretation of the ZLC response curve data is also checked in two completely different regimes, showing that a single ZLC response curve is not enough to conclude if a system is under a kinetic or an equilibrium regime. 相似文献
The dilute solution properties of nine poly(vinylpyrrolidone) fractions in methanol covering the molecular weight range 6.76 × 104 to 1.02 × 107 were studied. Constants a and Km of the Mark-Houwink-Sakurada (M.H.S.) equation were found to be 0.60 and 2.64 × 10?4 respectively using light scattering and intrinsic viscosity data and were compared with the literature values. The second virial coefficient, A2 decreases gradually as the molecular weight increases while the root-mean-square radius of gyration, 2 increases. The dependence of A2 on molecular weight is in agreement with other flexible polymers dissolved in moderate to good solvents. The unperturbed chain dimension, (r/M) was calculated using the Stockmayer-Fixman (S—F) equation and a value of 4.9 × 10?17 cm was obtained. The S—F plot slightly bends in the region of high molecular weight which is according to expectation. 相似文献
The complexation of La3+, Ce3+, Pr3+ and Sm3+ ions with isopropylmercaptan has been studied by potentiometric and conductometric titration techniques in aqueous – 10% ethanolic (V/V) medium . Title metal ions form 1:1, 1:2 and 1:3 complexes in the pH range 6.0–8.0 with considerable overlapping. Their log Kstab. values are determined at 15°, 25° and 35°C at ionic strength μ = 0.1 M (NaClO4) by applying Calvin and Melchior's extension of Bjerrum method. The values of thermodynamic parameters ΔG, ΔH and ΔS have been calculated at 25°C with the help of an isobar and Gibb's Helmholtz equation. The trend in the stability constant values of the metal-complexes has been found to be . 相似文献
Dynamic stress intensity factors KD were measured by the caustic method and crack propagation velocity ? by the velocity gauge techniques for PMMA [poly(methyl methacrylate)] during dynamic crack propagation at various strain rates \documentclass{article}\pagestyle{empty}\begin{document}$ \rm \dot \varepsilon $\end{document} . No definite applied strain rate effects on the dynamic stress intensity factor were observed for applied strain rates ranging from 8.33 × 10?4 to 30/sec; however, the test results do show crack propagation velocity dependency in KD ~ ? relations. The high local strain rate region may be realized at the running crack tip even under the quasi-static loading case of \documentclass{article}\pagestyle{empty}\begin{document}$ \rm \dot \varepsilon $\end{document} = 8.33 × 10?4/sec, since all the crack propagation velocities obtained were greater than 50 m/sec even up to 450 m/sec. 相似文献