首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
Ｉｎｔｈｅｆｉｅｌｄｏｆｐｏｌｙｍｅｒｐｈｙｓｉｃｓ,ｔｈｅｃｒｙｓｔａｌｌｉｎｅｓｔａｔｅｏｆｐｏｌｙｍｅｒｓｈａｓｌｏｎｇｂｅｅｎｏｆｉｎｔｅｒｅｓｔ.ＴｈｅｅｘｉｓｔｅｎｃｅｏｆｐｏｌｙｍｅｒｓｉｎｇｌｅｃｒｙｓｔａｌｗａｓｆｉｒｓｔｄｉｓｃｏｖｅｒｅｄｂｙＪａｃｃｏｄｉｎｅ[1]ｉｎ1955.Ｔｈｅｔｈｉｃｋｎｅｓｓｏｆｍｏｓｔｓｏｌｕｔｉｏｎｇｒｏｗｔｈｃｒｙｓｔａｌｓｉｓｆｏｕｎｄｔｏｂｅｏｆｔｈｅｏｒｄｅｒｏｆ～10ｎｍ.Ｔｈｉｓｏｂｓｅｒｖａｔｉｏｎｉｓｓｏｍｅｗｈａｔｓｕｒｐｒｉｓｉｎｇ.Ｓ…  相似文献   

2.
The carbon dioxide reforming of methane in a cell with a solid oxygen-conducting electrolyte:
has been studied. The effect of anodic current (or electrochemical oxygen pumping to the reaction zone) on the catalytic properties of the Pt electrode for CO2−CH4 reaction is discussed.  相似文献   

3.
Based on the structure of characterization of Au/Fe2O3 catalysts, the mechanism of gold activation in supported gold catalysts was proposed as follow:
The possible catalytic active state is the partially oxidized gold (Au+) with unoccupied outer d orbitals, similar to the outer d orbital structure of Pt. Thus "inert" gold can become very active for CO oxidation.  相似文献   

4.
The theory of the polarographic catalytic currents (mechanism CE) has been developed for the system: Ni2+-L-Xp− where L: pyridine (Py), nicotinamide (NA), N,N-diethylnicotinamide (DEN), nicotine (NC) and Xp−: NO− 3, AcO−, HPO2− 4 . The theory is based on the kinetic parallel heterogeneous catalytic reactions:
(1a)
(1b)
with the use of Langmuir’s adsorbed isotherm. The kinetic equations obtained for average and instantaneous currents allowed to determine the Langmuir’s parameters (NA<DEN<NC), kinetic parameters and the contribution of reactions 1a and b to the summary catalytic currents. The k h″ value rises with the increase of the NiX2−p stability constant. The correlation k h″≫k h′ was explained by the additional effect of the field electrode through Xp−. These effects base the reaction 1b instead of accepted early alternative reaction of the ligand exchange. In spite of the fact that k h″≫k h′, the contribution of the reaction 1a in the summary catalytic current attained more than 60% (Py, DEN) due to the influence of the ψ0 potential. Dedicated to Professor Zbigniew Galus on the occasion of his 70th birthday and in recognition of his many contributions to electrochemistry  相似文献   

5.
The solubility of siderite (FeCO3) at 25°C under constant CO2 partial pressure [p(CO2)] was determined in NaCl solutions as a function of ionic strength. The dissolution of FeCO3(s) for the reaction
has been determined as a function of pH = – log[H+]. From these values we have determined the equilibrium constant for the stoichiometric solubility to FeCO3(s) in NaCl
These values have been fitted to the equation
with a standard error of s = 0.15. The extrapolated value of log(K o sp) – 10.9 in water is in good agreement with data in the literature (– 10.8 to – 11.2) determined in solutions of different composition and ionic strength.The measured values of the activity coefficient, T(Fe2+) T(CO3 2–), have been used to estimate the stability constant for the formation of the FeCO3 ion pair, K*(FeCO3). The values of K*(FeCO3) have been fitted to the equation (s = 0.09)
The value of log[K o(FeCO3)] in water found in this study (6.3 ± 0.2) is slightly higher than the value found from extrapolations in 1.0 m NaClO4 solutions (5.9 ± 0.2). These differences are related to the model used to determine the activity coefficients of the Fe(II) and carbonate species in the two solutions.  相似文献   

6.
The kinetics of the environmentally important oxidation of sulfur(IV) by oxygen in acetate buffered medium in the presence of Fe(III) and the pH range 5.27–5.70 has been studied. The results were in agreement with the rate law:
The role of iron(III) appears to be that of production of SO3− radicals in Fe(III)SO32− complex by an internal 1-equivalent redox reaction. Subsequently, a radical mechanism involving oxysulfur radicals, viz., SO3−, SO4−, and SO5− operates. Addition of ethanol leads to the introduction of an induction period and decrease in reaction rate, most likely due to scavenging of SO4− radicals. The value of apparent energy of activation is 45.4 kJ mol−1.  相似文献   

7.
The equilibrium constant for the hydrolytic disproportionation of I2
has been determined at 25°C and at ionic strength 0.2 M(NaClO4) in buffered solution. The reaction was followed in the pH range where the equilibrium concentration of I2, I–, and IO3 –are commensurable, i.e., the fast equilibrium
is also established. The equilibrium concentrations of I2and I3 –were determined spectrophotometrically, and the concentrations of all the other species participating in process (1) were calculated from the stoichiometric constraints. The constants determined are \log K_1 = -47.61\pm 0.07 and \log K_2 = 2.86 \pm 0.01.  相似文献   

8.
For getting an insight into the mechanism of atmospheric autoxidation of sulfur(IV), the kinetics of this autoxidation reaction catalyzed by CoO, Co2O3 and Ni2O3 in buffered alkaline medium has been studied, and found to be defined by Eqs. I and II for catalysis by cobalt oxides and Ni2O3, respectively.
(I)
(II)
The values of empirical rate parameters were: A{0.22(CoO), 0.8 L mol−1s−1 (Co2O3)}, K 1{2.5 × 102 (Ni2O3)}, K 2{2.5 × 102(CoO), 0.6 × 102 (Co2O3)} and k 1{5.0 × 10−2(Ni2O3), 1.0 × 10−6(CoO), 1.7 × 10−5 s−1(Co2O3)} at pH 8.20 (CoO and Co2O3) and pH 7.05 (Ni2O3) and 30 °C. This is perhaps the first study in which the detailed kinetics in the presence of ethanol, a well known free radical scavenger for oxysulfur radicals, has been carried out, and the rate laws for catalysis by cobalt oxides and Ni2O3 in the presence of ethanol were Eqs. III and IV, respectively.
(III)
(IV)
For comparison, the effect of ethanol on these catalytic reactions was studied in acidic medium also. In addition, alkaline medium, the values of the inhibition factor C were 1.9 × 104 and 4.0 × 103 L mol−1 s for CoO and Co2O3, respectively; for Ni2O3, C was only 3.0 × 102 only. On the other hand, in acidic medium, the values of this factor were all low: 20 (CoO), 0.7 (Co2O3) and 1.4 (Ni2O3). Based on these results, a radical mechanism for CoO and Co2O3 catalysis in alkaline medium, and a nonradical mechanism for Ni2O3 in both alkaline and acidic media and for cobalt oxides in acidic media are proposed.  相似文献   

9.
The low-pressure discharge flow technique with resonance fluorescence monitoring of OH has been applied to study the kinetics of the overall reaction:
(1)
The rate constant of k 1 = (1.09 ± 0.09(1σ)) × 10−12 cm3 molecule−1 s−1 has been determined at T = 297 ± 3 K. This value agrees well with the IUPAC recommendation which is based on photolysis kinetic studies.  相似文献   

10.
The solubility of rhodochrosite (MnCO3) at 25°C under constant carbon dioxide partial pressure p(CO2) was determined in NaCl solutions as a function of ionic strength I. The dissolution of MnCO3(s) for the reaction
has been determined as a function of pH. From these values, we have determined the equilibrium constant for the stoichiometric solubility of MnCO3(s) in NaCl solutions
These values have been fitted to the equation
with a standard error of = 0.1 with Iand concentrations in molalities. The extrapolated value of log K o sp(–10.3) in water is in good agreement with literature data (–10.1 to 10.8) determined in solutions of different composition and ionic strength. The measured values of the activity coefficient, T(Mn2+) and T(CO3 2–), have been used to estimate the stability constant for the formation of the MnCO3ion pair, K *(MnCO3 0). The value of K 0(MnCO3 0) calculated from the values of K *(MnCO3) by the Pitzer equation ( = 0.1) in this study (4.8 ± 0.1) is in reasonable agreement with literature data.  相似文献   

11.
The osmium(VIII) catalysed IO4 − oxidation of DMF in aqueous alkaline medium follows the rate law:
  相似文献   

12.
The oxidation of H2NOH is first-order both in [NH3OH+] and [AuCl4 –]. The rate is increased by the increase in [Cl–] and decreased with increase in [H+]. The stoichiometry ratio, [NH3OH+]/[AuCl4 –], is 1. The mechanism consists of the following reactions.
The rate law deduced from the reactions (i)–(iv) is given by Equation (v) considering that [H+] K a.
The reaction (iii) is a combination of the following reactions:
The activation parameters for the reactions (ii) and (iii) are consistent with an outer-sphere electron transfer mechanism.  相似文献   

13.
The oxidation of l-valine (l-val) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 3.0 × 10−3 mol dm−3 was studied spectrophotometrically at 298 K and follows the rate law;
where K 4, K 5 and K 6 are the equilibrium constants for the different steps involved in the mechanism, k is the rate constant for the slow step of the reaction. The appearance of [l-val] term in both numerator and denominator explains the observed less than unit order in [l-val]. Similarly the appearances of [H3IO6 2−] and [OH−] in the denominator obey the experimental negative less than unit order in [H3IO6 2−] and [OH−], respectively. The oxidation reaction in alkaline medium proceeds via a DPC-l-valine complex, which decomposes slowly in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test and spectroscopic studies.  相似文献   

14.
The kinetics of osmium(VIII)-catalyzed oxidation of hypophosphite with hexacyanoferrate(III) in alkaline medium has been studied. The rate is independent of the concentration of the oxidant. The order with respect to hydroxide ion is variable. Rate law (1) conforms with the experimental observations.
The equilibrium constant 'K 1' for step (2)
has been evaluated kinetically to be (21 ± 5.0), (23 ± 5.0), (26 ± 6) and (32 ± 6) at 25, 30, 32 and 35 °C and I = 1.0 mol dm–3 respectively. The energy and entropy of activation were calculated to be (42 ± 2.0) kJ mol–1 and (82 ± 6.0) J K–1 mol–1 respectively. A plausible reaction mechanism has been suggested.  相似文献   

15.
The activity coefficients of HCl (γA) in aqueous mixtures of HCl and NdCl3 were determined by the electromotive-force (emf) measurement of cells without liquid junctions of the type:
((A))
The experiments were carried out at nine constant total ionic strengths of I = 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 1.5, and 2.0 mol-kg−1, and at 11 temperatures from 5 to 55 ∘C, but at I = 2.0 mol-kg−1 the experimental temperatures were 5, 25 and 55 ∘C only. Harned's rule was used to represent all 728 experimental emf data points at the experimental ionic strengths and temperatures. The quadratic terms in the Harned equations for the values of logγA were required for a good fit to the emf data, indicating the significance of ternary interactions at the experimental ionic strengths. The adjoining paper deals with the application of the Pitzer ion-interaction theory to estimate the Pitzer's mixing parameters for binary and ternary interactions.  相似文献   

16.
The state of the water-soluble salt iron(III) chloride in AOT reverse micelles dispersed in carbon tetrachloride has been investigated by FT-IR spectroscopy. Interestingly, while the entrapment of a lot of water-soluble inorganic salts in AOT reverse micelles requires preliminarily the presence of significant amounts of water within the micellar core, solubilization of FeCl3 occurs without the need to add water in the micellar solution reaching the very high solubility value, expressed as the maximum salt-to-surfactant molar ratio, of 1.30. The analysis of the spectral features of the investigated samples leads to hypothesize that iron(III) chloride is confined within the reverse micellar core as small size melted clusters of ionic species arising from the reactions
accompanied by a marked structural rearrangement of the AOT head group domain surrounding the micellar core and a shift of the sodium counterion from the micellar core surface to its interior. This picture has been further corroborated by conductivity measurements of FeCl3/AOT/CCl4 solutions as a function of the salt-to-surfactant molar ratio.  相似文献   

17.
Oxidation of 3-(4-methoxyphenoxy)-1,2-propanediol (MPPD) by bis(hydrogenperiodato) argentate(III) complex anion, [Ag(HIO6)2]5− has been studied in aqueous alkaline medium by use of conventional spectrophotometry. The major oxidation product of MPPD has been identified as 3-(4-methoxyphenoxy)-2-ketone-1-propanol by mass spectrometry. The reaction shows overall second-order kinetics, being first-order in both [Ag(III)] and [MPPD]. The effects of [OH−] and periodate concentration on the observed second-order rate constants k′ have been analyzed, and accordingly an empirical expression has been deduced:
where [IO4 −]tot denotes the total concentration of periodate and k a = (0.19 ± 0.04) M−1 s−1, k b = (10.5 ± 0.3) M−2 s−1, and K 1 = (5.0 ± 0.8) × 10−4 M at 25.0 °C and ionic strength of 0.30 M. Activation parameters associated with k a and k b have been calculated. A mechanism is proposed, involving two pre-equilibria, leading to formation of a periodato–Ag(III)–MPPD complex. In the subsequent rate-determining steps, this complex undergoes inner-sphere electron-transfer from the coordinated MPPD molecule to the metal center by two paths: one path is independent of OH−, while the other is facilitated by a hydroxide ion.  相似文献   

18.
In the search of a useful method for determining excess enthalpies as a function of temperature Calvet calorimetry was employed. To this end, excess molar enthalpies
at 298.15 and 333.15 K and excess molar heat capacities
within 283.15–333.15 K were determined for the 1-decanol+n-decane system over the whole composition range. An isothermal flow Calvet-type calorimeter was used for
measurements, whereas
were determined by means of a Setaram Micro DSC calorimeter. Excess enthalpies within 283.15–333.15 K were indirectly obtained through the integration of
(T) data using
at 298.15 K. The results obtained at 333.15 K agreed with those determined directly, implying the thermodynamic consistency of the measured data and, therefore, the reliability of the indirect method.  相似文献   

19.
The aqueous reactions,
  相似文献   

20.
In this work some calorimetric measurements were also carried out on the electrorefining silver by using different current densities with a Calvet type microcalorimeter at room temperature. The ratio (R) of the measured heat (
m) to the input electric energy (
in) and the excess heat (
ex), i.e., difference between
m and
in during the electrorefining process, were discussed in terms of general thermodynamics. It was found that the R and
ex for silver were related with the current density or cell voltage employed in the experiment. The results obtained here also indicate that the heat generation under different conditions, such as different currents or voltages may be caused partially by the irreversibility of the process or by some unknown processes.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号