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911.
The ion product of water and the dissociation constants of carbonic acid have been determined in 0.1, 1.0, 3.0, and 5.0M NaClO4 at 25°C. The ion product of water K w ' has been evaluated by emf measurements with a combined glass electrode in NaClO4 solutions containing 0.001–0.1M HCLO4 or NaOH. The product K H ' K l ' K 2 ' of the Henry constant for CO2 and the dissociation constants for H2CO3 have been determined by titration of carbonate solutions equilibrated with pCO2 =10–3.52 atm, and K 2 ' has been evaluated by potentiometric titration and by measuring the H+ concentration at fixed HCO 3 and CO 3 2- concentrations. The ion interaction (Pitzer) equations are applied to describe the constants K w ' , K 2 ' and K H ' H 1 ' K 2 ' as a function of the NaClO4 concentration. The experimental data are used to evaluate the mixing parameters i/ClO 4 and i/ClO 4 -/Na+ fori = OH -,HCO 3 - andCO 3 2-  相似文献   
912.
Controlled-rate thermal analysis (CRTA) and differential scanning calorimetry (DSC) were used to investigate the adsorbed water layers and the surface properties of different commercial activated carbons. A simple method is proposed to obtain information on the properties of the adsorbed water film and the surface heterogeneity of the materials studied. This method utilizes TG mass loss and the first derivative of the DTG mass loss curves with respect to temperature and time, obtained during programmed liquid thermodesorption. The obtained TG mass loss curves, which reflect the energetic heterogeneity, consisted of steps and inflections which were associated with the mechanism of wetting of the solid surfaces. The heights of these steps and inflections depend on the adsorption capacity, the adsorption potential and the nature and number of the active centers of the carbon samples studied. The values of the total porosity and the surface phase capacity obtained by this method are in good agreement with those estimated on the basis of independent methods. The behaviour of water/carbon samples was studied by means of DSC at subambient and elevated temperatures. The experimental results provided novel data on the structural heterogeneity, the thermal stability of the water/carbon interface and its phase and structural transitions.Support from the Research Council of Kent State University (Ohio, USA) is acknowledged. The author is pleased to thank Drs M. Jaroniec, R. K. Gilpin, J. Choma and R. Dobrowolski for fruitful discussions and the active carbon samples.  相似文献   
913.
The energy of combustion of 2,5-dimethoxybenzoic acid has been determined using a static bomb calorimeter. The vapor pressures of the compound have been measured over a 18 K temperature interval by the Knudsen effusion technique. Heat capacity measurements betweenT=270 K andT=338 K were carried out by DSC. From these experimental results the standard molar enthalpies of combustion, sublimation, and formation in the crystalline and gaseous state at the temperature 298.15 K have been derived. With this compound, the series of mono- and dimethoxy-benzoic acids have been completed. Theirf H m o values were expressed by an additive relationship, taking into account the number of methoxy groups and the number of all 1,2 interactions: an accuracy of 3.3 kJ·mol–1 was achieved. In an alternative approach the substituent effect of the methoxy groups was evaluated within the framework of isodesmic reactions. The effect of disubstitution was referred to mono derivatives and the excess energy—the so-called buttressing effect—was evaluated (2–24 kJ· mol–1 for individual bis derivatives). These values were explained in terms of the conformation of the methoxy group around the Car-O bond.  相似文献   
914.
The results of studies on the synthesis of porphyrin-quinone compounds and investigation of their photochemical properties are summarized. Effects of various factors (the redox potential, the distance between donor and acceptor moieties, their spatial orientation, the free energy of the reaction, and solvents) on the photoinduced electron transfer in these model systems are discussed. The dyad and triad model systems have been compared. The possibility of using these systems for modeling the primary steps of photosynthesis is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1. pp. 9–24, January, 1996.  相似文献   
915.
The kinetics of the AIBN-initiated free radical bulk polymerization of fiveo-alkylphenyl methacrylates was studied by means of DSC in the temperature range 353–373 K, and the enthalpy of polymerization, the overall reaction rate constant and the activation energy were determined. The results were compared with those published recently on correspondingp-alkylaryl methacrylates. All measured reaction rate constants were found to increase with increasing temperature and to decrease with increasingo-alkyl substituent mass and size. It was shown thato-substituents influence the rates of polymerization to a greater extent thanp-substituents. At about 373 K, all differences in rate, most probably resulting from steric hindrance caused by the alkyl groups, disappear in both series, a phenomenon earlier observed for dimethyl phenyl methacrylates.This work was supported by the Ministry of Science of the Republic of Serbia.  相似文献   
916.
The reaction of 2,6-dibenzylidenecyclohexanone with PCl5 occursvia the sequential stages of desoxychlorination and substitutional phosphorylation to form (after oxidation, methoxylation, and hydrolysis on the surface of the chromatographic SiO2 adsorbent) organophosphorus products of the 1-(a-chloro-, a-hydroxy-, or -alkoxy)benzyl-2-chloro-3-(-(dimethylphosphoryl)benzylidene)cyclobex-1-ene series.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 441–443, February, 1996.  相似文献   
917.
The treatment of zeolite with a solution of NaOH at different concentrations creates modified forms of natural zeolites.These modified zeolites exhibit an increased uptake of caesium and a satisfactory uptake of cobalt. The structural changes in the modified zeolites were studied by XRD analysis, which reveals the mineral compositions of the studied materials. The thermodynamic properties of the modified zeolites were studied by means of DTA and thermogravimetry, and the chemical composition too was determined.  相似文献   
918.
Hold-up times and peak widths have been measured in long fused silica GC capillary columns at high temperature with helium as the carrier gas. The results lead to the conclusion that the helium permeates through the column walls. The conventional Poiseuille theory of carrier gas flow has been extended to include this phenomenon. The resulting “loss modified Poiseuille” model, which uses literature values for the permeability of fused silica to helium, has been used to simulate the observed behavior. Good agreement between simulation and experiment validates the model. Simulations have been used to explore the effect of column permeability on hold-up times, peak widths, and velocity profiles over a broad range of column geometries.  相似文献   
919.
柳萍  周定 《分析试验室》1996,15(4):73-75
本文建立了流动注射二甲酚橙光度法测定镀锌纯化液中Zn ̄2+的自动分析方法。利用区域采样技术和调整管路参数自动完成对样品的上千倍稀释,确定了最佳分析条件并研究了干扰离子的影响及消除办法。所建方法仪器简单,分析速度为84次/小时,变异系数(Zn ̄2+16.0g/L,n=20)为1.O%,用于实际钝化液分析,相对误差小于±10%。  相似文献   
920.
介绍了非均匀相催化剂的MOVS制备方法,以该法制得的MoO3催化剂在甲醇选择氧化制甲醛、CO加氢制高级和喹啉加氢脱氮中均显示出常规催化剂更为优异的催化性能,并探讨了MOVS催化剂的内在特性与催化性能的关系。  相似文献   
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