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Table of Content
25 December 1982, Volume 33 Issue 4
    化工学报
    Investigation of Chemical and Electrochemical Changes within Corrosion Cracks I. Interrelations between currents, Cl~- migration and pH values
    Zuo Jingyi and Jin Zhiqiang Beijing Institute of Chemical Technology
    1982, 33(4):  291-301. 
    Abstract ( 677 )   PDF (615KB) ( 254 )  
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    A simulated occluded corrosion cell was used to study the changes within corrosion cracks or crevices of Cr 18 Ni 9 Ti austenitic stainless steel in NaCl solution. As anodic currents passed the cell a series of changes took place, the most important of which were pH fall and Cl- migration. It was found that the pH fall was proportional to current density and time of current flowing. Consequently, pH fall was a function of the quantity of electricity passing the occluded anode. The pH in the occluded cell might attain negative value whencurrent density was 3.5mA/cm2 after 168 hrs. Meanwhile the Cl- migration into occluded cell increased the Cl- concentration 18 times as much as original concentration. As a rule, the Cl- migration versus unit anode area was proportional to time of current flowing. A linear relationship existed between Cl-migration in g-equivalents per cm2 of anode area and current density, and also a linear relation existed between Cl- migration per hour and current intensity. Consequently, the number of equivalents of Cl- migration into crack tip was proportional to the quantity of electricity passing it. It was interesting to discover that while each faraday passed almost always 1/2 g-equivalent of Cl-migrated into the occluded cell. This relationship did not change whatever were the concentration of bulk solution (from 0.01N to 5N NaCl), current density, temperature and time. Two empirical formulas regarding to the relationship between pH and Cr3+ concentration or Cl- migration respectively were derived based on the relationships between quantity of electricity passing and other variables found in the present experiments, i. e. PH=-2.60-log[Cr3+] pH=-1.84-log[Cl-]
    II. Relations between potential and pH in the bulk and occluded cell
    Zuo Jingyi, Zhang Shuxia, Xu Yubao and Wang Quangyao (Beijing Institute of Chemical Technology)
    1982, 33(4):  302-309. 
    Abstract ( 515 )   PDF (495KB) ( 183 )  
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    A simulated occluded cell which can be loaded by lever system was designed to study the changes of potential and pH in occluded cell with polarization of bulk specimen. The system studied was Crl8Ni9Ti austenitic stainless steel-0.5M NaCl at 40℃. It was found that the critical crevice (or stress cor-rosion) potential of this system lies almost in the same range as the corrosion potentials of the occluded and bulk potential (0V to -0.2V SCE). The rule of changes of the potentials and pH values in the occluded cell could be classified into three categories as follows. 1. When the bulk specimen was polarized above the critical potential, the occluded potentials did not rise with bulk potential, but remained nearly constant within corrosion potential range (-0.10 to- 0.13V SCE). Meanwhile, the pH in the occluded cell decreased rapidly from 7 to 2-3.5. 2. When the bulk specimen was polarized below the critical potential, the occluded potential always kept a few mV more positive than the bulk potential, and the pH in the occluded cell increased higher than bulk pH (>7). 3. When the potential of bulk specimen remained in the range of the critical potential, no change of pH and potential in the occluded cell took place within a long period. The tensile load of occluded specimen caused both the potential and pH in the occluded cell lower than those without load under anodic polarization of the bulk specimen, but no effect under cathodic polarization. The important phenomenon of incubation period for crevice or stress corrosion could be interpreted properly by the present results. The crevice or stress corrosion starts only when the bulk potential rises above the critical po-tential so that a corrosion cell of sufficient voltage difference between bulk cathode and occluded anode could be established. A rapidly accelerating process will result from pH fall and Cl- migration in the occluded cell. While the bulk potential is lower than the critical potential (cathodically polarized), the crevice or stress corrosion will not occur since no significant voltage difference exists between bulk and occluded cell. It is very interesting that the potential and pH in the occluded cell have a simple relation with the bulk potential. It could be easily to evaluate occluded potential or pH if one knows the bulk potential. By controlling the bulk potential one could make the initiation and propagation of crevice or stress corrosion prevented. Besides, one may determine whether there is danger of crevice or stress corrosion by measuring the bulk potential.
    A Process Based upon Solvent Extraction for the Purification of Phosphoric Acid.
    Jiang Yuming, Li Daochun and Su Yuanfu. East China Institute of Chemical Technology.
    1982, 33(4):  310-318. 
    Abstract ( 586 )   PDF (503KB) ( 233 )  
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    A process based upon solvent extraction has been developed for the recovery of phosphoric acid from a leaching liquor obtained by decomposition of phosphate rock with sulfuric acid. Using Di-n-Butyl Sulfoxide (DBSO) as extractant and multistage counter-current extraction and stripping, pure phosphoric acid or potassium dihydro-gen phosphate can be produced on one hand, and precipipated calcium phosphate on the other. The proportion of both products may be economically adjusted in accordance with varying demands. This process will leave an effluent which is less polluting than any existing process.
    Studies on Ultrasonic Degradation and Block Copolymerization of Polyacrylamide and Poly (Ethylene Oxide)
    Hu Xingqi and Xu Xi Polymer Research Institute, Chengdu University of Science and Technology
    1982, 33(4):  319-326. 
    Abstract ( 607 )   PDF (366KB) ( 109 )  
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    The kinetics of the ultrasonic degradation of aqueous solution of poly-acrylamide and poly(ethylene oxide) as well as ultrasonic block copolymeriza-tion of aqueous solution of the mixture of polyacrylamidepoly (ethylene oxide) were studied respectively. The degradation reaction of poly (ethylene oxide) follows a linear relationship between 1/ (Pt - P) and irradiation time, while that of polyacrylamide follows a linear relationship between 1/ (Pt - P)1/2 and irradiation time. As the structure of the copolymer was identified by IR, DTA and NMR, the hydrogen atoms in polyacrylamide remain unchanged, and the copolymer prepared is a block copolymer.
    An Applied Study on Nafion Membrane in Electrolytic Preparation of Potassium Carbonate
    Yang Weiyi and Fumio Hine Jinxi Research Institute of Chemical Industry Department of Synthetic Chemistry, Nagoya Institute of Technology, Japan
    1982, 33(4):  327-336. 
    Abstract ( 559 )   PDF (535KB) ( 204 )  
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    This investigation describes the one step preparation of potassium carbonate by electrolysis of potassium chloride solution in the electrolyzers with various kinds of Nafion membranes. Potassium bicarbonate solution was fed to the cathode compartment, where it was converted into carbonate by reacting with the hydroxide formed at the cathode. Because of the low OH-concentra-tion in the cathode compartment, the back migration of OH-through the membrane was almost negligible, resulting in a higher current efficiency, say 90% or more. In the study, the electroconductivity, the mass transfer through the membrane, current efficiency and the cell voltage were measured, the feasibility was examined, and the optimal electrolytic condition selected.
    The Kinetics of Vapor Phase Benzene Hydrogenation Reaction on a Commercial Nickel Catalyst
    Li Shaofen, Liu Bangrong, Gao Wenxin and Liao Hui Department of Chemical Engineering, Tianjin University
    1982, 33(4):  337-347. 
    Abstract ( 797 )   PDF (540KB) ( 298 )  
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    The kinetics of vapor phase benzene hydrogenation reaction on a commercial nickel catalyst was studied in an internal recycle gradientless reactor under atmospheric pressure. The molar ratio of hydrogen to benzene was varied between 6.0 and 18. The temperature range investigated was 90℃-180℃. The catalyst loading of liquid benzene was 1-46 ml/h·g-cat. Assume that there are two kinds of sites on the catalyst surface, benzene vapor adsorbs on one type of site X and hydrogen dissociate upon adsorption on another, say S. Reaction scheme consists of the following steps: Assume that the third step is the rate determining step, and hydrogen are weakly adsorbed on the surface, the intrinsic kinetic equation of cyclohexane formation is derived as follow: where pB and pH are the partial pressures of benzene and hydrogen respectively, k is rate constant and bB, the adsorption equilibrium constant of benzene. The experimental results fitted in this equation with an average absolute deviation of 6.1% The activation energy of reaction was found to be equal to 1.31×104 cal/ mol, and the heat of adsorption of benzene 9840 cal/mol, which are close to the values from literature.
    Evaporation of Droplets Containing Various Dissolved Inorganic Salts
    Wu Yuan, Zheng Chong and Fu Jufu Beijing Institute of Chemical Technology
    1982, 33(4):  348-358. 
    Abstract ( 528 )   PDF (692KB) ( 231 )  
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    The evaporation of single droplets containing various dissolved inorganic salts was studied experimentally. It was found that the drying process of most sample droplets in a high temperature gas stream comprised four rather than two periods, namely, (1) a constant rate period at wet-bulb temperature, (2) a falling rate period, (3) a boiling-evaporation period or constant rate period at the boiling point of the saturated solution and(4) a second falling rate period. Such a four-stage mechanism should be taken as a general one for the evaporation-drying process of droplets containing dissolved solid substances, and the disappearance of certain stages is but a special case under certain conditions. The effects of some variables such as medium temperature, initial concentration and initial diameter of droplet on the drying charateristics were investigated. The critical moisture contents corresponding to the turning points of various drying stages have been measured.
    A Review on Research Works and Applications of Enhanced Heat Transfer Element——Spirally Corrugated Tube
    Li Heungming, Ye Kuosing and Deng Songjiu Research Institute of Chemical Engineering South China Institute of Technology
    1982, 33(4):  359-367. 
    Abstract ( 744 )   PDF (639KB) ( 161 )  
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    Research, works and applications of enhanced heat transfer element- spirally corrugated tube, including the heat transfer and friction experimental data and correlations both with and without phase change as well as its scaling characteristics, are reviewed. Some subjects are also proposed for further work in this field.
    A Method for Simultaneous Evaluation of Axial Mixing Coefficients and True -HTU in the Extraction Column from Concentration Profiles under Steady State
    Lei Xia, Fei Weiyang, Shen Zhongyao and Wang Jiading Chemistry and Chemical Engineering Department, Tsinghua University
    1982, 33(4):  368-376. 
    Abstract ( 662 )   PDF (458KB) ( 141 )  
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    A method for simultaneous evaluation of axial mixing coefficients and True -HTU of the extraction column is suggested. By this method the measured steady state concentration profiles of the two phases in the column are fitted with the optimal technique based on the diffusion model in the form given by Miyauchi and Vermeulen. This method has been successfully applied in the study of the performance of mass transfer of the system HNO3 (aq. )-30% TBP (kerosene as diluent) in a pulsed sieve plate extraction column.
    A Rapid Automatic Method for Determining the Crosslink Density of Vulcanizates
    Liu Yadong and Zhang Xinhui Changchun Institute of Applied Chemistry, Academia, Sinica
    1982, 33(4):  377-382. 
    Abstract ( 589 )   PDF (269KB) ( 163 )  
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    The apparatus designed can record the volume changes of a vulcanizate (0.2 mm in thickness) in the swelling process in the solvents with photoelectric transformation. It may be used to measure the value of Vr of vulcanizates, and investigate the swelling kinetics of vulcanizates on the basis of the swelling curves. By changing the solvent, the apparatus can be used to study kinetics of oil-or other medium (such as acids, bases)-absorption, and to determine the oil-absorption and medium-absorption number of the sample. The apparatus designed is characterized by its being automatic and rapid in operation, ease in handling and accuracy.
    The Relationship between Freezing Point Depression of Aqueous Inhibitor Solution and Depression of Gas-Hydrate Formation Temperature
    He Chengzu Department of Petroleum Development Engineering, South-West Petroleum Institute
    1982, 33(4):  383-387. 
    Abstract ( 497 )   PDF (258KB) ( 208 )  
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    In this paper, the correlation between depression of gas hydrate formation temperature AT and freezing point depression of aqueous inhibitor solution △T has been established according to the principle of thermodynamics: where n is water molecular number in the gas hydrate, T0, T0 are gas hydrate formation temperature and freezing point of water in the absence of inhibitors, respectively, λ, λ are gas hydrate formation heat and ice fusion heat respectively. △T can be calculated from △T with this coreelation. The results obtained are close to experimental values. Pieroens mehtod can only be used for non-electrolyte inhibitors, whereas this method is independent of the types of inhibitors. Since △T is obtained more easily than △T, this method is useful practically.