INVESTIGATION OF CHEMICAL AND ELECTROCHEMICAL CHANGES WITHIN CORROSION CRACKS Ⅱ.Relations between potential and pH in the bulk and occluded cell

A simulated occluded cell which can be loaded by lever system was designed to study the changesof potential and pH in it with polarization of hulk specimen for the system "lCrl8NigTi-Cl-".It wasfound that the critical stress corrosion potential lies in the same range as the corrosion potentials ofthe occluded cell.The rule of changes of potentials and pH in the occluded cell could be classifiedinto three categories:1.When the bulk specimen is polarized above the critical potential,the occluded potentials re-main nearly constant within corrosion potential range.Meanwhile,the pH in the occluded cell decreasesrapidly from 7 to 2-3.5.The stress corrosion starts and propagates because a corrosion cell of sufficientvoltage difference is established.2.When the bulk s tyecimen is polarized below the critical potential,the occluded potential alwayskeeps a few mV more positive than the bulk potential,and the pH in the occluded cell increases to higherthan bulk pH (>7).The crevice is cathodically protected.3.When the potential of bulk specimen remained in the range of the critical potential,no changeof pH and potential in the occluded cell took place.By the above relations it would be easy to evaluate occluded potential of pH from the bulk poten-tial,and one may determine whether there is danger of crevice or stress corrosion by measuring the bulkpotential.By controlling the bulk potential one could make the initiation and propagation of crevice orstress corrosion prevented.     

Influence of the operating parameters over the current efficiency and corrosion rate in the Hall-Heroult aluminum cell with tin oxide anode substrate material

A systematic laboratory study was conducted on current efficiency and corrosion obtalned in cryolite–alumina melts with SnO2–Sb2O3–CuO ceramic inert anodes. The current efficiency (CE) was determined by measuring the total amount of oxygen evolved at the anode and was found to be~95%. The influence of operating parameters (inter-elec-trode distance, temperature and current density) was evaluated. The quantitative interdependencies as wel as the ranges of CE optimal values were established (2–3 cm, 940–960 °C and 0.7–0.8 A·cm?2). The corrosion process of these anodes was evaluated by the mass loss method. The evaluation also took care of the corrosion data, as the prob-lem of the anode corrosion appeared to be the maln obstacle for the use of those anodes in the commercial cel s. Low-ering of the ACD up to 2 cm did not aggravate anode corrosion.     

低浓度含氯介质中氯离子向局部腐蚀闭塞区内的迁移规律及其对应力腐蚀破裂的影响

The enrichment of chloride anion within the occluded cell （OC） for Type 304 austenitic stainless steel in low chloride concentration solution has been investigated by means of a simulated OC. The influence of the enrichment of chloride anion on stress corrosion crack （SCC） of Type 304 stainless steel has been studied. It was observed that the amount of chloride anion migration was proportional to the charge flowing through the anode. Owning to the effects of enrichment of chloride anion, low chloride concentration solution could induce SCC for Type 304 stainless steel.     

应用铝和铁电极电化学处理酒精废醪蒸馏废水(英文)

Electrochemical treatment of distillery spent wash was carried out using different combinations of aluminum and iron electrodes in batch mode of operation.The spent wash was characterized for various parameters as per standard method of analysis and the treatment results were analyzed in terms of chemical oxygen demand(COD) removal efficiency of the spent wash.The experiments were performed to study the effect of operating parameters such as current density,pH of the spent wash,agitation speed,electrolysis time and the distance between the electrodes on the COD removal efficiency of the spent wash.It was observed that aluminum electrodes were more suitable for treatment of distillery spent wash as compared to iron electrodes.The maximum COD removal efficiency of 81.3% was obtained with Al-Al electrodes at the current density of 0.187 A·cm-2 and pH 3 for an electrolysis time of 2 h.     

Density,refractive index and liquid–liquid equilibrium data of polyethylene glycol 3000 + potassium formate + water at different pH values

New liquid–liquid equilibrium data for polyethylene glycol(PEG) 3000 + CHO_2K + H_2O systems were measured at 298.15 K and pH values of 7.95, 8.40 and 9.98. It was found that an increase in pH caused the binodal curve to be displaced downward and the two-phase region to expand. Accordingly, the binodal curve was adjusted to the Pirdashti equation and the tie-line compositions were correlated using the Othmer–Tobias, Bancroft and Hand equations. The study measured the refractive index and densities of several homogeneous binary and ternary solutions. The solutions were used for calibration within a range of 0% to 30% of the mass of the PEG and potassium formate. The density and refractive index data show a linear variation with the mass fraction of the polymer and the salt. The effect of pH on the binodal, tie-line lengths(TLL) and slope of the tie-line(STL) in the systems was examined. It was found that an increase in pH increased the TLL and decreased the STL. It was observed that the density of the aqueous two-phase system was influenced by the TLL. The difference in density between phases(Δρ) increased as the TLL and pH increased. It was found that the TLL and Δρ showed a linear relationship. The effective excluded volume(EEV) of the PEG was obtained and it was found that EEV also increased as the pH increased.     

Preliminary Study on E. coli Microbial Fuel Cell and On-electrode Taming of the Biocatalyst

A mediator microbial fuel cell (MFC) was constructed by using E. coli as biocatalyst and new methylene blue as electron mediator. E. coli cells were carried out in anaerobic growth prior to inoculating them into the MFC in order to pre-adapt bacterial metabolism in an anaerobic environment, the electricity generation of MFC was tested, its maximum power density reached 263.94 mW/m2 with the corresponding current density 1287.50 mA/m2, the internal resistance of MFC was 200 W, and capability of the MFC was even better than those reported so far. Moreover, on-electrode taming method was adopted to improve electrochemical activity of E. coli, namely a combination of E. coli taming and electricity generation simultaneously in the same MFC without scraping off the biofilm of MFC, after the 4th on-electrode taming, the tamed E. coli MFC showed a 54% improvement in peak current density, being 612.50 mA/m2, and a 64% improvement in the maximum power output, being 166.67 mW/m2, compared with that of parental E. coli MFC. And the maturation time of tamed biofilm was obviously reduced to 240 min, quickening up 1 times compared with that of parental E. coli biofilm.     

INVESTIGATION ON ELECTROCHEMISTRY INSIDE STRESS CORROSION CRACKS OR PITS

Techniques are developed for studying the mechanism of localized corrosion and protectivemeasures against such corrosion are suggested.The pH values and composition of the occluded sol-ution at different propagation stages are determined.Measurements of the critical pH value and cor-rosion rate inside the occluded cells are conducted.Potential-pH diagrams depicting kinetic andthermodynamic behaviors of occluded cell corrosion are being established.The mechanism of inhibi-tion of pitting and stress corrosion cracking have also been investigated.     

平板式直接内重整固体氧化物燃料电池的一维动态建模与仿真

This article aims to investigate the transient behavior of a planar direct internal reforming solid oxide fuel cell (DIR-SOFC) comprehensively. A one-dimensional dynamic model of a planar DIR-SOFC is first developed based on mass and energy balances, and electrochemical principles. Further, a solution strategy is presented to solve the model, and the International Energy Agency (IEA) benchmark test is used to validate the model. Then, through model-based simulations, the steady-state performance of a co-flow planar DIR-SOFC under specified initial operating conditions and its dynamic response to introduced operating parameter disturbances are studied. The dynamic responses of important SOFC variables, such as cell temperature, current density, and cell voltage are all investigated when the SOFC is subjected to the step-changes in various operating parameters including both the load current and the inlet fuel and air flow rates. The results indicate that the rapid dynamics of the current density and the cell voltage are mainly influenced by the gas composition, particularly the H2 molar fraction in anode gas channels, while their slow dynamics are both dominated by the SOLID (including the PEN and interconnects) tem-perature. As the load current increases, the SOLID temperature and the maximum SOLID temperature gradient both increase, and thereby, the cell breakdown is apt to occur because of excessive thermal stresses. Changing the inlet fuel flow rate might lead to the change in the anode gas composition and the consequent change in the current den-sity distribution and cell voltage. The inlet air flow rate has a great impact on the cell temperature distribution along the cell, and thus, is a suitable manipulated variable to control the cell temperature.     

在不分隔的反应器中原位电生成活性氯氧化降解蒽醌染料

The purpose of this paper was to investigate the possibility of treating C. I. Reactive Blue 19 wastewater by electrochemical oxidation via electrogenerated active chlorine, using metallic oxide coatings （dimensional stable anode, DSA） as anode. The electrolysis for the simulated wastewater was conducted at a constant current. Absorbances at 592 nm and 255 nm were measured to follow the decolorization of the dye and the degradatin of its aromatic ring. After 4 h of electrolysis under the experimental conditions： current density of 15 A·m^-2, 0.2 mol·L^-1 NaCl, 0.1 mol·L^-1 Na2SO4, 0.1 mmol·L^-1 dye, initial pH=6.4 and T=30℃, 100% decolorization of the dye and about 45% degradation of its aromatic ring were achieved, while no obvious change of total organic carbon was observed. The experimental results suggest that the decolorization of the dye and degradation of its aromatic ring were directly affected by current density, temperature, concentrations of the dye and sodium chloride, while slightly affected by initial pH and sodium sulfate concentration; the decolorization of the dye and degradation of its aromatic ring followed pseudo-first-order kinetics; and indirect electrooxidation, using electrogenerated active chlorine, predominated in the electrochemical oxidation.     

氯离子在含硫氮污染物的环境中对模拟铁器文物的大气腐蚀的影响

The effect of chloride on the atmospheric corrosion of cast iron in sulphur or nitrogen-bearing pollutant was investigated by using periodic wet-dry test, electrochemical experiment and surface tension test. Scanning electron microscopy coupled with energy dispersive atomic （EDAX） and stereoscopic microscopy was used to identify the corrosion processes and products. Cl^- and NO3^- were shown accelerating effects during the whole corrosion process but depression effects were observed in Cl^- and HSO3^- bearing pollutant at the initial corrosion stage. However, with the corrosion going on, the depression effects was less obviously and the initial corrosion process was investigated from the viewpoint of surface activity. At the initial corrosion stage, the corrosion rate was proportional to the adsorptivity of anions, but as corrosion went on, the penetration effect of anions and different characteristics of the corrosion products began to dominate the corrosion process, which led to changes on the corrosion rate.     

利用无膜微生物燃料电池废水处理并回收电能

An upflow mode membrane-less microbial fuel cell （ML-MFC） was designed for wastewater treatment. Granular graphite electrodes, which are flexible in size, were adopted in the ML-MFC. Microbes present in anaerobic activated sludge were used as the biocatalyst and artificial wastewater was tested as substrate. During the electrochemically active microbe enrichment stage, a stable power output of 536 mW.m-3 with reference to the anode volume was generated by the ML-MFC running in batch mode. The voltage output decreased from 203 mV to about 190 mV after the ML-MFC was changed from batch mode to normally continuous mode, indicating that planktonic electrochemically active bacterial strains in the ML-MFC may be carried away along with the effluent. Cyclic voltammograms showed that the attached microbes possessed higher bioelectrochemical activity than the planktonic microbes. Forced aeration to the cathode benefited the electricity generation obviously. Higher feeding rate and longer electrode distance both increased the electricity generation. The coulombic yield was not more than 20% throughout the study, which is lower than that of MFCs with membrane. It is proposed that dissolved oxygen diffused from the cathode to the anode may consume part of the substrate.     

金属硫化物作为阳极材料对H2S固体氧化物燃料电池性能研究

Two anode catalysts with Pt, MoS2 and composite metal sulfides (MoS2 NiS), are investigated for electrochemical oxidation of hydrogen sulfide in solid oxide fuel cell (SOFC) at temperatures 750-850℃. The catalysts comprising MoS2 and MoS2 NiS exhibited good electrical conductivity and catalytic activity. MoS2 and composite catalysts were found to be more active than Pt, a widely used catalyst for high temperature H2S/O2 fuel cell at 750-850℃. However, MoS2 itself sublimes above 450℃. In contrast, composite catalysts containing both Mo and transition metal (Ni) are shown to be stable and effective in promoting the oxidation of H2S in SOFC up to 850℃. However, electric contact is poor between the platinum current collecting layer and the composite metal sulfide layer, so that the cell performance becomes worse. This problem is overcome by adding conductive Ag powder into the anode layer (forming MoS2 NiS Ag anode material) to increase anode electrical conductance instead of applying a thin laver of platinum on the top of anode.     

An Intermediate-temperature H2S Fuel Cell with a Li2SO4-based Proton-conducting Membrane

A laboratory-scale intermediate-temperature H2S fuel cell with a configuration of H2S, （metal sulfide-based composite anode）/Li2SO4＋Al2O3/（NiO-based composite cathode）, air was developed and studied for production of power and for desulfurization of a fuel gas process stream. The cell was run at typical temperature （600-650℃） and ambient pressure, but its electrochemical performance may be limited by electrolyte membrane thickness. The membrane and its performance in cell have been characterized using scanning electron microscope （SEM） and electrochemical impedance spectrum （EIS） techniques. Composite anodes based on metal sulfides, Ag powder and electrolyte behaved well and stably in H2S stream, and composite cathodes based mainly on nickel oxide, Ag powder and electrolyte had superior performance to Pt catalyst. The maximum power density of up to 70mW.cm^-2 and current density of as high as 250mA.cm^-2 were obtained at 650℃. However, the long-term cell stability remains to be investigated.     

光谱学法研究直流放电等离子体条件下甲烷的分解和碳二烃的形成

The IR emission spectra of methane were measured under DC glow discharge conditions. The distinct difference in time between methane decomposition and C2 hydrocarbons formation was specially pointed out. C2 hydrocarbons formed at the end of methane decomposition. The optimum condition for C2 hydrocarbon formation was studied and the optimum combination between electric current density and methane input quantity was suggested. The appropriate reaction conditions for methane decomposition and C2 hydrocarbons formation are different, so high yield of C2 hydrocarbons will be probably obtained when different conditions are taken.     

Scalability of biomass-derived graphene derivative materials as viable anode electrode for a commercialized microbial fuel cell: A systematic review

Microbial fuel cell(MFC) is an advanced bioelectrochemical technique that can utilize biomass materials in the process of simultaneously generating electricity and biodegrading or bio transforming toxic pollutants from wastewater. The overall performance of the system is largely dependent on the efficiency of the anode electrode to enhance electron transportation. Furthermore, the anode electrode has a significant impact on the overall cost of MFC setup. Hence, the need to explore research focus...     

Effects of Precursors for Preparing Intermediate Layer on the Performance of Ti/SnO2+Sb2O3/PbO2 Anode

The Ti/SnO2+Sb2O3/PbO2 anode with SnO2+Sb2O3 intermediate layer obtained by the polymeric precursor method (PPM) and with the conventional route was studied. The morphology and microstructure of SnO2+Sb2O3 intermediate layer derived from different precursors and the top PbO2 active layer were examined by means of ESEM and XRD. The lifetime and electrocatalytic activity of the anode were also assessed by the cyclic voltammetry and accelerated lifetime test in 1.0 mol/L H2SO4 solution. It was found that precursor solvents affected lifetime, microstructure and morphology of the anode, and had little influence on electrocatalysis activity of the electrodes. The accelerated lifetime of Ti/SnO2+Sb2O3/PbO2 anode with intermediate layer prepared by PPM was 29.5 h in 1.0 mol/L H2SO4 solution, which was respectively about four times and twice that of the anode prepared with ethylene glycol and ethanol. After the anode was subjected to thermal corrosion, the lifetime still reached 27 h in contrast to the others.     

不同硫化氢流率与浓度对硫化氢固体氧化物燃料电池性影响

A solid state H2S/air electrochemical cell having the configuration of H2S, (MoS2 NiS Ag)/YSZ/Pt, air has been examined with different H2S flow rates and concentrations at atmospheric pressure and 750-850 ℃. Performance of the fuel cell was dependent on anode compartment H2S flow rate and concentration. The cell open-circuit voltage increased with increasing H2S flow rate. It was found that increasing both H2S flow rate and H2S concentration improved current-voltage and power density performance. This is resulted from improved gas diffusion in anode and increased concentration of anodic electroactive species. Operation at elevated H2S concentration improved the cell performance at a given gas flow rate. However, as low as 5% H2S in gas mixture can also be utilized as fuel feed to cells. Highest current and power densities, 17500mA·cm-2 and 200mW·cm-2, are obtained with pure H2S flow rate of 50ml·min-1 and air flow rate of 100ml·min-1 at 850℃.     

Correlating and Predicting the Solubilities of Solid n-Alkanes in Supercritical Ethane Using Carnahan-Starling-van der Waals Model

The solubilities of some solid n-alkanes in supercritical ethane were correlated and predicted in this paper using the Carnahan-Starling-van der Waals model with a density-dependent parameter of a12. At a given temperature, the linear fit of the parameter of a12 and the density of the supercritical solvent was used for solubility correlation, resulting in an average absolute average relative deviation（AARD） of 8.68%, which was between the values of the semiempirical models and the other compressed gas models used in this article. In the linear fit of the parameter of a12 and the density of the solvent, the regressed slope m and intercept n of the linear fit can be correlated with the carbon atom number of solid n-alkanes and then the solubilities of solid n-alkanes in supercritical ethane can be predicted with the intercept n and slope m. The average AARD in solubility prediction was 26.99%.     

仿古铸铁的局部腐蚀和相转移研究

The corrosion behaviors of simulated archaeological iron in solution （0.06 mol·L^-1 NaCl＋0.03 mol·L^-1 Na2SO4＋0.01 mol·L^-1 NaHCO3） simulating soil water composition was investigated by potentialdynamic polarization, constant potential polarization, and simulated occluded cell （O.C.） galvanostatic tests. X-ray diffraction （XRD）, energy dispersive spectrometry （EDS）, and scanning electron microscope （SEM） were used to study the corrosion morphology and the evolution of corrosion product. The objective was to discover the transformation process of archaeological iron, and determine the distribution of chlorinated corrosion products. The results showed that the presence of crevice, cavities, and channels facilitates the localized corrosion under rusts; the autocatalytic effect increases the concentration of Fe^2＋, Cl^-, and SO4^2- , and promotes local acidification within the crevices and cavities. Meanwhile, the phase transformation of corrosion products is concluded to proceed by means of two ways. One is that the ferrous ions are transformed into different kinds of FeOOH via the intermediate Fe（Ⅱ）-Fe（Ⅲ） hydroxyl-salt （i.e. Green Rusts）; the other is that the Fe^2＋ ions are transformed into FeCl2, FeCl3, and orange powders akaganeite at the crevices and cavities.     

STUDIES ON ULTRASONIC DEGRADATION AND BLOCK COPOLYMERIZATION OF POLYACRYLAMIDE AND POLY(ETHYLENE OXIDE)

The kinetics of ultrasonic degradation of aqueous solution of polyacrylamide(PAM)and poly(ethyleneoxide)(PEO)as well as ultrasonic block copolymerization of aqueous solution of the mixture of PAM/PEOwere studied respectively.The degradation reaction of PEO follows a linear relationship between(P_1-P_∞)~(-1)and irradiation time,while that of PAM follows a linear relationship between(P_1-P_∞)~(-1/2)and irradiation time.The structure of the copolymer was identified by IR,NMR and DTA,and the copolymer prepared is a blockone.The copolymer formed by irradiating 1% aqueous solution of PEO/PAM mixture(1:1)for a period of40min.at 18.2 kHz with a sonic intensity corresponding to 2.OA input current on the reversed main circuitamounts to 61.8%.