Methodology for zinc phosphate pigment incorporation into polypyrrole matrix

In this work, the incorporation of a commercial zinc phosphate pigment into polypyrrole (PPy) matrix during its electrochemical synthesis on mild steel was studied in order to produce PPy/zinc phosphate composite films as a protective layer against corrosion. Potassium nitrate, oxalic acid, tosylic acid and sodium salicylate solutions were used as electrolytes in cyclic voltammetry and galvanostatic polarisation studies. The influence of synthesis parameters such as nature, concentration, pH and stirring of the electrolyte on the degree of incorporation of the pigment was investigated, as well as time and current densities of the electropolymerisation process. Their influence on current efficiency was also evaluated. Sodium salicylate was the only electrolyte to show a high current efficiency in the polymerisation reaction and to yield a composite film with a reasonable amount of zinc phosphate. In this electrolyte medium, X-ray photoelectron spectroscopy (XPS) analysis showed that zinc phosphate may be found in the polymeric matrix: (i) as a conductive ionic minority form and (ii) as a non-conductive non-ionic majority one for higher incorporation levels. Scanning electron microscopy (SEM) showed that zinc phosphate is heterogeneously distributed on the surface of the polymer.     

Theoretical analysis of chronoamperometric transients in electrochemical machining and characterization of titanium 6/4 and inconel 718 alloys

An analytical expression is derived for the current–time transient for electrochemical machining (ECM) using a planar tool and workpiece configuration. This is obtained as a function of such parameters as the initial interelectrode gap, applied voltage, electrolytic conductivity, valency, density and feed rate. Good theoretical fits to experimental data are found for the alloys titanium 6/4 (Ti6/4) and Inconel 718 (In718) using both sodium chloride and sodium nitrate electrolytes, demonstrating the applicability of this theory. The values of the electrolytic molar conductivity obtained for chloride and nitrate are consistent with the expected conductivity obtained from molar conductivity measurements. The mean valency values obtained for Ti6/4 and In718 are 3.5 ± 0.2 and 3.0 ± 0.2, respectively. The fraction of the applied voltage used to drive the electrochemical surface reactions, V ₀, has also been obtained. The variation in V ₀ between alloys when using the same electrolyte and also for each alloy when using different electrolytes is attributed to differences in the thermodynamics of the removal of the metal from the surface metal oxide. For In718 using chloride electrolyte, an increase in V ₀ is observed at higher applied voltages, consistent with a change in the electrochemical dissolution reaction. Analysis of the variation of V ₀ at low applied voltages throughout the current–time transient has enabled the current–voltage characteristics of these surfaces electrochemical reactions to be determined, indicating Tafel behaviour. These data show this analysis to be a powerful methodology for understanding and measuring ECM characteristics under realistic ECM conditions.     

准毛细间隙反应器中直接电氧化合成茴香醛二甲基缩醛

以准毛细间隙反应器为电化学合成装置,采用恒电流电解技术考察了阳极材料、支持电解质、电流密度等工艺参数对茴香醚直接电氧化合成茴香醛二甲基缩醛的影响。结果表明,收率从高到低采用的阳极材料依次为：石墨>钛基铱钽>钛基钌铱>钛基铂;支持电解质依次为：对甲基苯磺酸钠>苯磺酸钠>氟化钾>甲醇钠>高氯酸钠>间硝基苯磺酸钠;在电流密度1～9 A·dm^-2范围内,反应选择性随着电流密度的增大而减小;添加适量的2,6-二甲基吡啶能抑制茴香醛二甲基缩醛的氧化从而提高反应选择性。在优化条件下,茴香醛二甲基缩醛的收率和电流效率分别达到75%和47%。     

Electrochemical polymerization of pyrrole in supercritical carbon dioxide-in-water emulsion

Supercritical carbon dioxide is an environmentally benign solvent but its low polarity limits electrochemical reactions in it. We now report the electrochemical polymerization of pyrrole in a supercritical carbon dioxide-in-water (C/W) emulsion in the presence of a surfactant. Black polypyrrole films were formed on Pt electrodes, whose conductivity was comparable with non-oriented polypyrrole prepared in conventional solvents. The structure of the polypyrrole films was confirmed by IR and Raman spectroscopic measurements. p-Toluenesulfonic acid was a suitable supporting electrolyte among the electrolytes examined for the electrochemical polymerization in the C/W emulsion. A typical nodular morphology was observed on the basis of the SEM and AFM measurements. Confocal scanning microscope revealed the formation of a fine uneven texture on the film prepared in the C/W emulsion.     

Electrochemistry of polyaniline: Study of the pH effect and electrochromism

Polyaniline was electrochemically synthesized from an aqueous medium with various acid electrolytes via potentiodynamic and potentiostatic techniques. The electrochemical synthesis of polyaniline was studied over various substrates, including Pt, Ti, Ni, and SnO₂ coated glass, and in various acid electrolytes. Cyclic voltammograms of electrochemically synthesized polyaniline were studied in HCl in a pH range of 1–4. Probable electrochemistry and chemical changes were deduced that occurred when polyaniline film was electrochemically oxidized and reduced between ?0.2 and 1.0 V versus a Ag/AgCl reference electrode in an acidic electrolyte at pH 1, and three corresponding oxidation and reduction peaks were described instead of two redox peaks (as observed by W. S. Huang, B. D. Humphrey, and A. G. MacDiarmid, J Chem Soc Faraday Trans 1 1986, 82, 2385). The electrochromic property was studied with changes in the chemical states of polyaniline during electrochemical oxidation and reduction. A new viscous electrolyte, aqueous AlCl₃ (pH 2), saturated with AgCl was used for the construction of an electrochromic display device. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 378–385, 2002     

Electrochemical and infrared spectroscopy studies of 4-mercaptobenzoic acid SAMs on gold surfaces

Cyclic voltammetry and Fourier transform infrared external reflection spectroscopy (FTIR-ERS) have been used to study self-assembled monolayers of 4-mercaptobenzoic acid (4-MBA) formed on gold surfaces. Electrochemical studies demonstrate that the carboxylic acid head group of 4-MBA can be protonated or deprotonated by application of an electric potential to the gold substrate. This effect is highly dependent on the pH of the electrolyte in accordance with models previously developed for acid-terminated monolayers. The voltammetric response decreases with prolonged exposure to moderate strength electrolytes as cations exchange with the acid terminus. The formation of either sodium or potassium carboxylate salts occurs relatively slowly but the presence of Ca²⁺ ions in the electrolyte immediately quenches the electric-field driven protonation/deprotonation process. The latter process leads to a very stable carboxylate salt film, which cannot be reprotonated by prolonged exposure to the pure incubating solvent. FTIR-ERS studies demonstrate that the observed electrochemical response of the 4-MBA SAMs is related to the degree of hydrogen bonding in the monolayer film. The addition of ultrapure acetic acid to the incubating solution leads to a film with reduced levels of intermolecular hydrogen bonding between MBA molecules. Electrochemically, the voltammetric peaks associated with the protonation/depronation process are greatly attenuated when the self-assembled films are formed from solutions containing 4-MBA and acetic acid.     

Decolorization and aromatic ring degradation of colored textile wastewater using indirect electrochemical oxidation method

In this research, decolorization and aromatic ring degradation of colored textile wastewater was investigated by indirect electrochemical process in a batch reactor. The graphite and sodium chloride were used as electrode and supporting electrolyte, respectively. Reactive Yellow 3 (RY3) was used as model compound. The effects of influential variables governing the efficiency of the process such as initial dye concentration, pH, current density, and electrolyte concentration were studied. The decrease of absorbance at UV region in UV-Vis spectra was indicative of the aromatic ring degradation. Kinetic analysis indicates that the electrochemical decolorization rates might be obeyed as a first order model. The UV-Vis data supported the decolorization and degradation of aromatic intermediates of RY3.     

硫化氢恶臭气体吸收液的电化学氧化处理过程

利用单槽无隔膜电化学反应器,研究了硫化氢恶臭气体碱性吸收液在圆形平板钌钛DSA电极上的电化学氧化处理过程,考察了电流密度、初始料液浓度、辅助电解质以及pH值对S2?电解去除效果的影响。结果表明：在电流密度25 mA/cm2、S2?初始浓度23 mmol/L时,S2?去除率可达95%以上;S2?的氧化产物主要为SO42?,约占总反应产物的95%,而硫单质占2%～3%,同时生成少量SO32?、S2O32?;S2?去除速率受到S2?浓度的较大影响,电流密度越高去除速率越快;pH值影响Sx2?的形成,强碱条件可避免阳极钝化;与NaCl等辅助电解质相比,NaOH最有利于提高电解氧化的速度和深度,S2?去除率达90%时,可缩短处理时间近40%。     

钝化工艺对无氰镉-钛合金镀层性能的影响

为了获得无氰镀镉-钛合金的最佳后处理工艺,利用金相显微镜、电化学工作站和盐雾试验测试了三种钝化膜的外观及耐蚀性,并进行了比较。实验结果显示,三种钝化工艺获取的钝化膜经96 h中性盐雾试验后,均未出现白锈;电化学测试结果显示低铬钝化工艺获取的钝化膜自腐蚀电流密度最大,重铬酸钠钝化工艺获取的钝化膜自腐蚀电流密度最小。从环保和耐蚀性方面考虑,建议选用重铬酸钠+硝酸钝化工艺作为无氰镉-钛合金镀层的后处理工艺。     

Ionic conductivity and lithium electrode stability in Hydrin: LiBF4 elastomers

Three commercial elastomers, Hydrin C, Hydrin H and Hydrin T, which contain ethylene oxide and epichlorohydrin repeat units, have been investigated as polymer electrolytes in contact with lithium electrode. The influence of polyethylene glycol and fine particles of zeolite on ionic conductivity of Hydrin-LiBF₄ electrolytes and the exchange current density of the lithium electrode reaction has been studied by using impedance spectroscopy and cyclic voltammetry. The specific conductivity of the elastomeric electrolyte is about 10^–5 S cm^–1 at room temperature when polyethylene glycol is present. But the mechanical stability of the film is less. The addition of zeolite particles to the elastomers also improves the specific conductivity. When present in low concentrations, the zeolite particles show catalytic effect on the electrochemical reaction at lithium electrode at ambient temperature. The lithium electrode reaction is reversible and the electrolyte possesses good electrochemical stability.     

On the influence of electrolyte concentration,pH and temperature on surface brightening of nickel under ECM conditions

High rate anodic dissolution of nickel in sodium nitrate electrolytes was studied under controlled hydrodynamic conditions in order to investigate the influence of electrolyte concentration, pH and temperature on surface brightening under conditions comparable to electrochemical machining. Dissolution experiments were performed on a rectangular flow channel cell through which the electrolyte was pumped at a constant linear velocity of 1000 cm s^–1. Results show that the onset of surface brightening depends on concentration and temperature of the electrolyte but is little affected by pH. The data are consistent with a previously described salt precipitation model for surface brightening.     

Transpassive dissolution of mild steel in NaNO3 electrolytes

A study has been made of the transpassive dissolution of mild steel in sodium nitrate solution over a range of current densities from 2 to 100 A cm^–2. The dissolution current efficiency and the anode potential free from the electrolyte IR component were measured in a flow cell; optical and scanning electron microscopy were then used to examine the sample surfaces after the dissolution tests. The results show that during the early stage of transpassive dissolution, the mild steel is covered with a compact, electronically conductive Fe₃O₄ film, and the current is consumed mainly in oxygen generation on the film/electrolyte interface. With increasing anode potential and current density, this film is gradually broken and the underlying metal surface becomes exposed to the electrolyte. At this stage, iron dissolution begins at a high rate. The film rupturing process is strongly dependent on nitrate concentration; the higher this is, the lower is the current density required to rupture the film.     

镁合金微弧氧化配方的优化及膜层耐蚀性能评价

在以氟化钠、甘油及硅酸钠作为稳定剂的电解液中采用恒电流密度对AZ31B镁合金进行微弧氧化处理。通过4因素3水平的正交实验,确定了电解液中以上3种稳定剂的适宜含量分别为2g/L、10ml／L、6g/L。研究了各种辅助成分如铝酸盐、氢氧化物等对微弧氧化过程及陶瓷膜层性能的影响,结果发现氢氧化钾的加入有利于火花的产生,但易于引起尖端放电现象,应严格控制其加入量;同时它还会使膜层的颜色从灰色逐渐转变为白色,显著提高膜层的耐蚀性。动点位极化曲线及电化学交流阻抗测试表明,微弧氧化处理后的镁合金耐蚀性显著提高     

聚丙烯酸锂/锂盐聚合物电解质的研究

以丙烯酸和氢氧化锂为原料用溶液聚合法合成聚丙烯酸锂(PAALi),将其熔于低共熔盐(一定比例的LiNO3-LiOOCCH3混合物)中得到新型高分子固体电解质(SPE),用IR技术进行了表征,讨论了影响合成PAALi工艺及新型固体电解质电导率的主要因素,在Li-NO3-LiOOCCH3质量比为1∶1时,将其按质量百分比80∶20与聚丙烯酸锂混合均匀并熔融,得到的电解质其室温离子电导率可达2×10-5S.cm-1.     

Properties of polyaniline formed at tin dioxide electrodes in weak acid solution: effect of the counterion

Polyaniline films have been formed at tin dioxide electrodes in aqueous 0.4m acetate buffer solutions of pH between 3.5 and 5.5 with added nitrate, perchlorate or halide electrolyte, in order to study the effect of the counterion on the structure and electrochemical properties of the polyaniline film. The films were characterized electrochemically by cyclic voltammetry and by impedance, and morphologically by scanning electron microscopy. Marked differences between the films are found, the highest conductivity and electrochemical response being with nitrate counterion. The films formed are generally flat and porous, with evidence of some small irregular growths. These results are compared to those obtained in sulphuric acid solution.     

Electrochemical Synthesis and Characterization of Poly(o-anisidine) Film with Various Dopants: A Comparative Study

In the present work, the doped (composite) films of póly(o-anisidine)–polyvinylsulphonic acid (POA-PVS), poly(o-anisidine)–toluenesulphonic acid (POA-pTS), and poly(o-anisidine)–dodecylbenzenesulphonic acid (POA-DBS) were synthesized on a platinum electrode, using electrochemical polymerization. These synthesized films were characterized by electrochemical techniques, conductivity measurement, UV-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The optimal film growth was achieved for synthesis of the POA film in the presence of dodecylbenzenesulphonic acid (DBS). The POA-DBS composite film exhibits good electrochemical properties, conductivity with a uniformly porous surface morphology which can be used for the immobilization of biocomponent.     

Synthesis and characterization of novel crosslinked polyurethane–acrylate electrolyte

Flexible, transparent, and crosslinked polymer films were synthesized by polymerization of PEG‐modified urethane acrylate using a simple method. A series of novel solid polymer electrolytes and gel electrolytes were prepared based on this type of polymer film. To understand the interactions among salt, solvent, and polymer, the swelling behaviors of the crosslinked polymer in pure propylene carbonate (PC) and liquid electrolyte solutions (LiClO₄/PC) were investigated. The results showed that the swelling rate in the electrolyte solution containing moderate LiClO₄ was greater than that in pure PC. Thermogravimetric analysis (TGA) also supported the interaction between the solvent and polymer. The morphology and crystallinity of the crosslinked polymer and polymer electrolytes were studied using atomic force microscopy (AFM) and wide‐angle X‐ray diffraction (WAXD) spectroscopy. The effects of the content of the electrolyte solution on the ionic conductivity of gel electrolytes were explored. The dependence of the conductivity on the amount of the electrolyte solution was nonlinear. With a different content of the plasticizer, the ionic conduction pathway of the polymer electrolytes would be changed. The best ionic conductivity of the gel electrolytes, which should have good mechanical properties, was 4 × 10^r?3 S cm^?1 at 25°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 340–348, 2003     

Electrolytes for hybrid carbon-MnO2 electrochemical capacitors

Different aqueous-based electrolytes have been tested in order to improve the electrochemical performance of hybrid (asymmetric) carbon/MnO₂ electrochemical capacitor (EC). Chloride and bromide aqueous solutions lead to the formation of Cl₂ and Br₂ respectively upon oxidation of the corresponding salt, thus limiting the useful electrochemical window of the MnO₂ electrode and producing gas evolution (in the case of chloride salts) detrimental to the cycling ability of an hybrid device. For sulfate and nitrate salts, MnO₂ electrode exhibits a 20% increase in capacitance when lithium is used as the cation compared to sodium or potassium salts, probably due to partial lithium intercalation in the tunnels of α-MnO₂ structure. The higher ionic conductivity and solubility of LiNO₃ has led to the investigation of this electrolyte in carbon/MnO₂ supercapacitor compared to standard hybrid cell using K₂SO₄. A lower resistance increase was evidenced when the temperature was decreased down to −10 °C. Long term cycling ability of carbon/MnO₂ supercapacitor was also evidenced with 5 M LiNO₃ electrolyte.     

Fabrication of polypyrrole micropatterns through microchannel-confined electropolymerization and their electrical conductivities

Creating micropatterns of electrically conductive polymers on solid substrates is important for the low-cost construction of organic microelectronic devices. This work develops a novel strategy for the preparation of large-area polypyrrole (Ppy) micropatterns through area-selected in situ electropolymerization of pyrrole within microchannels. The effects on micropattern formation of electropolymerization procedures such as dynamic potential polymerization (DPP), static potential polymerization (SPP), and constant current polymerization (CCP), the solvent, and the polymerization time were studied systematically. The electrical conductivities of the Ppy micropatterns were measured and compared with a homogeneous Ppy thin film synthesized under the same conditions. Given the straightforward and versatile nature of this method, it is expected to contribute greatly to the convenient fabrication of low-cost organic microelectronic devices.     

Influence of ammonium salt on electrowinning of copper from ammoniacal alkaline solutions

In order to develop an energy-saving copper recycling process from wastes, electrochemical measurements were conducted in ammoniacal alkaline solutions containing Cu(I) ions and an ammonium salt of sulfate, chloride or nitrate. The results of each system were then compared. The polarization measurements suggested that the voltage required for the electrode process is lower in the chloride and nitrate systems than that in the sulfate system. The cathode current efficiency during the copper electrodeposition varied from 39 to 97% and increased with current density in the chloride and sulfate systems. In the nitrate system, the lowest cathode current efficiency of 30% was observed because of nitrate ion reduction. Based on these results, the power consumption required for the electrowinning stage of the copper recycling process was calculated. Among these three systems, the chloride system showed the lowest power consumption of 500 kWh t⁻¹ at the current density of 200 A m⁻², which is about 25% of the conventional copper electrowinning process from a copper sulfate-sulfuric acid solution.