Investigation of the specific adsorption of HSO4(SO4) and Cl ions on Co and Fe by radiotracer technique in the course of corrosion of the metals in perchlorate media

The adsorption of sulphate and chloride ions on Co and Fe was studied in 0.5 mol dm⁻³ NaClO₄ supporting electrolyte at various pH values by radiotracer technique in the course of the corrosion (dissolution) of the metals. The effect of the reduction of ClO₄⁻ ions (leading to the formation of Cl⁻ ions) on the radiotracer measurements was investigated. It was found that the adsorption of chloride and sulphate ions occurs in different pH ranges. This phenomenon was explained by the assumption that the adsorption strength of the two species is very different on oxide covered and “pure” metal surfaces.     

The influence of sulphate,chloride and nitrate anions on the cyclic strain-enhanced dissolution behaviour of mild steel

The transient electrochemical behaviour of mild steel during cyclic plastic deformation in 0.5 M aqueous solutions of sulphate, chloride and nitrate ions was studied in the pH range 3–14. In all solutions dissolution current transients were observed during both tensile and compressive strain cycles. The magnitude of the dissolution effects, however, depended upon the solution composition, pH, potential and the extent of strain cycling. Analysis of the current transient characteristics revealed that for the anion concentration employed in this study, sulphate appeared to exhibit more aggressiveness than chloride and both these exerted a greater disruptive influence on surface films than nitrate ions. Tests in 0.25 M Na₂SO₄ revealed that the effect of sulphate could not be attributed simply to the increased ionic strength of the solution.     

The mechanism of pitting of high purity iron in NaCl solutions

Pitting of high purity iron was studied in chloride containing solutions, at various pH values, with and without borate buffer. It was found that for low pitting potential values, in alkaline solutions, where Fe(OH)_{2-oxide phase} is the initial passivation species, localized acidification, or OH^? ion depletion, was a necessary and sufficient condition for passivity breakdown. At high pitting potential values, where the presence of an adsorbed layer of Fe(OH)_{3-oxide phase} leads to passivity, OH^? ion depletion was a necessary but not a sufficient condition for passivity breakdown. Specific anion adsorption steps had to be assumed to explain the specificity of the aggressive anions, at those potentials, and the absence of Fe III species in the corrosion products inside the pits.     

Radiotracer study of embedding of SO4 and Cl ions into the surface film formed on Mn corroding in perchlorate solution

The adsorption of radiolabelled Cl⁻ and SO₄⁻ ions from aqueous perchlorate solutions onto powdered Mn metal was studied. It was found that the extent of the adsorption is determined by the continuous increase of the thickness of the surface oxide/hydroxide layer formed as a consequence of the slow corrosion of the metal in neutral or quasi-neutral media. At low pH values (pH < 6) the extent of the adsorption decrease significantly owing to the dissolution of the surface layer. At high pH values (pH > 10) the adsorption decreases presumably owing to the competitive adsorption of OH⁻ ions or the modification of the adsorption centres by some kind of deprotonation.     

The transpassive dissolution mechanism of highly alloyed stainless steels: II. Effect of pH and solution anion on the kinetics

The effect of pH and solution anion on the kinetics of transpassive dissolution of highly alloyed austenitic stainless steels (AISI 904L, 254SMO and 654SMO) was studied by a combination of electrochemical techniques. The experiments were performed in 0.5 M sulphate and 0.5 M chloride solutions, and in an equimolar mixture of the two. The transpassive dissolution was found to start at higher potentials in solutions with higher pH. The rate of transpassive dissolution was shown to decrease with increasing pH and to be the lowest in chloride solutions and the highest in sulphate electrolytes. The steady-state current vs. potential curves and the impedance spectra of the studied materials in the transpassive potential region were found to be consistent with a proposed kinetic model. The model describes the process as dissolution of Cr as Cr(VI) and Fe as Fe(III) through the anodic oxide film via parallel reaction paths. The kinetic parameters of the model in solutions with different pH values and different anions were determined. The role of pH and solution anion in the transpassive dissolution process is discussed in relation to changes induced by these parameters in the composition of the anodic passive film. The factors determining the efficiency of Fe as a secondary passivating agent are also considered.     

Corrosion mechanisms of steel concrete moulds in contact with a demoulding agent studied by EIS and XPS

The behaviour of E24 mild steel was studied by XPS analysis and electrochemical impedance spectroscopy (EIS) in a filtered solution of cement (pH 13), and an alkyl N-aminodiphosphonate aqueous solution called Aquadem^® (7?pH?13). XPS results showed that the corrosion products developed in both media consisted of Fe₂O₃, covered by a very thin layer of goethite. The thickness of this oxide layer was estimated to be 3 nm. XPS analysis also demonstrated the adsorption of Aquadem^® on the outer layer of FeOOH for pH lower than the zero charge pH of goethite (7.55). From XPS and EIS results, physical models of the E24 steel/electrolyte interface are proposed as a function of pH. For 11?pH?13, the steel is covered by a passive film, while for pH?10, pitting corrosion takes place. At pH 7, an additional mass transport phenomenon must be taken into account. The fitting procedure provided values for several physical parameters (electrolyte resistance, passive film resistance), from which the film capacitance and the dielectric constant of the oxide layer were calculated.     

Pitting and pitting inhibition of iron in sodium sulphate solutions

The anodic behaviour of high purity iron in 0.5 M sodium sulphate solutions was studied. Experiments were made in both acid and alkaline solutions (pH 2.7, pH 9.0, pH 10.0 without buffers; and pH 9.2 with borate buffer). Anodic polarization curves, and surface scratching experiments, showed pitting potentials in 0.5 M Na₂SO₄ pH 9.0 and pH 10.0 solutions. Their values were very close to the corrosion potential obtained in a 0.5 M Na₂SO₄, pH 2.7, pit-like solution. The pitting potential in a borate buffered 0.5 M Na₂SO₄ solution was 50 mV higher than that in the unbuffered solutions. The pitting inhibition potential measured in a 0.5 M Na₂SO₄ solution, pH 10.0, was very close to the passivation potential found in the pit-like solution. All these facts can be explained by the localized acidification mechanism for pitting. The pitting potential is the minimum potential at which an acidified solution can be produced and maintained in contact with the dissolving metal. Similarly the pitting inhibition potential is the electrode potential at which the metal becomes passive in the pit-like solution.     

Corrosion behaviour of steel in solutions containing mixed inhibitive and aggressive ions

The action of sodium benzoate, sodium chromate and sodium nitrite in relation to the presence of sodium chloride, sodium nitrate, sodium sulphate and sodium sulphide has been studied by means of visual observation as well as potential measurements. It has been found that the critical concentration of the inhibitor for protection in distilled water could tolerate a range of concentration of the aggressive anion. The linear double logarithmic relationship between the concentration of an inhibitive anion and the maximum tolerated concentration of an aggressive anion is only beyond a certain critical concentration of the aggressive anion. The results are interpreted in terms of competitive adsorption between the inhibitor and aggressive ions on the bare metallic parts.     

银离子在斛壳丹宁酸树脂表面的吸附和解吸(英文)

将斛壳丹宁酸与甲醛聚合来形成的凝胶作为吸附剂能有效地移去水溶液中的银离子。研究了不同银离子初始浓度、溶液温度、pH值条件下斛壳丹宁酸树脂的附和解吸行为。研究了有关经验动力学模型的适应性。伪二级动力学模型表明银离子的吸附是很快的。用FTIR和SEM对吸附和解吸银离子后的斛壳彤宁酸和斛壳丹宁酸树脂进行表征。银离子在斛壳宁酸树脂上的吸附随着银离子初始浓度的增加而增加,随着溶液温度的升高而减少。在低pH值的H2SO4、HNO3和HCl溶液中进行解吸实验。斛壳丹宁酸树脂在pH2.0~7.0溶液中对银离子表现出高的吸附容量,在银离子初始浓度100.0mg/L、温度296K和pH5.0的条件下达到最大的吸附量97.08mg/g。在1mol/LHCl+1%硫脲溶液中银离子的脱吸率达99.6%。     

The behavior of chromium and molybdenum in the propagation process of localized corrosion of steels

In order to clarify the effect of Cr and Mo on the propagation of localized corrosion of steels, the electrochemical behavior of pure chromium and molybdenum and of some stainless steels was studied under conditions similar to those existing inside occluded corrosion cells of steels. Oxygen-free FeCl₂ and/or CrCl₃ solutions were used for experiments. The surface films formed in these conditions were analyzed by means of AES and XPS. Cr is passive if the pH value >ca. 1.8 and Cr may retard the propagation of localized corrosion of steels in its early stage. The hydrolysis of Cr³⁺ may change the pH to even lower values. At such low pH and high Cl^? concentrations, Cr is active in the potential range of interest for localized corrosion of steels. Mo is passive under these more acidic conditions and the passivity of Mo in this potential range is attributed to the formation of a film of MoO₂ (or hydrated oxide), which is extremely thin but very protective. Mo is thus effective to retard the propagation of localized corrosion of steels in its more advanced stage.     

Eine charakterisierung der lochfraßkorrosion des nickels—I. Die bestimmung der lochfraßpotentiale in neutralen und alkalischen lösungen

Quasistationary values for the characteristic pitting potentials for nickel were determined by means of potentiokinetic polarization measurements and their dependence on chloride and hydroxide ion concentration was investigated. The pit nucleation potential U_np is a linear function of the logarithm of the anion concentration. The value being determined by the adsorption equilibrium of the anions on the passivated metal surface.The critical pitting potential U_cp depends on the pH of the solution only. Above pH 6-5 U_cp decreases with increasing pH. On the basis of the mechanism for crevice corrosion this behaviour may be explained by the influence of OH^?-ions being known to take part in the ionization of the metal atoms.     

羧甲基淀粉的取代度对其在反浮选中抑制一水硬铝石的影响(英文)

研究取代度不同的两种羧甲基淀粉(CMSL和CMSH分别表示取代度低和取代度高的羧甲基淀粉)在以十二胺(DDA)为捕收剂的阳离子反浮选中对一水硬铝石的抑制性能。考察了CMS的取代度对其抑制性能及作用方式的影响。单矿物浮选实验表明,在广泛pH值范围内,CMSL对一水硬铝石的抑制能力要好于CMSH。借助吸附量测试、动电位测量和原子力显微镜对CMS在一水硬铝石表面的吸附进行研究。结果表明:相对于CMSL,CMSH分子中具有更多的吸附点,因而在一水硬铝石表面具有较小的吸附量和较薄的吸附层厚度,并使一水硬铝石表面具有较强的电负性。溶液表面张力的测定和捕收剂DDA的吸附实验进一步揭示,CMSL分子的环式吸附构象可以罩盖更多的DDA从而显示优良的抑制性能,而CMSH/DDA体系则表现得更像一种表面活性剂。     

硼酸缓冲溶液中pH值和腐蚀产物对低碳钢活化/钝化敏感性的影响

研究了在pH值分别为8,9和10的除氧硼酸缓冲溶液中,低碳钢腐蚀产物对其活化/钝化敏感性的影响.实验结果表明,在pH值为8时,低碳钢一直处于活性溶解状态,不受腐蚀产物影响;在pH值为9和10时,表面腐蚀产物使低碳钢钝化,其腐蚀电位最后稳定于钝化区间.XPS和XRD等分析结果表明,腐蚀产物由FeB(OH)12B4O7和γ...     

壳聚糖-海藻酸钠吸附剂对电镀废水中 Cr( VI) 的吸附性能研究

以天然壳聚糖(CS)和海藻酸钠(SA)为原料,在CaCl2作用下,制备了壳聚糖-海藻酸钠(CS-SA)吸附剂。采用红外光谱仪对CS-SA吸附剂官能团进行表征,表明壳聚糖和海藻酸钠之间产生了静电吸引作用。以含低浓度Cr(Ⅵ)的电镀废水为处理对象,考察了CS-SA用量、吸附时间和pH值对CS-SA吸附性能的影响,同时对吸附动力学进行了研究。结果表明:当pH=6,吸附时间为120 min,CS-SA用量为0.15 g时,离子去除率最高,达到了98.86%;吸附动力学最符合拟二级动力学方程。解吸-再生实验表明,CS-SA吸附剂可以再生使用。     

硫酸盐和温度对钢筋腐蚀行为的影响

采用动电位极化曲线及电化学阻抗法研究了硫酸根和温度对钢筋在混凝土模拟孔隙液中腐蚀电化学行为的影响。发现在有氯离子存在时,硫酸根具有缓蚀作用,提高了钢筋表面钝化膜的抗腐蚀性能;随着温度的提高,钢筋的极化电阻逐渐降低;随着ｐＨ值的提高,极化电阻逐渐增大。文中计算了不同ｐＨ值下腐蚀反应的活化能,并提出了硫酸根离子的缓蚀作用机制。     

Some investigations into hydrogen sulphide adsorption by zinc

The adsorption of very low concentrations of H₂³⁵S from air by thin zinc foils was investigated using a continuous flow technique at room temperature. The H₂S uptake rate was markedly influenced by relative humidity, being very low below 65% r.h., having a higher constant value in the range 65–95% r.h. and reaching a maximum at 100% r.h. Autoradiography showed that adsorption was non-uniform and the lack of uniformity was suggested to be due to mechanical or chemical exposure of the underlying oxide surface.     

Polypyrrole and poly N-methylpyrrole — An electrochemical study in an aqueous medium

Polypyrrole (PP) and poly N-methylpyrrole (PMP) synthesized in acetonitrile solution containing 0.2 M LiClO₄ have been studied in an aqueous medium at different pH values by potentiometry at zero current, double pulse imposed current methods and cyclic voltammetry. The last was also used to determine the stability range. We observed from potential-pH measurements that PP has fairly good resistance towards sulphuric acid up to 4 M and shows less resistance towards strong basic media above pH 12. Cyclic voltammetry studies show that PP is more easily degraded at potentials greater than 1 V than in the less noble potential range. In the pH range studied, PP exchanges one proton for each electron. PP can exist in at least six forms and the exchange of the protons can precede or follow the electron exchange: two of these forms of PP can exist in oxidized and reduced forms without any counter anion.PMP presents a better stability from the electrochemical point of view, especially in a basic medium. Between pH 1 and pH 9.5 it exchanges only one proton for two electrons and above pH 9.5 two protons for one electron.     

Effect of acidic surface functional groups on Cr（VI） removal by activated carbon from aqueous solution

The activated carbon with high surface area was prepared by KOH activation. It was further modified by H2SO4 and HNO3 to introduce more surface functional groups. The pore structure of the activated carbons before and after modification was analyzed based on the nitrogen ad-sorption isotherms. The morphology of those activated carbons was characterized using scanning electronic microscopy (SEM). The surface functional groups were determined by Fourier transform infrared spectroscopy (FTIR). The quantity of those groups was measured by the Boehm titration method. Cr(Ⅵ) removal by the activated carbons from aqueous solution was investigated at different pH values. The results show that compared with H2SO4, HNO3 destructs the original pore of the activated carbon more seriously and induces more acidic surface functional groups on the activated carbon. The pH value of the solution plays a key role in the Cr(Ⅵ) removal. The ability of reducing Cr(Ⅵ) to Cr(Ⅲ) by the activated carbons is relative to the acidic surface functional groups. At higher pH values, the Cr(Ⅵ) removal ratio is im-proved by increasing the acidic surface functional groups of the activated carbons. At lower pH values, however, the acidic surface functional groups almost have no effect on the Cr(Ⅵ) removal by the activated carbon from aqueous solution.     

Recent trends in experimental and theoretical investigations of chemisorption on metal-electrolyte interface. II. Contact electric resistance method

New trends in experimental and theoretical investigations of chemisorption on electrodes are considered on examples of in situ spectroscopic studies and the density functional theory calculations. The partial charge transfer during ionic and molecular adsorption from aqueous solutions on coinage and platinum metals and the thermodynamic uncertainty regarding the direction of the charge transfer are discussed. The contact electric resistance technique (CER) was shown to offer a new approach to considering these problems. This technique provides information on the coefficient and direction of the charge transfer, the kinetics of the transformation of the electrode surface during the conversion of adsorbed ions to adatoms, and the role of competitive adsorption of water. It was examined how the charge transfer is related to the electrosorption valence of anions and what the role plays the tunneling of electrons in the generation of the CER signal. The CER was demonstrated to be dependent on the potential E, the coverage, and the residence charge of the adsorbate. For the adsorption of halide ions from aqueous solutions on 1B metals, the bell shaped CER vs. E dependences were obtained. The maxima in these dependences correspond to the onset of substantial charge transfer, their position and amplitudes being determined by the nature of the metal and anion and the concentration of the latter. At E < E_max, halide ions are adsorbed without appreciable charge transfer; within the range E_max (E_max + 0.1 V), the charge transfer for silver and gold approaches 1, being far less for copper. For a given metal, E_max increases in the series I⁻ < Br⁻ ≪ Cl⁻ while for a given anion, E_max increases in the series Au < Ag ≪ Cu. Based on the measured CER-E dependences, a quantitative criterion of the substantial charge transfer during ionic and molecular adsorption was proposed. This criterion was demonstrated to be consistent with the published data on charge transfer in various adsorbate-adsorbent systems. In particular, it shows that the hydrophilicity and electronic properties of 1B metals differently influence charge transfer during ionic and molecular adsorption. New electrosorption equations have been proposed describing the partial charge transfer and screening of the adsorbate charge due to partial ionization of the surface atoms. An experimental approach to solve the “anion problem” in the density functional theory has been developed basing on the CER-measured values of E_max in corresponding electrochemical systems. The article is published in the original. Marichev, V.A., Recent Trends in Experimental and Theoretical Investigations of Chemisorption on Metal-Electrolyte Interface. I. In situ Spectroscopic Studies and the Density Functional Theory Calculations, Protection of Metals and Physical Chemistry of Surfaces, 2009, vol. 45, no. 1.     

Adsorption of Ag（Ⅰ） on H2TiO3 from aqueous solutions

Adsorption of silver ions from aqueous solution onto H2TiO3 was studied. Equilibrium experimental studies were performed to determine the adsorption capacity of H2TiO3 for silver ion at various pH values. Batch experiments were conducted in the range of pH value 3-7 and silver ions concentration 10-200 mg/L. The results show that the adsorption is strongly dependent on pH value. The equilibrium absorption capacity of H2TiO3 increases significantly with the increase of pH value from 3 to 7. The adsorption of silver ion obeys the Langmuir isothermal equation well in the concentration range studied, the adsorption constant is 0.054 7, 0.052 4, 0.0881 at pH 5, 6 and 7, respectively, and the maximum adsorption capacities are 23.64, 29.76 and 40.82 mg/g.