Potentiodynamic and cyclic voltametric studies on the Passivity of Tin in neutral phosphate buffer

Passivity of tin has been investigated in phosphate buffer (pH 6.7) using potentiodynamic and cyclic voltammetric techniques. The formation of thin transparent electronically conducting passive film on which O₂ is evolved in the transpassive range is indicated. The solution remains clear. Potentiodynamic measurements performed from −1.2 to 2.5 V (SCE) and backward at scan rates between 1 and 100 mV/sec give one anodic peak. In the reverse scanning, two cathodic peaks appear at low scan rates and disappear completely at higher rates. Values of the open dircuit potential, the corrosion potentials Ecor (forward and reverse), the anodic peak potential Ep and the anodic peak cd Ip are recorded. The results are compared with our previous work in neutral chloride, bromide, iodide, and sulphate solutions. Thermodynamic data are used to predict the possible oxidized species constituting the anode film. Cyclic voltammetric measurements have been carried out in the potential range between H₂ and O₂ evolution, and in limited potential ranges at scan rates between 1 and 200 mV/sec. One anodic peak is detected in all cases. While a short arrest and a cathodic peak appear in the results between H₂ and O₂ evolution, two distinct cathodic peaks appear up to 100 mV/sec in the results taken between –1.2 and −0.224 V. Plots of Ip vs the square root of scan rate are linear, and indicate diffusion-controlled kinetics for the reactions initiating passivity. Linear relations are observed for Ep vs log scan rate indicating the irreversible nature of the anodic processes. While the formation of SnO and SnO₂ is predicted from thermodynamics at potentials more negative than Ep, the formation of Sn(OH)₄ is predicted at potentials more positive than Ep. The conclusions drawn from the results obtained with the two different techniques are generally the same. The results are compared with and discussed on the light of previous work using cyclic voltammetry.     

The anodic behaviour and Passivity of Tin in sulphate solutions

Passivation of spec-pure Sn was studied in aerated, unstirred solutions of acid sulphate (H₂SO₄/Na₂SO₄) and neutral suphate (Na₂SO₄) using the potentiodynamic technique from an initial cathodic potential (?ve to open circuit potential) in the anodic direction and backwards to the initial potential. Only one anodic peak is observed in all results. The effect of etching is manifested in pure 0.1 M H₂SO₄ and in the solution containing 75% acid and 25% by vol 0.1 M Na₂SO₄. In all solutions, a grayish white film devlops on the Sn anode, and a white precipitate is formed in solution. Data are complied for the corrosion potential Ecor, the cathodic and anodic Tafel slopes, the corrosion cd Icor, the peak potential and the peak cd for acid sulphate solutions. The effect of scan rate has been demonstrated in 0.1 M Na₂SO₄ in the range 1-100 m V/sec for unstirred and 1-50 m V/sec for stirred solutions. The plot of peak cd Icc (Ip) vs the square root of the scan rate gives a striaght line with positive slope indicating diffusion kinetics for the anode film formation. USe of thermodynamic data leads to the possible formation of SnO, SnO₂, Sn(OH)₂ and Sn(OH)₄ in the anode film. The limitations of the thermodynamic treatment is discussed. It is concluded that film formation is governed by a dissolution/precipitation mechanism based on diffusion kinetics. In the absence of the results of surface analysis, the anode film may be visualized to be composed of the oxides and hydroxides of Sn (thermodynamic evidence) together with sulphate anions (kinetic evidence). O₂ evolution has not been detected up to 2.5 V (SCE), and this throws some light on the poor electron conductance of the anode film, and the probable dominance of lonic conductance during film growth.     

Evidence for the activation-controlled galvanostatic growth of thin Anode Films on Tin in some neutral media

Growth of thin transparent anode films on Sn in neutral media has been studied by measuring galvanostatic anodic charging curves in phosphate buffer, 0.1M KCl and 0.1M Na₂SO₄ solutions (pH 6.6–6.7) at low current densities. The experimental technique is essentially the same as that used in previous investigations on valve metals. Although the rise in the anode potential of Sn does not exceed 2.0 V, the shape of the anodic charging curve is identical to that observed on valve metals: being thus composed of a linear and a non-linear region. Application of the kinetics of galvanostatic anodization to the results on Sn show that: (i) the oxide formation rate is linearly related to the ionic current density i by a double logarithmic plot, (ii) the reciprocal capacity is linearly related to log i, and (iii) the Tafel behaviour is exhibited at constant charge. These relations indicate that the anode film growth occurs by an activation-controlled ion conduction under the influence of the electric field across the film phase according to an exponential law. Treatment of the results allows the estimation of some kinetic parameters of film growth, e.g.: (i) the constants a and b of the empirical relation between oxide formation rate and i, (ii) the constants A and B of the exponential law, (iii) the electric field which is of the order of 10⁶ V/cm in phosphate, and 10⁷ V/cm in both chloride and sulphate solutions, and (iv) the effective activation distance for the ionic jump over the energy barrier associated with cation transport within the film, whereupon relative (and not absolute) values can only be obtained. Comparison between the present results and previous ones (also on Sn) taken by potentiodynamic technique shows that while diffusion kinetics play an important role in the formation of thick anode films by the potentiodynamic technique, activation-controlled kinetics explain the present results on the galvanostatic formation of thin transparent anode films.     

Investigation of NO detection in flames by the use of polarization spectroscopy

Various aspects of detection of NO molecules in a premixed H(2)/N(2)O flame were investigated by the use of polarization spectroscopy. The signals were recorded in the A(2)Σ(+)-X(2)II (0, 0) band of NO at 226 nm. Excitation spectra for circularly and linearly polarized pump beams are presented to illustrate the influence of the polarization state. The signal dependencies on the pump- and the probe-beam intensities were also investigated, as well as the influence of the setup geometry with respect to the pump-beam focusing and the crossing angle between the pump and the probe beams. A preliminary evaluation of temperature based on spectra recorded by the use of the Boltzmann plotting approach was performed. Finally the possibilities of two-dimensional imaging of the NO molecules were demonstrated.     

Corrosion monitoring of steel in concrete by galvanostatic pulse technique

Various non-destructive quantitative techniques based on electrochemical methods for measuring the corrosion rate of steel embedded in concrete have been used. The most important is the linear polarization method. In practice, this method gives lower corrosion rates of steel in concrete due to inclusion of the resistance of the concrete in the measurement. In order to eliminate the resistance of the concrete, a galvanostatic pulse method is used. In this method the current pulse is applied to the steel in concrete and the polarizing potential is sampled after the switching off the pulse. The performance of the galvanostatic pulse technique for monitoring the corrosion of steel in concrete has been assessed by comparing the corrosion rate values obtained by the weight loss method and linear polarization resistance method for steel reinforced in M15, M20, M30 and M35 grade concrete containing 0–5% NaCl. It is found that the galvanostatic pulse technique is able to give reliable corrosion rate values of steel in concrete.     

优质节锡钎料的研制

通过正交试验,研制出一种优质节锡钎料,其性能指标与ＨＬＳｎ６０Ｐｂ４０高锡钎料相当。该钎料大大降低了成本,具有明显的经济效益。     

Neutral points of skylight polarization observed during the total eclipse on 11 August 1999

We report here on the observation of unpolarized (neutral) points in the sky during the total solar eclipse on 11 August 1999. Near the zenith a neutral point was observed at 450 nm at two different points of time during totality. Around this celestial point the distribution of the angle of polarization was heterogeneous: The electric field vectors on the one side were approximately perpendicular to those on the other side. At another moment of totality, near the zenith a local minimum of the degree of linear polarization occurred at 550 nm. Near the antisolar meridian, at a low elevation another two neutral points occurred at 450 nm at a certain moment during totality. Approximately at the position of these neutral points, at another moment of totality a local minimum of the degree of polarization occurred at 550 nm, whereas at 450 nm a neutral point was observed, around which the angle-of-polarization pattern was homogeneous: The electric field vectors were approximately horizontal on both sides of the neutral point.     

Investigation of the dynamics of failure of individual structural elements by the optical polarization method

The article presents the results of the investigation of the state of stress and the kinetics of an internal crack in plates of epoxy resin ÉD-20 MTGFA with a central circular and elliptical hole under the effect of a tensile pulse. It was established that the crack growth is of pulsating nature consisting in alternating slowing down and speeding up of its motion. It is shown that the jumpwise motion of the crack is accompanied by a smooth change of the stress intensity factor (SIF). Diagrams of the change of crack growth rate and SIF vs. time are plotted. The process of failure of specimens with circular and elliptical hole is described.Translated from Problemy Prochnosti, No. 9, pp. 46–48, September, 1991.     

Enhancement of corrosion resistance of a biomedical grade 316LVM stainless steel by potentiodynamic cyclic polarization

The paper discusses the results on the use of a simple cyclic linear potentiodynamic polarization technique as a method of improving corrosion properties of passive oxide films formed on a biomedical-grade 316LVM stainless steel surface in phosphate buffer. The results demonstrate that the modification of 316LVM surface by cyclic potentiodynamic polarization between the potential of hydrogen and oxygen evolution results in the formation of a passive film that offers significantly increased corrosion resistance (both pitting and general) when compared to the naturally grown passive film. The effect of number of cycles and anodic potential limit on the resulting corrosion properties is discussed. The capacitance analysis demonstrates that the major difference between the electrochemically formed and naturally grown passive film is in the type of semiconductivity in the potential region where pitting on the unmodified surface occurs. The XPS analysis shows that this is due to the presence of Cr(VI)-species in the electrochemically formed passive film, which contribute to the increased density of metal vacancies, and thus to the increased pitting corrosion resistance of the passive film.     

Investigation of Tin films reactively sputtered using a sputter gun

TiN films were prepared by reactive sputtering of titanium in a gas mixture of argon and nitrogen using a sputter gun. The properties of the sputtered films were investigated with Rutherford backscattering spectrometry, electrical resistivity and optical reflectivity measurements, X-ray diffractometry and transmission electron microscopy. For a given input power to the sputter gun the film properties depend on the gas composition, the bias voltage applied to the substrates and oxygen contamination during sputtering. In addition, it was found that powering the sputter gun with r.f. causes an iron contamination in the films by material sputtered off the plasma confinement shield. This contamination is very much reduced when d.c. is employed to power the sputter gun.     

脉冲电流法制备聚苯胺/纳米银复合膜

以高导电率的Ag作为添加材料 ,首次采用换向脉冲电流法使PANI和Ag发生共沉积 ,制成PANI/Ag复合电极。并用循环伏安研究了复合电极在硝酸溶液中的电化学性能及沉积过程中电化学参数对膜层电化学性能的影响。当Ag 浓度为 0 0 1mol/L ,苯胺浓度为 0 3mol/L ,沉积平均电流密度为 3～ 4mA/cm2 ,且脉冲阳极峰电流和阴极峰电流比值适当时可获得电化学性能最为优异的膜层。     

Investigation of black phosphorus as a nano-optical polarization element by polarized Raman spectroscopy

Manipulating the polarization of light at the nanoscale is essential for the development of nano-optical devices. Owing to its corrugated honeycomb structure, two-dimensional (2D) layered black phosphorus (BP) exhibits outstanding in-plane optical anisotropy with distinct linear dichroism and optical birefringence in the visible region, which are superior characteristics for ultrathin polarizing optics. Herein, taking advantage of polarized Raman spectroscopy, we demonstrate that layered BP with a nanometer thickness can remarkably alter the polarization state of a linearly-polarized laser and behave as an ultrathin optical polarization element in a BP-Bi₂Se₃ stacking structure by inducing the exceptionally polarized Raman scattering of isotropic Bi₂Se₃. Our findings provide a promising alternative for designing novel polarization optics based on 2D anisotropic materials, which can be easily integrated in microsized all-optical and optoelectronic devices.

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Investigation of diffusional intermixing in Si/Co/Ta system by Secondary Neutral Mass Spectrometry

Low temperature analysis of diffusion and intermixing of Co-Si systems are very important in applications for microelectronics and Ultra Large Scale Integration (ULSI). In this communication a comprehensive report has been given on degradation and diffusion processes in the Si(substrate)/Co(150 nm)/Ta(10 nm) system. The samples were prepared by DC magnetron sputtering and were annealed in argon ambient at several temperatures ranging from 400 to 623 K for various times. The composition of the samples was investigated by Secondary Neutral Mass Spectrometry (SNMS). The degradation/intermixing starts with fast (grain boundary (GB)) diffusion of the Si into the Co layer. After some incubation time Si atoms appear and spread over the Co/Ta interface. This amount of Si accumulated at the Co/Ta interface acts as a reservoir for back-diffusion into the Co layer from the Co/Ta interface through the slower grain boundaries. At higher temperatures the formation of a Co-Si phase was detected at the Co/Si and Co/Ta interface. Three different diffusion coefficients were calculated from the SNMS concentration-depth profiles using “Central-gradient” (CG) and “First-appearance” methods. The observed intermixing was interpreted as a mixture of different “C-type” grain boundary diffusion processes. Furthermore, the experimental results are also compared with computer simulations modelling the grain-boundary diffusion through different grain-boundary paths. From the SNMS profiles measured at different temperatures the activation energy of the GB interdiffusion coefficients was deduced using the “CG method”.     

Deposition of thin cobalt films onto silicon by galvanostatic and potentiostatic techniques

In this study, thin cobalt films were electrodeposited directly onto n-Si (100) using two different electrodeposition techniques: galvanostatic and potentiostatic. The morphological difference between galvanostatic and potentiostatic deposits was observed by atomic force microscopy (AFM) and X-ray diffraction (XRD). Analysis of the deposits by an alternating gradient field magnetometer (AGFM) showed the influence of the electrodeposition process on the magnetic properties of the film.     

石墨炉原子吸收光谱测定防污漆中的锡总量

采用石墨炉原子吸收光谱法测定防污漆中的锡总含量.采用抗坏血酸作为基体改进剂,能有效的减少防污漆中的Cu对Sn的信号抑制和干扰,在Sn含量较低的情况下,能明显提高测定的灵敏度.该方法对检测防污漆中的锡总量是可靠有效的.