Borate Buffer Solution Research Articles

Comparison of corrosion behavior between coarse grained and nano/ultrafine grained alloy 690

The effect of grain refinement on corrosion resistance of alloy 690 was investigated. The electron work function value of coarse grained alloy 690 was higher than that of nano/ultrafine grained one. The grain refinement reduced the electron work function of alloy 690. The passive films formed on coarse grained and nano/ultrafine grained alloy 690 in borate buffer solution were studied by potentiodynamic curves and electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. The results showed that the grain refinement improved corrosion resistance of alloy 690. This was attributed to the fact that grain refinement promoted the enrichment of Cr2O3 and inhibited Cr(OH)3 in the passive film. More Cr2O3 in passive film could significantly improve the corrosion resistance of the nano/ultrafine grained alloy 690.

The electrochemical behavior and characteristic of passive film on 2205 duplex stainless steel under various hydrogen charging conditions

The electrochemical behavior and the characteristic of 2205 duplex stainless steel (UNS S32205) under various hydrogen charging conditions in borate buffer solution containing chloride ion were evaluated by potentiodynamic measurements, electrochemical impedance spectroscopy, capacitance measurements (Mott-Schottky approach), and anodic polarization experiments. The results indicate that the hydrogen generated by the cathodic charging process decreased the corrosion resistance of 2205 duplex stainless steel, especially the pitting resistance of passive film. As a result of the hydrogen charging, the semiconductor characteristic of the passive film changed from n-type and p-type coexisting to only n-type existing, and the pitting susceptibility increased. Along with the charging process, the critical concentration of chloride for breakdown of passive film decreased and the repassivation process was prevented by hydrogen.

Comparison of corrosion properties of passive films formed on coarse grained and ultrafine grained AISI 2205 duplex stainless steels

The ultrafine grained 2205 duplex stainless steel with an average grain size of 300 nm was obtained by cold rolling down to 95% reduction in thickness and reversion annealing at 900 °C for 200 s. The ultrafine grained sample showed higher corrosion resistance than coarse grain one in borate buffer solution at room temperature, indicating that the passive film formed on the surface of the ultrafine grained 2205 duplex stainless steel is more protective. Comparing the doping concentrations between coarse grain and ultrafine grained samples from the Mott–Schottky plots, higher corrosion resistance of ultrafine grained sample was probably attributed to lower donor density and the thicker passive film in borate buffer solution. The results of electrochemical impedance spectroscopy were further supported by Raman spectra and XPS analysis.

Passive Behavior of Ultra-Fine-Grained 1050 Aluminum Alloy Produced by Accumulative Roll Bonding in a Borate Buffer Solution

In this study, the effect of the ARB process on the passive behavior of ultra-fine-grained 1050 aluminum alloy in a borate buffer solution (pH 6.0) has been investigated. The result of the microhardness tests revealed that the microhardness values increase with an increasing number of ARB cycles. The potentiodynamic polarization plots revealed that the higher number of cycles for the specimens proceeds with the ARB process rather than annealing yield to lower corrosion and passive current densities and more noble corrosion potential values. Moreover, electrochemical impedance spectroscopy measurements showed that increasing the number of ARB cycles offers better conditions for forming the passive films.

Repassivation behavior of 316L stainless steel in borate buffer solution: Kinetics analysis of anodic dissolution and film formation

The repassivation behavior of metals or alloys after oxide film damage determines the development of local corrosion and corrosion resistance. In this work, the repassivation kinetics of 316L stainless steel (316L SS) are investigated in borate buffer solution (pH 9.1) by using the abrading electrode technique. The current densities flowing from bare 316L SS surface are measured by potentiostatic method and analyzed to characterize repassivation kinetics. The initial stages of current decay (t<500ms) are discussed according to a film growth model, which describes the initial current transient should be divided into substrate dissolution current and passive film formation current based on Avrami kinetics. Then the two independent components are analyzed individually. The film formation rate and the thickness of film are compared in different applied potential. It is shown that anodic dissolution dominates the repassivation for a short time during the early times, and a higher applied potential will promote the anodic dissolution of metal. The film growth rate increases slightly with increasing in potential. Correspondingly, increase in applied potential from 0VSCE to 0.8VSCE results in thicker monolayer, which covers the whole bare surface at the time of θ=1. The electric field strengths through the thin passive film could reach 3.97×106Vcm−1.

Corrosion and electrochemical behavior of nanoscale carbon layers deposited onto a surface of nonalloyed steel via pulsed laser deposition

Carbon films 5 to 7 nm thick with a graphite structure are obtained via high-speed laser exposure of ultrafine graphite powder distributed homogeneously on the surface of nonalloyed steel. Due to the created intermediate layer consisting of nonstoichiometric iron carbides, the obtained films have a high adhesion to the substrate. These films also exhibit high continuity and behave as ideally polarizable electrodes over an extended potential range in borate buffer solutions. Cathode and anode currents are much lower in the obtained graphite films than are those measured at the compact graphite materials. The deposited graphite layers completely stop the anodic dissolution of a steel substrate.

Influence of pre-deformation and oxidation in high temperature water on corrosion resistance of type 304 stainless steel

The passivation properties of deformed 304 stainless steels after immersion in borate buffer solution containing 0.2821 mol/L Cl− at 288 °C were investigated. The spinel and magnetite oxides were formed on all the samples. However, the hematite oxides reduced significantly with the increasing of strain. The sample with maximum strain possessed the poorest corrosion resistance. The hematite oxide could offer high corrosion resistance, while magnetite evidently deteriorated corrosion resistance. Moreover, the influence of the donors in outer layer of oxide film on corrosion resistance was more important than that of the acceptors in inner layer.

Absorptive stripping voltammetry for cannabis detection.

BackgroundGiven that Δ9-tetrahydrocannabinol, the active constituent of cannabis, has been shown to greatly reduce driving ability, thus being linked to many drug driving accidents, its reliable detection is of great importance.ResultsAn optimised carbon paste electrode, fabricated from graphite powder and mineral oil, is utilised for the sensitive detection of Δ9-tetrahydrocannabinol (THC) in both aqueous solutions of pH 10.0 and in synthetic saliva solutions. “Absorptive Stripping Voltammetry” is exploited to that effect and the paste is used to pre-concentrate the carbon paste electrode with the target molecule. Practical limits of detection of 0.50 μM and 0.10 μM are determined for THC in stationary and stirred aqueous borate buffer solutions, respectively. Theoretical limits of detection are also calculated; values of 0.48 nM and 0.41 nM are determined for stationary and stirred THC aqueous borate buffer solutions, respectively. THC concentrations as low as 0.50 μM are detected in synthetic saliva solutions. The sensitivity of the sensor was 0.12 μA μM−1, 0.84 μA μM−1 and 0.067 μA μM−1 for the stationary buffer, the stirred buffer and the saliva matrix, respectively.Conclusions“Absorptive Stripping Voltammetry” can be reliably applied to the detection of Δ9-tetrahydrocannabinol, after suitable optimisation of the assay. Usefully low practical limits of detection can be achieved.

Investigation of passive films formed on the surface of alloy 690 in borate buffer solution

The passive film formed on the surface of the alloy 690 in borate buffer solution was studied by potentiodynamic curves and electrochemical impedance spectroscopy. With the increasing of the passivation potential, the corrosion resistance of the alloy 690 reduced. Moreover, the corrosion resistance of the passive film was the lowest in the vicinity of 0.6 VSCE. These results were supported by XPS and Mott–Schottky analyses. The corrosion resistance of the alloy 690 increased with the increasing of passivated potential in borate buffer solution with chloride ion. The chloride ion decreased corrosion resistance of the alloy 690 according to point defect model.

The passive oxide films growth on 316L stainless steel in borate buffer solution measured by real-time spectroscopic ellipsometry

Passive film growth on 316L stainless steel was investigated in borate buffer electrolyte (pH=9.1) by real-time spectroscopic ellipsometry (SE) and the composition was estimated by X-ray photoelectron spectroscopy (XPS). Anodic passivation of 316L SS was carried out in the potential range from 0VSCE to 0.9VSCE, after potentiostatic polarization for 1800s, the current density decayed from 10−2Acm−2 to 10−6Acm−2. The passive film thickness was simulated from Frenel and Drude reflection equations, the average complex refractive index was assumed to be N=2.3−j0.445. The estimated thickness increased linearly with potential from 1.5nm at 0V to 2.6nm at 0.8V. The growth of passive film followed high electric field ion conduction model. The passive film mainly contained the oxide/hydroxide of iron and chromium. The selective solubility of oxide in passive film explained the change of iron and chromium content at different potentials. Few nickel and molybdenum also contributed to the passive film with a constant content.

Inhibitor properties of carboxylates and their adsorption on copper from aqueous solutions

Adsorption, protective and passivating properties of several sodium higher carboxylates on a copper surface was studied in a borate buffer solution at pH 7.4. Sodium oleyl sarcosinate is shown to possess the best protective and adsorptive properties. It is established that at E = 0.0 V, the adsorption of oleyl sarcosinate is poly-layered, giving the best protection of copper upon its anodic dissolution. In a moist atmosphere with periodic condensation of moisture on the samples, it exceeded that of 1,2,3-benzotriazole.

Effect of Perchlorate Ions Concentration on Passive State of Iron

The iron in a borate buffer solution is passive. [1-3]. Whereas the passivation film is of a phase nature and includes metal oxides and hydroxides. The chemisorbed borates on the surface of the oxidized iron increase its protective properties and the presence of the Cl¯-ions in the liquid phase disturb the stability of the passive state of the metal [2,4]. An analogous, but less pronounced effect is observed under the influence of expressed ClO4¯-ions [2]. However, the nature of the latter is not fully understood. In this relation, in this paper we will attempt to establish general and specific mechanisms of the aforementioned process in the perchlorate media with borates. For an integrated solution of this task a combination of physical and chemical methods was used (electrochemical, microscopic (MIM-7 microscope, JEOL JSM-6510LV scanning electron microscope (SEM)), energy dispersion analysis (EDA)). The experiments were performed with a stationary iron electrode (0.013% С) in a classic three electrode cell in a borate buffer solution (рН = 8.4) at 20±2 °С with free air access. The concentration of the activating additive in the form of NaClO4 varied in the range of C=(1.0 – 5.0)×10-2 M, potential scan rate - vp= 10 mV/sec. The voltammograms obtained (Fig.1) and combined with the SEM/ EDA research results showed that the composition of the passivating layer on the iron did not go through changes dependant on the activating additive concentration. Nevertheless, in the 0.300 to 1.000V potential range, the system becomes meta-stable (the element of chloride and increased content of the element of iron detected on the oxidized surface of the metal confirm the surface activation, which is also registered by the optical microscopy). At the same time, persistent pitting formation, probably, takes place at the potentials higher than 1.000 V. As for the spotted instability of the iron/ electrolyte system in the potential range given above it can be related to two other causes conditioned by both: the transformation (cracks) of the passivation layer as well as the increasing absorption of ClO- 4 – ions which increases their degree of participation in the anodic process insignificantly. In the potential region of peak A3 (Table 3), ClO4¯-ions go through electrochemical oxidation releasing Cl¯- ions (Е(ClO4¯/Cl¯) = 0,56 V), which are stronger activators. Meanwhile, the concentration at which an intensive pitting is initiated is reached. Table 1. Potentials of anodic peaks of the iron voltammogram in the borate perchlorate media with varying concentrations of the activators. С(ClO4¯), М Е(А1), В Е(А2), В Е(А3), В 0,00 -0,412 0,111 0,644 0,01 -0,401 0,116 0,664 0,02 -0,399 0,134 0,657 0,03 0,395 0,128 0,612 0,04 -0,404 0,130 0,614 0,05 -0,388 0,125 0,669 Thus, systematization and analysis of the results of the described researches show that the activating effect of the ClO4¯- ions on the passive iron in a borate buffer solution is of a complicated mechanism within which an additional electrochemical generation of Cl¯-ions is not a dominant stage.

Rapid screening of aflatoxin B1 in beer by fluorescence polarization immunoassay

This manuscript describes the development of a sensitive, fast and easily-performed fluorescence polarization immunoassay (FPIA) for the mycotoxin aflatoxin B1 (AFB1) in various beer samples, both lager and dark. The highest sensitivity was determined for six poly- and monoclonal antibodies selective towards aflatoxins. The sample pretreatment design was emphasized since beer samples are characterized by extremely diverse matrices. Herein, the choice of sorbent for effective removal of matrix interferences prior to analysis was crucial. The samples were diluted with a borate buffer solution containing 1% PEG 6000 and passed through the clean-up column packed with NH2-derivated silica. This sample pretreatment technique was perfectly suitable for the FPIA of lager beer samples, but for dark beer and ale it did not suffice. An artificial matrix was constructed to plot a calibration curve and quantify the results of the latter samples. The developed immunoassay was characterized by a limit of detection of 1ngmL−1. Apparent recovery values of 89–114% for lager and 80–125% for dark beer were established. The FPIA data for AFB1 was characterized by elevated linear regression coefficients, 0.9953 for spiked lager and 0.9895 for dark beer samples respectively.

Nickel-coated silicon photocathode for water splitting in alkaline electrolytes

Photoelectrochemical (PEC) water splitting is a promising approach to harvest and store solar energy [1]. Silicon has been widely investigated for PEC photoelectrodes due to its suitable band gap (1.12 eV) matching the solar spectrum [2]. Here we investigate employing nickel both as a catalyst and protecting layer of a p-type silicon photocathode for photoelectrochemical hydrogen evolution in basic electrolytes for the first time. The silicon photocathode was made by depositing 15 nm Ti on a p-type silicon wafer followed by 5 nm Ni. The photocathode afforded an onset potential of ∼0.3 V vs. the reversible hydrogen electrode (RHE) in alkaline solution (1 M KOH). The stability of the Ni/Ti/p-Si photocathode showed a 100 mV decay over 12 h in KOH, but the stability was significantly improved when the photocathode was operated in potassium borate buffer solution (pH ≈ 9.5). The electrode surface was found to remain intact after 12 h of continuous operation at a constant current density of 10 mA/cm2 in potassium borate buffer, suggesting that Ni affords good protection of Si based photocathodes in borate buffers.

Electrochemical Characterization of Passive Films on Ni-Based Alloys in Acidic and Neutral Solutions

The present work reports the structure, chemical composition and electronic properties of passive films formed on Alloy 600 and Alloy 690 in borate buffer and sulfuric acid solutions. Photoelectrochemical response from passive films varied depending on the alloy substrates and the solutions. XPS analysis revealed that the passive films formed on Alloy 600 and Alloy 690 consisted of an outer hydroxide layer and an inner oxide layer in the borate buffer solution as well as the sulfuric acid solution. The chemical composition of the layers was relatively different depending on the solutions, that is, more Fe was incorporated into the passive films formed in the borate buffer solution. [doi:10.2320/matertrans.M2014384]

Corrosion and Passivation of High Nitrogen Face-Centered-Cubic Phase Formed on AISI 304L Austenitic Stainless Steel in Borate Buffer Solution

The corrosion behavior of a high nitrogen face-centered-cubic (f.c.c.) phase (γN) formed on plasma-based low-energy nitrogen ion implanted AISI 304L austenitic stainless steel in a borate buffer solution with a pH value of 8.4 was investigated by using anodic polarization, electrochemical impedance spectroscopy, Mott-Schottky analysis and Auger electron spectroscopy/x-ray photoelectron spectroscopy. Compared with original austenitic stainless steel, the γN phase layer on austenitic stainless steel possessed a significant improvement in corrosion resistance in the borate buffer solution with an apparent decrease of passivation current density and an increase of corrosion potential. A larger electrochemical impedance with a maximal phase angle of the 83° over low frequency range was obtained for the γN phase layer. The donor and acceptor densities of the γN phase layer and the corresponding flat band potential decreased, relative to that of original austenitic stainless steel. The protective passive film on the γN phase layer was observed as n-type and p-type semiconductors in the potential range above and below the flat band potential, respectively. It was composed of hydroxide/oxides of iron and chromium in the outer region and oxides of chromium and iron in the inner region both accompanied by chromium and iron nitrides, unlike original stainless steel which had pure iron and chromium on outermost surface. The calculated passive film thickness of 2.82 ± 0.67 nm on the γN phase layer by the power law distribution was compared with the measured thickness of 6.5 nm by AES/XPS. The improvement mechanism of nitrogen atoms in the γN phase layer on corrosion properties in the borate buffer solution was proposed by means of an applied point defect model.

Synthetic of pH-Sensitive PEG-b-PHEMA(His) Polymers andthe Study of Micelle

通过点击化学(Click chemistry)与原子转移自由基聚合(ATRP)一锅法合成AB型嵌段聚合物聚乙二醇嵌段聚甲基丙烯酸羟乙酯(PEG-b-PHEMA),之后对所得聚合物进行组氨酸(His)修饰得到p H敏感型聚合物PEG-b-PHEMA(His),运用核磁共振(1H NMR)及凝胶渗透色谱(GPC)表征了该嵌段聚合物及组氨酸修饰后的产物的结构和分子量分布(Mn=8.2×103~13.0×103 g/mol,PDI=1.27~1.51),说明聚合物被成功地合成且具有较小的多分散系数.之后对嵌段聚合物PEG-b-PHEMA(His)进行了动态光散射(DLS)、透射电镜(TEM)和临界胶束浓度(CMC)的测试,结果表明,聚合物胶束呈球形且粒径分布均匀,并且粒径随组氨酸接枝率增大而减小.最后我们做不同接枝比的PEG-b-PHEMA(His)的酸碱滴定曲线,结果表明,组氨酸的接入使聚合物具备明显的p H响应能力,进一步的释药试验也证明了这一结果.

Analytical application of the reaction system alizarine-hydrogen peroxide in borate buffer media for the spectrophotometric kinetic determination of Ni(II)

A rapid, simple, sensitive and selective new spectrophotometric kinetic method for Ni(II) traces determination at room temperature was elaborated in this paper. It is based on the catalytic effect of nickel ions upon the oxidation of alizarine (AL) by hydrogen peroxide in borate buffer (BUF) solution. The method was confirmed by determination of Ni(II) traces in fresh water samples. The obtained results were compared to those obtained by ICP-OES method and good agreement of the results was found.

Simultaneous determination of ten macrolides drugs in feeds by high performance liquid chromatography with evaporation light scattering detection

Simultaneous determination of ten macrolides drugs using HPLC-ELSD.

Efficient Electrocatalytic Water Oxidation by a Copper Oxide Thin Film in Borate Buffer

A robust water oxidation catalyst based on copper oxide was prepared by facile electrodeposition of Cu2+ from borate buffer solution under near neutral conditions. The Cu–Bi thin film exhibits high activity and long-term stability in Cu2+-free pH 9 borate buffer. A steady current density of 1.2 mA/cm2 was sustained for at least 10 h at 1.3 V versus NHE without iR compensation, which sets a new benchmark for copper-based OEC.