Study of the effects of hydrogen on the pitting processes of X70 carbon steel with SECM

The effects of hydrogen on the pitting processes of X70 carbon steel in neutral chloride ions containing solution are investigated by using the scanning electrochemical microscope (SECM) technique. The tip of the SECM monitors the Fe²⁺ ions produced by the specimen during its anodic dissolution processes, thus the initiation and the propagation of the pitting processes can be observed. Pitting is much more easily observed after the specimen has been pre-charged with hydrogen, for the oxidation of the hydrogen in the X70 decreases the pH value at the X70/solution interface, which retards the formation of an oxide film and subsequently promotes the pitting processes. The observed behaviour is further verified by the decrease of the solution's pH.     

The electro-oxidation of chemisorbed carbon monoxide on polycrystalline rhodium in acid solution

The electrooxidation of CO adsorbed on Rh in 1 M HClO₄ at room temperature exhibits a complex potentiodynamic E/I profile which depends on the oxygen-containing species present on the electrode. The electrochemical behaviour of the system is explained through the participation of two CO-adsorbed states and the interaction of the latter with electrosorbed oxygen. The electro-oxidation of CO adsorbed on Rh can be correlated with the reaction occurring on Pt.     

Study of a cysteine derivative as a corrosion inhibitor for carbon steel in phosphoric acid solution

Inhibition of corrosion of carbon steel in phosphoric acid solution by use of l-cysteine methyl ester hydrochloride has been investigated by measurement of weight loss and use of electrochemical methods. The efficiency of inhibition was increased by increasing the concentration of the inhibitor and reduced by increasing the temperature. Polarization studies revealed that this compound behaves as mixed-type inhibitor. Electrochemical impedance spectroscopy showed that dissolution of the steel occurs as a result of charge-transfer. Adsorption of the inhibitor obeyed the Langmuir adsorption isotherm. Kinetic and thermodynamic data were calculated and are discussed.     

Experimental and theoretical studies of carbon steel corrosion protection in phosphoric acid solution by expired lansoprazole and rabeprazole drugs

The effects of expired lansoprazole and rabeprazole on the corrosion protection of carbon steel in phosphoric acid (3.0 ?M) solution were examined by Tafel polarization and electrochemical impedance spectroscopy (EIS). Lansoprazole and rabeprazole concentrations (0.5, 1.0, 5.0 and 10 ?mM) in acid solution were raised, which improved corrosion prevention. Both lansoprazole and rabeprazole as the mixed inhibitors retarded the anodic and cathodic processes, as indicated by polarization data. With the increasing temperature in the range of 25–55 ?°C, the inhibition efficiency drops from 92.9% to 69.3% for lansoprazole and from 94.8% to 74.2% for rabeprazole. The major decrease in the inhibition efficiency with ascending temperature proved the physisorption of the drugs. The activation energies for carbon steel corrosion in H₃PO₄solution were enhanced from 41.6 ?kJ ?mol^?1 to 81.9 ?kJ.mol^?1and 85.9 ?kJ ?mol^?1 for lansoprazole and rabeprazole, respectively. The influence of temperature on the corrosion process of carbon steel in the acid medium was used to derive the thermodynamic quantities of corrosion. The adsorption of both lansoprazole and rabeprazole on carbon steel followed the Langmuir adsorption isotherm. The polarization data yielded outcomes that were consistent with the results arising from impedance measurements. The theoretical study of both lansoprazole and rabeprazole was done by a density functional theory (DFT) approach to realize the effects of molecular structure on their inhibitive action. Both lansoprazole and rabeprazole contain a higher E_HOMO, a lower E_LUMO and a lower energy gap than some inhibitors earlier reported as good corrosion inhibitors in the literature.     

Scanning electrochemical microscopy of hydrogen electro-oxidation. Rate constant measurements and carbon monoxide poisoning on platinum

We describe an application of the scanning electrochemical microscope that uses tip–sample feedback to characterize the electro-oxidation of hydrogen on a polycrystalline platinum electrode in sulfuric acid solutions in the presence and absence of adsorbed carbon monoxide. The hydrogen oxidation reaction is probed by reducing protons at a diffusion-limited rate at the microscope's tip electrode while it is positioned near a platinum substrate. A series of approach curves measured as a function of the substrate potential provides hydrogen oxidation rate constant values over a wide range of substrate conditions. In the absence of CO, the rate of hydrogen oxidation exceeds 1 cm s⁻¹ at potentials within the hydrogen adsorption and double layer charging regions. A Tafel slope of 30 mV per decade is determined near the reversible potential. At increasingly positive substrate potentials, the hydrogen oxidation rate decreases exponentially with increasing potential as the surface is covered with an oxide layer. The adsorption of solution-phase carbon monoxide completely deactivates the platinum substrate towards steady-state hydrogen oxidation over a large range of substrate potentials. Approach curves indicate a near-zero rate constant for hydrogen oxidation on CO-covered platinum at potentials below oxide formation. An increase in the hydrogen oxidation rate is seen at potentials sufficiently positive that CO fails to adsorb and the platinum oxide forms. In comparison, dynamic tip–substrate voltammetry depicts a complex substrate response whereby the adsorbed carbon monoxide layer transforms from a weakly adsorbed state at low potentials to a strongly adsorbed state at high potentials. Although steady-state approach curve measurements depict the complete deactivation of catalytic activity at these potentials, a significant hydrogen oxidation current is observed during the potential-induced transformation between these weakly and strongly adsorbed CO states. The rate of hydrogen oxidation approaches that of a pristine platinum surface during this surface transformation before returning to the poisoned state.     

Enhanced catalytic activity of ternary Pd-Ni-Ir nanoparticles supported on carbon toward formic acid electro-oxidation

Journal of Solid State Electrochemistry - Aiming to further promote the performance of PdNi for formic acid electro-oxidation (FAEO), ternary Pd-Ni-Ir/C nanocatalyst was synthesized via an ethylene...     

Adsorption of uranium from crude phosphoric acid using activated carbon

The adsorption of uranium from crude phosphoric acid has been investigated using conventional activated carbons. It was found that treatment with nitric acid oxidized the surface of activated carbon and significantly increased the adsorption capacity for uranium in acidic solutions. The parameters that affect the uranium(VI) adsorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated. Equilibrium data were fitted to a simplified Langmuir and Freundlich isotherms for the oxidized samples which indicate that the uranium adsorption onto the activated carbon fitted well with Langmuir isotherm than Freundlich isotherm. Equilibrium studies evaluate the theoretical capacity of activated carbon to be 45.24 g kg^?1.     

Formation of elementary phosphorus during the action of hydrogen and organic vapors on a catalyst of phosphoric acid on activated charcoal

Summary Elementary phosphorus is formed when a catalyst of phosphoric acid on activated charcoal comes in contact with hydrogen or vapors of organic substances, beginning at 400° and above, and also when the catalyst is treated with nitrogen at 600° and above. A hypothetical explanation was presented for this phenomenon.     

Studies on the inhibitive effect of potassium ferrocyanide on the corrosion of steel in phosphoric acid

In this work, the effect of potassium ferrocyanide (Pf) on the corrosion of mild steel in solutions of phosphoric acid (H₃PO₄) has been investigated in relation to the concentration of the inhibitor by weight loss, potentiodynamic polarization and AC impedance (EIS) measurements. The results obtained revealed that this compound is good a mixed-type inhibitor. The effect of temperature on the corrosion behavior with the addition of optimal concentration of Pf was studied in the temperature range 298–328 K. The value of inhibition efficiency decreases slightly with the increase in temperature. Changes in impedance parameters (charge transfer resistance, R _t, and double layer capacitance, C _dl) were indicative of adsorption of Pf on the metal surface, leading to the formation of a protective film. Adsorption of Pf on the C38 steel surface was found to obey the Langmuir adsorption isotherm. Some thermodynamic functions of dissolution and adsorption processes were also determined.     

Adsorption and corrosion inhibitive properties of piperidine derivatives on mild steel in phosphoric acid medium

The present study describes the inhibition effect of 4-benzyl piperidine (P1), 1,6-bis(4-benzylpiperidine-1-carboxamide)hexane (P2) and bis(4-benzylpiperidine)thiuram disulfide (P3) towards the corrosion of mild steel in 5.5 M H₃PO₄ solution using weight loss measurements and polarization technique. The influence of inhibitor concentration and temperature on the inhibitory behavior of P2 and P3 was investigated. Meanwhile, the inhibition efficiency (IE) was found to depend on the molecule structure and the concentration of piperidine derivatives. The IE for 10^?3 M P2 and P2 in 5.5 M H₃PO₄ is around 90 %. Polarization studies clearly revealed that all the compounds used act as mixed-type inhibitors. Adsorption isotherms were fitted by the Langmuir isotherm. Adsorption energies ( $ \Updelta {\text{G}}^\circ_{\text{ads}} $ and $ \Updelta {\text{H}}^\circ_{\text{ads}} $ ) and kinetic parameters were evaluated. Significant correlations are obtained between inhibition efficiency with the calculated chemical indexes, indicating that the variation of inhibition with structure of the inhibitor may be explained in terms of electronic properties.     

Numerical reconstruction of digital holograms for the study of pitting dynamic processes of the X70 carbon steel in NaCl solution

In this paper, a new image processing method to reconstruct digital holograms is proposed. After the digital holograms were recorded in situ during the electrochemical experiment, three-dimensional images were numerically reconstructed to study pitting dynamic processes of the X70 carbon steel in neutral solution containing chloride ions. Compared with the digital holograms, the reconstructed images can capture subtle changes more readily, therefore, more revealing. The radii of the pits were different, for they were induced at different times and propagated at different rates. It is expected that this method can be used extensively in studying the electrochemical dynamic processes at the electrode/electrolyte interface.     

Effects of phosphoric acid as additive in the preparation of activated carbon fibers from poly(p-phenylene benzobisoxazole) by carbon dioxide activation

Poly(p-phenylene benzobisoxazole) (PBO) was impregnated with small amounts of H₃PO₄, and the effects of this additive on the porosity and other characteristics of chars and activated carbon fibers (ACFs) derived from this polymer were investigated. To this end, PBO-AS impregnated with 5, 10 or 15 wt.% H₃PO₄ was pyrolyzed at 850 °C, and the resulting chars were physically activated with carbon dioxide at 800 °C to different burn-off (BO) degrees. Thermal analysis techniques only detected minor effects of H₃PO₄ on PBO pyrolysis. The char yield and char reactivity towards CO₂ increased following PBO-AS impregnation with H₃PO₄. Structural (X-ray diffraction), porous textural (CO₂ adsorption) and surface chemical (temperature-programmed desorption, X-ray photoelectron spectroscopy) characterizations of the pyrolysis chars indicated that the increase in char reactivity is probably associated with a higher content of oxygenated functionalities. Following CO₂ activation, the surface area and pore volume of the obtained ACFs chiefly depended on the BO degree, but impregnation with H₃PO₄ restricted the pore size to the micropore and narrow mesopore range, thus producing adsorbents with a slightly narrower pore size distribution than in the absence of H₃PO₄. The results are compared with those previously obtained under equivalent conditions with other high-crystallinity polymers as precursors for ACFs.     

Selective precipitation of rare earth orthophosphates with hydrogen peroxide from phosphoric acid solutions

It has been shown for the first time that the use of hydrogen peroxide allows precipitation of rare earth orthophosphates (La–Tb) from phosphoric acid solutions at temperatures below 100°C. Either anhydrous or hydrated orthophosphates with monazite or rhabdophane structure, respectively, can be obtained depending on rare earth element position in lanthanide series and precipitation conditions (orthophosphoric acid and hydrogen peroxide concentration). Hydrated orthophosphates with rhabdophane structure can be prepared by precipitation with hydrogen peroxide for all studied rare earth elements.     

Thermochemistry and kinetics of the aspect of diammonium hydrogen phosphate precipitation in phosphoric acid solution

Journal of Thermal Analysis and Calorimetry - The thermochemical and kinetic studies of diammonium hydrogen phosphate precipitation in phosphoric acid with ammonia were followed using a...     

Investigations on the current oscillations during the electrolytic reduction of dichromates in acetic solutions

The reduction mechanism at a mercury electrode of Eriochrome Cyanine R, in a 0.9 M NaClO₄+0.1 M HClO₄ supporting electrolyte, has been investigated by several electrochemical techniques. By means of coulometry at constant potential and cyclic voltammetry it was demonstrated that a radical is formed, which suffers disproportionation, after the first electron transfer. The results of the cyclic voltammetric investigation and the impedance measurements evidenced the intrinsic reversible nature of the electron transfers. Apparent irreversible polarographic behaviour is a consequence of the existence of chemical reactions following the electron transfers. The impedance measurements demonstrated the strong adsorption of the Ox and Red form of Eriochrome Cyanine R as well as of the radical formed. On the basis of the experimental data a reduction mechanism is proposed.     

Enhanced electro-oxidation of formic acid by a PdPt bimetallic catalyst on a CeO2-modified carbon support

PdPt bimetallic catalysts that employ CeO2-modified carbon black as a support have been prepared using an organic colloidal method.PdPt/CeO2-C shows excellent performance toward the anodic oxidation of formic acid.The effects of varying both Pd to Pt ratio and CeO2 content have been investigated.The optimal Pd to Pt atomic ratio is 15,indicating that addition of small amounts of Pt can significantly enhance the activity of the catalyst.When the CeO2 content in the catalyst reaches as high as ～15 wt.%,the catalyst shows the maximum activity.Adding CeO2 not only enhances the catalytic activity of the material,but may also change the mechanism of its catalysis of the anodic oxidation of formic acid.Pd15Pt1/15CeO2-C exhibited 60% higher activity than Pd/C,and had a negative shift in onset potential of more than 0.1 V.Based on characterization by X-ray diffraction,X-ray photoelectron spectroscopy,thermogravimetric analysis and transmission electron microscopy,the interactions between the components are revealed and discussed in detail.     

Coulometric argentometric determination of microamounts of sulphur in iron and steel after reduction to hydrogen sulphide with iron(II) in strong phosphoric acid medium

A coulometric method was developed for the determination of microamounts of sulphur in iron and steel. Hydrogen sulphide is quantitatively evolved by reduction with iron(II) in strong phosphoric acid medium and is titrated with electrolytically generated silver ion from a silver anode. Microamounts of sulphide (2.96–224.3 μg) in sodium sulphide standard solutions could be determined with an error of only a few percent. Sulphur in a potassium sulphate standard solution is quantitatively reduced to hydrogen sulphide and could be separated from the solution by heating and determined accurately. Trace amounts of sulphur (7–100 μg g^?1) in iron and steels could be determined with a standard deviation of 0.7–2.1 μg g^?1.     

CeO_2修饰炭载体负载PdPt二元合金催化剂及其在甲酸氧化电催化中的应用

用CeO2修饰炭粉做载体,使用有机溶胶法还原PdPt二元合金的方法制备了一系列PdPt/CeO2-C催化剂.借助电化学测试,探讨催化剂中不同Pd与Pt原子比例的PdPt二元合金和不同含量的CeO2对于甲酸电氧化催化活性的影响.不断减少PdPt合金中Pt的比例可以促使甲酸氧化的起始电位前移,当Pd：Pt=15：1时氧化电流出现极值;同时,随着催化剂中CeO2含量的增加,催化剂对于HCOOH氧化的电流密度增加,当含量为15%时达到最大值.相对于Pd/C催化剂,在Pd15Pt1/15CeO2-C催化剂表面的甲酸氧化反应起始电位负移至少0.1V,氧化的电流密度提高60%以上.结合X射线衍射（XRD）,X射线光电子能谱（XPS）,透射电镜（TEM）和热重（TG）等测试数据可以发现,当极少量的Pt与Pd形成合金,Pt与Pd之间产生电子效应,使得合金表面HCOOH氧化的过电位降低;而CeO2的添加不仅有助于PdPt二元合金的分散,更有可能改变甲酸在PdPt表面的氧化反应路径,发挥双功能机理.