Products Of Anodic Oxidation Research Articles

Formation and Characterization of Dispersed Mixed Iron-titanium Oxide Systems by Electrochemical Method

Aims: Anodic polarization behavior of a combined iron-titanium electrode (two metals in electrical contact with each other) in aqueous solutions containing halide ions (F- and Cl-) was studied. Methods: he joint anodic dissolution of titanium and iron with subsequent thermal treatment makes it possible to obtain precursors of a highly dispersed mixed oxide system Fe2O3-TiO2. The phase and elemental composition and structural characteristics of obtained products were examined using X-ray diffraction and scanning electron microscopy. It has been experimentally confirmed that via changing the anode current density, hydrofluoric acid concentration in electrolyte and ratio of the working surface area of contacting metals, it is possible to effectively control the rate of anodic reactions and phase composition and morphology of anodic oxidation products for iron and titanium components in a combined electrode. Results: The main results of this study are as follows: Electrochemical method for the synthesis of complex dispersed oxide system Fe2O3-TiO2 based on joint anodic oxidation of contacting metals in aqueous media was suggested. Relationships between parameters of the electrochemical process and characteristics of the synthesized oxide system were revealed. Conclusion: By varying the parameters of the electrolysis process, it is possible to prepare complex oxyhydroxides with different ratios of iron and titanium, which makes it possible to synthesize precursors of iron titanates of preset composition and structure.

Direct and Scalable Electroreduction of Triphenylphosphine Oxide to Triphenylphosphine

The direct and scalable electroreduction of triphenylphosphine oxide (TPPO)-the stoichiometric byproduct of some of the most common synthetic organic reactions-to triphenylphosphine (TPP) remains an unmet challenge that would dramatically reduce the cost and waste associated with performing desirable reactions that are mediated by TPP on a large scale. This report details an electrochemical methodology for the single-step reduction of TPPO to TPP using an aluminum anode in combination with a supporting electrolyte that continuously regenerates a Lewis acid from the products of anodic oxidation. The resulting Lewis acid activates TPPO for reduction at mild potentials and promotes P-O over P-C bond cleavage to selectively form TPP over other byproducts. Finally, this robust methodology is applied to (i) the reduction of synthetically useful classes of phosphine oxides, (ii) the one-pot recycling of TPPO generated from a Wittig reaction, and (iii) the gram-scale reduction of TPPO at high concentration (1 M) with continuous product extraction and in flow at high current density.

Elucidation of the Structure of Products of Triphenylphosphine Electrooxidation in the Presence of Camphene

The structure of the products of anodic oxidation of triphenylphosphine in the presence of camphene carried out in acetonitrile with sodium perchlorate as supporting electrolyte has been studied. The major product, triphenylphosphine oxide, has been isolated from the solution in the form of cocrystals of free triphenylphosphine oxide and its complex with sodium perchlorate. The molecular structure of the cocrystals has been studied by X-ray diffraction analysis. Triphenylcamphenylphosphonium perchlorate, bornylacetamide, and a terpene compound with triphenylphosphonium and acetamide substituents in the cycle have been detected by NMR 13C as the electrolysis side products.

The electrochemical behaviour of enargite in ammoniacal solutions. I. Anodic reactions

The leaching of enargite in acidic solutions is known to be particularly slow and, as in the case of chalcopyrite, the use of alternative lixiviants has been extensively studied. In particular, the use of ammoniacal solutions has been a focus due to the faster kinetics in such media. However, there have not been any fundamental studies of the electrochemistry of enargite in such solutions. A fundamental study has therefore been made of the electrochemical behaviour of enargite in both ammonium sulfate and ammonium chloride solutions at pH values from 8 to 10 and comparisons have been drawn with the behaviour of chalcopyrite under similar conditions. Mixed potential measurements have shown that copper(II) is an effective oxidant for enargite in ammoniacal solutions and the potential region in which enargite is oxidised have been defined. Voltammetry under various conditions has shown that partial passivation also occurs in such solutions and that the anodic behaviour in chloride solutions is similar to that in sulfate. Potentiostatic measurements at potentials in the region of the mixed potentials in copper(II) solutions have been used to derive pseudo-steady-state curves that reveal Tafel-like behaviour with slopes of approximately 120 mV/decade suggesting a one-electron rate determining step. A first-order dependence of the rate of anodic dissolution on the ammonia concentration has been derived from this data. Coulometric measurements suggest that thiosulfate is the main product of anodic oxidation under these conditions. The relative rates of dissolution of chalcopyrite and enargite in ammoniacal solutions have been estimated using mixed potential theory that show that enargite dissolves more rapidly than chalcopyrite in such systems.

Self-enhanced electrical performance and less defective electrode/film structure for Al2O3 capacitor via interfacial anodic oxidation

Alumina (Al2O3) thin films derived from a sol-gel wet chemistry process were used to prepare capacitors with a simple MIM structure of Al/Al2O3/Pt. Driven by the external applied electric field, the phenomenon of anodic oxidation has been observed and confirmed at the Al/Al2O3 interface，resulting in the formation of a new alumina blocking layer (BL). Importantly, similar to the product of anodic oxidation of aluminum in liquid electrolytes, the blocking layer here exhibited excellent electrical characteristic and voltage-dependent growth mode as well, which endowed the capacitor with less defective electrode/film structure and self-enhanced electrical performance under the application of external voltage. Specifically, an ∼50% enhancement of the maximum working voltage and better capacitance characteristics of the thin film capacitor can be achieved. With the impedance and finite element analyses, the electrical characteristic of the BL and its corresponding effect on the alumina capacitor were explored in depth.

ANODIC PROCESSES ON NiSi ELECTRODE IN SODIUM HYDROXIDE SOLUTIONS

Anodic behavior of NiSi in (0.1 – 5.0) M NaOH in the range of potentials from corrosion potential up to oxygen evolution potential was studied using methods of polarization and impedance measurements. It was concluded that in the alkaline electrolyte the selective dissolution of silicon from the nickel silicide occurs. High chemical resistance of NiSi is due to the formation on its surface the passivating film, consisting mainly from poorly soluble products of anodic oxidation of nickel (it may also include a small content of silicon dioxide and silicates). The equivalent electrical circuit modeling the passive state of the silicide was proposed.

Electrochemical Oxidation of [1-X-12-I-CB11Me10-] Anions: Formation of Borenium Ylides [12-Dehydro-1-X-CB11Me10] and Iodonium Ylide Anions [{12-(1-X-CB11Me10-)}2I+

Cyclic voltammograms of 12-iodinated icosahedral carborane anions [1-X-12-I-CB11Me10-] (X = H, CH3, C2H5, C3H7, C4H9, C6H13, and COOCH3) show two one-electron anodic oxidation peaks at the Pt electrode in liquid SO2. Oddly, the first is irreversible and the second partially reversible. Mass spectrometry of the principal anionic product of preparative anodic oxidation of [1-H-12-I-CB11Me11-], identical with the anionic product of its reaction with [Et3Si-H-SiEt3]+ and/or Et3Si+, allows it to be identified as the iodonium ylide anion [{12-(1-H-CB11Me10-)}2I+]. Its reversible oxidation to a neutral ylide radical [{12-(1-H-CB11Me10•)}{12-(1-H-CB11Me10-)}I+] is responsible for the second peak. A DFT geometry optimization suggests that both the ylide anion and the ylide radical are very crowded and have an unusually large C-I-C valence angle of ∼132°; they are the first compounds with two bulky highly methylated CB11 cages attached to the same atom. Molecular iodine is another product of the electrolysis. We propose an electrode mechanism in which initial one-electron oxidation of [1-X-12-I-CB11Me10-] is followed by a transfer of an iodine atom from the B-I bond to SO2 to yield a weakly bound radical ISO2• which disproportionates into SO2 and I2. The other product is the borenium ylide [12-dehydro-1-X-CB11Me10], which has a strongly Lewis acidic naked vertex in position 12 that rapidly adds to another [1-X-12-I-CB11Me10-] anion to form the observed stable ylide anion [{12-(1-X-CB11Me10-)}2I+]. In acetonitrile, where it presumably exists as a solvent adduct, [12-dehydro-1-X-CB11Me10] has been trapped with H2O and, to a small extent, with MeOH, but not with several other potential trapping agents.

열 피로에 미치는 알루미늄 양극산화 제조방법의 융합연구

알루미늄의 양극산화는 황산법, 수산법과 황산과 수산을 활용한 혼산법 등이 있다. 산업체에서 만들어지는 양극산화는 황산법으로 전해액속의 황산농도가 15~20 wt %이다. 연질 양극산화피막을 생성할 경우는 전해액의 온도가 <TEX>$20{\sim}30^{\circ}C$</TEX> 범위에서 생산되고 있으며, 생산 전압은 직류전압으로 13~15 V 이내가 가장 많이 사용된다. 경질 양극산화피막을 생성할 경우는 전해액의 온도가 <TEX>$0{\sim}-5^{\circ}C$</TEX>에서 생산되어지고 있다. 본 연구에서는 황산법과 수산법을 이용하여 <TEX>$50{\mu}m$</TEX> 두께의 양극산화피막(알루미나)를 제작하였다. 황산법과 수산법에 의해 시편을 제조하여 열 피로시험을 수행하였다. 황산법과 수산법의 균열발생온도는 <TEX>$500^{\circ}C$</TEX>와 <TEX>$600^{\circ}C$</TEX>이었다. 황산법의 균열발생온도는 수산법의 균열발생온도보다 낮았다. 시험결과 수산법의 열 피로는 황산법의 열 피로 특성보다 좋았다. 그 이유를 알루미늄과 알루미나의 열팽창계수와 제조온도로 설명하였다. 고온에서 사용되는 양극산화제품의 제조방법을 여기서의 융합 연구를 통해 제안 가능하게 되었다. Anodic oxidation of aluminum has a sulfuric acid method and a oxalic acid method. Sulfuric acid concentration of the sulfuric acid method is 15~20 wt%. In the case of soft anodizing used in the <TEX>$20{\sim}30^{\circ}C$</TEX> range, and voltage is the most used within a DC voltage 13~15V. In the case of hard anodizing used in the <TEX>$0{\sim}-5^{\circ}C$</TEX> range. An aluminum oxide layer is made using sulfuric acid and oxalic acid. In this study, thermal fatigue of aluminum oxide layer which is made using sulfuric acid and oxalic acid is compared. Crack generating temperature of a sulfuric acid method and a oxalic acid method is <TEX>$500^{\circ}C$</TEX> and <TEX>$600^{\circ}C$</TEX>. Thermal fatigue of aluminum oxide layer which is made using oxalic acid is better than thermal fatigue of aluminum oxide layer which is made using sulfuric acid. The characteristic of thermal fatigue can be explained by using thermal expansion coefficient of Al and Al2O3 and manufacturing temperature on Al anodizing. It was made possible through the convergent study to propose the manufacturing method of the anodic oxidation product used at a high temperature.

Anodic oxidation of selenadiazoloquinolones in alkaline media

Newly synthesized derivatives of 6-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-h]quinoline variously substituted at position 7 (R = H, COOH, COCH(3), CN, COOC(2)H(5) and COOCH(3)) are established in strongly alkaline aqueous solutions (0.1 M NaOH; pH ∼ 13) as N(9)-deprotonated structures, but in less alkaline solutions (0.001 M NaOH; pH ∼ 11) the N(9)-protonated oxo tautomeric forms dominate. Upon their anodic oxidation in alkaline solutions, the selenadiazole ring is replaced, forming instead the paramagnetic species analogous to the ortho semiquinone radical anions as monitored by in situ EPR spectroscopy. The quantum chemical calculations for two representative selenadiazoloquinolones (R = H and COOH) and their anodic oxidation products presented are in agreement with experiments.

A spectroelectrochemical and chemical study on oxidation of 7,8-dihydroxy-4-methylcoumarin (DHMC) and some related compounds in aprotic medium

Electrochemical and chemical oxidation of 7,8-hydroxy-4-methylcoumarin (DHMC 1) and 7,8-diacetoxy-4-methylcoumarin (DAMC 4) were studied to investigate the mechanisms occurring in their antioxidant activities in acetonitrile, under electron transfer and H-atom transfer conditions. Electrolysis and chemical reactions were followed on-line by monitoring the UV spectral changes with time. The anodic oxidation of DHMC, studied by cyclic voltammetry and controlled potential electrolysis, occurs via a reversible one-step two-electrons process, yielding the corresponding stable phenoxonium cation. Moreover, the chemical oxidation with an H-atom acceptor also follows a similar path, yielding the stable neutral quinonic product. Intermediates were never evidenced in both cases. Only in the presence of a strong base, an anodic oxidation product mono-electronic was evidenced, likely the DHMC radical anion. However, the anodic oxidation of the acetoxy derivative DAMC occurs at very high potential values, ruling out the possibility that the antioxidant activity observed in vivo might occur via an electron transfer mechanism; no reactions were evidenced with an H-atom acceptor.

Adsorption of ochratoxin A (OTA) anodic oxidation product on glassy carbon electrodes in highly acidic reaction media: Its thermodynamic and kinetics characterization

Abstract We study the thermodynamics and kinetics of the adsorption of a redox couple having quinone nature on glassy carbon electrodes. This couple is produced by the anodic oxidation of mycotoxin ochratoxin A in 10% acetonitrile + 90% 1 M HClO 4 aqueous solution. The quasi-reversible redox couple was studied by both cyclic (CV) and square wave (SWV) voltammetric techniques. The Frumkin adsorption isotherm best described the specific interaction of the redox couple with carbon electrodes. By fitting the experimental data, we obtained values of −28.4 kJ mol −1 and 0.70 ± 0.02 for the Gibbs free energy of adsorption and the interaction parameter, respectively. SWV fully characterized the thermodynamics and kinetics of the adsorbed redox couple, using a combination of the “quasi-reversible maximum” and the “splitting of SW peaks” methods. Average values of 0.609 ± 0.003 V and 0.45 ± 0.06 were obtained for the formal potential and the anodic transfer coefficient, respectively. Moreover, a formal rate constant of 10.7 s −1 was obtained. SWV was also employed to generate calibration curves. The lowest concentration of mycotoxin was 1.24 × 10 −8 M (5 ppb), measured indirectly with a signal to noise ratio of 3:1.

Electrochemical Oxidation Behavior of Iodide on Platinum Electrode in Acid Solution

The oxidation behavior of iodide ion on platinum electrode in sulfuric acid media was investigated by the technique of cyclic voltammetry. The electrochemical performance showed that the electrochemical reaction of 2I--2e→ I2 occurred when the potential scanning range lowered than 0.6 V(vs Hg/Hg2SO4). The obtained cyclic voltammograms were affected by the formation of iodine film and triiodide species. The whole reaction performance is consistent with electrochemical-chemical (E-C) model. Iodine film can be formed during electrochemical oxidation process and dissolved by chemical reaction of I2+I-葑I3-. When the electrode was polarized to over 0.6 V(vs Hg/Hg2SO4), high-valent iodine- containing compounds could be formed by I-+3H2O→IO3- +6H++6e, not by iodine which was the product of anodic oxidation. Two reduction peaks occurred during reverse cathodic potential scanning and they could be assigned to the reduction of iodine film and triiodide ion in the solution, respectively. The anodic oxidation of iodide ion is controlled by the liquid-phase diffusion process of iodide ion when there is no iodine film formed on the electrode. However, when iodine film is formed on the electrode, solid-phase diffusion process of iodide ion through the iodine film would become the rate determining step. In addition, the acidity of the solution would affect the process of anodic oxidation of iodide ion seriously. The onset potential and peak potential corresponding to the anodic current in linear sweep voltammetry are shifted to lower direction with the increase of acid concentration.

Anodic behavior of gold in acid thiourea solutions: A cyclic voltammetry and quartz microgravimetry study

It is shown that at potentials E 100 μA cm−2) starts at E ≥ 0.65 V, with the primary process being the oxidation of thiourea, which gives rise a current peak at E ≃ 1.0 V. The thiourea oxidation at E ≥ 1.1 produces the appearance of catalytically active species, which drastically accelerate the gold dissolution process in the potential region extending from a steady-state value to 0.6 V, where the current efficiency for gold approaches 100% and a peak emerges at E ≃ 0.55 V. The peak’s height is commensurate with the value of the limiting diffusion current associated with the ligand supply. The species in question make no discernible impact on the thiourea oxidation process. Formamidine disulfide, which forms during the anodic oxidation of thiourea or which is added in solution on purpose, exerts no noticeable catalytic influence on the anodic gold dissolution. The catalytically active species is presumably the S2− ion, product of decomposition and deep oxidation of thiourea and formamidine disulfide. Indeed, adding sulfide ions in solution has a strong catalytic effect on the gold dissolution, whose character is identical to that of the effect exerted by products of anodic oxidation of thiourea at E ≥ 1.1 V μA cm−2.

スルファミン酸浴におけるスルファミン酸イオンの陽極酸化とＮｉ電析に及ぼす影響

Anodic oxidation behavior of sulfamate ions during the electrodeposition of Ni from sulfamate baths was investigated using Pt, Ni and Ni-S anodes. The following results were obtained ; (1) The oxidation products of sulfamate ions showed an absorption peak at 245-250 nm in UV spectra and the absorbance was changed depending on the anode potential. (2) At potentials less noble than 0 V vs. NHE, no anodic oxidation products were formed, while the amount of anodic oxidation products was significantly increased when the anode was polarized to a greater noble potential than 0 V. (3) In the presence of Cl- ions in the baths, the Ni-S anode was maintained at potentials less noble than 0 V under most electrolysis conditions. (4) The content of S in the electrodeposited Ni was increased in proportion to the concentration of the anodic oxidation products in the baths. (5) By increasing the content of S, the deposited Ni became finer in size and showed the feature of unoriented dispersed type with high hardness.

Anodic oxidation of the dye materials methylene blue, acid blue 25, reactive blue 2 and reactive blue 15 and the characterisation of novel intermediate compounds in the anodic oxidation of methylene blue

AbstractAnodic oxidation of the dye molecules, methylene blue, acid blue 25, reactive blue 2 and reactive blue 15 in chloride solution leads to colour destruction but UV and TOC data show that the oxidation reactions do not lead to complete destruction of the organic molecules. Analysis of the anodic oxidation products of [3,7‐bis (dimethylamino) phenothiazinium] chloride (methylene blue) in a chloride solution provides evidence for formation of seven neutral and two charged intermediates. The main intermediate is identified by its X‐ray diffraction crystal structure and accurate mass spectrometry as the novel leuco dye 4,6‐dichloro‐7‐dimethylamino‐3H‐phenothiazin‐3‐one, C14H10Cl2N2OS (I) formed by replacement of one of the dimethylamino groups of methylene blue with oxygen accompanied by regiospecific chlorination of the carbocyclic systems. The mass spectra of other intermediates formed are interpreted in terms of the structure of I.© 2002 Society of Chemical Industry

Products of Anodic Oxidation of Carbamide: Effect of Anionic Composition of Solution

The current efficiency for carbamide oxidation on smooth platinum electrode to molecular nitrogen and nitrate in sulfate, fluoride, chloride, and bromide solutions are determined. The supporting-electrolyte anion has a complex effect on the ratio between rates of these processes. Independence of the current efficiency from the solution pH in electrolysis of sulfate solutions of carbamide is confirmed.

Products of Anodic Oxidation of Carbamide: Effect of Temperature

An unusual (extremum) temperature dependence of current efficiencies for parallel processes of carbamide anodic oxidation in 1 M NaF yielding nitrogen molecules and nitrate is discovered. The temperature effect on the current efficiencies for similar processes in a chloride solution is much weaker.

Overlap of the oxide and hydrogen regions of platinum electrodes in aqueous acid solution

Two unusual features of noble metal electrode surfaces, active states of the metal and their anodic oxidation products (hydrous oxides), are of increasing interest at the present time owing to the important role of such species in electrocatalysis. The extent to which the hydrous oxide reduction process overlaps with the hydrogen adsorption region was investigated for platinum in acid solution. At least three distinct hydrous oxide reduction peaks (or regions) were observed and in some cases one of these peaks commenced at ca. 0.0 V, i.e. it was almost totally within the hydrogen gas evolution region. Following repeated hydrous oxide growth and reduction, which disrupted and thus activated the metal surface, a sequence of four low-level premonolayer oxidation peaks (each of which has been noted earlier by other authors) appeared in the positive sweep. As discussed earlier for copper in base, the transitions giving rise to such peaks are assumed to be mediator generation reactions, which strongly influence electrocatalytic processes occurring on platinum at low potentials.

Antioxidative properties of probucol estimated by the reactivity with superoxide and by electrochemical oxidation.

The reaction of probucol with superoxide (O2(*-)) was investigated in acetonitrile using both electron spin resonance (ESR) and electrochemical techniques. The formation of phenoxyl radical was observed during the reaction of probucol with O2(*-) by ESR spectroscopy. The reaction of probucol with O2(*-) in acetonitrile was followed by cyclic voltammetry. With the addition of probucol, the oxidation peak current of O2(*-) decreased concentration dependently. This suggests that probucol reacts with O2(*-), that is, probucol scavenges O2(*-) in acetonitrile. 2,6-Di-tert-butyl-p-benzoquinone was identified as the major product of the reaction of probucol with O2(*-) in acetonitrile. Electrochemical oxidation of probucol was also performed. Probucol gives an irreversible oxidation peak at ca. +1.4 V vs. the saturated calomel electrode in the cyclic voltammogram. Controlled-potential electrolysis was carried out at +1.2 V in a divided cell. 2,6-Di-tert-butyl-p-benzoquinone, 4,4'-dithiobis(2,6-di-tert-butylphenol), and 4,4'-trithiobis(2,6-di-tert-butylphenol) were identified as the products of anodic oxidation. These redox properties of probucol may correlate with the physiological activities.

On-Line Linear Sweep Voltammetry−Electrospray Mass Spectrometry

A three-electrode electrochemical cell coupled to an electrospray (ES) mass spectrometer has been developed and employed for on-line linear sweep voltammetry-ES mass spectrometry and electrochemical reaction studies. Generated in this type of electrochemistry/mass spectrometry (EC/MS) experiment are ion abundance vs potential profiles that provide molecular weight and structural information pertaining to intermediates and products of anodic oxidation of diphenyl sulfide, anodic pyridation of 9,10-diphenylanthracene, and reduction of nitrobenzene. Anodic oxidation of diphenyl sulfide in methylene chloride media at the platinum electrode yielded diphenyl sulfoxide and pseudodimer sulfonium ion along with products of further oxidation. The obtained ion abundance vs potential profiles offer additional evidence to corroborate previously proposed reaction mechanisms for pseudodimer sulfonium ion generation from diphenyl sulfide, as well as pyridine addition to DPA radical cation also in methylene chloride at the platinum electrode. From the latter experiment, a newly found reaction product, [DPA(py) - H](+), is reported. Despite the inherent tendency of ES devices to induce oxidation processes in the positive ion mode, intermediates and products of nitrobenzene reduction in nonaqueous and organic/water media were detected in both negative and positive ES modes.