Synthetic Semiconductor Diamond Electrodes: Electrochemical Characteristics of Individual Faces of High-Temperature-High-Pressure Single Crystals

Effects of crystal structure on the electrochemistry of boron-doped high-temperature-high-pressure diamond single crystals grown from an Ni–Fe–C–B melt are studied. On the {111}, {100}, and {311} faces, the linear and nonlinear electrochemical impedance spectra and the electrochemical kinetics in the Fe(CN)₆ ^3_/4_ redox system are measured. The acceptor concentration in the diamond interior adjacent to these faces was determined from the Mott–Schottky plots and the amplitude-demodulation measurements. It varies in the 10¹⁸ to 10²¹ cm^–3 range. The difference in the electrochemical behavior of individual crystal faces is primarily attributed to different boron acceptor concentrations in the growth sectors associated with the faces.     

Vacuum-Annealed Undoped Polycrystalline Diamond: a New Electrode Material

Electrochemical behavior of undoped polycrystalline diamond films annealed in a vacuum at 1775 to 1915 K is studied. The annealing at temperatures over 1825 K imparts conductance to initially insulating films, which permits using them as electrode material. With further increase in the annealing temperature to above 1915 K, the effective resistivity decreases from initial value of 10¹¹ to 10¹² cm down to less than 0.1 cm, the differential capacitance increases from 10^–3 to 50 F per cm² of geometrical surface, the transfer coefficients for electrochemical reactions in the Fe(CN)₆ ^3–/4– redox solution increase from 0.2 to 0.5, and the degree of reversibility of the electrochemical reaction increases. The observed changes in the electrode properties are caused by the formation, upon the annealing, of a nondiamond phase at the intercrystallite boundaries and defect areas in the crystallites; the outcroppings of the conducting phase play the role of active sites at the electrode surface. With increasing annealing temperature, both the amount of this phase and its conductivity increase.     

Theoretical Study of Intradimer Mechanism for Diamond Growth over Diamond (100)

The study of the energetics of the accepted intradimer diamond growth mechanism over (100) diamond surface is presented. The calculations were made in a density functional approach with the DGauss code using a DZVP2 basis set and a BLYP interchange and correlation potential. A simple 9-carbon cluster modeling the (100) diamond surface was used; its validity is discussed in relation with other calculations that used larger model clusters. The mechanism, presented in six steps, is based in the Harris and Garrison's work that considers the methyl radical as the main growth precursor agent and the breaking of the dimer surface bond with the corresponding methylene radical formation as a prior step to the formation of a CH₂-bridge structure, which is a feasible step; in contrast to these molecular dynamics results, Huang and Frenklach, using semiempirical methods, consider the breaking of the dimer surface bond and the formation of a CH₂-bridge structure as one step and this step as the energetically determinant of the mechanism. They also found an activation energy barrier for the interaction between a radical surface center with a H and CH₃. The present work tries to discern between these two ideas by calculating the activation barriers and the reaction energies for each step of the Harris and Garrison's mechanism in a density functional approach and comparing them to the results of Huang and Frenklach. The energy calculations point toward the scission of the dimer bond (step 4) as the determinant step; this step is endothermic, with an energy barrier of 50.43 kcal-mol^–1. On the other hand, the formation of the CH₂-bridge structure (step 5) is a feasible step with an energy barrier of 13.57 kcal-mol^–1. The adsorption of CH₃ (step 2) and H (step 6) species over radical surface sites did not involve any energy barriers, as it would be hoped. These steps were strongly exothermic and are close to the thermodynamic values for C—C and C—H bond energies. The removal of methylic hydrogen (step 3) did not show any problem because the activation barrier is only 3.68 kcal-mol^–1 less than the removal of a surface hydrogen (step 1), which has an energy barrier of 19.59 kcal-mol^–1. All steps, except number 4, were exothermic.     

Sulfur-Doped n-Type Diamond: Preparation and Electrochemical Properties

Films of sulfur-doped synthetic diamond are chemical-vapor-deposited using codoping with sulfur and boron. The sulfur in diamond is detected with particle-induced x-ray emission (PIXE), x-ray photoelectron spectroscopy (XPS), and secondary ion mass spectroscopy (SIMS). Electrochemical and thermoelectric measurements show that the sulfur-containing diamond films grown in gas phase lean in boron are n-type, whereas those grown with higher boron content are overcompensated, hence, p-type. Electrochemical properties of the n-type diamond films are studied for the first time using methods of electrochemical impedance, open-circuit photopotential, and voltammetric curves in Fe(CN)₆ ^3-/4- solutions. A mechanism of boron-stimulated sulfur incorporation into diamond and the nature of donors thus formed is discussed.     

Complexation of Tetraphenyltetrabenzoporphine with Cu(II), Cd(II), Zn(II), and Co(II) Salts in Organic Solvents

The rate and activation parameters of tetraphenyltetrabenzoporphine (H₂TPTBP) complexation with 3d-metal acetates and acetylacetonates are shown to be determined by the solvent nature. With an increase in the electron-donor properties of a solvent, the reaction rate increases due to protonation of N–H bonds and decreases as MA _m (Solv) _{n – m} salt solvates become more stable. As the result, the rate of a reaction with ZnAc₂ increases in the series: DMF < dmso=">< py=">< proh-1="><>₃CN <>₆H₆. In inert and weakly coordinating solvents, the transition state of a reaction is supposed to be formed according to the mechanism of contraction of the salt coordination sphere. The rate of H₂TPTBP reaction with metal acetates in pyridine changes in the series: Cu(II) > Cd(II) > Zn(II) > Co(II), while the stability of the obtained complexes decreases in the series Cu(II) > Co(II) > Zn(II) > Cd(II). It is shown that the spectral criterion of the complex stability can be used in the series of metal complexes with one ligand, but it is violated if the ligand structure is changed.     

Interaction of Aluminium (III) with the f-Family Ions Np(VI), Pu(VI), Np(V), Np(IV), Pu(IV), Nd(III), and Am(III) in the Course of Simultaneous Hydrolysis

The interaction of Np(VI), Pu(VI), Np(V), Np(IV), Pu(IV), Nd(III), and Am(III) with Al(III) in solutions at pH 0–4 was studied by the spectrophotometric method. It was shown that, in the range of pH 3–4, the hydrolyzed forms of neptunyl and plutonyl react with the hydrolyzed forms of aluminium. In the case of Pu(VI), the mixed hydroxoaqua complexes (H₂O)₃PuO₂(-OH)₂Al(OH)(H₂O)₃ ²⁺ or (H₂O)₄PuO₂OAl(OH)(H₂O)₄ ²⁺ are formed at the first stage of hydrolysis. Np(VI) also forms similar hydroxoaqua complexes with Al(III). The formation of the mixed hydroxoaqua complexes was also observed when Np(IV) or Pu(IV) was simultaneously hydrolyzed with Al(III) at pH 1.5–2.5. The Np(IV) complex with Al(III) has, most likely, the formula (H₂O) _n (OH)Np(-OH)₂Al(OH)(H₂O)₃ ³⁺. At pH from 2 to 4.1 (when aluminium hydroxide precipitates), the Np(V) or Nd(III) ions exist in solutions with or without Al(III) in similar forms. When pH is increased to 5–5.5, these ions are almost not captured by the aluminium hydroxide precipitate.     

Simultaneous flow injection speciation of iron(II) and iron(III) cyano complexes utilizing electrochemical and atomic absorption detectors in series

Summary A method is described for the simultaneous speciation of Fe(CN) ₆ ^4– and Fe(CN) ₆ ^3– in a flow injection (FIA) system comprising electrochemical (EC) and flame atomic absorption spectrometry (AAS) detectors in series. One of these species is detected amperometrically at a Pt-electrode by applying the required potential and measuring the resulting reduction or oxidation current of the appropriate iron cyanide complex. Total iron in both species is determined by an AAS detector. The EC detector is inherently more sensitive, with a detection limit of 0.5 g Fe l^–1 and a relative standard deviation of 1.0% for a 0.040 g Fe ml^–1 sample. The limit of detection for the AAS detector is 0.5 g Fe ml^–1, and the relative standard deviation for a 5.70 g Fe ml^–1 sample is 0.40%. The method enables up to 60 analyses (120 speciations) per hour and obviates the problem of easy oxidation of Fe(CN) ₆ ^4– .

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Simultane Speziation von Eisen(II)- und Eisen(III)-Cyanokomplexen durch Flie\injektionsanalyse mit Hilfe von hintereinander geschalteten elektrochemischen und AAS-Detektoren

     

Synthesis,Spectral Properties,and Crystal Structure of {Methoxo[4-phenylbutane-2,4-dione(p-nitrobenzoyl) hydrazonato(2-)]oxovanadium(V)}

The hydrazino complex {methoxo[4-phenylbutane-2,4-dione(p-nitrobenzoyl)hydrazonato(2-)]oxovanadium(V)}, VO(p-NO₂bhbzac)OCH₃, (1), has been prepared by the direct reaction of bis(benzoylacetonato) oxovanadium(IV), VO(bza)₂, with p-NO₂-C₆H₄C(O)NHNH₂, p-NO₂bh, in CH₃OH. The resulting compound contains benzoylacetone-(p-NO₂)benzoyl hydrazone as tridentate Schiff base-type ligand and OCH₃ group as Lewis base, both ligated to vanadium. The crystals are orthorhombic, with Z = 8, space group Pbca, a = 11.699(5) Å, b = 14.035(5) Å, c = 22.564(5) Å, R1 = 0.0756 and wR2 = 0.1302. The crystal structure demonstrated the square-pyramidal geometry of the VO_oxo(ONO)O coordination sphere with the oxo ligand at the apical position. The electronic absorption spectra revealed a ligand-to-metal charge-transfer (LMCT) band in the near UV region at _max = 23,700 cm^–1 (B = 5640 dm³ mol^–1 cm^–1) in CH₃CN, _max = 23,420 cm^–1 (B = 5550 dm³ mol^–1 cm^–1) in DMSO, and _max near 26,950 (sh) cm^–1 (B = 10,550 dm³ mol^–1 cm^–1) in CH₂Cl₂. The FT-IR spectra of (1) show the characteristic strong (V = O) stretching vibration at 993 cm^–1 and support the view that the oxovanadium complex is pentacoordinated and monomeric.     

Organosilicon Amine Complexes of Cobalt(II), Cromium(III), and Neodymium(III): Synthesis and Properties

Organosilicon amine complexes [Co(NH₂R¹)₂Cl₂] (I), [Cr(NH₂R¹)₃Cl₃] (II), and [Nd(NH₂R¹)₃Cl₃] (III) [R¹ = CH₂CH₂CH₂Si(OEt)₃] were synthesized by reacting anhydrous cobalt, chromium, or neodymium chlorides with 3-aminopropyltriethoxysilane (NH₂R¹). Complexes I–III occur as colored viscous liquids that polymerize in air due to hydrolysis of triethoxy groups and condensation of the obtained silanol groups. Organosilicon films with a thickness of 10–200 m on glass and quartz substrates were obtained from liquid compositions containing complexes I–III, siloxanediols HO(SiMe₂O) _n H (n = 2–5), and alkoxysilanes NH₂R¹, MeSi(OMe)₃, and PhSi(OMe)₃ by solidification in air or vacuum. The obtained films were characterized by IR and electron spectroscopies, photoluminescence, transmission electron microscopy, and energy dispersion X-ray fluorescence analyses. IR and electron spectroscopies were used to study the structurization of the films and their behavior when heated to 100–300°C or exposed to gaseous O₂, NO, NH₃, or HCl. The film containing complex I was found to withstand heating in air to 250°C and to change its color in the atmosphere of NO, NH₃, and HCl. Complex I reversibly absorbs oxygen, and in the atmosphere of HCl, it converts into [NH₃R]₂[CoCl₄]. The Z-scanning method was used to uncover the cubic nonlinear-optical properties of the metal complexes.     

Kinetics and mechanism of pentacyanohydroxoferrate(III) formation from mono(aminocarboxylato)iron(III) complexes

Summary The kinetics and mechanism of the system: [FeL(OH)]^2–n + 5 CN^– [Fe(CN)₅(OH)]^3– + L^n–, where L=DTPA or HEDTA, have been investigated at pH= 10.5±0.2, I=0.25 M and t=25±0.1 C.As in the reaction of [FeEDTA(OH)]^2–, the formation of [Fe(CN)₅(OH)]^3– through the formation of mixed ligand complex intermediates of the type [FeL(OH)(CN)_x]^2–n–x, is proposed. The reactions were found to consist of three observable stages. The first involves the formation of [Fe(CN)₅(OH)]^3–, the second is the conversion of [Fe(CN)₅(OH)]^3– into [Fe(CN)₆]^3– and the third is the reduction of [Fe(CN)₆]^3– to [Fe(CN)₆]^4– by oxidation of L^n– The first reaction exhibits a variable order dependence on the concentration of cyanide, ranging from one at high cyanide concentration to three at low concentration. The transition between [FeL(OH)]^2–n and [Fe(CN)₅(OH)]^3– is kinetically controlled by the presence of four cyanide ions around the central iron atom in the rate determining step. The second reaction shows first order dependence on the concentration of [Fe(CN)₅(OH)]^3– as well as on cyanide, while the third reaction follows overall second order kinetics; first order each in [Fe(CN)₆]^3– and L^n–, released in the reaction. The reaction rate is highly dependent on hydroxide ion concentration.The reverse reaction between [Fe(CN)₅(OH)]^3– and L^n– showed an inverse first order dependence on cyanide concentration along with first order dependence each on [Fe(CN)_5– (OH)]^3– and L^n–. A five step mechanism is proposed for the first stage of the above two systems.     

Voltammetric study of the interaction of lomefloxacin (LMF)–Mg(II) complex with DNA and its analytical application

The voltammetric behavior of the LMF-Mg(II) complex with DNA at a mercury electrode is reported for the first time. In NH₃–NH₄Cl buffer (pH=9.10), the adsorption phenomena of the LMF–Mg(II) complex were observed by linear sweep voltammetry. The mechanism of the electrode reaction was found to be a reduction of LMF in the complex, and the composition of the LMF–Mg(II) complex is 2:1. In the presence of calf thymus DNA (ctDNA), the peak current of LMF–Mg(II) complex decreased considerably, and a new well-defined adsorptive reduction peak appeared at −1.63 V (vs. SCE). The electrochemical kinetic parameters and the binding number of LMF–Mg(II) with ctDNA were also obtained. Moreover, the new peak currents of LMF–Mg(II)–DNA system increased linearly correlated to the concentration of DNA in the 4.00×10⁻⁷–2.60×10⁻⁶ g ml⁻¹ range when the concentrations of LMF–Mg(II) complex was fixed at 5.00×10⁻⁶ mol l⁻¹, with the detection limits of 2.33×10⁻⁷ g ml⁻¹. An electrostatic interaction was suggested by electrochemical method.     

Mechanisms of oxidation of K4Fe(CN)6 by hypochlorous acid and catalytic activation by azide, bromide, and iodide

Summary HOCl reacts with Fe(CN) ₆ ^4– to generate an intermediate, presumably FeCl(CN) ₆ ^3– , which exhibits a weak absorption around 282 nm and decays simultaneously with the formation of Fe(CN) ₆ ^3– . When decreasing the HOCl/Fe(CN) ₆ ^4– concentration ratio fromR>1 toR<1, a drastic change in the kinetics of the oxidation is observed. Depending onR, the intermediate obviously oxidizes either Fe(CN) ₆ ^4– or HOCl. AtR1, a further intermediate appears which also precedes the oxidation and absorbs strongly around 360 nm. The intermediates detected may represent reactive high oxidation states of iron (Fe(IV) and Fe(VI)). HOCl induced oxidation of Fe(CN) ₆ ^4– is activated catalytically by Br^–, I^–, and N ₃ ^– , obviously due to generation of stronger oxidants (HOBr, HOI, and ClN₃), but oxidation is efficiently inhibited by CN^– and NCS^–.

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Mechanismen der Oxidation von K₄Fe(CN)₆ durch Hypochlorsäure und katalytische Aktivierung durch Azid, Bromid und Iodid

Zusammenfassung HOCl reagiert mit Fe(CN) ₆ ^4– unter Bildung eines Intermediats, vermutlich FeCl(CN) ₆ ^3– , das bei 282 nm eine schwache Absorption aufweist und parallel zum Erscheinen von Fe(CN) ₆ ^3– verschwindet. Man beobachtet eine drastische Änderung in der Oxidationskinetik, wenn das HOCl/Fe(CN) ₆ ^4– Konzentrationsverhältnis vonR>1 zuR<1 verändert wird. In Abhängigkeit vonR wird offenbar entweder Fe(CN) ₆ ^4– oder HOCl durch das Intermediat oxidiert. FürR1 erscheint ein weiteres Intermediat mit einer starken Absorptionsbande bei 360 nm, das ebenfalls der Oxidation vorangeht. Bei den beobachteten Intermediaten handelt es sich vermutlich um reaktive höhere Oxidationsstufen des Eisens (Fe(IV) und Fe(VI)). Die HOCl-induzierte Oxidation von Fe(CN) ₆ ^4– wird einerseits durch Br^–, I^– und N ₃ ^– katalytish aktiviert (offenbar infolge der Bildung stärkerer Oxidantien wie HOBr, HOI und ClN₃), andererseits durch CN^– und NCS^– effektiv inhibiert.

     

Separation of lanthanum,cerium and samarium from uranium samples

The radiation reduction yield of Fe³⁺ in complexes with various ligands (Cl^–, SO ₄ ^2– , CN^–) in methanol-water solutions has been studied. The effect of the dose, pH, scavenger concentration and matrix composition on the reduction, yield of Fe³⁺ in the above complexes and in Fe(acac)₃ was determined. Studies of methanol-water glasses (91) provided some interesting observations as to the effectiveness of scavenging the electrons by various ferric compounds. The effectiveness of scavenging decreases in the series Cl^–>SO ₄ ^2– >CN^–. As opposed to Co(acac)₃, Fe(acac)₃ appeared to be an ineffective scavenger.     

The outersphere complex of EuCl2+ in a mixed system of methanol and water of 1.0M (H, Na) (Cl, ClO4)

The stability constans, ₁, of each monochloride complex of Eu(III) have been determined in the methanol and water mixed system with 1.0 mol·dm^–3 ionic strength using a solvent extraction technique. The values of ₁ increase with an increase in the mole fraction of methanol (X _S ) in the mixed solvent system when 0X _S 0.40. The, distance of Eu³⁺–Cl^– in the mixed solvent system was calculated using the Born-type equation and the Gibbs' free energy derived from ₁. Calculation of the Eu³⁺–Cl^– distance and the preferential solvation, of Eu³⁺ by water proposed the variation of the outersphere complex of EuCl²⁺ as follows: (1) [Eu(H₂O)₉]³⁺Cl^–, [Eu(H₂O)₈]³⁺Cl^– and [Eu(H₂O)₇(CH₃OH)³⁺Cl^– inX _S0.014, (2) [Eu(H₂O)₈]^3–Cl^– and [Eu(H₂O)₇(CH₃OH)]³⁺Cl^– in 0.014<X _S <0.25 and (3) [Eu(H₂O)₇(CH₃OH)]^3–Cl^– and [Eu(H₂O)₆(CH₃OH)[₂ ³⁺Cl^– in 0.25<X _S 0.40.     

Electrodes of synthetic diamond: The effects of Ti substrate pretreatment on the electrode properties

The electrode properties of boron-doped diamond thin films grown on Ti substrates by a hot-filament chemical vapor deposition technique are evaluated. The Ti substrate surface modifying conditions are devised, involving the surface roughening, annealing, and etching, which effectively improve the diamond electrode properties. The preetching of the Ti substrate produces the titanium hydride layer that can affect the boron-doped diamond film growth significantly. The substrate roughened surface obviously improved the diamond film adhesion and reduced the inner stress. The electrodes reveal minimal background current and better stability. A wider potential window, up to 3 V, is observed for the boron-doped diamond on the etched/annealed samples. The electrochemical activity of the electrodes in the Fe(CN) ₆ ^3-/4- redox system somewhat increases with increasing surface roughness. The apparent increase in the reversibility of the reaction may be explained by the decrease in the true current density. Suitability of the Ti-based boron-doped diamond electrodes for electroanalytical applications is exemplified by sensing the trace metal ions, such as Hg²⁺ and Pb²⁺.__________From Elektrokhimiya, Vol. 41, No. 4, 2005, pp. 387–396.Original English Text Copyright © 2005 by Pleskov, Evstefeeva, Krotova, Lim, Chu, Ralchenko, Vlasov, Kononenko, Varnin, Teremetskaya, Shi.This article was submitted by the authors in English.     

Elektrochemisches Verhalten von Redox-Systemen in Lösungsmittelgemischen, 2. Mitt.: Das System K4[Fe(CN)6]-K3[Fe(CN)6] in Fettsäure-Wasser-Gemischen

Zusammenfassung Es wurden die elektrochemischen Eigenschaften des Redox-Systems K₄[Fe(CN)₆]-K₃[Fe(CN)₆] in Ameisensäure-Wasser-, Essigsäure-Wasser-, Propionsäure-Wasser- und n-Buttersäure-Wasser-Gemischen untersucht. Die Veränderungen des Redoxpotentials, der Leitfähigkeit und der Dielektrizitäts-konstante wurden studiert.Es wurde bewiesen, daß die Potentialveränderung des Redox-Systems bei kleiner Säurekonzentration (n _s<0,6–0,7) vor allem durch die Wasserstoffionen-Konzentration der Lösung bestimmt wird. Mit der Zunahme der H⁺-Konzentration nimmt die Aktivität des [Fe(CN)₆]^4– in größerem Maße ab als die des [Fe(CN)₆]^3–.Bei großer Säurekonzentration beeinflußt dagegen hauptsächlich die Anionsolvatation durch das Lösungsmittelgemisch die Verschiebung des Redoxpotentials. Die Solvatation ruft eine Strukturveränderung hervor, wodurch die Elektronen-population der Lösungsmittelmoleküle in der Nähe der Cyanoferrat-Ionen abnimmt, die Elektronen-Acceptor-Wirkung des Lösungsmittels wächst. Dieser Prozeß bewirkt in bekannter Weise die Zunahme des Redoxpotentials.

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The electrochemical behaviour of redox systems in mixed solvents, II.: TheK ₄[Fe(CN) ₆]-K ₃[Fe(CN) ₆] system in fatty acid-water mixtures

The electrochemical behaviour of the K₄[Fe(CN)₆]-K₃[Fe(CN)₆] system has been investigated in mixtures of water with formic, acetic, propionic and n-butyric acid, resp. The change of the redox potential, the conductivity and the dielectric constant has been studied. It has been proved that the change of the redox potential of the system at low acid concentration (n _s<0.6–0.7) is determined by the H⁺ concentration. Increasing the H⁺ concentration, the activity of the [Fe(CN)₆]^4– decreases in a higher extent than the activity of [Fe(CN)₆]^3–.On the other hand, at high acid concentration the shift in the redox potential is influenced first of all by the anion solvating effect of the solvent. The solvation causes such a change in the structure, that the electron population of the solvent molecules around the [Fe(CN)₆]^4– ions decreases, the acceptor strength of the solvent increases. It is well known that this process causes an increase in the redox potential.

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Mit 7 Abbildungen     

Ion and solvent transfer discrimination at a nickel hydroxide film exposed to LiOH by combined electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) techniques

A combined electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) instrument was used to monitor the mobile species transfers associated with the redox processes of thin (Γ100–150 nmol cm⁻²) α- and β-nickel hydroxide films exposed to aqueous LiOH solution. A comparison of the measured PBD signal with the predicted PBD profiles, calculated by temporal convolution analysis of the current and mass responses, enabled the contributions to redox switching of anion (OH⁻) and solvent (H₂O) transfers to be discriminated quantitatively. The responses from the combined instrument are reconciled in terms of H⁺ deintercalation/intercalation within the nickel hydroxide structure as OH⁻ ions enter/exit the film. Hydroxide ion movement is associated with a counterflux of water. Thin nickel hydroxide films show a gradual α→β phase transformation with continuous voltammetric cycling, especially when the films are exposed to high concentrations of electrolyte. α-Films are characterised by OH⁻ transfers that dominate the H⁺ and H₂O movements; β-films are characterised by an increased participation of water and protons to the exchange dynamics.     

Spectrophotometric determination of nitrite and nitrate in doped potassium chloride crystals

Summary KCl crystals, doped in the melt with KNO₂ or KNO₃, contain both NO₂ ^– and NO₃ ^– ions. Spectrophotometric methods are described for the determination of the admixture concentration after dissolving the crystals. Nitrite is determined by colorimetry of an azo dye formed in methanol-water-HCl medium from p-nitroaniline and -naphthylamine. The absorption is proportional to the nitrite concentration in the range of 5 · 10^–6 to 5 · 10^–5 M NO₂ ^– UV absorption measurement is employed for the spectrophotometric determination of nitrate, Beer's law being obeyed between 3 · 10^–5 and 3 · 10^–4 M NO₃ ^– at 220 nm. Here, nitrite is removed by adding sulfamic acid, and correction is made for chloride. Some results on nitrite- and nitrate-doped crystals are given.

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Zusammenfassung KCl-Kristalle mit zur Schmelze zugesetztem KNO₂ oder KNO₃ enthalten sowohl NO₂ ^–- wie NO₃ ^–-Ionen. Spektrophotometrische Methoden werden beschrieben zur Bestimmung des Gehaltes dieser Zusätze nach Lösen der Kristalle. Nitrit wird bestimmt durch Colorimetrieren einer Azoverbindung aus p-Nitranilin und -Naphthylamin in einem Methylalkohol-Wasser-Salzsäure-Gemisch. Die Absorption ist dem Nitritgehalt von 5 · 10^–6 bis 5 · 10^–5 m NO₂ ^– proportional. Die UV-Absorption wird zur spektrophotometrischen Bestimmung des Nitrats verwendet. Das Beersche Gesetz ist hier zwischen 3 · 10^–5 und 3 · 10^–4 m NO₃ ^– gÜltig (bei 220 nm). Nitrit wird dabei durch Zusatz von Sulfaminsäure entfernt, und es wird fÜr Chloride korrigiert. Einige Ergebnisse an Kristallen mit Nitrit- bzw. Nitratzusatz werden angefÜhrt.

     

Analytical separation of antimony(III) from bismuth(III), lead(II), gallium(III), thallium(III), tellurium(IV) and tin(IV) with cyanex 302

A method is proposed for the separation of antimony(III) (100–400 g) from bismuth(III), lead(II), gallium(III), thallium(III), tellurium(IV) and tin(IV) from an aqueous solution of pH 0.5–1.5 using 8×10^–3–1×10^–2 mol dm^–3 cyanex 302 dissolved in toluene as an extractant. The antimony is stripped from the cyanex phase with water and determined spectrophotometrically with iodide. Various experimental parameters are optimized and the probable 13 stoichiometry of the extracted species is evaluated. The method is applicable to the analysis of alloys and pharmaceutical samples. The separation and determination take only 20 min.     

A kinetic and mechanistic study of oxidation of arsenic(III) by hexacyanoferrate(III) in aqueous ethanoic acid

The kinetics of oxidation of As^IIIby Fe(CN)₆ ^3– has been studied spectrophotometrically in 60% AcOH–H₂O containing 4.0moldm^–3HCl. The oxidation is made possible by the difference in redox potentials. The reaction is first order each in [Fe(CN)₆ ^3–] and [As^III]. Amongst the initially added products, Fe(CN)₆ ^4– retards the reaction and As^Vdoes not. Increasing the acid concentration at constant chloride concentration accelerates the reaction. At constant acidity increasing chloride concentration increases the reaction rate, which reaches a maximum and then decreases. H₂Fe(CN)₆ ^–, is the active species of Fe(CN)₆ ^3–, while AsCl₅ ^2– in an ascending portion and AsCl₂ ⁺ in a descending portion are considered to be the active species of As^III. A suitable reaction mechanism is proposed and the reaction constants of the different steps involved have been evaluated.