Oxidation Of Zn Research Articles

Unoccupied states evolution with oxidation of ultrathin Mg, Zn and Cd layers on SrTiO3(100) surfaces

An unoccupied density of states (DOS) evolution under oxidation of ultrathin Mg, Zn and Cd layers on SrTiO3(100)-(2×2) substrates are investigated. The metal deposition and subsequent oxidation were studied in situ under UHV conditions by means of LEED, AES, TCS and work function measurements. An appearance of metal- and oxygen-derived bands of the unoccupied DOS was traced in the TC spectra. Metal oxidation was followed by the hybridization of metal and oxygen orbitals and by the appearance of the mainly O 2p oxygen-derived bands, which are characterized by a set of DOS maxima, located at the following energies (above the Fermi level): 8.0, 11.5, 14.3, 15.0 and 19.0eV for MgO; 6.0, 8.1, 16.8 and 20.5eV for ZnO and 7.5, 10.0 and 12.7eV for CdO. The results obtained are discussed in comparison with previously published experimental and theoretical data on unoccupied DOS in metal oxides.

00/02172 Combined thermal analysis and gas-analysis methods and software simulations for the investigation of the potential endangerment to the environ

The high-temperature tube furnace was applied to simulate the rotary hearth furnace (RHF) for the direct reduction of zinc-bearing dusts from steel plants. The removal mechanism of Zn, Pb and alkalis from cold bonded briquettes made by mixing metallurgical wastes, such as dust from bag house filter, OG sludge, fine converter ash and dust from the third electric field precipitator of the sinter strand, in various proportions was investigated. More than 70% of metallization rate, more than 95% of zinc removal rate, 80% of lead removal, as well as more than 80% of K and Na removal rates were achieved for the briquettes kept at 1473–1603 K for 15 min during the direct reduction process respectively. The soot generated in the direct reduction process was studied by chromatography, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results suggested that the main phases of the soot were ZnO, KCl, NaCl and 4ZnO · ZnCl2 · 5H2O. Furthermore, the content of Zn reached 64.2%, which could be used as secondary resources for zinc making. It was concluded that KCl and NaCl in secondary dust resulted from the volatilization from the briquettes, whilst ZnO and PbO were produced by the oxidation of Zn or lead vapour from briquettes by direct reduction.

Photoluminescence and ultraviolet lasing of polycrystalline ZnO thin films prepared by the oxidation of the metallic Zn

We report a simple method for preparing polycrystalline ZnO thin films with good luminescent properties: the oxidization of metallic Zn films. In photoluminescence (PL) studies at room temperature for wavelengths between 370 and 675 nm, we have observed a single exciton peak around 390 nm without any deep-level emission and a small PL full width at half maximum (23 meV), indicating that the concentrations of the defects responsible for the deep-level emissions are negligible. We have also observed optically pumped lasing action in these films. The threshold intensity for lasing was ∼9 MW/cm2.

Synthesis, Electrochemical, and Photophysical Study of Covalently Linked Porphyrin Dimers with Two Different Macrocycles

Four unsymmetrical covalently linked porphyrin dimers were synthesized, and their electrochemical, spectroelectrochemical, and/or photophysical properties were examined. The investigated compounds are represented as M[p-(TPP-DEHMP)]M and M[m-(TPP-DEHMP)]M (M = H2, Zn), where p-(TPP-DEHMP) is the tetraanion of 1-[5-(10,15,20-triphenylporphyrinyl)]-4-[10-(2,18-diethyl-3,7,8,12,13,17-hexamethylporphyrinyl)]benzene and m-(TPP-DEHMP) is the tetraanion of 1-[5-(10,15,20-triphenylporphyrinyl)]-3-[10-(2,18-diethyl-3,7,8,12,13,17-hexamethylporphyrinyl)]benzene. The oxidation and reduction potentials of Zn[p-(TPP-DEHMP)]Zn are virtually identical to combined oxidation and reduction potentials of (TPP)Zn and (OEP)Zn, i.e., cyclic voltammograms of the heterodimers resemble those of the superposed monomeric units under the same experimental conditions. The UV−visible spectra of neutral, singly oxidized, and/or singly reduced Zn[p-(TPP-DEHMP)]Zn also resemble superposed spectra of the respective neutral, oxidized, or reduced monomeric (TPP)Zn and (OEP)Zn derivatives. Hence, both the electrochemical and spectroelectrochemical data suggest that there is little electronic interaction between the two subunits of the heterodimers in their neutral, singly oxidized, or singly reduced forms. The photophysical properties of four related homoleptic dimers, M[p-(TPP-TPP)]M and M[m-(TPP-TPP)]M, where M = H2 or Zn, p-(TPP-TPP) = the tetraanion of 1, 4-bis[5‘-(10‘,15‘,20‘-triphenylporphyrinyl)]benzene, and m-(TPP-TPP) = the tetraanion of 1,3-bis[5‘-(10‘,15‘,20‘-triphenylporphyrinyl)]benzene, were also examined, and their data were compared to the data for the above heteroleptic dimers. Irradiation of H2[p-(TPP-DEHMP)]H2 and M[m-(TPP-DEHMP)]M (M = H2, Zn) with excitation wavelengths in the visible spectrum of the DEHMP subunit, results in an efficient energy transfer between the DEHMP and TPP moieties. Calculated energy transfer rate constants agree well with the experimental data and suggest that the energy transfer processes are best described by a Föster mechanism. H2[p-(TPP-DEHMP)]H2 and H2[m-(TPP-DEHMP)]H2 thus demonstrate highly efficient and directional energy transfer processes rather than charge separation between the two subunits after irradiation.

Cs promoted oxidation of Zn and CuZn surfaces: a combined experimental and theoretical study

The interaction of O 2 with Zn, Cs Zn and Cs CuZn surfaces was investigated using photoemission and ab initio self-consistent-field (SCF) calculations. On zinc films, the sticking probability of O 2 is extremely low (10 −3–10 −2), and O 2 exposures in the range of 10 3 to 10 4 langmuirs are necessary to produce a significant adsorption of oxygen and the transformation of metallic zinc into zinc oxide. The presence of sub monolayer coverages of cesium enhances the oxidation rate of zinc by 2–3 orders of magnitude. In the Cs Zn system, the alkali atom donates electrons to zinc. This charge transfer facilitates the formation of Zn→O 2 dative bonds and breaking of the OO bond. For the coadsorption of Cs and O 2 on Zn(001), the larger the electron transfer from Zn into the O 2 (1 π g) orbitals, the bigger the adsorption energy of the molecule and the elongation of the OO bond. In general, cesium does not promote the oxidation of copper. In the Cs CuZn system, copper withdraws electrons from zinc. The presence of copper in the Cs CuZn system inhibits the oxidation of the Zn component compared with the Cs Zn system by lowering the electron density on the Zn atoms. After exposing the Cs CuZn system to O 2, zinc is oxidized at a rate that is larger than that found for clean CuZn surfaces and smaller than seen in Cs Zn surfaces. Molecular hydrogen is found to have no effect on oxidized Cu, Zn and CuZn films. However, atomic hydrogen reduces ZnO to metallic zinc and CuO to Cu 2O. In the oxidized CuZn alloy, CuO is reduced first followed by the reduction of ZnO. A comparison of the behavior of O 2/Cs/Zn and H 2O/Cs/Zn systems shows that while O 2 causes severe oxidation of Cs promoted Zn surfaces, H 2O has little or no effect.

Comparison of Zn and Vitamin E for Protection against Hyperoxia-Induced Lung Damage

The objective of the present study was to demonstrate an antioxidant function for Zn in vivo by comparing the efficacy of Zn or Vitamin E without additional energy intake for protection of Zn-deficient (ZnDF) or energy-restricted (ER) rats from hyperoxia-induced lung damage. Zn (200 μmol ZnCl 2/kg b.wt.) or Vitamin E (100 mg α-tocopherol/kg b.wt.) was injected IP before exposure to 85% oxygen or air for 5 d. During the exposure period, all injected ZnDF or ER rats were restricted to 5 g Zn-deficient or Zn-adequate diet/day, respectively, the amount of diet consumed by the untreated ZnDF or ER rats. We clearly demonstrated that injection of Zn without additional energy intake can protect ZnDF and ER rats from hyperoxia-induced lung damage assessed by the histopathological scoring system and magnetic resonance imaging (MRI). Vitamin E was not as effective as Zn in either ZnDF or ER rats for preventing hyperoxia-induced lung damage. Zn injection did not exert its antioxidant effect through increased lung CuZn-superoxide dismutase activity or metallothionein. This difference in the effectiveness of Vitamin E and Zn for hyperoxic protection in lung injury may be due to the specificity of antioxidant function, i.e., vitamin E inhibits oxidation of membrane lipids and Zn protects sulfhydryl groups of proteins. Copyright © 1996 Elsevier Science Inc.

A New Synthetic Method of Some Acid Hydrazide Complexes and Their Adducts

Abstract The electrochemical oxidation of Co, Cu, Zn and Cd in non-aqueous (acetone) solution of cinnamic (CAH) and/or hippuric (HAH) acid hydrazides gave the corresponding 1:2 complexes in very good yields. The advantage of the method is discussed. When a neutral bidentate donor (1,10-phenanthroline) is present in solution, adducts with 1:1 ratio are formed. The compounds have been characterized on the basis of elemental analyses, electrical conductivity, magnetic and spectral studies. An octahedral structure is proposed for the Co(II) and Cu(II) complexes. Also, the biological activity of the ligands and their metal complexes has been investigated.

Decomposition of NO2 on metal surfaces: Oxidation of Ag, Zn, and Cu films

The dissociation probability of O2 on Cu(111), Ag(111), and Zn(001) surfaces is quite low (<10−2). The oxidation process using molecular oxygen is not practical for work under ultrahigh vacuum conditions. We have found that NO2 is a very good oxygen source for the oxidation of Ag, Zn, and Cu surfaces. At elevated temperatures (300–500 K), the dissociation probability of NO2 on thick Ag, Zn, and Cu films supported on Ru(001) is close to one. The decomposition of NO2 produces a large amount of adsorbed oxygen and gaseous NO and N2. The thermal stability and electronic properties of the O/Ag, ZnOx, and CuOx films were examined using temperature desorption spectroscopy, x-ray photoelectron spectroscopy (XPS), and x-ray Auger electron spectroscopy. Large amounts of oxygen can be adsorbed and dissolved in Ag films without oxidation of the noble metal. The zinc oxide films displayed the typical O 1s XPS and Zn L3M4,5M4,5 Auger spectra of polycrystalline ZnO. In addition, the high-resolution electron energy-loss spectroscopy spectra of these films exhibited the characteristic phonon losses of bulk ZnO. In the case of Cu films the NO2-oxidation leads to the formation of a mixture of CuO and Cu2O. The CuO species is relatively unstable and can be reduced to Cu2O by annealing at 700 K (2 CuO→Cu2O+1/2O2) or by direct reaction with metallic Cu at 300 K (CuO+Cu→Cu2O).

Decomposition of CO2 to Carbon Using Oxygen-Deficient Zn(II)-Bearing Ferrite

AbstractOxygen-deficient Zn(II)-bearing ferrites (ZnxFe3-xO4-δ, 0≤×≤l, δ>0) have been synthesized and studied for their reactivity in the decomposition of CO2 to carbon at 300 °C. They were prepared by reducing Zn(II)-bearing ferrites with H2 gas at 300 °C. The oxygen-deficient Zn(II)-bearing ferrites consisted of a single phase of a spinel-type structure which was oxygendeficient compared with their stoichiometric compositions. Their lattice constants were larger than those of the corresponding stoichiometric spinels. Decomposition of CO2 to carbon proceeded accompanied by an oxidation of the oxygen-deficient Zn(II)-bearing ferrite. The amount of carbon deposited on the ferrite decreased when Zn content in Zn(II)-bearing ferrite increased. The decrease in the amount of carbon deposited is due to changes in the electron conductivity according to the Zn content in Zn(II)-bearing ferrite. These changes contribute to their reactivity for decomposition of CO2 to carbon.

Identification of isomeric meso-Dioxo derivatives of octaethylporphyrin and separation and structural characterization of the nickel(II) complexes

Oxidation of Zn II (OEP) (OEP is the dianion of octaethylporphyrin) with thallium(III) trifluoroacetata is shown to form the previously unknown cis-dioxooctaethylporphodimethene (cis-H 2 OEPO 2 ) as well as the known, isomeric trans-dioxooctaethylporphodimethene (trans-H 2 OEPO 2 ). While these have not been separated, their nickel (II) complexes are readily separated by chromatography on silica gel. Electronic absorption and 1 H NMR spectra are reported for these diamagnetic planar complexes

Electrochemistry in liquid sulfur dioxide. 12. Electrochemical and pulse radiolysis studies on oxidation of tris(2,2'-bipyridine)zinc(2+), tris(2,2'-bipyridine)cadmium(2+) and 2,2'-bipyridine

The electrochemical oxidation of Zn(bpy) 3 2+ , Cd(bpy) 3 2+ , and 2,2'-bipyridine (bpy) in liquid sulfur dioxide was studied by cyclic voltammetry (CV) and spectroelectrochemical techniques. Both Zn(bpy) 3 2+ and Cd(bpy) 3 2+ are oxidize in three closely spaced one-electron reversible steps. The standard potentials for these processes referenced vs the ferrocenium/ferrocene couple are an follows: Zn, 2.33 (E o 3/2 ), 2.43 (E o 4/3 ), and 2.52 V (E o 5/4 ); Cd, 2.31 (E o 3/2 ), 2.39 (E o 4/3 ), and 2.47 V (E o 5/4 )

Residues from biological materials after pressure decomposition with nitric acid : Part 3. Influence of reaction products on inverse voltammetric element determination

After the pressure decomposition of biological sample materials with 69% nitric acid at 180°C, organic decomposition products frequently remain, leading to interference effects during inverse voltammetric trace metal determination. It is shown by the example of the determination of Zn, Cd, Pb and Cu by inverse square-wave voltammetry that the interference signals are caused by the two-stage reduction of nitrated benzoic acids to amines at the mercury electrode. Nitrobenzoic acids arise in the degradation of phenylalanine during decomposition. In addition, they also cause, as do oxidation products of tryptophan, an increased current due to hydrogen deposition in the potential range of Zn oxidation. Decomposition solutions of biological materials free from phenylalanine and tryptophan, on the other hand, can be analysed by inverse voltammetry without any interference.

Evidence from coadsorption studies for a molecular precursor state in the oxidation of Zn(0001)

The rate of dissociative chemisorption of dioxygen at a Zn(0001) surface at 110 K increases by a factor of nearly 103 when coadsorbed with ammonia; a model based on a precursor state involving an ammonia–dioxygen complex is suggested.

ChemInform Abstract: The Electrochemical Oxidation of Zinc Studied By Ellipsometry.

AbstractEllipsometry is combined with cyclic voltammetry to investigate the anodic oxidation of Zn (important for various reprographic processes) in neutral solutions of LiClO4.

ChemInform Abstract: The Direct Electrochemical Synthesis of Zinc and Cadmium Catecholates and Related Compounds.

AbstractThe electrochemical oxidation of Zn or Cd anodes for 2‐3 h in the extreme air‐sensitive non‐aqueous solution (acetone) of the corresponding aromatic diol under dry nitrogen leads to the also air‐sensitive complexes (I)‐(III).

Rates of pi-electron oxidation and reduction of free base and Zn(II) porphyrins, chlorins, and isobacteriochlorins

The rates of pi-electron oxidation and reduction of two homologous series of free base and Zn(II) porphyrins, chlorins, and isobacteriochlorins were studied by chronocoulometry at a platinum disk electrode. The macrocycles were octaethylporphyrin, tetraphenylporphyrin, and the chlorins and isobacteriochlorins derived therefrom. The rates were found to vary to within a factor of 3, and some consistent trends are noted. However, the most important conclusion of this work is that pi-electron redox processes for these macrocycles occur at essentially the same rate, despite the previously noted large differences in pi-electron redox potentials.

Concentrations and behavior of oxygen and oxide ion in melts of composition CaO · MgO · xSiO2

The concentrations and behavior of oxygen and oxide ion were studied in silicate melts of composition CaO · MgO · xSiO 2 (1.25 ≤ x ≤ 3) in the temperature range 1425 to 1575°C by cyclic voltammetry and chronopotentiometry. Electroreduction of oxygen is a reversible, 2 electron process involving dissociated oxygen atoms. The Henry's Law constant for O 2 in molten diopside (CaO · MgO · 2SiO 2) is 0.023 ± 0.004 mole/l atm at 1450°C. The diffusion coefficient for molecular oxygen in diopside melt is 4.5 ± .5 × 10 −6 cm 2/sec at 1450°C and the activation energy of diffusion is 80 ± 2 kcal/mole. Oxide ions produced by electroreduction of oxygen, rapidly dissociate silicate polymers, causing the concentration of free oxide ions in diopside melt to be buffered at a low level (4.7 ± .8 × 10 −5 mole/l). The concentration of free oxide ion increases at higher proportions of metal oxides but remains at this value in more silicic melts. The rate of formation of oxide ions by polymerization in diopside melt is 0.021 ± .007 mole/l sec. Thermodynamic parameters (the standard free energy, enthalpy and entropy) for the oxidation of Ni, Co, and Zn in diopside melt in equilibrium with gaseous oxygen agree with those for solid oxide systems. The platinum reference electrode in molten diopside is a reversible, oxygen electrode.

Initial oxidation of Zn(0001) surfaces: H2 adsorption and XPS studies

H2 adsorption capacity measurements have been combined with XPS intensity measurements to study the kinetics of O2 uptake on Zn(0001) surfaces. On clean Zn(0001) the temperature programmed desorption spectrum of H2 shows half-order desorption kinetics and an apparent desorption energy of 11 kcal/mole. As the surface is oxidized by progressive dosing with O2, two features are noted: The H2 desorption spectrum characteristic of clean Zn(0001) is attenuated in a nonlinear fashion and a new H2 desorption state with an activation energy of 18 kcal/mole is observed for surfaces with less than saturation oxygen coverage. XPS results indicate that H2 adsorption is not completely blocked until an oxygen coverage corresponding to approximately 3 monolayers is achieved. Both H2 uptake and XPS intensity measurements also indicate that the oxygen sticking coefficient increases with oxygen coverage up to about one half of the O2 saturation coverage. These results indicate that the initial oxidation of Zn surfaces involves the formation and growth of multilayer oxide islands, where oxygen incorporation at the perimeter of the islands is the rate limiting step.

Oxidative electrochemistry of electropolymerized metalloprotoporphyrin films

The course of electrochemical oxidation has been monitored by cyclic voltammetry, ring-disk voltammetry, and absorption spectroscopy for metalloporphyrin electrode films prepared by electropolymerization of Zn II and Fe III protoporphyrin IX (PP) complexes. In CH 2 Cl 2 both films show stable cyclic voltammograms (CV's) over the first oxidation wave, assigned to porphyrin radical cation formation. Addition of 2% H 2 O to the electrolyte is without effect on the first oxidation of Zn II PP, but contact with aqueous buffer (pH 6.9) enhances the anodic current six-fold, decreases the cathodic current and abolishes subsequent electroactivity; the inactivated film contains modified porphyrin species, as shown by its absorption spectrum on SnO 2 . It is suggested that oxidation proceeds via nucleophilic attack of H 2 O on the Zn II PP + radical cations, leading eventually to the six-electron product dioxoporphomethene. The same product is indicated for the Fe III PP film which also shows a six-fold anodic current enhancement in contact with aqueous buffer, and subsequent inactivation. But in this case a large negative shift in the anodic peak potential suggests (Fe IV =0)PP formation, and the inactivation pathway is suggested to involve O atom transfer to the porphyrin rings. For the Fe III PP film 2% H 2 O already produces a significant negative shift and broadening of the anodic peak, and a decrease in the cathodic current. Ring-disk voltammetry demonstrates some O 2 production accompanying oxidation of the Fe III PP film, but not the Zn II PP film, in contact with aqueous buffer; the yield accounts for only 2% of the oxidation current. Addition of (ClPh) 3 P, intended to intercept the O atoms of the (Fe IV =O)PP units, results only in accelerated film inactivated, probably via a radical process.

Photoemission and other photoexcitations as probes of the solid–liquid interface

Two ways of determining information about solid–liquid electrochemical interfaces on an atomic scale are in situ studies generally involving an optical probe and ex situ studies of electrodes transferred to vacuum. In situ photocurrent spectroscopy provides an approach bridging the gap between in situ optical spectroscopy and conventional electron spectroscopy measured ex situ. The method is sensitive to adsorbates, as shown by the observation of adsorption of a precursor to the electrochemical oxidation of Pt and Zn. In addition, bandgap, and band position information has been obtained for multilayer film formation in the electrochemical growth of oxides on Pt, Zn, and Ni. Coupling of these measurements with photoelectron spectroscopy provides a novel way of exploring the electronic structure of electrochemical interfaces.