Electrochemical preparation of cuprous oxid powder: Part II. Process conditions

Practical electrosynthesis of cuprous oxide powder was carried out on a laboratory scale in a cell specially constructed both with and without a diaphragm under the various operating conditions guided by the authors' previous research. The electrolysis was appraised in terms of the quality of the cuprous oxide product, the electrodissolution of the copper anode, and the SEM microstructure of the cuprous oxide powder. In a cell having a diaphragm, of which nylon fabric is the best, the optimal electrolysis operating conditions are: 250gl^–1 NaCl, 0.1–1.0gl^–1 NaOH, 500–1500Am^–2, 80°C, perforated titanium sheet as the cathode, and around 3% cell volume of electrolyte circulation per minute. Under these conditions a product containing more than 97% cuprous oxide can easily be produced with very stable electrolysis and quite uniform dissolution of the copper anode. To eliminate the use of a diaphragm in the cell, the addition of sodium chromate, sodium dichromate, or calcium gluconate is effective in a sense, depending upon the requirements of the cuprous oxide product. For a product in which more than 95% cuprous oxide and no copper powder are required but a slightly higher content of chloride is allowable, sodium chromate and dichromate can be proposed for use with the former around 0.03–0.05gl^–1 and the latter around 0.020–0.025gl^–1, although the copper anode will not be perfectly evenly dissolved. For a product in which more than 97% cuprous oxide is demanded and a very small amount of copper powder is tolerated, calcium gluconate would be acceptable at around 4.5gl^–1 with quite even dissolution of the copper anode. As to the auxiliary additives, hydrazine hydrate has a negative effect on the quality of the cuprous oxide product. Sucrose can cause a small increase in the chloride content but can make the particles of cuprous oxide more compact thereby increasing sharply its apparent density. Hydroxylamine hydrochloride is the best auxiliary additive which has a positive effect on the purity of the cuprous oxide product but produces no obvious change in the microstructure on the cuprous oxide particles. Even though most work has been concentrated on the electrolytic process, the subsequent processes are equally important: 65–70°C, distilled water for washing, benzotriazole in ethanol solution for stabilization of the cuprous oxide, and 100°C at a vacuum of less than 20mm Hg for drying seem to be satisfactory. A vacuum drying temperature of 55–60°C may be more appropriate to ensure against any oxidation of the product.     

Synergistic effect of TiO2 and iron oxide supported on fluorocarbon films. Part 1: Effect of preparation parameters on photocatalytic degradation of organic pollutant at neutral pH

Iron oxide and TiO₂ were immobilized on modified polyvinyl fluoride films in a sequential process. Synergic effects of iron oxide and TiO₂ on the polymer film were observed during the heterogeneous degradation of hydroquinone (HQ) in the presence of H₂O₂ at pH close to neutrality and under simulated solar irradiation. Within the degradation period, little iron leaching (<0.5 mg/L) was observed.The surface of commercial polyvinyl fluoride (PVF) film was modified by TiO₂ under light inducing oxygen group (C–OH, CO, COOH) formation on the film surface. During this treatment, TiO₂ nanoparticles simultaneously bind to the film, leading to PVF^f–TiO₂. The possible mechanistic pathway for the TiO₂ deposition and the nature of the polymer–TiO₂ interaction are discussed. Furthermore PVF and PVF^f–TiO₂ were immersed in an aqueous solution for the deposition of iron oxide layer by hydrolysis of FeCl₃, leading to PVF–Fe oxide and to PVF^f–TiO₂–Fe oxide respectively.HQ degradation and mineralization mediated by PVF^f–TiO₂, PVF–Fe oxide and PVF^f–TiO₂–Fe oxide were investigated under different conditions. Remarkable synergistic effects were observed for PVF^f–TiO₂–Fe oxide possibly due to Fe(II) regeneration, accelerated by electron transfer from TiO₂ to the iron oxide under light.     

Anodic Oxidation of Nitric Oxide on Au/Nafion®: Kinetics and Mass Transfer

The rate determining step for the anodic oxidation of nitric oxide on Au/Nafion^® was experimentally and theoretically found to beNO + Au Au–NO_ads The anodic oxidation of nitric oxide was first order with respect to nitric oxide. The reaction rate constant increased from 3.3×10^–5 to 9.6×10^–5cm s^–1 as the applied potential increased from 0.74 to 0.77V. The anodic oxidation of nitric oxide was controlled by the electrochemical kinetics when the anodic potential was less than 0.8 V. When the potential was greater than 1.0 V, it was located in the mass transfer region. The limiting current increased from 1184 to 1589A with increase in gas flow rate from 250 to 750ml min^–1 when the potential was set at 1.05 V and the concentration of nitric oxide was 100 ppm. The diffusion resistance in the gas diffusion layer can be neglected for gas flow rates greater than 750 ml min^–1. The diffusivity of nitric oxide and the equivalent diffusion layer thickness within the porous electrode were evaluated to be 3.43×10^–4cm²s^–1 and 0.051 cm, respectively.     

Electrosynthesis of propylene oxide in a bipolar trickle-bed reactor

The synthesis of propylene oxide by electrolysis of dilute sodium bromide solution with propylene gas was investigated in an electrochemical flow-by bipolar reactor consisting of six parallel fixed beds of graphite particles separated by polypropylene felt diaphragms. The reactor was operated in a single pass mode with a two-phase co-current flow of propylene and sodium bromide solution through the beds of graphite particles. The maximum pressure in the system was 2.2 atm absolute.The effects of superficial current density (0.4–2.7 kAm^–2), sodium bromide concentration (0.2 and 0.5 M), electrolyte load (4.4–13.2 kg m^–2s^–1), propylene gas load (0.08–1.66 kg m^–2s^–1), reactor outlet temperature (30 and 60°C), bed thickness (5–15 mm) and different carbon types (Union Carbide and Ultra Carbon) on the space-time yield and selectivity for propylene oxide were measured. Depending on conditions, the space-time yield for propylene oxide was between 5.5 and 97 kg m^–3h^–1, and the selectivity was between 55 and 87%. The current efficiency and the specific energy consumption varied from 14 to 58% and from 6 to 60 kWh kg^–1 of propylene oxide. The space-time yield for propylene oxide increased with increasing current density, increasing gas flow and decreasing bed thickness.The current efficiencies for hydrogen, oxygen, dibromopropane, hypobromite, bromite and bromate were also determined.Paper first presented at the AIChE Symposium on Electrochemical Reaction Engineering, Seattle, Washington, 15 August 1985.     

Firing chromium oxide refractories

Conclusions The best sintering of chromium oxide is obtained in a closed space in the presence of solid carbon in the form of Kryptol with a ratio between the weight of Kryptol and the weight of the articles being treated of not less than 10^–2–10^–3. The rules governing the change in the sintering behavior of chromium oxide obtained with laboratory specimens can be transferred to large industrial articles.Translated from Ogneupory, No. 3, pp. 12–14, March, 1979.     

Synergistic effect of TiO2 and iron oxide supported on fluorocarbon films: Part 2: Long-term stability and influence of reaction parameters on photoactivated degradation of pollutants

The degradation of hydroquinone (HQ) and nalidixic acid (NA) mediated by TiO₂ and iron oxide immobilized on functionalized polyvinyl fluoride films (PVF^f–TiO₂–Fe oxide) in the presence of H₂O₂ under simulated solar light has been examined. The results show that the contribution of homogeneous photo-Fenton oxidation to the initial mineralization process was low. The degradation rates were not dependant of initial pH. Heterogeneous photocatalytic activity of PVF^f–TiO₂–Fe oxide was enhanced by increasing temperature, NaCl addition and by long-term utilization.The PVF^f–TiO₂–Fe oxide surface was characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) at different states of utilization. Correlations between the catalyst surface composition and degradation kinetics are discussed. Long-term stability evaluated by repetitive pollutant degradations was outstanding. The presence of TiO₂ seems to (i) limit contact between polymer film and highly reactive radicals in the solution and (ii) act as a charge trap. Moreover, during the photocatalysis mediated by PVF^f–TiO₂–Fe oxide, some leaching of supported iron increased the amount of the top TiO₂ layer exposed to the light increasing the synergistic effects between the two oxides leading to enhanced pollutant degradation.     

Molecular Engineering of Supported Vanadium Oxide Catalysts Through Support Modification

Highly dispersed, multilayered surface metal oxide catalysts (V₂O₅/MO _x /SiO₂, M = Ti(IV), Zr(IV) or Al(III)) were successfully synthesized by taking into account various factors that govern the maximum dispersion of metal oxide species on silica. The characterization results revealed that the molecular structures of the surface vanadium oxide species on the modified supports are a strong function of environmental conditions. The surface vanadium oxide species under dehydrated conditions are predominantly isolated VO₄ units, similar to the dehydrated V₂O₅/SiO₂ catalysts. Upon hydration, the surface vanadium oxide species on the modified supports consist of polymerized VO₅/VO₆ units and/or less polymerized (VO₃) _n species, which depend on the vanadia content and the specific second metal oxide loading. The surface V cations are found to preferentially interact with the surface metal (Ti, Zr or Al) oxide species on silica. The V(V) cations in the dehydrated state appear to possess both oxygenated ligands of Si(IV)–O^– and M–O^–. Consequently, the reducibility and catalytic properties of the surface vanadium oxide species are significantly altered. The turnover frequencies of the surface VO₄ species on these modified supports for methanol oxidation to redox products (predominantly formaldehyde) increase by more than an order of magnitude relative to the unmodified V₂O₅/SiO₂ catalysts. These reactivity enhancements are associated with the substitution of Si(IV)–O^– oxygenated ligands by less electronegative M–O^– ligands in the O=V(–O–support)₃ structure, which strongly suggests that the bridging V–O–support bonds play a key role in determining the reactivity of the surface vanadium oxide species on oxide supports.     

Preparation of mesoporous benzene–silica nanoparticles

Nanoparticles of periodic mesoporous organosilica (PMO) with benzene bridging groups were prepared using a 1,4-bis(triethoxysilyl)benzene organosilica precursor and mixed surfactant templates composed of a poly(ethylene oxide)–poly(dl-lactic acid-co-glycolic acid)–poly(ethylene oxide) (PEO–PLGA–PEO) triblock copolymer and a fluorocarbon surfactant under acidic conditions. Mesoporous organosilica particles clearly exhibited a nanoscale diameter of 50–1000 nm by scanning electron microscopy. Moreover, these particles possessed a mesostructure with uniform pores in the range of 6.3–6.6 nm and core-shell type spherical morphology, which were confirmed by Synchrotron small angle X-ray scattering, transmission electron microscopy, and nitrogen adsorption analysis. Benzene bridging groups linked covalently to Si atoms were analyzed by solid state ¹³C- and ²⁹Si MAS NMR.     

Cesium-catalyzed oxidation of zinc surfaces

On zinc films, the adsorption probability of O₂ is extremely low (10^–3–10^–2), and O₂ exposures in the range of 10³–10⁴ langmuir are necessary to produce a significant transformation of metallic zinc into zinc oxide. The presence of submonolayer coverages of cesium enhances the oxidation rate of zinc by 2–3 orders of magnitude. The cesium adatoms interact with O₂ molecules, producing a reservoir of reactive oxygen species that oxidize zinc.     

Mesoporous H3PW12O40-silica composite: Efficient and reusable solid acid catalyst for the synthesis of diphenolic acid from levulinic acid

Mesoporous H₃PW₁₂O₄₀-silica composite catalysts with controllable H₃PW₁₂O₄₀ loadings (4.0–65.1%) were prepared by a direct sol–gel–hydrothermal technique in the presence of triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer. Powder X-ray diffraction (XRD) patterns and nitrogen sorption analysis indicate the formation of well-defined mesoporous materials. With H₃PW₁₂O₄₀ loading lower than 20%, the materials exhibit larger BET surface area (604.5–753.0 m² g⁻¹), larger and well-distributed pore size (6.1–8.6 nm), larger pore volume (0.75–1.2 cm³ g⁻¹), and highly dispersed Keggin unit throughout the materials. Raman scattering spectroscopy studies confirm that the primary Keggin structure remained intact after formation of the composites. As a novel kind of reusable solid acid catalyst, as-prepared H₃PW₁₂O₄₀-silica composite was applied for the synthesis of diphenolic acid (DPA) from biomass platform molecule, levulinic acid (LA), under solvent-free condition, and remarkably high catalytic activity and stability were observed.     

Semiconducting properties of TiO2 films thermally formed at 400° C

Titanium oxide films, TiO₂, were prepared on metallic titanium substrates employing a thermal treatment at 400° C under normal air atmosphere, with various annealing times (15, 25 and 45 min). Cyclic voltammetry and electrochemical impedance spectroscopy techniques were used to study the electrochemical and electrical characteristics of these films. The potential range for the voltammetric measurements was –0.80 to 8.00 V vs MSE (mercurous sulfate reference electrode). An analysis of the capacitance values of these semiconducting oxide films gave information about their electronic characteristics. From Mott-Schottky plots the donor concentration (N _D) and the flat band potential (E _fb) were obtained. N _D values ranged from 14 × 10²² cm^–3 to 3.3 × 10²² cm^–3, while E _fb values ranged from –0.40 to –0.98 V vs MSE, depending on the heating times for the oxide growth. The thickness of the space charge region, calculated from the minimum value of the capacitance at high band bending, varied between 1.45 and 2.13 rim.     

Thermal behaviour of Cu–Mg–Mn and Ni–Mg–Mn layered double hydroxides and characterization of formed oxides

Thermal behaviour of synthetic Cu–Mg–Mn and Ni–Mg–Mn layered double hydroxides (LDHs) with M^II/Mg/Mn molar ratio of 1:1:1 was studied in the temperature range 200–1100 °C by thermal analysis (TG/DTA/EGA), powder X-ray diffraction (XRD), Raman spectroscopy, and voltammetry of microparticles. Powder XRD patterns of prepared LDHs showed characteristic hydrotalcite-like phases, but further phases were indirectly found as admixtures. The Cu–Mg–Mn precipitate was decomposed at temperatures up to ca. 200 °C to form an XRD-amorphous mixture of oxides. The crystallization of CuO (tenorite) and a spinel type mixed oxide of varying composition Cu_xMg_yMn_zO₄ with Mn⁴⁺ was detected at 300–500 °C. At high temperatures (900–1000 °C), tenorite disappeared and a consecutive crystallization of 2CuO·MgO (gueggonite) was observed. The high-temperature transformation of oxide phases led to a formation of Cu^I oxides accompanied by oxygen evolution. The DTA curve of Ni–Mg–Mn sample exhibited two endothermic effects characteristic for hydrotalcite-like compounds. The first one with minimum at 190 °C can be ascribed to a loss of interlayer water, the second one with minimum at 305 °C to the sample decomposition. Heating of the Ni–Mg–Mn sample at 300 °C led to the onset of crystallization of oxide phases identified as Ni_xMg_yMn_zO₄ spinel, (Ni,Mg)O oxide containing Mn⁴⁺ cations, and easily reducible XRD-amorphous species, probably free Mn^III,IV oxides. At 600 °C (Raman spectroscopy) and 700 °C (XRD), the (Ni,Mg)₆MnO₈ oxide with murdochite structure together with spinel phase were detected. Only spinel and (Ni,Mg)O were found after heating at 900 °C and higher temperatures. Temperature-programmed reduction (TPR) profiles of calcined Cu–Mg–Mn samples exhibited a single reduction peak with maximum around 250 °C. The highest H₂ consumption was observed for the sample calcined at 800 °C. The reduction of Ni–Mg–Mn samples proceeded by a more complex way and the TPR profiles reflected the phase composition changing depending on the calcination temperature.     

Surface oxygen species and their reactivities in the mild oxidation of ethylene on cerium oxide studied by FT-IR spectroscopy

Surface oxidation of ethylene on cerium oxide was studied at mild temperatures (293–473K) by usingin situ FT-IR spectroscopy, and isotopic technique. Ethylene oxidation took place even at around 330 K on a well outgassed cerium oxide independent of the presence of gaseous O₂. At mild temperatures, the surface adsorbed product was mainly formate species. Adsorbed Superoxide (O ₂ ^– ) species was definitely observed at temperatures up to 373 K when gaseous oxygen was present. However isotopic experiment confirmed that the Superoxide was not the active form of oxygen due to the mild oxidation of ethylene. The principal oxygen species participating in the mild oxidation of ethylene was surface lattice oxygen which is supposed to be in O^–-like form created by an outgassing at high temperatures. The mild oxidation of ethylene could be also initiated by surface peroxide (O ₂ ^2– ) and O^– species which were formed via the adsorption of O₂ on a partially reduced cerium oxide.     

Preparation of Silver Nanoparticles in Oxide Matrices Derived by the Sol–Gel Method

Consideration is given to the processes proceeding in the Ag⁺–SiO₂ and Ag⁺–GeO₂ systems at a high silver content upon their heat treatment in air. These processes lead to the formation of silver–oxide nanocomposite films. It is revealed that the formation of silver nanoparticles is due to thermally stimulated interaction between silver ions and the oxide matrix with the formation of silver silicate (germanate), which, at temperatures above 600°C, undergoes decomposition into silver nanoparticles and silicon (germanium) dioxide. It is demonstrated that, under the given conditions, silver particles are encapsulated into oxide particles, which prevents their further oxidation up to 900°C.     

Electrochemical and reflectance study of the conversion of zinc oxide by hexacyanoferrate (II) in offset lithography

Zinc taken from –1.4 to –0.7 V/SCE in the presence of hexacyanoferrate(II) solution generates first a tough glassy material from –1.25 to –1.0 V, breaches through which then produce a gel. The two types of zinc hexacyanoferrate(II) product are probably related to their Zn^II oxide and Zn²⁺ (aquo) progenitors. The electrochemistry depends on the zinc pretreatment which governs the amount (from zero, to appreciable) of nucleating Zn^II oxide initially present. H₂PO₄ ^– is shown to play a crucially modifying part, while Na₂EDTA, malic acid, disodium 1-ethoxy-sulphosuccinate surfactant and isopropanol have minor roles in product modification. Possibly procrustean compositions for glass, gel and conversion product are suggested. Diffuse reflectance, AAS, SEM, XRD and i.r. spectroscopy were used in characterisations. The mechanism of electrophotographic conversion is discussed.     

Aspects of electrochemical behaviour of carbon steel in different Bayer plant solutions

Cyclic voltammetric and potentiodynamic studies were carried out on 300W carbon steel in Bayer plant solution, at 100 °C, with different alumina concentrations. Alumina behaves as an anodic inhibitor, shifting the critical passivation potentials positively and decreasing the critical passivation current with increasing concentration. Increase in alumina concentration promotes the formation of a uniform and less porous film. The pore resistance model describes the properties of the oxide films. Aluminium was found in all oxides formed, supporting the formation of a mixed oxide Fe_3–x Al _x O₄. Thermodynamic calculation of some equilibrium potentials was carried out using the Fe(OH)₃ ^– ion rather than HFeO₂ ^– ion. Moreover, the Al(OH)₄ ^– ion was considered instead of AlO₂ ^– ion in the oxidation process.     

Nitrous oxide flux from a solid dairy manure pile measured using a micrometeorological mass balance method

A micrometeorological mass balance technique was used to quantify the N₂O flux from a solid dairy manure pile under field conditions. Flux was determined using time-averaged measurements of wind speed, and nitrous oxide concentration using a tunable diode laser trace gas analyzer. A total of 66 hourly flux averages were collected and values were never lower than 200 ng N₂O-N m^–2 s^–1. The mean hourly N₂O flux was 4865 ng N₂O-N m^–2 s^–1 (0.42 g N m^–2 day^–1), which is of the same order of magnitude, albeit higher, as previously observed for a similar solid pig manure storage.     

The Bromine Electrode. Part I: Adsorption Phenomena at Polycrystalline Platinum Electrodes

A cyclic voltammetric study of the behaviour of Br^– and Br^– ₃ at Pt electrodes, in the potential range between hydrogen and oxygen evolution, is described. Different experiments were carried out, in the presence of Br^– and Br^– ₃, in which the ratio between the species has been kept constant and equal to 1. The halide concentration was varied between 4 × 10^–6 and 1 × 10^–3 and mol dm^–3, at constant ionic strength, in 1 M HclO₄ as well as in 1 M NaClO₄ adjusted to a pH of 2. Underpotential deposition of Br is observed at potentials as low as –0.125 V vs SCE. The adsorption parameters of Br species were determined from the adsorption/desorption peak pair in the hydrogen adsorption/desorption region, and from the oxide reduction peak data. In the absence of oxygen adsorption, a relatively high coverage of the electrode surface is attained. A Langmuir-type adsorption is observed under the different experimental conditions.     

Changes in the magnetic properties of chromite ore heated with scale

Conclusions Chrome spinel and gangue of Kimpersarski chromite ores has a low and scarcely distinguishable magnetic susceptibility which does not alter after heating at temperatures from 400° to 1300°C. The magnetic susceptibility of the ores fired with additions of iron oxide or scale at 1000–1300°C increases from (20–120)×10^–6 to (1650–3400)×10^–6 cm³/g. The increase in the magnetic properties of chromite ores after firing occurs on account of the increase in the magnetic susceptibility of the gangue from (50–120)×10^–6 to (6000–8000)×10^–6 cm³/g. Thus after firing of chromite ores with iron-containing additives the gangue acquires ferromagnetic properties. The magnetic susceptibility of the gangue is 50–115 times greater than chrome-spinel which permits us to use highly productive magnetic separators with low and medium magnetic field forces for their treatment.     

Interaction of iron,manganese, and silicon with magnesite refractories

Conclusions Metallic iron has a comparatively weak effect on the periclase constituent of a magnesite crucible. The new structures formed (magnesiowustite and magnesioferrite) develop from the periclase grains, which does not lead to breakdown of the refractory. The crucible fails as a result of the interaction between the iron oxides and the silica-containing constituent and of migration of the low-melting products of this interaction from the reaction zone.Metallic manganese modifies the structure of a magnesite crucible to a substantially greater extent, since it promotes formation of low-melting manganese- and magnesium-containing silicate phases such as monticellite, tephroite, etc.As a result of its high chemical activity, crystalline silicon has the most destructive effect on the structure of a magnesite crucible, apparently causing silicothermal reduction of the magnesium oxide and formation of metallic magnesium, some of the latter going into the vapor phase and being removed from the reaction zone of the crucible.The fact that iron and manganese are oxidized principally by atmospheric oxygen in the crucible pores, while silicon is oxidized mainly by oxygen from magnesium oxide, is of great practical interest, since silicon therefore breaks down a magnesite crucible very rapidly.Translated from Ogneupory, No.4, pp. 52–56, April, 1969.