Papers by Keyword: Redox Reaction

Abstract: Hierarchical porous SiO₂@C@MnO₂ monoliths have been fabricated by two step approaches: Elemental carbon was covered the internal surface of porous silica monoliths with impregnation and carbonized in inert atmosphere, and MnO₂ was directly grown on the skeleton of SiO₂@C accompanied by redox reaction between C and KMnO₄. The effects of glucose and KMnO₄ concentrations, and hydrothermal reaction on the morphology of MnO₂ particles on the surface of SiO₂ monoliths were investigated in detail. The results showed that the optimal factors of reaction condition involved 0.08 mol·L^-1 glucose solution, 0.03 mol·L^-1 KMnO₄ solution and the reaction time of 5 h. SEM images and BET results indicated that the macroporous structure of the as-prepared material was preserved after modification, while the specific surface area and pore volume decreased with increasing amount of MnO₂ to some degree. The XPS spectra of SiO₂@C@MnO₂ is in good agreement with reported data in MnO₂. The crystal phase of MnO₂ was α-MnO₂ after thermal treatment at the temperature of 600 °C from the XRD patterns. Three-dimensional porous well-defined morphological SiO₂@C@MnO₂ be promising materials for the catalytic elimination of air pollutants since large quantities can be obtained from porous structure combined with α-MnO₂ equipped with high active performance.

Abstract: The tableware soda-lime silicate glasses, contained with 0.06 wt% of iron oxide, which were annealed at different times and temperatures, were investigated by UV-Vis spectroscopy. The glasses were produced from high iron sand. The iron content was twice as high in the glasses as it is in normal tableware glasses. The redox reaction of iron around glass transition temperature, Fe²⁺(green) ↔ Fe³⁺(yellow), was found in the annealing process, according to the redox reaction of iron with polyvalent ions in the glass, nFe³⁺ + M^a+ ↔ nFe²⁺ + M^(a+-n) where M is the polyvalent ion in glass. In this study, the glasses were prepared by melting in a platinum crucible. After casting, they were annealed with variable times and temperatures. The results of color in CIE L*a*b* system and Fe²⁺/Fe³⁺ ratio of glasses showed the effect of the annealing process on the redox reaction of iron. The decolorizing was found during the annealing process. The results of this work led to the method for controlling the effect of iron oxide in the glass and the possibility to use high iron sand to produce tableware glasses.Tableware glass, Iron oxide, Redox reaction, Decolorizing

Abstract: The redox reaction of a tableware soda-lime silicate glass contained with 0.04 - 1.00 wt% of iron oxide is investigated by UV-Vis spectroscopy. The quality and purity of raw materials, especially sand is required to control the amount of iron oxide as low as possible. Normally tableware glass contains small amount of iron oxide (0.01 - 0.04 wt%) and iron effect (green color) is controlled by adding decolorizing agent. The heat treatment around transition temperature is another method to decolorize iron by redox reaction control. It is believed that the reaction of iron oxide Fe²⁺(green) « Fe³⁺(yellow) still occurs in annealing process. In this study, the glasses were prepared by melting in the platinum crucibles. After annealing, they are cut into four pieces and heated at 550 560 570 and 580°C with different times. The results of the transmittance showed no significantly change but the color in CIE L*a*b* system of glasses heat treated at 550 and 560 °C slightly change into whiter shade. According to the result of calculated Fe²⁺/Fe³⁺ ratio, the ratio of these glasses were decreased by 5 and 2.5 % respectively. On the contrary, the redox ratio of glass heated at 580 °C increased, due to Fe³⁺to Fe²⁺ and the color changed into green. The results proved the kinetic of the redox reaction of Fe₂O₃ and the possibility to use annealing process as another tool to control flint color of glass.

Abstract: The performance and phase behavior of Quartz - Aluminum Matrix Composites at different temperatures were studied. Quartz aluminum matrix composites were prepared by powder metallurgy method. At the temperature that was less than 660.4°C(the melting point of aluminum), a portion of quartz was happened decomposition and revivification to silicon, most aluminum still existed in the form of metal aluminum. All quartz were happened at the temperature that was higher than 660.4°C. When the temperature is 700°C, the compressive strength of S5(added 40% quartz) is up to 46.02MP. The higher the value of compressive strength was, the less the amount of quartz were happened decomposition. At the temperature more than the melting point of aluminum, Quartz was revivification to silicon, aluminum is oxidized to Al₂O₃. When the amount of silica exceeded 10%, the mechanical properties of composites declined consequently.

Abstract: The molecular weight of natural rubber (NR) can be reduced via depolymerization reaction to produce liquid natural rubber (LNR) with a molecular weight less than 50 000 g/mol. In the reaction, hydrogen peroxide and sodium nitrite were added to natural rubber latex to initiate a redox type reaction which then breaks the NR chain. Low permeation of reagents into latex particles allows the degradation to occur greater at the latex particle surface relative to the inner core contributes to high molecular weight distribution (MWD) or polydispersity of the LNR obtained. In this recent works, the reaction was carried out in a biphasic medium consisting of water and toluene phases. Toluene swells latex particles as indicated by the SEM micrographs showing changes in the size of latex particles. This occurrence is suggested to increase the influx of reagents into the latex particles. Consequently, with higher permeation of reagents into the latex particles resulted in the decrease of molecular weight and lower polydispersity of the LNR obtained. Chemical structure analysize showed that the LNRs obtained were attached with hydroxyl and carbonyl groups.

Abstract: Chemical hydrogen storage and release of iron-based oxide mediums were investigated by hydrogen reduction and water splitting oxidation (Fe3O4 + 4H2 ⇌ 3Fe + 4H2O). In this study, all metal oxide mediums were prepared by coprecipitation method using urea solution as precipitant. The redox reactions of the mediums were conducted using a fixed bed quartz reactor under atmospheric pressure. The theoretical amount of hydrogen storage that can be obtained from the redox reaction of iron oxide is calculated to be 4.8wt% on the basis of 1g-Fe. However, in case of using the iron oxide medium without additives, the medium was rapidly deactivated due to the agglomeration of Fe metals in the hydrogen reduction step of repeated redox cycles. In this study, therefore, Mo and Zr additives were added to iron oxide to improve the reactivity of the medium and to prevent the agglomeration of that. As a result, the reactivity for oxidation of the mediums was largely improved with the addition of Mo additive. It was concluded that change in the valence of Mo cations affected the redox behavior of the mediums.

Abstract: A mathematical model of the galvanic iron corrosion is, here, presented. The iron(III)-hydroxide formation is considered together with the redox reaction. The PDE system, assembled on the basis of the fundamental holding electro-chemistry laws, is numerically solved by a locally refined FD method. For verification purpose we have assembled an experimental galvanic cell; in the present work, we report two tests cases, with acidic and neutral electrolitical solution, where the computed electric potential compares well with the measured experimental one

Abstract: Sorption of Co(II) on the biogenic Mn oxide produced by a Paraconiothyrium sp.-like strain was investigated. The biogenic Mn oxide, which was characterized to be poorly crystalline birnessite (Na4Mn(III) 6Mn(IV) 8O27 ·9H2O) bearing Mn(III) and Mn(IV) in the structure, showed approximately 6.0-fold higher efficiency for Co(II) sorption than a synthetic Mn oxide. XP-spectra of Co 2p for the biogenic and synthetic Mn oxides after Co(II) sorption indicate that Co was immobilized as Co(III) on the surface of Mn oxides, clearly suggesting that redox reaction occurs between Co(II) ions and each Mn oxides. The Co(II) ions would be initially sorbed on the vacant sites of the surface of biogenic Mn oxide, and then oxidized to Co(III) by neighbor Mn(III/IV) atoms to release Mn(II). For the synthetic Mn oxide, release of Mn(II) was negligibly small because the oxidant is only Mn(IV) in ramsdellite (γ-MnO2). The Mn(II) release from the biogenic Mn oxide during Co(II) adsorption would be not only from weakly bounded Mn(II), but also from redox reaction between Mn(III/IV) and Co(II) ions.