Reactive Iron Oxide Research Articles

Effect of Chain-Length and Countersurface on the Tribochemistry of Bulk Zinc Polyphosphate Glasses

Zinc polyphosphate glasses are considered to be chiefly responsible for the anti-wear efficiency of ZnDTP tribofilms. In this work, the tribochemical properties of amorphous bulk zinc polyphosphates of different chain lengths (ranging from zinc metaphosphate to zinc pyrophosphate) have been investigated. Tribological tests on bulk polyphosphate discs have been carried out using steel and quartz balls as counter-surfaces in a poly-α-olefin (PAO) bath at room temperature. The composition in the wear track and on the contact region of the balls has been monitored by small-area and imaging X-ray photoelectron spectroscopy (i-XPS). The XPS analysis revealed that the composition of short-chain-length polyphosphates remained unchanged following tribological stress. Long-chain-length polyphosphates are depolymerized in the wear track as a consequence of a tribochemical reaction. By comparing the results obtained using quartz and steel balls, it could be observed that while the reaction of iron oxide with the polyphosphates certainly plays a role in the depolymerization of the samples under sliding conditions, pressure and shear stress alone and also in the presence of water or oil-oxidized species are able to depolymerize the glass when an inert material is used as counterpart; the composition of the wear track, in this case, is dependent on the applied load. All samples were able to form an adhesive, glassy transfer film on both steel and quartz balls, but the short-chain-length polyphosphates showed a lower friction coefficient and wear coefficient. The results suggest a third-body mechanism with the polyphosphates acting as a solid lubricant. Differences in tribological behavior of the different-chain-length polyphosphates are attributable to their mechanical and rheological properties.

Dissolution of mesoporous silica supports in aqueous solutions: Implications for mesoporous silica-based water treatment processes

Under pH 7–10 conditions, the mesoporous silica supports proposed for use in water treatment are relatively unstable. In batch experiments conducted in pH 7 solutions, the commonly used support SBA-15 dissolved quickly, releasing approximately 30mg/L of dissolved silica after 2h. In column experiments, more than 45% of an initial mass of 0.25g SBA-15 dissolved within 2 days when a pH 8.5 solution flowed through the column. In a mixed iron oxide/SBA-15 system, the dissolution of SBA-15 changed the iron oxide reactivity toward H2O2 decomposition, because dissolved silica deposited on iron oxide surface and changed its catalytic active sites. As with SBA-15, other mesoporous silica materials including HMS, MCM-41, four types of functionalized SBA-15, and two types of metal oxide-containing SBA-15 also dissolved under circumneutral pH solutions. The dissolution of mesoporous silica materials raises questions about their use under neutral and alkaline pH in aqueous solutions, because silica dissolution might compromise the behavior of the material.

Reactive iron and its buffering capacity towards dissolved sulfide in sediments of Jiaozhou Bay, China

Reactive iron (Fe) oxides in marine sediments play a critical role in removal of free sulfide. In this study, 0.5 and 6 N HCl-extractable Fe, acid volatile sulfide (AVS), and pyrite were examined in sediments at three sites of eutrophic Jiaozhou Bay to investigate the interactions of sulfur and Fe and possible influences of eutrophication on free sulfide removal. The results indicate that formation and accumulation of AVS and pyrite are limited by low availability of labile organic matter, despite eutrophication of the bay water. Quick buffering of free sulfide proceeded mainly via consumption of 0.5 N HCl-extractable Fe (labile Fe), however, the consumption did not result in a depletion of the Fe pool. High residual buffering capacity enables a quick removal of free sulfide in porewater, and thereby it is difficult for sulfide to accumulate and to cause detrimental effects on benthic organisms at the present steady state. Significant effects of eutrophication on Fe and sulfur geochemistry is restricted only to the estuarine sediments which were subject to direct wastewater discharges, whereas no such effects were observed in other sediments of the bay.

Jarosite dissolution rates and nanoscale mineralogy

Jarosite, (K,Na,H)Fe3(SO4)2(OH)6, commonly occurs as an ephemeral phase in acidic, oxidizing, sulfate and iron-rich environments on Earth. The discovery of jarosite within deposits on Mars provides evidence for oxidizing, acidic fluids in these regions during the time of jarosite deposition. In addition, the preservation of jarosite over billions of years on Mars places constraints on the post-jarosite geochemical environment, including the duration of aqueous diagenesis. Observations of hematite spherules within the same outcrops may further constrain the chemistry of these diagenetic fluids. In this study, the effects of pH and temperature on jarosite initial dissolution rates and iron oxide reaction products were determined in the laboratory at initial pH 1–10 and temperatures from 277 to 323K. Multivariate linear regression of the rate data shows that the dissolution rate varies with pH and temperature, resulting in Ea=∼79kJ/mol. At pH<3.5, the rate increases with increasing aH+, while at pH>3.5 increasing aOH- results in increased rates yielding a rate equation of r(molm-2s-1)=10-6.487αH+0.899+10-10.964aOH-0.392 at 296K. Transmission electron microscopy (TEM) reveals patchy jarosite dissolution textures, suggesting that dissolution proceeds through pitting, perhaps initiated in areas containing higher concentrations of H+ substitution or dislocations within the jarosite structure. Iron (hydr)oxide reaction products (determined by TEM and electron diffraction) varied with pH, temperature, and the extent of reaction, but were consistently crystalline, though <100nm in diameter. While hematite is predicted to be the thermodynamically most stable phase in dilute K–SO4–Fe waters, schwertmannite was observed as the initial reaction product at 277K and maghemite was the dominant initial phase at 296K. Hematite was the initial reaction product observed at 323K along with ferrihydrite. At pH 3.5–7, the dominant reaction products varied with the extent of reaction, forming hematite over time, likely as a result of kinetic effects following the Ostwald step rule. However, in MES buffered pH 7.5 experiments, ferrihydrite remains the dominant reaction products following weeks of reaction. Goethite was notably absent from the reaction products, except as a minor phase after 10days of dissolution at pH 4.4. These variations in mineralogy combined with textures of the reaction products indicate that sulfate adsorption may play a significant role in determining the mineralogy and texture of the iron oxides produced in the system. While goethite is commonly found as the dominant iron oxide associated with jarosite deposits on Earth, jarosite dissolution under water-limited conditions on Mars may have produced nanoscale maghemite and hematite which later aggregated to form coarser grained “specular” particles or were distributed globally as dust. Based on these reaction products and dissolution rates, abundant iron oxides observed at Meridiani Planum may have formed as secondary reaction products of jarosite dissolution at pH>3.5 over timescales less than tens to thousands of years.

The influence of vegetation and soil type on the speciation of iron in soil water

Soluble organic matter derived from exotic Pinus species has been shown to form stronger complexes with iron (Fe) than that derived from most native Australian species. It has also been proposed that the establishment of exotic Pinus plantations in coastal southeast Queensland may have enhanced the solubility of Fe in soils by increasing the amount of organically complexed Fe, but this remains inconclusive. In this study we test whether the concentration and speciation of Fe in soil water from Pinus plantations differs significantly from soil water from native vegetation areas. Both Fe redox speciation and the interaction between Fe and dissolved organic matter (DOM) were considered; Fe – DOM interaction was assessed using the Stockholm Humic Model. Iron concentrations (mainly Fe2+) were greatest in the soil waters with the greatest DOM content collected from sandy podosols (Podzols), where they are largely controlled by redox potential. Iron concentrations were small in soil waters from clay and iron oxide‐rich soils, in spite of similar redox potentials. This condition is related to stronger sorption on to the reactive clay and iron oxide mineral surfaces in these soils, which reduces the amount of DOM available for electron shuttling and microbial metabolism, restricting reductive dissolution of Fe. Vegetation type had no significant influence on the concentration and speciation of iron in soil waters, although DOM from Pinus sites had greater acidic functional group site densities than DOM from native vegetation sites. This is because Fe is mainly in the ferrous form, even in samples from the relatively well‐drained podosols. However, modelling suggests that Pinus DOM can significantly increase the amount of truly dissolved ferric iron remaining in solution in oxic conditions. Therefore, the input of ferrous iron together with Pinus DOM to surface waters may reduce precipitation of hydrous ferric oxides (ferrihydrite) and increase the flux of dissolved Fe out of the catchment. Such inputs of iron are most probably derived from podosols planted with Pinus.

Preparation of pyrrole with iron oxide precipitated on the surface of graphite nanosheet

Fe3O4/NanoG was firstly prepared by precipitation reaction of iron oxide (Fe3O4) on the surface of graphite nanosheet (NanoG). Then composites PPy/NanoG, PPy/Fe3O4 and PPy/Fe3O4/NanoG were prepared by in-situ polymerization of the monomer pyrrole polymerized on the surface of NanoG, Fe3O4 and Fe3O4/NanoG. The structures of Fe3O4/NanoG, PPy, PPy/NanoG, PPy/Fe3O4 and PPy/Fe3O4/NanoG were characterized by scanning electron microscopy, energy dispersive spectroscopy, fourier transmission infrared spectroscopy and X-ray diffraction . Results show that NanoG and Fe3O4/NanoG are encapsulated by PPy for the layered structure and their high aspect ratio (300–500). From the thermogravimetric analysis it can be seen that the introductions of NanoG, Fe3O4 and Fe3O4/NanoG into PPy based composites lead them to exhibit better thermal stabilities than pure PPy. The measurements of electromagnetic parameters show that the reflection loss of PPy/Fe3O4/NanoG is below −15dB at the X band (8.2–12.4GHz) and the minimum loss value is −18.30dB at 9.84GHz, while the reflection loss of PPy/Fe3O4 is below −10dB at 8.2–12.4GHz and the minimum loss value is −14.02dB at 10.26GHz. The reflection loss of PPy/NanoG is below −10dB at 8.2–12.4GHz and the minimum loss value is −13.44dB at 10.28GHz. The microwave absorbing properties of PPy/Fe3O4/NanoG, PPy/Fe3O4 and PPy/NanoG are superior to that of PPy.

Kinetic evaluation on the redox reaction of iron oxide to iron for chemically hydrogen compression

Kinetic evaluation on the redox reaction of iron oxide to iron for chemically hydrogen compression

Pilot Demonstration of the Activated Iron Process for Removing Heavy Metals from Flue-Gas-Desulfurization (FGD) Wastewater

Pilot Demonstration of the Activated Iron Process for Removing Heavy Metals from Flue-Gas-Desulfurization (FGD) WastewaterThe Activated Iron Process (AIP), a novel chemical water treatment platform, was developed for removing various micro-pollutants and impurities from a liquid stream. This integrated treatment system employs certain iron chemistry to create a hybridized reactive solid mixture that comprises three reactive components: zero-valent iron (ZVI) particles with activated surface, redox reactive iron oxide...Author(s)Yong H. HuangPhani K. PeddiCilai TangHui ZengXinjun (Jason) TengSourceProceedings of the Water Environment FederationDocument typeConference PaperPublisherWater Environment FederationPrint publication date Sep, 2012ISSN1938-6478DOI10.2175/193864712811704071Volume / Issue2012 / 7Content sourceWEFTECCopyright2012Word count305

Iron-Based Microbial Ecosystem on and Below the Seafloor: A Case Study of Hydrothermal Fields of the Southern Mariana Trough

Microbial community structures in deep-sea hydrothermal vents fields are constrained by available energy yields provided by inorganic redox reactions, which are in turn controlled by chemical composition of hydrothermal fluids. In the past two decades, geochemical and microbiological studies have been conducted in deep-sea hydrothermal vents at three geographically different areas of the Southern Mariana Trough (SMT). A variety of geochemical data of hydrothermal fluids and an unparalleled microbiological dataset of various samples (i.e., sulfide structures of active vents, iron-rich mats, borehole fluids, and ambient seawater) are available for comparative analyses. Here, we summarize the geochemical and microbiological characteristics in the SMT and assess the relationship between the microbial community structures and the fluid geochemistry in the SMT by thermodynamic modeling. In the high temperature vent fluids, aerobic sulfide-oxidation has the potential to yield large amounts of bioavailable energy in the vent fluids, which is consistent with the detection of species related to sulfide-oxidizing bacteria (such as Thiomicrospira in the Gammaproteobacteria and Sulfurimonas in the Epsilonproteobacteria). Conversely, the bioavailable energy yield from aerobic iron-oxidation reactions in the low-temperature fluids collected from man-made boreholes and several natural vents were comparable to or higher than those from sulfide-oxidation. This is also consistent with the detection of species related to iron-oxidizing bacteria (Mariprofundus in the Zetaproteobacteria) in such low-temperature samples. The results of combination of microbiological, geochemical, and thermodynamic analyses in the SMT provide novel insights into the presence and significance of iron-based microbial ecosystems in deep-sea hydrothermal fields.

Hydrogen Storage and Release by Redox Reaction of Iron Oxide Medium with Mo and Zr Additives

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.

Oxidation reaction kinetics for the steam-iron process in support of hydrogen production

A hydrogen generation research program is focused on solar-driven hydrogen production by means of reactive metal water splitting. In order to dissociate water molecules at significantly reduced thermal energies as well as providing a practical means for efficient hydrogen and oxygen separation, an intermediary reactive material is introduced to realize water splitting in the form of an oxidation reaction. Elemental iron is used as the reactive material in the process commonly referred to as the steam-iron process. In order to exploit the unique characteristics of highly reactive materials and ultimately achieve the potential efficiency gains at the solar reactor scale, a monolithic laboratory-scale reactor has been designed to explore the fundamental kinetic rates during the iron oxidation reaction at temperatures ranging from about 650 to 900 K. Results show hydrogen production rates on the order of 1E-8 g/cm 2 s. Micro-Raman spectroscopy is used to access information on the exact iron oxide phase produced, and high resolution SEM and electron dispersion spectroscopy (EDS) are used to assess the oxide morphology and further quantify the oxide state, including spatial distributions.

Intermediates of CO oxidation on iron oxides: An experimental and theoretical study

Reactions of laser-ablated iron oxides with CO in excess argon are investigated by infrared adsorption spectroscopy and density functional theoretical calculations. The carbonyl iron oxides OFe(CO)(n) (n = 1-3) and O(2)Fe(CO)(m) (m = 1, 2) are generated during sample deposition or annealing, whereas CO(2) is greatly produced at the expense of these carbonyl iron oxides upon UV irradiation, showing the formation of intermediate carbonyl iron oxides in the oxidation of carbon monoxide to carbon dioxide. These intermediate carbonyl iron oxides are characterized on the basis of isotopic substitution, stepwise annealing, change of CO concentration and laser energy, and comparison with theoretical calculations. The overall agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these complexes from the matrix infrared spectra. The reaction pathways for the formation of the products are proposed based on the experimental and theoretical results presented.

Experimental and theoretical study of the reactions of iron and manganese oxides with dinitrogen in a cryogenic matrix

Reactions of laser-ablated iron and manganese oxides with dinitrogen in excess argon have been investigated by matrix-isolation infrared spectroscopy. The NNMO (M=Fe, Mn), (NN)2FeO, and NNFeO2 complexes are formed as reaction products during sample deposition and/or further annealing. These complexes are characterized on the basis of the results of the isotopic substitution and comparison with theoretical calculations. The agreement between the experimental and calculated vibrational frequencies and isotopic shifts supports the identification of these complexes from the matrix infrared spectra. Reaction mechanisms have been proposed for the formation of these products.

Role of metal oxide support in redox reactions of iron oxide for chemical looping applications: experiments and density functional theory calculations

Aided by an oxygen carrier such as iron oxide, the chemical looping process can convert carbonaceous fuels while effectively capturing CO2. Previous experimental studies indicate that adding TiO2 support to iron oxide can notably improve the reactivity of iron oxide over multiple redox cycles, making it more suitable for chemical looping applications. In this study, wustite (Fe1−xO) was used to represent pure iron(II) oxide and ilmenite (FeTiO3) was used to represent TiO2 supported iron(II) oxide. The underlying mechanisms for the improved iron oxide performance with TiO2 support are investigated through experiments and periodic Density Functional Theory (DFT) calculations. Both experimental and DFT studies indicate that TiO2 support is unlikely to reduce the activation energy for the reduction of iron(II) oxide. The support, however, can significantly lower the energy barrier for O2− migration within the dense solid phase, thereby enhancing the O2− diffusivity. The good agreements between experiments and DFT calculations confirm that the improved reactivity and recyclability of TiO2 supported iron oxide particles are likely to result from the significantly enhanced O2− diffusivity with the presence of support.

Controlling barrier penetration via exothermic iron oxidation

Exothermic iron oxidation is an elegant means to generate heat, with the potential to modulate barrier penetration if reaction kinetics can be controlled. This aim of this study was to gain a fundamental understanding of how these temperature change kinetics influenced barrier diffusion rate. Lidocaine transport through a hydrophilic carboxymethyl cellulose (CMC) gel was compared using two rapid iron oxidation reactions initiated by water (ExoRap50, Tmax—47.7±0.6°C, tmax—3.3±0.6min, ExoRap60, Tmax—60.4±0.3°C, tmax—9.3±0.6min) and a slower reaction initiated by oxygen (ExoSl45Tmax—ca. 44°C, tmax ca. 240min). Temperature change induced by the oxygen initiated reaction (ExoSl45) was almost double those initiated by water (over 4h), but lidocaine diffusion was approximately 4 times higher for the latter (ExoRap50, 555.61±22.04μg/cm2/h; ExoRap60, 663.1±50.95μg/cm2/h; compared to ExoSl45, 159.36±29.44μg/cm2/h). The large influence of temperature change kinetics on lidocaine diffusion suggested that transport was heavily dependent on temperature induced structural changes of the barrier. CMC, like many polymers adsorbs more water when exposed to moderate increases in temperature and this appeared to be a critical determinant of lidocaine barrier diffusion rate.

Spatial Variation in Sediment-Water Exchange of Phosphorus in Florida Bay: AMP As a Model Organic Compound

Dissolved organic phosphorus (DOP) has been recognized as dominant components in total dissolved phosphorus (TDP) pools in many coastal waters, and its exchange between sediment and water is an important process in biogeochemical cycle of phosphorus. Adenosine monophosphate (AMP) was employed as a model DOP compound to simulate phosphorus exchange across sediment-water interface in Florida Bay. The sorption data from 40 stations were fitted to a modified Freundlich equation and provided a detailed spatial distribution both of the sediment's zero equilibrium phosphorus concentration (EPC(0-T)) and of the distribution coefficient (K(d-T)) with respect to TDP. The K(d-T) was found to be a function of the index of phosphorus saturation (IPS), a molar ratio of the surface reactive phosphorus to the surface reactive iron oxide content in the sediment, across the entire bay. However, the EPC(0-T) was found to correlate to the contents of phosphorus in the eastern bay only. Sediment in the western bay might act as a source of the phosphorus in the exchange process due to their high EPC(0-T) and low K(d-T), whereas sediments in the eastern bay might act as a sink because of their low EPC(0-T) and high K(d-T). These results strongly support the hypothesis that both phosphorus and iron species in calcareous marine sediments play a critical role in governing the sediment-water exchange of both phosphate and DOP in the coastal and estuarine ecosystems.

Formation, aggregation and reactivity of amorphous ferric oxyhydroxides on dissociation of Fe(III)–organic complexes in dilute aqueous suspensions

While chemical reactions that take place at the surface of amorphous ferric oxides (AFO) are known to be important in aquatic systems, incorporation of these reactions into kinetic models is hindered by a lack of ability to reliably quantify the reactivity of the surface and the changes in reactivity that occur over time. Long term decreases in the reactivity of iron oxides may be considered to result from changes in the molecular structure of the solid, however, over shorter time scales where substantial aggregation may occur, the mechanisms of reactivity loss are less clear. Precipitation of AFO may be described as a combination of homogeneous and heterogeneous reactions, however, despite its potentially significant role, the latter reaction is usually neglected in kinetic models of aquatic processes. Here, we investigate the role of AFO in scavenging dissolved inorganic ferric (Fe(III)) species (Fe′) via the heterogeneous precipitation reaction during the net dissociation of organically complexed Fe(III) in seawater. Using sulfosalicylic acid (SSA) as a model ligand, AFO was shown to play a significant role in inducing the net dissociation of the Fe–SSA complexes with equations describing both the heterogeneous precipitation reaction and the aging of AFO being required to adequately describe the experimental data. An aggregation based mechanism provided a good description of AFO aging over the short time scale of the experiments. The behaviour of AFO described here has implications for the bioavailability of iron in natural systems as a result of reactions involving AFO which are recognised to occur over time scales of minutes, including adsorption of Fe′ and AFO dissolution, precipitation and ageing.

Promotional effect of metal encapsulation on reactivity of iron oxide supported Pt catalysts

We studied reactivity of well-defined Pt model catalysts, supported on crystalline iron oxide Fe 3O 4(1 1 1) films, in low temperature CO oxidation. It is shown that pre-annealing in vacuum at ∼850 K suppresses CO adsorption but increases CO 2 production rate. This finding is rationalised in terms of strong metal–support interaction between Pt and iron oxide resulting in particles encapsulation by a thin FeO(1 1 1) film that catalyses CO oxidation similarly to the extended FeO(1 1 1)/Pt(1 1 1) surfaces previously studied [10]. The results show that the stability and the atomic structure of the encapsulated layer under reaction conditions play a critical role in oxidation reactions over Pt catalysts supported on reducible oxides.

Mobilization of arsenic and iron from Red River floodplain sediments, Vietnam

Sediments from the Red River and from an adjacent floodplain aquifer were investigated with respect to the speciation of Fe and As in the solid phase, to trace the diagenetic changes in the river sediment upon burial into young aquifers, and the related mechanisms of arsenic release to the groundwater. Goethite with subordinate amounts of hematite were, using Mössbauer spectroscopy, identified as the iron oxide minerals present in both types of sediment. The release kinetics of Fe, As, Mn and PO 4 from the sediment were investigated in leaching experiments with HCl and 10 mM ascorbic acid, both at pH 3. From the river sediments, most of the Fe and As was mobilized by reductive dissolution with ascorbic acid while HCl released very little Fe and As. This suggests As to be associated with an Fe-oxide phase. For oxidized aquifer sediment most Fe was mobilized by ascorbic acid but here not much As was released. However, the reduced aquifer sediments contained a large pool of Fe(II) and As that is readily leached by HCl, probably derived from an unidentified authigenic Fe(II)-containing mineral which incorporates As as well. Extraction with ascorbic acid indicates that the river sediments contain both As(V) and As(III), while the reduced aquifer sediment almost exclusively releases As(III). The difference in the amount of Fe(II) leached from river and oxidized aquifer sediments by ascorbic acid and HCl, was attributed to reductive dissolution of Fe(III). The reactivity of this pool of Fe(III) was quantified by a rate law and compared to that of synthetic iron oxides. In the river mud, Fe(III) had a reactivity close to that of ferrihydrite, while the river sand and oxidized aquifer sediment exhibited a reactivity ranging from lepidocrocite or poorly crystalline goethite to hematite. Mineralogy by itself appears to be a poor predictor of the iron oxide reactivity in natural samples using the reactivity of synthetic Fe-oxides as a reference. Sediments were incubated, both unamended and with acetate added, and monitored for up to 2 months. The river mud showed the fastest release of both Fe and As, while the effect of acetate addition was minor. This suggests that the presence of reactive organic carbon is not rate limiting. In the case of the river and aquifer sediments, the release of Fe and As was always stimulated by acetate addition and here reactive organic carbon was clearly the rate limiting factor. The reduced aquifer sediment apparently can sustain slower but prolonged microbially-driven release of As. The highly reactive pools of Fe(III) and As in the river mud could be due to reoxidation of As and Fe contained in the reducing groundwater from the floodplain aquifers that are discharging into the river. Deposition of the suspended mud on the floodplain during high river stages is proposed to be a major flux of As onto the floodplain and into the underlying aquifers.

Shrinkage of an oxygen bubble rising in a molten glass

Abstract The mechanisms controlling the evolution of a bubble surrounded by molten glass are important to understand in order to improve melting in glass furnaces, particularly during a change in composition. In order to provide insight into this phenomenon, the behavior of an isolated bubble rising in molten glass is examined both experimentally and numerically. An experimental procedure developed specifically to observe, in situ, a rising bubble is described. Two soda-lime-silica compositions are tested, with low and high iron content, respectively. The numerical model used to describe bubble shrinkage is based on the results recently proposed in Pigeonneau (2009) . A specific mass transfer coefficient is used for oxygen where the oxidation–reduction reaction of iron oxides is taken into account. A comparison between the experimental and numerical results shows the importance of the oxidation–reduction reaction of iron in the mass transfer of oxygen. The shrinkage rate of a pure O2 bubble is enhanced with reduced molten glass iron content.