Resistance of blast furnace refractories to the action of aggressive reactants under conditions of an oxidizing gaseous atmosphere

Conclusions Investigations have been made of the resistance of ShPD-41, ShPD-39, and ShUD-37 chamotte refractories to the action of K₂CO₃, Fe₂O₃, blast furnace dust, and initial and final blast furnace slags under conditions of an oxidizing atmosphere. The investigation results showed that iron oxides and slag break down these refractories at 1400–1500°C. Dense ShPD-41 refractory is more resistant to the action of the reactants.The most resistant to the action of slags and iron oxides at 1400–1500°C are silicon carbide refractories with binders of silicon nitride and oxynitride.Translated from Ogneupory, No. 7/8, pp. 24–27, July–August, 1992.     

The influence of impurities in the original materials on the properties of refractories made of zirconia

Conclusions The effects of admixtures of the oxides of iron, aluminum, titanium, silicon and phosphorus on sintering, strength factors, thermal shock resistance, deformation under load, linear expansion and microstructure of articles made from zirconia stabilized with calcium oxide, were studied.According to their influence on the properties of the refractories, the impurities can be divided into three groups:those which prevent stabilization;those which have practically no effect on stabilization;and those which help stabilization.The first group includes P₂O₅, SiO₂, Al₂O₃; the second group includes TiO₂; and the third group includes Fe₂O₃.Oxides preventing stabilization adversely affect deformation of the bodies under load, but increase the compressive strength. No general rale for the influence of these additions on the other properties of the products was evolved, which is probably connected with the different amounts and properties of the new phase which develops.Titania reduces the compressive strength but does not influence the other properties of zirconia.Oxides of iron, although they help stabilization of zirconia, lead to the formation of porous hearts in the products, which very adversely affects all properties of the products.According to the reduction of the working properties of the articles of ZrO₂ the admixtures investigated can be placed in the following order: phosphorus pentoxide, iron oxide, silica, titania and alumina.Commercial zirconia for the production of high-grade refractories should contain the minimum amount of impurities, the presence of phosphorus pentoxide, iron oxide, and silica being particularly undesirable.     

Development of iron oxide sorbents for Hg removal from coal derived fuel gas: Sulfidation characteristics of iron oxide sorbents and activity for COS formation during Hg removal

The aim of this study is to develop a process for the removal of Hg⁰ using H₂S over iron oxides sorbents, which will be located just before the wet desulfurization unit and catalytic COS converter of a coal gasification system. It is necessary to understand the reactions between the iron oxide sorbent and other components of the fuel gas such as H₂S, CO, H₂, H₂O, etc. In this study, the sulfidation behavior and activity for COS formation during Hg⁰ removal from coal derived fuel gas over iron oxides prepared by precipitation and supported iron oxide (1 wt% Fe₂O₃/TiO₂) prepared by conventional impregnation were investigated. The iron oxide samples were dried at 110 °C (designated as Fe₂O₃-110) and calcined at 300 and 550 °C (Fe₂O₃-300 and Fe₂O₃-550). The sulfidation behavior of iron oxide sorbents in coal derived fuel gas was investigated by thermo-gravimetric analysis (TGA). COS formation during Hg⁰ removal over iron oxide sorbents was also investigated using a laboratory-scale fixed-bed reactor. It was seen that the Hg⁰ removal activity of the sorbents increased with the decrease of calcinations temperature of iron oxide and extent of sulfidation of the sorbents also increased with the decrease of calcination temperature. The presence of CO suppressed the weight gain of iron oxide due to sulfidation. COS was formed during the Hg⁰ removal experiments over Fe₂O₃-110. However, in the cases of calcined iron oxides (Fe₂O₃-300, Fe₂O₃-550) and 1 wt% Fe₂O₃/TiO₂, formation of COS was not observed but the Hg⁰ removal activity of 1 wt% Fe₂O₃/TiO₂ was high. Both FeS and FeS₂ were active for Hg⁰ removal in coal derived fuel gas without forming any COS.     

Structural analysis of iron oxide coated n-silicon heterojunction photoanodes

The iron oxide/n-Si heterojunction electrode was investigated as a possible efficient photoanode with the iron oxide prepared under various conditions. The oxide structure was studied by RBS (Rutherford backscattering spectrometry) and XPS (X-ray photoelectron spectroscopy) techniques and the correlation between photocharacteristics and its oxide structure was discussed. The iron oxide prepared by thermal oxidation and reactive-evaporation methods. The photocurrent in a 0.2 mol dm^?3 KOH solution was found to strongly depend on the preparation of the iron oxide. The reactive-evaporated Fe₂O₃/n-Si electrode showed the most effective characteristics of photoresponse and the 60 min thermally oxidized Fe₂O₃/n-Si electrode gave the best results in the thermally oxidized oxide system. The compositional analysis by RBS indicated that the oxide is formed stoichiometrically as Fe₂O₃ and that small amounts of a heavy-mass and a tungsten impurity are present in the thermally oxidized and the reactive-evaporated oxides, respectively. The XPS analysis of the chemical state of the iron in the oxide showed that the chemical state of the iron oxide formed by thermal oxidation varies as a function of depth and that the iron oxide formed by reactive- evaporation is in a almost constant chemical state throughout the film.     

Sorption and thermal polymerization of vinyl monomers in low density polyethylene-iron (III) oxide composite

The nature of the species produced after sorption and thermal polymerization of acrylic acid, methyl methacrylate and 4-vinylpyridine in low density polyethylene-iron (III) oxide composite was investigated by Mössbauer and IR spectroscopies. The values of the Mössbauer parameters indicate no change in the oxidation state of iron (III) in the LDPE-Fe₂O₃ composite before and after sorption and thermal polymerization of the monomers. Acrylic acid interacts with iron (III) oxide particles yielding acrylates, hydroacrylates, polyacrylates and polyhydroacrylates. The iron (III) oxide particles remained unchanged after sorption and thermal polymerization of methyl methacrylate although some thermal polymerization is observed in the presence of Fe₂O₃-doped LDPE. Iron (III) oxide acts as catalyst for the radical polymerization of methyl methacrylate on LDPE-Fe₂O₃. The interaction of iron (III) oxide and 4-vinylpyridine after its sorption and thermal polymerization in LDPE-Fe₂O₃ is mainly by coordination bonding of the pyridine ring of the polymer to the iron of Fe₂O₃.     

Action of iron melts on spinel-periclase refractories

Conclusions Using methods of phase, chemical, x-ray, and petrographic analysis we investigated the reaction between melts of Fe₃O₄ and MgFe₂O₄ with certain compositions on the basis of the systems MgO-Al₂O₃-Cr₂O₃.The phase inversions with the action of the melt consist in the development of solid solutions between the spinel phase and the iron reagent.Destruction by the iron melt of the spinel phases in the system MgO-Al₂O₃-Cr₂O₃ is due to the laminating scaling of the solid solutions, expecially those enriched by MgCr₂O₄ which in a large degree is expressed in the MgCr₂O₄ itself. The cause of this is that owing to the sharp differences in the composition of the zones as a result of bad wetting of MgCr₂O₄ by the iron melt, apparently, we get substantial stresses which produce lamination of the scaly growths.In the system MgO-Al₂O₃-Cr₂O₃ the lower resistance to iron melts is possessed by compositions enriched with MgCr₂O₄.The free magnesia exerts a positive effect on the resistance of the spinels to the action of iron melts. However the worst properties, as previously, are shown by compositions enriched with MgCr₂O₄.The melt of MgFe₂O₄ gives rise to substantial volume changes in the reaction zone, and to a lower degree, the same destruction of the refractories as the magnetite melts.Our practical conclusions for the technology of refractories is to express a preference for the compositions with substantial preponderence of periclase over spinels, of which, in turn, the magnesia-alumina spinel should be preferred to compositions of the type periclase-chromite, when we are considering the thermal resistance of magnesia refractories working in conditions of iron-reagent action.     

Kinetic studies on the reactions involved in the hot gas desulfurization using a regenerable iron oxide sorbent—II: Reactions of iron sulfide with oxygen and sulfur dioxide

In the hot gas desulfurization process using iron oxide sorbent, the regeneration of the sulfided iron oxide sorbent consists of two reactions: the oxidation of iron sulfide with air, and its reaction with the sulfur dioxide formed during the air oxidation. This part describes the kinetic studies on the reactions of iron sulfide (formed by the reactions of Fe₂O₃ with H₂CO mixture and subsequendy with H₂S) with oxygen and sulfur dioxide. The experimental and analysis procedures used are similar to those outlined in Part I of this paper.The activation energies for the oxygen and the sulfur dioxide reactions are found to be 15.63 and 17.5 kcal/mol, respectively. Notably, the product oxides formed in the two cases are different. With air, the reaction is fast and the final product is Fe₂O₃, whereas with SO₂, the major product is Fe₃O₄, which slowly oxidizes to Fe₂O₃ in a secondary step. Also, in the latter reaction elemental sulfur is formed.     

氧化铁石墨固相还原非等温反应动力学

准确测试固固反应,如铁矿炭还原反应的动力学在科学研究和实际应用中均具有重要意义。利用热重程序升温的方法研究了氧化铁石墨还原的固固反应特性,在惰性气氛下分别考察了研磨与浸渍混合后焙烧制得的Fe₂O₃/C样品的失重曲线,采用Flynn-Wall-Ozawa公式和Coats-Redfern公式相结合的方法分别求算了两种混合样品的固固反应动力学参数,研究发现氧化铁在炭表面的聚集形态与其活化能变化规律直接相关,且浸渍焙烧法所得样品的活化能符合强吸热反应活化能变化规律。结合固体原位XRD表征与气体产物在线分析手段,发现在初始阶段Fe₂O₃即可与C直接反应生成Fe₃O₄和CO₂。该反应的活化能约为530 kJ·mol^-1,反应机理为二级化学反应模型。     

A study on the wetting behavior of liquid iron on forsterite,mullite, spinel and quasi-corundum substrates

Wetting characteristics of liquid iron on magnesia, alumina and silica mixture substrates were studied by sessile drop experiments. Chromium-free forsterite, mullite, spinel and quasi-corundum phases were selected as alternative refractories in MgO-Al₂O₃-SiO₂. Morphological changes of molten electrolytic iron on the oxide substrates were investigated via apparent contact angle measurements. The results showed that the wetting behavior was significantly influenced by FeO compounds that were formed via oxidation of the liquid iron. Morphologies of the reacted layer were studied by Scanning Electron Microscope (SEM)/EDX analysis. The ternary phases FeO-MgO-SiO₂ and FeO-Al₂O₃-SiO₂ improved the wetting of liquid iron on the forsterite and mullite substrates by providing liquid phases at solid (refractory)–liquid (iron) interfaces. However, corrosion by liquid iron was significantly inhibited at spinel phase which did not feature FeO based compounds at the interface. Quasi-corundum (10MgO-25SiO₂-65Al₂O₃) showed a much enhanced resistance to liquid iron compared to forsterite or mullite refractories.     

Preparation and formation mechanism of nano-iron oxide black pigment from blast furnace flue dust

A mixed solution of ferrous and ferric sulfate leached from blast furnace (BF) flue dust was used to prepare nanometer-sized iron oxide black pigment (Fe₃O₄, magnetite) by the co-precipitation method. The pH value played a very important role in affecting the color and particle size of Fe₃O₄ and the evolution of green rust in to Fe₃O₄ or FeOOH. The experimental conditions including the solution pH, the way of adding precipitant, volume of air and reaction time for the formation of nano-iron oxide black pigment were investigated carefully in order to determine the optimal ones. The color, morphology and particle size of as-prepared Fe₃O₄ pigment were characterized by means of a color measurement instrument, X-ray diffraction (XRD) and transmission electron microscopy (TEM) respectively. The results showed that the obtained pigment had low average spectral reflectance (<4%), good oil absorption (～23%), high black intensity and narrow size distribution of 60–70 nm. Furthermore, the formation mechanism of Fe₃O₄ from the mixed solution of ferrous and ferric sulfate was discussed.     

Catalytic Redox Transformations in Rock Matrices

The properties of catalytic systems based on iron oxide and inorganic matrices of oil-bearing rocks (basalt, clay, sandstone) in the decomposition of ammonium nitrate, oxidation of methane, and hydrocracking of asphaltenes were studied. The catalytic systems were iron oxide (hematite with a particle size of D = 11.0–20 nm, preparation temperature 453–473 K) fixed on matrices during co-hydrolysis of carbamide and iron chloride under hydrothermal conditions at temperatures of T = 433–473 K and pressures of 0.6–1.6 MPa. The iron oxide catalysts based on basalt and clay were most active in deep oxidation of methane (at 773 K, \({X_{C{H_4}}}\) = 83% and 72.9%, respectively); the Fe₂O₃/basalt and Fe₂O₃/sandstone systems were more active in the decomposition of ammonium nitrate. In hydrocracking of asphaltenes to maltenes, the catalyst activity decreased in the series Fe₂O₃/basalt > Fe₂O₃/clay > Fe₂O₃/sandstone, the iron oxide catalysts on clay being most selective. The obtained experimental data confirm that natural materials (oil-bearing rocks: basalt, clay, and sandstone) may be used for the development of catalytic systems for reactions in oil beds and of advanced technologies for increasing the oil recovery.     

Room temperature in situ chemical synthesis of Fe3O4/graphene

A simple, cost-effective, efficient, and green approach to synthesize iron oxide/graphene (Fe₃O₄/rGO) nanocomposite using in situ deposition of Fe₃O₄ nanoparticles on reduced graphene oxide (rGO) sheets is reported. In the redox reaction, the oxidation state of iron(II) is increased to iron(III) while the graphene oxide (GO) is reduced to rGO. The GO peak is not observed in the X-ray diffraction (XRD) pattern of the nanocomposite, thus providing evidence for the reduction of the GO. The XRD spectra do have peaks that can be attributed to cubic Fe₃O_4. The field emission scanning electron microscopy (FESEM) images show Fe₃O₄ nanoparticles uniformly decorating rGO sheets. At a low concentration of Fe²⁺, there is a significant increase in the intensity of the FESEM images of the resulting rGO sheets. Elemental mapping using energy dispersive X-ray (EDX) analysis shows that these areas have a significant Fe concentration, but no morphological structure could be identified in the image. When the concentration of Fe²⁺ is increased, the Fe₃O₄ nanoparticles are formed on the rGO sheets. Separation of the Fe₃O₄/rGO nanocomposite from the solution could be achieved by applying an external magnetic field, thus demonstrating the magnetic properties of the nanocomposite. The Fe₃O₄ particle size, magnetic properties, and dispersibility of the nanocomposite could be altered by adjusting the weight ratio of GO to Fe²⁺ in the starting material.     

Colored rubber vulcanizates with some magnetic properties

A new composite based on natural rubber vulcanizates loaded with the newly prepared iron oxide–aluminum oxide (Fe₂O₃·Al₂O₃) fillers were prepared and their physical and magnetic studies were investigated. The prepared fillers were evaluated as reinforcing fillers with some magnetic properties; these properties were dependent on the ratio of iron oxide to aluminum oxide in each prepared ratio of these fillers. Rheological properties of rubber mixes containing (1Fe₂O₃:3Al₂O₃) and (1Fe₂O₃:1Al₂O₃) fillers exhibited better properties than mixes containing (3Fe₂O₃:1Al₂O₃) and (α‐Fe₂O₃), which showed almost the same behavior. Physical properties such as tensile strength, stress at 100 and 200% strain, Young's modulus, and hardness were increased by increasing the volume fraction of the investigated fillers concentration in the mixed vulcanizates. Measured rheological and physical results were inversely related to the magnetic properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:494–505, 2006     

Characteristics of heat-insulating refractories produced by some foreign companies

Conclusions Studies were made of heat insulating aluminosilicate products produced by certain companies. The articles are divided into four groups. It is found that within the limits of any one group there is a substantial spread in the properties: strength, apparent density, and temperature of deformation.The main form of raw material for producing insulating products is kaolin, including beneficiated kaolin. Out of 22 specimens investigated eight contained no more than 0.64% Fe₂O₃, which is important for the service of the products in reducing atmospheres; the semiacid and kaolin products contained iron oxide varying in the range 1.0–1.5%.The use of pure kaolins and low-ash combustible additives in the production of insulating refractories contributes to the production of refractories with a low concentration of fusible impurities.Translated from Ogneupory, No. 8, pp. 57–59, August, 1972.     

Refractory materials based on ash-and-slag mixtures of the apatity thermoelectric plant

Experiments on magnetic separation of ash-and-slag mixtures (ASM) of the Apatity thermoelectric plant have shown that they contain easily separable magnetic and nonmagnetic phases with a yield of about 40 and 60%, respectively. The iron content in the fractions on conversion to Fe₂O₃ is 20 and 8% respectively. The magnetic fraction includes a highly magnetic part (about 5 wt.% of the total mass of the ASM) the iron content of which (Fe₂O₃) amounts to 44%. The nonmagnetic fraction of the ASM has been used for obtaining refractory materials with a strength and thermal insulation capacity much higher than that of chamotte refractories and the softening properties only somewhat inferior to the latter. The maximum operational temperature of the obtained materials is 1300°C.     

Hydrogen evolution on iron pyrite (FeSy) in sodium chloride solution

The sulphur derivatives of iron rust and a mixed iron oxide from the co-precipitation of Fe^II-Fe^III chlorides in 6M NaOH have been found to posses high hydrogen evolution in sodium chloride solution. The enhanced performance of these suphides for hydrogen evolution is observed to depend on the sulphide constituents, prepared by the combinations of Fe_1-x), α-Fe₂O₃ and Fe₃O₄ oxide mixtures, and reduced by hydrogen gas. Pyrite, prepared from iron rust-H₂S with optimum sulphide mixture, has the best performance for hydrogen evolution reaction (h.e.r.) of 100 MA/cm², -270mV vs scein 3.5% sodium chloride solution at 25°C after ohmic corrections.     

Analysis of Fe2O3 and Fe3O4 Dissolution Kinetics in Terms of the Chain Mechanism Model

Kinetic data on Fe₂O₃ and Fe₃O₄ dissolution in solutions of hydrochloric and sulfuric acids of different concentrations are analyzed in terms of the chain mechanism model at different solution temperatures under different conditions of synthesis of oxide samples. A kinetic model of dissolution of iron oxides is proposed. It is shown that features of the iron oxide dissolution kinetics are explained by the difference between the concentrations of dislocations and other defects on the surface of particles.     

Mullite refractories from bauxites of the iksinskoe deposit

Bauxites with 76% Al₂O₃ and 2.65% Fe₂O₃ were used to produce mullite refractories and mixtures for steel-teeming ladles. Tests in service have shown that the strength of these refractories is no worse than or comparable with that of refractories based on commercial alumina and Chinese bauxites.Translated from Ogneupory, No. 2, pp. 28–31, February, 1995.     

Wear and tear of refractories in blast furnaces when melting fluorine-containing iron ores

Conclusions We basically clarified the process of the destruction of refractories in various areas of blast furnaces using ferrugineous fluorine-containing ores and made recommendations with regard to the selection of refractories.A number of experiments were carried out in the laboratory on the study of the destructive effect of a gas mixture with hydrogen fluoride, fluorine-containing blast furnace slags and calcium fluoride on alumosilicate refractories; we have explained the mechanism of the destruction of refractories in the system of interaction between CaF₂ and Al₂O₃-SiO₂.     

The kinetics of the reduction of iron oxide by carbon monoxide mixed with carbon dioxide

Results are reported for the repeated reduction of iron oxide particles, 300–425 μm diameter, by a mixture of CO, CO₂, and N₂ in a fluidized bed of 20 mm internal diameter. The conclusions were as follows: (1) Reduction of either Fe₂O₃ to Fe₃O₄ or of Fe₃O₄ to Fe_0.947O is first‐order in CO. (2) With the particle sizes used, the rates of the reduction reactions are controlled by intrinsic chemical kinetics. Activation energies and pre‐exponential factors are reported. (3) The first cycle gave anomalous results, but (a) the rate of reduction of Fe₂O₃ to Fe₃O₄ remained constant over cycles 2–10; (b) the rate of reduction of Fe₃O₄ to Fe_0.947O declined by 60–85% over cycles 2–10. (4) The rates of reduction declined with solids conversion down to zero at 80% conversion. The rates were incorporated into a conventional model of a fixed bed, which was used to predict, satisfactorily, the reduction behavior of iron oxide. © 2009 American Institute of Chemical Engineers AIChE J, 2010