Oxygen Content of Nickel Ferrites at 1300°C

The oxygen contents for compositions with the spinel structure in the system Fe-Ni-O were determined at 13OO°C for oxygen pressures from 10^−3.6 to 10°atm. The ferrite region, from an Fe/Ni ratio of 2.035 to magnetite, was investigated. Below Fe/Ni = 2.5 only oxygen-deficient ferrites exist. Above Fe/Ni = 7.6 only ferrites with an oxygen excess were found and for the intermediate nickel contents, ferrites with both types of oxygen nonstoichiometry were found. Previous phase equilibria studies, which do not report single-phase ferrite with an oxygen deficiency, are discussed.     

Solubility and Aging of Calcium Silicate Hydrates in Alkaline Solutions at 25°C

Calcium silicate hydrate (C-S-H) gels are the principal bonding material in portland cement. Their solubility properties have been described, enabling pH and solubilities to be predicted. However, the gels also interact with other components of cements, notably alkalis. C-S-H has been prepared from lime and silicic acid in solutions of sodium hydroxide or potassium hydroxide and by the hydration of tricalcium silicate (C₃S) in sodium hydroxide solutions. Analyses of aqueous phases in equilibrium with 85 gels show that the aqueous calcium and silicon concentrations fit smooth curves over the range of increasing sodium concentrations. Where anomalous data occur, they correspond to solids with low lime contents: such gels are tentatively assumed to fall into a region where the presence of another gel phase influences the aqueous composition. Dimensional changes have been observed in the hydration products of C₃S as a function of alkali content and these may be relevant to the alkali-silica reaction. The significance of this and other data is discussed with reference to real cement systems.     

Structure of Borosilicate and Borogermanate Melts at 1300°C; a Viscosity and Density Study

An improved counterbalanced sphere viscometer-densitometer was used to obtain information at temperatures between 1000° and 1400°C for (a) molten B₂O₃, (b) a series of borosilicate melts containing up to 55 mole % SiO₂, and (c) a series of borogermanate melts containing up to 65 mole % GeO₂. The dependence on composition of these structure-sensitive parameters was used to develop a model for the alteration of molten B₂O₈ by other network-forming species. The B/Si or B/Ge ratio is shown to be a significant factor in determining melt structure. The silicon (or germanium) atoms appear to be widely separated in the B₂O₂ solvent for compositions in the 0 to 10-20 mole % SiO₂ (or GeO₂) region. The evidence suggests that a gradual microclustering of SiO₂ (or GeO₂) accompanies moderate departures from ideality for B₂O₃ in the 10-20 to 60 mole % SiO₂ (or GeO₂) region. Extensive micro-clustering of SiO₂ (or GeO₂), approaching network formation, appears to occur in the 60 to 100 mole % SiO₂ (or GeO₂) region; some of the boron atoms remain in clusters and/or are forced to adopt a tetrahedral configuration in this region.     

Use of Mixed-Rare-Earth Oxide in the Preparation of Reaction-Bonded Mullite at ≤1300°C

A process for production of near-net-shape mullite-matrix ceramic composites at ≤1300°C has been achieved by reaction-bonding Al₂O₃, silicon, mullite seeds, and eutectics of Al₂O₃–SiO₂–mixed-rare-earth oxide. The fusion temperature of the eutectic composition utilized is 1175°C. This liquid phase facilitates silicon oxidation, mullitization, and sintering. Mullite phase develops with low residual Al₂O₃ when 7.5 wt% mixed-rare-earth oxide and 5 wt% mullite seeds are used. The final sinter is >90% of theoretical density, >90% mullite (by quantitative XRD), and suffers 2.2% sintering shrinkage.     

Effect of Yttria and Yttrium-Aluminum Garnet on Densification and Grain Growth of Alumina At 1200°–1300°C

Densification and grain growth of alumina were studied with yttria or yttrium-aluminum garnet (YAG) additives at the relatively low temperatures of 1200°–1300°C. Yttria doping was found to inhibit densification and grain growth of alumina at 1200°C and, depending on dopant level, had a lesser effect at 1300°C. At 1200°C, yttria inhibits densification more than it hinders grain growth. The rate of grain growth increases faster with temperature than the rate of densification. Alumina-YAG particulate composites were difficult to sinter, yielding relative densities of only 65% and 72% after 100 h at 1200° and 1300°C, respectively. Pure YAG compacts exhibited essentially no densification for times up to 100 h at 1300°C.     

Air oxidation of Beypazari lignite at 50°C, 100°C and 150°C

Structural changes occurred in Beypazari lignite while oxidizing at 50°C, 100°C and 150°C in a dynamic air atmosphere was detected by infrared spectroscopy. Relative changes in the amount of various oxygenated functional groups with respect to time were determined by curve resolution procedures. Investigation of the spectra of the samples at different oxidation conditions reveal that as the duration and temperature of the oxidation reactions increased the absorption in the aliphatic C–H stretching region decreased, while the absorption in the C=O stretching region presented a significant increase.     

Limits of the Thermodynamic Stability of Cobalt—Iron—Manganese Mixed Oxides at 1200°C

The thermodynamic stability of spinel and rock-salt structure phases has been investigated for the quasi-ternary mixed oxide system Co-Fe-Mn-O at 1200°C and at total pressures of the order of 1 atm (∼1.01 × 10⁵ Pa) using thermogravimetric and electrical conductivity measurements. The results reveal the stability limits of the spinel and rock-salt structure phases with varying cationic composition and oxygen partial pressure at 1200°C. The oxygen partial pressure was varied over 12 orders of magnitude, from log₁₀ a _o2= 0 to log₁₀ a _o2= -12, by using CO/CO₂ and N₂/O₂ gas mixtures and monitored by an electrochemical, stabilized zirconia-based EMF cell. The maximum cobalt mole fraction used in the investigation was about 0.33.     

焦炉煤气生产直接还原铁试验与研究新进展

分析了焦炉煤气生产直接还原铁没有发展起来的原因,介绍了焦炉煤气生产直接还原铁的4种工艺流程及国内外用焦炉煤气生产直接还原铁试验与研究进展情况等,认为山西省具备了用焦炉煤气大规模生产直接还原铁的基本条件,应积极争取条件,大规模发展焦炉煤气生产直接还原铁。     

Lanthanum-titanium-aluminum oxide: A novel thermal barrier coating material for applications at 1300 °C

Considerable efforts are being invested to explore new thermal barrier coating (TBC) materials with higher temperature capability to meet the demand of advanced turbine engines. In this work, LaTi₂Al₉O₁₉ (LTA) is proposed and investigated as a novel TBC material for application at 1300 °C. LTA showed excellent phase stability up to 1600 °C. The thermal conductivities for LTA coating are in a range of 1.0-1.3 W m⁻¹ K⁻¹ (300-1500 °C) and the values of thermal expansion coefficients increase from 8.0 to 11.2 × 10⁻⁶ K⁻¹ (200-1400 °C), which are comparable to those of yttria stabilized zirconia (YSZ). The microhardness of LTA and YSZ coatings were in the similar level of ∼7 GPa, however, the fracture toughness value was relatively lower than that of YSZ. The lower fracture toughness was compensated by the double-ceramic LTA/YSZ layer design, and the LTA/YSZ TBC exhibited desirable thermal cycling life of nearly 700 h at 1300 °C.     

Oxidation Behavior of Boron-Modified Mo5Si3 at 800°–1300°C

Mo₅Si₃ shows promise as a high-temperature creep-resistant material. The high-temperature oxidation resistance of Mo₅Si₃ has been found to be poor, however, limiting its use in oxidizing atmospheres. Undoped Mo₅Si₃ exhibits pest oxidation at 800°C. Mass loss occurs in the temperature range 900°–1200°C due to volatilization of molybdenum oxide, indicating that the silica scale that forms does not provide a passivating layer. The addition of boron results in protective scale formation and parabolic oxidation kinetics in the temperature range of 1050°–1300°C. The oxidation rate of Mo₅Si₃ was decreased by 5 orders of magnitude at 1200°C by doping with less than 2 wt% boron. Boron doping eliminates catastrophic pest oxidation at 800°C. The mechanism for improved oxidation resistance of borondoped Mo₅Si₃ is viscous sintering of the scale to close pores that form during the initial transient oxidation period, due to volatilization of molybdenum oxide.     

Subsolidus Phase Relationships in the System Fe2O3–Al2O3–TiO2 between 1000° and 1300°C

Subsolidus phase equilibria in the system Fe₂O₃–Al₂O₃–TiO₂ were investigated between 1000° and 1300°C. Quenched samples were examined using powder X-ray diffraction and electron probe microanalytical methods. The main features of the phase relations were: (a) the presence of an M₃O₅ solid solution series between end members Fe₂TiO₅ and Al₂TiO₅, (b) a miscibility gap along the Fe₂O₃–Al₂O₃ binary, (c) an α-M₂O₃( ss ) ternary solid-solution region based on mutual solubility between Fe₂O₃, Al₂O₃, and TiO₂, and (d) an extensive three-phase region characterized by the assemblage M₃O₅+α-M₂O₃( ss ) + Cor( ss ). A comparison of results with previously established phase relations for the Fe₂O₃–Al₂O₃–TiO₂ system shows considerable discrepancy.     

C207和C301甲醇催化剂精制气高氢还原浅析

介绍C207和C301甲醇催化剂的还原经验和使用情况。应用精制气高氢还原,催化剂具有起始还原温度低、出水集中在低温段、还原时间短、易操作等特点。还原后的催化剂活性好,使用寿命长,1炉催化剂可使用3年左右。     

Decomposition of Carbon Dioxide to Carbon with Active Wustite at 300°C

Active wustite (FeδO, with a δ value of 0.98) was prepared by keeping normal wustite (δ value of 0.94) in a N₂ atmosphere at 300°C for 10 min. This reaction is given by (4δ₂–3)Fe_δ1O→(4δ₁–3)Fe_δ2O + (δ₂–δ₁)Fe₃O₄ where δ₁= 0.94 and δ₂= 0.98. The equation indicates that the normal wustite undergoes eutectoid decomposition into active wustite and stoichiometric magnetite (Fe₃O₄). Carbon dioxide (1.013 × 10⁵ Pa) was almost completely (100%) decomposed into carbon (zero valence) by the active wustite at the low temperature of 300°C, which was associated with the transformation of the active wustite into the stoichiometric magnetite. The internal pressure of the reaction cell eventually became a vacuum.     

Oxygen reduction reaction on electrodeposited zinc oxide electrodes in KCl solution at 70 °C

The reduction of oxygen was studied in 0.1 M KCl at 70 °C using the rotating disk electrode (RDE) technique on platinum and electrodeposited ZnO thin film electrodes deposited on platinum substrates. In the absence of Zn²⁺ ions in solution, a Tafel slope of 139 mV dec⁻¹ was obtained, a value close to that measured on bare platinum electrode (133 mV dec⁻¹) and ascribed to the limitation of the reaction rate by the first electron transfer. The main difference between the noble metal and the oxide electrode was a shift of the curves towards more negative potentials. In the presence of Zn²⁺ ions, the current density decreased significantly and the Tafel slope was measured at 282 mV dec⁻¹ showing that the electrode was partially blocked by zinc oxide formation reaction intermediates.     

Mechanical Behavior at 20° and 1200°C of Nicalon-Silicon-Carbide-Fiber-Reinforced Alumina-Matrix Composites

Tensile and fracture tests were conducted at 20° and 1200°C on a ceramic-matrix composite that was composed of an alumina (Al₂O₃) matrix that was bidirectionally reinforced with 37 vol% silicon carbide (SiC) Nicalon fibers. The composite presented nonlinear behavior at both temperatures; however, the strength and toughness were significantly reduced at 1200°C. In accordance with this behavior, matrix cracks were usually stopped or deflected at the fiber/matrix interface, and fiber pullout was observed on the fracture surfaces at 20° and 1200°C. The interfacial sliding resistance at ambient and elevated temperatures was estimated from quantitative microscopy analyses of the saturation crack spacing in the matrix. The in situ fiber strength was determined both from the defect morphology on the fibers and from the size of the mirror region on the fiber fracture surfaces. It was shown that composite degradation at elevated temperature was due to the growth of defects on the fiber surface during high-temperature exposure.     

Equilibrium Relations in the System NiO–TiO2 in the Temperature Range 1300° to 1750°C

Phase relations in the system NiO–TiO₂ have been determined by heating oxide mixtures in air at selected temperatures in the range 1300° to 1750°C for sufficient periods of time to attain equilibrium, followed by rapid quenching to room temperature. The phases have been characterized by optical microscopy, X-ray diffraction, and electron microprobe analysis. The most striking feature is the presence, above 1430°C, of a spinel-type phase that decomposes below this temperature to a mixture of remnant spinel, NiO of periclase-type structure, and NiTiO₃ of ilmenite-type structure. There are two peritectic points in the system, one at 1730°C where spinel, NiO, and liquid coexist in equilibrium, and one at 1610°C where spinel, NiTiO₃, and liquid are the coexisting phases. A eutectic is present at 1570°C, with NiTiO₃, rutile, and liquid coexisting in equilibrium. Rapid transformation of the spinel phase, even during rapid quenching, imposes uncertainties on the interpretation of the experimental data obtained, but the equilibrium-phase relations are deduced essentially as shown in the phase diagram presented. Results of a small number of calculated activities of NiO in oxide-phase assemblages involving the spinel phase at high temperatures (∼1500°C) lend support to the interpretation of the phase relations as presented in this paper.