Sintering with Kovdor magnetite concentrates in the batch

Electron-microscope data show that the magnetite crystals in iron ore have different microstructure, depending on the temperature and time of ore formation. Thus, in sedimentary–metamorphic iron quartzites and magmatic skarns, the structure of the magnetite crystals is homogeneous and the composition is close to stoichiometric. In Kovdor ore, the magnetite crystals are heterogeneous. The matrix contains isomorphic Al, Mg, Ti, and other impurities as individual spinel microphases. The reduction of magnetite crystals in conditions that resemble sintering indicates that heterogeneous crystals disintegrate on sintering, with the formation of two ore phases: solid solutions of magnetite and wustite that are not involved in liquid-phase strengthening of the sinter. In the final stage of fluxed-sinter production, calcium–silicon silicate binders of melilite composition are formed in the product in place of the melt; these binders are not strong. On the basis of the research findings, it is important, in assessing iron-ore fields, to pay attention not only to the content of iron and silicon oxides in the ore but also to the structure of the magnetite crystals, since the iron in the magnetite determines the direction of melt formation in processing.     

Reduction by CO-CO2 and cracking of iron ore sinters,part 2: cracking

The cracking of iron ore sinters during their low-temperature reduction to magnetite, in the upper part of the blast furnace, is a considerable handicap for the operation of the furnace. However, in spite of numerous previous investigations, it is not fully understood. Dealing with two different sinters, a synthetic and an industrial one, their hematite was reduced to magnetite by CO-CO₂, with varied temperatures and gas compositions. Cracking is strongly favoured by low temperature and low CO partial pressure. Under such conditions, the cracks are initiated by localized nucleation and there is no need for extended stress along the hematite-magnetite interface. The crack propagation is independent of the hematite crystals orientation, and the glassy gangue grain boundaries easily transmit the stress.     

The apparent ’five-fold’ nature of large T2 (AI6Li3Cu) crystals

LargeT ₂ (Al₆Li₃Cu) crystals which display apparent five-fold symmetry have been studied using several different electron microscopy techniques. Electron microprobe X-ray analysis was used to determine the phases present in two different alloys cast with bulk compositions close to stoi-chiometricT ₂. Convergent beam electron diffraction (CBED) of these crystals indicates that they do not display five-fold rotational symmetry, and TEM images and selected area diffraction from thin foil specimens indicate a microcrystalline or twinned structure is responsible for the apparent five-fold symmetry ofT ₂. Microdiffraction patterns obtained from the thinnest regions of the crystals are consistent with a cubic structure having a lattice parameter of ≈0.40 nm.     

白光LED用LaPO4:Eu3+红色荧光粉的合成与表征

利用水热法制备了性能稳定的红色荧光粉LaPO4:Eu3+,同时研究了不同的Eu3+浓度、煅烧温度对荧光粉发光性能的影响.通过X射线粉末衍射(XRD)和扫描电子显微镜(SEM)来表征荧光粉的晶体结构和颗粒大小及形貌;用激发光谱和发射光谱以及荧光衰减曲线来表征荧光粉的荧光性能.结果表明:未煅烧时前躯体主要是六方晶相LaPO4·0.5H2O,煅烧温度在900℃时,所制备样品为单斜相LaPO4:Eu3+;SEM图像显示5 at.%Eu3+掺杂LaPO4呈椭球形,颗粒长约为500 nm,宽约为300 nm.最大发射波长和激发波长分别为592 nm和393 nm,发射光谱中592 nm和612 nm的发射峰对应的是Eu3+离子的5D0→7F1和5D0→7F2跃迁.其荧光寿命为3.32 ms.     

Micro and macroscopic aspects of shear band formation in internally nitrided single crystals of Fe-Ti-Mn alloys

The formation of localized shear bands in single crystals of internally nitrided alloys of Fe-Ti-Mn was studied experimentally and theoretically. The experimental studies included observation of the dislocation substructures that are formed at and near shear band/matrix interfaces along with documentation of the crystallography of the localized shearing process. Computational studies of tensile deformation of the crystals using the finite element method, that incorporated a large strain, strain rate dependent constitutive theory for crystalline slip, were carried out and the results were compared to the experimental observations. Mechanical tests, and in situ metallographic observations of shear band formation, showed that localized shearing occurs while the materials are continuously hardening and before “damage”, through microfracture, begins. Electron diffraction and imaging of the deformation substructures near shear band interfaces showed that an important part of the localization mechanism is nonuniform lattice reorientations that cause a “geometrical softening” of the lattice. The numerical studies are in good agreement with the experiments and demonstrate the role of material strain hardening and strain rate sensitivity.     

Hematite ore reduction to magnetite with CO/CO2 – kinetics and microstructure

Uncertainties and discrepancies are common in the first step of the reduction of hematite ore to magnetite, especially as regards the experimental conditions governing the transition from porous to lamellar magnetite. Hence the problem has been reinvestigated with an ore from Itabira (Brazil). This ore has been carefully characterized with X-ray diffraction, X-ray photoelectron spectroscopy, optical and scanning electron microscopy and electron microprobe analysis. It has been established that α-quartz and goethite are present, and iron combined on the surface with S or Si; most particles, in the range 50–200 μm, are hematite single crystals with 0.1% Al as the only substitution; there are also smaller crystals agglomerated by the gangue. Numerous experiments have shown that the transition from porous to dense lamellar magnetite is enhanced by an increase of temperature and a decrease of CO %. This is explained by a competition between the chemical reaction and solid state diffusion of ions along the hematite-magnetite interface. The shrinking-core model has been applied to the domain of porous magnetite, yielding a chemical rate constant ? = 15.5 exp (?69500/RT), roughly twice lower than in the reduction of hematite synthetic single crystals. The nucleation frequency increases sharply with temperature to ～700°C where it reaches ～10⁹ m^?2·s^?1, as with pure hematite.     

Lamellar stacking in three-dimensional crystals of Ca(2+)-ATPase from sarcoplasmic reticulum

Electron microscopy of multilamellar crystals of CA(2+)-ATPase currently offers the best opportunity for obtaining a high-resolution structure of this ATP-driven ion pump. Under certain conditions small, wormlike crystals are formed and provide views parallel to the lamellar plane, from which parameters of lamellar stacking can be directly measured. Assuming that molecular packing is the same, data from these views could supplement those obtained by tilting large, thin platelike crystals. However, we were surprised to discover that the lamellar spacing was variable and depended on the amount of glycerol present during crystallization (20% versus 5%). Projection maps (h,0,l) from these womklike crystals suggest different molecular contacts that give rise to the different lamellar spacings. Based on an orthogonal projection map (h,k,0) from collapsed, wormlike crystals and on x-ray powder patterns, we conclude that molecular packing within the lamellar plane is the same as that in thin, platelike crystals and is unaffected by glycerol. Finally, the orientation of molecules in the lamellar plane was characterized from freeze-dried, shadowed crystals. Comparing the profile of molecules in these multilamellar crystals with that previously observed in helical tubes induced by vanadate gives structural evidence of the conformational change that accompanies binding of calcium of Ca(2+)-ATPase.     

Transforming Hematite into Magnetite Using Mechanochemical Approach as a Pretreatment of Oolitic Hematite

Potential transformation of oolitic hematite into magnetite by mixing iron powder using the mechanochemical method has been achieved and discussed in this paper. The phase transition of pure hematite in the preliminary test was identified by X-ray diffractometer (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The experimental results have shown that the crystallographic planes of magnetite, (220), (311), (400), and (511) were observed clearly in the Fe/α-Fe₂O₃ mixture after milling for 15 h, indicating that α-Fe₂O₃ had been effectively transformed into Fe₃O₄. The diffraction peaks of magnetite were also observed at d = 0.29605 nm (2θ = 30.163°), 0.25226 nm (2θ = 35.559°), 0.24156 nm (2θ = 37.190°), and 0.20898 nm (2θ = 43.458°) after 13 h milling-time. It suggests that the oolitic hematite is transformed into magnetite successfully by mechanochemical processing. The processing might be applied potentially for the magnetic separation of oolitic hematite.     

Morphology of hematite to magnetite reduction zone

The reduction process of hematite to magnetite results in distinct changes in morphology of magnetite. These changes depend on structural properties of parent hematite and reduction conditions. The reduction experiments were performed in 3% CO and 97% CO₂ gas mixture at 450 and 850°C on selected crystals of natural hematite. The phase composition and morphological characteristics of the reduced layer were determined on the basis of microscopic analysis. Singular blasts or blastoidal colonies of magnetite were formed in 450°C on the boundaries of the hematite grains. They began to grow and joined the layer. Magnetite formed at 450°C is distinctly microporous. Cracks and desintegration of hematite grains appear together with reduction of hematite. At 850°C nucleation of the magnetite is quite different then at 450°C. The formation of singular magnetite lamellae or a palisade of crystallographically oriented magnetite lamellae were observed. Their growth results in the formation of the magnetite layer. Tunnel-shaped pores in magnetite layer show the same direction as lamellar front of reduction.     

Synthesis and characterization of BaCeO3 nanocrystals via solvothermal-based method

A facile approach to preparing well-dispersed nanocrystals of BaCeO3 was developed by a combination of solvothermal and annealing processes. The precursor consisted of amorphous BaCO3 and CeO2, and the conversion of the precursor to crystalline BafeO3 nanocrystals occurred upon heat treatment at a relatively low temperature. The as-processed BaCeO3 had an orthorhombic structure and the average size of such crystals was approximately 80 nm. The obtained products were characterized by Fourier Transform Infrared （FT-IR）, X-Ray Diffraction （XRD）, Laser Raman Spectroscopy （LRS）, Scanning Electron Microscopy （SEM）, Energy Dispersive X-Ray Spectrometry （EDS）, and Transmission Electron Microscopy （TEM）. This preparation process could also be used to synthesize doped barium cerate complex oxides Bafe0.95M0.05O3-δ （M=Y, Nd, Gd, and Sm）.     

Kinetics of the low-temperature hydrogen reduction of single-crystal magnetite

The hydrogen reduction of plates made from synthetic magnetite single crystals is studied in the temperature range 400–570°C. A mathematical model is developed and applied to describe the kinetics of gaseous reduction of plane finite objects. The following time contributions of individual process stages are distinguished with the least squares method and numerical integration: the nucleation of an iron phase, a chemical interaction of magnetite with hydrogen, and external and internal mass transfer. The diffusion and kinetic reduction parameters are calculated. The activation energy of the chemical stage (87.5 kJ/mol) is determined. An equation for the rate constant of the interaction of magnetite with hydrogen is proposed for temperatures below 570°C. A significant effect of the processes of consolidation and sintering of reduced iron on the internal diffusion parameters is detected in the low-temperature range.     

The chitin crystallite in arthropod cuticle

Electron microscopy has revealed that chitin from a representative selection of insect orders (plus one crustacean and one arachnid) is localized in crystallites about 2.8 nm across. Furthermore, these crystallites are arranged on an hexagonal or pseudo-hexagonal lattice, the lateral order of which varies considerably. The lattice becomes secondarily reoriented during cuticle expansion following an ecdysis. The size of the 'unit cell' has been measured both by optical diffraction and direct measurements of the micrographs, permitting an estimate of the chitin and resilin content for locust rubberlike cuticle. The number of poly-N-acetyl-glucosamine chains per sheet and sheets per crystallite can be estimated from the physical dimensions of the crystallite. Each crystallite is unlikely to comprise more than 3 sheets and 6 chains per sheet. The calculated and measured density of alpha-chitin can be shown to be in close agreement.     

Process mineralogy of suspended particles from a simulated commercial flash smelter

Polished sections of pyrometallurgical intermediate products from a simulated commercial flash furnace were examined by reflected light microscopy, scanning electron microscopy-energy dispersive spectrometry and electron backscatter analysis, and microprobe analysis for phase and textural relationships. The smelter feed is a copper concentrate from a porphyry copper deposit. The concentrate consists primarily of chalcopyrite, bornite, and pyrite with smaller amounts of covellite, chalcocite, molybdenite, magnetite, galena, and sphalerite. The flash furnace reactions for pyrite and chalcopyrite can be observed by reflected light microscopy. Reacted angular particles of pyrite exhibit successive rims of fibrous pyrrhotite and hematite or magnetite. Reacted angular chalcopyrite particles show successive rims of bornite, digenite, and chalcocite. Spherical particles, formed by the complete melting of former pyrite and chalcopyrite particles, consist of variable amounts of granular pyrrhotite with magnetite rims and minor hematite. Spherical particles, formed by the complete melting of former chalcopyrite particles, exhibit exsolution intergrowths with varying proportions of intermediate solid solution, bornite, digenite, and chalcocite, and have rims of hematite, magnetite, and copper-iron spinel. Electron microprobe analyses show that the iron oxides contain significant copper and minor zinc in their structures. Sphalerite and molybdenite do not show evident mineralogical reactions.     

The 3.0 A projection structure of microsomal glutathione transferase as determined by electron crystallography of p 21212 two-dimensional crystals

Two-dimensional crystals of rat microsomal glutathione transferase were grown during dialysis of detergent-solubilized enzyme after addition of a small amount of phospholipid. The crystals had two-sided plane group symmetry p21212 with a calibrated unit cell size of a=91.90 A, b=90.83 A. Electron diffraction patterns were recorded showing significant reflections extending to 3.0 A. A combination of these structure factor amplitudes with phases from high-resolution images following image processing was used to calculate a projection map of the protein. The asymmetric unit of the structure consists of three microsomal glutathione transferase molecules. The local 3-fold axis at the center of the trimer is delineated by six parallel alpha-helices, two from each monomer. The two helices differ significantly in their respective projection structure. The inner helical core of the trimer is partly surrounded by elongated domains with extensions towards the helices and which contain resolved density maxima at a spacing of 4 to 5 A. A well-defined strong peak is localized close to the elongated domain and at a distance of about 9.5 A from two of the inner helices.     

The stiffness of skeletal muscle in isometric contraction and rigor: the fraction of myosin heads bound to actin

Step changes in length (between -3 and +5 nm per half-sarcomere) were imposed on isolated muscle fibers at the plateau of an isometric tetanus (tension T0) and on the same fibers in rigor after permeabilization of the sarcolemma, to determine stiffness of the half-sarcomere in the two conditions. To identify the contribution of actin filaments to the total half-sarcomere compliance (C), measurements were made at sarcomere lengths between 2.00 and 2.15 microm, where the number of myosin cross-bridges in the region of overlap between the myosin filament and the actin filament remains constant, and only the length of the nonoverlapped region of the actin filament changes with sarcomere length. At 2.1 microm sarcomere length, C was 3.9 nm T0(-1) in active isometric contraction and 2.6 nm T0(-1) in rigor. The actin filament compliance, estimated from the slope of the relation between C and sarcomere length, was 2.3 nm microm(-1) T0(-1). Recent x-ray diffraction experiments suggest that the myosin filament compliance is 1.3 nm microm(-1) T0(-1). With these values for filament compliance, the difference in half-sarcomere compliance between isometric contraction and rigor indicates that the fraction of myosin cross-bridges attached to actin in isometric contraction is not larger than 0.43, assuming that cross-bridge elasticity is the same in isometric contraction and rigor.     

Convergent beam electron diffraction analysis of theT 1 (Al2CuLi) phase in Al-Li-Cu alloys

Point and space group analysis of largeT ₁ (Al₂CuLi) crystals was performed by convergent beam electron diffraction. The structure ofT ₁ was determined to be hexagonal, possessing a 6/mmm point group and P6/mmm (No. 191) space group. The lattice constants were found to bea ≈ 0.497 nm andc ≈ 0.93 nm. This structure is in agreement with an existing model of T₁, although discrepancies between the observed and calculated intensities of certain reflections were evident. Electron probe X-ray microanalysis of theseT ₁ crystals indicates the composition is on the copper-rich side of stoichiometric Al₂CuLi. The slight deviation in the composition ofT ₁ from stoichiometry and the presence of planar defects in the microstructure may account for the discrepancy in the intensity of certain reflections.     

Influence of age and processing stage on visual word recognition.

Used a lexical-decision task in 3 different experiments to examine whether age differences in word recognition were consistent across processing stage. In all experiments, word frequency and length were manipulated. In Exps 1 and 2, encoding difficulty was varied, and in Exp 3, response selection difficulty was varied. In all 3 experiments, there were no age differences for word frequency. However, in Exps 1 and 2, older adults showed a larger decrement for encoding. In Exp 3, age differences were larger when response selection load increased. These results suggest that age differences in word recognition occur because older adults exhibit primarily peripheral- rather than central-processing decrements. The implications of these data for generalized and localized slowing models are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Oxidation of magnetite

The oxidation of large octahedral single crystals of magnetite extracted from chlorite shale at Shabrovsk talc mine (Middle Urals) is experimentally studied. Differential heating curves show that the processes occurring in the oxidative roasting of magnetite (Fe₃O₄) are highly reproducible. The mechanism of martensite oxidation is considered, as well as the temperature ranges corresponding to exothermal and endothermal reactions. The thermal effect of martensite oxidation is determined from that of a standard (CaCO₃) and the areas under the differential heating curves on the corresponding thermograms. Those areas are proportional to the thermal effect. The results obtained are of considerable interest: knowing the temperature range of martensite oxidation, the heat sources in the various technological zones of the conveyer roasting machines may be taken into account in establishing the roasting conditions, thereby optimizing the thermal conditions and reducing the fuel consumption.     

Process mineralogy of suspended particles from a simulated commercial flash smelter

Polished sections of pyrometallurgical intermediate products from a simulated commercial flash furnace were examined by reflected light microscopy, scanning electron microscopy-energy dispersive spectrometry and electron backscatter analysis, and microprobe analysis for phase and textural relationships. The smelter feed is a copper concentrate from a porphyry copper deposit. The concentrate consists primarily of chalcopyrite, bornite, and pyrite with smaller amounts of covellite, chalcocite, molybdenite, magnetite, galena, and sphalerite. The flash furnace reactions for pyrite and chalcopyrite can be observed by reflected light microscopy. Reacted angular particles of pyrite exhibit successive rims of fibrous pyrrhotite and hematite or magnetite. Reacted angular chalcopyrite particles show successive rims of bornite, digenite, and chalcocite. Spherical particles, formed by the complete melting of former pyrite and chalcopyrite particles, consist of variable amounts of granular pyrrhotite with magnetite rims and minor hematite. Spherical particles, formed by the complete melting of former chalcopyrite particles, exhibit exsolution intergrowths with varying proportions of intermediate solid solution, bornite, digenite, and chalcocite, and have rims of hematite, magnetite, and copper-iron spinel. Electron microprobe analyses show that the iron oxides contain significant copper and minor zinc in their structures. Sphalerite and molybdenite do not show evident mineralogical reactions.