Catalytic activity of aluminium and copper-doped magnetite in the high temperature shift reaction

Aluminium and copper-doped magnetite was evaluated as high temperature shift catalyst and compared with a hematite-based sample. The first one is less active but can save energy in industrial processes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Interplay of surface conditions, particle size, stoichiometry, cell parameters, and magnetism in synthetic hematite-like materials

We have studied several synthetic hematite-like materials, produced via different reactions using various hydrothermal conditions and various temperatures of annealing in air, by bulk elemental analysis, weight loss measurements, scanning electron microscopy, powder X-ray diffraction, Mössbauer spectroscopy, and SQUID magnetometry. We conclude that hematite-like materials cannot be related to pure stoichiometric hematite via a single stoichiometric or physical parameter and that at least two degrees of freedom are required. This is most clearly seen when we introduce a plot of the cell parameter c versus the cell parameter a on which hematite-like materials do not fall on a single line but occupy an entire region that is bounded by hydrohematite-hematite and protohematite-hematite lines. A Morin transition boundary on this c-a plot separates a region where Morin transitions occur from a larger region where Morin transitions do not occur down to 4.2 K. Previous claims that particle size is the dominant factor controlling the Morin transition are understood in terms of correlations between stoichiometry and particle size that are produced at synthesis. Changing contents of incorporated molecular water and structural hydroxyls with associated cation vacancies have different characteristic effects on the crystal structure and move the sample coordinates in different directions on a c-a plot. It is also shown that an accessory sulphate content is adsorbed on the individual hematite crystallites and is not structurally incorporated. Mössbauer spectroscopy is used, as usual, to identify and characterize the spin structure. In addition, hyperfine field distributions from room temperature spectra, extracted by a new method, give a sensitive measure of sample conditions but not a unique one since several factors affect the extracted distributions in similar ways.     

NaCl与Fe2O3混合物对SO2的有效吸收

采用DRIFTS和XPS等方法研究了SO2在NaCl和α-Fe2O3混合物表面的复相反应, 并计算了反应的吸附常数. 结果表明, 反应生成物主要为硫酸盐、硫酸氢盐以及少量的亚硫酸(氢)盐; SO2与NaCl和α-Fe2O3混合物的反应符合零级反应动力学规律; NaCl的含量对反应有影响, 随着混合物中NaCl含量的增加, BET吸附常数呈现先上升而后再下降的变化规律, 当NaCl的质量分数达到70%左右时, BET吸附常数达到最大(4.62×10-6), 是纯α-Fe2O3(5.72×10-7)的8.08倍; 反应生成的FeCl2-SO3-中间体作为SO2的储存库, 促进了更多的硫酸盐生成.     

Use of Emanation Thermal Analysis in Characterisation of Nanosized Hematite Prepared by Dry Grinding of Goethite

Hematite nanoparticles of narrow size distribution were prepared by grinding of goethite. Intermediate and final products of grinding were characterised by different techniques, including the less-common emanation thermal analysis (ETA). ETA was shown to be a useful technique for characterising processes of surface annealing, initial sintering and growth of hematite particles under in situ conditions of thermal treatment. A good agreement was found between results of ETA, TG, XRD, IR spectrometry, transmission electron microscopy and scanning electron microscopy, used for characterisation of thermal behaviour of the goethite samples ground for varying time (0–70 h). This revised version was published online in August 2006 with corrections to the Cover Date.     

Spectroscopic method for the determination of crystallinity of hematite

The thermal transformation of goethite to hematite and the temperature dependence of the degree of crystallinity have been investigated using transmission and diffraction electron microscopy and infrared spectroscopy. The electron microscopy results reveal that the treatment of natural goethite by NaOH or citrate dithionite-bicarbonate (CDB) has no effect on its structure but leads to increase in the crystallinity of the ore. On the other hand, heat treatment of the untreated or treated sample is found to convert goethite ore to hematite with increase in its crystallinity. An infrared spectroscopic technique is applied for quantitative calculation of the crystallinity changes.     

巴西赤铁矿富矿粉直接还原试验研究

对粒度不大于4mm赤铁富矿粉原矿进行压球直接还原试验研究，以烧结常用的赤铁矿富矿粉和还原剂（碎焦粉或烟煤）为原料，采用复合型粘结剂进行压球试验。实验结果表明，成型球在1150～1280℃直接还原时，基本无粘结现象。因而可在较简易条件下实现生产DRI的目的。     

高分子絮凝剂在赤铁矿和尾矿表面的吸附动力学

应用紫外－可见光分光光度计，采用淀粉－三碘络合物显色法，对阴离子聚丙烯酰胺Magnafloc139、Magnafloc525和 M1017在赤铁矿和尾矿表面的吸附动力学进行了详细的研究，获得一些规律性的认识，可为实际生产应用奠定基础，提供科学依据。     

α—Fe2O3超微粒的制备及其气敏性能的研究

本文采用制备超微粒的方法制得α—Fe_2O_3,并用该材料制作成α-Fe_2O_3系气敏元件。由该材料及添加微量元素后所制作的元件对乙醇有良好的选择性和灵敏度。文中同时也讨论了不同加热功率、不同的电极材料对元件气敏性能的影响。并对α-Fe_2O_3的气敏机理作了扼要的讨论。     

Artificial neural network approach to assess selective flocculation on hematite and kaolinite

Because of the current depletion of high grade reserves, beneficiation of low grade ore, tailings produced and tailings stored in tailing ponds is needed to fulfill the market demand. Selective flocculation is one alternative process that could be used for the beneficiation of ultra-fine material. This process has not been extensively used commercially because of its complex dependency on process parameters. In this paper, a selective flocculation process, using synthetic mixtures of hematite and kaolinite in different ratios, was attempted, and the adsorption mechanism was investigated by Fourier transform infrared (FTIR) spectroscopy. A three-layer artificial neural network (ANN) model (4-4-3) was used to predict the separation performance of the process in terms of grade, Fe recovery, and separation efficiency. The model values were in good agreement with experimental values.     

Synthesis and Characterization of a Novel Ternary Hematite Nanocomposites Structure with Fullerene and 2D‐Electrochemical Reduced Graphene Oxide for Superior Photoelectrochemical Performance

In this study, a novel ternary hematite nanocomposites photoanode structure with superior photoelectrochemical (PEC) performance consisting of fullerene (C₆₀) and 2D‐electrochemical reduced graphene oxide (eRGO) used as the effective surface passivators is developed. The introduction of both the electron scavenging C₆₀ and highly conducting eRGO has mitigated the high interfacial recombination rate of hematite and led to the superior enhancement in PEC performance. UV–vis analysis reveals that the incorporation of C₆₀ and eRGO can provide a stronger light absorption at the visible light (400 nm < λ < 700 nm) and near infrared (IR) region (λ > 700 nm). Through the electrochemical impedance spectroscopy measurements, it can be concluded that the introduction of C₆₀ and eRGO onto hematite photoanode improves electron transfer and collection, reduces charge‐carrier recombination efficiency, and enhances PEC activity. The resultant ternary hematite photoanode structure exhibits 16.8‐fold enhancement in photocurrent density and 0.8‐fold reduction in charge transfer resistance when compared to the bare hematite structure only. This study has shown that the application of C₆₀, 2D‐eRGO, or in combination as a ternary structure provides the plasmonic effect that can enhance the PEC performance in hematite photoanode structure.