Pressure effect on the electronic structure of iron in (Mg,Fe)(Si,Al)O3 perovskite: a combined synchrotron Mössbauer and X-ray emission spectroscopy study up to 100 GPa     

J. Li  W. Sturhahn  J. M. Jackson  V. V. Struzhkin  J. F. Lin  J. Zhao  H. K. Mao  G. Shen 《Physics and Chemistry of Minerals》2006,33(8-9):575-585

We investigated the valence state and spin state of iron in an Al-bearing ferromagnesian silicate perovskite sample with the composition (Mg_0.88Fe_0.09)(Si_0.94Al_0.10)O₃ between 1 bar and 100 GPa and at 300 K, using diamond cells and synchrotron Mössbauer spectroscopy techniques. At pressures below 12 GPa, our Mössbauer spectra can be sufficiently fitted by a “two-doublet” model, which assumes one ferrous Fe²⁺-like site and one ferric Fe³⁺-like site with distinct hyperfine parameters. The simplest interpretation that is consistent with both the Mössbauer data and previous X-ray emission data on the same sample is that the Fe²⁺-like site is high-spin Fe²⁺, and the Fe³⁺-like site is high-spin Fe³⁺. At 12 GPa and higher pressures, a “three-doublet” model is necessary and sufficient to fit the Mössbauer spectra. This model assumes two Fe²⁺-like sites and one Fe³⁺-like site distinguished by their hyperfine parameters. Between 12 and 20 GPa, the fraction of the Fe³⁺-like site, Fe³⁺/∑Fe, changes abruptly from about 50 to 70%, possibly due to a spin crossover in six-coordinate Fe²⁺. At pressures above 20 GPa, the fractions of all three sites remain unchanged to the highest pressure, indicating a fixed valence state of iron within this pressure range. From 20 to 100 GPa, the isomer shift between the Fe³⁺-like and Fe²⁺-like sites increases slightly, while the values and widths of the quadruple splitting of all three sites remain essentially constant. In conjunction with the previous X-ray emission data, the Mössbauer data suggest that Fe²⁺ alone, or concurrently with Fe³⁺, undergoes pressure-induced spin crossover between 20 and 100 GPa.  相似文献   

Quantification of electron microprobe compositional maps of rock thin sections: an optimized method and examples   总被引：1，自引：0，他引：1  

V. DE ANDRADE  O. VIDAL  E. LEWIN  P. O'BRIEN  P. AGARD 《Journal of Metamorphic Geology》2006,24(7):655-668

Quantification of discrete pressure–temperature domains in deformed chlorite + white mica‐bearing metapelites was undertaken on mineral compositions derived by two‐dimensional microprobe compositional mapping of selected areas of rock thin sections. In order to achieve compositional information at sufficient analytical precision, spatial resolution and sample coverage within a typical analysis time of 1 day, an optimization of measurement methods was necessary. The method presented here allows collection of raw counts for eight different element concentrations at an analytical precision of ～1–2 wt%. X‐ray intensity multiplane maps (one map per measured chemical element) are translated into concentration multiplane maps, utilizing selected conventionally measured spot analyses combined with the Castaing approximation for each mineral. As this step requires identification of the different minerals present in the mapped area, a statistical clustering technique to identify different groups of composition was developed, guided by simple petrographic inspection of the thin section, to delineate the important minerals in the mapped area. Finally, the compositions of each pixel are translated into a mineral structural formula thus yielding a new kind of image with a high content of petrological information. The reliability of the mineral composition images was emphasized by carrying out precision tests on the analytical data. The possible use of chemical maps to infer the P–T–deformation history of metamorphic rocks is illustrated with two samples from the Spitzbergen and the Sambagawa blueschist facies belts. In both samples, a strong correlation between structures and chemistry is observed. Qualitative estimates of P–T conditions from the Si‐content of mica and chlorite are in good agreement with their location in microstructures that formed at different times. Therefore, the combination of chemical maps with microstructural observations is a very powerful approach to understand both the evolution of complex metamorphic rocks and the control by deformation of mineral reactivity.  相似文献   

High-temperature single-crystal neutron diffraction study of natural chondrodite     

Martin Kunz  George A. Lager  Hans-Beat Bürgi  Maria Teresa Fernandez-Diaz 《Physics and Chemistry of Minerals》2006,33(1):17-27

The H-atom environment in a Tilly Foster chondrodite was analyzed using single-crystal neutron-diffraction data collected at 500, 700 and 900 K and previously published low temperature data collected at 10, 100 and 300 K on the same crystal (Mg_4.64Fe_0.28Mn_0.014Ti_0.023(Si_1.01O₄)₂F_1.16(OH)_0.84; Friedrich et al. in Am Mineral 86:981–989, 2001). The full mean square displacement matrix Σ of the O–H pair was determined from the temperature dependence of the anisotropic displacement parameters, enabling a proper correction of the O–H bond for thermal vibration without assumptions about the correlation of O and H movements. The results show that the perpendicular O–H motions in chondrodite are intermediate between the riding and the independent motion models. The corrected O–H bond lengths do not change with temperature whereas the corrected H···F distances show an increase of ~0.02 Å with temperature, as do the Mg–O distances. This result shows that spectroscopic observations on the strength of the covalent O–H bond cannot be interpreted unambiguously in terms of a corresponding behaviour of the associated H···O/F hydrogen bond.  相似文献   

关于地震波散射波场属性的基本研究     

QIN Xue-fei HAN Li-guo SHAN Gang-yi College of GeoExploration Science  Technology  Jilin University  Changchun  China 《吉林大学学报(地球科学版)》2006,(Z2)

当地震波传播过程中遇到异常体时往往会在间断点处产生绕射现象,这是识别断层及其他构造的一个重要因素。然而,在实际情况下,绝大多数异常体尤其是金属矿藏,由于其形态并不是规则的,且尺度较小,从而无法产生很好的绕射波,取而代之的却是大量富含介质不规则信息的散射现象.近年来,特别是在金属矿地震勘探中,很多人错误地将散射理解为绕射。通过对一个特殊模型的正演模拟,系统地说明二者之间的差别以及散射波场的一些基本特征。  相似文献   

Landslides at Qingjiang River in the Downstream Area of Shuibuya Dam Site, China   总被引：1，自引：0，他引：1  

Kallen  D  项伟  Ehret  D  Rohn  J 《中国地质大学学报(英文版)》2006,17(2):158-162

INTRODUCTIONLandslides annually cause a great amount of cas-ualties withinthe Chinese population and great lossesin the Chinese economy . The number of casualtiesreached 232 killed and 2 missing people in 2003 and283 killed and 69 missing people in 2004 . The eco-nomic losses amount to a total of 730 billion US $in2003 and 475 billion US $in 2004 (Zanetti ,2005 ,2004) .The DAAD (German Academic Exchange Serv-ice) is financing a project to investigate landslides .The project is a coo…  相似文献   

Metamorphism of mineral matter in coal from the Bukit Asam deposit, south Sumatra, Indonesia   总被引：1，自引：3，他引：1  

Rita Susilawati  Colin R. Ward   《International Journal of Coal Geology》2006,68(3-4):171-195

The coal of the Miocene Bukit Asam deposit in south Sumatra is mostly sub-bituminous in rank, consistent with regional trends due to burial processes. However, effects associated with Plio–Pleistocene igneous intrusions have produced coal with vitrinite reflectance up to at least 4.17% (anthracite) in different parts of the deposit. The un-metamorphosed to slightly metamorphosed coals, with Rv_max values of 0.45–0.65%, contain a mineral assemblage made up almost entirely of well-ordered kaolinite and quartz. The more strongly heat-affected coals, with Rv_max values of more than 1.0%, are dominated by irregularly and regularly interstratified illite/smectite, poorly crystallized kaolinite and paragonite (Na mica), with chlorite in some of the anthracite materials. Kaolinite is abundant in the partings of the lower-rank coals, but is absent from the partings in the higher-rank areas, even at similar horizons in the same coal seam. Regularly interstratified illite/smectite, which is totally absent from the partings in the lower-rank coals, dominates the mineralogy in the partings associated with the higher-rank coal beds. A number of reactions involving the alteration of silicate minerals appear to have occurred in both the coal and the associated non-coal lithologies during the thermal metamorphism generated by the intrusions. The most prominent involve the disappearance of kaolinite, the appearance of irregularly interstratified illite/smectite, and the formation of regular I/S, paragonite and chlorite. Although regular I/S is identified in all of the non-coal partings associated with the higher-rank coals, illite/smectite with an ordered structure is only recognised in the coal samples collected from near the bases of the seams. The I/S in the coal samples adjacent to the floor of the highest rank seam also appears to have a greater proportion of illitic components. The availability of sodium and other non-mineral inorganic elements in the original coal to interact with the kaolinite, under different thermal and geochemical conditions, appears to be the significant factor in the formation of these new minerals, and distinguishes the mineralogical changes at Bukit Asam from those developed more generally with rank increases due to burial, and from the effects of intrusions into coals that were already at higher rank levels.  相似文献   

Reduction roasting of limonite ores: effect of dehydroxylation   总被引：2，自引：0，他引：2  

F. O'Connor  W.H. Cheung  M. Valix   《International Journal of Mineral Processing》2006,80(2-4):88-99

The effect of pre-calcination in the reducibility of tropical limonite ore, obtained from New Caledonia, was investigated in this study. A series of reduction tests were carried out with pre-calcined and raw limonite ores. The extent of metallisation was determined from nickel and iron which dissolved in ammoniacal solution. Mineralogical transformations that occurred during reduction were analysed using thermal gravimetric, differential thermal analysis (TGA/DTA) and in situ high temperature synchrotron based X-ray diffraction. Bulk mineral analysis of the raw ore was also obtained using neutron diffraction. This study suggests that there is benefit in the pre-calcination of limonite ores. Pre-calcination of the ores which opens the main gangue mineral structure, goethite, allows a rapid interaction between the reductant gases and the nickel species during reduction. The greater nickel metallisation achieved in reduction of pre-calcined ores resulted in higher dissolved nickel whilst reduced raw limonite showed poorer nickel recovery. Reduction of metal minerals was also accompanied by diffusion of nickel into the reduced iron matrix that resulted in the formation of ferro-nickel alloy (Ni₃Fe). The formation of this solid solution was monitored by in situ synchrotron based X-ray diffraction and was also reflected by the lower nickel leachability in ammoniacal solution. It was found that incorporation of nickel into the reduced iron oxide resulting from pre-calcination is significantly less in comparison to the diffusion occurring in reduced raw or uncalcined limonite ores. This effect is prevalent in prolonged reduction periods (greater than 20 min), at higher temperatures (>500 °C) and highly reducing conditions (H₂/CO₂=1:1). This study showed that optimal nickel recovery can be achieved by controlling the incorporation of nickel into the reduced iron structure by pre-calcination of the limonite ore.  相似文献   

Speciation of Cr and V within BOF steel slag reused in road constructions   总被引：1，自引：0，他引：1  

Perrine Chaurand  Jrme Rose  Jrmie Domas  Jean-Yves Bottero 《Journal of Geochemical Exploration》2006,88(1-3):10

Basic Oxygen Furnace (BOF) steel slag is a residue from the basic oxygen converter in steel-making operations, which is partially reused as an aggregate for road constructions. It is essentially composed of calcium, silicon and iron but also contains potential toxic elements present as traces, like chromium (Cr, 2600 mg kg^− 1) and vanadium (V, 690 mg kg^− 1), which can be released. The linked results of chemical analysis, XRD and SEM-EDX enabled to identify the main mineral phases composing BOF slag and EDX micro-analyses indicated that V and Cr were associated to dicalciumferrite. A 47-days static leaching test at a laboratory scale with a controlled pH of 5 (pH_stat leaching test) showed that Cr was little released, while V was significantly released. Finally, X-ray absorption near-edge structure (XANES) spectra of 3 BOF slag samples were recorded (“raw”, leached 47 days at pH 5 and aged 2 years in a lysimeter). XANES spectra showed that Cr is present at octahedral coordination in the trivalent form, the less mobile and less toxic one, and that its speciation does not evolve during natural ageing and leaching at pH 5. They also indicated that V is predominantly present in the + 4 oxidation state and seems to become oxidized to the pentavalent form (the most toxic form) during natural ageing.  相似文献   

应用同步辐射微束X射线荧光光谱法研究单个大气PM2．5颗粒物的源特征   总被引：3，自引：0，他引：3  

李晓林岳伟生  刘江峰万天敏  张桂林李燕  黄宇营何伟 华魏 《岩矿测试》2006,25(3):206-210

将高灵敏度的同步辐射微束x射线荧光光谱分析方法与计算机模式识别技术相结合，用于上海市大气PM2.5，单颗粒物的源识别。分析了污染排放源的PM2.5，单颗粒物，结果表明，来自不同污染排放源的颗粒物具有不同的能谱特征。同时分析了环境空气监测样品PM2.5，单颗粒物，结果表明，在上海市中心区大气PM2.5，的污染源主要以机动车尾气为主，而在吴淞工业区大气PM2.5，的污染源主要以钢铁工业尘和燃煤烟尘为主。  相似文献   

X射线荧光光谱法测定土壤样品中氯的不确定度评定   总被引：11，自引：7，他引：11  

陈爱平王烨  王苏明 《岩矿测试》2006,25(3):270-275

用实例对x射线荧光光谱法测定土壤样品中氯的不确定度进行了评定。测量结果的不确定度由仪器综合稳定性、制样、标准物质、回归工作曲线、重复测量等所引入的不确定度分量组成。在对各个不确定度分量进行量化的基础上，通过合成得到测量结果的标准不确定度，再乘以95％置信概率下的扩展因子2，得到测量结果的扩展不确定度。  相似文献