Atom probe tomography (APT) of carbonate minerals

Atom probe tomography (APT) combines the highest spatial resolution with chemical data at atomic scale for the analysis of materials. For geological specimens, the process of field evaporation and molecular ion formation and interpretation is not yet entirely understood. The objective of this study is to determine the best conditions for the preparation and analysis by APT of carbonate minerals, of great importance in the interpretation of geological processes, focusing on the bulk chemical composition. Results show that the complexity of the mass spectrum is different for calcite and dolomite and relates to dissimilarities in crystalochemical parameters. In addition, APT bulk chemistry of calcite closely matches the expected stoichiometry but fails to provide accurate atomic percentages for elements in dolomite under the experimental conditions evaluated in this work. For both calcite and dolomite, APT underestimates the amount of oxygen based on their chemical formula, whereas it is able to detect small percentages of elemental substitutions in crystal lattices. Overall, our results demonstrate that APT of carbonate minerals is possible, but further optimization of the experimental parameters are required to improve the use of atom probe tomography for the correct interpretation of mineral geochemistry.     

Accuracy evaluation of an X-ray microtomography system

Microstructural parameter evaluation of reservoir rocks is of great importance to petroleum production companies. In this connection, X-ray computed microtomography (μ-CT) has proven to be a quite useful method for the assessment of rocks, as it provides important microstructural parameters, such as porosity, permeability, pore size distribution and porous phase of the sample. X-ray computed microtomography is a non-destructive technique that enables the reuse of samples already measured and also yields 2-D cross-sectional images of the sample as well as volume rendering. This technique offers an additional advantage, as it does not require sample preparation, of reducing the measurement time, which is approximately one to three hours, depending on the spatial resolution used. Although this technique is extensively used, accuracy verification of measurements is hard to obtain because the existing calibrated samples (phantoms) have large volumes and are assessed in medical CT scanners with millimeter spatial resolution. Accordingly, this study aims to determine the accuracy of an X-ray computed microtomography system using a Skyscan 1172 X-ray microtomograph. To accomplish this investigation, it was used a nylon thread set with known appropriate diameter inserted into a glass tube. The results for porosity size and phase distribution by X-ray microtomography were very close to the geometrically calculated values. The geometrically calculated porosity and the porosity determined by the methodology using the μ-CT was 33.4 ± 3.4% and 31.0 ± 0.3%, respectively. The outcome of this investigation was excellent. It was also observed a small variability in the results along all 401 sections of the analyzed image. Minimum and maximum porosity values between the cross sections were 30.9% and 31.1%, respectively. A 3-D image representing the actual structure of the sample was also rendered from the 2-D images.     

Studies of the anisotropy of the microstructure of oil and gas reservoir rocks by electron microscopy methods

The paper presents the features of applying the scanning electron microscopy method for studying the anisotropy of the pore space of carbonate rocks in oil and gas reservoirs. The results of studies into the horizontal anisotropy of the microstructure and pore space are presented. The significance of the pore space horizontal anisotropy for filtration properties, which should be taken into account during the development of 3D-hydrodynamic models of hydrocarbon deposits, has been experimentally found for rocks with a complex structure.     

Iron speciation and mineral characterization of upper Jurassic reservoir rocks in the Minhe Basin,NW China

Six samples from a natural outcrop of reservoir rocks with oil seepage and two control samples from surrounding area in the Minhe Basin, northwestern China were selectively collected and analyzed for mineralogical composition as well as iron speciation using X-ray powder diffraction (XRD) and Mössbauer spectroscopy, respectively. Iron species revealed that: (1) the oil-bearing reservoir rocks were changed by water-rock-oil interactions; (2) even in the same site, there was a different performance between sandstone and mudstone during the oil and gas infusion to the reservoirs; and (3) this was evidence indicating the selective channels of hydrocarbon migration. In addition, these studies showed that the iron speciation by Mössbauer spectroscopy could be useful for the study of oil and gas reservoirs, especially the processes of the water-rock interactions within petroleum reservoirs.     

Three-dimensional structure of the calcite-water interface by surface X-ray scattering

The three-dimensional structure of the calcite (104)-water interface has been determined with surface X-ray scattering. Nine crystal truncation rods (including specular and non-specular rods) were measured providing both vertical and lateral sensitivity to the interfacial structure. The results reveal that calcite is nearly ideally terminated with a single surface hydration layer that includes two inequivalent water molecules having distinct heights of 2.3 ± 0.1 and 3.5 ± 0.2 Å, each with a well-defined lateral registry with respect to the calcite surface. No additional layering of water is observed beyond this surface hydration layer. Small displacements in the outer two calcium carbonate layers were also observed. These results are compared with previous experimental and computational results.     

粉晶X射线衍射在矿物岩石学研究中的应用

文章简单介绍了粉晶X射线衍射在岩石矿物学研究中的主要应用.指出粉晶X射线衍射不仅在矿物的定性/定量分析、晶胞参数测定、类质同像研究、多型研究、有序/无序结构研究、岩组学研究等传统领域继续发挥着重要作用,在矿物结晶过程和相转变研究、矿物表面物相研究、矿物缺陷研究和矿物晶体结构测定等新领域也展现出广阔的应用前景.     

艾比湖滨岸盐碱土中碳酸盐的XRD衍射特征与微观形态分析

结合X射线衍射(XRD)、扫描电镜(SEM)和能谱分析(EDS)方法,对现代盐湖沉积环境下,新疆艾比湖滨岸盐碱土中碳酸盐的分布特征、存在形式以及与其他土壤原生、次生矿物之间的关系进行探讨,结果表明：艾比湖滨岸盐碱土中的原生矿物主要是石英和长石,粘土矿物主要为绿泥石和伊利石,土壤矿物的风化程度顺序为北部>西部>东部,西部样点的现代盐湖化学沉积作用最为显著,北部样点则生物风化过程十分强烈;XRD方法和气量法分别测得的碳酸盐含量之间呈极显著正相关关系,判定系数R2达0.640 9。当盐碱土中含有较高的绿泥石时,碳汇潜力会增加,同时,XRD方法对碳酸盐相对含量的鉴定误差也明显增加,衍射峰形变得复杂,碳酸盐含量明显被低估,低估原因可能与有机质含量高导致的弥散散射增加及粘土矿物含量高使得类质同象现象增加有关;西部和北部土壤矿物溶蚀强烈,石膏以纤维状或长柱状晶体分散或放射状分布于方解石晶体之间,方解石则以异质成核形式呈颗粒状或片状在其他矿物或底质表面生长,表现为次生碳酸盐形貌特征。     

Features of X-ray fluorescence determination of rock-forming elements in powder samples of peat sediments

The features of rock-forming elements determination in powder samples of peat sediments are considered. Based on theoretical calculations and experimental data, the mineralogical and particle size effects on the X-ray fluorescence intensity have been estimated. For routine analysis, powder rock samples are usually milled to a particle size of 10–60 μm. Theoretically, estimated variations of rock-forming elements analytical lines intensities in different minerals are up to 30%, and the particle size effect cannot be eliminated simultaneously for all rock-forming elements. Experimental estimation shows that the impossibility of the particle size distribution control can lead to significant variations in the intensities of the analytical lines (3%–18%) that is mainly corresponding to theoretical estimation. Fine milling allowed us to achieve an average particle size of fewer than 20 μm and reduce the measurement uncertainty by 1.5–2 times. 12 samples of peat sediments with organic matter content up to 70 wt% were analyzed by X-ray fluorescence analysis using different sample preparation techniques, as well as by certified methods. The accuracy of X-ray fluorescence analysis of peat sediments prepared as pressed pellets varies from 1.5 to 11 rel% depending on compound contents. It is more than for samples prepared as fused beads, however, the proposed method can be used to determine the variations of rock-forming elements contents in peat sediments where the content variations exceed the measurement uncertainty, and accuracy of analysis is sufficient for further paleoecological reconstructions.     

Spectroscopic study of phase transitions in dolomite mineral

The process and the formation of new minerals upon heating carbonate rocks containing clay minerals together with dolomite are determined by thermal analysis, X‐ray diffraction (XRD), infrared and Raman spectroscopy. The dolomite–calcite–calcium oxide phase transition sequences were followed up to 947 °C in a naturally occurring dolomite sample. The spectral variations of the internal modes of the carbonate trigonal (ν₁, ν₂, ν₃ and ν₄) were used to probe the structural phase transitions. A new Raman mode emerged at 1090 cm⁻¹ in the ν₁ mode region, and infrared modes emerged at 713, 874, and 1420 cm⁻¹ in the ν₄, ν₂ and ν₃ regions at 750 °C, indicating the onset of the dolomite phase. The calcium oxide phase, (which on reaction with atmospheric water forms portlandite) with an onset temperature of around 950 °C, was also characterized by the appearance of the infrared mode around 450 cm⁻¹. The minerals, which were formed upon heating the dolomite, were calcite, calcium oxide and diopside. Copyright © 2007 John Wiley & Sons, Ltd.     

汝阳地区熊耳群火山岩内夹层硅质岩的微区特征及地质意义

熊耳群是前寒武纪火山-沉积作用的产物,其顶部的马家河组(玄武)安山质火山岩内发育了夹层状热水成因硅质岩。选择熊耳群马家河组硅质岩夹层中的碧玉岩为对象,利用偏光显微镜,XRD,Raman和EBSD等方法剖析了其微区特征。研究结果显示：硅质岩内石英颗粒的显微镜和EBSD照片均表现出颗粒细小、结晶程度低和紧密堆积结构等特点,这完全吻合热水沉积硅质岩的特征;硅质岩内粒径不同的颗粒呈条带(或薄层)状交互出现,不同条带(或薄层)内矿物的组成存在明显的差异,这应该反映了原始物质供给的周期性变化;XRD分析结果指示硅质岩内的主要矿物为低温石英,其晶胞参数为a=b=0.491 3 nm,c=0.540 5 nm和Z=3;EBSD照片和Raman分析结果显示硅质岩内微量的杂质矿物形成于不同阶段,其中粘土矿物和黄铁矿呈零星分布并反映了原始沉积成因,长英质矿物和铁镁硅酸盐矿物均来源于火山凝灰质沉积;火山凝灰质矿物的颗粒偏大并构成了硅质岩内的粗颗粒条带(或薄层),它们与热水沉积为主的细颗粒矿物条带(或薄层)交互产出,这反映了火山作用的周期性反复活动;后期的碳酸盐热液沉淀于硅质岩内裂隙中,它们还导致石英颗粒边缘有序度升高。虽然熊耳群硅质岩内的矿物种类和成因均极为复杂,但火山物质的输入是导致熊耳群硅质岩SiO₂含量偏低的根本原因并得到了硅质岩内大量火山成因矿物的证实。在硅质岩的微组构研究中,Raman光谱分析可以有效的揭示微区上矿物的类型、微区结构及有序度,这些特征是反映硅质岩内部矿物形成与演化过程中微区变化的重要信息。     

Fabrication of quasi-optical selective elements for the terahertz range in the form of pseudometallic structures via deep X-ray lithography

A technique for fabricating self-bearing pseudometallic structures, which hold promise for utilization as quasi-optical frequency-selective elements in the terahertz range of the electromagnetic spectrum, is discussed. The technique is based on microstructuring a continuous dielectric layer via stencilled X-ray lithography involving synchrotron radiation with subsequent metallization of the entire structure surface. The main manufacturing schemes are described, including fabrication of the initial substrates and X-ray masks. Examples of samples of the produced selective elements, such as frequency filters and flat lenses, as well as their operating characteristics, are presented.     

Confocal three-dimensional micro X-ray fluorescence based on synchrotron radiation for mineral analysis

The confocal three-dimensional micro X-ray fluorescence using polycapillary optics and a synchrotron radiation was applied to nondestructively analyze elemental compositions of minerals, and thereby obtain the three-dimensional distributions of elements in the minerals. Such confocal micro X-ray fluorescence had potential applications in the mineral prospecting, identification of jades, differentiation of stones.     

Mössbauer and X-ray study of the firing process for production of improved roofing tiles

The effects of firing atmosphere parameters on the microstructural characteristics and physical properties of clay roofing tiles were studied. For these investigations, ⁵⁷Fe Mössbauer spectroscopy, X-ray diffractometry and dilatometry were used. XRD of the raw material exploited from the clay pit belonging to the roofing tile factory “Potisje-Kanjiza”, revealed the presence of montmorillonite, kaolinite, illite and some chlorite clay minerals, as well as, quartz, albite, calcite and dolomite. Gradual changes were observed both in the ⁵⁷Fe Mössbauer spectra and X-ray diffractograms with samples fired in reducing CO/N₂ gas atmosphere at temperatures between 700 and 1060 °C. These changes reflect the dehydroxylation processes, oxide (Fe₃O₄) formation, carbonate decomposition, densification and new silicate (plagioclase) formation. The firing conditions in reducing atmosphere were determined to produce roofing tiles with improved properties.     

Elemental distribution and Pb speciation in vegetable and cereal seeds during germination by micro X-ray fluorescence and X-ray absorption near-edge structure

The distribution of the chemical elements in plants is closely correlated with biological functions. Micro X-ray fluorescence (μXRF) and X-ray absorption near-edge structure (XANES) spectrometry can be used to determine uptake, translocation, and accumulation of the elements in plants. In this research, μXRF and XANES were applied in studying distribution of the elements in the vegetable and cereal seeds during germination and the mobilization. It was found that (a) the distribution of the elements in the seeds was element specific; (b) K and Ca were mainly located in the embryo. Fe and Zn, as well as Mn and Cu, concentrated near the radicle and new developed root. Most of Pb was located in the new developing root; (c) the organic-Pb complexes functioned as the main components of translocation of Pb in the seeds during germination, and the formation of Pb₅(PO₄)₃Cl and Pb₃(PO₄)₂ in seed and plant tissues was the mechanism of tolerance and detoxification to Pb in plants.     

WDXRF和FTIR对古滇国遗址出土陶器的初步分析

利用波长色散型X射线荧光光谱（WDXRF）和傅里叶变换红外光谱（FTIR）对环抚仙湖分布的澄江学山、金莲山和江川光坟头3个古滇国遗址出土的陶器从化学、结构组成以及烧成温度3方面进行了初步分析.WDXRF主次量元素分析结果表明,各遗址同类陶器（尤其是红陶）的基本制陶原料具有相似性,黑（褐）陶中添加的助熔剂含量明显高于红陶.FTIR分析结果显示同类陶器中包含的矿物具有一致性,红陶中含有石英和疑似铁矿物,黑（褐）陶中则都添加了大量的碳酸盐矿物.基于FTIR结果还对两类陶器的烧成温度做出了初步判断,估计黑（褐）陶在600-700℃,红陶在800℃左右.黑（褐）陶中较高含量的助熔剂可能在降低烧成温度方面起到了重要作用.以上初步分析表明,3个遗址出土的同类陶器在原料选择和烧成温度方面具有相似处,遗址间可能存在密切的联系.     

Oxygen and Carbon Isotope Variations of Carbonates and Silicates from the Carbonatite Massif Tiksheozero (Northern Karelia)

Abstract

Carbon and oxygen isotope compositions have been determined for carbonate minerals from different types of carbonatites (large carbonatite bodies, veins, eruptive breccia), as well as from different temperature classes of carbonatites (according to Samoilov [1]). It could be shown, that only high temperature carbonatites exhibit small variations of δ¹⁸O and δ¹³C falling in the range of “high temperature mantle carbonates”, whereas low temperature calcites and dolomites show wide variations in δ¹⁸O. These changes in both isotope and mineral compositions of low temperature carbonatites are interpreted as a result of repeated interaction with fluids. The oxygen isotope ratios in most of the eruptive breccia have been changed by secondary processes. The primary deep-seated isotope record has been preserved only in samples, in which carbonate occurs as fine-grained calcite groundmass.

Preliminary results on oxygen isotope composition of different silicate minerals (amphibole, magnetite, biotite, albite, apatite) indicate isotope equilibrium for the mineral pair calcite-amphibole with isotope temperatures representing superimposed processes.     

Mössbauer spectroscopy description of limonite from Taraco, in the Huancane Province of the Puno Region, Peru

Natural iron oxides are very common in nature and are the main components of many minerals, rocks and soils. There are a great variety of these minerals in Peru, especially in the Andes region. The mineral studied was extracted from the Taraco District in the Huancané Province of the Puno Region. The extracted sample is a yellowish mineral with very small particles which is called limonite. X-ray diffraction indicates the presence of goethite as the principal mineralogical phase and quartz as the secondary phase. The ⁵⁷Fe Mössbauer spectra at room temperature show broadened spectra that were fitted using a distribution model. The most probable field of the magnetic component is 21T, corresponding to the presence of small particles of goethite, confirmed by the 4.2 K spectrum. MS of the calcinated sample in air at 900°C show the presence of two hematite sextets, one related to bulk particles and another to surface particles. Chemical analysis using Scanning Electron Microscopy and Energy Dispersive X-ray Spectrometer indicates that O and Fe are the major components; other elements such as Al, Si, Mg and Ca are also present.     

缝洞型油藏致密基质灰岩的压力敏感性规律的NMR研究

相比于常规储层,缝洞型油藏灰岩储具有集体结构复杂、缝洞尺度差异大、裂缝起主要沟通作用等特点,使用常规方法研究其流动特性和流体分布规律异常困难．该文采用自行研制的核磁共振（NMR）在线驱替装置对塔河奥陶系油藏15块致密基质灰岩岩芯进行了压力敏感性实验,获得了高压及流动状态下岩芯的横向弛豫时间（T₂）谱变化情况．在此基础上分析了灰岩在压敏实验过程中微裂缝尺寸、孔隙度及渗透率的变化规律,并与常规测试分析结果进行了对比．结果表明：NMR在线检测技术可以定量测量岩芯孔隙及微裂缝的变化,为岩芯渗透率变化规律提供微观解释．     

High-pressure synchrotron X-ray diffraction study of tremolite and actinolite in various fluids

Pressure-dependent structural and morphological changes of two amphibole minerals, tremolite and actinolite, were investigated up to 7.0 GPa using synchrotron X-ray powder diffraction underthree different pressure transmission media (PTM): water (W), CO₂ and silicone oil (SI). The elastic response of tremolite and actinolite are found to be dependent on the PTM used. When using water (W) as PTM, tremolite and actinolite show normal volume contractions with bulk moduli of 74(1) and 78(1) GPa, respectively. When using CO₂ as PTM, we observe the formation of calcite from tremolite above 3.8(1) GPa, whereas actinolite did not show any carbonation reaction. Under silicone oil PTM, we observe modulated volume contraction behaviors in both samples, compared to water and CO₂ PTM, with bulk moduli in the order of 90(1) and 94(4) GPa for tremolite and actinolite, respectively.     

Thermally induced adjustment of the parameters of X-ray diffraction peaks from crystals

The effect of nonuniform thermal action of a light beam on the parameters of a diffraction peak for a calcite crystal is studied. It is shown that the spatial intensity distribution in an X-ray beam can be corrected by controlling the thermally induced mismatch between Bragg reflections from local areas in a crystal.