Evidence of native radiation-induced paramagnetic defects in natural illites from unconformity-type uranium deposits     

E. Morichon  T. Allard  D. Beaufort  P. Patrier 《Physics and Chemistry of Minerals》2008,35(6):339-346

This study presents the first unequivocal identification of natural radiation-induced defects in illites. Middle Proterozoic illites related to unconformity-type uranium deposits of Canada and Australia were studied using electron paramagnetic resonance (EPR) spectroscopy at X- and Q-band frequencies. The saturation behaviour of EPR spectra as a function of power demonstrates that native defects of illites are different from those known in other clays as kaolinite, dickite or smectite. Q-band spectra indicate the presence of several––at least two––native defects. The EPR signal is dominated by an axially distorted spectrum with apparent principal components as follows: g _∥ = 2.032 and g _⊥ = 1.993. The corresponding defect is named as A_i center. The study of oriented specimen confirms the strong anisotropy, and shows that the main defect has its g _∥ component perpendicular to the (ab) plane of illite. These defects in illite correspond to electron holes located on oxygen atoms of the structure and likely associated to Si, according to the lack of hyperfine structure. The A_i center in illite has similar EPR parameters to the A center in kaolinite and dickite. The isochronal annealing data suggest that illite can be used as a dosimeter in the geosphere. However, the determination of half-life and activation energy of the A_i center requires additional work.  相似文献   

Caractérisation par résonance paramagnétique électronique (RPE) de quartz naturels issus de différentes sources     

Mathieu Duttine  Gérard Villeneuve  Françoise Bechtel  Gérard Demazeau 《Comptes Rendus Geoscience》2002,334(13):949-955

Natural quartz crystals coming from Madagascar, Angola, Brazil, and Spain were studied by EPR after β irradiation in order to characterise the paramagnetic centres due to impurities, and examine in which way their relative proportion could constitute a useful criterion for origin researches. In all our samples, EPR experiments revealed germanium centres [GeO₄/M⁺]° with M = Li or Na, aluminium ones [AlO₄/h]° and two titanium centres ([TiO₄/H⁺]° and [TiO₄/M⁺]°) also appeared, except for samples coming from Spain. The comparison of the relative concentrations of paramagnetic species led us on to draw diagrams that allowed distinguishing the origins of the studied samples using only EPR spectra. To cite this article: M. Duttine et al., C. R. Geoscience 334 (2002) 949–955.  相似文献   

Point defects and cation tracer diffusion in (Ti _x Fe _1?x ) _3?δ O₄ 1. Non-stoichiometry and point defects     

S. Aggarwal  R. Dieckmann 《Physics and Chemistry of Minerals》2002,29(10):695-706

 The deviation from stoichiometry, δ, in spinel solid solutions of the type (Ti _x Fe _1−x )_3−δ O₄ with x=0.1, 0.2 and 0.25 was studied thermogravimetrically as a function of oxygen activity, a _O2, at 1100, 1200 and 1300 ^∘C. The experimental results, S-shaped curves for δ vs. log a_O2, are presented and discussed with regard to the type of point defects prevailing under different conditions in the deviation from stoichiometry. It is concluded that cation vacancies are the predominant point defects at high oxygen activities, while cation interstitials prevail at low oxygen activities. The temperature and composition dependencies of point defect concentrations are also discussed. Received: 1 October 1996 / Accepted: 15 September 2002 Acknowledgements The authors thank the US Department of Energy for support of this work under Grant no. DE-FGO2–88ER45357. This work made use of the Cornell Center of Materials Shared Experimental Facilities, supported through the National Science Foundation Materials Research Science and Engineering Centers program (DMR-0079992).  相似文献   

Causes of variations in morphology and impurities of diamonds from the Udachnaya Pipe eclogite     

A.S. Stepanov  V.S. Shatsky  D.A. Zedgenizov  N.V. Sobolev 《Russian Geology and Geophysics》2007,48(9):758-769

A unique xenolith of eclogite, 23×17×11 cm in size and 8 kg in weight, was found in the Udachnaya kimberlite pipe. One hundred twenty-four diamond crystals recovered from it were analyzed by a number of methods. The diamonds differ in morphology, internal structure, color, size, and composition of defects and impurities. The xenolith contains diamonds of octahedral and cubooctahedral habits. In cathodoluminescence, the octahedral crystals have a brightly glowing core with octahedral zones of growth and a weakly glowing rim. In the cores of these crystals the N impurity is mostly present in the B1 form (30 to 60%). At the same time, N in the rim is chiefly in the A form. The cubooctahedral crystals show a weak luminescence. The content of nitrogen and degree of its aggregation are close to those in the rim of octahedral crystals. The diversity of morphology and impurity composition of diamonds from the xenolith can be explained by their formation in two stages. At the first stage, the diamonds formed which became the cores of octahedra. After a long-time interruption, at the second stage of diamond formation crystals of cubooctahedral habit appeared and the octahedral crystals were overgrown. Wide variations in nitrogen contents in the xenolith crystals allowed their use to estimate the kinetics of aggregated nitrogen. The data obtained show that the aggregation of A centers into B1 centers in the diamonds is described by a kinetic reaction of an order of 1.5.  相似文献   

Water diffusion in synthetic iron-free forsterite   总被引：2，自引：1，他引：2  

Demouchy  S.  Mackwell  S. 《Physics and Chemistry of Minerals》2003,30(8):486-494

The kinetics of hydrogenation of dry synthetic forsterite single crystals was determined by performing experiments under hydrothermal conditions. The experiments were performed at 1.5 GPa, 1000 °C for 3 h in a piston-cylinder apparatus, or at 0.2 GPa, 900–1110 °C, for 3–20 h in TZM cold-seal vessels. The oxygen fugacity was buffered using Fe–FeO or Ni–NiO powders. Polarized Fourier transform infrared spectroscopy was utilized to quantify the hydroxyl distributions in the samples after the experiments. Hydrogenation rates were measured parallel to the three crystallographic axes from profiles of water content as a function of position in the samples. The chemical diffusion coefficients are marginally slower than in natural iron-bearing olivine for the same diffusion process, but the anisotropy of diffusion is the same, with the [001] axis the fastest direction of diffusion and [100] the slowest. Fits of the diffusion data to an Arrhenius law yield similar activation energies for each of the crystallographic axes; a global fit to all the diffusion data gave 211 ± 18 kJ mol^–1, in reasonable agreement with the previous results for natural olivine. Thus hydrogenation most likely occurs by coupled diffusion of protons and octahedrally coordinated metal vacancies. The diffusion rates are fast enough to modify water contents within xenoliths ascending from the mantle, but probably too slow to permit a total equilibration of forsterite or olivine crystals.  相似文献   

铁路路基病害类型、机理及检测与整治技术   总被引：9，自引：1，他引：8  

彭华  张鸿儒 《工程地质学报》2005,13(2):195-199

针对既有铁路的特点,分析了常见铁路路基病害的类型、机理;提出路基病害的检测应运用现代化检测工具,采用原位和区段测试相结合的方法;针对路基病害整治技术的复杂多样,整治具体路基病害的困难性,指出了铁路路基病害智能管理系统能较好地解决此问题。  相似文献   

混凝土构件缺陷超声无损检测的研究     

傅竹武  王鑫 《岩土力学》2007,28(Z1):783-788

对混凝土构件进行超声无损检测,超声波的振幅参数对混凝土构件中的缺陷（裂缝）最敏感,在耦合良好和测试条件基本一致时,振幅值的大幅衰减可作为判断混凝土构件存在缺陷的主要依据。超声波的速度参数对微小裂隙不敏感,缺陷较大会引起速度值的显著下降;频率参数用于检测混凝土构件缺陷不够敏感;对混凝土构件缺陷进行超声检测,速度变化和频率变化只能作为参考因素。超声波通过裂缝与未过裂缝,波形存在明显差异,通过裂缝后,有时会出现很大周期的波列,可作为判断缺陷的重要依据。综合分析超声波运动学和动力学各参数的变化,能够提高检测的准确性。  相似文献   

水泥土防渗墙完整性多电极电阻率法检测研究     

郭秀军  郭健  贾永刚  潘友宏  杨乃磊 《岩土力学》2006,27(Z1):572-576

基于不同水灰比水泥土防渗墙成墙后较短时间内的电性变化特征,沿墙体走向利用布设在墙体上方的多个电极对设有不同缺陷的防渗墙进行了电性探测试验。防渗墙施工过程中形成的深度不够、序间接缝、桩体开叉、搅拌不匀等完整性缺陷会引起探测剖面上电异常特征变化,异常区分布位置和缺陷位置具有对应关系。2.5维有限元方法数值模拟计算结果和模型试验结果具有相同的特征,并进一步表明不同缺陷的异常特征受缺陷类型、缺陷位置的电性特征、缺陷尺寸控制。  相似文献   

膨润土防水毯破损条件下渗流特性试验研究     

盛金昌  白柯含  杨旭  郑忠巍  詹美礼  孙永军  杨慧 《岩土力学》2015,36(Z2):315-320

为了从渗流量和渗透稳定角度深入研究膨润土防水毯破损处的防渗问题,开发了由压力控制系统和模型试验系统两部分组成的渗流试验装置,建立了针对坝体防渗工程中的防水毯破损情况的渗流物理试验方法,并通过膨润土防水毯不同破损工况下的渗流试验,初步探讨了影响破损防水毯与坝身土体联合抗渗的因素。结果表明,对破损防水毯和土体的综合渗透系数的影响,孔洞大小比破损率要敏感;对于孔洞修复能力,主要的敏感的因素包括孔洞直径D及防水毯规格（材料本身性能）。在工程中要做好以下两点：（1）工程中刺破孔洞直径D小于0.5 cm,超过0.5 cm的孔洞应当做修补;（2）局部刺破率不宜大于0.5%,尽量保证防水毯接触面的平整。  相似文献   

不同成因类型石英与石英玻璃气泡缺陷间关系探讨     

孙亚东  严奉林 《江苏地质》2005,29(4):204-206

对不同成因类型石英的气液包体含量与石英玻璃气泡缺陷间的关系进行了对比研究，总结了一些规律，对石英玻璃工业原料的地质找矿具有一定的指导意义。  相似文献