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11.
The thermal behaviour of β-anhydrite CaSO4 has been investigated to 1,263 K in-situ real-time using laboratory parallel-beam X-ray powder diffraction data. The cell
parameters expanded anisotropically, the c axis being the “softest”. This behaviour is due to the deformation of the CaO8 polyhedron. In fact the two longest, independent, Ca–O bond distances show a significant component along the z direction. 相似文献
12.
A regional analysis of the anisotropy of the magnetic susceptibility on low-grade metamorphic, chloritoid-bearing slates of the Paleozoic in Central Armorica (Brittany, France) revealed very high values for the degree of anisotropy (up to 1.43). Nonetheless, high-field torque magnetometry indicates that the magnetic fabric is dominantly paramagnetic. Chloritoid's intrinsic degree of anisotropy of 1.47 ± 0.06, suggests that chloritoid-bearing slates can have a high degree of anisotropy without the need of invoking a significant contribution of strongly anisotropic ferromagnetic (s.l.) minerals. To validate this assumption we performed a texture analysis on a representative sample of the chloritoid-bearing slates using hard X-ray synchrotron diffraction. The preferred orientation patterns of both muscovite and chloritoid are extremely strong (∼38.6 m.r.d. for muscovite, 20.9 m.r.d. for chloritoid) and display roughly axial symmetry about the minimum magnetic susceptibility axis, indeed suggesting that chloritoid may have a profound impact on the magnetic fabric of chloritoid-bearing rocks. However, modeling the anisotropy of magnetic susceptibility by averaging single crystal properties indicates that the CPO of chloritoid only partially explains the slate's anisotropy. 相似文献
13.
Ian M. Power Siobhan A. Wilson Anna L. Harrison Gregory M. Dipple Jenine McCutcheon Gordon Southam Paul A. Kenward 《Sedimentology》2014,61(6):1701-1733
This study formulates a comprehensive depositional model for hydromagnesite–magnesite playas. Mineralogical, isotopic and hydrogeochemical data are coupled with electron microscopy and field observations of the hydromagnesite–magnesite playas near Atlin, British Columbia, Canada. Four surface environments are recognized: wetlands, grasslands, localized mounds (metre‐scale) and amalgamated mounds composed primarily of hydromagnesite [Mg5(CO3)4(OH)2·4H2O], which are interpreted to represent stages in playa genesis. Water chemistry, precipitation kinetics and depositional environment are primary controls on sediment mineralogy. At depth (average ≈ 2 m), Ca–Mg‐carbonate sediments overlay early Holocene glaciolacustrine sediments indicating deposition within a lake post‐deglaciation. This mineralogical change corresponds to a shift from siliciclastic to chemical carbonate deposition as the supply of fresh surface water (for example, glacier meltwater) ceased and was replaced by alkaline groundwater. Weathering of ultramafic bedrock in the region produces Mg–HCO3 groundwater that concentrates by evaporation upon discharging into closed basins, occupied by the playas. An uppermost unit of Mg‐carbonate sediments (hydromagnesite mounds) overlies the Ca–Mg‐carbonate sediments. This second mineralogical shift corresponds to a change in the depositional environment from subaqueous to subaerial, occurring once sediments ‘emerged’ from the water surface. Capillary action and evaporation draw Mg–HCO3 water up towards the ground surface, precipitating Mg‐carbonate minerals. Evaporation at the water table causes precipitation of lansfordite [MgCO3·5H2O] which partially cements pre‐existing sediments forming a hardpan. As carbonate deposition continues, the weight of the overlying sediments causes compaction and minor lateral movement of the mounds leading to amalgamation of localized mounds. Radiocarbon dating of buried vegetation at the Ca–Mg‐carbonate boundary indicates that there has been ca 8000 years of continuous Mg‐carbonate deposition at a rate of 0·4 mm yr?1. The depositional model accounts for the many sedimentological, mineralogical and geochemical processes that occur in the four surface environments; elucidating past and present carbonate deposition. 相似文献
14.
Thermal behaviour and kinetics of dehydration of gypsum in air have been investigated using in situ real-time laboratory parallel-beam
X-ray powder diffraction data evaluated by the Rietveld method. Thermal expansion has been analysed from 298 to 373 K. The
high-temperature limits for the cell edges and for the cell volume, calculated using the Einstein equation, are 4.29 × 10−6, 4.94 × 10−5, 2.97 × 10−5, and 8.21 × 10−5. Thermal expansion of gypsum is strongly anisotropic being larger along the b axis mainly due to the weakening of hydrogen bond. Dehydration of gypsum has been investigated in isothermal conditions within the 348–403 K range with a temperature
increase of 5 K. Dehydration proceeds through the CaSO4·2H2O → CaSO4·0.5H2O → γ-CaSO4 steps. Experimental data have been fitted with the Avrami equation to calculate the empirical activation energy of the process.
No change in transformation mechanism has been observed within the analysed temperature range and the corresponding E
a is 109(12) kJ/mol. 相似文献
15.
Sytle M. Antao Ishmael Hassan Willem H. Mulder Peter L. Lee Brian H. Toby 《Physics and Chemistry of Minerals》2009,36(3):159-169
The temperature dependences of the crystal structure and intensities of the (113) and (211) reflections in calcite, CaCO3, were studied using Rietveld structure refinements based on synchrotron powder X-ray diffraction data. Calcite transforms
from to at about T
c = 1,240 K. A CO3 group occupies, statistically, two positions with equal frequency in the disordered phase, but with unequal frequency in the partially ordered phase. One position for the CO3 group is rotated by 180° with respect to the other. The unequal occupancy of the two orientations in the partially ordered
phase is obtained directly from the occupancy factor, x, for the O1 site and gives rise to the order parameter, S = 2x − 1. The a cell parameter shows a negative thermal expansion at low T, followed by a plateau region at higher T, then a steeper contraction towards T
c, where the CO3 groups disorder in a rapid process. Using a modified Bragg–Williams model, fits were obtained for the order parameter S, and for the intensities of the (113) and (211) reflections.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
16.
Thermal behaviour of γ-anhydrite (γ-CaSO4, soluble anhydrite) has been investigated in situ real-time using laboratory parallel-beam X-ray powder diffraction data.
Thermal expansion has been analysed from 303 to 569 K with temperature steps of 4 K. Lattice parameters and volume were fitted
with a second-order polynomial to calculate thermal expansion coefficients. Thermal expansion of γ-anhydrite is anisotropic
being larger along the c axis. Within the 343–383 K thermal range, γ-anhydrite has been found to partially re-hydrate to bassanite CaSO4·0.5H2O. At 455 K the transformation γ-CaSO4 → β-CaSO4, insoluble anhydrite, starts reaching completion at 653 K. 相似文献
17.
Mineral particles could have influenced on the climate of Oviedo, a non-industrial city situated in the centre of an industrial
zone of the North of Spain, increasing the temperature and the precipitations, in spite of the fact that “greenhouse gases”
concentrations have diminished in this city in recent years. The directive (1999/30/EC) of the European Commission began to
be applied in Oviedo in the year 2003. In agreement with this norm, our first aim was the identification of the inorganic
particulate matter of the PM10 and PM2.5 fractions sampled in this city. X-ray diffraction and scanning electron microscopy
coupled with X-ray dispersive energy spectrometry were used. The percentages of the different mineral phases of the PM were
obtained by a Rietveld refinement of powder X-ray diffraction data. The compositions of the PM10 and PM2.5 fractions of this
city are similar. Sulphates are the most abundant particles in the both fractions. Most sulphates, nitrates and sal-ammoniac
would have formed by reaction between solid, liquid and/or gas particles and they could be associated with the power stations
near to the city and traffic. Wüstite and haematites come from the iron and steel industries of Gijón and Avilés. The main
natural sources of halite and carbonates and silicates are sea spray and soil resuspension by the wind, respectively. 相似文献
18.
X射线衍射全谱拟合法快速分析长石矿物含量 总被引:4,自引:2,他引:2
长石中矿物的含量需要根据化学分析结果计算获得,分析流程长、计算复杂,而光学显微镜测定长石含量易受切片位置的影响。本文利用High Score软件对长石样品进行X射线衍射全谱拟合分析,能有效降低衍射峰重叠影响,修正择优取向造成的衍射强度误差,方法的准确度优于参比法(RIR法);样品定量分析结果与绝热法结果接近,相对偏差小于1.69%;与化学分析结果换算的矿物含量比较,绝对误差小于5%,满足了DZ/T 0130—2006所规定的绝对误差允许限。采用钾长石国家一级标准物质进行验证,主要矿物成分的分析误差小于1.34%,与钾长石化学成分标准值相比,绝对误差均小于1%。对长石物相进行定量分析的结果表明:X射线衍射全谱拟合法操作简单,分析质量能够满足相关标准对衍射分析的要求,用于地质实验中岩石矿物物相含量分析是可行的。 相似文献
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20.
X射线衍射全谱拟合法分析蓝晶石的矿物含量 总被引:1,自引:1,他引:0
蓝晶石矿物定量分析通常采用的化学物相法分析流程繁琐,易受同质异象矿物和难熔矿物的干扰;采用X射线衍射内标法需要提纯矿物绘制标准曲线,但矿物包体的存在使得获取纯净单矿物成为难题;由于不同矿区蓝晶石矿物成分之间存在着差异性,以上两种方法都仅仅适用于同一矿区样品的矿物定量分析。为简化分析流程,提高测试效率,本文采用X射线衍射(XRD)全谱拟合法对蓝晶石国家二级标准物质和野外样品进行分析,并与RIR法、绝热法和K值法等衍射定量方法及化学分析结果进行了比较验证方法的可靠性。结果表明:全谱拟合法无需采用标准物质,也不用引入内标物,一次扫谱分析能获得样品中所有成分的信息,操作简单,能有效降低择优取向对衍射定量结果的影响;对于含量大于5%的矿物,组分分析结果的绝对误差小于1%,显著低于绝对误差允许限;采用Highscore和Jade两种衍射数据处理软件获得的定量结果吻合度高,目标矿物蓝晶石分析结果的双差均小于0.8%,相对偏差小于2.5%;蓝晶石的加标回收率在95.3%~101.0%之间,能实现不同矿区蓝晶石矿的快速定量分析。 相似文献