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11.
R. J. Angel R. M. Hazen T. C. McCormick C. T. Prewitt J. R. Smyth 《Physics and Chemistry of Minerals》1988,15(4):313-318
The compressibilities of the three end-member feldspars have been determined between 1 bar and 50 kbar by single crystal X-ray diffraction techniques, using a Merrill-Bassett type diamond anvil cell with three crystals loaded simultaneously. Low albite (ordered aluminium-silicon distribution) and high sanidine (disordered Al-Si) show similar behaviour on compression, with bulk moduli (linear fit to volume-pressure data) of 0.70 and 0.67 Mbar respectively. The most compressible cell axis of all three feldspars studied is a, indicating that the major change in the feldspar framework with pressure is a shortening of the overall length of the “crankshaft chains” by reduction of T-O-T angles. Anorthite shows anomalous behaviour in that we have observed a previously unreported reversible phase transition at a pressure between 25.5 and 29.5 kbar. This transition is marked by large discontinuities in the unit cell angles and a small decrease of 0.2 percent in the cell volume with increasing pressure. The high-pressure phase is less compressible than the low-pressure phase, the bulk moduli being 0.94 and 1.06 Mbar respectively. There was no evidence of a monoclinic to triclinic inversion in sanidine that was expected to occur between 20 and 30 kbar on the basis of previous work on intermediate alkali feldspars. 相似文献
12.
David C. Palmer Russell J. Hemley Charles T. Prewitt 《Physics and Chemistry of Minerals》1994,21(8):481-488
The pressure dependence of the cristobalite Raman spectrum has been investigated to 22 GPa at room temperature, using single-crystal Raman spectroscopy with a diamond-anvil cell. We observe a rapid, first-order phase transition on increasing pressure, consistent with the cristobalite I?II transition revealed in previous x-ray diffraction experiments. The phase transition has been bracketed at 1.2±0.1 GPa on increasing pressure and 0.2±0.1 GPa on decreasing pressure. The pressure shifts II) of 11 Raman bands in the high-pressure phase (cristobalite have been measured. Evidence for an unusual hybridization of modes at 490–500 cm?1 is found. Changes in the Raman spectra also reveal an additional phase transition to a new phase at P ≈ 11 GPa, which remains to be fully characterized. 相似文献
13.
目的;以通用ＭＯＤ代替专用ＭＯＤ模块,解决ＣＴ机数据资料的存储问题。方法：用ＭＡＸＯＰＴＩＸＭＯＤ来代换ＰＩＯＮＥＥＲ ＭＯＤ。结果;很好的解决了ＣＴ机数据资料的存储问题,保证了ＣＴ数据的安全性。结论：ＭＡＸＯＰＴＩＸ ＭＯＤＳ可以成功地应用在ＳＹＴＥＣ４０００ＣＴ机上,成果很有推广价值。 相似文献
14.
本文利用薄层CT扫描技术,对支气管微细结构和改变,对肺内结节性病变大小、边缘、钙化、CT值及定位进行观察,分析了炎性纵隔淋已结肿大的特点。对肺内不肯定结节行CT 导引下活检,可明确诊断。切凹征、胸膜牵拉征、小泡征、小蜘蛛状改变、血管聚集等对肺癌的定性诊断具有重要价值。 相似文献
15.
Crystals of a high-pressure phase of MnTiO3 have been synthesized at pressures of 60 kbar using the SAM-85 cubic-anvil high pressure apparatus. Although all crystals examined were twinned on (10 \(\bar 1\) \(\bar 2\) ), a set of diffraction intensities that are essentially unaffected by the twinning were obtained. Three possible structure models were considered: (1) the corundum (completely disordered Mn and Ti), (2) the partially-disordered ilmenite, and (3) the LiNbO3 structures. The R factors of the corundum and the disordered ilmenite models were much larger than that of LiNbO3. Using structure factors unaffected by twinning, the final LiNbO3-type refinement gave R w=0.037 and R=0.034. The averaged bond lengths for Mn-O and Ti-O were consistent with ones calculated using Shannon and Prewitt's (1969) radii. The study concludes that MnTiO3 II actually has an ordered LiNbO3-type structure rather than the disordered one as reported previously. From the analysis of the two MnTiO3 structures, the transition can be related to a cation reordering process, in which half of the cations participate, accompanied by the rotation of oxygens to accommodate the cations. 相似文献
16.
The stable polymorph of MnTiO3 at room temperature and pressure has the ilmenite structure. At high temperatures and pressures, MnTiO3 ilmenite transforms to a LiNbO3 structure through a cation reordering process (Ko and Prewitt 1988). Single crystals of both phases have been studied with X-ray diffraction to 5.0 GPa. We have obtained the first experimental verification of the close relationship between the LiNbO3 and perovskite structures, first postulated by Megaw (1968). MnTiO3 with the LiNbO3 structure (MnTiO3 II) transforms directly to an orthorhombic perovskite structure (MnTiO3 III) between 2.0 and 3.0 GPa. The transition involves a change of volume of -5%, is reversible and has pronounced hysteresis. Only pressure is required to drive the transition because it involves no breaking of bonds; it simply involves rotation of the [TiO6] octahedra about their triad axes accompanied by displacement of the Mn cations to the distorted twelve-coordinated sites formed by the rotations. An unusual aspect of this transition is that twinned MnTiO3 II crystals transform to untwinned MnTiO3 III crystals with increasing pressure. The twin plane of MnTiO3 II,
, corresponds to the (001) mirror plane of the orthorhombic perovskite structure. MnTiO3 III examined at 4.5 GPa is very distorted from the ideal cubic perovskite structure. The O(2)-O(2)-O(2) angle describing the tilting in the ab plane is 133.3(7)°, in contrast to 180° for a cubic perovskite and the O(2)-O(2)-O(2) angle describing the tilting in the ac plane is 109.3(4)°, as opposed to 90° in a cubic perovskite. 相似文献
17.
Synthesis of NaTiSi2O6 at high pressure and temperature (65 kbar and 1550° C) results in transparent, light-green crystals when quenched to ambient conditions. These crystals have a pyroxene structure and belong to the series NaRSi2O6 where R is (in order of increasing ionic radius) Al, Cr, Fe, Ti, Sc, and In. X-ray diffraction patterns and a diffuse reflectance spectrum help to characterize this material which is one of the few oxides known containing Ti3+.Contribution No. 1715. 相似文献
18.
A series of molecular dynamics simulations have been performed on organic–water mixtures near mineral surfaces. These simulations show that, in contrast to apolar compounds, small polar organic compounds such as phenols can penetrate through thin water films to adsorb on these mineral surfaces. Furthermore, additional simulations involving demixing of an organic–water mixture near a surfactant-covered mineral surface demonstrate that even low concentrations of adsorbed polar compounds can induce major changes in mineral surface wettability, allowing sorption of apolar molecules. This strongly supports a two-stage adsorption mechanism for organic solutes, involving initial migration of small polar organic molecules to the mineral surface followed by water film displacement due to co-adsorption of the more apolar organic compounds, thus converting an initial water-wet mineral system to an organic-covered surface. This has profound implications for studies of petroleum reservoir diagenesis and wettability changes. 相似文献
19.
Y. Kudoh L. W. Finger R. M. Hazen C. T. Prewitt M. Kanzaki D. R. Veblen 《Physics and Chemistry of Minerals》1993,19(6):357-360
The unique cation-disordered crystal structures of two samples of phase E, a non-stoichiometric, hydrous silicate synthesized in a uniaxial, split-sphere, multi-anvil apparatus at conditions above 13 GPa and 1000° C, have been solved and refined in space group $\bar 3$ . The compositions and unit cells for the two materials, assuming six oxygens per cell, are Mg2.08Si1.16H3.20O6, a=2.9701(1) Å, c=13.882(1) Å V = 106.05(4) Å3 for sample 1, and Mg2.17Si1.01H3.62O6, a=2.9853(6) Å, c=13.9482(7) Å, V= 107.65(4) Å3 for sample 2. The structure contains layers with many features of brucite-type units, with the layers stacked in a rhombohedral arrangement. The layers are cross linked by silicon in tetrahedral coordination and magnesium in octahedral coordination, as well as hydrogen bonds. Interlay er octahedra share edges with intralayer octahedra. Interlayer tetrahedra would share faces with intralayer octahedra. To avoid this situation, there are vacancies within the layers. There is, however, no long-range order in the occupation of these sites, as indicated by the lack of a superstructure. Selected-area electron diffraction patterns show walls of diffuse intensity similar in geometry and magnitude to those observed in short-range-ordered alloys and Hågg phases. Phase E thus appears to represent a new class of disordered silicates, which may be thermodynamically metastable. 相似文献