Local relaxation around [6]Cr 3+ in synthetic pyrope–knorringite garnets, [8]Mg 3 [6](Al 1-X Cr X 3+) 2 [4]Si 3O 12, from electronic absorption spectra

Pyrope-knorringite garnets, Mg₃(Al_1-X Cr³⁺_X)₂Si₃O₁₂ with X=0.25, 0.50, and 1.00, were synthesized between 9 and 16 GPa and 1300 and 1600 °C, using multianvil high-pressure techniques. The garnets with X=0.25 and 0.50 are fine-grained, pink and violet in color. The end-member knorringites with X=1.00 are black when compact and gray when coarse-grained. The fine powder is greenish gray in natural light and pale pink under a tungsten lamp. Powder remission spectra in the wavenumber range 30 000–10 000 cm^–1 on finely powdered crystals were measured by two different methods: (I.) by the use of a small integrating sphere for small samples or (II.) microscope-spectrometric measurement using diffusely reflected radiation from a 45° illuminated microsample. Both methods yielded similar diffuse reflectance spectra. The following crystal-field parameters of ^[6]Cr³⁺ were determined for garnets with X=0.25, 0.50, 1.00: 10 Dq=17 856, 17 596, 17 286 cm^–1; and B=654, 677, 706 cm^–1; nephelauxetic ratio =(B_field/B_free)= 0.71, 0.74, 0.77. The -values indicate decreasing covalency of the Cr–O bond with increasing Cr content. The 10 Dq value for together with the mean Cr–O distance in end-member knorringite, 1.96 Å (Novak and Gibbs 1971), were used to calculate from the spectral data, local mean Cr–O distances (Langer 2001a) as a function of composition. The results indicate relatively strong local site relaxation with a value of =0.77.     

Phase transition and compression behavior of gibbsite under high-pressure

In situ high-pressure synchrotron X-ray diffraction and infrared absorption experiments for gibbsite were performed at room temperature up to 53 and 25 GPa, respectively. A phase transition was confirmed at about 2.5 GPa. The high-pressure phase is indexed as an orthorhombic structure, rather than a triclinic structure as reported in previous studies. The compressibility of gibbsite and its high-pressure polymorph were studied, and their bulk moduli K₀ were determined to be 49 and 75 GPa, respectively with K₀ as 4. The in situ high-pressure infrared absorption spectra revealed the gradual disordering of hydrogen substructure above 15 GPa in quasihydrostatic compression.     

A non-reflecting boundary condition for the finite element modeling of infinite reservoir with layered sediment

The design of seismic resistant concrete gravity dam necessitates accurate determination of hydrodynamic pressure developed in the adjacent reservoir. The hydrodynamic pressure developed on structure is dependent on the physical characteristics of the boundaries surrounding the reservoir including reservoir bottom. The sedimentary material in the reservoir bottom absorbs energy at the bottom, which will affect the hydrodynamic pressure at the upstream face of the dam. The fundamental parameter characterizing the effect of absorption of hydrodynamic pressure waves at the reservoir bottom due to sediment is the reflection coefficient. The wave reflection coefficient is determined from parameters based on sediment layer thickness, its material properties and excitation frequencies. An analytical or a closed-form solution cannot account for the arbitrary geometry of the dam or reservoir bed profile. This problem can be efficiently tackled with finite element technique. The need for an accurate truncation boundary is felt to reduce the computational domain of the unbounded reservoir system. An efficient truncation boundary condition (TBC) which accounts for the reservoir bottom effect is proposed for the finite element analysis of infinite reservoir. The results show the efficiency of the proposed truncation boundary condition.     

流动注射在线置换吸附预富集与火焰原子吸收联用分析地质样品中痕量银

介绍了应用编结反应器为吸附介质,流动注射在线置换吸附预富集消除Fe、Ca、Mn、Pb等共存金属离子的影响,与火焰原子吸收联用分析痕量银的方法,Ag(Ⅰ)吸收信号峰高比直喷时增感26倍,检出限为0.60μg/g。方法用于国家一级地质标准物质中Ag的测定,结果与标准值相符,5次测定的RSD≤4.8%。     

Characterization of NH4-phlogopite (NH4) (Mg3) [AlSi3O10] (OH)2 and ND4-phlogopite (ND4) (Mg3) [AlSi3O10] (OD)2 using IR spectroscopy and Rietveld refinement of XRD spectra

 A synthesis technique is described which results in >99% pure NH₄-phlogopite (NH₄) (Mg₃) [AlSi₃O₁₀] (OH)₂ and its deuterium analogue ND₄-phlogopite (ND₄) (Mg₃) [AlSi₃O₁₀] (OD)₂. Both phases are characterised using both IR spectroscopy at 298 and 77 K as well as Rietveld refinement of their X-ray powder diffraction pattern. Both NH₄ ⁺ and ND₄ ⁺ are found to occupy the interlayer site in the phlogopite structure. Absorption bands in the IR caused by either NH₄ ⁺ or ND₄ ⁺ can be explained to a good approximation using T_d symmetry as a basis. Rietveld refinement indicates that either phlogopite synthesis contains several mica polytypes. The principle polytype is the one-layer monoclinic polytype (1M), which possesses the space group symmetry C2/m. The next most common polytype is the two-layer polytype (2M ₁ ) with space group symmetry C2/c. Minor amounts of the trigonal polytype 3T with the space group symmetry P3₁12 were found only in the synthesis run for the ND₄-phlogopite. Electron microprobe analyses indicate that NH₄-phlogopite deviates from the ideal phlogopite composition with respect to variable Si/Al and Mg/Al on both the tetrahedral and octahedral sites, respectively, due to the Tschermaks substitution ^VIMg²⁺+^IVSi⁴⁺↔^VIAl³⁺+^IVAl³⁺ and with respect to vacancies on the interlayer site due to the exchange vector ^XII(NH₄)⁺+^IVAl³⁺↔^XII□+^IVSi⁴⁺. Received: 30 August 1999 / Accepted: 2 October 2000     

Texture effect on polarized EXAFS amplitude

 Application of polarized extended X-ray absorption fine structure (P-EXAFS) spectroscopy to thin films of fine-grained minerals is emerging as a powerful method to investigate the in-plane and out-of-plane local structure of phyllosilicates. Mineral platelets have no preferential orientation in the plane of the film, and their c* axes are oriented essentially along the film normal. The angular dependence of the EXAFS amplitude critically depends on the orientation distribution of c* axes due to mosaic spread. The effect of film texture on EXAFS amplitude has been calculated as a function of the mosaic spread, the orientation of the electric field vector, and the crystallographic orientation of the atomic pair. Calculations show that the reduction in amplitude for partially ordered films is more important when the electric field vector is perpendicular to the film plane. For phyllosilicates, no significant deviation from single crystal dichroism occurs when the mosaic spread is less than ±20–25° half-width at half-maximum (HWHM) for parallel measurement, and ±15–20° HWHM for normal measurement. Graphs are given for correcting EXAFS-derived coordination numbers for texture effects. Received: 3 February 2000 / Accepted: 26 July 2000     

原子吸收法测定炼银炉渣中的金

采用HF－H2SO4除硅，萃取－原子吸收法测定炼银炉渣中的金。样品加标回收率为92.0％－104.0％，相对标准偏差为3.8％（n＝11）。将该法应用到炼银炉渣中金的测定，结果符合分析质量要求。     

NK8310螯合树脂分离富集地质样品中痕量金银铂钯及其测定

研究了硫脲螯合树脂（NK8310）分类富集地质样品中痕量Au、Ag、Pt和Pd的实验条件。在φ=10％的王水介质中，[AuCI4]^-、[AgCI2]^-、[PtCI6]^2-和[PdCI4]^2-定量吸附于树脂上并与大量贱金属分离；用5g/L硫脲－0.12mol/L HCI溶液洗脱Au、Ag、Pt和Pd，回收率为97％－104％。用硫镍矿管理样以及国家一级标准物质进行分析验证，分析结果与推荐值及标准值吻合，表明NK8310螯合树脂适用于地质样品中Au、Ag、Pt和Pd的分离富集。