(Cr1−x Al x )N as a candidate for corrosion protection in high temperature segments of CCS plants

Three (Cr_1?x Al _x )N (x = 0.33, 0.5, 0.66) coatings were deposited on Ni-super alloy IN718 using reactive magnetron sputtering. The oxidation behavior of all coatings at 900 °C up to 500 h in air was studied. Furthermore, the corrosion behavior of the (Cr_0.33,Al_0.66)N coating at 900 °C (corrosion type I) by spraying a uniform salt scale of Na₂SO₄ on the sample surface (1 mg/cm²) was investigated. It was found that the coated samples indicate significantly higher oxidation and corrosion resistance compared to uncoated Ni super alloy. This is mainly due to the formation of protective Cr₂O₃ and Al₂O₃ layers on the coating surface. With the increase of Al content, the coatings exhibited improved oxidation resistance. The formation of thin and adherent Al₂O₃ scale on the surface of Al rich coating is the reason for its better oxidation behavior. The detailed structures of the oxide scales and the interdiffusion between coating and substrate were studied using energy dispersive X-ray spectroscopy-analysis.     

Cordierite-garnet-sillimanite-quartz equilibrium: I. New experimental calibration in the system FeO−Al2O3−SiO2−H2O and certain P-T-X H2O relations

The equilibrium in which hydrous Fe-cordierite breaks down to almandine, sillimanite, quartz, and water was previously experimentally determined by Richardson (1968) and Holdaway and Lee (1977) using QMF buffer and by Weisbrod (1973) using QIF buffer. All these studies yielded similar results — a negative dP/dT slope for the equilibrium curve. However, based on theoretical arguments, Martignole and Sisi (1981), and based on Fe-Mg partitioning experiments on coexisting cordierite and garnet in equilibrium with sillimanite and quartz, Aranovich and Podlesskii (1983) suggested that this equilibrium curve has a positive dP/dT slope and its position depends on the water content of the equilibrium cordierite. We have redetermined this equilibrium using a much improved tecnique of detecting reaction direction, and cordierite starting material that contained virtually no hercynite. Hercynite was present as a contaminant in the cordierites of previous experimental studies and possibly reacted with quartz during the experimental runs to expand the apparent stability field of Fe-cordierite. We synthesized Fe-cordierite from reagent grade oxides at 710°C and 2 kbar (using QMF buffer) with two intermediate stages of grinding and mixing. The cordierite has a unit cell volume of 1574.60 ų (molar volume=23.706 J/bar) and no Fe³⁺ as indicated by X-ray diffraction and room temperature Mössbauer studies respectively. Reaction direction was concluded by noting20% change of the ratios of intensities of two key X-ray diffraction peaks of cordierite and almandine. Our results show that the four-phase equilibrium curve passes through the points 2.1 kbar, 650°C and 2.5 kbar, 750°C. This disagrees with all previous experimental studies. H₂O in the Fe-cordierite, equilibrated at 2.2 kbar and 700°C and determined by H-extraction line in the stable isotope laboratory, is 1.13 wt% (n=0.41 moles). H₂O content of pure Mg-cordierite equilibrated under identical conditions and determined by thermogravimentric conditions and determined by thermogravimetric analysis is 1.22 wt% (n=0.40). Similar determinations on Fe-cordierite and Mg-cordierite equilibrated at 2.0 kbar and 650°C show 1.27 wt% (n=0.46) and 1.47 wt% (n=0.48) of H₂O respectively. Thus, H₂O content appears to be independent of Fe/Mg ratio in cordierite, a conclusion which supports previous experimental determinations. The experimentally determined equilibrium curve represents conditions of P_H2O=P_total. From this we calculated the anhydrous curve representing equilibrium under conditions of X _H2O ^V =0.0. A family of calculated equilibrium curves of constant n _H2O ^Cord cut the experimentally determined curve at a very small angle indicating a slight variation in n _H2O ^Cord in cordierite in equilibrium with almandine, sillimanite, and quartz under the conditions of constant X _H2O ^V . Ancther set of calculated equilibrium curves, each representing constant a _H2O ^V demonstrate that the slopes of the curves vary with X _H2O ^V , and are all positive in the full range of 0.0X _H2O ^V 1.0.     

Crystal chemistry of perovskite-type compounds in the tausonite-loparite series, (Sr1−2 x Na x La x )TiO3

Perovskite-type compounds in the series tausonite-loparite, (Sr_{1?2 x} Na _x La _x )TiO₃, were synthesized by solid-state reaction (final heating at 1200–1300?°C), and studied using “conventional” and synchrotron X-ray powder diffractometry. The structures of intermediate compositions were determined using the Rietveld profile refinement method. In the compositional range 0?≤x?≤ 0.1, the series comprises perovskites characterized by an undistorted cubic structure (space group Pm3¯m, a?≈ 3.905–3.902?Å, Z?=?1). Intermediate compounds in the range 0.15?≤?x?≤?0.35 crystallize with tetragonal symmetry (I4/mcm, a?≈? , c?≈? , Z?=?4) derived from the cubic aristotype by antiphase rotation of the TiO₆ octahedra about a fourfold axis. The angle of rotation estimated from the positional parameters of oxygen atoms ranges from 2.5(7)° to 5.5(4)°. The cubic-to-tetragonal transition arises from substitution of Sr²⁺ by the comparatively smaller Na¹⁺ and La³⁺ cations. A further transition from the tetragonal to rhombohedral symmetry (R3¯c, a?≈? , c?≈?2 , Z?=?6) occurs between x?=?0.35 and 0.40, and apparently does not involve formation of perovskite with an intermediate two-tilt structure (Imma). The rhombohedral structure is characterized by a multicomponent octahedral tilt about a threefold axis ranging in magnitude from 6.5(2)° to 7.7(2)°. In the series (Sr_{1?2 x} Na _x La _x )TiO₃, the unit-cell dimensions decrease, and the degree of structural distortion increases with x.     

Copper-substituted manganese-denningites,Mn(Mn1−x Cu x )(Te2O5)2 (0 ≤x ≤ 1): Synthesis and crystal chemistry

Summary The crystal structures of copper-substituted manganese-denningites, Mn(Mn_1–x Cu _x )(Te₂O₅)₂ (0 x 1), were refined in space groupP4₂/nbc from single-crystal X-ray data. Single crystals with different degree of Cu-substitution suitable for X-ray investigation were synthesized under hydrothermal conditions, varying the Cu/Mn ratio and thepH-value. One main feature of the crystal structure is the distribution of Mn and Cu atoms among an eight and a six-coordinated site, respectively. Bond strength calculations support the site occupancies of the MnO₈-polyhedra and MeO₆-octahedra (Me = Cu., Mn_1–x ). The decrease in length of the four Me^[6]-O bonds clearly correlates with the increase of the Cu-substitution resulting in a distortion of the octahedra according to the Jahn-Teller effect of divalent copper. The stronger decrease of the lattice parameterc as compared toa is probably due to the variations of the bond lengths.

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Kupfer-substituierte Mangan-Denningite, Mn(Mn_1–x Cu _x )(Te₂O₅)₂ (0 x 1): Synthese und Kristallchemie

Zusammenfassung Die Kristallstrukturen von Kupfer-substituierten Mangan-Denningiten, Mn(Mn_–x Cu _x )(Te₂O₅)₂ (0 x 1) wurden mittels Einkristall-Röntgenbeugungsdaten in der RaumgruppeP4₂/nbc verfeinert. Geeignete Einkristalle mit unterschiedlich starker Cu-Substitution wurden unter hydrothermalen Bedingungen durch Variieren des Cu/Mn-Verhältnisses bzw. despH-Wertes dargestellt. Ein wesentlicher struktureller Gesichtspunkt ist die Verteilung der Mn und Cu-Atome auf eine acht- bzw. sechskoordinierte Punktlage. Die Verringerung von vier Me^[6]-O Bindungslängen ist klar korrelierbar mit zunehmender Cu-Substitution, und führt zu einer Verzerrung der Oktaeder gemäß dem für zweiwertiges Kupfer bekannten Jahn-Teller Effekt. Bindungsstärkenberechnungen belegen die Besetzung der MnO₈-Polyeder und MeO₆-Oktaeder (Me = Cu _x Mn_1–x ). Die bevorzugte Verkleinerung der Gitterkonstantec gegenübera kann auf die Variationen der Bindungslängen zurückgeführt werden.

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Dedicated to Prof Dr. Josef Zemann on the occasion of his 70th birthday

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With 10 Figures     

Low-temperature thermodynamic model for the system Na2CO3−MgCO3−CaCO3−H2O

A comprehensive low-temperature thermodynamic model for the geochemically important Na₂CO₃−MgCO₃−CaCO₃−H₂O system is presented. The model is based on calorimetrically determined Δ_fH°₂₉₈ values, S°₂₉₈ values and C°_p(T) functions taken from the literature as well as on μ°₂₉₈ values of solids derived in this work from solubility measurements obtained in our laboratories or by others. When these thermodynamic quantities were combined with temperature-dependent Pitzer parameters taken from the literature, solubilities calculated for a wide range of conditions agree well with experimental data. The results for several subsystems were summarized by depicting the respective phase diagrams. For the MgO−CO₂−H₂O subsystem, it was found that the commonly believed stability relations must be revised, i.e., in the temperature range covered, nesquehonite never becomes more stable than hydromagnesite at p_CO2 ≤ 1 atm. Although the recommended set of thermodynamic data on sparingly soluble solids was derived from experimental results on mainly NaClO₄ systems, it can be incorporated in databanks containing additional Pitzer parameters for modeling more complex fresh- or seawater systems.     

The crystal chemistry of synthetic potassium-bearing neighborite, (Na1− x K x )MgF3

A series of fluoride perovskites related to neighborite was investigated using X-ray and neutron diffraction techniques, and Rietveld profile refinement of powder diffraction data. The series (Na_{1? x} K _x )MgF₃ comprises orthorhombic (Pbnm, a?≈? , b?≈? , c?≈?2a _p , Z=4) perovskites in the compositional range 0?≤?x?≤?0.30, tetragonal perovkites (P4/mbm, a?≈? , c?≈?a _p , Z=2) in the range 0.40?≤?x?≤?0.46, and cubic phases (Pm3¯m, Z=1) for x?>?0.50. The structure of the orthorhombic neighborite is derived from the perovskite aristotype by rotation of MgF₆ octahedra about the [110] and [001] axes of the cubic subcell. The degree of rotation, measured as a composite tilt Φ about the triad axis, varies from 18.2° at x=0 to 11.2° at x=0.30 (as determined from the fractional atomic coordinates). Orthorhombic neighborite also shows a significant displacement of Na and K from the “ideal” position (≤0.25?Å). The tetragonal members of the neighborite series exhibit only in-phase tilting about the [001] axis of the cubic subcell (φ) ranging from 4.5° to 4.8° (determined from the atomic coordinates). The solid solution (Na_{1? x} K _x )MgF₃, shows a regular variation of unit-cell dimensions with composition from 3.8347?Å for the end-member NaMgF₃ (reduced to pseudocubic subcell, a _p ) to 3.9897?Å for KMgF₃. This variation is accompanied by increasing volumes of the A-site polyhedra, whereas the volume of MgF₆ octahedra initially decreases (up to x=0.40), and then increases concomitantly with K content. The polyhedral volume ratio, V _A /V _B , gradually increases towards the tetragonal structural range, in agreement with diminishing octahedral rotation in the structure. The P4/mbm-type neighborite has an “anomalous” polyhedral volume ratio (ca. 5.04) owing to the critical compression of MgF₆ polyhedra.     

Thermodynamics of (Fe2+, Mn2+, Mg, Ca)3− Al2Si3O12 garnet: a review and analysis

Summary The thermodynamic properties of garnets in the system (Fe²⁺, Mn²⁺, Mg, Ca)₃A1₂Si₃O₁₂ are reviewed. The thermodynamic properties of the three end-member garnets pyrope, almandine and grossular, including their volume, enthalpy of formation, entropy, compressibility and thermal expansion have been well determined. For spessartine enthalpy of formation and heat capacity at low temperatures are needed. Pyrope's unusual behavior in some of its properties is probably related to the presence of the small, light Mg cation, which has a large anisotropic thermal vibration. The thermodynamic mixing properties of the six binaries are also discussed. Good volume of mixing data exist now for all of the binaries, but much work is still required to determine the enthalpies and third-law vibrational entropies of mixing. It is shown that the magnitude of the positive deviations in the volumes of mixing is related to the volume difference between the two end-member components. It is probable that excess entropies, if present, originate at low temperatures below 200 K. Recent²⁹Si NMR experiments have demonstrated the presence of short-range ordering (SRO) of Ca and Mg in pyrope-grossular solid solutions. Short-range order will have to be considered in new models describing the entropies of mixing. Its possible presence in all garnet solid solutions needs to be examined. The mixing properties of pyrope-grossular garnets, which are the best known for any garnet binary, can, in part, be described by the Quasi-Chemical approximation, which gives insight into the microscopic interactions which determine the macroscopic thermodynamic mixing properties. Microscopic properties are best investigated by spectroscopic and computational approaches. Hard mode IR measurements on binary solid solutions show that the range of local microscopic structural distortion is reflected in the macroscopic volumes of mixing. The nature of The contents of this contribution was presented at the IMA Meeting in Toronto in August, 1998. It precedes issues of Mineralogy and Petrology containing thematic sets of IMApapers strain tiields and site relaxation needs to be studied in order to obtain a better understanding of the solid-solution process and energetics in garnet. Critical areas for future experimentation are also addressed.[/p]

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Eine kritische Zusammenstellung und Analyse der thermodynamischen Daten der (Fe²⁺, Mn²⁺, Mg, Ca)₃Al₂Si₃O₁₂ granate

Zusammenfassung In dieser Studie werden die thermodynamischen Eigenschaften der Granate im System (Fe²⁺,Mn²⁺, Mg, Ca)₃Al₂Si₃O₁₂ kritisch zusammengestellt. Die thermodynamischen Eigenschaften der drei Endglied-Granate Pyrop, Almandin und Grossular, einschließlich ihrer Volumina, Bildungswärmen, Entropien, Kompressibilitäten und thermischen Ausdehnungen wurden bereits hinreichend gut bestimmt. Dagegen müssen die Bildungswärme und Tieftemperatur-Wärmekapazität von Spessartin noch gemessen werden. Die Eigenschaften des Pyrops sind wahrscheinlich mit den großen anisotropen Schwingungen des kleinen, leichten Mg-Kations verbunden. Die thermodynamischen Mischungseigenschaften der sechs binären Mischkristallreihen werden ebenfalls diskutiert. Während die Mischungs-Volumendaten der binären Mischreihen gut bekannt sind, müssen ihre Mischungs-Enthalpien und Standard-Mischungsentropien noch ermittelt werden. Es wurde gezeigt, daß die Größe der positiven Exzeß-Volumina mit dem Volumen-Unterschied der zwei Endglied-Komponenten der jeweiligen Mischreihe verknüpft ist. Es ist wahrscheinlich, daß Exzeß-Entropien, wenn vorhanden, erst bei Tieftemperaturen unter 200 K auftreten. Neue²⁹Si NMR-Experimente belegen, daß in Pyrop-Grossular-Mischkristallen Nahordnung von Mg und Ca vorliegt. Der Effekt der Nahordnung muß in künftigen thermodynamischen Modellen berücksichtigt werden. Hieraus ergibt sich die Notwendigkeit, alle Granat-Mischreihen auf mögliche Nahordnung hin zu untersuchen. Die Mischungseigenschaften der Pyrop-Grossular-Mischreihe, die von sämtlichen Granat-Mischreihen am besten bestimmt wurden, können teilweise mit dem Quasi-Chemical-Model beschrieben werden. Dieses Modell ermöglicht die Beschreibung der mikroskopischen Wechselwirkungen, die die makroskopischen thermodynamischen Eigenschaften bestimmen. Mikroskopische Eigenschaften werden am besten mit spektroskopischen Messungen und theoretischen Berechnungen untersucht. Hard-mode IR-Spektroskopie-Messungen an binären Mischreihen zeigen, daß die lokalen mikroskopischen strukturellen Verzerrungen in den makroskopischen Mischungs-Volumina widergespiegelt werden. Die Art der Spannungsfelder und Platz-Relaxationen muß detaillierter untersucht werden, um ein besseres Verständnis des Mischkristall-Bildungsprozsses und der Energetik der Granate zu erreichen. Darüber hinaus werden wichtige künftige Forschungsgebiete diskutiert.

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With 11 Figures     

A re-examination of the role of hydrogen in Al−Si interdiffusion in feldspars

Recent experimental studies have shown that the rates of Al–Si order-disorder and interdiffusion in alkali feldspars at high pressures under dry conditions increase dramatically in the approximate pressure range 7–14 kb, depending on temperature and feldspar composition (Goldsmith 1987, 1988). Enhancement of Al–Si interdiffusion rates is ascribed to the involvement of hydrogen, but the species of hydrogen involved is undetermined.A simple kinetic analysis of the data of Goldsmith (1987) on disordering of dry albite at 800°–950° C and 6–24 kb in the solid media press is consistent with the NaCl pressure cell acting as a proton donor by enhancing dissociation of water in the pressure medium, generating a high in the experimental environment. The rate constant for disordering of albite is found to increase linearly with the estimated experimental and with the density of aqueous salt solution, implicating H⁺ as the rate-enhancing species.Further experimental studies confirm the importance of . At 16 kb and 850° C, dry albite in sealed Pt capsules in a NaCl cell containing tantalum powder (which reduces H₂O to H₂) remains highly ordered over the same time that complete disordering would occur in the absence of Ta. H₂ cannot therefore be the rate-enhancing species. At 1 kb and 850° C, the extent of Al–Si disorder in albite in direct contact with various NaCl–H₂O solutions increases from partially disordered for pure H₂O to completely disordered for saturated aqueous NaCl solution, giving strong support to the proton model. SIMS scanning ion imaging of albite run products demonstrates conclusively that solution-reprecipitation is not responsible for enhanced disordering rates.Results of disordering experiments in the solid media apparatus cannot be duplicated in Ar gas media internally-heated pressure vessels, even with the same experimental configuration around the albite-bearing capsules, due to the different proton-buffering capacities of the solid and gas media apparatus.     

Cu 2p absorption spectroscopy as a probe for the site occupancy of (ZnxCu1−x)WO4 solid solution

The solid solution sanmartinite (ZnWO₄)—cuproscheelite (CuWO₄) has been studied using Cu 2p X-ray absorption spectroscopy. While a single L₃ absorption peak is observed for CuWO₄, two distinct L₃ absorption peaks with a separation of ～0.8 eV are observed for the intermediate samples in the solid solution. The two peaks represent distinct Cu sites: one with all CuO₆ next nearest neighbours in the (Cu,Zn)O₆ chains, another having at least one ZnO₆ next nearest neighbour. Both sites show a linear increase in covalency as a function of increasing Cu-content. The relative intensities of the two absorption peaks is dependent upon the Cu-content and has been used to model the site occupancies. The results reveal that the local structural effects can be associated with a composition-dependent structural phase transition from P2/c (ZnWO₄) to P $\bar 1$ (CuWO₄). Deviations from a single-site model are explained in terms of the local environments, and evidence for site preferences and local clustering are explored.     

Depmeierite Na8[Al6Si6O24](PO4,CO3)1−x · 3H2O (x < 0.5): A new cancrinite-group mineral species from the Lovozero alkaline pluton of the Kola Peninsula

A new mineral depmeierite, the first cancrinite-group member with the species-forming extraframework anion PO ₄ ^3? , has been found at Mt. Karnasurt in the Lovozero alkaline pluton on the Kola Peninsula in Russia. Natrolite and depmeierite are the major components of a hydrothermal peralkaline veinlet 1.5 cm thick, which cross cuts the foyaite-urtite-lujavrite complex. The associated minerals are steenstrupine-(Ce), vuonnemite, epistolite, sodalite, aegirine, serandite, natisite, and vitusite-(Ce). Depmeierite occurs as colorless transparent isometric grains up to 1 cm in size. Its luster is vitreous. The mineral is brittle, and its cleavage (100) is perfect. Its Mohs hardness is 5, and D(meas) = 2.321(1) and D(calc) = 2.313 g/cm³. Depmeierite is optically biaxial positive, ω = 1.493(2), and ? = 1.497(2). The IR spectrum is given. The chemical composition is as follows (wt %, the average of 10 microprobe analyses with the H₂O and CO₂ determined by selective sorption): 23.04 Na₂O, 0.54 K₂O, 0.03 Fe₂O₃, 29.07 Al₂O₃, 36.48 SiO₂, 3.30 P₂O₅, 0.08 SO₃, 0.97 CO₂, and 5.93 H₂O; the total is 99.44. The empirical formula based on (Si,Al)₁₂O₂₄ is (Na₇₅₈K_0.12)_Σ7.70(Si_6.19Al_5.81O₂₄)[(PO₄)_0.47(CO₃)_0.22(OH)_0.02(SO₄)_0.01]_Σ0.72 · 3.345H₂O. The simplified formula is Na₈[Al₆Si₆O₂₄](CO₃)_{1 ? x} · 3H₂O (x < 0.05). Depmeierite is hexagonal with space group P6₃, and the unit-cell dimensions are a = 12.7345(2), c = 5.1798(1), V = 727.46(2) ų, and Z = 1. The strongest reflections of the X-ray powder pattern (d, Å (I, %) [hkl]) are as follows: 6.380(30) [110], 4.695(91) [101], 3.681(37) [300], 3.250(100) [211], 2.758 (33) [400], 2.596(31) [002], and 2.121(24) [330, 302]. The crystal structure was studied using a single crystal, and R _hkl = 0.0362. Depmeierite differs from cancrinite in the development of wide channels containing Na cations, H₂O molecules, prevailing PO ₄ ^3? -anionic groups, and CO ₃ ^2? . The mineral is named in honor of the German crystallographer Wulf Depmeier (born in 1944). The type specimen is deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences in Moscow. The cancrinite sensu stricto subgroup separated within the cancrinite group comprises six minerals with AB frameworks, the smallest unit cell is (a ≈ 12.55–12.75, c ≈ 5.1–5.4 Å), and the chain […Na…H₂O…]^∞ exists in narrow channels: cancrinite, vishnevite, cancrisilite, hydroxycancrinite, kyanoxalite, and depmeierite. The P-bearing varieties of the cancrinite-group minerals are discussed, as well as the formation conditions of the noncarbonate members of the group related to intrusive alkaline complexes.     

Equilibrium dihedral angles in the system H2O−CO2−NaCl-calcite,and implications for fluid flow during metamorphism

Fluid-calcite-calcite dihedral angles have been measured for fluids in the system H₂O−CO₂−NaCl, between 1 and 2 kbar, and 550–750° C. It is found that the calcite-calcite-H₂O dihedral angle decreases steadily with addition of NaCl from a value of about 80° (pure water) to 44° (60 wt% NaCl). The CO₂−H₂O system displays a well-defined minimum at , with a dihedral angle of 50°, in contrast to those of pure CO₂ and H₂O which are 90° and 80° respectively. Experiments containing fluids which are immiscible at run conditions showed a bimodal distribution of dihedral angles in the CO₂−H₂O−NaCl system, which can be approximately correlated with the compositions of the two fluid phases. Such bimodality was only observed for immiscible fluids in the H₂O−NaCl system if the quench rate exceeded about 200°C per min. This is probably due to the extremely rapid establishment of the single phase dihedral angle on quenching. The fluid phase topology in devolatilising marbles will only be a connected network for very saline brines and fluids with close to 0.5. Fluids trapped in fluid inclusions in calcite grains in marbles may be predominantly H₂O-rich or CO₂-rich, and of low salinity. All other fluid compositions in the H₂O−CO₂−NaCl-calcite system will occupy isolated pores, the largest of which will grow at the expense of the smallest. Escape of fluid produced during devolatilisation reactions under such conditions will occur by fluid overpressuring and hydrofracture. In contrast, previous experimental studies of quartz-fluid dihedral angles between 950° and 1100° C (Watson and Brenan 1987) predict that quartz-dominated lithologies will permit pervasive flow of H₂O−NaCl fluids, but not of H₂O−CO₂ fluids. Documented geological examples of differences in permeability and fluid flow mechanism between metamorphic argillites, psammites and limestones which support the results of the experimental studies are discussed.     

土−桩基−隔震支座−核岛地震反应试验研究

通过开展大型地震模拟振动台试验,对比研究了土−桩基−隔震支座−核岛结构和土−桩基−核岛结构的地震反应。试验采用橡胶铅锌支座作为基础隔震,放置于桩基承台和上部核岛结构之间,地基土采用某工程场地的均匀粉质黏土,试验输入的地震动时程,是由美国核电设计的 RG1.60 反应谱拟合而成。试验结果表明：隔震支座不仅可以改变上部结构频率、减小加速度和反应谱幅值大小,还可以减少下部桩的弯矩,起到降低上部结构的反应的隔震作用。但隔震支座的使用会改变桩基础的弯矩分布,核电工程采用隔震支座时应对桩基受力和变形进行特殊抗震设计,以保证土−桩−上部结构整体系统的抗震稳定性。     

The Al (Nb,Ta) Ti(in−2) substitution in titanite: the emergence of a new species?

Summary The highest (Nb, Ta) content ever encountered in titanite is reported from the Maríkov 11 pegmatite in northern Moravia, Czech Republic. This dike is a member of a pegmatite swarm of the beryl-columbite subtype, metamorphosed under conditions of the amphibolite facies. The pegmatite carries, i.a., rare tantalian rutile intergrown with titanian ixiolite, titanian columbite-tantalite, fersmite and microlite. Fissures generated in the Nb, Ta oxide minerals during deformation are filled with titanite, formed by reaction of the oxide minerals with metamorphic pore fluids. The titanite displays limited degrees of substitutions Na(Ta > Nb)(CaTi)_–1, (Ta > Nb)₄Ti_–4Si_–1 and AI(OH, F)(TiO)_–1, but an extensive (and occasionally the sole significant) substitution (Al > Fe³⁺)(Ta > Nb)Ti_–2, responsible for widespread oscillatory zoning. This substitution reduces the proportion of the titanite componentsensu stricto, CaTiSiO₄,O, to less than 50 mole % in many analyzed spots. The extreme composition corresponds to (Ca_0.994Na_0.011)(Ti_0.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). However, so far this substitution fails to generate compositions that would define a new species.

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Zusammenfassung Die AI(Nb, Ta)Ti_–2 Substitution im Titanit: Auftauchen einer neuen Mineralspecies? Die höchsten (Nb, Ta) Gehalte, die jemals für Titanit gefunden wurden, werden für den Maríkov II Pegmatit in Nordmähren, Tschechei, berichtet. Der Intrusivgang ist Teil eines Amphibolit-faziell überprägten Pegmatitschwarms vom Beryll-Columbit Subtypus Der Pegmatit führt u.a. seltene tantalbetonte Rutile verwachsen mit titanbetontem Ixiolith, titanbetontem Columbit-Tantalit, Fersmit and Mikrolith. Deformationsbedingte Frakturen in den (Nb, Ta) Oxiden sind mit Titanit, als Folge der Reaktion der metamorphen Porenlösungen mit den Oxidmineralen, verkittet. Titanit zeigt begrenzte Substitutionen Na(Ta > Nb)(CaTi)_–1,(Ta > Nb)₄Ti_–4Si_–1 and Al(OH, F)(TiO)_–1, aber extensive (und gelegentlich einzig bedeutsame) Substitution (Al >> Fe³⁺)(Ta > Nb)Ti_–2, die eine weitverbreitete, oszillierende Zonierung hervorruft. Diese Substitution verringert den Anteil der Titanit-Komponentesensu stricto, CaTiSiO,O, auf weniger als 50 Mol% in vielen Analysen. Die Extremzusammensetzung entspricht Ca_0.994Na_0.11) (T_10.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). Das AusmaB dieser Substitution ist unzureichend, um eine neue Mineralspecies zu definieren.

     

EPR investigation of NO2 and CO2 − and other radicals in beryl

A number of different impurities are located in the open channels of natural beryl crystals. The rare Maxixe beryl contains an unusual amount of NO₂. The isoelectronic CO₂ ⁻ radical is found in the irradiated Maxixe-type beryl. The NO₂ radicals are distributed in the Be–Al plane of the crystal, with the nitrogen atom close to the oxygens of the beryl cavity wall. These oxygens repel the negative CO₂ ⁻ radical, which is located at the center of the beryl cavity and rotates around its O–O axis, which is parallel to the crystal c-axis. When there is a nearby alkali ion at the center of the beryl channel, it reorients the CO₂ ⁻ radical so that its bisector is parallel to the c-axis and points toward the positive ion. Different signals are analyzed for Li⁺, Na⁺, and another counter-ion, which probably is Cs⁺. The related NO₃ and CO₃ ⁻ radicals are the color centers in the investigated deep blue beryls. The slow decay of the color, which makes these beryls useless as gem stones, is related to the decay of the hydrogen atoms which are present in these crystals. Evidence is given that NO₃ is created in Maxixe beryl by a natural process, while CO₃ ⁻ in Maxixe-type beryl has been created by irradiation. The temperature dependence of the EPR signals of these two radicals was investigated, but a definitive proof that they rotate at the center of the beryl cavity could not be given. EPR signals from some other radicals in beryl have been observed and described.     

High-pressure phase relations in the system TiO2–ZrO2 to 12?GPa: stability of αPbO2-type srilankite solid solutions of (Ti1?x , Zr x )O2 (0?≤?x?≤?0.6)

Phase relations in the system TiO₂–ZrO₂ were examined in the pressure range of 3.5–12?GPa at 1,800?°C, using multianvil apparatus. At 1,800?°C, TiO₂ rutile transforms to αPbO₂ structure at 10?GPa, and the αPbO₂-type solid solution is stable in compositional range between TiO₂ and about (Ti_0.6, Zr_0.4)O₂ at 3.5–12?GPa. Combination of the present results with the published data at 0–3?GPa demonstrates that continuous solid solution with the αPbO₂-type structure is stable between TiO₂ and (Ti_1?x , Zr _x )O₂ (x?≈?0.6) at 0–12?GPa. This indicates that both the αPbO₂-type TiO₂ and srilankite Ti₂ZrO₆ with the same structure belong to the continuous solid solution system though the two phases have been regarded as different minerals. With increasing ZrO₂ content, lattice parameters of a- and c-axes of the αPbO₂-type solid solution increase, but b-axis is almost constant or slightly decreases. At higher pressure, the αPbO₂-type solid solution dissociates into two phases, αPbO₂-type phase and tetragonal zirconia. Srilankite with more TiO₂-rich composition than Ti₂ZrO₆ might be found in natural rocks derived from the deep upper mantle.     

Nitrate removal from water using UV-M/S2O4 2− advanced reduction process

In this work, a new process called advanced reduction process (ARP) was used for nitrate removal from water. This ARP process combines sodium dithionite as reducing agent with ultraviolet irradiation using medium pressure lamps (UV-M) as an activating method. Experimental results showed that UV-M/S₂O₄ ^2? process achieved almost complete removal of nitrate from aqueous solutions containing 25 mg NO₃ ^?/L using stoichiometric dose of dithionite of 68.8 mg/L at neutral pH conditions. Analysis of final products and material balance confirmed that NO₃ ^? ions were reduced to ammonium with formation of nitrite as intermediates in addition to the formation of small amounts of volatile species, mainly ammonia and nitrogen gas. Effects of certain experimental parameters including dithionite dose, initial pH, initial nitrate concentration, and UV light source on the kinetics and efficiency of nitrate reduction were evaluated. Increasing dithionite dose augmented the rate of nitrate reduction and enhanced the efficiency of ARP process. Dithionite doses higher than stoichiometric ratios led to complete removal of nitrate in shorter reaction time. UV-M/S₂O₄ ^2? process was found to be effective only under neutral pH or alkaline conditions, and its removal efficiency is negligible in acidic medium (pH < 4). Irradiation with UV-M was more effective than low pressure or narrow band lamps. These results can be attributed to the contribution of several mechanisms for nitrate reduction to ammonium. These include the following: direct photolysis, chemical reduction of nitrate dithionite, and mediated reduction of nitrate by free reducing radicals.     

Vigrishinite, Zn2Ti4 − x Si4O14(OH,H2O,□)8, a new mineral from the Lovozero alkaline complex, Kola Peninsula, Russia

A new mineral vigrishinite, epistolite-group member and first layer titanosilicate with species-defining Zn, was found at Mt. Malyi Punkaruaiv, in the Lovozero alkaline complex, Kola Peninsula, Russia. It occurs in a hydrothermally altered peralkaline pegmatite and is associated with microcline, ussingite, aegirine, analcime, gmelinite-Na, and chabazite-Ca. Vigrishinite forms rectangular or irregularly shaped lamellae up to 0.05 × 2 × 3 cm flattened on [001]. They are typically slightly split and show blocky character. The mineral is translucent to transparent and pale pink, yellowish-pinkish or colorless. The luster is vitreous. The Mohs’ hardness is 2.5–3. Vigrishinite is brittle. Cleavage is {001} perfect. D _meas = 3.03(2), D _calc = 2.97 g/cm³. The mineral is optically biaxial (?), α = 1.755(5), β = 1.82(1), γ = 1.835(8), 2V _meas = 45(10)°, 2V _calc = 50°. IR spectrum is given. The chemical composition (wt %; average of 9 point analyses, H₂O is determined by modified Penfield method) is as follows: 0.98 Na₂O, 0.30 K₂O, 0.56 CaO, 0.05 SrO, 0.44 BaO, 0.36 MgO, 2.09 MnO, 14.39 ZnO, 2.00 Fe₂O₃, 0.36 Al₂O₃, 32.29 SiO₂, 29.14 TiO₂, 2.08 ZrO₂, 7.34 Nb₂O₅, 0.46 F, 9.1 H₂O, ?0.19 O=F₂, total is 101.75. The empirical formula calculated on the basis of Si + Al = 4 is: H_7.42(Zn_1.30Na_0.23Mn_0.22Ca_0.07Mg_0.07K_0.05Ba_0.02)_Σ1.96(Ti_2.68Nb_0.41Fe _0.18 ³⁺ Zr_0.12)_Σ3.39(Si_3.95Al_0.05)_{Σ4 20.31}F_0.18. The simplified formula is: Zn₂Ti_4?x Si₄O₁₄(OH,H₂O,□)₈ (x < 1). Vigrishinite is triclinic, space group P $\bar 1$ , a = 8.743(9), b = 8.698(9), c = 11.581(11)Å, α = 91.54(8)°, β = 98.29(8)°, γ = 105.65(8)°, V = 837.2(1.5) ų, Z = 2. The strongest reflections in the X-ray powder pattern (d, Å, ?I[hkl]) are: 11.7-67[001], 8.27-50[100], 6.94-43[0 $\bar 1$ 1, $\bar 1$ 10], 5.73–54[1 $\bar 1$ 1, 002], 4.17-65[020, $\bar 1$ $\bar 1$ 2, 200], and 2.861-100[3 $\bar 1$ 0, 2 $\bar 2$ 2, 004, 1 $\bar 3$ 1]. The crystal structure model was obtained on a single crystal, R = 0.171. Vigrishinite and murmanite are close in the structure of the TiSiO motif, but strongly differ from each other in part of large cations and H-bearing groups. Vigrishinite is named in honor of Viktor G. Grishin (b. 1953), a Russian amateur mineralogist and mineral collector, to pay tribute to his contribution to the mineralogy of the Lovozero Complex. The type specimen is deposited in the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow.     

Günterblassite, (K,Ca)3 − x Fe[(Si,Al)13O25(OH,O)4] · 7H2O, a new mineral: the first phyllosilicate with triple tetrahedral layer

A new mineral, günterblassite, has been found in the basaltic quarry at Mount Rother Kopf near Gerolstein, Rheinland-Pfalz, Germany as a constituent of the late assemblage of nepheline, leucite, augite, phlogopite, åkermanite, magnetite, perovskite, a lamprophyllite-group mineral, götzenite, chabazite-K, chabazite-Ca, phillipsite-K, and calcite. Günterblassite occurs as colorless lamellar crystals up to 0.2 × 1 × 1.5 mm in size and their clusters. The mineral is brittle, with perfect cleavage parallel to (001) and less perfect cleavage parallel to (100) and (010). The Mohs hardness is 4. The calculated and measured density is 2.17 and 2.18(1) g/cm³, respectively. The IR spectrum is given. The new mineral is optically biaxial and positive as follows: α = 1.488(2), β = 1.490(2), γ = 1.493(2), 2V _meas = 80(5)°. The chemical composition (electron microprobe, average of seven point analyses, H₂O is determined by gas chromatography, wt %) is as follows: 0.40 Na₂O, 5.18 K₂O, 0.58 MgO, 3.58 CaO, 4.08 BaO, 3.06 FeO, 13.98 Al₂O₃, 52.94 SiO₂, 15.2 H₂O, and the total is 98.99. The empirical formula is Na_0.15K_1.24Ba_0.30Ca_0.72Mg_0.16F _0.48 ²⁺ [Si_9.91Al_3.09O_25.25(OH)_3.75] · 7.29H₂O. The crystal structure has been determined from a single crystal, R = 0.049. Günterblassite is orthorhombic, space group Pnm2₁; the unit-cell dimensions are a = 6.528(1), b = 6.970(1), c = 37.216(5) Å, V = 1693.3(4) ų, Z = 2. Günterblassite is a member of a new structural type; its structure is based on three-layer block [Si₁₃O₂₅(OH,O)₄]. The strong reflections in the X-ray powder diffraction pattern [d Å (I, %) are as follows: 6.532 (100), 6.263 (67), 3.244 (49), 3.062 (91), 2.996 (66), 2.955 (63), and 2.763 (60). The mineral was named in honor of Günter Blass (born in 1943), a well-known amateur mineralogist and specialist in electron microprobe and X-ray diffraction. The type specimen of günterblassite is deposited in the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia, with the registration number 4107/1.     

The crystal chemistry of lithium in the alluaudite structure: a study of the (Na1− x Li x )1.5Mn1.5Fe1.5(PO4)3 solid solution (x = 0 to 1)

Summary Phosphates of compositions (Na_1–xLi_x)_1.5Mn_1.5Fe_1.5(PO₄)₃ were synthesized by solid state reactions in air, and pure alluaudite-type compounds were obtained for x=0.00, 0.25, and 0.50. Rietveld refinements of X-ray powder diffraction data indicate the occurrence of Mn²⁺ in the M(1) site, and of Fe³⁺ and Mn²⁺ in the M(2) site. For x=0.25 and 0.50, A(1) is occupied by Li⁺ and Na⁺, whereas A(2) is occupied by Na⁺ and vacancies. A careful examination of the number of electrons occurring in the A sites of the alluaudite-type compounds (Na_1–xLi_x)MnFe₂(PO₄)₃ and (Na_1–xLi_x) CdIn₂(PO₄)₃ confirms that lithium occupies only the A(1) crystallographic site of the alluaudite structure.