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.     

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     

Electron paramagnetic resonance of Sc3+-stabilized CO 3 3− molecule-ion in natural calcite

Electron paramagnetic resonance (EPR) spectra of CO ₃ ^3– molecule-ions stabilized by Sc³⁺ in natural calcite were identified and studied at X-band frequencies and room temperature. The principal values of the g-tensor (g _xx= 1.9997, g _yy = 2.0030, g _zz = 1.9972) and the direction cosines of the g and A tensors for CO ₃ ^3– -Sc³⁺ center were found to be close to that for the well-known CO ₃ ^3– -Y³⁺ center. A quantitative comparison of different impurity contents in calcite samples and analysis of the intensities of forbidden transitions were used to identify Sc³⁺. An estimation of the unpaired electron spin density on the nuclei of paramagnetic centers confirms that both centers, CO ₃ ^3– -Sc³⁺ and CO ₃ ^3– -Y³⁺, have the same nature.     

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。     

An optical transform and Monte Carlo study of the diffuse X-ray scattering in mullite,Al2(Al2+2xSi2−2x)O10−x

Diffuse X-ray scattering distributions have been recorded for reciprocal layers normal to c ^* of a synthetic mullite with composition Al₂(Al_2+2xSi_2–2x) O_10–xx, where represents an oxygen vacancy and x is close to 0.4. The effect on the diffuse scattering pattern of different schemes for ordering of the oxygen vacancies and the accompanying cation shifts within a single ab-layer of mullite has been investigated using optical diffraction analogue experiments in conjunction with Monte Carlo simulation.A simple scheme in which the only driving force for the ordering is that the O_c oxygens are precluded from being bonded to four T/T^* cations, results in a 2D diffuse intensity distribution which displays many of the features that are observed in the x-ray scattering patterns. An alternative scheme in which bonding to four T/T^* cations was favoured, resulted in a domain structure consisting of islands of the -alumina structure within a matrix of sillimanite. This gave diffraction patterns bearing no resemblance to the observed x-ray patterns and can, we believe, be discounted completely.     

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.     

The solubility control of rare earth elements in natural terrestrial waters and the significance of PO 4 3− and CO 3 2− in limiting dissolved rare earth concentrations: A review of recent information

Rare earth element (REE) concentrations in alkaline lakes, circumneutral pH groundwaters, and an acidic freshwater lake were determined along with the free carbonate, free phosphate, and free sulfate ion concentrations. These parameters were used to evaluate the saturation state of these waters with respect to REE phosphate and carbonate precipitates. Our activity product estimates indicate that the alkaline lake waters and groundwaters are approximately saturated with respect to the REE phosphate precipitates but are significantly undersaturated with respect to REE carbonate and sulfate precipitates. On the other hand, the acidic lake waters are undersaturated with respect to REE sulfate, carbonate, and phosphate precipitates. Although carbonate complexes tend to dominate the speciation of the REEs in neutral and alkaline waters, our results indicate that REE phosphate precipitates are also important in controlling REE behavior. More specifically, elevated carbonate ion concentrations in neutral to alkaline natural waters tend to enhance dissolved REE concentrations through the formation of stable REE-carbonate complexes whereas phosphate ions tend to lead to the removal of the REEs from solution in these waters by the formation of REE-phosphate salts. Removal of REEs by precipitation as phosphate phases in the acid lake (pH=3.6) is inconsequential, however, due to extremely low [PO ₄ ^3– ] _F concentrations (i.e., 10^–23 mol/kg).     

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.     

Zemannite-type Selenites: Crystal structures of K2[CO2(SeO3)3] · 2H2O and K2[Ni2(SeO3)3] · 2H2O

Summary Crystals of K₂[Co₂(SeO₃)₃]-2H₂O and K₂[Ni₂(SeO₃)₃]-2H₂O were synthesized under low-hydrothermal conditions. Their structures were determined using single crystal X-ray data up to sin / = 0.7Å^-1. [Space group P6₃/m; a = 9.091(3),9.016(2)Å; c = 7.562(2), 7.476(2)Å; Z = 2; R_W = 1.6, 2.5%]. The investigations confirmed that K₂[Co₂(SeO₃)₃].2H₂O and K₂[Ni₂(SeO₃)₃]-2H₂O represent the first selenites belonging to the zemannite structure type, a framework structure with wide channels running parallel [0001]. In both compounds four maxima were clearly located in the channel by Fourier summations and attributed to two K atoms and two H₂O molecules, each with an occupancy factor of 1/6; a possible ordering scheme (full occupancy) with local symmetry 1 and [6]-coordinated K atoms could be derived for the channel atoms.Zusammenfassung Kristalle von K₂[Co₂(SeO₃)₃]-2H₂O und K₂[Ni₂(SeO₃)₃]-2H₂O wurden unter niedrig-hydrothermalen Bedingungen synthetisiert. Die Strukturen wurden unter Verwendung von Einkristallröntgendaten bis sin /= 0.7Å^-1 bestimmt. [Raumgruppe P6₃/m; a = 9.091(3), 9.016(2)Å; c = 7.562(2), 7.476(2)Å; Z = 2; R_W = 1.6, 2.5%] Die Untersuchungen bestätigten, daß K2[Co₂(SeO₃)₃] - 2H₂O und K₂ [Ni₂(SeO₃)₃] - 2H₂O als erste Selenite dem Strukturtyp des Zemannits angehören, einer Gerüststruktur mit weiten, parallel [0001] verlaufenden Kanälen. In beiden Verbindungen wurden im Kanal vier Maxima durch Fourier-Summationen eindeutig lokalisiert und zwei Kalium-atomen sowie zwei H₂O Molekülen, jeweils mit einem Besetzungsfaktor von 1/6, zugeschrieben. Für die Kanalatome konnte ein möglicher Ordnungszustand (volle Besetzung) mit lokaler Symmetrie 1 und [6]-koordinierten Kaliumatomen abgeleitet werden.

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Selenite des Zemannittyps: Kristallstrukturen von K₂[Co₂(SeO₃)₃] - 2H₂O und K₂[Ni₂(SeO₃)₃]-2H₂O

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

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With 2 Figures     

Co2+ in trigonal fields of oxygen based structures: Electronic absorption spectra of buetschliite-type K2Co(SeO3)2, K2Co2(SeO3)3 and zemannite-type K2Co2(SeO3)3 · 2H2O

Polarized single crystal absorption spectra, in the spectral range 40 000–5 000 cm^-1, were obtained on Co²⁺ in trigonally distorted octahedral oxygen fields of buetschliite-type K₂Co(SeO₃)₂ (I), K₂Co₂(SeO₃)₃ (II) and zemannite-type K₂Co₂(SeO₃)₃ · 2H₂O (III). Site symmetries of Co²⁺ are m (D_3d) in I, 3m (C_3v) in II, and 3 (C₃) in III. The spectra can be interpreted on the basis of an electric dipole mechanism, wherein transitions of Co²⁺ in the centrosymmetric site in I gain intensity from dynamic removal of the inversion centre by vibronic coupling. In accordance with the elongation of the CoO₆ octahedra along the trigonal axis, the split component E_(g) of the ground state ⁴T_1g in octahedral fields is the ground state in all three compounds. Trigonal field parameters Dq_(trig), D, D and the Racah parameters B have been fitted to the energies of spin allowed transitions (293 K) as follows: I: 744, 94, -16, and 838 cm^-1, resp.; II: 647, 227, 42, and 798 cm^-1, resp.; III: 667, 181, 21, and 809 cm^-1, respectively. Racah parameters C were estimated from the energy of some observed spin-forbidden transitions to be 3770 (I), 3280 (II), and 3465 cm^-1 (III). Values of Dq and of the Racah parameters B and C indicate slight differences of Co²⁺-O bonding in I as compared to II and III, with somewhat higher covalency in compounds II and III which contain face-sharing CoO₆ octahedra with short Co-Co contacts. Also, in II and III the observed D values do not agree with theoretical D values, predicted from the magnitude of the mean octahedral distortions.     

絮凝−真空−电渗联合加固滩涂软土的模型试验研究

针对真空预压作用下排水板淤堵与排水条件受限等问题,提出絮凝−真空−电渗联合加固法。首先通过沉降柱试验确定合适的有机絮凝剂,然后采用该絮凝剂,分别在 48 h（开始介入真空预压,固结度为0 ）、60 h（排水速率明显下降,固结度为60%）及 84 h（排水速率近乎 0,固结度为 80%）时介入电渗,开展不同电渗介入时间的絮凝−真空−电渗联合加固试验。试验从排水量、十字板剪切强度、含水率与孔压等对比分析联合加固的有效性,确定其最佳电渗介入时间。试验结果表明：当固结度为 80% 时介入电渗,絮凝−真空−电渗联合加固法能够有效地抑制排水速率减小的趋势,增长有效排水时间。同时,土体的抗剪强度和承载力亦得到大幅提升,孔压消散更加均匀。此外,在阳离子聚丙烯酰胺絮凝剂的作用下,初始排水速率快,在一定程度上使土体的渗透性得到提升,有效地解决了排水板淤堵问题,说明絮凝−真空−电渗联合加固法具有较强的优越性。     

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.     

非饱和土中热−湿−盐耦合作用的稳态分析

以多孔介质理论为基础,研究了稳态条件下非饱和土中温度?水分?盐分多场耦合问题。考虑非饱和土的孔隙被液态水、溶解的盐分、水蒸气和干燥气体等填充,在质量和能量守恒的基础上获得了非饱和土中水分、气体、盐分的质量守恒方程以及能量守恒方程。考虑一维稳态问题,选取温度、孔隙气压、孔隙水压和盐溶液浓度以及它们的导数作为状态变量,得到了问题的状态方程组。在给定的边界条件下,采用打靶法求解了该强耦合的非线性变系数微分方程组,通过与已有的试验结果相比较,验证了模型的有效性。基于数值算例,参数分析了含水率、温度边界、孔隙率等条件对非饱和土中温度场、水分场和盐分场分布的影响规律。     

强震区桩−土−断层耦合作用下桩基动力响应

为研究桩-土-断层耦合作用下桩基动力响应特性,利用振动台试验选取0.35g地震动峰值加速度时4种类型地震波,研究断层上下盘桩基加速度响应、桩顶相对位移、弯矩及桩基损伤情况。试验表明：断层上盘桩基各项参数明显大于断层下盘,呈现出上盘效应;桩顶峰值加速度大于桩底峰值加速度,上部土层对输入地震波具有滤波作用;桩顶加速度响应相较于桩底具有滞后性;桩顶峰值加速度与桩顶加速度放大系数α在输入El-Centro波时最大;上、下盘α 差值在输入Kobe波时最大;弯矩和桩顶相对位移峰值在输入Kobe波时最大;弯矩在土层分界面处较大,输入不同地震波时弯矩峰值均未超过桩身抗弯能力;提出了强震区近断层桩基可根据验算内容选取合理地震波进行验算的抗震设计建议。     

The molar volume of FeO–MgO–Fe2O3–Cr2O3–Al2O3–TiO2 spinels

We define and calibrate a new model of molar volume as a function of pressure, temperature, ordering state, and composition for spinels in the supersystem (Mg, Fe²⁺)(Al, Cr, Fe³⁺)₂O₄ ? (Mg, Fe²⁺)₂TiO₄. We use 832 X-ray and neutron diffraction measurements performed on spinels at ambient and in situ high-P, T conditions to calibrate end-member equations of state and an excess volume model for this system. The effect on molar volume of cation ordering over the octahedral and tetrahedral sites is captured with linear dependence on Mg²⁺, Al³⁺, and Fe³⁺ site occupancy terms. We allow standard-state volumes and coefficients of thermal expansion of the end members to vary within their uncertainties during extraction of the mixing properties, in order to achieve the best fit. Published equations of state of the various spinel end members are analyzed to obtain optimal values of the bulk modulus and its pressure derivative, for each explicit end member. For any spinel composition in the supersystem, the model molar volume is obtained by adding excess volume and cation order-dependent terms to a linear combination of the five end-member volumes, estimated at pressure and temperature using the high-T Vinet equation of state. The preferred model has a total of 9 excess volume and order-dependent parameters and fits nearly all experiments to within 0.02 J/bar/mol, or better than 0.5 % in volume. The model is compared to the current MELTS spinel model with a demonstration of the impact of the model difference on the estimated spinel-garnet lherzolite transition pressure.     

热−水−力耦合条件下黏土岩蠕变特性研究

黏土岩作为放射性核废料处置的备选介质,长期处于热-水-力耦合的复杂条件下。为研究围岩的长期稳定性,开展了一系列不同围压和偏应力下的黏土岩加温-降温排水蠕变试验。得出以下结论：温度的升高会提升黏土岩的蠕变速率,延长衰减蠕变阶段的时间,但是降温过程中试样主要以冷缩变形为主,并未见明显的蠕变变形;围压的降低以及偏应力的增加会提高黏土岩的蠕变速率,并且这种影响会随温度的升高明显加剧。基于试验结果,在Perzyna过应力理论的基础上引入蠕变硬化、蠕变损伤以及热损伤,建立了黏土岩热-水-力耦合蠕变模型。通过ABAQUS软件及其子程序对该模型进行数值实现,模拟结果与试验结果的对比初步表明该模型可以很好地描述热-水-力耦合条件下黏土岩的蠕变特性。     

Electron spin-lattice relaxation of SO 3 − radical ion in a single crystal of barite

The electron spin-lattice relaxation time (T_1e) of the paramagnetic radical-ion center SO ₃ ^? in a naturally occurring single crystal of barite was studied in the temperature range 10–300 K by the pulse saturation recovery technique. The changes in T_1e from 30 K to 300 K are much smaller than those expected from usual Raman processes in solids. The results suggest a very weak connection between SO ₃ ^? center and lattice.     

全吸力范围生物炭−黏土混合土的土−水特性

土−水特征曲线在研究非饱和土的水力与力学特性中发挥着重要的作用。生物炭具有多孔结构、高比表面积和强吸附的特性。将生物炭改性土应用于垃圾填埋场上覆盖层,因受自然环境因素的影响会使其水力特性发生改变。为了研究全吸力范围内生物炭掺量对生物炭−黏土混合土保水特性的影响,利用蒸汽平衡法（吸力范围 3～368 MPa）、滤纸法（吸力范围 0 ～40 MPa）和压力板法（吸力范围 0～1.5 MPa）控制土样的吸力,测定吸力平衡后土样的含水率和饱和度,得到全吸力范围内生物炭−黏土混合土的土−水特征曲线。试验结果表明：（1）3种吸力测试方法很好地表达了生物炭−黏土混合土全吸力范围内的土−水特征曲线。（2）生物炭能够影响黏土的保水性,但在一定的吸力范围内,生物炭−黏土混合土的保水性还与孔隙结构和孔隙中水的形态相关。（3）通过压力板法测得,试样的进气值随着生物炭掺量的增加而减小。当吸力值小于进气值时,曲线出现水平段,土样始终处于饱和状态,生物炭掺量越大,试样的保水性越好。（4）由生物炭−黏土混合土微观孔隙结构以及生物炭在黏土中的分布形态来解释生物炭改性黏土的保水能力随生物炭掺量的变化关系。     

Thermodynamic properties of copper carbonates — malachite Cu2(OH)2CO3 and azurite Cu3(OH)2(CO3)2

The thermodynamic properties of the copper carbonates malachite and azurite have been studied by adiabatic calorimetry, by heat-flux Calvet Calorimetry, by differential thermal analysis (DTA) and by thermogravimetrie (TGA) analysis. The heat capacities, C _p ⁰ of natural malachite and azurite have been measured between 3.8 and 300 K by low-temperature adiabatic calorimetry. The heat capacity of azurite exhibits anomalous behavior at low temperatures. At 298.15 K the molar heat capacities C _p ⁰ and the third law entropies S _298.15 ⁰ are 228.5±1.4 and 254.4±3.8 J mol^?1 K^?1 for azurite and 154.3±0.93 and 166.3±2.5 J mol^?1 K^?1 for malachite. Enthalpies of solution at 973 K in lead borate 2PbO·B₂O₃ have been measured for heat treated malachite and azurite. The enthalpies of decomposition are 105.1±5.8 for azurite and 66.1±5.0 kJ mol^? for malachite. The enthalpies of formation from oxides of azurite and malachite determined by oxide melt solution calorimetry, are ?84.7±7.4 and ?52.5±5.9 kJ mol^?1, respectively. On the basis of the thermodynamic data obtained, phase relations of azurite and malachite in the system Cu²⁺-H₂O-CO₂ at 25 and 75 °C have been studied.