Infrared spectroscopic characterization of dehydration and accompanying phase transition behaviors in NAT-topology zeolites

Relative humidity ( P_{\textH 2 \textO} P_{{{\text{H}}_{ 2} {\text{O}}}} , partial pressure of water)-dependent dehydration and accompanying phase transitions in NAT-topology zeolites (natrolite, scolecite, and mesolite) were studied under controlled temperature and known P_{\textH 2 \textO} P_{{{\text{H}}_{ 2} {\text{O}}}} conditions by in situ diffuse-reflectance infrared Fourier transform spectroscopy and parallel X-ray powder diffraction. Dehydration was characterized by the disappearance of internal H₂O vibrational modes. The loss of H₂O molecules caused a sequence of structural transitions in which the host framework transformation path was coupled primarily via the thermal motion of guest Na⁺/Ca²⁺ cations and H₂O molecules. The observation of different interactions of H₂O molecules and Na⁺/Ca²⁺ cations with host aluminosilicate frameworks under high- and low- P_{\textH 2 \textO} P_{{{\text{H}}_{ 2} {\text{O}}}} conditions indicated the development of different local strain fields, arising from cation–H₂O interactions in NAT-type channels. These strain fields influence the Si–O/Al–O bond strength and tilting angles within and between tetrahedra as the dehydration temperature is approached. The newly observed infrared bands (at 2,139 cm⁻¹ in natrolite, 2,276 cm⁻¹ in scolecite, and 2,176 and 2,259 cm⁻¹ in mesolite) result from strong cation–H₂O–Al–Si framework interactions in NAT-type channels, and these bands can be used to evaluate the energetic evolution of Na⁺/Ca²⁺ cations before and after phase transitions, especially for scolecite and mesolite. The 2,176 and 2,259 cm⁻¹ absorption bands in mesolite also appear to be related to Na⁺/Ca²⁺ order–disorder that occur when mesolite loses its Ow4 H₂O molecules.     

High-<Emphasis Type="Italic">P</Emphasis>, <Emphasis Type="Italic">T</Emphasis> phase relations in the NaAlSi<Subscript>2</Subscript>O<Subscript>6</Subscript> system from first principles computation

Vibrational density of states of the NaAlSi₂O₆ jadeite and NaAlSiO₄ calcium ferrite (CF)-type, and SiO₂ stishovite is calculated as a function of pressure up to 50 GPa using density functional perturbation theory. The calculated frequencies are used to determine the thermal contribution to the Helmholtz free energy within the quasi-harmonic approximation and to derive the equation of state and several thermodynamic properties of interest. A dissociation of jadeite into a mixture of a CF-type phase and stishovite is predicted to occur at 23.4 GPa and 1,800 K with a positive Clapeyron slope of 2.8 MPa/K. Elastic anisotropy for jadeite, the CF-type phase, and stishovite also computed clearly shows that stishovite and the CF-type phase are the most anisotropic and isotropic in these three phases, respectively.     

ESEEM of industrial quartz powders: insights into crystal chemistry of Al defects

A set of raw industrial materials, that is, pure quartz and quartz-rich mixtures, were investigated through electron paramagnetic resonance and electron spin echo-envelope modulation spectroscopies, with the aim of evaluating the effective role played by defect centres and of assessing whether they can be used to monitor changes in the physical properties of quartz powders with reference to their health effects. The obtained results point to two interactions of the Al defect centres with H⁺, hosted in sites within the channels parallel and perpendicular to the c axis of quartz, respectively. These two Al/H⁺ (h_Al) centres exhibit a weak chemical bond, and their relative amounts appear to be modified/controlled by the thermo-mechanical processes underwent by powders. Indeed, a mechanically promoted inter-conversion between the two kinds of site is suggested. As a consequence, the h_Al centres are effective in monitoring even modest activations of powders, through thermal or mechanical processes, and they are also supposed to play a specific, relevant role in quartz reactivity during the considered industrial processes.     

Cation substitution in synthetic meridianiite (MgSO<Subscript>4</Subscript>·11H<Subscript>2</Subscript>O) I: X-ray powder diffraction analysis of quenched polycrystalline aggregates

Meridianiite, MgSO₄·11H₂O, is the most highly hydrated phase in the binary MgSO₄–H₂O system. Lower hydrates in the MgSO₄–H₂O system have end-member analogues containing alternative divalent metal cations (Ni²⁺, Zn²⁺, Mn²⁺, Cu²⁺, Fe²⁺, and Co²⁺) and exhibit extensive solid solution with MgSO₄ and with one another, but no other undecahydrate is known. We have prepared aqueous MgSO₄ solutions doped with these other cations in proportions up to and including the pure end-members. These liquids have been solidified into fine-grained polycrystalline blocks of metal sulfate hydrate + ice by rapid quenching in liquid nitrogen. The solid products have been characterised by X-ray powder diffraction, and the onset of partial melting has been quantified using a thermal probe. We have established that of the seven end-member metal sulfates studied, only MgSO₄ forms an undecahydrate; ZnSO₄ forms an orthorhombic heptahydrate (synthetic goslarite), MnSO₄, FeSO₄, and CoSO₄ form monoclinic heptahydrates (syn. mallardite, melanterite, bieberite, respectively), and CuSO₄ crystallises as the well-known triclinic pentahydrate (syn. chalcanthite). NiSO₄ forms a new hydrate which has been indexed with a triclinic unit cell of dimensions a = 6.1275(1) Å, b = 6.8628(1) Å, c = 12.6318(2) Å, α = 92.904(2)°, β = 97.678(2)°, and γ = 96.618(2)°. The unit-cell volume of this crystal, V = 521.74(1) ų, is consistent with it being an octahydrate, NiSO₄·8H₂O. Further analysis of doped specimens has shown that synthetic meridianiite is able to accommodate significant quantities of foreign cations in its structure; of the order 50 mol. % Co²⁺ or Mn²⁺, 20–30 mol. % Ni²⁺ or Zn²⁺, but less than 10 mol. % of Cu²⁺ or Fe²⁺. In three of the systems we examined, an ‘intermediate’ phase occurred that differed in hydration state both from the Mg-bearing meridianiite end-member and the pure dopant end-member hydrate. In the case of CuSO₄, we observed a melanterite-structured heptahydrate at Cu/(Cu + Mg) = 0.5, which we identify as synthetic alpersite [(Mg_0.5Cu_0.5)SO₄·7H₂O)]. In the NiSO₄- and ZnSO₄-doped systems we characterised an entirely new hydrate which could also be identified to a lesser degree in the CuSO₄- and the FeSO₄-doped systems. The Ni-doped substance has been indexed with a monoclinic unit-cell of dimensions a = 6.7488(2) Å, b = 11.9613(4) Å, c = 14.6321(5) Å, and β = 95.047(3)°, systematic absences being indicative of space-group P2₁/c with Z = 4. The unit-cell volume, V = 1,176.59(5) ų, is consistent with it being an enneahydrate [i.e. (Mg_0.5Ni_0.5)SO₄·9H₂O)]. Similarly, the new Zn-bearing enneahydrate has refined unit cell dimensions of a = 6.7555(3) Å, b = 11.9834(5) Å, c = 14.6666(8) Å, β = 95.020(4)°, V = 1,182.77(7) ų, and the new Fe-bearing enneahydrate has refined unit cell dimensions of a = 6.7726(3) Å, b = 12.0077(3) Å, c = 14.6920(5) Å, β = 95.037(3)°, and V = 1,190.20(6) ų. The observation that synthetic meridianiite can form in the presence of, and accommodate significant quantities of other ions increases the likelihood that this mineral will occur naturally on Mars—and elsewhere in the outer solar system—in metalliferous brines.     

The assessment of health impact caused by energy use in urban areas of China: an intake fraction–based analysis

The Indian Ocean Tsunami of December 2004 caused inundation of seawater along the Northern coast of Tamil Nadu, India, resulting in loss of 8,000 people with extensive damage to properties. The paper describes the inundation of seawater in two northern districts, namely Kancheepuram and Villupuram districts, which showed distinct patterns of inundation of seawater and run-up levels due to variations in geomorphic features. TUNAMI N2 model was used to predict the seawater inundation for earthquakes occurred in 1881 at Car Nicobar, Sumatra 2004 and a worst-case scenario. The coastal areas with beaches having gentle slope showed more inundation compared with coastal areas having varied slope and habited by sand dunes and coastal vegetation. Appreciable inundation of seawater with tsunami simulated for 1881 Car Nicobar indicated that proximity to the source plays a major role besides earthquake parameters in causing inundation. The worst-case scenario generated from subduction zone of Car Nicobar using Sumatra 2004 earthquake parameters revealed extreme vulnerability of coasts of both the districts to giant tsunamis.     

Two-dimensional dam break flooding simulation: a GIS-embedded approach

In the twenty-first century, around 200 notable dam and reservoir failures happened worldwide causing massive fatalities and economic costs. In order to reduce the losses, managers usually define mitigation strategies identifying flooding area due to dam break by using standalone hydrodynamic models and then importing the results within a GIS to perform risk analysis. This two-step procedure is time expensive, error prone due to export/import requirements and not user friendly. For this reason with this work, a new numerical model for the solution of the two-dimensional dam break problem has been implemented in the GRASS GIS with a GIS-embedded approach. The model solves the conservative form of the 2D shallow water equations using a finite volume method; the intercell flux is computed by one-side upwind conservative scheme extended to a two-dimensional problem. The newly developed GIS module, among others outputs, allows to derive maximum intensity maps that can be directly used for risk assessment. Finally, the model has been (1) tested against two standard synthetic problems referenced in literature showing differences in estimated water depth of 2, 3 and 15% and (2) verified against official flooding map of an existing dam (Verzasca) detecting 75% of similarity. The problem formulation, the new GRASS module and its validation is presented.     

Comparison of near-fault and far-fault ground motion effects on geometrically nonlinear earthquake behavior of suspension bridges

This paper presents a comparison of near-fault and far-fault ground motion effects on geometrically nonlinear earthquake behavior of suspension bridges. Bo?azi?i (The First Bosporus) and Fatih Sultan Mehmet (Second Bosporus) suspension bridges built in Istanbul, Turkey, are selected as numerical examples. Both bridges have almost the same span. While Bo?azi?i Suspension Bridge has inclined hangers, Fatih Sultan Mehmet Suspension Bridge has vertical hangers. Geometric nonlinearity including P-delta effects from self-weight of the bridges is taken into account in the determination of the dynamic behavior of the suspension bridges for near-fault and far-fault ground motions. Near-fault and far-fault strong ground motion records, which have approximately identical peak ground accelerations, of 1999 Chi-Chi, 1999 Kocaeli, and 1979 Imperial Valley earthquakes are selected for the analyses. Displacements and internal forces of the bridges are determined using the finite element method including geometric nonlinearity. The displacements and internal forces obtained from the dynamic analyses of suspension bridges subjected to each fault effect are compared with each other. It is clearly seen that near-fault ground motions are more effective than far-fault ground motion on the displacements and internal forces such as bending moment, shear force and axial forces of the suspension bridges.     

Risk evaluation of China’s natural disaster systems: an approach based on triangular fuzzy numbers and stochastic simulation

To deal effectively with the evaluation problem of natural disaster risk system affected by many uncertain factors, a multivariate connection number expression is presented. This expression is based on the index samples and evaluation grade criterions of natural disaster risk system and is capable of describing the hierarchy property and fuzziness of membership relationship between index samples and evaluation grade criterions. In this proposed method, the fuzzy evaluation grade criterion problem is resolved by combining triangular fuzzy numbers with multivariate connection number theory, and triangular fuzzy numbers are used to express the discrepancy degree coefficients of connection number and evaluation index weights. Accordingly, a connection number-based evaluation method for the natural disaster system of China (named CN-TFN for short) is established using triangular fuzzy numbers and stochastic simulation. The application results show that the spatial distribution of natural disaster risk grades of China has the trend of aggrandizement from west to east of China. The economically developed and densely populated coastal areas are very likely to have a high level of natural disaster risk grade or above; thus, these areas are the key regions of the natural disaster risk management of China. The results also show that the CN-TFN is able to reflect practical conditions of the evaluation problem of natural disaster system and to provide more reliability information as compared to the existing evaluation methods. This is as a result of its comprehensive usage of various information of subjective and objective uncertainties in the evaluation process of natural disaster risk system and its expression by confidence intervals. Due to the simplicity and generalization, the CN-TFM is applicable to comprehensive risk grade evaluation of various natural disaster systems.     

Structure and nuclear density distribution in the cheralite—CaTh(PO4)2: studies of its behaviour under high pressure (36?GPa)

The crystal structure of the cheralite—CaTh(PO₄)₂—has been revisited by neutron diffraction and its behaviour under high pressure investigated by X-ray diffraction up to 36?GPa. The neutron diffraction data at ambient pressure gave a more accurate determination of the Ca/Th cation position than previous XRD data, taking advantage that the neutron scattering lengths of calcium and thorium are of same order of magnitude. The nuclear density distribution was also determined using the maximum entropy method (MEM) confirming that the two cations are not located at the same position in the unit cell but are slightly displaced from one another along a specific direction in order to minimize the electrostatic repulsion with the surrounding phosphorus atoms. At high pressure, the compound did not show any phase transition or amorphization. From the evolution of the unit-cell volume as a function of the pressure, the zero-pressure bulk modulus B₀ and its pressure derivative B₀ ^′ have been determined by fitting the experimental compressibility curve to the Birch–Murnaghan equation of state. The results are B₀?=?140(2) GPa and B ₀ ^′ ?=?4.4(4) GPa.     

Detection of smectites in ppm and sub-ppm concentrations using dye molecule sensors

Methylene blue and rhodamine 6G were used as molecular sensors for the spectrophotometric titrations of the aqueous colloids of clay minerals (montmorillonite, illite and kaolinite). The dyes adsorbed on colloid particles form molecular aggregates, which exhibit spectral properties significantly different from those of dye solutions. Spectrophotometric titrations provide the most sensitive detection of smectites in aqueous colloids (sub-ppm concentrations); and the sensitivity further increases using second derivative spectroscopy. The endpoint of spectrophotometric titrations can be used for the determination of exchange capacity of the mineral in colloids and in this way to estimate its amount. The method is selective only to expandable clays, which was proven by experiments with kaolinite and illite. Spectrophotometric titrations have promising future in the analysis of clays and can be applied in many fields of geology, mineralogy, chemistry, material sciences or in industry. Its application may expand to the analysis of other nanomaterials built from charged particles and exhibiting metachromasy in the systems with organic dyes.