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A 3D Finite Element Analysis model was developed to describe the temperature distribution inside a novel neutron transparent high-pressure sample assembly. The validity of the model was established by conducting experimental validation. The Finite Element Analysis model was utilised to evaluate the sample assembly's temperature gradients and optimise its geometry and components. The results indicate that the discrepancy between the temperature recorded in the laboratory using thermocouples and the temperature calculated by the Finite Element Analysis model was only 4% under the assumption that the thermocouple was positioned in the middle of the sample assembly. The models further demonstrate that the Finite Element Analysis approach is a valuable tool for optimising the sample assembly by considering the impact of different materials and variations in the shape of its components. [ABSTRACT FROM AUTHOR]

Magnesium doped Amorphous Calcium Carbonate was synthesised from precursor solutions containing varying amounts of calcium, magnesium, H2O and D2O. The Mg/Ca ratio in the resultant Amorphous Calcium Carbonate was found to vary linearly with the Mg/Ca ratio in the precursor solution. All samples crystallised as aragonite. No Mg was found in the final aragonite crystals. Changes in the Mg to Ca ratio were found to only marginally effect nucleation rates but strongly effect crystal growth rates. These results are consistent with a dissolution-reprecipitation model for aragonite formation via an Amorphous Calcium Carbonate intermediate. [ABSTRACT FROM AUTHOR]

The effects of pressure on the OH stretching frequencies of natural talc and two samples of synthetic 10-[Angstrom], phase have been measured using a diamond-anvil cell and a synchrotron infrared source. The 10-[Angstrom] phase was synthesized at 6.0-6.5 GPa, 600[degrees]C for 46 hours (sample 10[Angstrom],-46) and 160 hours (10[Angstrom]-160). Spectra were collected up to 9.0 GPa (talc), 9.9 GPa (10[Angstrom]-46), and 9.6 GPa (10[Angstrom]-160). The OH stretching vibration of [Mg.sub.3]OH groups in talc occurs at 3677 [cm.sup.-1] at ambient pressure, and increases linearly with pressure at 0.97(2) [cm.sup.-1] G[Pa.sup.-1]. The same vibration occurs in 10-[Angstrom] phase, but shows negligible pressure shift up to 2 GPa, above which the frequency increases linearly to the maximum pressure studied, at a rate of 0.96(3) [cm.sup.-1] G[Pa.sub.-1] (10[Angstrom]-46) and 0.87(3) [cm.sup.-1] G[Pa.sup.-1] (10[Angstrom]160). Two other prominent bands in the 10-[Angstrom], phase spectrum are suggested to be due to stretching of interlayer [H.sub.2]O, hydrogen-bonded to the nearest tetrahedral sheet. These bands also show little change over the first 2 GPa of compression, as most of the compression of the structure is taken up by closing non-hydrogen bonded gaps between interlayer [H.sub.2]O and tetrahedral sheets. Between 2 and 4 GPa, changes in band intensities suggest a rearrangement of the interlayer [H.sub.2]O. Keywords: Talc, 10-[Angstrom] phase, high-pressure studies, IR spectroscopy

An asymmetric binary Margules formulation for excess Gibbs energy, enthalpy, and entropy is adequate to describe the 1 bar halite-sylvite solvus in NaCl-KCl (Thompson and Waldbaum 1969). However, a binary Margules formulation is not adequate to describe excess volumes of single-phase chlorides in P-V-T-X from ambient P-T to ~20 kbar and 700 [degrees]C. Excess volumes across NaCl-KCl increase with temperature, decrease with pressure, and show systematic deficits in the consolute region. These patterns can be explained by the importance of a third component--vacancy defects that relieve the lattice stresses of K-Na size mismatch. New, two-phase observations in P-V-T-X allow delineation of the excess Gibbs energies to high pressures where the excess enthalpies and entropies do not depend on Tat each P, but show significant variation between 1 bar and ~20 kbar. The volume, entropy, and enthalpy of K-Na mixing become more ideal at high pressure. But the solvus expands with pressure because entropy approaches ideality faster than enthalpy and, therefore, Gibbs energy of K-Na mixing becomes less ideal with pressure. The consolute temperature rises about 80 [degrees]C in 17 kbar, with little change in consolute composition. The binary Margules equation of state provides a prediction of the rise of the solvus that is impressively convergent with the new observations. This convergence is especially impressive given the clear inadequacies of the binary excess volume formulation on which the prediction is based.

Unit-cell volumes of four single-phase intermediate halite-sylvite solid solutions have been measured to pressures and temperatures of ~28 kbar and ~700 [degrees]C. Equation-of-state fitting of the data yields thermal expansion and compressibility as a function of composition across the chloride series. The variation of the product [[alpha].sub.0]*[K.sub.0] is linear (ideal) in composition between the accepted values for halite and sylvite. Taken separately, the individual values of [[alpha].sub.0] and [K.sub.0] are not linear in composition. [[alpha].sub.0] shows a maximum near the consulute composition (XNacl = 0.64) that exceeds the value for either end-member. There is a corresponding minimum in [K.sub.0]. The fact that the [[alpha].sub.0]*[K.sub.0] product is variable (and incidentally so well behaved as to be linear across the composition series) reinforces the significance of the complementary maxima and minima in [[alpha].sub.0] and K0 (significantly, near the consolute composition). These extrema in [[alpha].sub.0] and [K.sub.0] provide an example of intermediate properties that do not follow simply from values for the end-members. Cell volumes across this series show small, well-behaved positive excesses, consistent with K-Na substitution causing defects through lattice mismatches. Barrett and Wallace (1954) showed maximum defect concentrations in the consolute region. Defect-riddled, weakened structures in the consolute region are more easily compressed or more easily thermally expanded, providing an explanation for our observed [[alpha].sub.0] and [K.sub.0] variations. These compliant, loosened lattices should resist diffusive transfer less than non-defective crystals and, hence, might be expected to show higher diffusivities. Tracer diffusion rates are predicted to peak across the consolute region as exchange diffusion rates drop to zero.

Volatile-sensitive electrical soundings are becoming more widely adopted, with large nationwide arrays currently being acquired globally. This boom in new data is despite several key uncertainties relating to the electrical responses of a wide range of minerals that make up crustal regions. Complications include the influence of mineral chemistry, hydrous or nominally hydrous phases, and oxygen fugacity on charge-carrying ion activity within a mineral substrate. Feldspars are the most abundant mineral group in the Earth's crust, comprising about 60% of its mineral assemblages and are particularly prevalent within subduction zones and lower crustal sequences. These areas are known locations where ore systems are commonly rooted, making them among the most widely studied regions in the Earth. To date, few studies exist that cover the electrical behavior of the feldspar mineral albite. To help address some of these issues and complications, we have undertaken electrical conductivity investigations on a single crystal of gem-quality albite (Ab49An48Or3) from Nuevo Casas Grande, Chihuahua, Mexico. Electrical conductivity measurements using impedance spectroscopy were performed at a pressure of 1 GPa over a temperature range of 373–1273 K in a multi-anvil high-pressure apparatus. Experiments were carried out using different metal electrodes: molybdenum, nickel, and rhenium to vary the oxygen fugacity during the experiments. FTIR measurements of the starting and final materials confirm that the initial samples are completely dry but absorb an average of 67 ppm H2O by mass during the experiments from the surrounding pressure medium materials. We observe no correlation in the amount of water absorbed in the feldspar to the oxygen fugacity under water-undersaturated conditions. Our investigations show that the activation enthalpy increases from ~0.77 to ~1.0 eV from the nominally hydrous to the completely dry feldspar. The activation enthalpy decreases with increasing oxygen fugacity for comparable water contents. An oxygen fugacity exponent of –0.069 is calculated at the nominal water content measured in the experiments, indicating an electrical conductivity mechanism that also involves the mobility of hydrogen. [ABSTRACT FROM AUTHOR]

Starting with the same sample, the electrical conductivities of quartz and coesite have been measured at pressures of 1, 6, and 8.7 GPa, respectively, over a temperature range of 373–1273 K in a multi-anvil high-pressure system. Results indicate that the electrical conductivity in quartz increases with pressure as well as when the phase change from quartz to coesite occurs, while the activation enthalpy decreases with increasing pressure. Activation enthalpies of 0.89, 0.56, and 0.46 eV, were determined at 1, 6, and 8.7 GPa, respectively, giving an activation volume of –0.052 ± 0.006 cm3/mol. FTIR and composition analysis indicate that the electrical conductivities in silica polymorphs is controlled by substitution of silicon by aluminum with hydrogen charge compensation. Comparing with electrical conductivity measurements in stishovite, reported by Yoshino et al. (2014), our results fall within the aluminum and water content extremes measured in stishovite at 12 GPa. The resulting electrical conductivity model is mapped over the magnetotelluric profile obtained through the tectonically stable Northern Australian Craton. Given their relative abundances, these results imply potentially high electrical conductivities in the crust and mantle from contributions of silica polymorphs. The main results of this paper are as follows: • The electrical conductivity of silica polymorphs is determined by impedance spectroscopy up to 8.7 GPa. • The activation enthalpy decreases with increasing pressure indicating a negative activation volume across the silica polymorphs. • The electrical conductivity results are consistent with measurements observed in stishovite at 12 GPa. [ABSTRACT FROM AUTHOR]

The pressure and temperature dependent fluorescence line-shift of strontium tetraborate has been measured concurrently with x-ray diffraction from the pressure standards sodium chloride or gold. Temperature was found to have a small effect on the fluorescence line-shift under pressure. We found a maximum pressure uncertainty of ±1.8 GPa at 25 GPa (7.2%) and 857 K when making no temperature correction. The fluorescence line-shifts for ruby, Alexandrite, and samarium-doped yttrium aluminum garnet were also determined, using our strontium tetraborate calibration to determine pressure and a thermocouple to measure temperature. Fluorescence measurements were extended up to 800 K for ruby and Alexandrite. Temperature was found to have a small effect on the fluorescence line-shift of samarium-doped yittrium aluminum garnet. We found a maximum uncertainty of ±2.7 GPa at 25 GPa (11.1%) and 857 K when no temperature correction was applied. We determined equations relating to the fluorescence line position from these data, which include a cross derivative term to account for the combined effect of pressure and temperature. We present a method to independently determine pressure and/or temperature from combined fluorescence line-shift measurements of a pair of optical sensors. [ABSTRACT FROM AUTHOR]

Ultra-incompressible, hard materials are created by using valence electron density and bond covalency as design parameters. A report on the synthesis, bulk modulus and preliminary hardness testing of osmium diboride, OsB(sub 2) is presented.

Many reactions in the solid state occur in multiple reaction steps. Here, I present a method of determining the kinetics of a two-step consecutive reaction from isothermal, time resolved, powder diffraction data. This method is illustrated with a study of the kinetics of the formation of cordierite from a glass precursor with and without doping with zinc. [ABSTRACT FROM AUTHOR]

Systematic correlation in alkaline-earth carbonate compounds between the deviation of the CO3 units from the perfect D3h symmetry and their 13C nuclear magnetic resonance (NMR) chemical shift anisotropy (CSA) parameters is established. The 13C NMR CSA parameters of amorphous calcium carbonate (ACC) are measured using two-dimensional 13C phase adjusted spinning sidebands (PASS) NMR spectroscopy and are analyzed on the basis of this correlation. The results indicate a distortion of the CO3 units in ACC in the form of an in-plane displacement of the C atom away from the centroid of the O3 triangle, resulting from hydrogen bonding with the surrounding H2O molecules, without significant out-of-plane displacement. Similar distortion for all C atoms in the structure of ACC suggests a uniform spatial disposition of H2O molecules around the CO3 units forming a hydrogen-bonded amorphous network. This amorphous network is stabilized against crystallization by steric frustration, while additives such as Mg presumably provide further stabilization by increasing the energy of dehydration. [ABSTRACT FROM AUTHOR]

The application of pressure on [CoII(dpzca)2], which at ambient pressure undergoes abrupt spin crossover (SCO) with thermal hysteresis, gives unique insights into SCO. It reversibly separates the crystallographic phase transition (I41/a↑P21/c) and associated abrupt SCO from the underlying gradual SCO, as shown by detailed room temperature (RT) X-ray crystallography and temperature dependent magnetic susceptibility studies, both under a range of 10 different pressures. The pressure effects are shown to be reversible. The crystal structure of the pressure-induced low-spin state is determined at RT at 0.42(2) and 1.78(9) GPa. At the highest pressure [1.78(9) GPa] the Co–N bond lengths are consistent with the complex being fully LS, and the conjugated terdentate ligands are significantly distorted out of plane. The abrupt SCO event can be shifted up to RT by application of a hydrostatic pressure of ∼0.4 GPa. These magnetic susceptibility (vs. temperature) and X-ray crystallography (at RT) studies, under a range of pressures, show that the SCO can be tuned over a wide range of temperature and pressure space, including RT SCO. [ABSTRACT FROM AUTHOR]

The 1 bar Curie temperature, TC, at which cementite (anthropogenic form of the mineral cohenite, nominally Fe3C) abruptly loses ferromagnetism, is found to be sensitive to small deviations from the stoichiometric cementite composition. Stoichiometric Fe3C begins to lose magnetic susceptibility at 187 °C. The TC of ferromagnetic loss in cementite falls by about 13-14 °C, in either compositional direction, to the limits at either Fe-saturation or graphite-saturation. Formation of C vacancies in, or C stuffings into, Fe3C produces non-stoichiometry, disrupts and weakens the Fe magnetic ordering, and produces excess configurational entropy that is proportional to the disruption magnitude. C-excess (~0.6 at% C) at graphite-saturation is less than the C-deficiency at Fe-saturation (~2.6 at% C), so the rate at which Curie TC drops with cementite C% variation is asymmetric about the stoichiometric composition, being steeper on the C-excess side. This asymmetry reflects the higher excess configurational entropy (and consequently greater weakening of Fe magnetic ordering) generated by C excesses than by C vacancies. The application of ~6 GPa pressure to stoichiometric Fe3C leads to a drop in TC, of more than 160 °C, to below room T. This large drop in TC with pressure is shown by loss of ferromagnetism in a specimen compressed in a multi-anvil device at room T. Densely sampled synchrotron XRD cell volumes through the transition pressure interval at room T show that there is also a small drop in compressibility near 6 GPa for non-stoichiometric cementites. C-rich cementite retains its magnetism to ~1 GPa higher P than C-poor cementite. The drop in TC with pressure for stoichiometric cementite was tracked in an externally heated diamond-anvil cell by the jump in thermal expansion experienced when cementite loses its magnetostriction above TC (Wood et al. 2004; Litasov et al. 2013). TC drops parabolically with pressure, as do the Invar alloys (Leger et al. 1972; Winterrose et al. 2009). Both high T and P favor the magnetically disordered (Curie) paramagnetic over the ferromagnetic form of cementite. The observed large positive change in thermal expansion and small negative change in compressibility at the TC transition give a good quantitative account of the negative dTC/dP slope mapped by the ferro-paramagnetic phase stability boundary through Ehrenfest's (1933) second relation. Our observations of cementite demagnetization at P~6 GPa, room T confirm the synchrotron Mössbauer work of Gao et al. (2008). The demagnetization pressures based upon experiment are lower than those estimated from existing theoretical treatments by about an order of magnitude. Stability calculations for carbide in the mantle and core are influenced by the choice among ferromagnetic, paramagnetic, and non-magnetic equations of state. Because the ferromagnetic phase is more compressible, the calculated P-T range for cementite stability would be too large under the assumption of ferromagnetism persisting to higher pressures than shown here experimentally. Our results diminish the theoretical P-T range of cementite stability. [ABSTRACT FROM AUTHOR]

We report the crystallite-size-dependency of the compressibility of nanoceria under hydrostatic pressure for a wide variety of crystallite diameters and comment on the size-based trends indicating an extremum near 33 nm. Uniform nano-crystals of ceria were synthesized by basic precipitation from cerium (III) nitrate. Size-control was achieved by adjusting mixing time and, for larger particles, a subsequent annealing temperature. The nano-crystals were characterized by transmission electron microscopy and standard ambient x-ray diffraction (XRD). Compressibility, or its reciprocal, bulk modulus, was measured with high-pressure XRD at LBL-ALS, using helium, neon, or argon as the pressure-transmitting medium for all samples. As crystallite size decreased below 100 nm, the bulk modulus first increased, and then decreased, achieving a maximum near a crystallite diameter of 33 nm. We review earlier work and examine several possible explanations for the peaking of bulk modulus at an intermediate crystallite size. [ABSTRACT FROM AUTHOR]

GSE_ADA/RSV is a free software package for custom analysis of single-crystal micro X-ray diffraction (SCμXRD) data, developed with particular emphasis on data from samples enclosed in diamond anvil cells and subject to high pressure conditions. The package has been in extensive use at the high pressure beamlines of Advanced Photon Source (APS), Argonne National Laboratory and Advanced Light Source (ALS), Lawrence Berkeley National Laboratory. The software is optimized for processing of wide-rotation images and includes a variety of peak intensity corrections and peak filtering features, which are custom-designed to make processing of high pressure SCμXRD easier and more reliable. [ABSTRACT FROM PUBLISHER]

Pressed for time: Amorphous calcium carbonate (ACC) undergoes a reversible amorphous–amorphous phase transition at 10 GPa, adopting an aragonite‐like local order. This result suggests a mechanism by which Mg2+—a cation with smaller ionic radius than Ca2+—modifies the local order of ACC to an aragonite‐like order by helping to decrease the molar volume of the amorphous phase. [ABSTRACT FROM AUTHOR]

The structure and elasticity of tricalcium aluminate ( C3 A) have been experimentally and theoretically studied. From high-pressure X-ray diffraction experiments, the bulk modulus of 102(6) and 110(3) GPa were obtained by fitting second- and third-order finite strain equation of state, respectively. First-principles calculations with a generalized gradient approximation gave an isotropic bulk modulus of 102.1 GPa and an isothermal bulk modulus of 106.0 GPa. The static calculations using the exchange-correlation functional show an excellent agreement with the experimental measurements. Based on the agreement, accurate elastic constants and other elastic moduli were computed. The slight difference of behavior at high pressure can be explained by the infiltration of pressure-transmitting silicone oil into structural holes in C3 A. The computed elastic and mechanical properties will be useful in understanding structural and mechanical properties of cementitious materials, particularly with the increasing interest in the advanced applications at the nanoscale. [ABSTRACT FROM AUTHOR]

The high-pressure structures of nickel monosilicide (NiSi) have been investigated to 124 GPa by synchrotron-based X-ray powder diffraction studies of quenched samples from laser-heated diamond anvil cell experiments, and the equations of state of three of these phases have been determined at room temperature. NiSi transforms from the MnP (B31) structure (space group Pnma) to the ɛ-FeSi (B20) structure (space group P213) at 12.5 ± 4.5 GPa and 1550 ± 150 K. Upon further compression, the CsCl (B2) structure (space group Pm3 m) becomes stable at 46 ± 3 GPa and 1900 ± 150 K. Thus, NiSi will be in the B2 structure throughout the majority of the Earth's mantle and its entire core, and will likely form a solid solution with FeSi, which is already known to undergo a B20 → B2 transition at high pressure. Data from the quenched (room-temperature) samples of all three phases have been fitted to the third-order Birch-Murnaghan equation of state. For the MnP (B31) structure this yields K0 = 165 ± 3 GPa with K0′ fixed at 4 and V0 fixed at 12.1499 Å3 atom−1 [ V0 from unpublished neutron diffraction measurements on the same batch of starting material; Wood (2011), personal communication]. For the ɛ-FeSi (B20) structure, K0 =161± 3 GPa and K0′ = 5.6 ± 0.2 with V0 fixed at 11.4289 Å3 atom−1. For the CsCl (B2) structure, K0 = 200 ± 9 GPa, K0′ = 4.6 ± 0.1 and V0 = 11.09 ± 0.05 Å3 atom−1. The ambient volume of NiSi, therefore, decreases by 6% at the first phase transition and then by a further 3% at the transition to the CsCl structure. Traces of additional NiSi structures predicted by Vočadlo, Wood & Dobson [ J. Appl. Cryst. (2012), 45, 186-196; part I], and labelled therein as Pbma-I, Pnma-II, and possibly also Pnma-III and P4/ nmm, have been detected. [ABSTRACT FROM AUTHOR]

Abstract: Using a diamond anvil cell, 14Å tobermorite, a structural analogue of calcium silicate hydrates (C–S–H), was examined by high-pressure synchrotron X-ray diffraction up to 4.8GPa under hydrostatic conditions. The bulk modulus of 14Å tobermorite was calculated, K o =47GPa. Comparison of the current results with previous high pressure studies on C–S–H(I) indicates that: (1) the compression behavior of the lattice parameters a and b of 14Å tobermorite and C–S–H(I) are very similar, implying that both materials may have very similar Ca–O layers, and also implying that an introduction of structural defects into the Ca–O layers may not substantially change in-plane incompressibility of the ab plane of 14Å tobermorite; and (2) the bulk modulus values of 14Å tobermorite and C–S–H(I) are dominated by the incompressibility of the lattice parameter c , which is directly related to the interlayer spacing composed of dreierketten silicate chains, interlayer Ca, and water molecules. [Copyright &y& Elsevier]

Abstract: Crystalline zeolitic materials, such as hydroxycancrinite, hydroxysodalite, herschelite and nepheline, are often synthesized from geopolymerization using fly-ash and solutions of NaOH at high temperatures. Comprised mainly of 6-membered aluminosilicate rings that act as basic building units, their crystal structures may provide insight into the reaction products formed in NaOH-activated fly ash-based geopolymers. Recent research indicates that the hydroxycancrinite and hydroxysodalite may play an important role as possible analogues of zeolitic precursor in geopolymers. Herein is reported a high pressure synchrotron study of the behavior of hydroxycancrinite exposed to pressures up to 6.1GPa in order to obtain its bulk modulus. A refined equation of state for hydroxycancrinite yielded a bulk modulus of Ko =46±5GPa (assuming =4.0) for a broad range of applied pressure. When low pressure values are excluded from the fit and only the range of 2.5 and 6.1 GPa is considered, the bulk modulus of hydroxycancrinite was found to be Ko =46.9±0.9GPa ( =4.0±0.4, calculated). Comparison with the literature shows that all zeolitic materials possessing single 6-membered rings (i.e., hydroxycancrinite, sodalite and nepheline) have similar bulk moduli. [Copyright &y& Elsevier]

Abstract: This study examines the influence of Al substitution for Si on the bulk modulus of calcium silicate hydrate I [C–S–H(I)], a structural analogue of C–S–H, by performing high-pressure synchrotron X-ray diffraction experiments in two C–S–H(I) samples: one a hydration product of alkali-activated slag and the other a synthetic C–S–H(I). The test result shows that not only the bulk modulus but also the incompressibility of the lattice parameters a, b, and c of two C–S–H(I) samples are very similar to each other, regardless of the Al substitution. This result may be due to the four-coordinated configuration of the substituted Al, which makes the dreierketten silicate chains maintain the same arrangement after the substitution. [ABSTRACT FROM AUTHOR]

Characterizing the nature of medium-range order (MRO) in liquids and disordered solids is important for understanding their structure and transport properties. However, accurately portraying MRO, as manifested by the first sharp diffraction peak (FSDP) in neutron and X-ray scattering measurements, has remained elusive for more than 80 years. Here, using X-ray diffraction of amorphous red phosphorus compressed to 6.30 GPa, supplemented with micro-Raman scattering studies, we build three-dimensional structural models consistent with the diffraction data. We discover that the pressure dependence of the FSDP intensity and line position can be quantitatively accounted for by a characteristic void distribution function, defined in terms of average void size, void spacing and void density. This work provides a template to unambiguously interpret atomic and void-space MRO across a broad range of technologically promising network-forming materials. [ABSTRACT FROM AUTHOR]

Examines the B1 and B2 phases of potassium chloride (KCl) using an in-situ X-ray diffraction pressure-temperature. Discussion of the decrease in infrared mode frequency; Ambient-temperature compression data; Correlation of the level of cellulose nitrate and density of potassium.

Deals with a study which investigated the kinetics, thermodynamics and reaction mechanisms of the hydrothermal crystallization of gyrolite. Structure and stability of gyrolite and related phases; Experimental methods; Results and discussion.

Presents a study which investigated the thermal decomposition of KClO[sub 3] using a multianvil high-pressure device and in-situ energy-dispersive X-ray diffraction and off-line quenching experiments. Experimental techniques; Characterization of the multianvil device; Pressure calibration.