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The decomposition of synthetic siderite (FeCO3) in air atmosphere at room temperature conditions was studied. Siderite was formed by mechanochemical reaction of Fe3O4 and graphite at high CO2 pressure in the presence of water. Kinetics of decomposition reaction was studied over period up to 9 days and it is shown that decomposition reaction obeys geometrical contraction solid-state reaction mechanism model. It was found that the water influences not only the kinetics of siderite formation but also its stability. Siderite completely decomposes at ambient conditions yielding magnetite (Fe3O4) and hematite (Fe2O3) which can reversibly re-absorb carbon dioxide.

Carbon dioxide capture/release reactions using magnetite, Fe3O4, and hematite, Fe2O3, as sorbents were studied. Kinetics of mechanically activated chemical reactions between iron oxides and CO2 was investigated as a function of CO2 pressure and planetary ball mill process parameters. It was found that complete carbonation of iron oxides can be accomplished at room temperature and elevated CO2 pressure (10–30 bar). Siderite calcination was studied in vacuum and argon atmospheres. FeCO3 can be decomposed at 367 °C yielding magnetite, carbon and/or iron. This mixture can reversibly re-absorb carbon dioxide in multiple carbonation–calcination cycles. These results suggest that siderite or iron oxides are prospective and efficient reversible sorbents for CO2 capture. Keywords: Iron oxides, CO2 capture capacity, Carbonation, Mechanically activated chemical reactions, Calcination, Reversible sorbent

High-pressure x-ray diffraction on Ni3Al, non-hydrostatically compressed at room temperature to 30 GPa in radial geometry can be interpreted in terms of a hydrostatic pressure–volume equation of state. We found the yield strength of Ni3Al to increase from about 0.2 to 2 GPa as pressure increases from 0 to 30 GPa. Yield-strength values determined from x-ray diffraction in axial geometry by including a Poisson ratio effect and pressure gradient methods are in good accord with each other. Our results indicate that the strengths of both pure and Cr-doped (7 at. %) Ni3Al increase with pressure, with the yield strength of Ni3Al slightly higher than Ni-Al-Cr alloy.

Human Immunodeficiency Virus Type 1 (HIV-1) remains one of the leading causes of death worldwide. Present combination antiretroviral therapy has substantially improved HIV-1 related pathology. However, delivery of therapeutic agents to the HIV reservoir organ like Central nervous system (CNS) remains a major challenge primarily due to the ineffective transmigration of drugs through Blood Brain Barrier (BBB). The recent advent of nanomedicine-based drug delivery has stimulated the development of innovative systems for drug delivery. In this regard, particular focus has been given to nanodiamond due to its natural biocompatibility and non-toxic nature–making it a more efficient drug carrier than other carbon-based materials. Considering its potential and importance, we have characterized unmodified and surface-modified (-COOH and -NH2) nanodiamond for its capacity to load the anti-HIV-1 drug efavirenz and cytotoxicity, in vitro. Overall, our study has established that unmodified nanodiamond conjugated drug formulation has significantly higher drug loading capacity than surface-modified nanodiamond with minimum toxicity. Further, this nanodrug formulation was characterized by its drug dissolution profile, transmigration through the BBB, and its therapeutic efficacy. The present biological characterizations provide a foundation for further study of in-vivo pharmacokinetics and pharmacodynamics of nanodiamond-based anti-HIV drugs.

In situ x-ray synchrotron diffraction experiments were carried out on nickel-based high-strength superalloys under pressure to understand their deformation mechanism using a diamond anvil cell (DAC). Radial x-ray diffraction determines the room-temperature equations of state and yield strengths of binary Ni3Al alloy and 500 ppm boron-doped Ni3Al to pressures of 20 and 46 GPa, respectively. Crystallographic preferred orientations observed in these superalloys due to anisotropic stress field in DAC indicate the onset of plastic deformation. Inverse pole figure analysis reveals that the underlying deformation mechanisms change from an octahedral slip to a simultaneous activation of octahedral and cube slips upon doping with boron. The yield-strength values were found to increase with pressure and are comparable to those determined from axial diffraction experiments. The results indicate that the yield strength of Ni3Al:B is about 0.5 GPa higher (at pressures below 20 GPa) due to grain boundary strengthening by boron. It is shown that due to high elastic anisotropy of Ni3Al alloy, the yield-strength estimations from diffraction experiments strongly depend on the micromechanical model used to convert the measured elastic strains into stresses.

Laser-assisted processing and in-situ characterization of a Ni0.7-Al0.1235-Co0.15-Ti0.0265 alloy were carried out under a range of simultaneous hydrostatic high pressures of ∼30 GPa and high temper...

Ni based superalloy Ni–Al–Cr with γ and γ′ phase was studied under high pressure up to 30 GPa using diamond anvil cell technique. In-situ X-ray diffraction data was collected on these alloys under hydrostatic and non-hydrostatic conditions. Cubic phase remains stable up to the highest pressure of about 30 GPa. Bulk modulus and its pressure derivative obtained from the volume compression of pressure data are K = 166.6 ± 5.8 GPa with K′ set to 4 under hydrostatic conditions and K = 211.3 ± 4.7 GPa with K′ set to 4 for non-hydrostatic conditions. Using lattice strain theory, maximum shear stress ‘t’ was determined from the difference between the axial and radial stress components in the sample. The magnitude of shear stress suggests that the lower limit of compressive strength increases with pressure and shows maximum yield strength of 1.8 ± 0.3 GPa at 20 GPa. Further, we have also determined yield strength using pressure gradient method. In both the methods, yield strength increases linearly with applied pressure. The results are found to be in good agreement with each other and the literature values at ambient conditions.

Earth's core is believed to consist of a solid inner core and an outer liquid core. Since the inner core is mostly solid iron, most geophysical work has focused on melting of pure iron at core conditions. The inner core density is well matched with seismological data if some S is added to iron. The available phase equilibrium experimental data in the binary Fe–S system to pressures as high as ~200 GPa is used to create a thermodynamic database extending to core pressures that can be used to calculate the inner core density if S were the only other constituent. Such a calculation gives the maximum temperature of the solid inner core as 4428 (±500) K (363.85 GPa, density=13.09 g/cm 3 ) with a sulfur content of ~15 wt%. To be consistent with the seismically determined density, the outer liquid core requires mixing of yet another light element or elements; both oxygen and carbon are suitable.

A thermodynamic database on all iron phases (BCC, FCC, HCP and melt) has been created using thermochemical and equations of state data from experiments and theory. The database permits the calculation of the phase diagram of iron to physical conditions of the Earth's core (pressure of 365 GPa and temperature of 6453 K). If the inner core were all iron, its upper temperature would be 6453 (500) K. The average heat capacity of a pure iron HCP inner core is calculated as 29.4 J/mol/K with an entropy of 92 J/mol/K and a gruneisen parameter of 1.81.

Samples of Ni 3 Al, Ni 3 Al:B and Ni–Al–Cr super alloys were prepared by directional solidification method and their effect of alloying with ternary elements on the mechanical properties was investigated. In-situ X-ray diffraction studies were carried out on undoped Ni 3 Al, Ni 3 Al:B with boron 500 ppm and Ni–Al–Cr with 7.5 at.% of chromium super alloys at high pressure using diamond anvil cell. The results indicate that micro-alloying with B forms γ′-phase (L1 2 structure), similar to the pure Ni 3 Al, while Ni–Al–Cr alloy consists of γ′ precipitates in a matrix of γ-phase (Ni-FCC structure). The crystal structure of all three alloys was stable up to 20 GPa. Micro alloying with boron increases bulk modulus of Ni 3 Al by 8% whereas alloying with chromium has the opposite effect decreasing the modulus by 11% when compared to undoped alloy. Further, the elastic modulus and hardness of Ni 3 Al, Ni 3 Al:B and Ni–Al–Cr alloys were determined using the nano-indentation technique, in combination with compressibility data which enabled the estimation of shear modulus and Poisson’s ratio of these alloys.

Compressibility of the Ti3AlH6 and Ti3AlD6 has been studied by X-ray diffraction method using advanced synchrotron technique up to 38 GPa. Significantly higher values of bulk modulus have been revealed for the hydride and deuteride compounds as compared to the initial pure intermetallic compound. The consequences of this observation have been discussed in terms of ductility and strength of obtained materials. Possible explanation of the peculiarity in the equation of states for both compounds is proposed on the base of the difference in repulsion interactions of hydrogen and deuterium species in the metallic lattice. All advantages of the hydrogenation of titanium aluminum compound have been summarized.

Pressure induced phase transformation in terbium trihydride has been studied by X-ray diffraction and Raman spectroscopy up to 20 GPa. Theoretical calculations were performed using density functional theory (DFT) with the Perdew–Burke–Ernzerhof parameterizations of the generalized gradient approximation as implemented in the VASP code. X-ray diffraction analysis and Raman measurements show structural transformation from original hcp to cubic structure at pressure of ∼7.0 GPa. The result is in good agreement with the theoretical predictions. Characterization of the new phase along with equations of state of both phases is presented.

We demonstrate that the condensation theory of planet formation yields solids of suitable compositions in the solar nebula that accrete to form the terrestrial planetary bodies. The mineral chemistry of the condensed objects provides definite criteria to establish the pressure and temperature of their formation. The solids condensing at a high nebular pressure of 0.01 to 0.001 bar and temperature of ∼ 1530 K had the best chemical composition and density to form Mercury (64 wt% iron and 36 wt% oxides, density ∼ 5.32 g cm 3 ). Solids that condensed around a pressure of 0.0001 bar or less and a temperature of ∼ 700 K formed Earth and Venus (31 wt% iron, Ni and S and 69 wt% oxides, density ∼ 4 g cm 3 ), and Mars (33.6 wt% Fe and S and 66.4 wt% oxides, density ∼ 3.7 g cm 3 ). Iron sulfide provided S (3 wt%) for the core. Hydrous minerals forming in the lower temperature region provided water to the mantle. These results are highly significant because we have used only the chemical composition of the solar nebula, thermochemistry and astrophysical data on densities of the planets.

NaOH(s) + C(s) +H2O (g) = Na2CO3(s) + H2 (g). Our study reveals that in the presence of 2 h ball milled Raney nickel (average crystallite size of 209 A) this reaction is completed at 500 0 C in 120 minutes. X-ray diffraction technique is used for the characterization of the catalysts. Catalyst’s surface morphology is analysed by using scanning electron microscope. From a study of the surface morphology and activity of the used catalysts, a direct correlation of coal particle size with the reaction kinetics has been established. The findings reveal that the globular particles have better catalytic effect than flaky disk shaped particles.

SUMMARY The steam–methane-reformation (SMR) reaction has been modified by including sodium hydroxide in the reaction. It is found that the reaction: 2NaOH+CH4+H2O = Na2CO3+4H2 takes place at much lower temperatures (300–600°C) than the SMR reaction (800–1200°C). The reaction rate is enhanced with a nickel catalyst. We have studied the effect of variously ball-milled nickel on the reaction rate and determined the optimum particle size of the catalyst. Best results were achieved by grinding the catalyst for 2 h. Prolonged ball milling caused the nickel platelets to coalesce and grow in size decreasing the reaction rate. Copyright © 2011 John Wiley & Sons, Ltd.

Hydrogen is mostly produced by the Steam Methane Reforming (SMR) reaction which adds many tonnes of carbon emissions to the environment for each tonne of hydrogen. A modified scheme for carbon-emission free production of hydrogen, which involves sodium hydroxide, methane and steam, has been explored here. The modification of the SMR reaction is CH 4 + 2NaOH + H 2 O = Na 2 CO 3 + 4H 2 The modified reaction has several advantages: it does not require catalysis, the temperature of reaction is considerably reduced and the products are industrially important. By this process, we can produce hydrogen without any carbon dioxide emission as shown in this theoretical and experimental study. The reaction has been studied in the temperature range of 873–1073 K in an open configuration for 30 min and at various methane and constant water vapor flow. It is determined that at a methane flow rate of 25 ml/min the reaction is 98% complete at 873 K.

We have used the CALPHAD-compatible equation of state (EOS) based on the explicit Gibbs free energy concept for the solid state of ten important elements: V, Nb, Ta, Mo, W (groups VB and VIB), Pd, Pt (group VIIIB) and Cu, Ag and Au (group IB). The new formulation uses SGTE data for ambient pressure and converges to the quasi-harmonic model at the limit of extreme pressure to calculate the Gibbs free energy as a function of pressure and temperature. The model is based on the available pressure–volume–temperature ( P V T ) data on the elements and can be usefully extrapolated to extreme pressures. When compared to shock wave data, the modeled EOS holds well, but the fit is not totally satisfactory in the ultrahigh-pressure range. A great advantage of this formulation is that it can be used to calculate thermodynamic properties such as the heat capacity and entropy at very high temperatures and pressures.

The validity and usefulness of thermodynamic models commonly used to model the physical and chemical properties of Earth's interior at high to ultrahigh pressures and their associated geophysical databases are discussed. All calorimetric data used in these models must have the quality of fitting to experimental phase diagrams derived from work not only at high temperatures and pressures but also under ambient conditions. The density and temperature profiles calculated for Earth's mantle and core and the phase diagram of iron calculated under core conditions illustrate how thermodynamic modeling helps us understand the physics of Earth's deep interior.

Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependencies of the lattice parameters of two Ga-containing polycrystalline MAX phases: Ti 2 GaN and Cr 2 GaC. The bulk moduli were calculated to be 189 ± 4 and 188 ± 5 GPa, respectively. Up to a pressure of about 50 GPa, no phase transformations were observed. Ti 2 GaN compresses more easily along the c -axis, while Cr 2 GaC compresses equally in both directions.

Alkali and alkali– earth metal hydrides have high hydrogen storage capacity, but high operation temperature hinders their use. The alanates and borohydrides of alkali and alkali– earth metals are widely studied because of their light weight and high hydrogen content. Borohydrides are highly stable and decompose only at elevated temperatures while alanates decompose in two steps. A detailed study of the properties of these hydrides is required for further understanding of their stability. A lot of thermodynamic information can be derived from investigation of materials under pressure or temperature. Structural measurements on the hydride compounds at ambient and high P–T conditions result in a better understanding of the stability of the hydride structures and will assist us in the design of suitable storage materials with desired thermodynamic properties. The structural data are potential source of information regarding inter-atomic forces which determine pressure/temperature induced changes. During the past few years, structural stability of hydrides is widely investigated under pressure and temperature, both experimentally and theoretically. In this review we discuss structural phase transition and decomposition behavior of light metal hydrides, borohydrides and alanates of the elements that belong to first and second group in the periodic table.

Using a synchrotron X-ray radiation source and a diamond anvil cell we measured the dependences of the lattice parameters on quasi-hydrostatic pressure of the order of 50 GPa of the following MAX phases: Ti2InC, (Ti0.5,Zr0.5)2InC, Zr2InC and Ti2SnC, Nb2InC and Hf2InC. Like other MAX phases, the phases studied herein were all stable up to ≈50 GPa. In both series, the substitution of Ti ( r = 1.32 A ) by the larger sized metals, Zr or Nb (with r varying between 1.34 and 1.55 A) resulted in larger unit cell parameters and volumes. At 152±3 and 148±3 GPa, the respective bulk moduli, K o , of Ti2SnC and Ti2InC are quite comparable. Replacing Ti by Hf or Nb in Ti2SnC leads to increases in K o by 11% and 18%, respectively. Conversely, replacing half the Ti by Zr in Ti2InC leads to a 13% drop in K o ; replacing all of the Ti drops it by 16.5%. Most of these trends are reproduced in our ab initio calculations of K o . For all compositions, the compressibilities along the c -direction were greater than those along the a -direction. For the M2SnC series, the compressibilities along the c -axes were quite similar; the compressibilities along the a -axis of Ti2SnC were greater than in the Nb- or Hf-containing ternaries. The c -axis compressibilities of the In-containing compounds were almost indistinguishable. The compressibilities along the a -axes of (Ti0.5,Zr0.5)2InC and Zr2InC were also quite comparable; those of Ti2InC was less compressible.

Zirconium oxide (ZrO2) nanostructures were synthesized by hydrothermal route. Surface morphology analysis depicts the formation of the nanobars and hexagonal-shaped nanodiscs at different synthesis conditions. The structural analysis confirms that the as-synthesized ZrO2 product is of pure monoclinic phase (m-ZrO2) with crystallite size of about 25 nm. The product consists of monodispersed nanoparticles of uniform composition,highpurity,andcrystallinity.TheRamanspectraarequantitativelyanalyzedandtheobservedpeaksareattributedtovariousvibration modes of the m-ZrO2. The UV‐vis absorption spectrum showed a strong absorption peak at about 292 nm and the estimated optical band gap was around 3.57 eV. Photoluminescence (PL) spectrum of ZrO2 nanostructure showed a strong and broad emission peak at around 410 nm at room temperature, which can be attributed to the ionized oxygen vacancy in the material. # 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Structural properties of calcium borohydride, Ca(BH4)2, containing α and β polymorphs are investigated under pressure by in situ synchrotron X-ray diffraction up to 13 GPa and by Raman spectroscopy up to 25 GPa. Results show that the β phase transforms to a highly disordered structure above 10.2 GPa, whereas the α phase is stable in the pressure range studied. Rietveld analysis of the X-ray diffraction pattern collected at ambient conditions shows that the α phase is an orthorhombic F2dd structure with lattice parameters a = 8.82(7) A, b = 13.05 (10) A, c = 7.404(5) A, and V = 851.8(10) A3 (64.13 cm3/mol). The β phase was checked for all the suggested tetragonal structures, and the best match is obtained with space group P42/m; the lattice parameters are a = 6.88(4) A, c = 4.32(5) A, and V = 204.82(18) A3 (61.68 cm3/mol). Pressure volume data obtained for α-Ca(BH4)2 are fitted with the third-order Birch−Murnaghan equation of state that yields a bulk modulus value of K0 = 22.95(4) GPa with K0′ = 2.63(0.5).

Principal component analysis (PCA) is used to investigate interrelationship among material properties of hydrides. Property data which consist of ∼200 compounds (binary and ternary metal hydrides) were analyzed. A comparative study was carried out among the metal properties with that of their hydrides. The observed decrease or increase of entropy, molar volume and specific heat of hydrides from that of the metals can be attributed to hydrogen bond formation, charge transfer and corresponding change in crystal structure.

In this paper we report for the first time the synthesis of a new ternary layered ceramic (Cr 0.5 V 0.5 ) 2 GeC, a 211 M n +1 AX n compound by hot-pressing. Scanning electron microscopy and X-ray diffraction were used to characterize and confirm the hexagonal crystal structure of this ternary layered ceramic. The calculated lattice parameters are a = 2.9773 A and c = 12.1619 A. Using a diamond anvil cell and synchrotron radiation we also report the pressure dependencies of the lattice parameters. No phase transformation was observed and the phase is stable up to 49 GPa. The bulk modulus of (Cr 0.5 V 0.5 ) 2 GeC calculated using the Birch–Murnaghan equation of state is 219 ± 5 GPa with K ′ = 4.1 ± 0.3, which is higher than the end members V 2 GeC and Cr 2 GeC.

Mg2FeH6 was synthesized by ball milling MgH2 and Fe (2:1 molar ratio) mixture for 72 h followed by heating at 400 °C under H2 pressure. The hydride formation, its structure and homogeneity were investigated by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and Raman spectroscopy. High pressure in situ synchrotron X-ray diffraction and Vienna ab initio simulation were used to determine bulk modulus of the sample. The bulk modulus of Mg2FeH6 was found to be 75.4(4) GPa by optimized experiment and 76.3 GPa by theoretical simulation. From high temperature in situ X-ray diffraction study the volumetric thermal expansion coefficient of Mg2FeH6 was found to be αv = 5.85(3) × 10−5 + 7.47(7) × 10−8 (T − To)/°C. Decomposition of Mg2FeH6 was observed at 425 °C and the decomposition products were Mg, Fe and H2.

In this paper we report the synthesis of a ternary-layered ceramic, Ti2GeC, a 211 Mn+1AXn compound by hot-pressing. X-ray analysis confirmed the hexagonal crystal symmetry. Using a synchrotron radiation and a diamond anvil cell, we measured the pressure dependencies of the lattice parameters. The phase is structurally stable up to the 49 GPa—the maximum experimental pressure reached. The bulk modulus of Ti2GeC calculated using the Birch-Murnaghan equation of state is 211 ± 4 GPa with K′ = 3.9 ± 0.2. Surprisingly the bulk modulus was found to be greater than both Ti2AlC and Ti2SC by 13% and 10%. Also, Ti2GeC has the highest bulk modulus among M2GeC phases where M = Ti, V, Cr.

We have calculated the mineralogical properties of the Earth's mantle and the lithological units constituting the subducting oceanic slabs within a wide range of P–T conditions within the CaO–FeO–MgO–Al2O3–SiO2 system, except for the basalt top-layer of a slab, for which the system is extended to include Na2O. The mineralogical data are then converted, using the appropriate P–V–T relations, to bulk densities. The calculated adiabatic density vs. depth profile of the mantle between 200 and 725 km depths is in good agreement with geophysical and experimental data. The density data of the different compositional units are combined with calculated thermal structures for a variety of slab–mantle systems to construct equilibrium density profiles as a function of depth. The mean equilibrium densities of the slabs within the transition zone (400–660 km depth) are found to be ∼0.04–0.05 g/cm3 greater than those of the ambient mantle within the same depth interval. For the entire upper mantle, density differences between slabs and ambient mantle are slightly less, but the slabs still remain denser than the latter. At 670 km depth, slabs have lower density than the ambient lower mantle because of the commencement of perovskite forming reactions within the mantle, and displacements of these reaction boundaries to higher pressures within the slabs as a consequence of their negative P–T slopes. If perovskite forming reactions within slabs are hindered for kinetic sluggishness, then neutral buoyancy would be achieved when the slabs have penetrated ∼100 km into the lower mantle. However, using the available data on the kinetics of spinel to perovskite plus periclase reaction, we conclude that the reaction would go to completion in a Peru-type young slab (41 Myr), and very likely also in a Tonga-type old slab (110 Myr), before these penetrated 100 km into the lower mantle. Thus, slabs should always remain negatively buoyant, and therefore continue to subduct through the lower mantle once it penetrates through the 660 km discontinuity. Despite a negative buoyancy force, a slab could deflect at the top of the lower mantle (660 km) because of factors resisting subduction, namely viscosity jump, low dip angle, slab roll back, and metastable persistence of olivine in cold slabs. If published scale model experiments represent realistic approximations of the factors affecting plate subduction, then according to our density data, any slab with a dip angle of ≤40–50° would bend at the 660 km discontinuity if there is a viscosity jump of at least by a factor of ∼10 and trench migration. The basalt top-layer of a slab is denser than other slab components and the ambient mantle at all depths to 660 km, and therefore should continue to sink into the lower mantle, especially if a slab directly penetrates the 660 km barrier, instead of peeling off in the transition zone to form a “perched eclogite” or “piclogite” layer, as previously proposed. The harzburgite layer, which is sandwiched between denser basalt and lherzolite layers, faces greater resistance to subduction, especially in a young slab, and thus could significantly contribute to the deformation of a slab near the 660 km discontinuity.

The structural stability of Mg(BH4)2, a promising hydrogen storage material, under pressure has been investigated in a diamond anvil cell up to 22 GPa with combined synchrotron X-ray diffraction and Raman spectroscopy. The analyses show a structural phase transition around 2.5 GPa and again around 14.4 GPa. An ambient-pressure phase of Mg(BH4)2 has a hexagonal structure (space group P61, a = 10.047(3) A, c = 36.34(1) A, and V = 3176(1) A3 at 0.2 GPa), which agrees well with early reports. The structure of high-pressure phase is found to be different from reported theoretical predictions; it also does not match the high-temperature phase. The high-pressure polymorph of Mg(BH4)2 is found to be stable on decompression, similar to the case of the high-temperature phase. Raman spectroscopic study shows a similarity in high-pressure behavior of as-prepared Mg(BH4)2 and its high-temperature phase.

Phase stability of titanium hydride (TiH2) was studied at high pressure-high temperature conditions using synchrotron radiation under non-hydrostatic conditions. Resistive heating method was used to heat the sample to a maximum temperature of 873 K in a diamond anvil cell (DAC) under pressure up to 12 GPa. Pressure–temperature behavior was studied by varying the temperature upto 823 K in steps of 50 K with pressure variations within 3 GPa. Structural phase transformation from tetragonal (I4/mmm) to cubic (Fm-3 m) was observed with increase in temperature. Tetragonal phase was found to be stabilized when the sample was subjected to pressure and temperature cycle.

Using synchrotron radiation and Raman spectroscopy and a diamond anvil cell we measured the pressure dependence of the lattice parameters and Raman modes of polycrystalline Sr 2 CoWO 6 . Angle-dispersive X-ray diffraction patterns were indexed and showed that at 2.2 GPa, the material transforms from the I 4/ m tetragonal structure to the P 2 1 / n monoclinic structure. For pressure values between 2.2 and 12.7 GPa only monoclinic symmetries were found. We had difficulties with the convergence of the profile matching of the diffractogram taken at 12.7 GPa, indicating that the second phase-transition took place. To get more informations about these structural changes, an in-situ Raman spectroscopic study was conducted to explore the pressure-induced phase-transition sequence of Sr 2 CoWO 6 to pressures of 40.8 GPa at room-temperature. Group theory yields nine Raman-active modes for Sr 2 CoWO 6 ( I 4/ m ), all the predicted bands are observed at ambient conditions (phase I). The experimental results indicate that structural changes are observed at 2.15 and 11.15 GPa, which we attribute to phase transitions; thus, giving rise to two new phases, named as phase II and phase III, respectively. In the 9.33–14.84 GPa interval a coexistence of phases II and III is observed.

M(n+1)AX(n) compounds have gathered huge momentum because of its exciting properties. In this paper we report the synthesis of ternary layered ceramic Cr2GeC, a 211 M(n+1)AX(n) compound by hot-pres ...

For the first time, Raman spectroscopy of α and γ polymorphs of AlH3 has been performed in the pressure range from ambient up to 16.9 and 32.7 GPa, respectively using the diamond anvil cell (DAC) technique. An analysis of pressure response wavenumbers (ν) for α-AlH3 showed a change of dνi/dP at a pressure of about 8 GPa and may indicate a monoclinic distortion from the initially hexagonal α-AlH3. The distortion is stable at least up to 16.9 GPa. The γ form exhibited more complex behavior transforming to the α form at a pressure of about 12 GPa. The structural phase transition was shown to be an irreversible and kinetically slow process that required at least 5 h to complete. Copyright © 2008 John Wiley & Sons, Ltd.

A zero-emission process of hydrogen production from fossil fuel through a system of reactions involving hydroxide, carbon, CO, CO2 and water is described here. It provides for a complete sequestration of carbon (CO2 and CO) from coal/natural-gas burning plants. The CO and or CO2 produced in coal or natural gas burning power plants and the heat may be used for producing hydrogen. Economically hydrogen production cost is less than the current price of fossil-fuel produced hydrogen with the added benefit of carbon sequestration. The reduced cost of the hydrogen may aid in making a hydrogen fueled automobile economically viable.

High-pressure investigations of NaCo(H2PO3)3·H2O dihydrogenphosphite, in diamond anvil cell have been performed at room temperature using in situ Raman spectroscopy. The endeavor was to acquire information on pressure-induced structural transformations such as phase transitions and amorphization occurring in the crystal lattice. Group theory yields to 69Ag + 69B1g + 69B2g + 69B3g Raman active modes for NaCo(H2PO3)3·H2O, of which only 36 bands are observed at ambient conditions. The pressure-induced phase transition sequence of NaCo(H2PO3)3·H2O dihydrogenphosphite to pressures up to 20 GPa was explored. Raman spectra showed that the investigated compound, NaCo(H2PO3)3·H2O, compressed smoothly up to 4.2 GPa and starts amorphizing at 6.8 GPa. The amorphous phase persists down to 1 atm upon release of pressure. The amorphization was due to a chemical decomposition and also might be due to pressure-induced distortions of the lattice upon compression associated with the Na+ and Co2+ cation displacements and strongly coupled with rigid rotations of the (PO3) units. No P–H vibrations were seen after pressure release which means that P–H bonds were broken. The frequencies seen in the Raman spectra for the amorphous phase are characteristic of (PO4)3− or P 2 O 7 4 − tetrahedral short-range structure.

The pressure dependence of the lattice parameters of the ternary layered carbide, Ti2SC, was measured by using synchrotron radiation X-ray diffraction and a diamond anvil cell setup. The experiment ...

A pressure-induced splitting of the Cu-O chains was found in SrCuO2 at pressures >7 GPa and room temperature. The high-pressure phase is a superstructure of the infinite-layered tetragonal superconducting phase of SrCuO2 and is not stable under ambient conditions. The Cu-O chains buckle with further increasing pressure, and a new high-density polymorph of SrCuO2 is formed at 34.2 GPa.

Hydrogen generating reaction between sodium borohydride, NaBH4, and magnesium hydroxide, Mg(OH)2 (brucite), was studied. Reaction rate was found to depend on the degree of reactants homogenization and/or their particle size. Kinetic of the reaction was studied in isothermal approach in the temperature range of 240–360 °C. It is shown that the reaction obeys 2D diffusion mechanism and its activation energy is 155.9 kJ/mol. Powder XRD analysis and Raman spectroscopy reveal that mechanically activated mixture of NaBH4 and Mg(OH)2 reacts yielding MgO as the only crystalline phase in the temperature range of 240–318 °C. At higher temperatures a new crystalline tetragonal phase of as yet undetermined composition is developed.

The analysis of the diffraction data under nonhydrostatic stress condition created in a diamond anvil cell suggests that the compressive strength of NbC crystallites is at least 24 ± 4 GPa at a confining pressure of 57 ± 0.5 GPa. When using Al as a pressure transmitting medium in the diamond anvil cell pressure conditions become nearly hydrostatic. The bulk modulus derived from the compression data under quasi-hydrostatic pressure condition gives K 0 = 274 ± 3 GPa when fixing K 0 ′ = 4 . This value agrees well with the value obtained from the first-principles numerical calculations.

Herein, we report on the thermal expansion and stability of V2AlC in the 25°–950°C temperature range. The sample was heated in an Argon atmosphere in a quartz capillary and the thermal expansion was measured using a X-ray synchrotron radiation source. Up to the maximum temperature explored, there were no signs of decomposition or phase transitions. The temperature variation of volumetric thermal expansion is given by αv=2.53(5) × 10−5+5.75(3) × 10−9T°C−1. At ≈9.40 × 10−6°C−1, the thermal expansions along both the a and c lattice directions are quite comparable; in other words, there is little thermal expansion anisotropy in V2AlC.

The structural characteristics of Sm2Zr2O7, an ordered pyrochlore, were studied by angle-dispersive X-ray diffraction (XRD) and Raman scattering methods with increasing pressure. A structural distortion was observed at low pressures; but the distortion disappeared at pressures above 13.5 GPa. Above 18 GPa, the pyrochlore structure is unstable and a pressure-induced phase transition occurred. The high-pressure phase is a distorted fluorite structure in which the cations and anion vacancies are disordered. The disordered structure is accompanied by the formation of partially amorphous domains. With the release of pressure, the high-pressure phase partially transforms to the amorphous state.

Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Ti3GeC2 sample up to a pressure of 51 GPa. No phase transformations were observed. Like Ti3SiC2, and most other compounds belonging to the same family of ternary carbides and nitrides, the so-called MAX phases, the compressibility of Ti3GeC2 along the c axis is greater than that along the a axis. The bulk modulus is 197 ± 4 GPa, with a pressure derivative of 3.4 ± 0.1. We also characterized Ti3GeC2 by infrared spectroscopy; four of the five expected infrared modes were observed for this material.

Structural changes in the layered compound γ -Na x CoO 2 ( x =0.74) are studied by in situ Raman scattering and energy-dispersive X-ray diffraction methods at pressures up to 41 GPa. The pressure dependence of the lattice parameters indicate that γ -Na x CoO 2 has a strong anisotropic compressibility before 15 GPa and the unit cell is easily compressed between layers. The discontinuity of the lattice parameters and Raman observations reveal that a phase transition occurred at pressures between 10 and 12 GPa. The high-pressure phase has the same hexagonal symmetry and the phase transition may be due to the pressure-induced rearrangement of one of the Na cations in the unit cell.

The perovskite-related layered structure of La 2 Ti 2 O 7 has been studied at pressures up to 30 GPa using synchrotron radiation powder X-ray diffraction (XRD) and Raman scattering. The XRD results indicate a pronounced anisotropy for the compressibility of the monoclinic unit cell. The ratio of the relative compressibilities along the [100], [010] and [001] directions is ∼1:3:5. The greatest compressibility is along the [001] direction, perpendicular to the interlayer. A pressure-induced phase transition occurs at 16.7 GPa. Both Raman and XRD measurements reveal that the pressure-induced phase transition is reversible. The high-pressure phase has a close structural relation to the low-pressure monoclinic phase and the phase transition may be due to the tilting of TiO 6 octahedra at high pressures.

A data driven methodology is developed for tracking the collective influence of the multiple attributes of alloying elements on both thermodynamic and mechanical properties of metal alloys. Cobalt-based superalloys are used as a template to demonstrate the approach. By mapping the high dimensional nature of the systematics of elemental data embedded in the periodic table into the form of a network graph, one can guide targeted first principles calculations that identify the influence of specific elements on phase stability, crystal structure and elastic properties. This provides a fundamentally new means to rapidly identify new stable alloy chemistries with enhanced high temperature properties. The resulting visualization scheme exhibits the grouping and proximity of elements based on their impact on the properties of intermetallic alloys. Unlike the periodic table however, the distance between neighboring elements uncovers relationships in a complex high dimensional information space that would not have been easily seen otherwise. The predictions of the methodology are found to be consistent with reported experimental and theoretical studies. The informatics based methodology presented in this study can be generalized to a framework for data analysis and knowledge discovery that can be applied to many material systems and recreated for different design objectives.