Non-ambient Conditions Research Articles

Measurement of Interface Thermal Resistance With Neutron Diffraction

A noncontact, nondestructive neutron diffraction technique for measuring thermal resistance of buried material interfaces in bulk samples, inaccessible to thermocouple measurements, is described. The technique uses spatially resolved neutron diffraction measurements to measure temperature, and analytical or numerical methods to calculate the corresponding thermal resistance. It was tested at the VULCAN instrument of the Spallation Neutron Source, Oak Ridge National Laboratories on a stack of three 6061 alloy aluminum plates (heat-source, middle-plate, and heat-sink), held in dry thermal contact, at low pressure, in ambient air. The results agreed with thermocouple-based measurements. This technique is applicable to all crystalline materials and most interface configurations, and it can be used for the characterization of thermal resistance across interfaces in actual engineering parts under nonambient conditions and/or in moving/rotating systems.

Grazing incidence X-ray absorption spectroscopy under non-ambient conditions: Investigations of liquid surfaces at DELTA beamline 8

A setup for the investigation of liquid surfaces using grazing incidence X-ray absorption spectroscopy has been installed at the hard X-ray beamline BL 8 at the 1.5 GeV electron storage ring DELTA. While the 6-axis diffractometer endstation of the beamline accommodates a Langmuir trough, the double mirror device which is originally used for the harmonic rejection of low energy beams was used to deflect the beam downwards, defining thereby the incidence angle for the reflection and fluorescence mode EXAFS experiments in a Θ-Θ-geometry. Results obtained during the biomineralization of iron oxides on a Langmuir film of stearic acid show the feasibility of grazing incidence EXAFS measurements that may provide valuable information about the molecular structure of the formed iron oxide phases.

The calculation of the heat release rate by oxygen consumption in a controlled‐atmosphere cone calorimeter

ABSTRACTThe standard cone calorimeter according to ASTM E 1354 and ISO 5660 enables reaction‐to‐fire tests to be performed in ambient atmospheric conditions. A controlled‐atmosphere chamber modifies the standard apparatus in a way that allows tests to be performed in nonambient conditions as well. The enclosed chamber is placed underneath the standard exhaust hood and does not have a closed connection to the hood. With this open arrangement, the exhaust gases are diluted by excess air drawn in from the laboratory surroundings. Heat‐induced changes in the consequential dilution ratio affect the calculation of fire quantities and, when neglected, lead to deviations of up to 30% in heat release rate. The paper introduces a test protocol and equations to calculate the heat release rate taking dilution effects into account. A mathematical correction is shown that compensates for the dilution effects while avoiding extensive mechanical changes in the equipment. Copyright © 2013 John Wiley & Sons, Ltd.

Accuracy (Trueness and Precision) of Cone Calorimeter Tests with and Without a Vitiated Air Enclosure

Over the last few years, new many laboratory fire tests have been developed. One such test is the controlled atmosphere cone calorimeter (CACC). Until now this bench-scale test has not been standardized and the device design differs from one laboratory to another. These differences can affect measurement accuracyaaAccuracy: The closeness of agreement between a test result and the accepted reference value. (truenessbbTrueness: The closeness of agreement between the average value obtained from a large series of test results and an accepted reference value. and precisionccPrecision: The closeness of agreement between independent test results obtained under stipulated conditions.) and direct comparison of literature results is difficult. No studies have been conducted to understand the effect of the design on the fire behaviour of materials and measurement accuracy in the CACC. The present publication focuses on these effects under ambient and non-ambient oxygen conditions. Several designs were investigated using Poly(methyl)methacrylate (PMMA) as the test material. Statistical analyses were performed in some cases to assess the data. The results are presented and discussed.

Phase transitions in the Mg[sbnd]CO2[sbnd]H2O system and the thermal decomposition of dypingite, Mg5(CO3)4(OH)2 · 5H2O: Implications for geosequestration of carbon dioxide

The application of hydrated Mg-carbonates as CO2 sequestering media is a pressing environmental challenge, which requires a deep knowledge of the phase transitions occurring in the MgCO2H2O system as well as the thermal and structural stability of these phases. In this paper we investigate the phase transition of nesquehonite (MgCO3·3H2O) to dypingite (Mg5(CO3)4(OH)2·5H2O), occurring after an incubation of months and years in solution, at ambient conditions. However, as the kinetics of this process resulted to be slow, the phase transition of dypingite to hydromagnesite (Mg5(CO3)4(OH)2·4H2O) was investigated at non-ambient conditions using in situ real-time high-resolution X-ray powder diffraction. Moreover, the thermal behaviour of dypingite and its decomposition have been also investigated with the aim to explore the appropriateness of this carbonate and the products of its decomposition as sinks of anthropogenic carbon dioxide. The results suggest that the dypingite structure remains unaffected up to 438K. At temperature above this threshold, dypingite transforms into hydromagnesite. A further increase in temperature converts the well-ordered hydromagnesite into a “collapsed form” at 528K. The heating of dypingite does not produce a loss of CO2 as the intermediate phases have the same CO2:Mg molar ratio. The final product of the heating is periclase MgO. Its nucleation occurs at temperature ranging from 573 to 663K and it becomes the only phase in the temperature range 633–678K. These results highlighted that dypingite assures a stable storage of CO2 in the conditions that prevail at the Earth's surface. Moreover, the transformation of dypingite in more thermodynamically stable hydromagnesite, occurring without release of CO2, enhances the safety of carbon dioxide disposal in solid form. Furthermore, the observed volume changes during phase transitions, which in turn could affect the porosity and permeability of the geological reservoir, have been evaluated in order to improve the prediction of the safe and permanent storage of CO2 in underground.

The Oxford-Diamond In Situ Cell for studying chemical reactions using time-resolved X-ray diffraction

A versatile, infrared-heated, chemical reaction cell has been assembled and commissioned for the in situ study of a range of chemical syntheses using time-resolved energy-dispersive X-ray diffraction (EDXRD) on Beamline I12 at the Diamond Light Source. Specialized reactor configurations have been constructed to enable in situ EDXRD investigation of samples under non-ambient conditions. Chemical reactions can be studied using a range of sample vessels such as alumina crucibles, steel hydrothermal autoclaves, and glassy carbon tubes, at temperatures up to 1200 °C.

CaCO3-III and CaCO3-VI, high-pressure polymorphs of calcite: Possible host structures for carbon in the Earth's mantle

Calcite, CaCO3, undergoes several high pressure phase transitions. We report here the crystal structure determination of the CaCO3-III and CaCO3-VI high-pressure polymorphs obtained by single-crystal synchrotron X-ray diffraction. This new technical development at synchrotron beamlines currently affords the possibility of collecting single-crystal data suitable for structure determination in-situ at non-ambient conditions, even after multiphase transitions. CaCO3-III, observed in the pressure range 2.5–15GPa, is triclinic, and it presents two closely related structural modifications, one, CaCO3-III, with 50 atoms in the unit cell [a=6.281(1)Å, b=7.507(2)Å, c=12.516(3)Å, α=93.76(2)°, β=98.95(2)°, γ=106.49(2)°, V=555.26(20)Å3 at 2.8GPa], the second, CaCO3-IIIb, with 20 atoms [a=6.144(3)Å, b=6.3715(14)Å, c=6.3759(15)Å, α= 93.84(2)°, β=107.34(3)°, γ=107.16(3)°, V=224.33(13)Å3 at 3.1GPa]. Different pressure–time experimental paths can stabilise one or the other polymorph. Both structures are characterised by the presence of non-coplanar CO3 groups. The densities of CaCO3-III (2.99g/cm3 at 2.8GPa) and CaCO3-IIIb (2.96g/cm3 at 3.1GPa) are lower than aragonite, in agreement with the currently accepted view of aragonite as the thermodynamically stable Ca-carbonate phase at these pressures. The presence of different cation sites, with variable volume and coordination number (7–9), suggests however that these structures have the potential to accommodate cations with different sizes without introducing major structural strain. Indeed, this structure can be adopted by natural Ca-rich carbonates, which often exhibit compositions deviating from pure calcite. Mg-calcites are found both in nature (Frezzotti et al., 2011) and in experimental syntheses at conditions corresponding to deep subduction environments (Poli et al., 2009). At these conditions, the low pressure rhombohedral calcite structure is most unlikely to be stable, and, at the same time, Mg and Fe solubility in aragonite is hindered energetically in the 9-fold coordination site. Above 15GPa, and up to the maximum pressure investigated (40GPa), we observe the high-pressure polymorph CaCO3-VI, triclinic [a=3.3187(12)Å, b=4.8828(14)Å, c=5.5904(14)Å, α=103.30(2)°, β=94.73(2)°, γ=89.21(2)°, V=87.86(20)Å3 at 30.4GPa] with 10 atoms in the unit cell. It is characterised by coplanar CO3 groups but the structure is no longer layered, as in the lower pressure polymorphs. The density of the CaCO3-VI structure (3.78g/cm3 at 30.4GPa) is higher than aragonite. For this reason it could be supposed that a region may exist where this polymorph replaces aragonite in the Earth's intermediate mantle. The lower coordination number for the Ca site [7+2] instead of [9] in aragonite suggests that this structure could be easily adopted by an extended solid-solution range from calcite towards the dolomite [CaMg(CO3)2]–ankerite [CaFe(CO3)2] compositional join. The transitions from calcite to CaCO3-III, CaCO3-IIIb and CaCO3-VI are perfectly reversible and after pressure release we always observe the calcite structure, with the sample recovered as a single-crystal. Indeed, it is highly unlikely that these structures can be observed in samples recovered from high-pressure environments.

I19, the small-molecule single-crystal diffraction beamline at Diamond Light Source

The dedicated small-molecule single-crystal X-ray diffraction beamline (I19) at Diamond Light Source has been operational and supporting users for over three years. I19 is a high-flux tunable-wavelength beamline and its key details are described in this article. Much of the work performed on the beamline involves structure determination from small and weakly diffracting crystals. Other experiments that have been supported to date include structural studies at high pressure, studies of metastable species, variable-temperature crystallography, studies involving gas exchange in porous materials and structural characterizations that require analysis of the diffuse scattering between Bragg reflections. A range of sample environments to facilitate crystallographic studies under non-ambient conditions are available as well as a number of options for automation. An indication of the scope of the science carried out on the beamline is provided by the range of highlights selected for this paper.

Carbonate formation in non-aqueous environments by solid-gas carbonation of silicates

We have produced synthetic analogues of cosmic silicates using the Sol Gel method, producing amorphous silicates of composition Mg(x)Ca(1-x)SiO3. Using synchrotron X-ray powder diffraction on Beamline I11 at the Diamond Light Source, together with a newly-commissioned gas cell, real-time powder diffraction scans have been taken of a range of silicates exposed to CO2 under non-ambient conditions. The SXPD is complemented by other techniques including Raman and Infrared Spectroscopy and SEM imaging.

Mechanochemical synthesis of pyrazine:dicarboxylic acid cocrystals and a study of dissociation by quantitative phase analysis

Cocrystals of pyrazine with dicarboxylic acids were synthesised by mechanochemical methods. Crystal structure determination was performed by single crystal and powder X-ray diffraction (PXRD). The cocrystals consist of infinite 1D hydrogen-bonded chains exploiting the familiar pyridine-carboxylic acid synthon. The kinetics of dissociation of the pyrazine:phthalic acid cocrystal was studied at non-ambient conditions using PXRD and quantitative Rietveld phase analysis. We show that the dissociation process is both temperature and humidity dependent providing useful information about a possible dissociation mechanism.

High-resolution neutron powder diffractometer SPODI at research reactor FRM II

SPODI is a high-resolution thermal neutron diffractometer at the research reactor Heinz Maier-Leibnitz (FRM II) especially dedicated to structural studies of complex systems. Unique features like a very large monochromator take-off angle of 155° and a 5 m monochromator–sample distance in its standard configuration achieve both high-resolution and a good profile shape for a broad scattering angle range. Two dimensional data are collected by an array of 80 vertical position sensitive 3He detectors. SPODI is well suited for studies of complex structural and magnetic order and disorder phenomena at non-ambient conditions. In addition to standard sample environment facilities (cryostats, furnaces, magnet) specific devices (rotatable load frame, cell for electric fields, multichannel potentiostat) were developed. Thus the characterisation of functional materials at in-operando conditions can be achieved. In this contribution the details of the design and present performance of the instrument are reported along with its specifications. A new concept for data reduction using a 2 θ dependent variable height for the intensity integration along the Debye–Scherrer lines is introduced.

Multipurpose high-pressure high-temperature diamond-anvil cell with a novel high-precision guiding system and a dual-mode pressurization device

A novel diamond-anvil cell (DAC) design has been constructed and tested for in situ applications at high-pressure (HP) operations and has proved to be suitable even for HP sample environments at non-ambient temperature conditions. The innovative high-precision guiding mechanism, comparable to a dog clutch, consists of perpendicular planar sliding-plane elements and is integrated directly into the base body of the cylindrically shaped DAC. The combination of two force-generating devices, i.e., mechanical screws and an inflatable gas membrane, allows the user to choose independently between, and to apply individually, two different forcing mechanisms for pressure generation. Both mechanisms are basically independent of each other, but can also be operated simultaneously. The modularity of the DAC design allows for an easy exchange of functional core-element groups optimized not only for various analytical in situ methods but also for HP operation with or without high-temperature (HT) application. For HP-HT experiments a liquid cooling circuit inside the specific inner modular groups has been implemented to obtain a controlled and limited heat distribution within the outer DAC body.

Ultra fast formation of CrO 2 by a novel single step self ignition combustion reaction at ambient condition

CrO 2 requires non-ambient conditions to stabilize Cr in 4+ state. Usually it is prepared by the hydrothermal method which requires high pressure and super criticality of water. For more than a sesqui century there are no reports on the preparation CrO 2 by a simple single step rapid synthesis method at ambient condition. The self ignition exothermic combustion reaction between CrO 3 and acetone vapor cloud leads to ultra fast formation of CrO 2 particles enroute Cr 2O 3 from CrO 3 at ambient condition. The condition for commencement of self ignition and the reaction mechanism are discussed. The structural, morphological, electrical and magnetic studies of the formed CrO 2 particles are also presented.

High-resolution 27Al MAS NMR spectroscopic studies of the response of spinel aluminates to mechanical action

The response of the local structure of various types of spinel aluminates, ZnAl2O4 (normal spinel), MgAl2O4 (partly inverse spinel), and Li0.5Al2.5O4 (fully inverse spinel), to mechanical action through high-energy milling is investigated by means of 27Al MAS NMR. Due to the ability of this nuclear spectroscopic technique to probe the local environment of Al nuclei, valuable quantitative insight into the mechanically induced changes in the spinel structure, such as the local cation disorder and the deformation of the polyhedron geometry, is obtained. It is revealed that, independent of the ionic configuration in the initial oxides, the mechanical action tends to randomize cations over the two non-equivalent cation sublattices provided by the spinel structure. The response of the spinels to mechanical treatment is found to be accompanied by the formation of a non-uniform core–shell nanostructure consisting of an ordered crystallite surrounded by a structurally disordered interface/surface shell region. Based on the comparative NMR studies of the non-treated and mechanically treated spinels, an attempt is made to separate the surface effects from the bulk effects in spinel nanoparticles. The non-equilibrium cation distribution and the deformed polyhedra are found to be confined to the near-surface layers of spinel nanoparticles with the thickness extending up to about 0.7 nm. The cation inversion parameter of the mechanically treated spinel is compared with that of the non-treated material at non-ambient conditions.

Hydrodynamics and flow regime transition study of trickle bed reactor at elevated temperature and pressure

The hydrodynamics in a trickle bed reactor (TBR) in non-ambient conditions are studied for air–water and air–acetone (pure organic liquid of low surface tension) systems. A flow map experiments for air–water and air–acetone systems are performed in a pilot plant reactor of 0.05 m i.d. and 1.25 m height. It has been demonstrated from the experimental results that the pressure drop tends to increase with increasing superficial gas and liquid velocity and reactor pressure, while it tends to decrease with increasing bed temperature. The results also show that the dynamic liquid holdup increases with increasing liquid velocity and decreases with increasing superficial gas velocity, reactor pressure and bed temperature. The dynamic liquid holdup and pressure drop values are obviously higher than those measured for air–water system at the same fluid fluxes, reactor pressure and bed temperature due to the surface tension effects. For higher reactor pressure and temperature, the trickle to pulse transition boundary shifts towered higher superficial velocities of both gas and liquid.

ChemInform Abstract: X‐Ray and Neutron Diffraction in the Study of Organic Crystalline Hydrates

AbstractReview: 83 refs.

Isostructural phase transitions and crossovers under non-ambient conditions

Isostructural phase transitions and crossovers under non-ambient conditions

On the behaviour of natrolite under hydrostatic pressure

Natrolite (NAT) is a zeolite which exhibits negative Poisson's ratios (auxetic) in its (001) plane (i.e. expands laterally when uniaxially stretched and becomes narrower when compressed), a property which has now been verified experimentally. It was recently shown that the empty SiO 2 equivalent of the NAT framework is more auxetic if it is tested in conditions of positive external hydrostatic pressures. Here, we report results of additional simulations which show that the extent of auxetic behaviour of NAT having the standard composition (i.e. Na 2(Al 2Si 3O 10).2H 2O) is also highly dependent on the magnitude of external pressure where it is tested. However, in contrast with the behaviour of its empty silica equivalent, NAT exhibits maximum auxetic behaviour at negative external hydrostatic pressures (i.e. partial vacuum conditions). This is very significant as it highlights the fact that auxetic behaviour may be more prominent in materials if they are tested at non-ambient pressure conditions. An attempt is made to explain this behaviour.

X-ray and Neutron Diffraction in the Study of Organic Crystalline Hydrates

A review. Diffraction methods are a powerful tool to investigate the crystal structure of organic compounds in general and their hydrates in particular. The laboratory standard technique of single crystal X-ray diffraction gives information about the molecular conformation, packing and hydrogen bonding in the crystal structure, while powder X-ray diffraction on bulk material can trace hydration/dehydration processes and phase transitions under non-ambient conditions. Neutron diffraction is a valuable complementary technique to X-ray diffraction and gives highly accurate hydrogen atom positions due to the interaction of the radiation with the atomic nuclei. Although not yet often applied to organic hydrates, neutron single crystal and neutron powder diffraction give precise structural data on hydrogen bonding networks which will help explain why hydrates form in the first place.

Application of micro-FTIR imaging in the Earth sciences

In this paper we describe recent applications of micro-infrared imaging in the Earth sciences. We address, in particular, the use of Fourier-transform infrared (FTIR) spectroscopy in characterizing the zoning and speciation of H and C in a variety of geological materials, including microporous minerals, nominally anhydrous volcanic minerals (NAMs), and crystal inclusions. These investigations show that use of the modern techniques of FTIR imaging enables detection of the zoning of volatile species across the studied samples, and possible configuration changes of structurally-bound carbon molecular species (e.g., CO(2) vs CO(3)) during crystal growth. Such features, which are not accessible with other micro-analytical techniques, may provide information about the physicochemical properties which act as constraints in the genesis of the samples, and important information about the evolution of the geological system. Tests performed with focal-plane-array detectors (FPA) show that resolution close to the diffraction limit can be achieved if the amounts of the target molecules in the sample are substantially different. We also point out the possibility of using FTIR imaging for investigations under non-ambient conditions.