I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[10025]
Open Access
Abstract: The precipitation of hydrated phases from a chondrite-like Na–Mg–Ca–SO4–Cl solution is studied using in situ synchrotron X-ray powder diffraction, under rapid- (360 K h−1, T = 250–80 K, t = 3 h) and ultra-slow-freezing (0.3 K day−1, T = 273–245 K, t = 242 days) conditions. The precipitation sequence under slow cooling initially follows the predictions of equilibrium thermodynamics models. However, after ∼50 days at 245 K, the formation of the highly hydrated sulfate phase Na2Mg(SO4)2·16H2O, a relatively recent discovery in the Na2Mg(SO4)2–H2O system, was observed. Rapid freezing, on the other hand, produced an assemblage of multiple phases which formed within a very short timescale (≤4 min, ΔT = 2 K) and, although remaining present throughout, varied in their relative proportions with decreasing temperature. Mirabilite and meridianiite were the major phases, with pentahydrite, epsomite, hydrohalite, gypsum, blödite, konyaite and loweite also observed. Na2Mg(SO4)2·16H2O was again found to be present and increased in proportion relative to other phases as the temperature decreased. The results are discussed in relation to possible implications for life on Europa and application to other icy ocean worlds
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Oct 2021
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I11-High Resolution Powder Diffraction
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Abstract: The source of atmospheric methane on Saturn’s satellite Titan is currently unknown. However, one possibility is that it originates from clathrate hydrates formed below the surface. Titan’s sub-surface ocean is believed to be composed of saline, rather than pure, water and in situ experimental data on clathrate formation under these conditions are largely absent in literature. Here, synchrotron X-ray powder diffraction (SXRPD) is used to study the properties of methane clathrate hydrates formed in the presence of ammonium sulphate solutions under low temperature conditions with a pressure of 26 bar.
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Sep 2019
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[9703]
Open Access
Abstract: Water on the present day Martian surface is thought to exist in two thermally distinct sub-surface reservoirs: as ice in the cryosphere and as groundwater located deeper in the crust. These sub-surface environments are thought to contain saline, rather than pure, water and laboratory studies on whether or not clathrate hydrates can form in such environments are lacking. We fill this gap by performing synchrotron radiation X-ray powder diffraction to investigate the formation and evolution of clathrate hydrates in weak chloride solutions at CO2 pressures, and over temperature ranges, that are similar to those found in the Martian regolith. We have found that clathrate hydrates can form under conditions relevant to the Martian cryosphere, despite the presence of chloride salts. We find that the dissociation temperatures for CO2 clathrate hydrates formed in saline solutions are depressed by 10–20 K relative to those formed in pure water, depending on the nature of the salt and the CO2 pressure. We suggest that the inhibiting effect that salts such as MgCl2, CaCl2 and NaCl have on clathrate hydrate formation could also be related to the salts’ effect on the formation of the low temperature phase of ice. However, despite the inhibiting effect of the salts, we conclude that the presence of clathrate hydrates should still be possible under conditions likely to exist within the Martian cryosphere.
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Nov 2018
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I11-High Resolution Powder Diffraction
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Stephen P.
Thompson
,
Hilary
Kennedy
,
Sarah
Day
,
Annabelle R.
Baker
,
Benjamin M.
Butler
,
Emmal
Safi
,
Jon
Kelly
,
Andrew
Male
,
Jonathan
Potter
,
Tom
Cobb
,
Claire A.
Murray
,
Chiu C.
Tang
,
Aneurin
Evans
,
Ronaldo
Mercado
Diamond Proposal Number(s):
[10025]
Open Access
Abstract: Liquid oceans and ice caps, along with ice crusts, have long been considered defining features of the Earth, but space missions and observations have shown that they are in fact common features among many of the solar system's outer planets and their satellites. Interactions with rock-forming materials have produced saline oceans not dissimilar in many respects to those on Earth, where mineral precipitation within frozen seawater plays a significant role in both determining global properties and regulating the environment in which a complex ecosystem of extremophiles exists. Since water is considered an essential ingredient for life, the presence of oceans and ice on other solar system bodies is of great astrobiological interest. However, the details surrounding mineral precipitation in freezing environments are still poorly constrained, owing to the difficulties of sampling and ex situ preservation for laboratory analysis, meaning that predictive models have limited empirical underpinnings. To address this, the design and performance characterization of a transmission-geometry sample cell for use in long-duration synchrotron X-ray powder diffraction studies of in situ mineral precipitation from aqueous ice–brine systems are presented. The cell is capable of very slow cooling rates (e.g. 0.3°C per day or less), and its performance is demonstrated with the results from a year-long study of the precipitation of the hydrated magnesium sulfate phase meridianiite (MgSO4·11H2O) from the MgSO4–H2O system. Evidence from the Mars Rover mission suggests that this hydrated phase is widespread on the present-day surface of Mars. However, as well as the predicted hexagonal ice and meridianiite phases, an additional hydrated sulfate phase and a disordered phase are observed.
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Aug 2018
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[9703, 11174]
Abstract: Context. There is evidence to suggest that clathrate hydrates have a significant effect on the surface geology of icy bodies in the Solar System. However the aqueous environments believed to be present on these bodies are likely to be saline rather than pure water. Laboratory work to underpin the properties of clathrate hydrates in such environments is generally lacking. Aims. We aim to fill this gap by carrying out a laboratory investigation of the physical properties of CO2 clathrate hydrates produced
in weak aqueous solutions of MgSO4. Methods. We use in situ synchrotron X-ray powder diffraction to investigate clathrate hydrates formed at high CO2 pressure in ice that has formed from aqueous solutions of MgSO4 with varying concentrations. We measure the thermal expansion, density and dissociation properties of the clathrates under temperature conditions similar to those on icy Solar System bodies. Results. We find that the sulphate solution inhibits the formation of clathrates by lowering their dissociation temperatures. Hysteresis is found in the thermal expansion coefficients as the clathrates are cooled and heated; we attribute this to the presence of the salt in solution. We find the density derived from X-ray powder diffraction measurements is temperature and pressure dependent. When comparing the density of the CO2 clathrates to that of the solution in which they were formed, we conclude that they should sink in the oceans in which they form. We also find that the polymorph of ice present at low temperatures is Ih rather than the expected Ic, which we tentatively attribute to the presence of the MgSO4. Conclusions. We (1) conclude that the density of the clathrates has implications for their behaviour in satellite oceans as their sinking and floating capabilities are temperature and pressure dependent, (2) conclude that the presence of MgSO4 inhibits the formation of clathrates and in some cases may even affect their structure and (3) report the dominance of Ih throughout the experimental procedure despite Ic being the stable phase at low temperature.
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Jan 2017
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
I15-Extreme Conditions
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Diamond Proposal Number(s):
[8614, 8692]
Abstract: The production of amorphous pyroxene nanoparticles (~20 nm) with controlled Fe-Mg content is described. Homogenous
particle compositions closely matching required target stoichiometries are obtained by drying a precursor
gel under high vacuum conditions. The silicate nature of the particles is characterised using TEM,
synchrotron radiation and FTIR. No oxide phase separation occurs, even at high Fe concentration. Structural domains
exist within the nanoparticles that are typically ten times smaller than the physical particle size consistent
with either a core-shell, or, random network with multiple embedded domains, particle structure. Thermal annealing
below the crystallisation temperature allows the ordered domain size to be further reduced by a factor
of ~2.
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Sep 2016
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[8037]
Abstract: Context. Clathrate hydrates are believed to play a significant role in various solar system environments, e.g. comets, and the surfaces and interiors of icy satellites. However, the structural factors governing their formation and dissociation are poorly understood.
Aims. We demonstrate the application of a high pressure gas cell, combined with variable temperature non-contact cooling and fast, time-resolved data collection, to the in situ study of clathrate hydrates under conditions relevant to solar system environments.
Methods. Clathrates formed and processed within the sample cell are monitored in situ using time-resolved synchrotron X-ray powder diffraction and laser Raman spectroscopy.
Results. X-ray diffraction allows the formation of clathrate hydrates to be observed as CO2 gas is applied to ice formed within the cell. Complete conversion is obtained by annealing at temperatures just below the ice melting point. A subsequent rise in the quantity of clathrate is observed as the cell is thermally cycled. Four regions between 100-5000 cm-1 are present in the in situ Raman spectra that carry features characteristic of both ice and clathrate formation.
Conclusions. This novel experimental arrangement is well suited to studying clathrate hydrates over a wide range of temperature (80 - 500 K) and pressure (1 - 100 bar) conditions relevant to solar system bodies and can be used with a variety of different gases and starting aqueous compositions (e.g. saline solutions). We propose the increase in clathrate formation observed during thermal cycling may be due to the formation of a quasi liquid-like phase that forms at temperatures below the ice melting point, but which allows either easier formation of new clathrate cages, or the retention and delocalisation of previously formed clathrate structures, possibly as amorphous clathrate. The structural similarities between hexagonal ice, the quasi liquid-like phase, and crystalline CO2 hydrate mean that differences in the Raman spectrum are subtle; however, all features out to 5000 cm-1, when viewed together, are diagnostic of clathrate structure.
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Feb 2015
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I11-High Resolution Powder Diffraction
I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[6515, 7124]
Abstract: The structural evolution of sol–gel-produced amorphous Mg(x)Ca(1–x)SiO3 silicates is investigated. Mid-IR Fourier transform infrared spectroscopy and synchrotron X-ray diffraction are used to confirm the amorphous nature of the as-prepared silicates, while subsequent in situ synchrotron X-ray powder diffraction measurements are used to study the evolution of crystalline mineral phases as a function of annealing temperature. Multiple silicate phases, including diopside, enstatite, forsterite, and SiO2, are identified, while Rietveld (i.e., structure) refinement of the diffraction data is used to quantify phase change relationships. Investigated as possible analogs for the refractory dust grain materials likely to have been present in the early solar nebula, the likely relevance of these investigations to the observed silicate compositions of chondritic meteorites and cometary bodies and the processing of their precursor materials is discussed.
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Jul 2013
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I11-High Resolution Powder Diffraction
I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[7124]
Abstract: Samples of amorphous MgSiO3 annealed at temperature steps leading up to their crystallization temperature show a rise in photoluminescence activity, peaking at ?450°C. The photoluminescence band has a main peak at 595?nm and a weaker peak at 624?nm. We present laboratory data to show that the maximum in photoluminescence activity is related to substantial structural reordering that occurs within a relatively narrow temperature range. We attribute the origin of the photoluminescence to non-bridging oxygen hole centre defects, which form around ordered nanosized domain structures as a result of the breakup of tetrahedral connectivity in the disordered inter-domain network, aided by the loss of bonded OH. These defects are removed as crystallization progresses, resulting in the decrease and eventual loss of photoluminescence. Thermally processed hydrogenated amorphous silicate grains could therefore represent a potential carrier of extended red emission.
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Jul 2013
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[6515]
Abstract: Aims. We study the formation of calcium carbonate, through the solid-gas interaction of amorphous Ca-silicate with gaseous CO2, at elevated pressures, and link this to the possible presence of calcium carbonate in a number of circumstellar and planetary environments. Methods. We use in-situ synchrotron X-ray powder diffraction to obtain detailed structural data pertaining to the formation of the crystalline calcium carbonate phase vaterite and its evolution with temperature. Results. We found that the metastable calcium carbonate phase vaterite was formed alongside calcite, at elevated CO2 pressure, at room temperature and subsequently remained stable over a large range of temperature and pressure. Conclusions. We report the formation of the calcium carbonate mineral vaterite whilst attempting to simulate carbonate dust grain formation in astrophysical environments. This suggests that vaterite could be a mineral component of carbonate dust and also presents a possible method of formation for vaterite and its polymorphs on planetary surfaces.
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Mar 2013
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