Time-resolved Energy Dispersive X-ray Diffraction Research Articles

An in situ study of thermal crystallization of amorphous calcium phosphates.

The heat-induced crystallization of amorphous calcium phosphate (ACP) is an intriguing process not yet well comprehended. This is because most of the works on this topic are based on ex situ studies where the materials are characterized after the heat and cooldown cycles, thus missing transient structural changes. Here, we used time-resolved energy dispersive X-ray diffraction and infrared spectroscopy to study, for the first time, the thermal crystallization of ACP in situ. The thermal crystallization of two kinds of citrate-stabilized carbonated ACP was studied, as they are promising materials for the preparation of advanced bioceramics. The behavior of these samples was compared to that of two citrate-free ACPs, either doped or non-doped with carbonate ions. Our results evinced that several phenomena occur during ACP thermal annealing. Before crystallization, all ACP samples undergo a decrease in the short-range order process, followed by several internal reorganizations. We have assessed that differently from carbonate-free ACP, carbonated ACPs with and without citrate directly crystallize into a biomimetic poorly crystalline carbonated hydroxyapatite. Citrate-stabilized ACPs in comparison to citrate-free ACPs have a faster hydroxyapatite formation kinetics, which is due to their higher specific surface area. This work reveals the necessity and the potentialities of using in situ techniques to effectively probe complex processes such as the heat-induced crystallization of ACPs.

In situ space-resolved X-ray diffraction and time-resolved EDXD on efficient polymer-based photovoltaic devices: Microstructural properties and aging effects

Abstract

Electric field effect on chemical and phase equilibria in nano-TiB2–TiO2–TiBO3system at <650 °C: an in situ time-resolved energy dispersive x-ray diffraction study with an ultrahigh energy synchrotron probe

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Impact of the Nature of the Organic Spacer on the Crystallization Kinetics of UiO-66(Zr)-Type MOFs.

The influence of the constitutive dicarboxylate linkers (size, functional group) over the crystallization kinetics of a series of porous Zr metal-organic frameworks with the UiO-66 topology has been investigated by in situ time-resolved energy dispersive X-ray diffraction (EDXRD). Both large aromatic spacers (2,6-naphthalene-, 4,4'-biphenyl- and 3,3'-dichloro-4,4'-azobenzene-dicarboxylates) and a series of X-functionalized terephthalates (X=NH2 , NO2 , Br, CH3 ) were investigated in dimethylformamide (DMF) at different temperatures and compared with the parent UiO-66. Using different crystallization models, rate constants and further kinetic parameters (such as activation energy) have been extracted. Finally, the impact of the replacement of the toxic DMF by water on the crystallization kinetics was studied through the synthesis of the functionalized UiO-66-NO2 solid.

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.

Liquid-Phase Adsorption and Separation of Xylene Isomers by the Flexible Porous Metal–Organic Framework MIL-53(Fe)

We report a study of the use of the porous metal–organic framework material MIL-53(Fe), FeIII(OH)0.8F0.2[O2C–C6H4–CO2], for the separation of BTEX mixtures (benzene, toluene, ethylbenzene, and the three xylene isomers). Crystal structures of the three host:guest materials MIL-53(Fe)[xylene], where xylene = the ortho, meta, or para isomer of dimethylbenzene, have been solved and refined from powder X-ray diffraction. Each exhibits a fully expanded form with a variety of host:guest and guest:guest interactions responsible for stabilizing the structure. While the ortho- and meta- isomers present a similar arrangement when occluded in the MIL-53 host, the para-xylene shows a distinctly different set of interactions with the host. Upon thermal treatment, xylenes are partially lost to give crystalline phases MIL-53(Fe)[xylene]0.5, the structures of which have also been solved. The kinetics of uptake of each xylene by MIL-53(Fe)[H2O], in which the water is replaced by the organic guest, have been studied using time-resolved energy-dispersive X-ray diffraction: this shows differences in kinetics of the adsorption of the three isomers. Under chromatographic conditions in heptane at 293 K, anhydrous MIL-53(Fe) is able to separate the three xylene isomers with elution of the para-xylene before the other two isomers, and at 323 K the host is able to resolve all components of the BTEX mixture.

The kinetics and mechanisms of amorphous calcium carbonate (ACC) crystallization to calcite, viavaterite.

The kinetics and mechanisms of nanoparticulate amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite, were studied at a range of environmentally relevant temperatures (7.5-25 °C) using synchrotron-based in situ time-resolved Energy Dispersive X-ray Diffraction (ED-XRD) in conjunction with high-resolution electron microscopy, ex situ X-ray diffraction and infrared spectroscopy. The crystallization process occurs in two stages; firstly, the particles of ACC rapidly dehydrate and crystallize to form individual particles of vaterite; secondly, the vaterite transforms to calcite via a dissolution and reprecipitation mechanism with the reaction rate controlled by the surface area of calcite. The second stage of the reaction is approximately 10 times slower than the first. Activation energies of calcite nucleation and crystallization are 73±10 and 66±2 kJ mol(-1), respectively. A model to calculate the degree of calcite crystallization from ACC at environmentally relevant temperatures (7.5-40 °C) is also presented.

The application of statistical methodology to the analysis of time-resolved X-ray diffraction data

We demonstrate for the first time the application of Principal Component Analysis (PCA) to the analysis of time-resolved energy-dispersive X-ray diffraction data. Previously well-characterised model systems are studied. PCA is shown to offer significant advantages over traditional curve-fitting methods in terms of speed and lack of potential user bias.

Time and position resolved in situ X-ray diffraction study of the hydrothermal conversion of gypsum monoliths to hydroxyapatite

Time-resolved energy dispersive X-ray diffraction (EDXRD) data have been measured in situ from cast blocks of gypsum, CaSO(4) x 2 H(2)O, in the presence of reactive phosphate solutions under hydrothermal conditions (100 < or = T < or = 180 degrees C) in order to understand the formation of hydroxyapatite monoliths, for applications such as in artificial bone or dental materials. Measurement of data in short (60 s) intervals has thus permitted information about the kinetics and mechanism of transformation of gypsum to hydroxyapatite to be obtained in a non-invasive way, avoiding the irreversible conversion of hydrous intermediate phases that would occur on quenching. At the lower temperatures used gypsum first converts to an amorphous intermediate phase during reaction, but as the temperature is raised to 130 degrees C and above, hydrothermal dehydration to the subhydrate CaSO(4) x 1/2 H(2)O always occurs before hydroxyapatite crystallises. The final crystal size of the hydroxyapatite is estimated from the peak broadening of the EDXRD data and this reveals an increase in crystal dimension with increasing reaction temperature. Comparing measurements from the surface and from the core of the blocks shows that an additional phosphate phase, CaHPO(4), is observed in the core at two temperatures and also that the crystal growth of hydroxyapatite does not penetrate the core of the block on the time scales we have investigated (up to 6 hours). The observations have important implications in the fabrication of hydroxyapatite monoliths from cast gypsum for applications, since the conversion via several intermediate phases may compromise the integrity and mechanical properties of the monoliths.

Green rust as a precursor for magnetite: an in situ synchrotron based study

AbstractIn this study, direct evidence for the formation of magnetite via a green rust intermediate is reported. The Fe(II) induced transformation of ferrihydrite, was quantified in situ and under O2-free conditions using synchrotron-based time-resolved energy dispersive X-ray diffraction. At pH 9 and Fe(II)/Fe(III) ratios of 0.5 and 1, rapid growth (6 min) of sulphate green rust and its subsequent transformation to magnetite was observed. Electron microscopy confirmed these results, showing the initial rapid formation of hexagonal sulphate green rust particles, followed by the corrosion of the green rust as magnetite growth occurred, indicating that the reaction proceeds via a dissolution-reprecipitation mechanism. At pH 7 and Fe(II)/Fe(III) ratio of 0.5, sulphate green rust was the stable phase, with no transformation to magnetite.

A new experimental setup for the study of lipid hydration by energy dispersive X-ray diffraction

A new hydration cell has been constructed that allows to fully hydrate aligned lipid multibilayers as well as to study lipid hydration by using in situ time-resolved energy dispersive X-ray diffraction. The cell has been used to investigate the evolution of the lamellar d-spacing of dioleoylphosphocoline oriented membranes as a function of both relative humidity (RH) and time. The extreme sensitivity of d to RH was shown and two hydration regimes were detected.

Effect of hydration on the structure of oriented lipid membranes investigated by in situ time-resolved energy dispersive x-ray diffraction

In situ time-resolved energy dispersive x-ray diffraction (EDXD) was applied to investigate the effect of hydration on the structure of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)-oriented membranes. The measurements allowed a very high density time sampling of the evolution of the structural properties of the DOTAP bilayer such as the lamellar d-spacing, the membrane thickness, and the size of the interbilayer water region. Time-resolved EDXD has been found to provide important information on the role played by free water molecules on the structure and fluidity of lipid bilayer.

Effect of hydration on the long-range order of lipid multilayers investigated by in situ time-resolved energy dispersive X-ray diffraction

In situ time-resolved energy dispersive X-ray diffraction (EDXD) was applied to investigate the hydration kinetics of oriented dioleoylphosphocoline (DOPC) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) membranes. The long-range order in the investigated lipid multilayers has been found to vary as a function of hydration in a nonmonotic way. In the first stage, water adsorption increased the long-range order along the normal to the lipid bilayer whereas, in the second one, a progressive loss of interbilayer coherence was observed. Possible molecular mechanisms underlying the experimental observations are discussed.

In situ formation of solid-supported lipid/DNA complexes

Solid-supported lipid/DNA complexes were prepared by using highly aligned 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) multibilayers as a template. The complex formation was promoted in situ and followed in time. The resulting DOTAP/DNA complex shows a good degree of orientation along the normal to the support as revealed by combined time-resolved energy dispersive X-ray diffraction (EDXD) and surface synchrotron small angle X-ray scattering (SAXS) measurements.

Observation and Reactivity of the Chainlike Species ([Al(PO4)2]3-)n during the X-ray Diffraction Investigation of the Hydrothermal Synthesis of the Super-sodalite Sodium Aluminophosphate MIL-74 (Na2Al7(PO4)12·4trenH3·Na(H2O)16)

The hydrothermal synthesis of the aluminum phosphate Na2Al7(PO4)12·4trenH3·Na(H2O)16 (MIL-74) has been studied by X-ray diffraction (conventional source) and in-situ time-resolved energy-dispersive X-ray diffraction (synchrotron radiation). Before the crystallization of MIL-74, the reaction of the starting aqueous aluminophosphate gel containing the tren species (tris(2-aminoethyl)amine) and sodium hydroxide gives rise to the formation of a hydrated chainlike solid Al(PO4)2·trenH3·6H2O (phase 1), which transforms into the hydrate Al(PO4)2·trenH3·2.5H2O (phase 2) upon heating at 180 °C. Its structure was determined by means of single-crystal X-ray diffraction and consists of a one-dimensional inorganic chain of tetrahedral unit AlO4 alternating with the phosphate group PO4. The resulting ([Al(PO4)2]3-)n chains interact through hydrogen bonds with the trenH3 and water molecules, generating a layerlike inorganic−organic network. Phase 2 was observed to be an intermediate, which disappears when the MIL-74 solid starts to crystallize. The observation of such an intermediate phase allows for the proposition of a chemical reaction pathway for the formation of the three-dimensional network of MIL-74. It seems that the sodium cations play a crucial role and directly react with the chainlike precursor. They would participate in the construction of the inorganic framework as anchorage nodes during the condensation process.

In situ Study of the Formation of Crystalline Bismuth Molybdate Materials under Hydrothermal Conditions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

In Situ Study of the Formation of Crystalline Bismuth Molybdate Materials under Hydrothermal Conditions

The three well-known and catalytically important phases of bismuth molybdate have been prepared, in a phase pure form, employing hydrothermal methods at temperatures below 200 °C. An in situ study of the formation of these phases using the time-resolved energy-dispersive X-ray diffraction (EDXRD) technique revealed that the α and γ crystalline phases are formed directly from the amorphous gel mixture without forming any intermediate phases. Kinetic data analysis using the Avrami-Erofe'ev nucleation-growth model suggests that the mechanisms for formation are different for each phase. This hydrothermal method of preparation yielded materials with a higher surface area as compared to the solids prepared by conventional techniques.

Synthesis and Structure of Low-Dimensional Gallium Fluorodiphosphates Seen during the Crystallization of the Three-Dimensional Microporous Gallium Fluorophosphate ULM-3

Two one-dimensional gallium fluorodiphosphates Ga(P2O7)F·H3N(CH2)3NH3·3H2O, 1, and Ga(P2O7)F·H3N(CH2)3NH3·H2O, 2, have been synthesized under mild conditions (<100 °C) from aqueous mixtures of Ga(NO3)3·6H2O, P2O5, 1,3-diaminopropane, and HF. Their structures consist of anionic chains of formula Ga(P2O7)F2- containing corner-sharing {GaO4F2} octahedra linked together via fluorine and P2O7 units, which are charge-balanced by propyldiammonium dications. During the hydrothermal synthesis of the open-framework three-dimensional ULM-3, compound 2 has been identified as the crystalline intermediate phase when phosphorus pentoxide is used as a starting material. This process has been followed in situ with time-resolved energy-dispersive X-ray diffraction (EDXRD), which reveals that dissolution of the one-dimensional phase 2 occurs before the rapid crystallization of ULM-3. If compound 2 is quenched from hydrothermal conditions, rapid and reversible conversion to compound 1 takes place. The two chain phases are thus solid precursors of the microporous ULM-3, and tracking the transformation process using in situ EXDRD shows that dissolution of 1 takes place before crystallization of 2 and then further transformation into the 3D phase, with the 1 and 2 acting as reservoirs of reactive species for ULM-3 crystallization.

In Situ X-ray Diffraction Measurements of the Self-Preservation Effect of CH4 Hydrate

In situ observations of CH4 hydrate dissociation using X-ray diffraction were carried out at atmospheric pressure and at both 168 and 189 K. Dissociation rates of the hydrate and the rate of transformation into hexagonal ice were measured using time-resolved energy-dispersive X-ray diffraction. The dissociation of CH4 hydrate had an initially fast regime followed by slower dissociation. Thus, the data support a previously suggested two-step process. In addition, we observed dynamic behavior of the X-ray diffraction intensities of ice Ih, which implies a transient crystal structure at the beginning of the dissociation. Our analyses indicates that the first step, which lasted several tens of minutes, was the formation of an ice Ih layer around the CH4 hydrate, and the second step was relatively slow because the CH4 had to diffuse through the thickening ice layer. This second step determined the hydrate lifetime. The resulting diffusion coefficients were estimated at 2.2 × 10-11 m2/s at 189 K and 9.6 × 10-12 m2/s at 168 K.

A furnace for the in situ study of the formation of inorganic solids at high temperature using time-resolved energy-dispersive x-ray diffraction

The design, construction, and use of a furnace from which time-resolved x-ray diffraction data may be measured from reacting mixtures of solids or of solids and liquids is described. The furnace is a vertical tube design, constructed from commercially available components, and can operate at temperatures of up to 1000 °C. The apparatus is designed to heat sample tubes of up to 3 cm diameter. The use of high-intensity synchrotron-generated white-beam x rays allows the tube and its contents to be penetrated; thus x-ray diffraction data can be measured from reactions taking place in laboratory-sized reaction vessels. The energy-dispersive diffraction geometry allows rapid data collection (of the order of seconds); hence reactions can be followed continuously in real time. The use of the furnace is demonstrated by results from experiments performed on Station 16.4 of the Daresbury Synchrotron Radiation Source, UK. Two distinct reaction types are studied, both used to prepare the layered perovskite RbCa2Nb3O10: first, a solid state route at 800 °C and second a flux route, performed in molten RbCl, also at 800 °C.