In Situ Neutron Powder

Redfern, S.A.T., Artioli, G., Rinaldi, R., Henderson, C.M.B., Knight, K.S., Wood, B.J. (2000) Octahedral cation ordering in olivine at high temperature. II An in situ neutron powder diffraction study on synthetic MgFeSi04 (Faso). Phys Chem Minerals (in press)... 

In addition to these conventional methods of examining catalyst deactivation we have examined the effects of hydrothermal conditioning (using D2O) of TS-1 in the in situ neutron powder diffraction cell capable of flow studies described above. The TS-1 sample was steamed using D2O saturated He at progressively higher temperatures for successive periods of an hour... 

Figure 15.3 Schematic of the Oxford/ISIS hydrothermal reaction cell for recording in situ neutron powder diffraction data.

Eidong Wu. Erich H. Kisi, Shane J. Kennedy et al.. In Situ Neutron Powder Diffraction Study of TijSiC Synthesis,. /..,4in.Cerain.Sioc. 84 (10). 2281 (2001). 

Chon, CM., Lee, C.K., Song, Y., Kim, S.A. (2006) Structural changes and oxidation of ferroan phlogopite with increasing temperature in situ neutron powder diffraction and Fourier transform infrared spectroscopy. Phys. Chem. Minerals, 33, 289-299. 

Skinner SJ, Amow G (2007) Stmctural observations on La-2(Ni, CO)0-4 +/-delta phases determined from in situ neutron powder diffraction. J Solid State Chem 180(7) 1977-1983... 

Redox behaviour of potential SOFC cathode materials Lai.6Sro.4Nii.xCOx04+6 (x = 0.6 and 0.8) determined from in situ neutron powder diffraction under fiowing O2 and 5%H2... 

Keywords In situ Neutron Powder Diffraction, Cathode materials. Solid Oxide Fuel Cell, Ruddlesden-Popper Oxides, Thermal analysis... 

The defect structure of Fei O with the NaCl-type structure had been estimated to be a random distribution of iron vacancies. In 1960, Roth confirmed, by powder X-ray diffraction, that the defect structure of wiistite quenched from high temperatures consists of iron vacancies (Vp ) and interstitial iron (Fcj) (there are about half as many FCj as Vpe). This was a remarkable discovery in the sense that it showed that different types of crystal defects with comparable concentrations are able to exist simultaneously in a substance, Roth also proposed a structure model, named a Roth cluster, shown in Fig. 1.84. Later this model (defect complex = vacancy -F interstitial) was verified by X-ray diffraction on a single crystal and also by in-situ neutron diffraction experiments. Moreover, it has been shown that the defect complex arranges regularly and results in a kind of super-structure, the model structure of which (called a Koch-Cohen model) is shown in Fig. 1.85 together with the basic structures (a) and (b). 

Harrison RJ, Redfem SAT, O Neill HSC (1998) The temperature dependence of the cation distribution in synthetic hercynite (FeAl204) from in situ neutron diffraction. Am Mineral 83 1092-1099 Harrison RJ, Redfem SAT, Smith R1 (2000a) In situ study of the i 3 to i 3c phase transition in the ilmenite-hematite solid solution using time-of-flight neutron powder diffraction. Am Mineral 85 194-205... 

In-situ neutron diffraction was used to monitor the structural evolution of the phase decomposition of MAX phases at high-temperature in real time. Diffraction patterns were collected using WOMB AX at OPAL or the Polaris at ISIS, both are high-intensity medium-resolution powder diffractometers. Samples were mounted in a high-temperature niobium furnace which was fitted with a thin tantalum foil element and tantalum and vanadium heat shields that allows it to reach 2000°C, and operates under a high dynamic, i.e., it is continuously evacuated with a vacuum of 10 - 10 torr. A precision electronic scale was used to weigh the sample before it was loaded into the furnace. 

The principal breakthrough of the P-E press was the ability to compress a sufficient volume of powder (or size of single crystal) in a pressure cell and press small enough to mount in situ on a neutron beamline. P-E presses have opened high-pressiue neutron diffraction to a much wider range of users, and have become a standard experimental facility at several neutron sources. As a result, they have been used to study a wide range of materials, both crystalline and amorphous [79-83]. The presses have also been widely used at synchrotron sources for studies of non-crystalline materials and liquids, for example [84-86]. 

Very High Density Amorphous Ice (VHDA). By annealing HDA to T > 160 K at pressures > 0.8 GPa, a state structurally distinct from HDA can be produced, which is called VHDA ice [152]. The structural change of HDA to a distinct state by pressure annealing was first noticed in 2001 [152]. Even though VHDA was produced in experiments prior to 2001 [170], the structural difference and the density difference of about 10% at 77 K, and 1 bar in comparison with HDA remained unnoticed. Powder X-ray diffraction, flotation, Raman spectroscopy, [152] neutron diffraction [171], and in situ densitometry [172, 173] were employed to show that VHDA is a structural state distinct from HDA. Alternatively, VHDA can be prepared by pressurization of LDA to P > 1.1 GPa at 125 K [173, 174] or by pressure-induced amorphization of hexagonal ice at temperatures 130 K < T < 150 K [170]. The density of this amorphous state at 77 K and 1 bar is 1.26 g/cm3 [152]. 

JOrgensen JD, Beyerlein RA, Watanabe N, Worlton TG (1984) Structure of D20 Ice VIII from in-situ powder neutron diffraction. J Chem Phys 81 3211-3214... 

In parallel with the development of powerful X-ray and neutron sources, development of increasingly more efficient detectors has made it possible to obtain very good powder diffraction data in a very short time. The use of position sensitive and area detectors allow a large part of the diffraction pattern to be collected simultaneously. Therefore, non-ambient and in situ powder diffraction studies which were unthinkable a few decades back can now be performed routinely. 

These studies were of great interest to understand cement hydration and since then many in situ studies have been performed following the reactions using neutron and synchrotron X-ray powder diffraction. The development in time resolution is demonstrated by a synchrotron study of the hydration of tricalcium aluminate, C3A, which is an important component of Portland cement. Using a time resolution of down to 0.3 s a hitherto unknown shortlived intermediate phase was detected in the very early stage of hydration. 

Portions of neutron powder diffraction patterns recorded on the high resoiution powder diffractometer (HRPD) instrument at ISIS (UK) from LaNis charged with deuterium in situ to approx. D/M = 0 to 0.6 in the a + p two-phase region. Dotted iine after muitipie pseudo-isobaric absorption steps. Soiid iine after a singie isochoric absorption step from D/M = 0. The iatter data are uninterpretabie except that they obviousiy represent regions of sampie with wideiy distributed iattice parameters. The highest peaks come from the aiuminium sampie ceii and demonstrate that the oniy difference between the two measurements is the state of the sampie. 

Order-disorder of Si and A1 in tetrahedral sites as a function of temperature was the object of several studies, with controversial results. The behavior of phengite-3r from Dora Maira at high T was studied by in situ single-crystal X-ray diffraction (Amisano-Canesi et al. 1994 Amisano-Canesi 1995) and powder neutron diffraction (Pavese et al. 1997, 2000). These authors found that this sample seems to exhibit cation ordering both on the tetrahedral and on the octahedral sites, supporting the hypothesis of Sassi et al. 

Instrumentation. The experimental setup is similar to that employed for in situ X-ray diffraction. The material under investigation is pressed into a thin sheet and mounted together with suitable counter and reference electrodes into a silica cell. In order to decrease the large incoherent scattering contributions from protons in aqueous electrolyte solutions, deuterated solutions are used. In a typical study, the reaction mechanism of Ni(OH)2 (employed in nickel accumulators) was studied with neutron powder diffraction NPD [46]. A direct and continuous structural transformation of both the y- and jS-NiOOH phases into j8-Ni(OH)2 was observed during reduction with no direct relationship or discontinuity related to the transition from the first discharge electrode potential to the second one, which was located about 0.4 V lower. 

By the 1980s most of the aluminosilicate zeolites currently used industrially were known, and the emphasis shifted to the study of these materials using a range of powerful new techniques that came of age at this time. These included, in particular, solid state NMR, X-ray and neutron powder diffraction analysis, high resolution electron microscopy and computational methods. All were ideal for the study of structural details of solids that were rarely available, and never used in industrial applications, other than as microcrystalline powders. All these techniques are applicable to the bulk of the solid - this in turn makes up the (internal) surface, which is accessible to adsorbed molecules. Since the techniques are able to operate under any conditions of gas pressure, they may be used to extract structural details in situ under the operating conditions of ion exchange, adsorption and catalysis. In particular, zeolitic systems have proved ideal for the study, understanding and subsequent improvement of solid acid catalysts. 

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