A thermosyphon-driven hydrothermal flow-through cell forin situand time-resolved neutron diffraction studies

Abstract

A flow-through cell for hydrothermal phase transformation studies by in situ and time-resolved neutron diffraction has been designed and constructed. The cell has a large internal volume of 320 ml and can operate at temperatures up to 573 K under autogenous vapor pressures (ca 8.5 Â 10 6 Pa). The fluid flow is driven by a thermosyphon, which is achieved by the proper design of temperature difference around the closed loop. The main body of the cell is made of stainless steel (316 type), but the sample compartment is constructed from non-scattering Ti-Zr alloy. The cell has been successfully commissioned on Australia's new high-intensity powder diffractometer WOMBAT at the Australian Nuclear Science and Technology Organization, using two simple phase transformation reactions from KAlSi 2 O 6 (leucite) to NaAlSi 2 O 6 ÁH 2 O (analcime) and then back from NaAlSi 2 O 6 ÁH 2 O to KAlSi 2 O 6 as examples. The demonstration proved that the cell is an excellent tool for probing hydrothermal crystallization. By collecting diffraction data every 5 min, it was clearly seen that KAlSi 2 O 6 was progressively transformed to NaAlSi 2 O 6 ÁH 2 O in a sodium chloride solution, and the produced NaAlSi 2 O 6 ÁH 2 O was progressively transformed back to KAlSi 2 O 6 in a potassium carbonate solution.

A Novel Route for the Synthesis of Mesoporous and Low-Thermal Stability Materials by Coupled Dissolution-Reprecipitation Reactions: Mimicking Hydrothermal Mineral Formation

“…Leucite crystals contain inherent 3D ordered networks of nanometer-sized lamellar twins (Fig. 7c and 7e), and Xia et al [49,51] demonstrat- these analcime nanocrystals have uniform size and crystallographic orientation due to epitaxial nucleation and growth facilitated by the similarity of the crystal lattice between leucite and analcime. The morphology of the nanocrystals is tuneable by ed that such highly ordered 3D patterns could be precisely preserved during hydrothermal pseudomorphic replacement reactions in pH-buffered NaCl solutions, resulting in 3D ordered arrays of analcime nanocrystals (Fig.…”

“…[54] Leucite (KAlSi 2 O 6 ) was used as the precursor to synthesize analcime NaAlSi 2 O 6 . H 2 O as an illustration of this new synthesis route, [49,51] because leucite crystals are abundant in Nature, and their 3D ordered lamellar twinning has been studied in detail. [55] Conclusions CDR reactions are often extremely complex, since they result from a complex dynamic interplay between dissolution and precipitation, controlled critically by phenomena such as surface nucleation, porosity creation/destruction, and transport of aqueous species to and from the reaction front.…”

A large volume cell for in situ neutron diffraction studies of hydrothermal crystallizations

“…21 Our previous in situ neutron diffraction kinetic study on this reaction was carried out at 230°C. 18 This study is to obtain the reaction kinetics at a second temperature, so that accurate reaction activation energy can be determined and thus the reaction rate under natural environments can be estimated.…”

“…3,16,17 To achieve a higher working temperature and pressure, and a larger fluid volume, we have previously constructed a thermosyphon driven flow-through cell and commissioned on Wombat, Australian's new high intensity powder diffractometer at the OPAL research reactor, run by Nuclear Science and Technology Organization ͑ANSTO͒. 18 The cell worked smoothly but the thermosyphon is sensitive to local temperature and air flow variations in the neutron guide hall. In practice, the temperature profile along the flow-through loop is not always stable during the course of hydrothermal reactions.…”

“…4͑b͔͒ gives rate constant k = 1.93Ϯ 0.14ϫ 10 −5 s −1 and the time exponent n = 2.04Ϯ 0.01. The reaction condition used in this study was identical to our previous in situ neutron diffraction study except the reaction temperature, 18 and the same nucleation Note that the total mass of the sample changed from 1.25 g at the beginning of the reaction to 0.92 g at the end because of the loss of small particles from the mesh tube; however, the mass of the stainless steel mesh tube remained constant at 0.57 g, so the mass fraction of ͑Fe,Ni͒ slightly increased during the process, serving as an excellent internal standard for quantification. ͑b͒ An Avrami plot yields the rate constant k and the time component n as shown in the plot.…”