In situ hydrothermal synthesis using 13 BM-D at the APS

A collaborative team between GSE-CARS at the Advanced photon source (APS), Argonne National Laboratory, a group from the Daresbury Laboratory (SRS) and SUNY at Stony Brook was recently set up to investigate the advantages of performing in situ energy dispersive powder diffraction (EDPD) hydrothermal experiments on station 13-BM-D at the APS. The main aim of this project was to develop and further understand the techniques used for this type of research. Experiments of this nature are routinely performed at the SRS but not to 230 deg. C, as the X-ray beam can only penetrate reaction cells capable of operating above this temperature. It was hypothesized that, with the extra benefits of a third generation synchrotron source, i.e. higher X-ray energy and flux, these same experiments could be performed with reaction cells with thicker walls rated for higher temperatures. A secondary aim of the investigation was to develop an on-line injection facility for the reaction cell thus enabling the user to introduce a fluid to the hydrothermal cell held at elevated temperature and hence pressure. This work was carried out on station 13-BM-D from 15th to 25th January 1998. The experiments are performed by placing the starting mixture into a specially prepared hydrothermal cell. This cell was then heated to the desired temperature, and while the cell is at temperature the reaction mixture was monitored using energy-dispersive powder diffraction (EDPD) with one spectrum being collected every few tens of seconds. These time-resolved diffraction patterns were used to monitor the entire reaction from starting material to end product. Experiments were performed on two systems, the first being the hydrated calcium silicate system in an attempt to follow the high temperature crystallization of the mineral phases tobermorite, xonotlite and gyrolite. The second was the iron sulphide system in order to observe the formation of pyrite via its various intermediates and to utilize the newly developed injection system. Results from the hydrated calcium silicate system proved very productive with all 3 phases being successfully formed, as well as transformations from one phase to another being observed. Temperatures up to 315 deg. C were attained and the pressure was successfully contained within the reaction setup. The time-resolved diffraction data enabled the mechanism and kinetics of the reaction to be observed and many interesting and informative results were obtained (see figure a). The iron sulphide experiments proved more challenging allowing collection of only limited diffraction data, although all aspects of the hydrothermal cell worked perfectly, including the injection system. (author)