Modified design and use of a high-pressure environmental stage for laboratory X-ray powder diffractometers

The popularity of supercritical CO₂ for materials processing makes the in situ study of pressures up to 10 MPa in the laboratory particularly interesting. This paper describes a modified design for a 12.4 MPa (1800 psi) variable-temperature pressure vessel based on an existing cell reported by Koster van Groos, Guggenheim & Cornell [Rev. Sci. Instrum. (2003), 74, 273-275]. The modifications satisfied the demands of the American Society of Mechanical Engineers design code 31.3, leading to legal design registration, construction and subsequent hydrostatic test. The thinner windows that the finite element analysis indicated as sufficient allow for rapid data collection, even using a laboratory-based Mo source. This type of application is demonstrated with a time-resolved data set showing the crystallization of a polylactic acid-clay nanocomposite under 6.8 MPa CO₂.