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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)


Journal of Sedimentary Research, Section B: Stratigraphy and Global Studies
Vol. 70 (2000), No. 4. (July), Pages 964-967

Examining Hydrated Minerals Using Optically Stimulated X-Ray Previous HitDiffractionNext Hit, an Inexpensive Modification of Traditional Diffractometers: RESEARCH METHODS PAPERS

Javier Garcia-Guinea (1), Rafael Abella (1), Sergio Sanchez-Moral (1), Raul Benito (1), Daniel Martin-Ramos (2)


Optically stimulated X-ray Previous HitdiffractionNext Hit (OSXRD) modifies a traditional powder XRD by attaching a thermocouple, a precision temperature controller (PID control), and a thyristor power regulator firing a halogen lamp (75 w, 220 V, red-infrared) that provides up to 210°C to the sample. The included OSXRD software allows the diffractometer to be controlled and sequential profiles (ASCII files) to be obtained. These profiles are subsequently processed, obtaining new files: (1) Three-dimensional (cps versus 2theta.jpg versus time-temperature), (2) peak areas and (3) maximum 2theta.jpg positions. The automatic temperature control loop, using the proportional-integral-derivative control (PID) method, and the modifications of the XRD chamber are described. Some examples of hydrated minerals were examined in the OSXRD prototype: (1) the epsomite-hexahedrite phase transition in different isothermal analyses (28°C, 30°C, 32°C) and (2) the dehydration of the interfaces of a fibrous aragonite. Three-dimensional plots show the epsomite-hexahedrite phase transition in detail. However, in the case of aragonite (no phase transition) the 3D plot does not show visible changes, but the graph of peak-areas distribution versus temperature increases in sinusoidal shape, suggesting steps during the dehydration processes.

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