Examining hydrated minerals using optically stimulated X-ray diffraction, an inexpensive modification of traditional diffractometers

Optically stimulated X-ray diffraction (OSXRD) modifies a traditional powde r 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 degrees C to the sample. The inclu ded OSXRD software allows the diffractometer to be controlled and sequentia l profiles (ASCII files) to be obtained. These profiles are subsequently pr ocessed, obtaining new files: (1) Three-dimensional (cps versus 2 theta ver sus time-temperature), (2) peak areas and (3) maximum 2 theta positions. Th e automatic temperature control loop, using the proportional-integraI-deriv ative control (PID) method, and the modifications of the XRD chamber are de scribed. Some examples of hydrated minerals were examined in the OSXRD prot otype: (1) the epsomite-hexahedrite phase transition in different isotherma l analyses (28 degrees C, 30 degrees C, 32 degrees C) and (2) the dehydrati on of the interfaces of a fibrous aragonite. Three-dimensional plots show t he 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 s inusoidal shape, suggesting steps during the dehydration processes.