RESEARCH IN HIGH-TEMPERATURE X-RAY DIFFRACTION TECHNOLOGY
Abstract : High accuracy (0.005 degree 2-theta) and high precision (0.002 degree 2-theta) for x-ray diffraction measurements at angles from less than zero to 155-160 degrees 2-theta at sample temperatures to 2600-2800C in oxidizing, neutral, reducing, or evacuated atmospheric environments are characteristics of a high-temperature x-ray diffractometer system specifically designed for research studies. Within the noble-metal thermocouple temperature range, very rapid thermal equilibrium -- 500C intervals in less than 3 seconds -- can be attained. The crystallometry of zirconium dioxide, ZrO2, has been surveyed in the range from room temperature to 1750C in normal air atmosphere at ambient pressure. Topics studied in some detail have been (a) the hysteresis of the monoclinic-tetragonal zirconia transformation, (b) the axial thermal expansion of tetragonal zirconia to 1750C, (c) the determination of axial expansion data for platinum and beryllium oxide for use as sample temperature indicators, and (d) new mathematical solutions of the classical d-value equations for lattice constants calculations. It has been shown that significant physical properties and constants can be measured for ZrO2 if the oxygen stoichiometry is established and maintained at an (unknown) equilibrium, or pseudo-equilibrium, value. (Author)