A nonlinear calibration curve for volume fraction vs integrated intensity ratio was obtained for the monoclinic-tetragonal Z r 0 2 system by using X-ray powder pattern-fitting and pattern-decomposition techniques. The empirical equation agrees well with the theoretical one. B y using this equation, the deviation from linearity (6.8% maximum) resulting from the intensity difference of corresponding reflections of the two phases can be estimated quite accurately.

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Ultrafine tetragonal ZrOz powder was prepared by hydrothermal treatment at 100 MPa of amorphous hydrous zirconia with distilled water and LiCl and KBr solutions. The resulting powder consisted of well-crystallized particles; at 2OO0C, the particle size was 16 nm and at 500°C, 30 nm. Under hydrothermal conditions tetragonal ZrOt appears to crystallize topotactically on nuclei in the amorphous hydrous zirconia.

This is a review and an overview on hydrothermal synthesis of fine oxide powders. The term hydrothermal today includes methods which involve water at pressures (from 1 atm-several kilobars) and high temperatures from 100-10,000°C. Hydrothermal is one of the best methods to produce pure fine oxide powders. The authors describe (i) hydrothermal decomposition, (ii) hydrothermal metal oxidation, (iii) hydrothermal reaction, (iv) hydrothermal precipitation and hydrothermal hydrolysis, (v) hydrothermal electrochemical, (vi) reactive electrode submerged arc, (vii) hydrothermal microwave, (viii) hydrothermal sonochemical, etc and also ideal and real powders.