Preparation of Diopside Fine Powders by Spray Pyrolysis and Its Sinterability

Abstract

Fine powders of diopside, CaMgSi₂O₆, were prepared by the spray pyrolysis method. Ca(NO₃)₂4H₂O, Mg(NO₃)₂6H₂O and Si (OC₂H₅)₄ were dissolved into ethanol and refluxed under various time-temperature conditions before pyrolysis. Refluxing at 70°C for 1 day was necessary to prepare homogeneously mixed diopside precursor powders. Spray pyrolysis was made between 800° and 1000°C under the following conditions: volume of flowing solution, 2 to 15ml/min, volume of flowing air, 2 to 15l/min, and concentration of solution, 0.05 to 0.33mol/l. Almost all powder particles were hollow spheres of a few micron meter, which were composed of fine primary particles of submicron or less. These powders were calcined at 1000°C and sintered at 1275° to 1350°C after ground with a vibration mill. Relative densities up to 97.4% were achieved by firing at 1300°C for 1h without additives. This specimen showed dielectric losses much lower than those sintered with additives reported before.