Ultrafine oxide powders (MgO and ZrO_2, 0.01 μm order of size) were prepared by spraying nitrate solutions into an argon inductively coupled plasma of ultra-high temperature (ICP). A conventional induction heater (5 kw, 400 kHz and thyratron-controlled) was modified for generating the argon ICP flame. The basic modification consisted in increasing its power and frequency (15 kw, 4-16 MHz and thyristor-control led). In order to quench the formed powders rapidly, a water-cooled powder collector was used. The particle shape of the magnesium oxide was not cubic but roundish, and the main phase of the zirconium oxide was metastable tetragonal-ZrO_2. These suggest that the powders formed by ICP should be quenched so rapidly that they could not grow large or could not convert to high temperature phases. The particle size distribution of the magnesium oxide followed the Gaussian type of formula proposed by Aboav (range 0.016-0.044 μm, modal diameter 0.028 μm)
