The following reasons can account for this phenomenon. Through the supersonic stream, the short resident time of nanopowders in plasma jet resist growing. Secondly, molten crust hinders transmission of heat energy. In addition, rapid solidification also restrains mergering each other among nanopowders and growth.d)As a result of difference between Al2O3 and TiO2 in melting point, almost all TiO2 nanopowders are melted and Al2O3 nanopowders not melted, as shown as case ‘D’ in Fig. 7.