| Title |
A Study on the Morphological Changes due to Reduction of WO3 to α - W |
| Authors |
장재규(Chae Gyoo Chang); 나형용(Hyong Yong Ra) |
| Abstract |
Morphological changes of intermediate tungstic oxide particles, prepared by reducing WO₃with hydrogen and a mixture of hydrogen and nitrogen over the temperature range from 800℃ to 1000℃, were studied using scanning electron microscope. Two different morphologies of W_(18)O_(49), bundles of needle crystals and short pole-type particles, were obtained at 800℃, whereas W_(18)O_(49), obtained at 900℃ and above, consisted of pale-type particles and fine whiskers. The growth of W_(18)O_(49) particles was faster in the length than the width with increasing reduction temperature. The size and morphologies of W_(18)O_(49) particles were greatly influenced by those of WO₃particles. Transformation of W_(18)O_(49) to WO₂and WO₂to α-W was accompanied by the rounding of W_(18)O_(49) particles and the recrystallization of α-W in spherical shape respectively. Extremely fine α-W powder was obtained by reduction of WO₃powder at 500℃ for 4 hrs in hydrogen followed by immediate reduction at 650℃ for 1 hr. |