Abstract
Microscopic observation revealed that the reduction product of a single piece of WO3 crystal is consisted of about 0.5μ. particles, or primary particles, which are single crystals of metal formed by the atomic sintering of W atoms produced by the reduction. If the oxide crystal lying flat on a supporting surface is reduced, these primary particles remain scattered on the substratum, marking the exact contour of the original oxide crystal. But, if reduced in a free space, they loosely stick together to form an aggregate, or a secondary particle, which retains the original shape with about 30 per cent contraction. If a mass of WO3 crystals are reduced, secondary particles may loosely cling together to form tertiary particles and so on.
