Abstract
Molybdenum trioxide crystals were mounted on the sharply pointed end of a fine tungsten wire and exposed to heated hydrogen gas under about one atmospheric pressure in the specimen-treating adaptor attached to the electron microscope, previously devised by the author and others, and the morphological and chemical changes in a certain chosen region of the specimen were followed by taking micrographs and selected-area electron-diffraction patterns. Many informations on the formation of molybdenum metal particles were obtained. The mechanism of formation of metallic particles is discussed.
