Novel Preparation Technique of Inorganic Ultrafine Particles through Liquid phase and Application to High Technology Materials

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Ultrafine particles of alumina combined with anionic surfactants were prepared through the processes including (1) the preparation of the hydrosol of hydrated alumina, (2) the coagulation of hydrosol with the solution of a surfactant, (3) the flashing in an organic solvent of hydrated alumina particles from the coagu- lated hydrosol, and (4) the separation of the solvent from the particles by heating. These particles were dehydrated throught the heat treatment at tempera- tures of 180 to 200゜C under reduced pressure. The alumina particles with surfactants after the above dehydration treatment were estimated to be less than 10nm (average about 5nm) in diameter, and were easily dispersed with trans- parency into a variety of organic solvents and plastics.Through the research of the hydrosol in the system gydrated titania-hydrated alumina for the improvement in weatherability (stability to ultraviolet radiation) of the fine particles of hydrated titania, a novel technique was found for the white coloring of the anodic oxide film on the aluminum metal surface: The coloring was performed by the electrolytic deposition of the fine particles of hydrated titania into pores of the oxide film, which was subjected to the secondary electrolysis in the hydrated titania sol. Much improvement in weather- ability was achieved by the electrolytic dephosition of the fine particles of hyudrated alumina. instead of hydrated titania, into pores of the anodic oxide film kept in the hydrated alumina sol. The coloring of a high grade in whiteness was meterialized by tghe electrolytic deposition of the fine particles in the system hydrated alumina-hydrated calcia into pores of the oxide film.