An Electron Microscope Study on Fine Metal Particles Prepared by Evaporation in Argon Gas at Low Pressure

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Abstract
Fine particles of various metals (Mg, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Cd, Sn, Au, Pb and Bi) were prepared by evaporation in argon gas at low pressure. The evaporation was carried out in an ordinary vacuum evaporation unit using a tungsten wire basket heater, after introducing the gas into the vacuum chamber. The average particle size was controlled by changing the pressure of the argon. Particle diameter varied from about one hundred Angstoms at 1 mm Hg to a few tenths of a micron at 30 mm Hg. It was proved by electron diffraction that the particles of all the metals (except Pb) were not seriously oxidized in the air. Electron micrographs showed well defined crystal habits for some metals, e.g. hexagonal plates for magnesium and cubes for chromium. Remarkable "necklace-like arrangements" were observed for particles of the ferromagnetic metals. Many electron micrographs and diffraction patterns are reproduced to show the size, shape, arrangement and state of oxidation of the particles.