Sintering of Ultrafine Metal Powders. I. Coalescence Growth Stage of Au and Ag

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Abstract
Sintering of ultrafine powders of Au and Ag, produced by a gas evaporation technique, has been studied by the electron microscopy and X-ray diffraction methods. The critical temperature, above which the particle size increases, is found to be room temperature for Au powders and 60°C for Ag powders with a particle size of about 200 Å. Retardation of sintering is observed for both Au and Ag powders exposed to air before heating. Decrease of strains as well as stacking disorders with increase of temperature is detected by X-ray diffraction and electron microscopic study. Experimental formulae for the variations of particle size and strain with temperature are obtained from the half-value breadth of X-ray diffraction profile. Particle size effect on sintering is also examined for Ag powders.