The Particle Size and Shape of Colloidal Carbon as Revealed by the Electron Microscope

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Abstract
1. The particle diameter of Micronex colloidal carbon black, originally estimated to be 80 mµ by microscopic methods, later as 50–60 mµ by ultrafiltration and counting methods, now appears, on the evidence of direct measurements with the electron microscope, to require further downward revision to about 30 mµ. 2. The original estimate of specific surface of 1,900,000 square inches per cubic inch based on 80 mµ, and that of 2,500,000 corresponding to 60 mµ, would now appear to require upward revision to the value of about 5,000,000. Effects ascribable to the high specific surface of colloidal carbon do not require nor in fact permit the assumption of burr or featherlike surface configurations, but may be attributed to fineness of subdivision alone. 3. The preponderating geometrical form of the ultimate particles of colloidal carbon is spheroidal, with some evidence of plane surfaces, the general conclusion being that the particles may be treated as sensibly isotropic. 4. The establishment by direct observation of a much lower ultimate particle size for carbon black suggests the possibility of more efficient employment of the total available carbon surface in reinforcement phenomena.

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