The surface areas of a number of commercial carbon blacks have been determined by the low-temperature adsorption isotherm technique. Thermal decomposition and other nonimpingement type blacks possess areas of 15 to 64 M 2 per gram. Channel blacks commonly employed as reinforcing agents in rubber have areas around 100 M' per gram. Ink and color blacks range from 100 to nearly 1000 M per gram. The color values of these carbons increase with surface area. The relation of iodine and diphenylguanidine adsorption to surface area has also been studied. Iodine adsorption is a direct function of surface area and, with the NE of the outstanding characteristics of carbon blacks is the large surface they possess by virtue of their ex-0 tremely small particle size. In the past many attempts have been made to measure this surface in an effort to correlate it with the properties carbon black is capable of imparting to various media in which it is dispersed. Various methods of direct microscopic observations have been most widely employed (IO, Id, 16, 26). While these direct methods are reliable for particles having diameters larger than 1000 A,, we have found that they are not reliable for particles with diameters smaller than 500 A.Since the majority of the carbon blacks of commercial importance fall within this range, it must be concluded that surface areas calculated from diameters obtained by these methods are of doubtful significance. The electron microscope (5) is an exception to the above general criticism of direct optical methods. Recent investigations (2) with this instrument have been remarkably successful. In addition to electron microscopy, other methods have been recently described for determining not only particle size and distribution, but also the direct determination of total surface area. The present paper deals with our attempts to apply certain of these methods to a variety of commercial carbon blacks.Hauser and his co-workers (16, 17) used the supercentrifuge to determine particle size distribution in a variety of finely divided substances. We have applied their method to a standard channel black dispersed in a rubber cement. Fortyfive parts of black by weight were milled with 100 parts of rubber. This stock was then dissolved in xylene to give a final concentration of about 2 X gram of black per cc. of suspension. After centrifuging and analysis, a distribution curve was obtained with maxima in the region 300-400 A. in fair agreement with the published electron microscopic value (8). Unfortunately the rubber in which the black was dispersed also fractionated along the sides of the centrifuge liner. This made it necessary to analyze each interval sample for rubber. Consequently several weeks were required to evaluate IL single black. Because of these difficulties it did not exception of certain high-volatile blacks, may be used as a direct measure of total surface. The adsorption of diphenylguanidine depends much more strongly on the volatile content of the black rather than its total surface. While rubber...

The surface areas of a number of commercial carbon blacks have been determined by the low-temperature adsorption isotherm technique. Thermal decomposition and other nonimpingement type blacks possess areas of 15 to 64 M2 per gram. Channel blacks commonly employed as reinforcing agents in rubber have areas around 100 M2 per gram. Ink and color blacks range from 100 to nearly 1000 M2 per gram. The color values of these carbons increase with surface area. The relation of iodine and diphenylguanidine adsorption to surface area has also been studied. Iodine adsorption is a direct function of surface area and, with the exception of certain high-volatile blacks, may be used as a direct measure of total surface. The adsorption of diphenylguanidine depends much more strongly on the volatile content of the black rather than its total surface. While rubber reinforcement depends in a general manner on surface area, certain blacks of nearly identical surface vary widely in the properties they impart to compounded rubber. That the state of the surface is probably of equal importance is indicated by the fact that the activity of the surface, as judged by relative ease of oxidation, may vary widely in blacks of equal area.