โ Scribed by Yoshimi Matsumura; Shigeji Hagiwara; Hiroshi Takahashi
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Acid strength distribution on commercial carbon blacks and chemically oxidized carbon blacks was measured by automatic titration using sodium hydroxide solutions as titrants. The titration curves show that the weaker acids with pKa between 7.0 and 11.0 occur in the amount of 0.025-0.490 m eq/g, the stronger ones with pKa between 2.0 and 7.0 in the amount of O-O.475 m eq/g and trace amount of pKa range below 2.0. The acid strength distribution obtained by this method coincides with that by the Boehm method. The observed amounts of total acid exceed active hydrogen contents obtained by the Zerewitinoff method in the carbon blacks. Three different oxidizing agents were used to determine their effect on carbon black acidity. Nitric acid produced acidic groups at the highest surface density; H,O, produced a predominance of weaker acids; hot air produced stronger acids with an increase of specific surface area.
๐ SIMILAR VOLUMES
PoteRtiometric titration, in which carbon black was reduced in aqueous medium with excess NaBH,, and then titrated backwards with 12, showed the presence of two kinds of reducible surface groups on carbon black, i.e. reversibly reducible and irreversibly reducible groups. The former was attributed t