STUDIES OF ACTIVATED-CHARCOAL CLOTH .4. INFLUENCE OF PHOSPHATE IMPREGNANTS ON THE RATE OF ACTIVATION IN CARBON-DIOXIDE GAS

The influence of aqueous solutions of phosphates as impregnants of viscose rayon cloths on the subsequent activation of the derived carbonized materials in CO//2 gas at 850 degree C has been studied. In all cases, the observed rate of activation was less than that for the untreated cloth indicating that the species present in such solutions are effective retardants of the activation process. In contrast to the situation with boron-containing impregnants, the effect of Na** plus ions depends on the left bracket Na** plus right bracket / left bracket P right bracket ratio (and hence the pH value) of the system, with the rate of activation being initially depressed further by the presence of such ions. The results have been interpreted in terms of a mechanism which suggests that the effectiveness of phosphate ions as retardants depends on their ease of attachment to accessible cellulose molecules within the cloth. Divalent HPO**2** minus //4 ions have the greatest ability in this respect, and accordingly they are suggested as the main agents responsible for generating mesoporosity in such materials.